the book - molexthe information given herein, including drawings, illustrations and schematics (that...

The Bookon the technologies of

Polymicro

• Specialty Optical Fiber

• Flexible Fused Silica Capillary Tubing

• Fiber Optic and Capillary Assemblies

• Fused Silica and Quartz Micro-Components

www.polymicro.com

© Polymicro Technologies, a Subsidiary of molex.

Forward

Welcome to Polymicro Technologies’ catalog. We pride ourselves on the quality of our productsand our service. This catalog represents an effort to provide a tool to aid our customers inunderstanding our products, the materials with which we work, and the capabilities we canprovide. We are unique in our ability to work with the customer from design, to prototype, tolarge-scale production. We provide a breadth of expertise unparalleled in the industry withcustom preform capabilities, tower capabilities to draw fiber and tubing, laser capabilities tocreate micro-components, and assembly capabilities to put it all together. It is our goal tocontinually improve our products, our capabilities, and ourselves to meet the challenges ofour customers’ technological requirements. Production, Engineering, and Sales at Polymicroare dedicated to your success. We believe firmly in the basic idea that our customers’success translates to our success. For the latest in new procedures, application notes, andgeneral information visit our website.

In spite of our best efforts, this catalog is not perfect. We welcome any recommendations orsuggestions. We are here to meet your needs.

Thank yyou

THE PPEOPLE OOF PPOLYMICRO TTECHNOLOGIES

Polymicro TTechnologies, aa SSubsidiary oof MMolex18019 NNorth 225th AAvenue

Phoenix, AArizona 885023-1200Phone: ((602) 3375-4100

Fax: ((602) 3375-4110e-mail: [email protected]

URL:http://www.polymicro.com

TTeecchhnniiccaall DDaattaa DDiissccllaaiimmeerrThe information given herein, including drawings, illustrations and schematics (that are intended for illustration purposes only), is believed to be

reliable. However, Polymicro Technologies, makes no warranties as to its accuracy or completeness and disclaims any liability in connection with

its use. Polymicro Technologies, only obligation shall be as set forth in Polymicro Technologies, standard terms and conditions of sale for this

product and in no way will Polymicro Technologies, be liable for any incidental, indirect or consequential damages arising out of the sale, resale,

use or misuse of the product. Users of Polymicro Technologies, products should make their own evaluation to determine the suitability of each

such product for the specific application.


Table oof CContents

Page#1 Introduction

History - from 3000 BC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 - 1Glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 - 2Quartz and Synthetic Fused Silica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 - 2Drawn Glass And Glass Tubing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 - 3Physical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 - 3High Technology Synthetic Fused Silica and Common Quartz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 - 3Difference in Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 - 4Solarized Glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 - 4

2 Fiber OOptics aand OOptical FFiberOptical Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1Light Sources and Distributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1Getting Light Where You Want It . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 2The Science of Optical Fiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 2Total Internal Reflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 2Numerical Aperture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 3Input-Output Phenomena . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 4Tapered Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 5Matching Numerical Apertures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 5Fiber Types & Modes of Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 7Dispersion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 9Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 9Focal Ratio Degradation (FRD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1 0Attenuation & Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1 0Low -OH and High -OH Optical Fiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 11Internal & External Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 11Bend Radius - Optical Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1 2Evanescent Wave Losses in Small Diameter Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1 2Power Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1 3Fluorescence in Fiber Optical Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1 4UV Fiber Performance Solarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1 4Infrared Waveguides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1 6Coatings and Buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1 6Broadband Fiber (FBP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1 7Mechanical and Environmental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1 8Mechanical Stress and Fiber Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1 8Radiation Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 2 0

3 Flexible FFused SSilica CCapillary TTubingWhat is a Capillary? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 1Applications Employing Capillary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 1Characteristics Offered by Capillary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 2Gas Chromatography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 2Capillary Electrophoresis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 3Capillary Liquid Chromatography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 3Mass Flow Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 4Other Uses for Synthetic Fused Silica Capillary Tubing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 4Capillary Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 5Cutting and Cleaving Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 5Coupling and Connecting Capillary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 6Pressure Handling Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 6Estimating the Flow Rate in Capillaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 6Bending Stress in Capillary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 7Optical Properties of a Capillary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 7

i


Table oof CContents

ii

Page#Light Guiding Capillary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 8Internal and External Coatings and Chemistries: Interior Surface Chemistry of Capillary . . . . . . . . . . . . . . . .3 - 9Internal and External Coatings and Chemistries: Coatings, Interior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 9Internal and External Coatings and Chemistries: Coatings, Exterior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 1 0Alternative Cross-Sectional Geometries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 1 0

4 Fiber OOptic && CCapillary AAssembliesWhat are Assemblies? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 1Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 1Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 2What Does Polymicro Need From You? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 2The Assembly Designer Will Determine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 2Low Fiber Count Assemblies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 2High Power Laser Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 3Fiber Optic Cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 4Bundles and High Fiber Count Assemblies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 5Capillary Assemblies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 8The Polymicro Advantage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 8

5 Fused SSilica MMicro-ComponentsSculpted Fiber Tips - Tapers, Cones, Diffusers and Ball Lenses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 1Sculpted Tips Integral with Optical Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 2Polishing, Shaping and Finishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 2Tapered Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 3High Power Lasers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 3Beam Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 4Ferrules & Splices - For Optical Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 4Connectors, Ferrules & Splices - For Capillaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 5Special Capillaries: Multi-lumen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 5Special Capillaries: Square/Rectangular . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 5Special Capillaries: Windowed Capillaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 5MEMS/NEMS Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 5

G Technical GGlossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .G-1 to G-6

A AppendixPolyimide Removal from Silica Fibers or Capillary Tubing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A - 1Cleaving Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A - 2General Handling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A - 3Units of Measure - Useful Conversion Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A - 4Units of Measure - Conversion Units for Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A - 5Units of Measure - Wavelength Units, Wavenumbers and Photon Energy. . . . . . . . . . . . . . . . . . . . . . . . . . . . A - 5Polyimide Characteristics - Polyimide Physical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A - 6Polyimide Characteristics - Physical Properties - Chemical Resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A - 6Quartz/Silica Characteristics - Typical Trace Elements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A - 7Quartz/Silica Characteristics - Typical Thermal Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A - 7Quartz/Silica Characteristics - Typical Electrical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A - 8Quartz/Silica Characteristics - Typical Mechanical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A - 8


Table oof CContents

iii

Inner-lokTM is a registered trademark of Polymicro TechnologiesTeflon® AF is a trademark of E.I. du Pont de Nemours and Company

Page#

Optical Information - Refractive Index versus Wavelength Reference Table measured at 20o C. . . . . . . . . . . A - 9Optical Information - Product Application Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A - 9Optical Information - Optical Properties Optical Window Transmittance,

Corning #7980, Fused Silica, 10mm thick . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A -10

D Product RReference DDescriptorOptical FFiberSILICA/SILICA Optical Fiber - High -OH Core . . . . . . . . . . . .FV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D - 1SILICA/SILICA Optical Fiber - Ultra Low -OH Core . . . . . . . .FI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D - 2SILICA/HARD CLAD Optical Fiber - Low -OH Core . . . . . . .JTFLH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D - 3SILICA/HARD CLAD Optical Fiber - Ultra Low -OH Core . . .JTFIH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D - 4SILICA/SILICA Optical Fiber - Broadband Optical Fiber . . . .FBP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D - 5SILICA/SILICA Optical Fiber - Broadband Optical Fiber . . . .FBPI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D - 6

for Industrial ApplicationsSILICA/SILICA Optical Fiber - High-OH Deep UV Enhanced .FDP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D - 7SILICA/SILICA Optical Fiber - Solarization Resistant . . . . . .DUV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D - 8SILICA/TEFLON® Clad Optical Fiber . . . . . . . . . . . . . . . . . . .FSU, FLU . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D - 9

High -OH or Low -OH CoreSILICA/SILICA Optical Fiber - Hollow Silica Waveguide . . . .HSW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D - 11

Capillary TTubingFlexible Fused Silica Capillary Tubing . . . . . . . . . . . . . . . . . .TSP/TSG . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-12Thick Wall Flexible Fused Silica Capillary Tubing . . . . . . . . .TSP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-13Flexible Fused Silica Cap.Tubing – Deep UV Transparent Coating .TSU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-14Flexible Fused Silica Cap.Tubing – UV Transparent Coating . . . . .TSH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-15Precision Windowed Silica Capillary Tubing . . . . . . . . . . . . .WIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-16Flexible Fused Silica Capillary Tubing Pieces – Cleaving/Cutting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-17Square Flexible Fused Silica Capillary Tubing . . . . . . . . . . . .WWP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-18Light Guiding Flexible Fused Silica Capillary Tubing . . . . . . .LTSP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-19

Polyimide Coated Light Guiding Capillary

Fiber OOptic aand CCapillary AAssemblies . . . . . . . . . . . . . . . .FOA, CTA, FOC . . . . . . . . . . . . . . . . . . . . . . . .D-20

Fused SSilica MMicro-ComponentsSculpted Silica Fiber Tips . . . . . . . . . . . . . . . . . . . . . . . . . . . .Custom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-22Fused Quartz/Silica Ferrules and Sleeves . . . . . . . . . . . . . . .Various . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-23Inner-LokTM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .MLC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .D-24

EquationsOptical FFiberEq. 2-1 & 2-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Snell’s Law - Law of Refraction . . . . . . . . . . . .2 - 3Eq. 2-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Numerical Aperture . . . . . . . . . . . . . . . . . . . . . .2 - 4Eq. 2-4 & 2-5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Fiber End/Angle vs. Output . . . . . . . . . . . . . . .2 - 4Eq. 2-6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Tapered Fiber Input - Output Equation . . . . . . .2 - 5Eq. 2-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Numerical Aperture Mismatch . . . . . . . . . . . . .2 - 6Eq. 2-8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .F-number . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 6Eq. 2-9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Relation Between F# and NA . . . . . . . . . . . . . .2 - 6Eq. 2-10 & 2-11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .NA Match Between Lens System/Optical Fiber . .2 - 6Eq. 2-12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1 0Eq. 2-13 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Evanescent Wave Field . . . . . . . . . . . . . . . . . .2 - 1 2Eq. 2-14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Depth of Wave Penetration . . . . . . . . . . . . . . .2 - 1 2Eq. 2-15 & 2-16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Power Density . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1 3Eq. 2-17 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Raleigh Range Perimeter . . . . . . . . . . . . . . . . .2 - 1 3Eq. 2-18 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Weibull Plot Function . . . . . . . . . . . . . . . . . . . .2 - 1 8


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Eq. 2-19 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Static Fatigue or Stress Corrosion . . . . . . . . . .2 - 1 9Eq. 2-20 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Stress - Strain Equation . . . . . . . . . . . . . . . . . .2 - 1 9Eq. 2-21 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Fiber Bend Stress . . . . . . . . . . . . . . . . . . . . . . .2 - 1 9Eq. 2-22 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Fiber Bend Radius . . . . . . . . . . . . . . . . . . . . . .2 - 1 9

Capillary TTubingEq. 3-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Flow Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 6Eq. 3-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Poiseuille’s Law . . . . . . . . . . . . . . . . . . . . . . . .3 - 7Eq. 3-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Flow Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 7

Fused SSilica MMicro-ComponentsEq. 5-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Fiber Taper Beam Expansion . . . . . . . . . . . . . .5 - 4Eq. 5-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Spot Size to NA Relationship . . . . . . . . . . . . . .5 - 4Eq. 5-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Recommended Maximum Input NA . . . . . . . . .5 - 4Eq. 5-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Maximum Acceptance Angle . . . . . . . . . . . . . .5 - 4

FiguresOptical FFiberFigure 1-1 . . . . . . ."Line Drawing, Glass Blower At Work" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 - 1Figure 1-2 . . . . . . .Photophone, A. G. Bell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 - 1Figure 1-3 . . . . . . .Modern Fiber Drawing Tower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 - 3Figure 2-1 . . . . . . .Light and Nature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1Figure 2-2 . . . . . . .Reflections of Some Metal Coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 3Figure 2-3 . . . . . . .Refraction, Reflection and Numerical Aperture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 3Figure 2-4 . . . . . . .Numerical Aperture - Acceptance Cone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 4Figure 2-5 . . . . . . .Conical Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 4Figure 2-6 . . . . . . .Bevel Cut Fiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 4Figure 2-7 . . . . . . .Bent Fiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 4Figure 2-8 . . . . . . .Tapered Fiber Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 5Figure 2-9 . . . . . . .Large-end to Small-end Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 5Figure 2-10 . . . . . .Mae West - Fiber Collimator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 5Figure 2-11 . . . . . .Stray Light Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 5Figure 2-12 . . . . . .Quartz Refractive Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 6Figure 2-13 . . . . . .Fused Quartz Lens, 100mm, f/2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 7Figure 2-14 . . . . . .Effects of Focal Length Change with Wavelength and Optical Fiber Coupling . . . . . . . .2 - 7Figure 2-15 . . . . . .Optical Fiber Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 8Figure 2-16 . . . . . .Dispersion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 9Figure 2-17 . . . . . .Attenuation versus Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1 0Figure 2-18 . . . . . .Attenuation, Type FI - Low -OH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 11Figure 2-19 . . . . . .Attenuation, Type FV - High -OH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 11Figure 2-20 . . . . . .Effects of Cladding Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1 3Figure 2-21 . . . . . .Typical Attenuation of Polymicro High -OH UV Fiber Products . . . . . . . . . . . . . . . . . . . .2 - 1 4Figure 2-22 . . . . . .UV Effects from Deuterium Lamp on Transmission of Various Optical Fibers . . . . . . . . .2 - 1 5Figure 2-23 . . . . . .UV Damage Following 4 Hour UV Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 1 5Figure 2-24 . . . . . .FVP-UVM Fiber 214nm Degradation/Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 15 Figure 2-25 . . . . . .FDP Fiber 214nm Degradation/Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 15Figure 2-26 . . . . . .Comparison of Polymicro UV Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 16Figure 2-27 . . . . . .Spectral Attenuation of Fiber Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 17Figure 2-28 . . . . . .Characteristics of Fiber Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 17Figure 2-29 . . . . . .Weibull Plot for Fused Silica Optical Fiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 18Figure 2-30 . . . . . .Bend Radius vs Stress Level For Different Core Sizes . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 19Figure 2-31 . . . . . .Radiation Sensitivity of Optical Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 20

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Capillary TTubingFigure 3-1 . . . . . . .Capillary Tubing Bend Stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 7Figure 3-2 . . . . . . .Light Path Through Capillary Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 1 0Figure 3-3 . . . . . . .Examples of Capillary Geometries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 - 11

Fiber OOptic && CCapillary AAssembliesFigure 4-1 . . . . . . .Polymicro Technologies Low Fibert Count Assemblies . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 3Figure 4-2 . . . . . . .Polymicro Technologies Laser High Power Connector . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 4Figure 4-3 . . . . . . .Termination Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 4Figure 4-4 . . . . . . .Sample Cable Constructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 5Figure 4-5 . . . . . . .Example Hex-pack Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 6Figure 4-6 . . . . . . .Fiber Hex-pack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 6Figure 4-7 . . . . . . .Bundle Diameter vs Number of Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 7Figure 4-8 . . . . . . .Tight vs Linear Fiber Packing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 7

Fused SSilica MMicro-ComponentsFigure 5-1 . . . . . . .Fiber and Focusing Sphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 1Figure 5-2 . . . . . . .Two Sphere Lenses as Fiber Coupler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 1Figure 5-3 . . . . . . .Sculpted Fiber Tip Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 2Figure 5-4 . . . . . . .Laser Coupling into Taper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 3Figure 5-5 . . . . . . .Laser Induced Damage Threshold Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 3Figure 5-6 . . . . . . .Taper Optical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 4Figure 5-7 . . . . . . .Mechanical Splice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 4Figure 5-8 . . . . . . .Dual Fiber Ferrule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 5Figure 5-9 . . . . . . .Capillary Inner-Lok™ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 - 5

v

1 Introduction


History –– ffrom 33000 BBC

Occasionally history is reshaped by a single invention that changessome aspect of our world or environment. Optical fiber is one of thoselandmark inventions that is having a positive influence on many techno-logical developments world wide.

Humankind has communicated with light long before scientists inventedthe first low-loss optical fiber. Many thousands of years ago signal fireswere lit on prehistoric hills. Ancient Egyptians reflected the sun’s light tosend solar signals. Revolving lenses magnified small flames in light-houses long before electricity was harnessed or Alexander Graham Bellsaid his historic words to Watson.

Naturally occurring glasses have been used by man as far back asthere is archeological evidence. Glasses are known to be manufacturedas early as 1200 B.C.1 The oldest pieces of glaze and glass were dis-covered in Egypt, but it is unclear whether they originated in the MiddleEast or in Asia. Initially, glasses were used only as decorative and orna-mental objects, such as jewelry. As the techniques for manufacturingglass developed, so did practical applications. Vessels were manufac-tured through molding and pressing of the glass. The first known glassvessels date back to the reign of Thutmose III (1504-1450 B.C.).2

The invention of glassblowing in the first century B.C. greatly increasedthe use of glass for practical applications. Applications extended from

ornaments to vessels to windows. Glassblowing soon spread as the standard method of shaping glass until the 19thcentury. Skilled craftsmen further developed the techniques and tools used in glassblowing. A common technique uti-lized a hollow iron pipe approximately 4ft long with a fitted mouthpiece on one end. The craftsman, known as a“gaffer,” would collect a small amount of molten glass or “gather” on the far end of the pipe. The gaffer would moldthe exterior of the gather on a paddle or metal plate. This shaping is known as “marvering.” When sufficiently cooled,the gaffer would blow into the pipe, thereby expanding the gather into a bubble or “parison.” Through reheating andmarvering, the gaffer could control the form of the glass piece.3 Glass manufacturing developed into a major industry,and by the year 1903, a fully automated glass blowing machine had been perfected.

As glass was being developed for use primarily in vessels and window panes in the 1700 and 1800’s, other technolo-gies were being developed for communication. In the 1790’s, Claude Chappe invented “optical telegraphy.” Usingtowers mounted on hilltops, messages could be relayed from tower to tower through light signals. This was eventu-ally replaced in the mid-19th century by the electric telegraph. The idea of using light for a communication signalcame up again in 1880 when Alexander Graham Bell patented the photophone, an optical telephone system.

Separately in 1870, John Tyndall demonstrated the principle of total internal reflection to the British Royal Society.This principle demonstrates how light could be directed around curves, illustrated by Tyndall through light traveling

down a stream of pouring water. The concept of using light tosend communication signals, the principle of total internal reflect-ion, and the development of high purity glass were combined inthe mid to late 1900’s into the field of fiber optics.

By the late 1950’s, glass optical fibers were developed similar tothose now used in science, medicine, and industry. During the1950’s, image-transmitting fibers were developed by BrianO’Brien at the American Optical Company and by Narinder S.Kapany and colleagues at the Imperial College of Science andTechnology in London. Many credit Kapany with the invention ofthe glass-coated glass rod and coining the term fiber optics in 1956.

1 G.W. Morey, The Properties of Glass, 2nd ed., Reinhold, New York, (1954)2 "Glass," Microsoft® Encarta® 97 Encyclopedia, Microsoft Corporation (1993-1996)3 Reference the Internet at www.pennynet.org/glmuseum/glgloss.htm

Figure 1-1 “Line Drawing, Glass Blower At Work,”Curtesy of Corning Glass Museum

Figure 1-2 Photophone, A. G. Bell

1-1

1 Introduction


Glass-clad fibers had attenuation of about one decibel per meter by 1960, fine for medical imaging, but much toohigh for communications.4 In 1966, Charles Kao and Charles Hockham, of Standard Telecommunication Laboratoryin England published a paper proposing that optical fibers could be used as a transmission medium if their lossescould be reduced to 20dB/km. They speculated that the current high losses of over 1000dB/km were the result ofimpurities in the glass, not of the glass itself. Reducing these impurities would produce low-loss fibers suited for communications.

In 1970, Robert Maurer and colleagues at Corning Glass Works produced the first fiber with losses under 20dB/km.By 1972 losses were reduced to 4dB/km in laboratory samples, well below the level Kao and Hockham suggestedwas required for a practical communication system. Today, losses in the best fibers are less than 0.2dB/km.

Application of glass and optics continues to grow at a rapid pace. As a leading manufacturer of fused silica glassproducts, Polymicro has taken high purity glass materials and optics to even higher levels in fields such as gas chromatography, capillary electrophoresis, and specialty fiber optics. Our flexible manufacturing process provides the product you need in diameters from 30µm to 6.5mm, in lengths from 1mm to several kilometers. Stringent in-linedimensional controls yield tolerances as tight as ±1µm. Polymicro began business in 1984 and is now the leadingsupplier in many specialized market applications of synthetic fused silica optical fiber, capillary tubing and precisionsynthetic fused silica components.

Glass

The word “glass“ refers to the solid phase of a material with no long-chain molecular order. It is used almost interchangeably with “amorphous,” “non-crystalline,” and “vitreous.” Glass is a disordered structure, as compared to a crystalline material that exhibits a symmetrical, ordered structure. The most common glasses are oxide based,such as Silicates (SiO2), Borates (B2O3), Germanates (GeO2) or mixtures of these. Examples of glass in nature are volcanic material obsidian and tektites. Fused silica used in optical fiber and capillaries is a very high quality, syntheticglass of almost pure SiO2 (Silicon dioxide). Glass is usually transparent, but can also be translucent or opaque. The color may vary with the constituents of the particular glass.

Due to its structure, glass materials do not have specific melting points, but transition from solid to molten over atemperature range. This allows glasses to be easily shaped and formed. Glasses can also be modified with additivesto adjust certain physical properties such as strength, thermal expansion, transparency, index of refraction, viscosity,dielectric strength, or other characteristics. The ease of processing and modification has led to many useful applications of glass from windowpanes to insulators to optical fibers.

Quartz aand SSynthetic FFused SSilica

Modern quartz products can be many things to many people. The purestof quartz is Silicon dioxide (SiO2). Natural quartz has many impurities;some are good and some not so good for high technology use. For use inindustry, science and communications, it is rarely pure SiO2, but rather amixture of SiO2 with controlled trace impurities. Most of the trace impuritiesare introduced on purpose to give the quartz specific properties that itneeds to do the task at hand.

The name used to describe the end-product may vary as much as thetrace impurity amounts. Names like quartz, silica, fused silica, fusedquartz, synthetic quartz, synthetic fused silica or synthetic fused quartzhave been used in various publications, sometimes to describe the same

product. Much of the terminology used in silicate glasses is inconsistent, and tends to be confusing when discussedon an introductory level. To help in this handbook, we will use the following definitions.

• QQuuaarrttzz is a natural grade of crystalline Silicon dioxide (SiO2). This is the most common phase of SiO2.This is also referred to as “rock crystal.”

4 See "History of Fiber Optics,” Jeff Hetcht at www.sff.net/people/Jeff.Hecht/index.html

1-2

1 Introduction


• Fused QQuartz is a natural grade of amorphous SiO2. Typically produced from the melting (fusing) ofcrystalline quartz and refined such that an amorphous (glass) is formed.

• Silica is silicon dioxide (SiO2).

• Fused SSilica is silicon dioxide (SiO2) in its amorphous (glassy) state.

• Synthetic FFused SSilica is amorphous silicon dioxide that has been produced through chemical deposi-tion rather than refinement of natural ore. This synthetic material is of much higher purity and quality ascompared to fused quartz made from natural minerals.

• Doped ((Synthetic) FFused SSilica is amorphous silicon dioxide that has been produced through chemicaldeposition. It has been intentionally doped with trace elements such as Germanium, Fluorine, Boron, Phosphorous, Titanium, etc. to adjust the optical properties of the glass.

Drawn GGlass aandGlass TTubing

Molten glass can be drawndirectly from the furnace to maketubing, sheets, fibers, and rods ofglass that must have a uniformcross section. Large tubing canbe formed by extrusion orcasting. Smaller tubing is mostoften produced by drawing orpulling a larger cylinder of semi-fluid glass down to the desireddimension. Fused quartz/syn-thetic fused silica tubing is a littlemore difficult to manufacturerthan borosilicate glass becauseof the higher required tempera-ture. Temperature and drawspeed or rate must be controlledprecisely to maintain accuratefinal dimensions. An example of amodern-day draw tower is shownin Figure 1-3.

Physical PProperties

Depending on the composition,some “glasses” will soften at tem-peratures as low as 500oC (900oF); others only soften above 1,650oC (3180oF). Tensile strength, normally between280 and 560kg/cm2 (4.0 and 8.0kpsi), can exceed 7,000kg/cm2 (100kpsi) for a material such as high quality bulkfused silica. High performance optical fibers made from high grade synthetic fused silica typically exceed49,000kg/cm2 (700kpsi) break strength. Specific gravity ranges from 2 to 8, or from less than that of aluminum tomore than that of steel. Similarly wide variations occur in optical and electrical properties.

High TTechnology SSynthetic FFused SSilica aand CCommon QQuartz

Many manufacturers define silica glass as a generic term to describe both fused quartz (made by melting naturalquartz crystals) and synthetic fused silica (created through a chemical deposition process). Both forms provide anexceptional range of properties including:

• Very low expansion coefficient

• Broad transparency range from the deep ultraviolet to the near infrared

• High corrosion resistance

• High temperature capability

Figure 1-3 Modern Draw Tower

1-3

1 Introduction


Difference iin TTypes

A comparison of the basic trace elements in fused qquartz from rock crystal and synthetic ffused ssilica is a goodstarting point in describing a base line for typical trace impurities in quartz materials. Different manufacturers as wellas different measurement techniques will give slightly different values for the various constituents. Buyers should beaware that there are differences and care should be taken when selecting one for use.

In addition to the trace elements shown in the Appendix there are other characteristics that are important in manyapplications. One such characteristic is the -OH content in the material used for optical fiber (especially the core) andsometimes for capillary tubing use.

For optical fiber use, certain hydroxyl (-OH) absorption bands may limit the performance. Material with a high con-centration of -OH (180 to 1150ppm) offers excellent transmission in the UV wavelength range from 190nm to1064nm. It is well suited for broadband and laser applications in the UV if the energy densities are not too high. Thetransmission in the 800nm region is excellent even with high doses of Gamma radiation. Certain regions in thevisible and near IR are limited due to absorption around 724nm, 880nm, 944nm and 1242nm. There are usefulwindows (minimums) around 670nm, 800nm and 1030nm.

For longer visible and near-IR wavelengths a Low -OH material is typically used. Typical -OH contents are frequentlybelow 1ppm and give only one minor absorption peak around 1385nm in the near-IR range. This type of material isused in optical fiber from 500nm to 2100nm.

Solarized GGlass

Certain types of colorless, transparent glasses, when exposed to sunlight for extended periods, develop a pink orpale purplish color. Bottles, insulators, and other objects having color are often called “desert glass,” but the scientistprefers the term “solarized glass.”

The major constituent of most glasses is silica which is usually introduced as a raw material in the form of sand.Although silica itself is colorless in glass form, most sands contain iron as an impurity, and this imparts a greenishtint to glass. By adding other ingredients to molten glass, it is possible to offset the greenish color and produce color-less glasses. Such ingredients are known as decolorizers, and one of the most common is Manganese dioxide(MnO2). In chemical terms, the Manganese acts as an oxidizing agent and converts the iron from its reduced state(which is a strong greenish blue colorant) to an oxidized state (which has a yellowish, but much less intense, color).In the course of the chemical reaction the Manganese goes into a chemically reduced state, which is virtually color-less.

If pieces of decolorized glass containing reduced Manganese are exposed to ultraviolet radiation for long periods oftime the Manganese may become photo-oxidized. This converts it back into an oxidized form, which, even in ratherlow concentrations, imparts a pink or purplish color to glass. The ultraviolet rays of the sun can promote this processover a matter of a few years or decades, thus accounting for the color of desert glass. The effect has been repro-duced in the laboratory.

Other chemical elements that are subject to photo-oxidation can also undergo color changes in glasses whenexposed to ultraviolet light. Some of these elements, such as Selenium and Cerium have occasionally been used as a decolorizer and can produce solarization colors similar to Manganese. The colors developed by these two elements are said to range from yellow to amber.5

Solarization becomes more than an aesthetic problem when it occurs on glass components of an optical system. Thesolarization causes deterioration of the UV performance and eventual failure of the glass and the system.

Polymicro has developed solarization resistant optical fiber. It resists darkening as a result of high UV radiationlevels. More about solarization resistant optical fiber characteristics in the Fiber OOptics && OOptical FFiber chapter.

1-4

5 Education Department, The Corning Museum of Glass, One Museum Way, Corning, NY 14830-2253 U.S.A.


2 FFiber OOptics && OOptical FFiber

2-1

Optical CConcepts

A few general optical concepts and definitions should be covered before going into morespecific details on fiber optics and optical fibers. Optics is a branch of physical sciencedealing with the propagation and behavior of light and its interaction with materials. In ageneral sense, light is that part of the electromagnetic spectrum that extends from X-rays(~0.1nm) to millimeter waves (~1mm). It includes the radiant energy of the visible spectrum(~400 to 750nm) that produces the sensation of vision.

In our discussion, we will focus on an expansion of the visible spectrum from the ultraviolet (200nm) to the infrared (20µm). This is the optical spectral range where most of the major applications have been for optical fibers, quartz capillaries and hollow silicawaveguides (HSW). We will cover a few basics in optics before reviewing some more specific areas related to optical fibers.

If you find yourself in need of more information after perusing this handbook and do not want to become an opticalengineer, you might try The Photonics Design & Applications Handbook.1

Light SSources aand DDistributions

White light to lasers – collimated, coherent, Lambertian; light comes in all colors, shapes and distributions. Onesource defines light as “the electromagnetic radiation that may be perceived by the human eye.” Light can also bedefined as the form of radiant energy acting on the retina of the eye to make sight possible. The eye is remarkable inits ability to see color as well as handle more than six orders of magnitude in brightness automatically.

Humans only see the light from a portion of theoptical spectrum. The rest of the optical spectrumis in the ultraviolet (UV) or in the infrared (IR).Several animals use their IR capability to hunt.Insects use UV reflection to locate pollensources.

The main characterization of light is by its wave-length, most often specified in nanometers (nm).We can also define a frequency to each wave-length by dividing the speed of light by the wave-length. The human eye is most sensitive to lightat a wavelength of 555nm, which is equal to 5.4x 1014 Hz. This high frequency (and its inherentbandwidth) is what makes light such a goodinformation carrier in optical fibers.

The range of light wavelengths we see is calledthe Visible Spectrum. It covers a range fromabout 400nm to 555nm to 750nm (violet to greento red). The near-UV wavelength range just shorter than the visible is the range from which we most often want toprotect our eyes and skin. Varying amounts are present in sources like high power quartz halogen lamps, fluores-cence lamps, the sun and lasers used in medicine. The range just longer than the visible, the near-IR, is most com-monly used in IR remote controls and is the dominant wavelength in the night sky spectrum. Even though we can notsee these near-visible wavelengths our technology advancement over the past few centuries has led to the develop-ment of electro-optical sensors to detect and measure them, new light sources to produce them, and optical fiber totransmit them.

LLiigghhtt comes in all colors. If it is only one color or wavelength, it is called monochromatic, like a laser. If it is a blendof many colors, it is called polychromatic, such as the sun. For a good reason there is a very good match betweenthe sun and the eye. Nocturnal animals usually have peak eye sensitivity shifted toward the near infrared where thenight sky illumination peaks.

1 The Photonics Design & Applications Handbook, 43rd Edition, 1997, Laurin Publishing Co., Inc., Pittsfield, MA

Figure 2-1 Light and Nature



Two additional properties of light that are important in many areas of optics are the spatial distribution of the light andthe coherence of the lightwaves. The spatial distribution describes the direction(s) that the light is traveling. If itappears uniform in all directions, that is it has uniform brightness from any viewing angle, it is called Lambertian. Theother extreme is collimated light, which essentially travels in only one direction such as a laser. The coherence oflight refers to the way the light waves are ordered or phased with each other. Common incandescent lamps are inco-herent (random phase) while lasers are coherent (in-phase).

A Lambertian source is a plane surface that emits (reflects) a flux proportional to the cosine of the angle to thenormal to the surface, but appears to have uniform brightness at all angles. Matte “white” paint and phosphors areapproximate examples of such source planes and the light diffused by opal glass is a close approximation for mostmeasurements.

Getting LLight WWhere YYou WWant IIt

We are all familiar with a mirror reflecting light. Unfortunately there are significant losses associated with this reflection.The loss at the glass-air interface is about 4% and there is approximately another 4% loss at the glass-mirror surfaceinterface. This means for each reflection of light there is about a 10% loss. As a waveguide, this would not be a veryeffective means to direct light for any distance since after 50 reflections only about 0.5% of the light would remain.

We can also get reflection under certain conditions from a glass-air or glass-glass interface. These losses can belower than 0.1% per reflection. For the case where each reflection gives 99% of the light back, there will be about37% left after 100 reflections. That’s a little improvement. None of these losses, however, included the effects of anylight lost due to the light beam spreading and not hitting the next surface. We could use a hollow glass tube or capil-lary to prevent this but we still need better reflection. Under the right conditions a glass rod with a different opticalmaterial surrounding it can be produced in a long fiber with a much higher reflection per bounce.

With today’s optical fiber and thousands of reflections it is now quite common to have an average power loss of lessthan 5dB per kilometer. This equates to about 32% of the input power remaining at the output end, after 1km.Astonishingly better transmission than a thousand very good mirrors or 10 sheets of window glass.

The SScience oof FFiber OOptics

The science of fiber ooptics deals with the transmission or guidance of light (rays or waveguide modes in the opticalregion of the spectrum) along transparent fibers of glass, plastic, or a similar medium. The phenomenon responsiblefor the optical ffiber or light-pipe performance is the law of Total IInternal RReflection ((TIR).

Total IInternal RReflection

A ray of light incident upon the interface between two transparent optical materials of different indices of refractionwill be totally internally reflected under certain conditions. When the ray is incident from the direction of the moredense material and the angle made by the ray with the normal to the interface is greater than the critical angle, thelight will be reflected, not refracted. The critical angle is dependent only on the indices of refraction of the media.

Rays may be classified as meridional and skew. Meridional rays are those that pass through the axis of a fiber whilebeing internally reflected. Skew rays are those that never intersect the fiber axis although their behavior patternsresemble those of meridional rays in all other respects. For convenience, we will deal only with the geometric opticsof meridional ray tracing.

An off-axis ray of light traversing a fiber 50µm in diameter may be reflected 3,000 times per foot of fiber length. This number increases in direct proportion to diameter decrease. In principal, total internal reflection between twotransparent optical media results in a loss of zero loss per reflection; thus a useful quantity of illumination can betransported. This spectral reflectance differs significantly from that of metallic coatings shown graphically. An aluminum mirror cladding on a glass fiber core would sustain a loss of approximately 10 percent per reflection, a level that could not be tolerated in practical fiber optics as shown in Figure 2-2. The reflection at the core-clad interface must be much higher in optical fiber to obtain useful light transmission over long distances.

2-2



As indicated in Figure 2-3, the angle of reflection isequal to the angle of incidence. (By definition, theangle is that measured between the ray and thenormal to the interface at the point of reflection.)

Light is transmitted over the length of a fiber at aconstant angle with respect to the fiber axis.Scattering from the true geometric path can occurdue to:

• Irregularities in the core/clad interface of the fiber.

• Surface scattering at the interfaces.

• Scattering in the bulk material.

Light will be scattered in proportion to fiber lengthand depends on the angle of incidence. To be functional long fibers must have an optical qualitysuperior to that of short fibers. End face scattering

occurs readily if optical polishing has not produced a smooth surface. Pits, scratches, and scuffs scatter light significantly. Additional losses such as bending are covered in the Internal && EExternal LLosses section.

The speed of light in matter is less than the speed of light in air.The change in velocity that occurs when light passes from onemedium to another results in refraction. A portion of the light inci-dent on a boundary surface from a higher index media to air isnot transmitted but is instead reflected back into the air. Themajority that is transmitted is totally reflected from the interface,assuming that the angle is less than the critical angle as inFigure 2-3.

The relationship between the angle of incidence, I, and the angleof refraction, R, is expressed by Snell’s llaw as:

where, nii is the index of refraction of first media (air in many cases) and nrr the index of refraction in which the lightcontinues to travel (in this case the core). When nii = 1(air) for all practical purposes, the refractive index of the corewould be calculated from:

Numerical AAperture

NNuummeerriiccaall aappeerrttuurree ((NNAA)) is a basic optical characteristic of a specific fiber configuration. It can be thought of as rep-resenting the size or “degree of openness” of the input acceptance cone in Figure 2-4. Mathematically, numericalaperture is defined as the sine of the half-angle of the acceptance cone (sin θ).

The light-gathering power or flux-carrying capacity of a fiber is proportional to the square of the numerical aperture.This is the ratio between the area of a unit sphere within the acceptance cone and the area of a hemisphere (2πsolid angle). A fiber with a numerical aperture of 0.66 has 43 percent of the flux-carrying capacity of a fiber with anumerical aperture of 1.0.

2-3

(Eq. 2-1)

(Eq. 2-2)

Figure 2-3 Refraction, Reflection and Numerical Aperture

Figure 2-2 Reflection of Some Metal Coatings

ni • sin I = nr • sin R

nr = sin Rsin I



Snell’s law can be used to calculate the maximum angle withinwhich light will be accepted into and conducted through a fiber:

Where, θMMAAXX is the half-angle, n00 the refractive index outside thefiber end (air =1.0), nCCOO the refractive index of the core, and nCCLL

the refractive index of the clad.

As light emerges from the more dense glass medium into a less dense medium such as air, it is again refracted. Theangle of refraction is greater than the angle of incidence, R >> II, when emerging into a lower index media. Because Ris by necessity less than 90 degrees, there must be a limiting value of I, the incident angle, beyond which no incidentray is refracted. This becomes the critical angle, and rays that strike at a greater angle are reflected. This is the prin-ciple behind Total IInternal RReflection ((TIR) in optical fiber.

It should be noted that this formula, for the calculation of numerical aperture, does not take into account striae,surface irregularities, and diffraction, all of which tend to decollimate the beam bundle. Decreasing the clad indexand/or increasing the core index will increase the NA, which increases the Full Acceptance Angle and the Field of View.

Input-Output PPhenomena

If a ray is incident at angle θ, it will ideally emerge from a fiber atangle θ. In practice, however, the azimuthal angle on emergencevaries so rapidly with θ, the length and diameter of the fiber, etc.that the emerging ray spreads to fill an annulus of a cone twiceangle θ, as shown in Figure 2-5.

The exit end of a fiber will act as a prism if it is not cut perpendicu-lar to the fiber axis. A bias cut will tip the exit cone as shown inFigure 2-6. Thus,

where α is the axis of the deflected ray and β is the cut angle tothe normal of the fiber.

The preservation of angle θ on exit is only an approximation.Diffraction at the ends, bending, striae, and surface roughness willcause decollimation or opening of the annulus. The striae androughness cause progressive decollimation; diffraction and bendingmay be regarded as end finish factors (Figure 2-7). The effect ismost apparent in systems in which collimated transmission isemphasized.

2-4

(Eq. 2-3)

Figure 2-4 Numerical Aperture - Acceptance Cone

Figure 2-5 Conical Output

(Eq. 2-4)

(for small angles) (Eq. 2-5)

Figure 2-6 Bevel Cut Fiber

Figure 2-7 Bent Fiber



Tapered FFibers

Tapered fibers are governed by one important relationship,

where diameters and angles are as shown in Figure 2-8. The angleof reflection of a light ray is equal to the angle of incidence.

Therefore, light entering the small end of a fiber becomes more colli-mated as the diameter increases because the reflecting surface isnot parallel to the fiber axis. Collimated light entering tapered fibers at the large end, on the other hand, becomesdecollimated, and if the angle of incidence exceeds the acceptance angle, it will pass through the side of the fiber.The error perhaps most frequently made by the novice is to attempt to condense an area of light that is Lambertianusing a taper. As illustrated in Figure 2-9, this merely “throws” light out the sides. If the incoming light is in a smallangle, the outgoing flux per unit area can be increased.

When working with a system of the “Mae West” variety (Figure 2-10), it is important to remember that the smallestdiameter determines the acceptance angle of the system. This is in conformity with the relationship previously citedthat governs tapered fibers.

Light entering the side of a fiber or taper can be trapped if the angle of incidence is greater than the critical angle.The stray-light cone thus produced forms the basis for one type of injection lighting (Figure 2-11).

Matching NNumerical AApertures

In optical fiber use, it is extremely important to attempt to match mating fiber NA’s. With the same fiber core diameterit is usually best to center the two fiber ends using a tapered sleeve or set of mating connectors. If there is a largemismatch in the fiber diameters, a tapered optical fiber may be a good solution. Two different diameter spheres in acoupler may also achieve the needed result.

2-5

Figure 2-8 Tapered Fiber Transmission

Figure 2-9 Large-end to Small-end Transmission

Figure 2-10 Mae West - Fiber Collimator

Figure 2-11 Stray Light Injection

(Eq. 2-6)



The target is to match the NA’s as best possible since the light loss in a lens coupling will vary as the square of the NA. You should also take care that the NA’s of two coupled fibers are matched. Optical loss due to fiber NAmismatch is represented by:

Where NA11 is transmitting fiber and NA22 is the receiving fiber. If NA11 is less than NA22 then the mismatch loss is zero.When there is a difference in NA between the two fibers, the higher NA should be the second in line so that all ormost of the flux from the first fiber is accepted by the second.

The total flux lost will be a function of how well the input acceptance cone of the second fiber is filled (without over-filling) by the output source fiber. These fiber-to-fiber matches are also a function of other conditions besides NA,such as core alignment, angle, distance between the fibers, surface cuts, angles and finishes, as well as any opticalcoupling media characteristics.

When using optical fiber in an optical system, the acceptance cones should match at each interface. The f-number,f#, of a lens is given by:

where efl is the lens effective focal length and D is the diameter of its entrance pupil. The relation between the f#and the numerical aperture (NA) is:

So in order to match NA’s between the lens system and the optical fiber, we need:

This means, if we have a lens with an efl of50mm and a 18mm aperture (f# = 2.8), wewould need an optical fiber with an NA of atleast 0.18 to get an ideal match. This doesnot include any losses due to Fresnelreflections and lens focal spot size versuscore size mismatches.

Because of the rapid change of the refrac-tive index of quartz in the UV (Figure 2-12),great care should be taken when designingspectrometers or other systems that mustwork in both the visible and the UV. Eitherfocus adjustments need to be included or acompromise focus position must bechosen. Since the focal length decreaseswith wavelength (about 13% from 550nm to220nm), the NA increases. Matching theNA’s and assuring the focus spot is justinside the fiber core at the shortest wave-length would be the best situation. Thebalance between these two characteristicsmay still leave some losses.

2-6

(Eq. 2-7)

(Eq. 2-8)

(Eq. 2-9)

(Eq. 2-10) (Eq. 2-11)or,

Figure 2-12 Quartz Refractive Index

f

f



The efl and NA characteristics for a fused quartz plano-convex, singlet lens versus wavelength can be seen in Figure 2-13.

This axial chromatic aberration problem is solved in visible and IR optical systems, to some extent, by adding colorcorrection using optical elements with complementary characteristics. In the UV there are very few choices of materials to obtain color correction. The refractive index versus wavelength curve in the graph illustrates the reasonfor some of the problem.

A generalized illustration of lens coupling into an optical fiber for two different wavelengths may help to clarify thephenomena of UV chromatic aberrations in quartz. As can be seen in the illustration, not only is the focal lengthshorter at 220nm (~13% less), but the exit cone angle is larger. Both of these changes from the 550nm case cancause losses when trying to use optical fiber over an extended wavelength range.

Fiber TTypes && MModes oof TTransmission

In fiber optics, the term “mode” refers to a stable propagation state of light down the fiber. Fibers can have anynumber of stable propagation states (modes), giving rise to two basic types of optical fibers, mmuullttiimmooddee and ssiinnggllee--mmooddee. Multimode obviously refers to a fiber that has many modes of propagation, while a singlemode, by design,only has one. Whether a particular fiber is multimode or singlemode depends on the fiber geometry, core/clad refrac-tive indices, and the wavelength of operation. Multimode fibers can be further broken down into two subcategories,sstteepp--iinnddeexx and ggrraaddeedd--iinnddeexx. Each type has distinctive advantages and disadvantages, which will be discussed inmore detail.

2-7

Figure 2-14 Effects of Focal Length Change with Wavelength and Optical Fiber Coupling

Figure 2-13 Fused Quartz Lens, 100mm, f/2

e ef fl l, ,

m mm m



Step-Index MMultimode FFiber This was the first fiber type to find practical application, and continues to be in wideuse today. A step-index multimode fiber allows the light to travel at many different angles within the fiber, therebyallowing many modes of propagation. The term “step” refers to the step function the refractive index takes at thecore/clad interface.

The advantages of a step-index multimode fiber are related to the relatively large core area and high numerical aper-tures. Both of these properties allow light to be easily coupled into the fiber. In turn, this allows the use of inexpen-sive termination techniques, low cost diodes, and high power handling capability. These fibers are therefore widelyused in high power laser delivery applications (medical procedures, material processing), industrial process controllinks (factory automation), short distance data communications, and fiber sensors.

A disadvantage to step-index multimode is bandwidth. Referring toFigure 2-15, the path the light takes down a step-index multimodefiber will be longer or shorter depending on the angle of propaga-tion. This difference in path length causes the pulse of light tospread out during its journey down the fiber. This is known asmodal dispersion (see Dispersion section). As one pulse spreads,it eventually interferes with neighboring pulses, distorting the trans-mission signal. The longer the fiber length the more severe thispulse spreading will become. However, this is only a problem inapplications that require a coherent signal, as in communicationslinks. Power delivery or sensor systems do not require coherenttransmission and many data communication or industrial processcontrol links are relatively short distances (less than 2km) allowingthe widespread use of step-index multimode fiber.

There is a wide selection of step-index multimode fiber available.Sizes vary from ~50 to >2000 µm core diameters. Their construc-tion can be silica or plastic cladding using silica, plastic, or liquidas a core. There are also applications with no core called hollowwaveguides. The silica constructions allow lower attenuation,greater spectral range, higher power handling capability, andgreater environmental range. Plastic fibers offer lower cost and

greater flexibility but are limited in transmission and environmental properties. Hollow waveguides are used princi-pally in the IR, with some recent developmental work to construct hollow waveguides for use in the UV range.

Polymicro offers a wide selection of step-index, multimode fibers, particularly for laser power delivery and stringent orharsh environmental conditions. Please refer to our data sheets located in the back of this handbook.

Graded-Index MMultimode FFiber As the name implies, the refractive index of this fiber gradually decreases from thecore out through the cladding, as opposed to the abrupt step change of step-index. Instead of taking a zigzag pathdown the fiber, the gradual change in refractive index directs the light in a sinusoidal path as previously illustrated.Since the light travels faster in a material of lower refractive index, the light traveling on the outer reaches of thegraded region moves more quickly, thereby reducing the amount of pulse spreading. The result is a dramatic >25-fold increase in bandwidth over step-index multimode fibers.

Graded-index is actually a compromise between step-index multimode and singlemode fibers, trading off bandwidthfor ease of termination and light launch. The graded profile and smaller core increases bandwidth over step-indexmultimode, but the core sizes are still large enough for convenient termination and use of lower cost diodes. In morerecent years, the components and techniques for terminating singlemode has improved dramatically, so graded-indexhas seen a decline in market share. However, graded-index remains a popular standard for use in medium distance(2-15km) data communication links.

The most common core sizes for graded-index multimode fibers are 50, 62.5, and 100µm. These sizes have becomeindustry standards. The construction is always silica core/silica clad based, with dopants (typically Ge, B, P, and F)used to adjust the refractive index in the graded profile. This fiber is used almost exclusively for medium distancedata communication (local area networks), although it is sometimes used for fiber sensor systems. The smaller core

2-8

Figure 2-15 Optical Fiber Modes



area makes this fiber less useful for power delivery applications, however new special, larger core designs specifi-cally for high power applications are available.

Singlemode FFiber In singlemode fiber the core size is reduced to the point (5-10µm diameter) where only onemode, the primary mode, can be guided. This mode essentially travels straight through the fiber and thus is notsubject to the pulse spreading seen in multimode fiber due to different path lengths. The net effect is a substantialincrease in bandwidth since all the light is traveling at the same speed for the fiber length. In addition, using theprimary mode and higher operational wavelengths (1310 and 1550nm) results in very low attenuation. For thesereasons, singlemode is the fiber of choice for long distance data and voice communication.

Singlemode does experience some distortion of the signal, but this is due primarily to chromatic dispersion, which isvariation in light speed due to the pulse not being purely monochromatic. This type of dispersion is very small whencompared to the modal dispersion experienced in multimode fibers.

Singlemode fiber typically consists of a silica core/silica clad construction with a step-index refractive index profile.The core and/or clad is doped to obtain the index difference between the core and clad. The core size, being verysmall, is more difficult and costly to terminate versus the multimode fibers, but for long distance systems this cost isacceptable. In contrast, the small core size does not allow a great deal of power input, and therefore this fiber is gen-erally not suitable for power delivery and many sensor applications.

Dispersion

As they travel down an optical fiber, optical pulses willbroaden. This is called dispersion. Since eventually thepulses will overlap and the data will be lost, dispersiondetermines the data carrying capacity.

Step-index optical fibers generally have many modes ofpropagation. Modes are represented by different angleswith which the light rays hit and reflect from the core-cladinterface. These various angles can be caused by the various angles that light enters the fiber or by other effects inthe fiber such as scattering or changes in angle due to bending. The time it takes the light in a particular mode totravel from one end to the other is directly proportional to the distance it has traveled in the optical fiber. Low ordermodes get to the output end quicker than higher order modes. There are three main types of dispersion:

• Chromatic ddispersion … is a result of different wavelengths of light traveling at different velocities in thecore material. Since typical light sources provide power distributed over a range of wavelengths, ratherthan a single, discrete "line," the pulses spread out as they travel through the fiber. This is predominantin single-mode fibers.

• Modal ddispersion … is due to different fiber modes traveling along different paths through multimodefiber. The result is broadening of the pulse as the higher-order modes reach the output behind the fundamental mode. This is predominant in step-index, multimode fibers.

•• WWaavveegguuiiddee ddiissppeerrssiioonn … is due to the geometry of the fiber and results in different velocities of thevarious modes for different wavelengths. It is the least important of the causes of dispersion.

Bandwidth

The data-carrying capacity of an optical fiber (just as with a wire or coax) is called bbaannddwwiiddtthh. It is normallyexpressed as a distance-frequency product such as MHz-km (megahertz-kilometers) or more often as GHz-km(GigaHertz-kilometers). What this really means is, if you need to transmit a 27MHz signal (common frequency for CBradio) up to 1 kilometer (0.6 miles) and still detect it as a useful signal at the other end, you need an optical fiber witha bandwidth of at least 27MHz-km. Step-index, multi-mode fiber would just barely do it. If you wanted to transmit atthe frequency of the newer wireless telephones, 900MHz, you would probably have to go to step-index, singlemodefiber to get a 1km range.

The main cause of bandwidth limiting is pulse broadening caused by modal and chromatic dispersion in the fiber.This is why step-index, singlemode fiber does so well over long distances. But, due to the very small core diameter, itdoes have major limitations when it comes to getting light into the fiber efficiently.

2-9

Figure 2-16 Dispersion



For step-index, multimode fiber pulse-broadening is a very difficult parameter to calculate, since macro-bending, fiberlength and the number of modes initially injected, all have a bearing on the pulse spreading.

Typical bandwidths for the different types of fiber are:

Focal RRatio DDegradation ((FRD)

Focal RRatio DDegradation ((FRD) is the decrease in focal ratio (decrease in effective F-number) in an optical fiberversus its length. This can be a significant parameter of an optical fiber when matching NAs in telescope-spectro-meter systems such as used in astronomy. The ability of a fiber to preserve the angular distribution of the input beamfrom the telescope to the spectrometer is very important.

The major causes of FRD are mechanical variations in the fiber dimensions with length (under the manufacturer’scontrol) and the mechanical set-up of the instrumentation (under the control of the user). Small variations in the fibercore diameter or core-clad interface can cause mode stripping, resulting in FRD. Both macro-bending and micro-bending will cause FRD.

Without proper NA matching between the telescope, spectrometer and the fiber, energy may also be lost from overfilling the acceptance cone of the optical fiber or not filling the NA of the spectrometer. Ramsey found that f-ratios off/3.0 to f/7.0 were the best matches for glass fibers depending on the fiber diameter.2 Over-filling or under-filling theoptical fiber acceptance cone appeared to produce higher losses. Macro-bending did not appear to have any majoreffect on FRD while micro-bending did.

Attenuation && TTransmission

The attenuation in an optical fiber is usually expressed in decibels per kilometer (dB/km) in the visible and IR spec-trums and in dB/m in the UV. The attenuation is calculated as:

Where Piinn is the input power injected intothe fiber core and Poouutt is the attenuationoptical output collected from the distal end.The NA of the input and output optical testsystem must be matched and effects oflens focal lengths at the test wavelengthmust be considered so that the acceptancecone of the fiber under test is not erro-neously over-filled. This can cause exces-sive attenuation values since input energypresent in the test standardization or cali-bration may not enter the input fiber undertest. Since both the core and the claddinghave transmission characteristics that varywith wavelength, attenuation is normallyplotted with respect to optical input wave-length.

FIBER TYPE BANDWIDTH

Step-Index, Single mode 100 GHz-kmGraded-Index, Multimode 500 MHz-km @ 1300nm

160 MHz-km @ 850nmStep-Index, Multimode 20 MHz-km

2-10

(Eq. 2-12)

Figure 2-17 Attentuation versus Transmission

2 Lawrence W. Ramsey, “Focal Ratio Degradation in Optical Fibers of Astronomical Interest,” Pennsylvania State University



Low --OH aand HHigh --OH OOptical FFiber

The optical attenuation characteristics are quite different for High -OH and Low -OH optical fiber core material. The-OH content of the core fused silica must be formulated into the raw boule material before the optical fiber is made.The choice is dependent on the user’s application. The Low -OH type optical fiber has very low attenuation through-out the near-IR wavelength range from 700nm to beyond 1800nm, except for a small peak at 1385nm.

The normal absorption peaks at 726nm, 880nm, 950nm, 1136nm and longer, that exist in the High -OH material usedin UV applications are not present in Low -OH material. Conversely, the Low attenuation of the High -OH in the UV issignificantly better than the Low -OH material. Typical curves for Polymicro’s type FI fiber (ultra Low -OH) used forvisible and NIR and FV fiber (High -OH core) used primarily for UV applications follow. Polymicro has recently introduced a new broad-spectrum FB fiber that operates between 275-2100nm. Please refer to FBP specificationsheet under Optical FFiber in the Product RReference section for more information.

Internal && EExternal LLosses

There are several sources of attenuation in optical fibers. In addition to losses due to mechanical variations in thefiber dimensions, there will be losses due to:

•• RRaayylleeiigghh ssccaatttteerriinngg ... microscopic irregularities in the index of refraction of the glass are the most important mechanism for attenuation in modern fiber. Rayleigh scattering is wavelength dependent (proportional to 1/λ4) and is thus less significant at longer wavelengths.

•• AAbbssoorrppttiioonn ... in silica can be significant at short-wavelengths due to UV (electronic) absorption, and at long-wavelengths (infrared) due to multiphoton (atomic vibrational) absorption. In addition, unwantedimpurities and intentional dopants in the fiber absorb optical energy around specific wavelengths. State-of-the-art manufacturing methods have reduced impurity levels to the point that their effect isalmost insignificant.

2-11

Figure 2-19 Attenuation FV - High -OH

Figure 2-18 Attenuation, Type FI - Low -OH



• Bending ... Micro-bending, the result of microscopic imperfections in the fiber geometry, is caused by themanufacturing process or mechanical stress. Macro-bending occurs when the fiber is bent into a larger,visible curvature. In both cases, light rays hit the core-cladding interface with angles greater than the crit-ical angle and optical energy is lost into the cladding. Bend sensitivity of fiber includes the attenuationlosses from both macro and micro-bending. It can be given in terms of dB of loss for a particular bendradius and wavelength. Proper selection of coating materials and optical properties can dramaticallyimprove microbending effects on transmission.

Bend RRadius –– OOptical EEffect

Any bend in a multimode optical fiber will cause mode stripping or loss of higher order modes in the fiber. Thesmaller the radius the higher the induced loss.

Long term exposure of optical fiber to bending stress will shorten the mechanical lifetime of the fiber but generallywill not change the attenuation until the fiber fails. See bending lloss in the glossary.

The bend rradius is generally defined as the radius of the drum or mandrel on which the fiber is to be wound or bent.

For a given radius of curvature, the loss due to bending becomes significant when the effective index of a mode isbelow a “cut-off” value. The actual loss in a step-index fiber is very complex to calculate. There are usually so manyassumptions by the time the calculation is finished that is better to depend on rule of thumb or actual measurementsrather than depend upon calculations. See Mechanical BBend RRadius LLimits && SStress section.

Evanescent WWave LLosses iin SSmall DDiameter FFibers

In the basic discussions on total internal reflection, it was indicated that under certain conditions between the coreand cladding indexes, light is reflected at the interface between the two surfaces. When the light wave meets theboundary between the two indexes the light standing wave actually penetrates about a quarter wavelength into thesecond media while being reflected. This penetrating wave is called an evanescent wave. It actually decays expo-nentially with distance from the interface, with a characteristic penetration depth of 50 to 100nm.

Since the field cannot go to zero immediately, it decays exponentially into the lower cladding according to the relation,

where δ is the distance from the interface. This exponentially decaying wave is the evanescent wave. The decay ofthis wave at an angle α, between the incidence ray and the normal to the surface, is characterized by a penetrationdepth, dpp, the distance from the interface at which the wave amplitude falls to 1/e of its initial value at the interface.3

The referenced article gives an excellent application for using the evanescent wave. Care should be taken, however,when specifying small fibers to make sure that the cladding is thick enough to contain the evanescent wave andthereby not create unwanted losses. As a rule of thumb, for multimode fibers, the cladding thickness should be atleast 10 times the operational wavelength.

An optical fiber that has a core to clad ratio of 1:1.1, i.e., a core of 50µm and an OD of 55µm has a cladding thicknessof only 2.5µm. This situation is barely 10 times the wavelength if used in the UV and only about 4 times if used at600nm. In this situation, it is advisable to use a larger fiber (thicker cladding and/or larger core) if possible. Since theloss in fused silica is higher in the UV, some additional cladding losses may be contributed if the cladding is too thin,but they will be even more noticeable in the red part of the spectrum and NIR. The FVP100110125 fiber has a 5µmcladding thickness. FV-data is typical of High -OH silica/silica fibers with cladding of 10µm or greater.

2-12

(Eq. 2-13)

3 See N. Nath & S. Anand, “Evanescent wave fiber optic fluorosensor: effect of tapering configuration on signal acquisition,” Optical Engineering, 3377(1) p220-228,January 1998, for excellent discussion on evanescent waves, tapers and V-number.

(Eq. 2-14)



The effect of having too thin a cladding can be seen in the chart below.

Power TTransmission

The amount of laser power that a fiber is transmitting without damage is specified as the power output of the laserdivided by the area of the laser spot,

where ω is the beam radius of the laser beam at distance L from the fiber surface. The radius ω is given by:

When the position of ω00, the focal waist, is inside an optical fiber of index n, then the Rayleigh range parameter z00 isgiven by:

The output of a pulsed laser, typically specified in millijoules (mJ) of energy per pulse, must first be converted to thepower per pulse. For example, a pulsed laser that produces 50mJ in a 10ns pulse produces an output power of5MW.

For a Nd:YAG laser (1064nm) emitting 10ns pulses, synthetic fused silica fibers have survived pulse energies up to0.4 - 0.6 Giga-Watts/cm2.

To achieve maximum power transmission the end face of the fiber must be optically smooth and perpendicular to thebeam. The beam must be focused properly to prevent light from leaking into the cladding or else the polymercladding or buffer coating may be damaged. The epoxy used for bonding the fiber to the connector can be affectedas well. For this reason, a silica/silica fiber is often used in a specially designed mounting or connector to better tolerate the high power densities and rapid heating levels. It is also recommended that the beam fill no more than70% of the core diameter, and with a uniform power distribution across the face of the fiber.

Configurations that help spread or reduce the energy density at the fiber surfaces have helped reduce laser damageat high energy levels. Options such as tapered end-tips, spheres, and other shaped end tips manufactured onto theend of the fiber are additional options offered by Polymicro. Some of the many possible configurations are shownand discussed in the Fused SSilica MMicro-Components chapter.

2-13

Figure 2-20 Effects of Cladding Thickness

(Eq. 2-15)

(Eq. 2-16)

(Eq. 2-17)



Fluorescence iin FFiber OOptical MMaterials

Fused silica glass, especially the lower -OH types, can exhibit fluorescence when illuminated with 254nm light with aSchott UG-5 glass filter. From Heraeus Amersil data, this apparently does not occur in the High -OH materials in theSuprasil® family. Slight blue to blue-violet appears in materials such as Homosil®, Herasil®, Infrasil® and HOQ 310.Quartz glass is free from visible fluorescence at excitation wavelength greater than 290nm.

Some varieties of sapphire have been reported to exhibit fluorescence under UV excitation. Cladding and buffermaterials used in the manufacturing of optical fiber may exhibit similar emission characteristics under some types ofexcitation, UV, soft X-ray or energetic particles. Polymicro offers a variety of fiber types that use low fluorescencesilica.

UV FFiber PPerformance ((Solarization)

Polymicro manufactures several categories of silica fibers that are capable of operation in the UV wavelength range.These include:

1) FVP (Standard High -OH)

2) FVP-UVM (Modified Core High -OH)

3) FVP-UVMI (Hydrogen Loaded UVM)

4) FDP (Deep UV Fiber)

In selecting the best product for a UV application, there are 3 main performance criteria that should be considered.These are:

1) Initial Attenuation.

2) Additional attenuation caused by UV radiation.

3) Stability following initial UV degradation.

Initial AAttenuation. This is the attenuation as a function of wavelength for new fiber prior to any UV exposure. Thisis typically measured in dB/km, and it can be changed to dB/m by dividing by 1000. Figure 2-21 below shows atypical initial attenuation for all of Polymicro’s UV products.

UV IInduced AAdditional AAttenuation. This is the damage induced by exposure to UV radiation. It is commonly known as solarization.Most of this damage occurs at wavelengthsless than 250nm, with peak damage occurringat approximately 214nm. The degree ofdamage varies greatly with the type of fiber.Figure 2-22 shows typical solarization levels asa function of time for various Polymicro UVproducts as shown in linear units for 1m length.Figure 2-23 shows comparison of 4hr exposurelevels as a function of wavelength. Typically,this additional attenuation is measured in unitsof dB/m and is scalable to any length.

FVP-UVM fiber has improved performance compared to the standard High -OH FVP fiber.

The hydrogen loaded fiber, FVP-UVMI, has almost no degradation, but this fiber has a limited lifetime and eventuallyreverts to typical FVP-UVM performance. This lifetime can be extended by keeping the fiber refrigerated and byusing larger diameter fibers. The deep-UV enhanced FDP fiber has low solarization degradation, but with no limit onlifetime and no need for refrigeration.

2-14

Herasil®, Homosil®, Infrasil® and Suprasil® are registered trademarks of Heraeus Quarzglas GmbH & Co.

Figure 2-21 Typical Attenuation of Polymicro High -OH UV Fiber Products



2-15

SSttaabbiilliittyy ((RReeccoovveerryy)).. When UV radiation is removed from a fiber, some of the solarization damage can recoverover the following several hours. When maximum transmission is a priority, this improvement in transmission isuseful. However, for applications where consistent, stable output is critical, this recovery can be detrimental. Figure2-24 shows the initial degradation as well as the subsequent degradation following 20 hours of recovery for a typicalFVP-UVM fiber. Figure 2-25 contains similar data for a typical FDP fiber.

SSuummmmaarryy.. The table in Figure 2-26 on the next page discusses each of the Polymicro UV fibers in detail with thecharacteristics of each type.

In selecting a fiber type for an application, the performance characteristics must be balanced against one another as wellas against the price. For example, applications that only require transmission from 250nm up through the visible range,standard FVP would work well and is very economical. For applications that have stringent stability requirements deep intothe UV, but have a short period of usage, FVP-UVMI would work very well. For applications that require stability and along lifetime in the deep UV, FDP would be the best option.

Figure 2-22 UV Effects frm Deuterium Lamp on Transmission ofVarious Optical Fibers Figure 2-23 UV Damage Following 4 Hour Exposure

Figure 2-24 FVP-UVM Fiber 214nm Degradation/Recovery Figure 2-25 FDP Fiber 214nm Degradation/Recovery



2-16

Infrared WWaveguides

At near-IR to IR wavelengths (2.1 to 20µm), fused silica does not transmit light particularly well due to multiphoton(atomic vibrational) absorbance. However, there are several materials that do transmit well at these wavelengths.Chalcogenide glasses, fluoride glasses, polycrystalline metal halides, and some germanate oxides perform wellbeyond 2.1µm and have all been fabricated into optical fibers. Unfortunately, these materials tend to be very difficultto process, and have inferior mechanical and durability properties when compared to fused silica. This has limitedtheir widespread use, but they are still utilized in specialized applications.

There is also a class of optical fiber known as Hollow WWaveguides (HSW). This type of waveguide can effectivelytransmit wavelengths in the IR (out to 20µm). A HSW can be one of two types of light guides:

1) “leaky” guide, or 2) attenuated total reflectance guide (ATR)

The HSW guide consists of a hollow tube coated on its inner surface with a reflective metal (e.g. Ag). This coatingmay or may not be followed by dielectric coating which serves to improve reflectivity and provide protection to themetallic surface. This type of waveguide has been produced using plastic, metal, and glass capillary tubing. Tubingproduced from synthetic fused silica is most effective due to its tight dimensional control, smooth surface properties,high strength, and lower cost. HSW fabricated with synthetic fused silica tubing approach the theoretical limits oftransmission for this type of waveguide. They are finding increased utilization in sensing and in Er:YAG (2.9µm) andCO2 (10.6µm) laser systems as well as in the medical and industrial fields. Please refer to our Product RReferencesection for more information on HSW.

Coatings aand BBuffers

Buffer coatings are applied to optical fiber while the fiber is being drawn. The purpose of the buffer is to protect thefiber from environmental conditions, especially moisture and abrasion, which might accelerate the generation ofstress-cracks in the silica surface. Several types of coatings are used depending on the application. The mostdurable is polyimide but acrylate, silicone, and fluoropolymers are also used.

Figure 2-26: Comparison of Polymicro UV Fibers

Fiber Type Wavelength Range Characteristics Cost

FVP 240-850nm • Economical Very Low• High Solarization • Damage below 240nm• Minimal Solarization Recovery• All Sizes Available• Alternate Coatings Available

FVP-UVM 200-850nm • Moderate Solarization Damage Low• Minimal Solarization Recovery• All Sizes Available• Alternate Coatings Available

FVP-UVMI <200-850nm • Very Small Solarization Damage Moderate• Diameter and Temperature Dependent

Degradation with Time• Only Larger Diameters Recommended (>400µm)• Refrigeration Recommended When Not In Use• Reverts to FVP-UVM Over Time• Available with Polyimide Coating Only

FDP <200-850nm • Small Solarization Damage Moderate• Minimal Solarization Recovery• No Shelf Life Issues• Diameters 100µm to 600µm Available• Available with Polyimide Coating Only

BBrrooaaddbbaanndd FFiibbeerr ((FFBBPP)

Traditionally, fibers with high -OH content perform better at UV wavelengths. However, the -OH content creates verylarge absorption regions in the Near Infrared (NIR) wavelengths. Conversely, fibers with Low -OH content canperform very well in the NIR region of the spectrum, but tend to have very poor UV performance. Both types of traditional fibers transmit well in most of the visible spectrum.

Polymicro has developed a fiber that combines the benefits of both types of fiber. The FBP series of fibers has goodtransmission from below 275nm to beyond 2100nm. A typical attenuation spectrum of the FBP fiber is shown inFigure 2-27 compared with a typical Low -OH (FIP) fiber and a typical High -OH (FVP) fiber.

The FBP fiber is solarization resistant down to its specified low wavelength of 275nm. It can be produced in corediameters from 50µm to 600µm and requires no refrigeration or other special storage or handling. Figure 2-28 belowis a table comparing FBP properties with those of High and Low -OH fibers. FBP fiber has found use in astronomicalapplications and spectroscopic applications, among others. FBP fiber is recommended in applications where trans-mission in both UV and NIR wavelengths is needed.

FFiibbeerr TTyyppee WWaavveelleennggtthh RRaannggee CChhaarraacctteerriissttiiccss CCoosstt

High -OH 200-850nm • High -OH – Good for UV and Visible Transmission Varies by type• Solarization Varies by Type• All Diameters Available• Various Coatings Available

Low -OH 500-2400nm • Very Low -OH - Good for Visible and NIR Transmission Very Low• All Diameters Available• Various Coatings Available

FBP 275-2100nm • Low -OH - Good UV, Visible and NIR Transmission Moderate• Minimal Solarization in Specified Wavelength Range• All Diameters Available• Polyimide Coating Needed• Unspecified Attenuation below 275nm


2-17

Figure 2-27 Spectral Attenuation of Fiber Types

Figure 2-28 Characteristics of Fiber Types


Spectral Attenuation

0

100

200

300

400

500

600

700

800

900

1000

200 400 600 800 1000 1200 1400 1600 1800 2000 2200

Wavelength (nm)

Att

en

uati

on

(d

B/k

m)

FIP

FVP

FBP

Polyimide is generally applied in a thickness from 5µm to 25µm depending on the fiber size. Acrylate and siliconethickness can be varied from 10µm to 140µm and depend on the application and fiber size. Aluminum generallyvaries from 20µm to 45µm, increasing with increasing fiber size.

Mechanical aand EEnvironmental

In extreme mechanical, thermal and other environmental conditions the survival of synthetic fused silica optical fiberdepends on the packaging, handling and additional protective coatings used, not so much on the glass itself. In addi-tion to buffer coatings optical fiber is often cabled in assemblies or given a second buffer coating or over-jacket.These materials and the cable package design are key to the survival of the fibers in their final application. It is bestto team with someone experienced in designing optical fiber assemblies or cables to assure a reliable end product.Polymicro has years of experience in this type of custom and production assembly design work and is ready to assistyou with your design.

Acrylate buffered synthetic fused silica optical fiber can easily survive –55oC to 95oC required by many specifications.For more extreme temperature performance, there are other buffer materials available. Depending on the buffercoating, temperatures up to 400oC are survivable as well as below –55oC. Polymicro’s polyimide buffered fibers havebeen used in liquid nitrogen environments, as well as at 300oC continuous operation with intermittent use up to400oC.

Mechanical SStress aand FFiber SStrength

Optical fibers produced with synthetic fused silica have remarkable strength. Based on the Si-O bond strength, thefiber has a theoretical strength of ~2,000kpsi, which is stronger than steel! In practice the observed strength is con-siderably lower (typically 700kpsi) due to the presence of small flaws in the bulk and on the surface of the silica. Inorder to produce a reliable fiber these flaws must be minimized or eliminated. The size of the flaw determines thestress level needed to fracture the fiber, a larger flaw causing a lower strength fiber.

The dynamic strength of an optical fiber refers to the force required for an instantaneous break (as opposed to adelayed failure). Since failure in brittle materials, like glass, is a statistical process, many samples must be measuredin order to adequately represent the distribution of flaws (and strength) throughout the fiber. This distribution is

commonly presented as a Weibull plot. The Weibull function is represented by:

Where F is the fractional failure probability, m is the Weibull slope, Sis the failure stress, Soo is the Weibull characteristic stress (stress atF~0.632), L is the gage length, and Loo is the unit gage length. In a Weibull plot, a near vertical slope (m) with high stress valuesrepresents a tight strength distribution and a consistently strongproduct. This is demonstrated in the presented Weibull plot ofPolymicro’s FVP050055065 High -OH fiber type (Figure 2-23). It is a 50µm core, 55µm clad OD with a 65µm OD polyimide buffer coating.

The mechanical strength of glass optical fibers will also degradeover time. This effect is known as static fatigue or stress corrosion.The mechanism in silica based optical fiber is the propagation ofsurface flaws due primarily to a combination of stress, moisture,temperature, and time. With a fiber under stress a surface flaw actsas a stress concentrator with the maximum stress being at the tip of

(Eq. 2-18)

Figure 2-29 Weibull Plot for Fused Silica Optical Fiber



2-18



the flaw. Water attacks and breaks the silica bonds preferentially at the high stress area at this type. This causes theflaw, and consequently the stress, to increases in magnitude until the fiber catastrophically fails. Temperature, ofcourse, speeds up the reaction.

This mechanism is well described by Charles4 and can be represented by:

Where time to failure is in seconds and failure stress in kpsi. The static fatigue parameter, n, is an important constantthat is very dependent on the specific manufacturer’s fiber and the materials used to produce it. In most analyses,the safest failure stress to use is the proof test of the fiber since the fiber has been confirmed to be at least thatstrong.

Static fatigue results are typically plotted on a log time to failure vs. log stress curve. In this case the fatigue curvewill be straight with the slope being equal to n. Values for n range on the low end of ~10 for borosilicates up to >100for hermetic fibers. Typical n values for polymer coated synthetic fused silica fibers range from 20 to 28.

An effective method to assure fiber strength is to perform a proof ttest on the fiber. The proof test is used to filter outflaws of a given size or larger. This assures the fiber will meet a minimum strength requirement, typically 100kpsi formost optical fibers. This proof test value can be adjusted higher or lower to meet the strength and lifetime require-ments of the application. Proof testing can be performed by applying either a bend or a tensile force on the fiber.Polymicro proof tests 100% of their optical fibers and capillary to insure a strong, high quality product.

Stress on an optical fiber can be generated by tension, bending, or torsion. The calculation of the stress and theproof test method is typically based on either tensile force or bending stress. In tension the stress is simply the forcedivided by the cross sectional area of the glass. Note that the fiber coatings have Young’s moduli that are typicallyseveral orders of magnitude lower than the glass, and therefore do not bear a significant portion of the tensile load.Although the coatings do not add strength, they have the important function of protecting the glass surface fromabrasion and chemical damage, which in turn would degrade fiber strength.

Bending stress can be determined through the following equations. These equations are used to determine the bendstress imposed on a fiber during use as well as the wheel radius needed to perform a specific level proof test. If wedefine the applied stress, σaa, as the strain, ε, times Young’s Modulus, E, we can derive the relationship:

Where r is the fiber radius, R is bending radius, and Ctthh is the coating thickness. Thus, R is given by the following:

2-19

log(time-to-failure) == nn xx [[log(1 ssec ffailure-stress) –– llog(failure-stress)] (Eq. 2-19)

(Eq. 2-20) (Eq. 2-21)or

(Eq. 2-22)

4 R. J. Charles, J. Appl. Phys., 29, 1547, 1657 (1958)

Figure 2-30 Bend Radius vs Stress Level For Different Core Sizes

Radiation RResistancePure Silica core optical fibers generally exhibit superior radiation resistance as compared to doped Silica fibers.Unlike optical fiber used for telecommunication, Polymicro’s step-index multimode optical fibers are constructed of apure silica core material which is generally considered radiation resistant. These fibers are available in both high andLow -OH versions. For ionizing radiation, such as gamma and X-ray, the higher -OH content fiber is far superior.From recent technical articles radiation resistance, UV, and near-IR attenuation are all inter-related with the opticalfiber production parameters and buffer coating. Some of these results are presented in summary form in the tablebelow. For additional information, see the article “Influence of preform and draw conditions on UV transmission andtransient radiation sensitivity of optical fiber”

.5

In the referenced article, all of the fiber tested was drawn from the same lot of raw material by one university(Rutgers University) and one manufacturer (Polymicro Technologies). At Polymicro (PT), the draw conditions werevaried to analyze the effects. Draw rates ranged from 5-30 meters per minute at a tension of 55-130 grams and 2-56m/min at 25-185 grams tension. Fiber was drawn at 1950oC and 2100oC at both facilities. Rutgers University (RU)used draw rates of 15-45m/min at tensions from 12 to 148 grams. Polymicro applied both polyimide and acrylatebuffers while Rutgers only supplied acrylate. Portions of the results are given in the following table.

5“Influence of preform and draw conditions on UV transmission and transient radiation sensitivity of optical fiber,” P. Lyons and L.Looney, LANL, H. Henschel, O. Kohn,H.U. Schmidt, Fraunhofer INT, K. Klein and H. Fabian, Heraeus Quarzschmeize, M. Mills, Rutgers University, G. Nelson, Polymicro Technologies



2-20

Figure 2-31 Radiation Sensitivity of Optical Fibers


3 FFlexible FFused SSilica CCapillary

What iis aa CCapillary?

According to The American Heritage Dictionary, Capillary is defined as "Any tube with asmall internal diameter".1 In the realm of analytical chemistry and spectroscopy, capillary isunderstood to be small internal diameter glass tubing. The most highly specialized glasscapillary is referred to as Flexible Fused Silica Capillary Tubing. It is drawn from high puritysilica and externally coated with a protective polymer to yield a strong, durable, and yet flexible tube that is used across a wide range of applications.

Flexible synthetic fused silica capillary tubing from Polymicro is manufactured across a range ofinternal diameters from less than 1.0µm to over 2000µm. PT standard products range from 2µm to700µm. Standard capillary is fabricated from synthetic fused silica preforms using sophisticateddraw towers and following closely controlled manufacturing processes. The outside silica diametertypically ranges from 90µm to >3500µm. PT standard products range from 90µm to 850µm. In

most applications, an external polymer coating is applied to protect the silica outer surface from abrasion. The coating thick-ness will depend on the material and application. Similar tubing can be manufactured using natural quartz, borosilicate glass,or doped synthetic fused silica materials depending on the application requirements. Polymicro manufactures only thehighest quality fused silica, doped fused silica, and specialty natural quartz capillary.

Applications EEmploying CCapillary

When summarizing uses for capillary, it is difficult to make an all-inclusive list. As technology expands, so does thenumber and variety of applications. As a starting point for new ideas, here are a few well established techniques thatrely on capillary:

• Analytical CChemistry... Capillary is a fundamental component in Gas Chromatography, CapillaryElectrophoresis, Capillary Liquid Chromatography, Flow Cytometry, and a number of other techniques.

• Combined-Method AAnalytical CChemistry... Hyphenated techniques rely on capillary for easy, compactinterface designs. Examples include: GC-MS, LC-MS, CE-MS, and LC-NMR.

• Gas && FFluid DDelivery... Capillary can withstand high temperature and corrosive or hazardous environ-ments, making it a good choice for transfer lines and connecting to micro-accessible areas.

• Drug DDelivery SSystems.... The high purity, non-contaminating interior surface, and wide range of inter-nal diameters make capillary a key component in these systems.

• Flow CCells... Small ID capillary make excellent, low band-broadening transfer lines to flow cells. Uniquespectral properties make them ideal for on-column detection, even into the deep UV.

• Flow RRestrictors... Capillary provide accurate mass flow control, with strong adherence to Poiseuille’sEquation.

•• MMiiccrroo--ppiippeetttteess... Whether used as produced, or “pulled” to a Pasteur-type tip, capillary is widely used aspipettes, predominately in neurological sciences.

•• LLiiqquuiidd LLiigghhtt GGuuiiddeess... Capillary offers flexible fluid containment for energy transmission via high indexfluids.

•• HHoollllooww WWaavvee GGuuiiddeess... Dielectric interior coating of capillary generates low cost, long wavelength IRWaveguides.

•• MMiiccrroo IInnssuullaattoorrss... Capillary can be used over conductors to provide 25 kV/mm or more electrical insu-lation. Polymer coatings withstand up to 400oC (short term). Polymicro capillary with no external coatingcan withstand temperatures in excess of 1000oC.

•• CCoouupplliinngg FFeerrrruulleess aanndd CCoonnnneeccttoorrss... Laser micro-machined capillary is ideal for coupling optical fibersas well as capillary. The popular Inner-LokTM used for coupling GC columns is an example of this technology.

•• MMiiccrroo--ooppttiiccaall EElleemmeennttss... Capillary is found in a variety of instrument applications, from optical detec-tion cells to fiber optic alignment ferrules.

3-1

1 The American Heritage Dictionary, Houghton Mifflin Company, Boston, 1981Inner-lokTM is a registered trademark of Polymicro Technologies



Characteristics OOffered bby CCapillary

Synthetic fused silica capillary has several fundamental characteristics that make it such a unique material:

• Very strong and flexible

• Abrasion resistant when externally coated

• Mirror smooth interior surface

• Inert surfaces and high purity

• Accurately drawn to a wide range of internal and external diameters

• Internal surface modification possible

• Dimensionally stable over long lengths

• Transparent from the deep UV to near IR (coating removed)

• Superior temperature resistance

• High dielectric strength, very high breakdown voltage

• Easily cleaved or cut

• Variety of external coatings available

Capillary is strong and abrasion resistant, but can be easily cleaved. It has inert, high purity surfaces, yet stablechemical modifications are routinely produced. It can be made to a wide range of sizes, yet each size can beheld to exacting tolerances over long production lengths. Because of this impressive list of characteristics, synthetic fused silica capillary has claimed a unique position in the material sciences as an ideal product for anexpansive range of applications. A discussion on key applications follows below.

Gas CChromatography

Although capillary tubing is now used over a broad range of applications, its history is inseparable from that ofGas Chromatography. According to the International Union of Pure and Applied Chemistry (IUPAC),“Chromatography is a physical method of separation in which the components to be separated are distributedbetween two phases, one of which is stationary (stationary phase) while the other (the mobile phase) moves in adefinite direction”.2 In Gas Chromatography (GC), the mobile phase is a gas and the stationary phase is either asolid or a liquid, depending on the type of separation column selected. The actual separation of components in amixture is achieved due to the differential distribution of solutes between the mobile and stationary phases.Capillary is fundamental to the technique, as it is the support for the stationary phase and the conduit throughwhich the mobile phase travels.

One of the first applications for capillary tubing was in the Gas Chromatography industry. Dandeneau andZerenner’s pioneering efforts are recognized by many as the cornerstone for the introduction of fused silicabased capillary as a support for GC columns.3 Continued improvements in GC analysis have been aided by theunique properties of synthetic fused capillary tubing, with the majority of new methods rooted in proprietary newstationary phase coatings. Since its first use in the late 70’s, the range of capillary tubing internal diameters (ID)has grown, and specification tolerances have continually tightened to meet the exacting demands of the columnmanufacturing industry. Numerous GC column manufacturers offer a broad selection of columns used in theanalysis of food products, pharmaceuticals, clinical samples, petroleum, and a variety of other applications.

Polymicro produces a wide range of capillary designed specifically for GC applications. Capillary with ID’s rangingfrom 50µm up to 750µm are routinely used, with the majority of columns employing capillary between 180µm and530µm. Two product lines are commonly used, these being the standard TSP and high temperature TSG. AlthoughPolymicro communicates the specifications in micrometers, most column manufacturers list column diameters in millimeters. It is common to name a column by a combination of the ID and stationary phase.

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2 McNair, H. M., Miller, J. M., Basic Gas Chromatography, Chapter 1, John Wiley & Sons, Inc. New York, (1997)3 Dandeneau, R. D., Zerenner, E. H., HRC&CC 2(6), (1979) 351-356



Capillary EElectrophoresis

“Capillary Electrophoresis (CE) was born of the marriage of the powerful separation mechanisms of electrophoresiswith the instrumentation and automation concepts of chromatography.”4 CE is a separation method based on the dif-ferential migration rates of sample components within a capillary when an electrical field is applied axially to thatcapillary. The detection of sample components is usually “on-column” using UV spectrometric or fluorescence analy-sis through a “window” in the capillary. CE has become a powerful technique, finding a wide range of applicationsareas, including the analysis of proteins, peptides, chiral compounds, pharmaceuticals, inorganic ions, and DNA tomention a few. CE played a pivotal role in the Human Genome Project’s ultimate goal of unraveling the sequence ofhuman DNA. It is routinely used in sequencing facilities and DNA forensic laboratories worldwide.

Performing electrophoresis in small-diameter polyimide coated capillary allows the use of very high electric fields,and the efficient dissipation of the Joule heating that results. High electric field strengths produce very efficient sepa-rations while minimizing separation times. Key features that make fused silica capillary tubing the column material ofchoice in CE include:

• The surface ionization characteristics of fused silica when in an applied electrical field generates elec-troendomosis, also known as Electro-Osmotic Flow, or EOF. This basic pumping action drives most CEapplications and is responsible for the techniques high chromatographic efficiencies.

• Capillary tubing has a high dielectric strength, giving ample isolation for the high voltages (up to 30kV)used in CE.

• The polyimide coating can be easily removed in a process called “windowing”. Windowed capillary hashigh transmission in the UV-Vis spectral region, allowing for direct on-column absorbance measure-ments.

• Windowed capillary exhibits low background fluorescence, making it ideal for fluorescent detectionschemes, including LIF (Laser Induced Fluorescence).

• Capillary can be easily rinsed and filled with solutions and buffers by either positive pressure or vacuum.

• Modification of capillary surfaces through dynamic coatings, covalently bonded phases, or stabilizedgels, allow for control of EOF and can impart unique separation mechanisms.

• The durability and abrasion resistance of polyimide coated capillary allow for great flexibility in instrumen-tal design and hyphenation interfacing.

• Capillary can be easily cleaved to length, providing users great latitude in adjusting column length andeconomies of scale in tubing procurement.

CE has carved out a unique niche in the analytical laboratory, both as a fundamental separation tool and a complementary technique to established methodologies. Polymicro continues to be the primary supplier of tubingto this market, providing capillary ranging in ID from 2µm to 150µm. Polymicro set the standard in outside dia-meters (OD) by introduction of the 375µm and 150µm TSP product lines, and offers capillary for CE in a varietyof formats including: bulk capillary on spools, capillary cut to prescribed lengths, windowed capillary, capillaryassemblies, and custom capillary arrays. A number of CE manufacturers turn to Polymicro for custom sizes tomeet their specific instrumental design and rely on Polymicro’s expertise for design and development assistance.

Capillary LLiquid CChromatography

Chromatographic techniques that employ a liquid mobile phase loosely fall into a category referred to as LiquidChromatography (LC). In LC, the stationary phase is either a solid surface or a surface that has been modified, orcoated, to allow for partitioning of solutes into this thin layer of coating. As in GC, separation is achieved due to thedifferential distribution of solutes between mobile and stationary phases. In LC, the stationary phase is typically in theform of non-porous, semi-porous or porous particles that are “packed” into a metal or glass tube, referred to as thechromatographic column. New developments in this field have introduced the use of monolithic columns, a constructwherein a porous bed is formed in situ, as opposed to the packing of particles into the tubing.

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4 Heiger, D. N., High Performance Capillary Electrophoresis - An Introduction, (Forward by J. W. Jorgenson), Hewlett Packard GmbH, Waldbronn, Germany (1992)



Capillary fills two fundamental roles in LC applications, as connection lines and as columns. First, it is often used formaking fluidic connections between the chromatography columns and the other components of the system, i.e. flowcells, injectors, detectors, etc. Capillary is durable, yet easily cut to the exact length needed for such interfacing. Thewide range of available ID’s allows chromatographers great latitude in selecting tubing that offers the optimum performance under their experimental and instrumental design. To minimize system dead volume in Nano LC applications precision cleaving is required. Polymicro offers precision Cleaving && CCutting CCapabilities.

Second, trends toward miniaturization of systems has lead to the introduction of capillary-based columns, and thusthe advent of Capillary Liquid Chromatography (CapLC). In this technique, a capillary is either packed with particlesor used as the substrate for construction of a monolithic bed. The particles, or monolithic bed, contain the stationaryphase and the capillary has become the chromatographic column. Capillary diameters most commonly range from50µm up to 500µm, with a variety of different designs available. Standard TSP products are commonly used withTSU and TSH products gaining interest for some monolithic columns. Polymicro now offers a “Thick WWall TTSP”product line when internal diameters of 150µm or larger are desired.

Mass FFlow CControl

A wide range of applications take advantage of capillary for precision control of liquid and gas flow rates. Thisgeneral application area is referred to as Mass Flow Control, and relies on several unique properties of capillary.

• The smooth internal surface of capillary results in stable laminar flow profiles and good adherence toPoiseuille’s Law (Eq. 3-1), allowing accurate prediction of flow rates.

• Capillary flow rates can be adjusted by changing either the ID or overall length. Polymicro offers a broadrange of standard products with different ID’s so that users can select one that best fits their flow raterequirements.

• Capillary can be easily cleaved, providing users great latitude in manipulating flow rates through lengthadjustments.

• The tight tolerances of Polymicro’s capillary provide the needed dimensional consistency, both withineach lot and from lot to lot.

• Capillary, if handled with care, has excellent strength and durability. This, coupled with high temperaturecapabilities and chemical resistance properties, allows for usage in harsh and challenging environments.

• Combinations of capillary are often utilized in flow splitting devices, with LC/MS interfaces being a classicexample.

Capillary is a robust solution in any application that demands stable, reproducible control of fluid or gas flow rates.Insertion of a segment of appropriate length and ID generates a fixed restriction, given that the other key parametersof viscosity and pressure drop are controlled. Tips on estimating the expected flow rate are discussed in this chapter(see Estimating tthe FFlow RRate iin CCapillary).

Other UUses ffor SSynthetic FFused SSilica CCapillary TTubing

At the beginning of this chapter, a number of key uses of capillary were summarized. This is certainly not a completelist. There are a significant number of other uses, many involve variations in the basic design and composition ofcapillary itself. Some examples include:

•• An outer coating can be applied that is deep-UV transparent and can be used up to 160oC. These arereferred to as TSU products. The alternate TSH products are also UV transparent.

•• Square, rectangular, and other shaped cross sections offer new opportunities. The square capillary line ispopular in Flow Cytometry instruments, and is referred to as the WWP line of products. These, and otherunique geometries, are further discussed in detail later in this chapter (see Alternative CCross-SectionalGeometries).

•• Other coatings, both internal and external, expand the potential uses of capillary. These are discussedlater in this chapter (see Internal aand EExternal CCoatings aand CChemistries).

•• Custom sizes of both unique ID’s and OD’s are commonly produced. Standard sizes drawn to tighter tolerances are also considered custom products.

•• Capillary can be micro-machined into fittings and ferrules, used for coupling capillary as well as opticalfiber (discussed in the Fused SSilica MMicro-Components chapter).

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Capillary PProducts

Capillary can be purchased in a variety of formats, including:

• Bulk: The majority of capillary is supplied to the market in long, continuous lengths on Styrofoam® orplastic spools. Spool lengths depend on production specifications and customer order requirements;each spool is individually bagged. Capillary ends are fused closed to maintain a clean, inert internalsurface. All material is supplied with an appropriate label that includes the part number, lot number,length, and other pertinent information.

• Precut: Capillary is often precut to customer specified dimensions. Length can vary from a few milli-meters up to tens or hundreds of meters. Attention is given to critical parameters, such as length toler-ance, end finish quality, cleanliness, packaging, and lot traceability. Parts are packaged in groups, butcan be individually packaged if required.

• Windowed CCapillaries: Polymicro also supplies precision windowed capillary tubing. Parts are suppliedwith the polyimide coating removed over a defined length at a specified distance from one end of thecapillary section. This provides an optical quality window that has excellent mechanical properties aswell. In addition to the window location and quality, attention is given to other critical parameters such asoverall length, end finish quality, cleanliness, packaging, and lot traceability.

• Coils: GC columns can be pre-coiled to length, or more commonly multiples of their final length. Polymicroproduces these products, referred to as coils, which allows for efficient production of finished GC columns.

• Arrays aand AAssemblies: Capillary is routinely used to build arrays and other assemblies, just as withoptical fiber. It is even possible to combine capillary tubing with optical fiber into the same assembly,reducing the amount of assembly required in the final instrument. Handling techniques become veryimportant when dealing with capillary arrays and assemblies (discussed in the Appendix). Bondingmaterials and other potential contaminates must be kept from the interior of the capillary while building asturdy assembly that will survive the application requirements. Polymicro’s experience with handling andbuilding capillary assemblies can save product development time and optimize production efficiency,reducing overall costs.

Cutting && CCleaving CCapabilities

Fused silica capillary tubing is commonly produced in long, continuous lengths; in many cases these lengths canexceed 2km. Nearly every application requires sectioning of the capillary into lengths that appropriately match theapplication requirements. Lengths can vary from a few millimeters to over 100 meters. When selecting an appropri-ate option for producing the desired length there are a number of issues to consider. Although the ultimate perform-ance of the part in the target application is most critical, issues such as cost, packaging, durability, end-face finish,length tolerance and general ease of use should be considered. It is also important to understand the impact thatcapillary attributes (i.e. wall thickness, i.d., and o.d.) have on potential utilization of different cutting and cleavingoptions. The above issues and impacts have been discussed previously.5 Common methods employed for segment-ing capillary are (a) standard cleaving, (b) precision cleaving, (c) saw cutting and (d) laser cutting.

•SSttaannddaarrdd CClleeaavviinngg - Standard Cleaving is done manually with a cleaving stoneor diamond blade and often results in a slightly uneven end-face. For detailedinstructions on how you can cleave your tubing by this method, refer to CleavingProcedure in the Appendix.

•PPrreecciissiioonn CClleeaavviinngg - Precision cleaving is done using proprietary robotic cleavingsystems. These high-precision systems provide outstanding repeatability. Thismethod generates minimal debris; end-face quality and perpendicularity are excellent.

•SSaaww CCuuttttiinngg - Multiple capillary segments are bouled together and then sawedto length as a group. Sawing leaves a matte end finish; chips and cracks in theend-face are common. Subsequent lapping and then polishing can improvesurface quality in most cases.

•LLaasseerr CCuuttttiinngg - A proprietary CNC style, multi-axis high power laser workstation is utilized to perform thecutting operation. End-faces are typically defect-free, with no sharp edges, chips, or cracks. Due to the use ofhigh energy laser light, some polyimide is ablated from near the end face of the capillary.

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5Macomber, J., Lui, P., Acuna, R., LCGC Applications Notebook, (September 2009) 57Styrofoam® is a registered trademark of the Dow Chemical Company



Coupling aand CConnecting CCapillary

There are a number of methods and devices used for connection of capillary. Selecting an appropriate connectordepends on the application(s) and size of capillary being used. Suggestions are discussed below.

There are two basic connection types used in GC applications. 1) A Swagelok® or equivalent compression fitting withappropriate Vespel® insert is common for end of column connections. The capillary is held by a compression fit to thepolyimide buffer, making this a robust connection. A number of options are available from most GC Column manufac-turers. 2) Capillary to capillary connections are often accomplished using tapered silica or quartz micro componentscalled Inner-LoksTTMM. These connectors accept a range of capillary sizes and offer a simple, clean method for coup-ling. Using silica or quartz, as opposed to borosilicate, as the coupling material provides a good thermal expansionmatch. The capillary can be bonded after insertion into the Inner-LokTM making a more permanent connection.

Connections in LC and related fluidic applications normally employ compression fittings made of polymeric materials,such as PEEKTM. A number of manufacturers offer connector products compatible with Polymicro capillary. Many ofthese fittings are pressure rated, and are designed for simple, fast assembly of capillary into instrumentation.

Custom connections and terminations of capillary are available from Polymicro. Key design considerations includeend finish, ID cleanliness, strain relief, pressure requirements, operating temperature, solvent compatibility, and construction of the mating fitting.

Pressure HHandling CCapabilities

CAUTION: Great care should be taken when using capillary tubing with internally applied pressure. Although capil-lary is very robust, a small particle or a minute chemical etching can create an internal stress crack or flaw. The com-bination of pressure and heat should be given special consideration. If handling, environmental, and/or chemicalexposure after manufacturing has changed the internal surface or generated flaws, the added stress of high internalpressure can result in failure. When there is a possible chance for abnormally high internal pressure, we suggesttesting a sample of the actual material that will be used to obtain some confidence in its durability under increasedpressures. Always use safe laboratory practices when working with any pressurized devices.

NOTE: TThe mmaterial iis pproof ttested iin pproduction tto vverify sstrength aand qquality ((see Bending SStress iinCapillary); iit iis iimportant nnot tto iinterpret pproof ttesting aas aa mmeasure oof iinternal ppressure ccapability.

Estimating tthe FFlow RRate iin CCapillary

When a viscous fluid flows through a tube of fixed length and ID, a resistance to fluid flow exists. So long as theReynolds Number is less than 2000 and the fluid is considered to be Newtonian, some relatively simple equationscan be used to describe the system. Under these conditions, the maximum speed is at the center and near the wallsthe fluid tends to remain nearly stationary. In terms of the viscosity, the resistance to fluid flow, R, for steady flowthrough a circular tube of radius, r, can be shown to be:

where η is the coefficient of viscosity, and L is the length. The SI unit for the coefficient of viscosity is poise, after theFrench physician Jean Poiseuille (1797-1869), who is often credited with deriving the above expression.

As can be seen, the resistance is inversely proportional to the square of the radius of the tube. For example, achange from 200µm inside diameter capillary to 100µm inside diameter means an increase in resistance to flow by afactor of 4.

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(Eq. 3-1)

Inner-LokTM is a trademark of Polymicro TechnologiesPEEKTM is a Trademark of Victrex plcSwagelok® is a registered trademark of Swagelok Co.Vespel® is a registered trademark of DuPont Dow Elastomers



By rearrangement of Equation 3-1 on previous page, Poiseuille’s Equation is derived. It follows that the flow ratethrough a capillary can be expressed in terms of pressure drop. More importantly, the flow rate is expressed in termsof the capillary ID, and is given by:

The flow rate, F, varies as the 4th power of the radius, i.e., a 2-fold change in radius creates a 16-fold change in flowrate. Equation 3-3 offers an easy to use version that gives the flow rate, F, in mL/min:

where, the radius (r) is in µm, the pressure drop (∆P) is in psi, coefficient of the viscosity (η) is in cp, and the length(L) is in cm.

Bending SStress iin CCapillary

The bending stress on capillary is nearly identical to that of optical fiber, and as such, the same bending stress prin-ciples and test methods can be applied. A lengthy discussion can be found in the Fiber OOptics && OOptical FFiberchapter under Mechanical SStress aand FFiber SStrength. Polymicro proof tests most products to a nominal bendingstress level of 100kpsi. However, since the inner surface can be exposed to the elements, it is easy for users toaffect the strength of capillary during routine handling. If chemical reactions or particulate debris cause stress crackson the interior surface, they may reduce the resistance to bending stress damage. Proper storage of the capillaryand simple laboratory practices such as filtering solvents and gases, using quality connectors, and insuring qualitycleaves on capillary ends, can have direct impact on maintaining capillary strength. Storage, handling, and cleavingare discussed in the Appendix. Figure 3-1 shows the relationship of OD (including polyimide), bend radius, andapplied bending stress for a number of standard polyimide coated capillary.

Optical PProperties oof aa CCapillary

A review of the optical properties of capillary involves close examination of not only the glass substrate itself, but alsothe protective coatings often employed. These will be discussed further below. Optical properties such as transmis-sion, fluorescence, refractive index, and in some cases numerical aperture are all important to consider. It should benoted that capillary is used as a substrate for liquid light guides and hollow silica waveguides. Further, if appropriatecoatings or claddings are added, capillary can embody both fluidic and fiber optic properties simultaneously such asin Polymicro’s Light GGuiding CCapillary.

When examining transmission of light through Polymicro's standard capillary products, it is important to consider both thedirection of light propagation and the silica type. Since non-axial, or orthogonal, transmission (i.e. on-column detection

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Figure 3-1 Capillary Tubing Bend Stress

BBeenndd RRaaddiiuuss ((mmmm))

TToottaall OODD ((µµmm)) 44 66 88 1100 1155 2200 2255 3300 4400 5500 6600 8800 110000 113300 116600 220000

9900 87 58 43 35 23 17 14 12 9 7 6 4 3 3 2 2

110055 106 71 53 43 28 21 17 14 11 9 7 5 4 3 3 2

115500 165 110 83 66 44 33 26 22 17 13 11 8 7 5 4 3

116644 184 123 92 74 49 37 29 25 18 15 12 9 7 6 5 4

223388 270 180 135 108 72 54 43 36 27 22 18 14 11 8 7 5

334400 399 266 200 160 106 80 64 53 40 32 27 20 16 12 10 8

336600 425 284 213 170 113 85 68 57 43 34 28 21 17 13 11 9

336633 424 283 212 170 113 85 68 57 42 34 28 21 17 13 11 8

443355 524 349 262 209 140 105 84 70 52 42 35 26 21 16 13 10

666655 * 540 405 324 216 162 130 108 81 65 54 40 32 25 20 16

770000 * 571 428 342 228 171 137 114 86 68 57 43 34 26 21 17

885500 * * 526 421 281 211 168 140 105 84 70 53 42 32 26 21

* exceeds capillary break strength

Applied BBending SStress ((kpsi)

(Eq. 3-2)

(Eq. 3-3)F = [(r4 · ∆P) / (η · L)] · 1.625x10-8



schemes) is normally of key interest, the extremely thin walls of capillary make the actual transmission losses in the silicanegligible. However, this is dependent upon the type of silica used to make the capillary. Polymicro has selected anappropriate -OH content glass for applications in the deep UV and Visible spectral regions.

Fused silica glass, especially the lower -OH types, can exhibit fluorescence when illuminated with 254nm lightpassed through a Schott UG-5 color glass filter. From Heraeus data, this apparently does not occur in the high -OHmaterials. High -OH fused silica glass is essentially free from visible fluorescence at excitation wavelengths greaterthan 290nm. Slight blue-violet fluorescence appears in materials such as natural fused quartz products, and signifi-cant fluorescence is observed in most borosilicate glasses. It can be concluded that fused silica is indeed the mate-rial of choice for most capillary products.

The refractive index of the fused silica used to make capillary is often of interest to researchers. The actual value iswavelength dependent. A table of fused silica refractive index versus wavelength can be found in the Appendix. Onoccasion, the numerical aperture of capillary is sought. It is of course dependent upon the gas, fluid, or coating thathas been applied to the capillary surface. A discussion of numerical aperture and related topics is found in FiberOptics && OOptical FFiber.

As most capillary is coated with a thin layer of polyimide, this material will receive consideration here. Polyimidetransmission varies significantly from that of the silica. Standard polyimide is relatively translucent down to about550nm, with select custom polyimides exhibiting as much as 90% transmission at 425nm. All polyimides evaluatedhave shown less than 2% transmission below 350nm. This fact, when coupled with polyimide’s inherent fluores-cence, has lead to the wide spread use of windowed capillary for on-column spectral analysis applications. Polyimideexhibits significant fluorescence across a broad range of excitation wavelengths. This has been studied and is sum-marized in a Polymicro application note.6 The polyimide coating on capillary has fluorescence essentially equivalentto that of a 1mM solution of Rhodamine B in a 50µm ID capillary.

As mentioned earlier, Polymicro does employ other protective coatings, and their optical properties vary significantlyfrom polyimide. Acrylate coated capillary (TSA products) are more translucent in general and offer lower fluores-cence. When UV transmission through the coating is needed, Polymicro offers two product solutions. A novel Fluoro-polymer coated capillary (TSH products) offers >10% transmission at 310nm. This coating also offers improved background fluorescence when compared to the TSA products. Depending upon the signal to noise ratiorequirements, TSH capillary has proven useful for on-column fluorescence detection. Teflon® AF coated capillary(TSU products) are produced specifically for their unique optical properties. This fluoro-polymer coating is UV trans-parent, with transmission at 214nm typically greater than 90%. The refractive index yields an NA of 0.66 and this,coupled with the low absorbance properties of the coating, make it an excellent optical cladding material. A numberof applications take advantage of this by using TSU products as a light-guiding capillary. Others capitalize on thetransmission properties by using TSU for on-column detection applications, as removal of the coating is not required.Unfortunately, these unique optical properties are offset by the lack of abrasion resistance of the fluoro-polymer. TSUproducts must be handled with care to avoid breakage during use.

In addition to fluid handling capabilities for analytical instruments, capillary tubing can be used as a waveguide. Inhollow waveguides, the internal surface must be coated with an appropriate dielectric coating for the wavelength ofinterest. In this hollow core configuration, both metal and dielectric coatings have been applied to create a wave-guide for wavelengths further into the infrared than would be possible with conventional optical fiber.

It is also possible to use silica capillary tubing as the cladding for a fluidic waveguide, or liquid light-guide. As long asthe fluid has a refractive index higher than the capillary, a very effective light guide can be produced.

Light GGuiding CCapillary

The addition of an external coating or cladding that has a refractive index lower than that of the capillary itself willproduce a light guiding capillary. As mentioned above, Teflon® AF coated capillary TSU has inherent light guidingproperties. TSH will also act as a light guiding capillary. More durable light guiding capillary that employ an inorganiccladding can be manufactured. This line of products, referred to as LTSP, is produced with durable polyimide coatingand an NA of 0.22. Custom draws are available upon request.

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6Macomber, J. et.al., LCGC North America, June Suppl. (2004) 72Teflon® AF is a trademark of E.I. du Pont de Nemours and Company



Internal aand EExternal CCoatings aand CChemistries:

Interior SSurface CChemistry oof CCapillary

The interior surface of silica capillary is pristine when it comes from the initial draw process. It is considered to beinert as compared to other glasses, such as borosilicate and quartz, due to the low level of impurities. A list of impuri-ties and their typical abundance can be found in the Appendix. During the manufacturing process, the silica hasbeen heated to a temperature at which its viscosity allows it to be drawn down to the specified dimensions, typicallyin excess of 1,800o C . It is well understood that after exposure to these elevated temperatures, the surface of thecapillary is devoid of both chemically and physically absorbed water. The surface is rich in siloxane bridges (Si-O-Si)and the residual silanol groups (Si-OH) present are isolated. In many applications, the initial conditioning of thesurface before use is extremely important and should be given due consideration. Development of a protocol thatachieves the desired surface chemistry is well advised.

Common terms used when discussing conditioning of capillary are surface activity and deactivation. These wordshave different meanings depending on the application and the background of the user. Some would say that thedrawn capillary has high surface activity because it readily incorporates water back into the surface structure. Itfollows that a fully hydroxylated surface would be deactivated.

In GC column production, surfaces are sometimes said to be “too active”, and steps are taken to address this duringinternal coating operations. Some refer to these initial steps as deactivation. In other instances, such as in the caseof capillary column connectors for GC, deactivation refers to the addition of covalently bound ligands to the surfaceto reduce analyte adsorption.

In the case of CE, surfaces are treated to generate a uniform silanol population, a process some refer to as activa-tion, or more commonly as conditioning. Deactivation in CE is accomplished by the addition of coatings and dynamicadditives that eliminate EOF or unwanted analyte adsorption. Hewlett Packard (HP), in High Performance CapillaryElectrophoresis, suggests that “The most reproducible conditions are encountered when no conditioning other thanwith buffer is employed. However, adsorption of sample to the surface and changes in EOF often do not allow this.”The author further suggests “Base conditioning to remove adsorbates and refresh the surface by deprotonation ofthe silanol groups is most commonly employed. A typical wash method includes flushing a new capillary with 1NNaOH, followed by 0.1N NaOH and then buffer”.7

Silica related topics of common interest are the dissolution rate of silica, silica solubility, and their dependence on pH.Molecular diffusion in silica is also of interest to many researchers. A body of work on these topics is available.8, 9, 10, 11

Coatings, IInterior

Interior surface coating of capillary is routinely performed. These modifications fall into three basic categories.

• Wall Coated Open Tubular (WCOT) columns are used routinely in GC. The coating process involvesdeposition and subsequent cross-linking of the stationary phase. Some chemical bonding to silanolgroups is desired, and gives improved temperature stability and reduced bleed. Companies that marketGC columns are the primary source for these materials.

•• Covalently bonded chemistries find broad use in CE, both as finished columns and polymeric anchors forgel matrices. Bonding reaction schemes are numerous, with silanization using methoxy-, ethoxy-, or chloro-silanes being most common. Grignard reaction schemes are also popular. Often the goal of such coatingsis to stabilize, eliminate, or adjust EOF. CE instrument manufacturers and a few after-market suppliers offerthese types of coated columns. Polymicro can produce bulk capillary with covalently bonded chemistries.This type of internally coated capillary can be produced on a custom basis upon request.

•• Dynamic coatings involve the adsorption of specially designed solutions onto the walls of capillary androutine, periodic re-application is required. These typically target the same goals as covalently bondedchemistries.

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7 Heiger, D. N., High Performance Capillary Electrophoresis - An Introduction, Chapter 4 (88) Hewlett Packard Gmbh, Waldbronn, Germany (1992)8 Sjoberg, S., J of Non-Crystalline Solids 196, (1996) 51-579 Dove, P. M., Crerar, D. A. Geochimica et Cosmochimica Acta 54, (1990) 955-96910 Majors, R. E., LCGC North America 18 (12), (2000) 1215-122711 Doremus, R. H., Glass Science, John Wiley & Sons, inc., New York (1973) 134-142



Coatings, EExterior

Just as in optical fibers, many types of materials can be applied as the external capillary coating. These are appliedeither during the drawing operation, or as a secondary process. Further, the addition of specific agents to thecoating material can bring unique functionality to the resulting capillary. A general discussion of Coatings aandBuffers can be found in the Fiber OOptics && OOptical FFiber chapter and in the literature.

Alternative CCross-Sectional GGeometries

The most common geometry for capillary is circular or round. Non-circular geometries such as square cross-section capil-lary have been produced in response to customer requests, with square shaped capillary first introduced for use inCapillary Electrophoresis and later gaining popularity for Flow Cytometry devices. Rectangular designs are popular as fer-rules in telecom devices, such as DWDM. Other geometries, such as triangular, oval, and “race track” designs are beingexplored for cutting edge applications. Custom configured cross-sections are often explored through cooperative feasibilitystudies.

•• SSqquuaarree CCaappiillllaarryy:: Of the many geometric variations possible, the square cross-section tubing has seen the mostinterest and a line of standard products, referred to as WWWWPP, is available. The "Square" inside dimension of the tubinghas sides of 50µm, 75µm or 100µm. The outside glass dimension is nominally 320µm per side and the outer surfaceis protected by Polymicro’s standard polyimide. This polyimide coating is nearly round, but some irregularity can beexpected and can be felt by rolling the tubing in one’s fingers. In most instances, standard polymeric fittings will formsufficient seals to the polyimide even though it is not perfectly round.

Reported Advantages of Square Capillary:

•• Eliminates the need to correct for the optical effect of curved capillary surfaces in Capillary Electrophoresis,Flow Cytometry and other capillary based detection devices.

•• Offers larger effective internal surface area.

•• Flat sides create 27% more volume and 2X the transverse optical interaction path length (usinga collimated beam) than that of a round capillary configuration.

•• Behaves like a cuvette in standard fluorescent sensing devices such as those used in Flow Cytometry.

•• With polyimide coating WWP capillary will seal in most fittings designed for Polymicro capillary tubing products.

•• The glass substrate is the same high purity synthetic fused silica used in Polymicro’s wide range of standard capillary products (i.e. TTSSPP series); as a result, one can expect equivalent surface chemistries.

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Figure 3-2 Light Path Through Capillary Windows

© Polymicro Technologies, a Subsidiary of molex. 3-11


Figure 3-3 Examples of Capillary Geometries

•• OOtthheerr PPootteennttiiaall GGeeoommeettrriieess aanndd AAssssoocciiaatteedd DDeessiiggnn IIssssuueess:: A variety of different geometric variations are possible; it should be noted that the inside and outside geometries need not be the same. Several different combinations are shown in the figures below. Polymicro welcomes inquiries into other unique internal/external combinations. Beyond the basic geometry, there are a number of important design considerations; some key ones are discussed below.

Basic specifications to define include inner and outer dimensions, corner radii, flatness of sides, parallelismbetween opposing sides, angles between adjacent sides, and the concentricity of the inner and outer geometries.Another key consideration is the final product wall thickness. In general, the minimum allowable wall thickness atany radial point is ~100µm. Although most shaped capillary is made from synthetic fused silica, in some casesquartz has been specified.

Coatings are commonly employed to help protect the outer surface, but there are limitations. For products up to~600µm in outer dimension, polyimide is normally the coating of choice. As the outer dimension increases, or ifthe aspect ratio exceeds ~2.5:1, acrylate is often suggested. For outer dimensions in excess of 1.5mm it iscommon to produce the drawn product without a coating.

Although these shaped geometry capillaries are uniquely different from standard round tubing products, nearlyevery common post-processing technique can be performed equally on either type of capillary tubing. Thisincludes value added operations such as windowing, precision cleaving, laser cutting, ID coating, and customcapillary assembly.


4 FFiber OOptic && CCapillary AAssemblies

What aare AAssemblies?

Assemblies are easy to install units which can include optical, electrical, mechanical, and fluid functions, which areeconomical to produce. They can combine optical fibers, mechanical holding and mounting hardware, as well asfused silica capillaries, to transfer or manipulate light, gases, or fluids from one location to another. Most assembliesare based on specific user requirements. These can vary in complexity from a single terminated optical fiber to acomplex branching assembly. These can combine the advantages of fused silica optical fiber and capillary tubinginto an integral unit.

Optical fiber or fused silica capillaries can be clustered into bundles at one end and fanned out into various configu-rations at the opposite end. Special end shapes can be micro-machined directly onto the optical fiber or capillary,saving bonding and coupling losses. This handbook section will cover the basics in assembly configurations.

There are a number of opto-mechanical considerations when designing a fiber and/or capillary assembly that maynot be apparent. Products are very often proprietary to a customer. Because each assembly is intended to provide aunique interface or solution we will describe technical considerations and guidelines rather than specific details of“standard” products. It is important to choose a manufacturer with materials and product experience. This will help toinsure a high quality, successful result.

ApplicationsAssemblies consist of opto-mechanical and electro-optical componentsthat incorporate standard products in combination with custom configuredfused silica and precision optical products. Added optical or fluid featuressuch as micro-machined end tips, metal terminations, or precision coup-lings can be included. Customer requirements and/or specifications helpto determine whether standard products or custom designed optical andmechanical parts are required.

Optical fiber cables are specifically designed for applications demandinghigh optical transmission for the ultraviolet (UV), near infrared (NIR), andinfrared (IR). Specially designed fiber optic cables are ideally suited forapplications ranging from instrumentation and process control, to shortdistance data communication and laser power transmission. The widevariety of specialty optical fibers and cabling materials give the opticaldesigner unparalleled flexibility in system design. The fiber’s highmechanical strength is enhanced by the use of “state-of-the-art” bufferand cabling materials.

Polymicro offers the system designer unparalleled flexibility to incorporate a wide range of design options into theirassemblies. Customers have incorporated our assemblies into the manufacturing of devices and systems in the following areas:

4-1

* Polymicro Technologies, manufacturesoptical fiber cable, components, and assemblies only. Polymicro Technologies does not design or market medical devices.



Design CConsiderations

Polymicro offers the system designer unparalleled flexibility to incorporate a wide range of design options into theirassemblies. Everything from the termination style and technique, jacketing, and fiber type can be specified to ensureoptimum system performance. Our experience in designing and manufacturing assemblies for the industrial and sci-entific industries is a valuable resource for applications ranging from sensing, to laser power transmission, to processcontrol instrumentation, to short distance data communication. In order to do our best job for you, we will needanswers to as many of the following items as possible.

* The end manufacturer is responsible for bio-compatibility and sterilization testing and validation studies.

What DDoes PPolymicro NNeed FFrom YYou?

In response to the details of the assembly parameters listed above, our engineers will be able to take your require-ments, specifications and designs to suggest solutions. Before any design is finalized, the following items will gener-ally have to be specified. This helps to generate performance, cost, and test requirements. It will become the defini-tive guide when production of the assemblies begins.

The AAssembly DDesigner WWill DDetermine:

Low FFiber CCount AAssemblies

Because fused silica fibers are available in a broad range of sizes, simple assemblies are quite often made usingonly a few large fibers rather than a large number of smaller fibers. Combiners or fan-outs may have all channelsusing the same fiber diameter or may use different fiber sizes. These types of assemblies include simple patchcables for single fiber connections using most of the standard optical fiber connectors. The example in the photograph on page 4-3 combines three fiber channels and connectors into one single connector. Low fiber count assemblies such as this are very simple and compact. They are most often used when the light source can be focused small enough, the active areas are all circular, and the sensor(s) are small. With large light

4-2



sources, larger detectors, odd geometry sources, andsensors, fiber bundles are commonly used. Beingable to do special cable connections in an efficient,reliable package will result in maximum performancein the end use system.

Fiber pigtails (optical fiber cables with a connector atone end only) are supplied for customers to direct

couple to their own source or sensor. Simple patch cables, using industry standard connector types, can be supplied.A few of the standard connector types are shown in the illustration below.

All of the commercially available connectors used for step-index optical fiber can be supplied in patch cords orassemblies. Some types are SMA, ST, FC and custom designs for specified matches. Mating parts, including bulk-head connectors and types with special alignment features, can be supplied and will determine the total overall effi-ciency.

Polymicro has several end termination and connector designs to help solve unique customer optical fiber applicationrequirements including proven high power laser connectors designs.

High PPower LLaser CConnectors

The design of connectors for high power laser use is a specialized area. If the design is not done correctly bysomeone with experience in laser/fiber interface, the chances are very high that the heat load from the laser powerwill destroy the optical fiber and the connector assembly. Polymicro has provided several high-power connectordesigns over the years. The simplest design, for low to medium laser power, involves the proper choice of bondingmaterial, a well-designed stainless steel connector assembly, and an optional quartz isolation sleeve. The choice ofbonding the fiber into the sleeve at the end tip will depend to some extent on customer requirements, as well as onhow tightly focused and positioned the laser beam is relative to the fiber tip. In some applications, the fiber is laser

4-3

Figure 4-1 Polymicro Technologies’ Low Fiber Count Assemblies

Common Multimode Connectors

Less Common Multimode Connectors

welded to the quartz sleeve to eliminate epoxy at the tip altogether. In other high power applications, a special connector may be used with a counter-bored tip to allow the end of the fiber to be cantilevered away from the metaland epoxy. Temperature ranges depend on the materials chosen; however, designs for continuous operation at200oC with short term excursions to 300-400oC have been supplied. A general schematic of a single, quartz sleeve,

connector design is shown in the following illustration.

Polymicro has a “Standard Termination” and three types of “High Power Terminations.” The term “High Power” is rel-ative to the customer’s application since 10 Watts may be high to one customer but low to another. These are themost common types of terminations, but others can be designed based on specific customer requirements.

Fiber OOptic CCable

Optical fiber or fibers can be jacketed into cable form for added protection from environmental hazards includingmechanical damage, chemical attack and water erosion. The cabling materials and design together with optical fiberwill determine the environmental performance of the final cable. A fiber optic cable can be designed to work in a tem-perature range from -50°C up to >200°C. Besides cabling design, optical fiber can be a limiting factor to themaximum temperature fiber cable can withstand. For example, hard polymer clad fiber has an operating upper tem-perature limit of ~125°C, thus limiting the maximum temperature the cable can withstand.

The cabling materials are typically polymer but sometimes metal is also used. Common cabling materials include:

1) Polymer jacket materials: PE (polyethylene), Hytrel® (polyester), Nylon, Tefzel® (ETFE), Teflon® PFA, TFE, PU(polyurethane), and PVC

Kevlar® (aramid yarn), epoxy/fiberglass central members, and stainless steel tube.



4-4

Hytrel®, Kevlar®, Teflon®, and Tefzel® are trademarks of E.I. du Pont de Nemours and Company

Figure 4-2 Polymicro Technologies’ Laser High Power Connector

Figure 4-3 Termination Configurations

Standard TTermination:• Standard low stress epoxy• Epoxy to tip of connector• Polyimide left on fiber• Temperature Limit 150°C

High PPower: QQuartz SSleeve:• Special epoxy• Polyimide left on fiber• Quartz sleeve• Temperature Limit 200°C Continuous

High PPower: QQuartz SSleeve/Welded:• Special epoxy• No epoxy at tip of connector• Polyimide removed from fiber• Fiber Laser welded into quartz

sleeve • Temperature Limit >200°C

High PPower: CCantilevered CConnector:• Special epoxy• No epoxy at tip of connector• Polyimide removed from fiber• Cantilevered/counter-bored connector tip• Temperature Limit >200°C

continuous (>400°C intermittent)

There are a variety of cable configurations: simplex, duplex,multi-fiber breakout, ruggedized, high temperature aerospace,armored, tactical, loose tube, zipcord, optical coil cord, and othercustom designs. Hybrid cables containing both electric conductorand optical fiber are increasingly common for medical applica-tions.

• Primary Jacket Only: Simplest fiber cable design comesonly with a jacket over a buffered fiber.

• Simplex Construction: Buffered fiber with an outer-jacketstrengthened with linear aramid yarn between the buffered fiber and the outer jacket. In addition to improved mechani-cal pull strength, the yarn permits the fiber to be relatively loose inside the outer jacket, reducing or eliminating possi-ble micro-bending loss due to the over jacketing. For increased durability, the aramid yarn can be braided.

• High-temperature Aerospace Style Dual Jacketed Cable: Polyimide coated fiber with an extruded high temperature fluoropolymer jacket in a simplex construction with braided aramid yarn. The final outer jacket over the yarn is also a high temperature fluoropolymer material. This design is capable of high temperature up to >200°C, while being compact and lightweight with low micro-bending loss.

• Multi-cable Polymeric Conduit Construction: Multiple simplex fiber cables placed inside a polymer conduit to maintain low transmission loss for each individual fiber cable.

• Stainless Steel Stripwound Construction: Fiber is loosely placed inside stainless stripwound tubing that gives the fiber mechanical protection. A polymer tubing with or without braided aramid yarn may be used to enclose the fiber and be placed inside the stripwound. This fiber optic cable construction is often used in high end fiber optic assemblies that offer good mechanical and other environmental protection and quality finish. The stainless stripwound can additionally be covered with polymer material.

Bundles aand HHigh FFiber CCount AAssemblies

A fiber optical bundle is a cluster of optical fibers with some geometric arrangement at each end to accomplish thetransport of light from one place to another (or several others), usually along a non-linear path. Optical fiber is very

useful in this instance because of its ability to carry light very efficiently over pathswith many turns.

The end configurations can be almost any geometry … round, square, rectangular, orsome other shape. In some applications, the only requirement is to get the light fromone place to another. In this case, a fiber bundle is constructed with the optical fiberspacked into circular ferrules or end tips. The most efficient packing geometry ishexagonal. If some randomizing of the light intensity is wanted between the input andoutput, the fibers are put in a quasi-random position on one end relative to the other.In the photograph is a rectangular output bundle with stainless steel flexible armorsheath. It is used to transmit high intensity UV from the source to the rectangularoutput end.

An example of a circular to rectangular assembly would be one where the output ofa high intensity lamp is needed to illuminate a linear area. At one end, the fibers would form a circular bundle; and atthe other, the fibers would be lined-up in a linear stack, square or staggered. The linear stack could then be focusedon the area to be illuminated with a simple cylindrical lens or used in direct contact without a lens. In most applica-tions, this method is much more efficient than using conventional optics to get the light where it is needed.

Applications may require the source light to be split into several different positions. This can be done with a multiplebranch optical fiber assembly. The light is divided from the input to the output, in proportion to the number of fibers ineach branch. The fiber could be arranged in a circle at one end and a ring at the other to make a ring light, which isnow quite commonly used on microscopes.



4-5

Figure 4-4 Sample Cable Constructions



An important feature of synthetic fused silica fibers is that wavelengths can be transmitted over the entire spectrumfrom the ultraviolet to the near infrared. Borosilicate and plastic fibers do not have this ability. In addition, Polymicro’smultimode, step-index, all-silica fiber has extremely low fluorescence characteristics, low scattering losses, and astable index of refraction. Hollow waveguides can even be used in the Mid-Infrared region. See the HW specificationsheet in the Product RReference section under Optical FFiber.

Light at one or more wavelengths can be sent down fibers and reflections or interactions (e.g., fluorescence)returned through the same or additional fibers in the same fiber bundle assembly. This type of assembly is found inreflective readers as well as remote sensing applications.

The operating temperature range will depend on the materials used in the construction of the bundle, including thefiber buffer material. Jacketing materials, to protect the fiber bundle from damage, may also put some limitations onthe type of environment in which the assembly can be used.

A bundle assembly need not be limited to just optical fibers; fused silica capillary tubing, wiring or other filaments canbe integrated into the assembly as well. This feature might be used in applications requiring venting or flushing by

gasses, fluid transfer or wire insulation via flexible silicatubing. For example, thermocouple or heater wires could beincorporated into the assembly.

In applications where several optical fibers are clustered intoa bundle to form an end-tip, the true active area is the corearea. The percentage of active area is calculated by dividingthe total core area by the total geometrical area of thebundle. This active area is always less than 100% due toarea taken up by the buffer coating, cladding, packing geom-etry and bonding material.

The most cost-effective method in most fiber bundle appli-cations is to use an optical fiber with a thin buffer orpolymer cladding. This is the most reliable choice as wellsince once the buffer is removed from the fiber end the fiber

becomes very prone to damage or breakage. The littleextra gain in active area is often lost due to brokenfibers and usually results in reduced yield (increased cost) and reduced reliability and performance.

The fiber-bundling approach is the best for large area applications or where flexibility is required. Routing light viaoptical fiber is much more efficient than lenses and mirrors. Using lenses to relay a light spot with an f/1.0 lens (at a1:1 ratio), you will still lose 50% or more of the light. Whether it is 50% or more depends on the lens assembly trans-mission losses.

4-6

Figure 4-5 Example Hex-pack Characteristics

Figure 4-6 Fiber Hex-pack



For a bundle with 91 fibers or greater, the tolerance build-up makes it very difficult to get a perfect hex pack. To givethe designer a gauge as to how many fibers of a specific diameter yield a certain bundle diameter, a chart has beengenerated. The nominal circumscribed diameter for some polyimide buffered silica fibers with perfect hex pack isshown.

In general, the smaller the number of fibers in the bundle the less expensive the final assembly. For instance 37fibers, 500µm in diameter gives approximately a 4µm diameter as does 91 fibers, 300µm in diameter or 217 fibers,200mm diameter. The 37 fiber bundle will also take less time to assemble.

If a linear array is needed at one end of the assembly, the fibers can be arranged in rows and columns or every otherrow nested in between the previous row to obtain tighter packing. In either case, the tolerance build-up in outsidediameter of the fibers must be accounted for in designing the termination hardware configuration. The fiber size mayhave to be selected based on the resolution required in the linear array. Still, a fewer number of larger fibers will turnout to be the least expensive, all other requirements being equal.

4-7

Figure 4-7 Bundle Diameter vs Number of Fibers

Figure 4-8 Tight vs Linear Fiber Packing



From these two simple illustrations, it can be seen that we can dra-matically change the optical distribution by going from say a circleon one end to a rectangle or line on the other. The choice of stack-ing method on the rectangular end will depend on the applicationrequirements. A general light gathering or illumination applicationwill most likely use the hex pack for maximum packing density; the in-line stack is more likely to be used for imaging such asspectrometer imaging relay or other coherent applications.

Other losses that should be taken into account are:

1. Media Losses (attenuation) – will depend on the length and type of fiber used.

2. Fresnel Losses – typically 4% per polished surface.

3. Potential fiber breakage – typically less than 2% of bundle area.

The total loss from input to output will be the summation of all four factors: Packing, media, Fresnel and fiber breakage.

Capillary AAssemblies

In many ways, fused silica capillaries can be handled the same as fibers are in assemblies. They can be bundledand divided into several paths. The major difference is in the end finishing. If the interior of the capillaries needs tobe kept clean, special handling and materials are needed. Cleaving, end finishing and bonding must be based on theapplication requirements and prior experience. It is important to choose a manufacturer and designer familiar withspecial handling required for capillary tubing assemblies and finishing. Polymicro, being experienced in design, proto-typing, and production of these assemblies, can save you time and material.

The PPolymicro AAdvantage

Designing and fabricating optical fiber assemblies can be tricky and expensive for the first time user. Polymicro offersa custom engineering service to help with new requirements or to help improve the cost or performance of cus-tomers’ current configurations.

To best serve customers’ needs, Polymicro has developed an excellent customer service and engineering supportorganization. Working with your design and manufacturing engineers at our facility and yours, we can quickly andcost effectively solve your problems. Using concurrent engineering methods and our capabilities in standard productsas well as customized products yields a result that is readily manufactured at a reasonable cost. Polymicro can cus-tomize preforms, materials, and/or processes to meet the customer design and manufacturing requirements.Resource limited companies will especially appreciate this engineering outsourcing opportunity.

Polymicro’s fiber optic assemblies are specifically designed for applications demanding high optical transmissionfrom the ultraviolet (UV) to the infrared (IR). Polymicro offers the system designer unparalleled flexibility to incorpo-rate a wide range of design options into their assemblies. Everything from the termination style and technique, jack-eting, and fiber type can be specified to ensure optimum system performance. Scientific applications in designingand manufacturing assemblies for industrial and scientific industries is a valuable resource, Polymicro can assist youin designing and building fiber optic assemblies for applications ranging from sensing, to laser power transmission, toprocess control instrumentation, and to short distance data communication.

4-8


5 FFused SSilica MMicro-Components

Sculpted FFiber TTips – TTapers, CCones, DDiffusers aand BBall LLenses

With the latest technological advances in laser micro-machining, it is now possible to incorporate special optical fea-tures onto the end of an optical fiber. Fused silica capillary tubing can also be reshaped to modify the end shape or

to generate custom couplers for capillaries or optical fibers. In thissection, we will refer to these devices as micro-components. They gen-erally have diameters less than 2mm.

There are many applications for optical fiber where a simple, flat, fiberend is not ideal. The ability to obtain an optical fiber incorporatingoptical coupling features can alleviate design problems. The problemsassociated with getting light in or out can be greatly improved by havinginterface features micro-machined into the fiber material.

Similar coupling problems exist with fused silica capillaries. The designcan be made simpler and more efficient using micro-machined ends orcouplers. Fused silica or quartz couplers offer a good solution for con-necting fused silica capillary tubing. They also offer a good thermalmatch as well as a clean, non-contaminating, chemically durable con-nection.

Before going into a few of the various shapes that can be sculpted onoptical fiber ends, a quick review of spherical lenses might be useful.When we discuss spherical lenses relative to optical fibers, we are

usually talking about a complete sphere of quartz, glass or other optical material. The choice of material will bebased on the wavelength range for which it is to be used. It will also depend on how strong a focusing effect isneeded. Higher refractive index materials will give shorter effective focal lengths, but may have other problems rela-tive to cost, durability or mounting.

A “Ball Lens” or full sphere is often used to coupleoptical fibers. The back focal length, BFL, increases asthe ratio of D/d increases. The collimated beam diameteris d and the Sphere diameter is D. The market has theseball lenses available in various materials to allow choicesof wavelength range, diameter and focal length.Materials such as BK-7, SF-8 or LaSFN-9, quartz, sap-phire, ruby, doped Al2O3, and fused silica are used. Highindex materials normally must be anti-reflection coateddue to higher Fresnel reflections. For many applications,an optical fiber with an integral spherical end surfacemay be less expensive and give better performanceresults with less cost.

The most common fiber coupling, after the use of directcoupling, is the double sphere. The first sphere roughlycollimates the light exiting one fiber and the second refo-cuses the collimated light into the second fiber. Thismethod reduces the lateral alignment requirementbetween the two fibers. They can also be used to reducethe divergence of a light source, such as an LED, to helpcouple more light into the fiber.

5-1

Figure 5-1 Fiber and Focusing Sphere

Figure 5-2 Two Sphere Lenses as Fiber Coupler



Sculpted TTips IIntegral wwith OOptical FFibers

Tapers or cones can be formed at the end of an optical fiber. As mentioned before in Fiber OOptics aand OOpticalFiber, tapers can be used to reduce or increase the NA (the output divergence). The evanescence wave effect in ataper with the cladding partially or entirely removed can be used as a fluorosensor component.1

Sculpted tips can also include a spherical surface such as mentioned previously. These end configurations are preci-sion micro-formed on an optical fiber end using a laser. Some typical shapes are shown below.

From the drawings, the optical fiber tip-end shape and characteristic are listed in the table. Keep in mind that thetypical optical fiber diameter in these devices is typically in the range of 200µm to 2mm. The shapes are made fromthe fiber itself, thus there are no coupling losses or interface contamination that might exist if the shape was bondedor fusion spliced onto the fiber end. Many other shapes that combine prism surfaces, spherical lensing surfaces, andflat facets havebeen produced.

The componentscan also be cut tospecific lengths andused as micro-optical compo-nents. They can becoupled to existingoptical fibers orused as individualoptical elements.Several of the con-figurations shownare used for laserbeam manipulationto re-shape thebeam pattern onsilica glass.

Polishing,Shaping aandFinishing

Industrial standardmechanical polish-ing techniques areoften used. Thereare special applica-tions where eventhese high qualitypolishing proce-dures are not ade-quate. In theseextremely demand-ing cases, automatedlaser machiningmethods developed by Polymicro has been used for custom and production optical fiber finishing. Some of theshapes are shown in the previous section on sculpted tips. When silica core with doped silica clad optical fiber isused, the cladding is left intact on several of the configurations. Most often, the configuration is rotationally symmetricabout the fiber axis. This is not a rigid requirement. Many surface shapes and finishes can be applied to meet spe-cific optical characteristic requirements. Features such as spiral grooves through the cladding, hemispherical or othershapes on the end, and various combinations of mechanical shapes can be engineered.

5-2

1 N. Nath, et al., "Evanescent Wave Fiber Optic Fluorosensor: Effect of Tapering Configuration on Signal Acquisition"

Figure 5-3 Sculpted Fiber Tip Examples



Tapered FFibers

Tapered optical fibers are fibers that have a diameter that varies along their length. Optical tapers have properties that makethem useful as input/output devices. They can be used as a passive optical component to alter the fiber’s input and/or outputdivergence (NA). They can also be used as a high power coupler for laser energy (decreases the power density by allowinga larger input spot size), or simply as a device to loosen alignment tolerances in an optical system.

In general, there are several facts about tapers that should be kept inmind when considering their use. When light travels in an “Up” tapertowards a smaller radius, the angle the light makes with the taperaxis will increase with each reflection. It is important to rememberthat if this angle exceeds the critical total internal reflection angle ofthe fiber at the bottom of the taper, then the light will not be con-

tained in the core. This means that the NA at the entrance of the taper must be reduced to avoid significant loss atthe end of the taper. A first order approximation is that to avoid losses, the input NA must be reduced by the taperdown ratio. For example, with a 2:1 “Up” taper on a 0.22NA fiber, one should keep the input NA at or below 0.11. Inthe case of a “Down” taper, as light travels towards a larger radius, the angle will decrease with each reflection.

Polymicro can fabricate tapers using two separate methods. Laser machined tapers are formed out of the existingglass material at the end of a fiber and tend to be relatively short, typically 5 to 15mm in length. The other methodinvolves forming the fiber taper on the draw tower by automatically controlling the draw parameters. These tapersare longer, typically in the range of one to two meters.

High PPower LLasers

Another consideration is the concentration effect of tapers as the diameter decreases. Q-switched laser systemsproduce high peak powers that are difficult to couple into fiber. Typically, the bulk fiber material can withstand thispower, but the fiber surface may become damaged due to dielectric breakdown of the surrounding medium orsurface contamination may initiate the breakdown. Both effects degrade the fiber surface rapidly.

With an “Up” taper integrated into the proximal end of the fiber, the power density at the larger input surface can bereduced to levels well below the damage threshold in many cases. In cases where the minimum beam waist islarger than the fiber diameter, the use of a taper can greatly improve the coupling efficiency.

Depending on conditions, some of which are listed in the table following, the laser induced-damage threshold ofPolymicro’s fiber at 1064nm is up to 1 Giga-Watt/cm2 for pulsed lasers and up to 2 Mega-Watts/cm2 for CW. Thisthreshold decreases at shorter wavelengths.

Some of the significant factors that affect optical fiber damage in laser applications are given in the following table.Depending on the specific application, there may be other effects as well.

5-3

Figure 5-4 Laser Coupling into Taper

Figure 5-5 Some Laser Induced Damage Threshold Variables



Beam EExpansion

An optical taper can be used on the output-end of an optical fiber using its angle changing property to alter theangular distribution of the output intensity. For example, if a lower output divergence than the fiber normally exhibitsis desired, an “Up” taper can be used at the distal end. Alternately, if a larger divergence is required, a “Down” tapercan be used.

The well-known concept of conservation of brightness states that iflight losses are negligible, the spatial and angular content of the lightanywhere within or at either end of a taper are described by:

Where subscript i refers to input, o to output parameters.

A = cross sectional area of the light distribution normal to the taper axis

θ = maximum angular extent of the light distribution

n = refractive index of the medium where θ is measured

dii = input diameter

doo = output diameter

Since n ssin θ = NNA and Aii/Aoo = ddii22/doo

22, it follows that:

However, if the product of the input NA and the ratio of the diameters exceeds the greatest NA that the taper cansupport, light will escape into the cladding and be lost. This relation will no longer be valid. Therefore, the recom-mended maximum input NA is:

As an example, choose a 2:1 input taper and the output NA is 0.22:

Light is confined to the core if it strikes the interface between the core and the cladding at an angle to the surface,θcc, of equal to or less than:

To obtain the best possible coupling efficiency, the launch NA must be 0.073 or less, and the focal point of the beamshould be in the neck down region of the taper.

Ferrules && SSplices -- FFor OOptical FFibers

One type of optical fiber coupling ferrule is a precision quartz tubein which the center region is sized to allow a precision fit for thediameter of the optical fiber being used. The ends are flared to

5-4

(Eq. 5-1)

(Eq. 5-2)

(Eq. 5-3)

NAin = 00.22 ((1/3), thus we have NAin = 00.11

(Eq. 5-4)

Figure 5-6 Taper Optical Characteristics

Figure 5-7 Mechanical Splice



allow easy fiber insertion with minimal risk of damaging the cleaved or polishedfiber ends. The precision bore allows excellent alignment of two fiber ends whenthey are inserted from opposite ends of the coupler.

Another type of coupler ferrule is used in WDM and other applications where twofibers need to be aligned side by side very accurately. Thermal, mechanical and optical parameters must be takeninto account. A quartz capillary with a center that has a rectangular shape or precision separate dual ID’s can be fab-ricated. The entrance has a taper to simplify alignment when the two fibers are inserted. For other multiple fiberapplications, the quartz tube can have a variety of shapes. With appropriately engineered preforms, Polymicro canproduce various geometries including square, circular, elliptical, rectangular and triangular shapes.

Connectors, FFerrules && SSplices -- FFor CCapillaries

For coupling capillary tubing Polymicro offers Inner-Lok™ Capillary Connectors. Theseconnectors are designed for quick, contamination-free coupling of polyimide coated silicacapillary tubing in applications such as Gas Chromatography. Two standard products areavailable, a universal union and a Y-shaped splitter. The capillaries are inserted into thetapered ends and press fit to seal. If needed, a drop of adhesive or polyimide can beapplied into the tapered ends to help hold the capillary (appropriate curing may berequired). Proper cleaving is essential to form a good seal and is discussed in theCleaving Procedure section of this Handbook’s Appendix. Polymicro’s standard Inner-Lok™ products have a 2mm outside diameter and are nominally 38mm long. They aredesigned to accept tubing with OD’s ranging from 360µm to 670µm. Custom sizes ofInner-Lok™ style connectors can be manufactured.

Although less common, Ferrules and Splices like those used on Optical Fibers can be employed with capillary tubing. Inmany cases an existing larger size capillary tubing can be used as the ferrule or splice component. Custom tubing can bedrawn to provide an exact fit if needed. Polymicro is well experienced with cutting, polishing, and flaring ferrules prior to use.These preparatory operations can reduce manufacturing time and improve final product quality. In addition, Polymicro cando the final assembly operations if needed; see Fiber OOptic && CCapillary AAssemblies.

Special CCapillaries -- MMulti-lumen

Multi-lumen or multi-element capillaries are a class of flexible quartz or glass capillary tubing having multiple pas-sageways. The number, size, and shape of the individual passageways depend on the application requirements. Onecan be used to guide an optical fiber for illumination at the distal end, while another can guide a gas or anotherinstrument. The openings do not have to all be the same size.

Special CCapillaries -- SSquare/Rectangular

Polymicro introduced a flexible silica square capillary in response to requests from the capillary electrophoresis (CE)scientific community. This square capillary offers an improved optical beam-sampling path over traditional circularcross-section silica capillaries for in line spectrometry. This square configuration allows for a simplified optical systemfor the spectrometer due to the lack of cylindrical lens effects found in normal round tubing. See the Flexible FFusedSilica CCapillary TTubing section of this handbook under Alternative CCross-Sectional GGeometries for more details.

Special CCapillaries -- WWindowed CCapillaries

Polymicro also supplies windowed silica capillary. The window is made using a laser-based technique to completelyremove the polyimide while leaving the silica capillary extremely strong with excellent optical surface qualities. Seethe Flexible FFused SSilica CCapillary TTubing section of this handbook under Capillary PProductss for more details.

MEMS/NEMS Technologies

Polymicro is constantly evaluating and supporting emerging technologies, including the areas of Micro- and Nano-Electro Mechanical Systems. Polymicro is integrally involved in a number of applications in this arena.

5-5Inner-LokTM is a registered trademark of Polymicro Technologies

Figure 5-8 Dual Fiber Ferrule

Figure 5-9 Capillary Inner-LokTM



Polymicro capillary is finding wide usage in fluidic interfacing between MEMS/NEMS devices and the macro world. Infact, a number of companies have developed connectors for MEMS/NEMS devices that dimensionally mate withPolymicro capillary. Some researchers bond capillary directly into their Microfabricated devices instead of using con-nectors. Polymicro draws capillary to the specifications needed in order to meet the application requirements.Further, Polymicro can provide pre-cut capillary, simplifying the production requirements of the customer.

Polymicro optical fiber is also being used in the MEMS/NEMS research market. These fibers efficiently guide light toand from the devices, with significant use in microfluidic structures. Polymicro has drawn a number of custom opticalfibers to satisfy the specific demands that each device requires. In many instances, Polymicro builds the finishedassemblies to the customer's specifications. When needed, Polymicro can assist in basic design issues related tofiber optics.

5-6


Technical GGlossary

AAbbssoorrppttiioonnIn optics, the loss or attenuation that is due to material proper-ties of an optical fiber. Absorption is quite often wavelengthdependent.

AAcccceeppttaannccee aanngglleeThe maximum cone half-angle for which incident light is cap-tured by and will travel through the optical fiber. If the accept-ance angle is θ then the acceptance cone is defined by a solidcone of 2θ. See NNAA for more details.

AAccrryyllaatteeA polymer material used in optical fibers as a buffer coatingor cladding or in capillary as a coating.

AAddssoorrppttiioonnIn chemistry, the taking up by the surface of a solid or liquid(adsorbent) of the atoms, ions, or molecules of a gas orother liquid (adsorbate). Porous or finely divided solids canhold more adsorbate because of the relatively large surfacearea exposed.

AAtttteennuuaattiioonnThe amount of light loss experienced in an optical fiber oroptical media as a function of length. For optical fiber it isusually expressed in dB (decibels) per kilometer (km). SeeTTrraannssmmiissssiioonn.

BBaannddwwiiddtthhThe range of frequencies (or wavelengths) which is useful fora device or system. In optical fiber, it is a measure of informa-tion carrying capacity. The frequency bandwidth is usuallydescribed as the frequency where the signal power is one-halfthe power at zero frequency. The wavelength bandwidth isusually expressed in terms of spectral wavelength-dependentattenuation or transmission, and is not necessarily related tothe signal bandwidth.

BBeennddiinngg lloossssLoss in an optical fiber caused by bending of the fiber. Thisloss is usually due to internal light paths exceeding the criticalangle for TIR. Both mmiiccrroo--bbeennddiinngg and mmaaccrroo--bbeennddiinngg areloss mechanisms in optical fibers.

BBeenndd RRaaddiiuussThe radius of a drum or mandrel around which an optical fiberor cable is wrapped or wound. The radius at the center of thefiber or cable is the bend radius plus one-half the fiber orcable diameter.

BBrrooaadd SSppeeccttrruumm ffiibbeerrAn optical fiber that has a relatively wide transmission spectrum window ranging from ~300nm to ~2µm.

BBuuffffeerrThe buffer is an outer coating on an optical fiber. Typically aplastic material, it protects the fiber from external stresses andabrasion.

CCaabbllee,, ffiibbeerr ooppttiiccA package or assembly for an optical fiber or bundle of fibersthat may include buffering, strength members and/or an outerjacket.

CCaappiillllaarryy EElleeccttrroopphhoorreessiiss ((CCEE))Capillary Electrophoresis is a separation method based on thedifferential electrophoretic migration rate of sample compo-nents in a capillary when a voltage is applied. The detectionmethod is usually “on-column” using UV spectrometric or fluo-rescence analysis through a window in the capillary.Performing electrophoresis in small-diameter capillaries allowsthe use of very high electric fields because the small capillar-ies efficiently dissipate the heat that is produced. Increasingthe electric fields produces very efficient separations andreduces separation times. CE detection includes absorbance,fluorescence, electrochemical, and mass spectrometry.

CCaappiillllaarryy ttuubbiinnggQuartz or glass tubing which has internal diameters fromless than 2µm to more than 2000µm. The outside diametercan range from 90µm to greater than 3500µm, dependingon the application requirements. An outside buffer coatingof polyimide, silicone, acrylate or fluoropolymers can beadded.

CChhrroommaattiicc ddiissppeerrssiioonnThe separation of a beam into its various wavelength compo-nents. In an optical fiber, dispersion occurs because of the dif-fering wavelengths propagating at different speeds. Thiscauses pulse spreading or broadening. See DDiissppeerrssiioonn.

CChhrroommaattooggrraapphhyyIn chemistry, analytical technique used for the chemical sepa-ration of mixtures and substances. The technique depends onthe differential distribution of solutes between the mobile andstationary phases.

CCllaaddddiinnggA low refractive index optical material that surrounds the coreof an optical fiber. It is used to cause reflection of the core lightwhile preventing scattering from surface contact. In all-glassfibers, the cladding is glass. In plastic-clad Silica fibers, theplastic cladding also may serve as the buffer coating.1 In someapplications, multiple cladding layers can be used.

CCoolloorr The attribute of visual perception that can be described ashaving characteristics of hue, saturation, and brightness. Itdoes not include aspects of extent (e.g., size, shape, texture,etc.) and duration (e.g., movement, flicker, etc.). A color that isseen can be a single wavelength or a combination of wave-lengths. Most colors are a very complex combinations of manywavelengths of various amplitudes.

CCoorreeThe light-guiding portion of an optical fiber having a higherrefractive index than the cladding. It is usually made of a puresynthetic Silica material, but can be a doped material toprovide special fiber characteristics.

1The Photonics DictionaryTM, 43rd Edition, 1997, Laurin Publishing Co., Inc., Pittsfield, MA

G-1


Technical GGlossary

CCuutt--ooffff wwaavveelleennggtthh1. In detector technology, the long wavelength at which detec-tor response falls to a set percentage (usually 20 or 50percent). 2. In fiber optics, the wavelength below which awaveguide can transmit multiple modes rather than purelysingle mode.

DDeecciibbeellThe standard unit used to express gain or loss and relativepower levels. The decibel (dB) = -10 log (Po/Pi), where Po isthe output power and Pi is the input power.

DDiiffffuusseeThe type of reflection/transmission from many powders (e.g.,phosphors, MgO2 or BaSO4), matte surfaces and transmittingmaterials such as ground quartz, flashed opal glass or Teflon®

(PTFE). Flat white paint is an example of a nearly Lambertian,diffuse coating. Diffusers are often used to remove imagingcharacteristics from an optical beam. See also SSppeeccuullaarrrreefflleeccttiioonn,, SSpprreeaadd and LLaammbbeerrttiiaann.

DDiissppeerrssiioonn The separation of a beam into its various wavelength compo-nents. In an optical fiber, dispersion occurs because the differ-ing wavelengths propagate at differing speeds. In fibers, it isthe cumulative effect of three types: cchhrroommaattiicc, mmooddaall andwwaavveegguuiiddee ddiissppeerrssiioonn.

DDooppeedd ((ssyynntthheettiicc)) ffuusseedd ssiilliiccaa See FFuusseedd ssiilliiccaa.

DDuuaall CCllaaddAn optical fiber constructed with Silica core and doped Silicacladding coated with optical quality polymer that has a lowerrefractive index than the doped Silica cladding. Dual clad isdesigned to transmit higher optical power as compared to asingle clad.

EEffffeeccttiivvee nnuummeerriiccaall aappeerrttuurreeSee NNuummeerriiccaall aappeerrttuurree ((NNAA)).

EEllaassttoo--ooppttiicc eeffffeeccttA change in the refractive index of an optical fiber caused byvariation in the length of the fiber core in response to mechani-cal stress.

FFiibbeerr ooppttiiccssA branch of optics that deals with the transmission of lightthrough fibers, tubes or thin rods of a transparent material. Iflight is injected into one end of an ooppttiiccaall ffiibbeerr or rroodd, it cantravel through it with very little loss, even if the fiber is curved.The amount of loss depends on the color of light (wwaavvee--lleennggtthh), the optical fiber design, the materials used, and themanufacturing process.

FFlluuoorreesscceenncceeThe emission of light or other electromagnetic radiation oflonger wavelengths by a substance as a result of the absorp-tion of some other radiation of shorter wavelengths, providedthe emission continues only as long as the stimulus producingit is maintained. In other words, fluorescence is the lumines-

cence that persists for less than about 10ns after excitation.Radiation which persists for longer time is known as phospho-rescence.

FFooccaall rraattiioo ddeeggrraaddaattiioonn ((FFRRDD))The reduction of relative f-number (or f-ratio) in an optical fiberdue to the characteristics of the fiber. Basically, the emittancelight cone is always greater than or equal to the incident lightcone in an optical fiber. The effect of FRD results in the outputcone of light being larger than the input cone of light. Becauseof this effect, insertion of optical fiber in an f-number matchedoptical train (e.g., a astronomical fiber optic spectrometer) willcause a signal loss greater than that expected from the normalloss per unit length values. Failure to account for FRD intransmission measurements, e.g., measuring light output withan integrating sphere, will give optimistically high transmissionvalues for higher f-number systems.

FFuusseedd qquuaarrttzzSee FFuusseedd ssiilliiccaa.

FFuusseedd SSiilliiccaaFFuusseedd SSiilliiccaa is Silicon dioxide (SiO2) in its amorphous(glassy) state. SSiilliiccaa is Silicon dioxide (SiO2). SSyynntthheettiiccffuusseedd SSiilliiccaa is amorphous Silicon dioxide that has been produced through chemical deposition rather than refinementof natural ore. This synthetic material is of much higher purityand quality as compared to ffuusseedd qquuaarrttzz made from naturalminerals. DDooppeedd ((ssyynntthheettiicc)) ffuusseedd SSiilliiccaa has been intention-ally doped with trace elements such as Germanium, Boron,Phosphorous, Titanium, Fluorine or other elements to adjustthe optical properties of the glass. QQuuaarrttzz is a natural gradeof crystalline Silicon dioxide (SiO2), the most common phaseof SiO2. FFuusseedd qquuaarrttzz is a natural grade of amorphous SiO2.Typically produced from the melting (fusing) of crystallinequartz and refined such that an amorphous (glass) is formed.

GGaass CChhrroommaattooggrraapphhyy ((GGCC))Gas Chromatography is a method for separating substancesin a mixture and measuring the relative quantities of sub-stances. It is a useful technique for substances that do notdecompose at high temperatures and when a very small quan-tity of sample (micrograms) is available.

In this type of chromatography, a sample is rapidly heated andvaporized, and then a stream of gas carries it along a columnthat contains a stationary phase. The sample becomes dis-tributed between the mobile gas phase and the stationaryphase. The higher a substance’s affinity for the stationaryphase, the more slowly it travels through the column.

GGllaassssThe word “Glass” refers to the solid phase of a material withno long-range molecular order. It is used almost interchange-ably with “amorphous,” “non-crystalline,” and “vitreous.” Glassis a disordered structure, as opposed to a crystalline materialthat exhibits a symmetrical, ordered structure. The mostcommon glasses are oxide based, such as Silicates (SiO2),Borates (B2O3), Germinates (GeO2) or mixtures of these.

Teflon® AF is a trademark of E.I. du Pont de Nemours and Company

G-2


Technical GGlossary

GGrraaddeedd iinnddeexxDescriptive of an optical fiber having a core refractive indexthat decreases almost parabolically and radially outwardtoward the cladding. This type of fiber combines high band-width with moderately high coupling efficiency. Sometimescalled gradient-index.

HHaarrdd ccllaaddAn optical quality fluorinated polymer that has a lower refrac-tive index than pure Silica glass. It is applied in a thin layer(5-15µm thick) and has a hardness in the range of 60-70Shore A. Often, it also refers to the fiber constructed with apure Silica core surrounded with hard clad.

HHiigghh--PPeerrffoorrmmaannccee LLiiqquuiidd CChhrroommaattooggrraapphhyy ((HHPPLLCC))High-Performance Liquid Chromatography (HPLC) is a form ofLiquid Chromatography used to separate compounds that aredissolved in solution. HPLC instruments consist of a reservoirof mobile phase, a pump, an injector, a separation column,and a detector. Compounds are separated by injecting a plugof the sample mixture onto the column. The different compo-nents in the mixture pass through the column at different ratesdue to differences in their partitioning behavior between themobile liquid phase and the stationary phase. Solvents mustbe degassed to eliminate formation of bubbles. The pumpsprovide a steady high pressure with no pulsating, and can beprogrammed to vary the composition of the solvent during thecourse of the separation. Typical detectors rely on a change inrefractive index, UV-VIS absorption, or fluorescence after exci-tation with a suitable wavelength.

HHoollllooww wwaavveegguuiiddee ((HHSSWW))A flexible hollow capillary with an internal surface coatingwhich is highly reflective at the wavelength unlike opticalfibers, this does not utilize total internal reflection. It is usuallyused where there are no transmissive materials that can beformed into a flexible optical fiber at the wavelength of interest.Most commonly used in the IR.

HHPPCCSSAcronym for "Hard Polymer Clad Silica". Another term forhard clad fiber.

IIssoottrrooppiiccInvariant with respect to direction. The property of an opticalmaterial that allows the velocity of propagation of electro-mag-netic radiation to be the same for all directions.

JJaacckkeettiinnggUsually the outer material used on an optical fiber or fiberbundle. Inner jackets are also used in multifiber assemblies.

kkppssiiKilo-pounds per square inch is a common unit used for tensilestrength testing of optical fiber.

LLaammbbeerrttA unit of luminance (brightness) equal to 11//π candela persquare centimeter.

LLaammbbeerrttiiaannA relation between the illumination on to a surface and thelight flux from a surface versus angle. Lambert’s Cosine Lawstates that the light flux, EE , at some angle, , is equal to the

illumination perpendicular to the surface, EE, times the cosineof the angle.

LLiigghhtt11.. Electromagnetic radiation in the visual spectrum. 22.. aa.. Asource of light, especially a lamp or electric fixture. bb.. The illumination derived from such a source.

LLiiqquuiidd CChhrroommaattooggrraapphhyy ((LLCC))Liquid Chromatography (LC) is an analytical chromatographictechnique that is useful for separating ions or molecules thatare dissolved in a solvent. If the sample solution is in contactwith a second solid or liquid phase, the different solutes willinteract with the other phase to differing degrees due to differ-ences in adsorption, ion-exchange, partitioning, or size. Thesedifferences allow the mixture components to be separatedfrom each other by using these differences to determine thetransit time of the solutes through a column.

MMaaccrroo--bbeennddiinnggBending of an optical fiber or fiber bundle at a radius compara-tively larger than the fiber diameter. Attenuation is increaseddue to light escaping beyond the critical angle at the claddinginterface.

MMEEMMSS//NNEEMMSSAcronyms for "Micro- and Nano- Electro Mechanical Systems".

MMiiccrroo--bbeennddiinnggMicroscopic curvatures in optical fiber that create local axialdisplacements of a few microns. One frequent cause is longi-tudinal shrinking of the fiber buffer or jacket. But it can alsoresult from poor fiber or cable manufacturing methods orinstallation issues. Micro-bending causes transmission lossthrough a power-coupling effect from the guided modes to theradiation modes.

MMiiccrroonn ((µµmm))Alternative name for micrometer (µm or 1x10-6 meters).

MMooddaall ddiissppeerrssiioonnSynonym for mmuullttiimmooddee ddiissttoorrttiioonn or modal distortion.

MMooddaall ddiissttoorrttiioonnSynonym for mmuullttiimmooddee ddiissttoorrttiioonn.

MMooddee11.. The characteristic of the propagation of light through awaveguide that can be designated by a radiation pattern in aplane transverse to the direction of travel. 22.. The state of alaser that corresponds to a particular field pattern and one ofthe possible resonant frequencies of the system.

MMuullttiimmooddee ddiissttoorrttiioonnIn an optical waveguide, the distortion resulting from differen-tial mode delay. Axial rays, with the shortest path length, willhave the shortest transmission time, while rays entering thefiber at its maximum acceptance angle will travel further andrequire the maximum time. As a result, narrow light pulses, willbroaden as they propagate along the fiber.

G-3

MMuullttiimmooddee ffiibbeerrAn optical waveguide that will allow more than one mode topropagate.

NNaannoommeetteerr ((nnmm))A unit of measure most often used for light in the visible(1x10-9 meters). The peak of the human eye sensitivity is at awavelength of 550 nm (green light). In the UV range whereAngstroms are still sometimes used, 200 nm is 2000 Å. In thenear infrared where microns (µm) are used, 1000 nm equals1 micron (µm).

NNuummeerriiccaall AAppeerrttuurree ((NNAA))The larger the NA, the greater the amount of light that isaccepted into the fiber for propagation to the distal end.

The NA for a glass-core to glass-clad interface is often derivedfrom calculations using the equation:

where nnco is the core index and nncl is the cladding index.

Values calculated in this manner do NNOOTT take into accountlosses from Fresnel reflection or degradation of NA with fiberlength. See FFrreessnneell lloossss and FFRRDD.

OOppttiiccssA branch of physical science dealing with the propagation andbehavior of light.

OOppttiiccaall ffiibbeerrDrawn filament made of glass or plastic with a high refrac-tive index core surrounded by a lower index claddingthrough which light can be transmitted using the principle ofTotal Internal Reflection (TIR). When light traveling inside afiber strikes the surface at an angle of incidence greaterthan the critical angle, the light is reflected back toward thecenter of the fiber with negligible loss. Thus, light can betransmitted over long distances by being reflected manytimes, as long as the loss per reflection is extremely low.

The most common optical fiber configuration is based on theuse of two materials concentrically arranged as a centercore and outer tubing (ccllaaddddiinngg). This arrangement avoidslosses that would result from the scattering of light by impu-rities on the surface of the fiber. The optical fiber core ismuch higher in refractive index (nnCCOO), than the claddingindex (nnCCLL); the reflections occur at the interface of the glassfiber core and the cladding. Sometimes a second outer layer(secondary-cladding) is added to the fiber to increase trans-mission, prevent lost light from coupling into adjacent fibers,or to increase the strength or environmental durability of thefiber. See FFiibbeerr ooppttiiccss..

PPaacckkiinngg ffrraaccttiioonn ((PPff ))The fraction of the area of an optical fiber bundle surface thatis actual core area. The actual number of fibers, NN, which canbe packed in a circle of diameter, DD == ((22mm++11))dd, is given by thegeometric summation:

where mm is the number of rings around the central fiber in thepack.

For circular fibers packed in a tight hexagonal array, thenumber of fibers, NN, is given approximately by:

Where dd is the fiber core diameter and DD is the fiber bundlediameter. The packing fraction is thus given by:

Where AA == ππDD22//44, is the area of the bundle. See the FFiibbeerrOOppttiiccss && CCaappiillllaarryy AAsssseemmbblliieess chapter for additional infor-mation.

PPCCSSAcronym for a "Polymer Clad Silica" optical fiber. PCS fiber isusually constructed from Silica core and Silicone clad.Sometimes HPCF is referred as PCS.

PPoollyyiimmiiddeePolyimide is an aromatic, linear polymer typically produced bycondensation reaction, such as polymerizing aromatic dian-hydride and aromatic diamine. The most notable propertiesare its solvent resistance, barrier properties, and performanceat both high and low temperatures.

PPrreeffoorrmm The starting form of glass or silica that is used to generatefiber or capillary by heating and drawing to produce the finalsmaller product size.

PPrrooooff tteessttiinngg A non-destructive means of applying tensile stress to anoptical fiber or capillary during the manufacturing process toidentify mechanical flaws that might otherwise exhibit or break-age during later use thereby assuring a minimal strength level.


Technical GGlossary

4 "Optics", Microsoft® Encarta® 97 Encyclopedia, Microsoft Corporation (1993-1996)

G-4

=


Technical GGlossary

QQuuaarrttzzA natural grade of crystalline SiO2.

RRaammaann ssppeeccttrroossccooppyyThe field of spectroscopy that uses optical frequency shiftsand intensity changes in the Raman chromophore(s) producedby monochromatic illumination, to determine the characteris-tics of the sample.

RRaayylleeiigghh ssccaatttteerriinnggScattering of light from particles smaller than the wavelengthof the radiation incident. A feature of Rayleigh scattering is thatthe scattered flux is inversely proportional to the fourth powerof the wavelength. Thus in the visible region, blue light is scat-tered more strongly in air than longer wavelengths, accountingfor the blue color of the sky.6

RReeffrraaccttiivvee iinnddeexxThe ratio of the speed of light in a vacuum to the speed oflight in the material. Also called the IInnddeexx ooff RReeffrraaccttiioonn, it isdependent on wavelength for optical materials.

SSeeccoonnddaarryy ccllaaddddiinnggAn optical material surrounding the primary ccllaaddddiinngg whichhas a lower index than the cladding. Sometimes the buffermaterial can act as a secondary cladding, giving rise to unex-pected higher order modes. Some bonding materials as wellas liquids can also act as secondary claddings.

SSIISysteme Internationale d’Unites, the international metricsystem of units.

SSiilliiccaaSilicon dioxide (SiO2)

SSiilliiccoonnee((ss))A class of polymer materials. In optical fiber, some are used asbuffer materials and others for optical cladding. Not to be con-fused with silica (SiO2) or silicon (the element, Si).

SSiinngglleemmooddee ffiibbeerrAn optical fiber in which only one mode, the fundamentalmode, is transmitted. This mode travels straight through thefiber without reflection at the core-clad interface. Core dia-meters are typically 5-10µm, making the alignment very criti-cal. Coupling losses tend to be higher than with multimodefibers.

SSnneellll’’ss LLaawwThe relationship between an incident ray at angle II in refrac-tive index media nn1, and the refracted at angle RR in refractiveindex media nn2 is:

SSoollaarriizzaattiioonnA change in material characteristics due to illumination of amaterial with ultraviolet light. High intensities of UV illumina-tion can cause photo-thermal damage in Silica optical fibers,dramatically increasing the scattering and attenuation.

SSppeeccttrruummA range of wavelengths. In optics, the electromagnetic spec-trum includes the wavelength region extending from thevacuum ultraviolet at 40nm to the far-infrared at 20µm.

SSppeeccttrruumm,, VViissiibblleeThe region of the electromagnetic spectrum to which thehuman retina is sensitive. It covers the range from about 400to 750nm in wavelength.

SSppeeccuullaarr rreefflleeccttiioonnWhen light obeys the law of reflection, it is termed to be specular reflection. See also ddiiffffuussee, and LLaammbbeerrttiiaann.

SSttaattiicc ffaattiigguueeDegradation of the strength over time of an optical fiber that isunder stress. The stress can be due to a bend, tension,torsion or a combination thereof. Also, see tteennssiillee ssttrreennggtthh.

SStteepp--iinnddeexx ffiibbeerrAn optical fiber that has a uniform core index and a loweruniform cladding index, creating a step change in refractiveindex profile. Also, see ggrraaddeedd iinnddeexx.

SSyynntthheettiicc FFuusseedd SSiilliiccaaSee FFuusseedd SSiilliiccaa.

TTaappeerrA section of optical fiber or a micro-component that has a con-tinuously changing outer dimension, along its length, from oneend to the other. It can be a separate component or an inte-gral part of the optical fiber tip. Although most have a circularcross-section, they can be made in other shapes.

TTeennssiillee ssttrreennggtthhThe strength of an optical fiber when placed in tension.Usually given in units of kilo-pounds per square inch (kpsi).Also, see pprrooooff tteessttiinngg and kkppssii.

TToottaall IInntteerrnnaall RReefflleeccttiioonn ((TTIIRR))The condition resulting in total reflection at an interface. Inoptical fiber, it is the angle defined as ssiinn--11 ((nn2//nn1)), where nn2 isthe lower index media and nn1 is the higher index media. Foroptical fiber, the cladding is nn2 and the core is nn1. As the angleof incidence is increased from the normal to the surface, theccrriittiiccaall aannggllee is that angle where total internal reflectionbegins to take place.

TTrraannssmmiissssiioonnIn optics it is often given as the percentage of light or energypropagating through an optical system (light output divided bythe light input). Transmission data may or may not includesurface losses, such as Fresnel reflections.

6 The Photonics DictionaryTM, 43rd Edition, Laurin Publishing Co., Inc., Pittsfield, MA (1997)

G-5


Technical GGlossary

UUllttrraavviioolleett ((UUVV))The wavelength range below the lower end of the visible spec-trum. The UV most often refers to the range from 400nmdown to 40nm. Below 200nm a vacuum system is used to getuseful transmission. In addition to fused Silica, only a fewcrystal materials transmit UV below about 350nm such as,Magnesium fluoride, sapphire, Calcium fluoride and Lithiumfluoride.

WWaavveegguuiiddee ddiissppeerrssiioonnFor each mode in an optical waveguide, the term used todescribe the process by which an electromagnetic signal isdistorted by virtue of the dependence of the phase and groupvelocities on wavelength as a consequence of the geometricproperties of the waveguide. Also, see ddiissppeerrssiioonn.

WWaavveelleennggtthhThe length of one wave cycle of a light wave. It is most com-monly expressed in nanometers (nm) for the visible and UV,and “microns” (1000nm/µm) in the IR spectral regions. Thefrequency is inversely proportional to the wavelength.

WWaavvee NNuummbbeerrThe frequency of a wave divided by its velocity of propagation;the reciprocal of the wavelength.

XXeennoonn aarrccThe arc formed when the Xenon gas is excited electrically andemits a brilliant white light. Xenon is used to fill electronic andstroboscopic flashlamps, and also large discharge tubes forlighting large areas.

XX--rraayyA region of the electromagnetic spectrum at wavelengthsshorter than ultraviolet (shorter wavelengths). X-rays are cus-tomarily expressed in energy units rather than wavelength.Wavelengths range from <1nm to >0.01nm.

G-6


Appendix

Polyimide RRemoval ffrom SSilica FFibers oor CCapillary TTubing

The majority of the optical fiber and capillary sold by Polymicro is externally coated with polyimide to provide abra-sion resistance and maintain product strength. Occasionally the need arises for the controlled removal of polyimide.A variety of methods can be employed to remove polyimide and care should be taken in selecting the appropriatetechnique. Some methods leave the glass surface relatively unaffected, while others embrittle the glass making theproduct extremely fragile and prone to breakage during handling. Listed below are a variety of removal methods andassociated comments. In many cases Polymicro may have direct experience using the technique and a Polymicrosales technician can provide assistance.

Thermal TTechniques

• Open fflame: Matches and lighters are quick, easy, and effective at removing polyimide, but they tend toleave the glass surface brittle and are not recommended if strength of the final product is important.

• Gas ttorch: Oxygen/hydrogen flames do a good job of removing polyimide, leaving the final productstrong. Care should be taken regarding the inherent dangers in using this type of torch and the potentialfor distortion of the filament from overheating does exist. Propane, etc. are often acceptable, but are notas good as the oxygen/hydrogen flame. If the flame temperature is not high enough residual polyimidecan be present.

• Oven: At temperatures >600°C the polyimide will carbonize and flake off. This generally takes 30 to 60minutes, and can be expedited with higher temperature or the addition of oxygen. This method workswell to remove large sections of polyimide. The finished product retains excellent strength after process-ing.

• Electric ccoil hheater: Coiled NiChrome® wire, or a NiChrome® wire wrapped around a quartz insulatingtube, makes a resistive coil heater capable of rapidly burning off the polyimide. The coil heater approachworks, but one must be careful not to touch the glass to the wire or insulating tube. This will damage theglass surface, making the glass brittle. Residue is common and post-process cleaning is generallyrequired.

• Electric aarc: Plasma is effective at burning off the polyimide and leaves the glass strong. However,plasma removal can be challenging to control and overheating is difficult to avoid. In fact, this overheat-ing can be useful; Polymicro uses an electric arc plasma technique to melt and seal all capillary endsprior to product release.

• CO22 Laser: Removes the polyimide thermally, just as the above techniques. This method is excellentdue to the clean heat source and the fine control over the hot zone. Distortion from overheating shouldbe monitored.

Chemical TTechniques

• Sulfuric aacid*: When heated to approximately 130°C, sulfuric acid (concentrated) removes the poly-imide very rapidly. Multiple applications are recommended and the finished product should be rinsedwith DI water after the polyimide is removed.

• Strong bbases*: Caustic solutions, such as Sodium hydroxide, will also attack the polyimide. Althoughthese will remove polyimide, they generally etch the filament surface and are generally not recom-mended as a removal method.

*Caution: Proper laboratory safety practices should be followed when working with these types of chemical reagents.

Laser TTechniques

• Excimer llaser: Ablates the polyimide without heat, providing a clean, undamaged silica surface.Polymicro uses this technique routinely, especially on products where a thermal char line is undesirable.This is the method of choice for volume production, but is not very practical for general lab use due tolaser expenses.

• CO22 Laser: See above discussion under Thermal Techniques.

NiChrome® is a registered trademark of Driver Harris Corp.

A-1


Appendix

Mechanical SStripping

• Machining: Removing the polyimide with a mechanical technique, such as an X-ACTO® knife, razorblade, or cutting tool, can work, but damage to the glass surface by the cutting tool will cause brittleness.

• Wire sstrippers ddo nnot wwork. Generally the polyimide is bonded to the glass surface. Wire strippers willdamage the glass during stripping of the polyimide and breakage is almost certain.

Cleaving PProcedureCutting capillary tubing and optical fiber can be accomplished by a number of methods. Matching the cutting methodquality to the application requirements is essential and should be given due consideration. Cleaving is a quick,simple method that can yield a high quality end finish and works well for many applications.

The goal of any cleaving tool is to penetrate through the polyimide and impart a sub-micron defect into the outerglass surface. Ceramic cleaving stones and diamond tip devices are common and effective tools for imparting therequired defect. Once a defect is generated, applying a linear tension to the defect separates the capillary or opticalfiber. This is the preferred method and leads to the highest quality end faces. The most common error in cleaving isto bend the capillary or fiber, which normally yields a low quality cleave with an uneven and sometimes jagged endfinish.

A general misconception when dealing with capillary tubing is that cleaving and breakage are unrelated. A poorcleave generates excessive glass debris inside of the capillary which can lead to internal flaws and subsequentbreakage. It is not uncommon for this debris to be swept down the capillary by gases or liquids that are introduced,leading to flaws and breakage some distance down the capillary from the cleave itself. This effect is most common inlarge ID capillary, but can happen in any capillary product.

When dealing with optical fiber, a subsequent lap and polish is commonly employed to provide a final end finish withoptimal transmission properties. Alternately, laser cutting of optical fiber and capillary tubing has proven to be a reli-able method for many applications that require a flaw free end face.

The following general procedure should be followed when cleaving capillary tubing and optical fiber with a Polymicroceramic cleaving stone.

Procedure:

1. Place the capillary tubing or optical fiber on a clean, flat surface.

2. Holding the cleaving stone at approximately 30° angle to the tubing or fiber, draw the non-serrated edgeof the cleaving stone across the tubing or fiber. Apply just enough pressure to penetrate through thepolyimide coating.

3. Pull the tubing or fiber axially until it breaks. If it won't break, the polyimide coating has not been fullypenetrated. Repeat the above steps, pressing down with slightly more force while drawing the cleavingstone across the tubing or fiber.

4. Once cleaved, inspect the end finish to ensure the cleave quality meets the application requirements.

NNoottee:: If end finish is not of concern, the tubing or fiber can be bent as opposed to pulling axially. The tubing willbreak more easily, but the end finish will be of lesser quality and excessive debris may be generated.

UUsseeffuull TTiipp:: It is not uncommon for users to practice the above cleaving procedure in order to become familiar withproper technique.

X-ACTO® is a registered trademark of Hunt Corporation.

A-2


Appendix

General HHandlingCareful consideration should be given to the general handling of capillary tubing and optical fiber. A few key guide-lines are discussed below.

Storage oof ccapillary ttubing aand ooptical ffiber ccan bbe ccritical, ddepending oon tthe aapplication.

• Most Polymicro products are packaged with a protective foam wrapped around the outside layer ofproduct. The product is then shipped in a sealed plastic baggie. Efforts to reduce exposure to moisturewill prolong lifetime, therefore keep the shipping baggie sealed until the product is ready to be used.Purchasing in spool lengths that appropriately match consumption is recommended. To minimize collec-tion of debris and dust onto stored material, replace the protective foam after removing product from thespool.

• If exposure of capillary tubing internal surfaces to the atmosphere is of concern, make sure to reseal theends after removing product. This can be done by thermal fusing or by placing a septa or similar materialover the end of the capillary tubing.

• When purchasing large diameter tubing or fiber, be sure to store the product so it is setting on the flangeedges. This will avoid cascading and subsequent entanglement during product removal.

Cleanliness oof aany ssurface tthat ccomes iinto ccontact wwith tthe ccapillary ttubing oor ooptical ffiber iis ccritical.

• Debris on work surfaces, such as glass particles from previous cleaving operations, can lead to break-age and is often perceived as apparent brittleness. Especially troublesome, are small particles thatbecome embedded in the polyimide, and lead to breakage during further processing or use. Considerplacing butcher paper on your workbench and change it regularly to provide a clean work area. If this isnot possible, clean the work surface frequently.

• If tubing or fiber is placed onto, or routed through, a manufacturing device, consider all surfaces or fea-tures that could contact the product and make sure these are routinely cleaned of any debris, especiallyafter any breakage. Surfaces should be smooth and free of manufacturing defects such as burrs orsharp edges. Keep this in mind during fixture design and manufacture.

Bending sstress iis aa kkey hhandling iissue tthat sshould bbe ggiven ccareful cconsideration.

• Capillary tubing and optical fiber are often exposed to bending during manufacturing processes and sub-sequent use. Bending these products produces localized tension, often referred to as bending stress.The smaller the bending radius, the greater the imparted bending stress. The acceptable bending radiusfor a given application should always be taken into account. For further discussion on bending stressrefer to Fiber OOptics && OOptical FFiber and Flexible FFused CCapillary TTubing chapters of this handbook.

• Note that product lifetime is directly related to the bend radius. The smaller the bending radius eitherduring handling, or in the final product design, the shorter the lifetime of the product.

• A common handling oversight is the incorporation of rollers or guides that expose the tubing or fiber toexcessively high stresses. It is recommended that the applied stress be calculated for each componentof the system. Related equations and tables are found in Fiber OOptics && OOptical FFiber and FlexibleFused CCapillary TTubing chapters of this handbook.

A-3

Parameters SI UUnit SI SSymbol Common CConversions oor DDefinitions

Length meter m1 m = 1.0936 yd = 39.37 in = 3.281 ft,

1 in = 2.54 cm, 1 km = 0.621 mi, 1 mi = 5280 ft1 mm = 1000 µm, 1000 nm = 1 µm

Mass kilogram kg 1 kg = 2.2046 lb, 1 lb = 453.59 g, 1 lb = 16 oz

Time second s 1 h = 3600 s, 1 day = 8.64 x 104 s

Temperature Kelvin K0 K = -273.15 °C = -479.67 °F, K = °C + 273.15 °C =

5/9 (°F – 32), °F = 1.8 °C + 32

Volume cubicmeter

m3 1 ft3 = 2.832 x 10-2m3, 1 L = 1000 cm3, 1 mL = 1 cm3, 1 in3 = 16.4 cm3

Energy Joule J1 J = 0.239 cal = 0.738 ft•lb = 107 erg =

6.24 x 1018 eV = 9.487 x 10-4 Btu

Force Newton N1 N = 0.2248 lb-force, 1 N = 0.1019716 kilopond,

1 N = 100,000 dynes

Pressure Pascal Pa1 Pa = 1.45 x 10-4 psi, 1 atm = 101,325 Pa,

1 atm = 760 Torr, 1 bar = 105 Pa

Power Watt W1 W = J•s = 0.738 ft•lb-force/s = 3.412 Btu/h =

2.65522 x 103 ft•lb-force/h


Appendix

A-4

UUsseeffuull CCoonnvveerrssiioonn FFaaccttoorrss

UUnniittss ooff MMeeaassuurree


Appendix

A-5

UnitsAngstroms

(Å)Nanometers

(nm)Micrometers

(µµm)Wavenumbers

(cm--11)Energy(keV)

Near IIR 10000 1000 1 10,000 0.0012398

Visible 5000 500 0.5 20,000 0.0024796

UV 2500 250 0.25 40,000 0.0049592

X-ray 10 1 0.001 10,000,000 1.2398

X-ray 0.1 0.01 0.00001 1,000,000,000 120.4

Wavelength UUnits, WWavenumbers aand PPhoton EEnergy

Power && EEnergy

11 WW ((wwaatttt)) = 683.0 Im at 555nm= 1700.0 scotopic Im at 507nm

11 JJ ((jjoouullee)) = 1 W-s (watt-second)= 107 erg= 0.2388 gram-calories

LLuummiinnoouuss FFlluuxx

11 llmm ((lluummeenn))

11 llmm--ss

= 1.464x10-3 W at 555nm= 1/4πcd (candela) if isotopic= 1 T (talbot)= 1.464 x10-3 J at 555nm

IIrrrraaddiiaannccee

11 WW//ccmm22 = 104 W/m2

= 6.83x 106 lux at 555nm= 14.33 g-cal/cm2/minute

IIlllluummiinnaannccee

11 llmm//mm22= 1 lux= 10-4 lm/cm2

= 10-4 ph (phots)

= 9.290 x10-2 lm/ ft2

= 9.290 x10-2 fc (foot-candles)

Conversion UUnits ffor LLight

Radiance

11 llmm//mm22//ssrr = 6.83x 106 lm/m2/sr at 555nm= 683 cd/cm2 at 555nm

LLuummiinnaannccee

11 llmm//mm22//ssrr= 1 cd/m2 (candela/m2)= 1 nt (nit)= 10-4 lm/cm2/sr= 10-4 sb (stilb)= 9.290x10-2 cd/ft2

= 9.290x 10-2 lm/ft/sr= π asb (apostilbs)= π x 10-4 L (Lamberts)= 2.919 x 10-1fL (foot-Lamberts)= 2.919 x10-1 lm/π/ ft2/sr

RRaaddiiaanntt IInntteennssiittyy

11 WW//ssrr = 12.556 W (isotropic)= 4π W= 683 cd at 555nm

IIlllluummiinnaannccee

11 llmm//ssrr = 1 cd= 4π lm (isotropic)= 1.464x 10-3 W/sr at 555nm

UUnniittss ooff MMeeaassuurree,, ccoonntt..


Appendix

A-6

PPoollyyiimmiiddee PPhhyyssiiccaall PPrrooppeerrttiieess

Mechanical DData

Density 1.42 g/cm3

Flexibility 180° bend, no cracks

Elongation >10%

Tensile Strength 15,000 psi

Optical DData

Refractive Index 1.78

Thermal DData

Melting Point None

FinalDecompositionTemperature

560°C

Coefficient ofThermalExpansion

2 x10-5/ °C

Coefficient ofThermalConductivity

37x10-5 cal / (cm) (sec)(°C)

Flammability Self-extinguishing

Specific Heat 0.26cal /gm/°C

PPoollyyiimmiiddee CChhaarraacctteerriissttiiccss

Resistance TTo: # oof DDays % oof TTensile % oof EElongation

Benzene 365 @ 23°C 100 82

Toluene 365 @ 23°C 99 91

Methanol 365 @ 23°C 100 73

Acetone 365 @ 23°C 67 62

10% Sodium 5 @ 23°C Degrades Degrades

Transformer Oil 180 @ 150°C 100 100

Water 14 @ 150°C 65 30

166 @ 100°C 65 20

5 @ 23°C 60 10

PPoollyyiimmiiddee PPhhyyssiiccaall PPrrooppeerrttiieess -- CChheemmiiccaall RReessiissttaannccee

Electrical ddata

Dielectric Strength 4000 volts /mil

Volume Resistivity 1016ohm-cm

Surface Resistivity 1015ohm

Dielectric Constant 3.5

Gas PPermeability

Carbon Dioxide [cc /100in2)

(24 hours) (atm / mil)]45

Hydrogen 250

Nitrogen 6

Oxygen 25

Helium 415

Hydroxide

pH = 1

pH = 7

pH = 10


Appendix

A-7

Trace EElements Fused QQuartzSynthetic FFused

Silica

Aluminum Al 15 < 0.04

Calcium Ca 0.5 < 0.02

Chromium Cr < 0.05 < 0.001

Copper Cu < 0.05 < 0.001

Iron Fe 0.1 < 0.03

Lithium Li 0.6 < 0.002

Magnesium Mg 0.05 < 0.01

Manganese Mn < 0.05 < 0.0005

Potassium K 0.4 < 0.01

Sodium Na 0.3 < 0.01

Titanium Ti 1.1 < 0.03

Zirconium Zr 0.7 < 0.04

TTyyppiiccaall TTrraaccee EElleemmeennttss:: FFuusseedd QQuuaarrttzz aanndd SSyynntthheettiicc FFuusseedd SSiilliiccaaParts pper MMillion ((ppm) bby WWeight

QQuuaarrttzz//SSiilliiccaa CChhaarraacctteerriissttiiccss

TTyyppiiccaall TThheerrmmaall PPrrooppeerrttiieess

Thermal DData Units Fused QQuartz Fused SSilica

Softening ttemperature °C 1710 1600

Annealing ttemperature °C 1220 1100

Strain ttemperature °C 1125 1000

Max. wworking TTemp.

Continuous °C 1160 950

Short-term °C 1300 1200

Mean sspecific hheatJ/kg-K

0 ... 100 °C 772 772

0 ... 500 °C 964 964

0 ... 900 °C 1052 1052

Heat cconductivityW/m-K

20 °C 1.38 1.38

100 °C 1.47 1.46

200 °C 1.55 1.55

300 °C 1.67 1.67

400 °C 1.84 1.84

950 °C 2.68 2.68

Mean eexpansion coefficient

0 ... 100 °C 5.1 x 10-75.1 x 10-7

0 ... 200 °C 5.8 x 10-75.8 x 10-7

Source: Heraeus Quarzglas



Appendix

A-8

Typical EElectrical PProperties

Mechanical Units Fused QQuartz Fused SSilica

Density g/cm3 2.203 2.201

Mohs hhardness 5.5 ... 6.5 5.5 ... 6.5

Micro hhardness N/mm2 8600 ... 9800 8600 ... 9800

Knoop hhardness N/mm2 5800 ... 6000 5800 ... 6200

Modulus oof eelasticity aat 220°C N/mm2 7.25 x 104

7.0 x 104

Modulus oof ttorsion N/mm2 3.1 x 104

3 x 104

Poisson’s rratio 0.17 0.17

Compression sstrength N/mm2 1150 1150

Tensile sstrength N/mm2 50 50

Bending sstrength ((approx.) N/mm2 67 67

Torsion sstrength ((approx.) N/mm2 30 30

Sound vvelocity m/s 5720 5720

Typical MMechanical PProperties

QQuuaarrttzz//SSiilliiccaa CChhaarraacctteerriissttiiccss,, ccoonntt..



Electrical Data Fused Quartz Fused Silica


Appendix

A-9

Wavelengthin µm

Index oofRefraction

R KWavelength

in µmIndex oof

RefractionR K

Wavelengthin µm

Index oofRefraction

R K

.185 1.57486 .0498 .903 .45 1.46557 .0356 .930 2.25 1.43420 .0318 .937

.193 1.56007 .0480 .906 .50 1.46233 .0352 .931 2.35 1.43250 .0316 .938

.195 1.55788 .0475 .907 .55 1.45991 .0349 .931 2.40 1.43163 .0315 .938

.200 1.55051 .0466 .909 .60 1.45804 .0347 .932 2.60 1.42789 .0311 .939

.205 1.54411 .0457 .911 .63 1.45702 .0346 .932 2.70 1.42588 .0308 .939

.210 1.53836 .0449 .912 .65 1.45654 .0345 .932 2.75 1.42484 .0307 .939

.215 1.53316 .0443 .913 .70 1.45529 .0344 .932 2.80 1.42377 .0306 .940

.220 1.52845 .0437 .914 .75 1.45424 .0342 .933 2.90 1.42156 .0303 .940

.225 1.52416 .0431 .916 .80 1.45332 .0341 .933 3.00 1.41925 .0300 .941

.230 1.52024 .0426 .916 .85 1.45250 .0340 .933 3.10 1.41682 .0297 .941

.235 1.51664 .0421 .917 .90 1.45175 .0339 .933 3.20 1.41427 .0294 .942

.240 1.51333 .0417 .918 .95 1.45107 .0339 .933 3.30 1.41161 .0291 .943

.242 1.51208 .0416 .919 1.06 1.44968 .0338 .934 3.40 1.40881 .0288 .943

.248 1.50855 .0411 .919 1.30 1.44692 .0334 .934 3.50 1.40589 .0285 .945

.250 1.50745 .0409 .920 1.40 1.44578 .0332 .935 3.60 1.40282 .0281 .945

.300 1.48779 .0384 .925 1.45 1.44520 .0332 .935 3.70 1.39961 .0277 .945

.320 1.48274 .0376 .926 1.5 1.44462 .0331 .935.35 1.47689 .0371 .927 1.7 1.44217 .0328 .936.365 1.47454 .0365 .928 2.00 1.43809 .0323 .936.40 1.47012 .0362 .929 2.15 1.43581 .0320 .937

Refractive IIndex vversus WWavelength ffor Synthetic FFused SSilica aat 220°C

KK== MMaaxxiimmuumm ppoossssiibbllee ttrraannssmmiittttaannccee aassssuummiinngg aabbssoorrppttiioonn == 00RR == SSiinnggllee ssuurrffaaccee rreefflleeccttaannccee

Source: Malittson I.H. Journal of the Optical Society of America, 1965

OOppttiiccaall IInnffoorrmmaattiioonn

Product AApplication SSpectrum


Appendix

OOppttiiccaall WWiinnddooww TTrraannssmmiittttaannccee,, CCoorrnniinngg ##77998800,, FFuusseedd SSiilliiccaa,, 1100mmmm tthhiicckk

Theoretical RReflection LLoss

Typical ffor 11 ccm tthickness, ssurface rreflection llosses iincluded. TTypical pproduction vvariation ffor 11cm tthickness, ssurface rreflection llosses iincluded.

To ccalculate ttransmittance ((T2) aat aa tthickness oother tthan 11 ccm:

T1 = TTransmittance ffrom pplotK == MMax. ppossible ttransmittance ffrom rrefractive iindex ttablet2 = NNew tthickness iin ccentimeters

T1(t22)

K(t22-1)

OOppttiiccaall IInnffoorrmmaattiioonn,, ccoonntt..

A-10

T2 =

© Polymicro Technologies, a Subsidiary of molex. A-10© Polymicro Technologies, a Subsidiary of molex. A-10© Polymicro Technologies, a Subsidiary of molex. A-10© Polymicro Technologies, a Subsidiary of molex. A-10

www.polymicro.com

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Email: [email protected]

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