characterization of optical fibers

DIPLOMARBEIT

Characterization of Optical Fibers

in the Mid-Infrared

ausgefuhrt am Institut furNachrichtentechnik und Hochfrequenztechnik der

Technischen Universitat Wienvon

Martin Dirnwober

Satzenweg 22211 Pillichsdorf

Matrikelnummer 9325512

Wien, im Mai 2005

Betreuer:

Dr. Martin PfennigbauerProf. Dr. Walter R. Leeb

Zusammenfassung

Diese Diplomarbeit befasst sich mit Fasern, die zur Ubertragung von elektromagnetischenWellen mit Wellenlangen im Bereich von 2 − 20 µm konzipiert sind. Der Einsatz von Fasernan Stelle von Freistrahloptik in optischen Instrumenten ist, neben geringerem Gewicht undPlatzbedarf, vor allem aufgrund der Moglichkeit der flexiblen Strahlfuhrung von Vorteil.

Teile dieser Arbeit sind in das Projekt Phase Cap “Phasing Cababilities for Fiber-OpticDevices” eingeflossen, das vom Institut fur Nachrichtentechnik und Hochfrequenztechnik derTechnischen Universitat Wien fur die Europaische Weltraumorganisation ESA durchgefuhrtwird. Das Ziel dieses Projektes ist es, Einsatzmoglichkeiten von Fasern in Weltrauminstru-menten zu untersuchen.

Wellenfuhrung innerhalb des erwahnten Wellenlangenbereiches lasst sich durch verschiedeneWellenleiterstrukturen (Fasern mit solider Kern-Mantel Struktur, hohle Wellenleiter sowiemikrostrukturierte Fasern) und mit verschiedenen Materialien (Fluorid, Chalcogenid, Ger-manat, Saphir, Silberhalid) realisieren. Der erste Teil der Arbeit beinhaltet eine Beschreibungder verschiedenen Faserstrukturen, Materialien und Wellenleitungsmechanismen.

Im zweiten Teil werden Parameter beschrieben, die eine Charakterisierung jener Fasereigen-schaften ermoglichen, die fur den Einsatz in Weltrauminstrumenten bedeutend sind. DieFasern werden hierbei hinsichtlich ihrer mechanischen, thermischen und optischen Eigen-schaften beschrieben.

Es wurde eine Suche nach den fur den Wellenlangenbereich 2− 20 µm erhaltlichen Faserndurchgefuhrt. Der dritte Teil meiner Diplomarbeit enthalt Informationen uber den Preis derFasern, die Hersteller, sowie einen Uerblick uber die von den Herstellern angegebenen Param-eter.

Im vierten Teil werden Messmethoden fur die wichtigsten der zuvor behandelten Parame-ter beschrieben, da viele hinsichtlich der gewnschten Einsatzbereiche wichtige Parameter vonden Herstellern nicht oder nur teilweise angegeben werden, und weiters fur Fasern fur dieseWellenlangenbereiche keine standardisierten Messmethoden existieren. Besonderes Augen-merk wurde dabei auf die Durchfuhrbarkeit dieser Messungen mit der im optischen Labor desInstitutes fur Nachrichtentechnik und Hochfrequenztechnik vorhandenen Ausstattung gelegt.

Summary

The topic of this thesis is fibers transmitting light of wavelenghts within 2 − 20 µm. Usingfibers instead of bulk optics in optical instruments enables flexible beam guiding as well asmechanical advantages of reduced weight and space consumption arise.

Parts of this work have been used for the project PhaseCap “Assessment of Phasing Ca-pabilities for Fiber-Optic Devices”, performed by the Insitute of Communications and Radio-Frequency Engineering of Vienna University of Technology for the European Space AgencyESA. The aim of this project is to investigate possible fields of application for fibers in spaceinstruments.

Waveguiding within the wavelength range of 2− 20 µm can be realized with various struc-tures (fibers with solid core-cladding structure, hollow waveguides, and microstructured fibers)and materials (Fluoride, Chalcogenide, Germanate, Sapphire, Silver Halide). The first part ofthis thesis contains a description of fiber structures, materials, and waveguiding mechanisms.

Parameters allowing to characterize fibers, especially concerning employment in spaceborne applications, are specified in part two. The fibers are characterized by their mechanical,thermal, and waveguiding properties.

In part three of this thesis the results of a comprehensive market survey are presented.Information of all infrared fibers (that can transmit light above 2 µm) presently offered, aswell as information about the vendors, and a comparison of parameters of these fibers is given.

Part four comprises descriptions of measurement methods for parameters important fordeployment of fibers in space instruments. A lot of parameters are not given by the vendorsand there are a no standardized measurement methods for fibers transmitting light above2 µm. Technical feasibility of this methods with labaratory equipment, presently available inthe optical labaratory of the Institute of Communications and Radio-Frequency Engineering,was especially taken into account.

Danksagung

Ich mochte mich bei allen bedanken, die zum Gelingen dieser Diplomarbeit beigetragen haben.

Ich bedanke mich bei meinen Eltern, Rosa und Martin Dirnwober, die mir das Studium derElektrotechnik ermoglicht haben, fur ihre Unterstutzung.

Herzlichen Dank an Herrn Prof. Dr. Walter Leeb, Vorstand des Institutes fur Nachrichten-und Hochfrequenztechnik, fur die zahlreichen Anregungen und Hilfestellungen in Bezug aufdiese Diplomarbeit.

Mein ganz besonderer Dank gilt Herrn Dr. Martin Pfennigbauer, fur die ausgezeichnete Betreu-ung, die vielen Ratschlage und aufschlussreichen Diskussionen, sowie seine kollegiale Unter-stutzung bei der Durchfuhrung meiner Diplomarbeit.

Ich danke Herrn Dr. Oswald Wallner und Herrn DI Franz Fidler fur ihre Hilfe, sowie meinenStudienkollegen fur aufschlussreiche Diskussionen und ihre Hilfe bei technischen Problemen.

Martin Dirnwober

Contents

1 Introduction 11.1 Infrared fibers − advantages and applications . . . . . . . . . . . . . . . . . . . 11.2 Fiber types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2.1 Solid-Core Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2.2 Crystalline Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2.3 Hollow Waveguides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.2.4 Photonic Crystal Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.3 Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2 Identification of fiber parameters 62.1 Physical parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.1.1 Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.1.2 Mechanical parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.1.3 Thermal parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2 Waveguiding parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.2.1 Transmission parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 82.2.2 Wavelength parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.2.3 Fiber coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.2.4 Dispersion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3 Market survey 123.1 Fibers offered . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123.2 Fiber vendors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.3 Comparison of fibers offered . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.3.1 Chalcogenide Fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203.3.2 Flouride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223.3.3 Polycrystalline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243.3.4 Other IR fibers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253.3.5 Standard single mode telecommunication fibers and photonic crystal

fibers for 1.5 µm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

4 Measurement methods 274.1 Attenuation vs. wavelength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4.1.1 Cut-back technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284.1.2 Taper-based technique . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

4.2 Attenuation vs. bending radius . . . . . . . . . . . . . . . . . . . . . . . . . . . 314.3 Minimum bending radius . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

i

4.4 Cut-off wavelength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324.4.1 Transmitted power technique . . . . . . . . . . . . . . . . . . . . . . . . 32

4.5 Mode field diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344.5.1 Theoretical background . . . . . . . . . . . . . . . . . . . . . . . . . . . 344.5.2 Far-field scan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364.5.3 Near-field scan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374.5.4 Variable aperture technique . . . . . . . . . . . . . . . . . . . . . . . . . 37

4.6 Effective numerical aperture . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384.7 Output divergence angle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394.8 Coupling efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394.9 Chromatic dispersion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

4.9.1 Non-Fourier-transform methods . . . . . . . . . . . . . . . . . . . . . . . 404.9.2 Fourier-transform methods . . . . . . . . . . . . . . . . . . . . . . . . . 44

4.10 Temperature coefficient of optical length . . . . . . . . . . . . . . . . . . . . . . 474.11 Coeffiecient of elasticity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

5 Outlook 52

A Data sheets 53A.1 IR Photonics: MID-infrared single mode fiber . . . . . . . . . . . . . . . . . . . 53A.2 IR Photonics: MID-infrared multi mode fiber . . . . . . . . . . . . . . . . . . . 54A.3 ARTPhotonics: CIR fiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55A.4 ARTPhotonics: PIR fiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56A.5 CeramOptec: Optran MIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58A.6 Beijing S-Fiber Technology: Infrared Fiber . . . . . . . . . . . . . . . . . . . . 60A.7 Amorphous Materials: C1, C2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62A.8 Polymicro: HWCA, HWEA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64A.9 Hitachi: hollow fiber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66A.10 CoreActive: IRT-SU, IRT-SE . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67A.11 Photran LLC: Sapphire optical fiber . . . . . . . . . . . . . . . . . . . . . . . . 69A.12 Infrared Fiber Sensors: Spectral grade Silverhalide fibers . . . . . . . . . . . . . 70A.13 Infrared Fiber Systems: HP fiber . . . . . . . . . . . . . . . . . . . . . . . . . . 71A.14 Infrared Fiber Systems: SG fiber . . . . . . . . . . . . . . . . . . . . . . . . . . 73A.15 FiberLabs Inc.: SMFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75A.16 FiberLas Inc.: MMFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

Bibliography 77

ii

Chapter 1

Introduction

The research done in this thesis is part of the project PhaseCap “Assessment of Phasing Ca-pabilities for Fiber-Optic Devices” for the European Space Agency on using fibers designedto guide light within the wavelength range of 2 − 20 µm in space borne applications. In thischapter, I will point out which advantages could arise by using fibers, especially in space-applications, as well as other fields of applications for infrared fibers. There are fibers ofdifferent structures and materials to cover this large wavelength-range. I will provide a classi-fication and description of these different fiber types.

1.1 Infrared fibers − advantages and applications

For components taken to space it is important to have low weight and space consumption.Concerning these facts, fiber-optic components are potentially superior to bulk optics forspecial applications. Besides from mechanical properties, advantages also arise due to thefiber’s waveguiding mechanism that allows for flexible beam guidance. Furthermore, fiberscould also be deployed advantageously as modal wavefront filters, optical path delay lengthcontrol, or for multiaxial beam combining [1].

There are various fields of application for infrared fibers, each one requiring special fiberproperties:

• In nulling interferometry, an extrasolar planet orbiting a star (with a light intensityhigher than that of the planet by several orders of magnitude) can be detected by in-terferometrically combining light received from spatially separated antennas. A certaindifference in optical path length between the two interferometer-arms (depending on thewavelength of the incoming light) is used for “nulling” the light emitted by the star bymeans of destructive interference.

• High precision, flexible and low mass imaging instruments based on phasing can be real-ized with fibers [2].

• In spectroscopy, the spectrum of light is determined. The use of a fiber-bundle allowsfor scanning large areas of the sky (“integral field spectroscopy”) or obtaining spectralinformation of many objects simultaneously by connecting each fiber of the bundle toa separate detector. To enable high packing density of the fibers the cladding diametershould be chosen not too large [2].

1

CHAPTER 1. INTRODUCTION 2

• Another field of application for infrared fibers is radiometry, where temperature radiationis measured. At room temperature thermal radiation has its maximum at a wavelengthof about 10 µm. Therefore fibers guiding light in the mid-infrared have used.

1.2 Fiber types

Fibers can be categorized by structure, guiding-type, and material. Figure 1.1 shows a classi-fication of fiber types by structure: solid-core fibers, hollow waveguides, and micro-structuredfibers (so-called photonic crystal fibers). Figure 1.2 gives a rough overview of attenuation andrange of transmission for different types of fibers. In the following, I will provide a descriptionof the different types.

Infrared Fiber

Glass

Heavy MetalFluoride

Chalcogenide

GermanateSapphire

Ag/AgI

Silver Halide

Poly−crystalline

LeakyGuide

Sapphire Silver HalideChalcogenide−Polyetherimide

Chalcogenide−Polyethersulfone

Solid Core

GuidingIndex

Single−Crystal

Crystalline

Hollow Waveguide

Attenuated Total

Reflection GuidingIndex Bandgap

Guiding

Bragg Fiber

Photonic CrystalFiber

Mat

eria

lG

uidi

ng T

ype

Stru

ctur

e

Figure 1.1: Classification of infrared fibers.

1.2.1 Solid-Core Fibers

Waveguiding in solid-core fibers obeys the principle of total reflection of light propagating in-side the core. Total reflection is caused by a difference in index of refraction between core- andcladding-material. Fibers transmitting light of wavelengths above 2µm can be manufacturedof glass or crystalline mateials. In Silica fibers, transmission range is limited by multiphononabsorption for large wavelengths and by Rayleigh scattering for short wavelengths. The trans-mission range of fibers can be increased when shifting multiphonon absorption towards higherwavelengths by employing heavy metal oxides, as in Fluoride fibers and Germanate fibers.

Flouride: Fluoride fibers show the lowest attenuation of all fibers transmitting in the mid-infrared. Interpolating intrinsic losses caused by Rayleigh-scattering and multiphononabsorption results in a theoretic value of attenuation of 0.24 dB/km at a wavelength of


Figure 1.2: Comparison of attenuation and wavelength-range of different types of infraredfibers (from [3]).

2.55µm, whereas the lowest measured value is about 0.45 dB/km [3]. Physical prop-erties of Fluoride fibers are inferior to those of Silica fibers. They are less durableand have less strength (Young’s modulus EFluoride = 54 GPa, ESilica = 73 GPa). Fur-thermore, the operating temperature range of Fluoride fibers is much lower becauseof the low glass transition point of Fluoride (TZBLAN = 265 ◦C, TSilica = 1175 ◦C).Most popular Fluoride glasses used for fiber fabrication are Fluorozirconate (ZBLAN:ZrF4−BaF2−LaF3−AlF3−NaF) and Flouroaluminate (AlF3−ZrF4−BaF2−CaF2−YF3).

Germanate: Better physical properties are shown by Germanate fibers, which have glasstransition temperatures up to 680 ◦C and an excellent durability. These fibers are basedon GeO2 and can guide light up to wavelengths of about 3 µm.

Chalcogenide: Chalcogenide fibers are usually based on one or more of the Chalcogene el-ements Sulfide, Selenide and Telluride. They are stable, durable, and insensitive tomoisture. In contrast to most infrared fibers, they can not transmit visible light. Mostof the Chalcogenide glasses show rather large values of the thermo-optic coefficient whichlimits power handling capabilities of the fiber [3].

1.2.2 Crystalline Fibers

Single-Crystal: Fibers made of sapphire show a transmission range of about 0.5 − 3 µm.Sapphire is an uniaxial crystal which gives the fiber excellent physical properties. It isvery hard and has a melting point higher than 2000 ◦C. Young’s modulus is much higherthan for any other fiber (ESapphire = 430 GPa), and the thermal expansion coefficientis about 10 times higher than that of Silica-fibers. Additionally, growth techniquesfor manufacturing this fibers need sufficiently more time than manufacturing of otherfibers [3].

Polycrystalline: There are a lot of halide crystals allowing for transmission in the infraredbut only silver- and thallium-halides have physical properties that allow extrusion into


a fiber. Silver-halide fibers are better than thallium-halide fibers for some reasons andwill be described in the following. Attenuation can be as low as 0.2 dB/m at 2.55 µmand transmission is possible nearly up to 20 µm. Disadvantages are low melting point,aging of the fiber, and photo sensitivity of the crystals. Additionally, they are corro-sive to many metals. Due to these facts, the fibers need a special coating as well asspecial connectors (e.g. gold). Moreover the tensile strength of this fibers is very low(Esilver-halide = 0.14 GPa) and exceeding a certain bending-radius can lead to permanentdamage and therefore higher attenuation of the affected region [3].

1.2.3 Hollow Waveguides

In hollow waveguides, light is propagating through an air core. Therefore, advantages of highlaser-power-thresholds, low insertion loss, and no end-reflections arise. Furthermore, hollowwaveguides show low beam divergence. Losses are indirect proportional to a3, where a givesthe bore radius. Drawbacks are high bending losses, which are indirect proportional to thebending radius R. Hollow waveguides can be realized as ATR-guides1 or as Leaky-guides [3].

ATR-guides: The refractive index of the inner wall material of ATR-guides is less than one.Together with the air-core (ncore = 1) a structure like in usual fibers (ncore > nclad)is achieved. Waveguiding works due to attenuated total reflection of light propagatinginside the core. Such a waveguide can be realized for instance with sapphire [3].

Leaky guides: In contrast to ATR-guides the refractive index of the inner wall material ofleaky guides is greater than one. Waves are guided due to reflection on the metallic innerwall. To minimize loss the inner wall of the waveguide is covered with a dielectric layer.The most popular structure is the Hollow Glass Waveguide (HGW), with inner layers ofsilver covered with silver iodide (see Figure 1.3). At 10 µm, losses are less than 0.5 dB/m

Silver iodide film

Glass substrate

Silver film

Polymer coating

Figure 1.3: Structure of a Hollow Glass Waveguide (from [4]).

for a HGW having a bore radius larger than 400 µm. HGWs are nearly single-mode(in waveguides with a bore radius less than 300µm only the LP01-mode propagates),because higher order modes suffer high attenuation and so in practice only the lowestorder modes propagate.

1(ATR . . . attenuated total reflectance)


1.2.4 Photonic Crystal Fibers

A novel kind of waveguides are Photonic Crystal Fibers (PCF). At present time PCFs trans-mitting above 2 µm are at an experimental stage and not commercially available. Figure 1.4shows index-guiding and bandgap-guiding PCFs.

Figure 1.4: Cross sections of photonic crystal fibers: index-guiding (left, from [5]) and bandgap-guiding (right, from [6]).

Index guiding: Waveguiding is realized as in solid-core fibers by creating a difference in indexof refraction between the core (solid, n > 1) and the cladding (microstructured) region.This is achieved by manufacturing a cladding region with air-holes which lower theeffective index of refraction. By varying size and number of the air-holes, the refractiveindex of the cladding area and thus also the difference of the refractive index of the coreand the cladding, can be chosen very precisely. Fibers with a high numerical aperture(up to 0.7) as well as fibers supporting single-mode operation over a wide wavelengthrange, or highly nonlinear fibers can be manufactured [7].

Bandgap guiding: By using special structures it is possible to create areas within a material,where light of a certain wavelength can not propagate. Such areas are realized around ahollow core so that light is confined to the core after being coupled into it. Due to thehollow core, high power levels can be transmitted without fiber damage or nonlinearities.There are no Fresnel reflections at the fiber ends [7].

1.3 Outline

Parameters allowing to characterize fibers are specified in Chapter 2. They are divided intophysical parameters and waveguide parameters. In Chapter 3 the results of a comprehensivemarket survey are presented. Information of all infrared fibers (transmitting light above 2 µm)offered presently, as well as information about the vendors, and a comparison of parameters ofthese fibers is presented. Chapter 4 gives a description of measurement methods for parametersimportant for deployment of fibers in space instruments. Technical feasibility of this methodswith presently existent labaratory equipment was especially taken into account.

Chapter 2

Identification of fiber parameters

The aim of this chapter is the identification of fiber parameters relevant and performance-critical for the possible applications mentioned in Chapter 1. Due to the different designs andguiding mechanisms of various infrared fibers, like step-index fibers, photonic crystal fibers,hollow fibers, Bragg grating fibers, etc., the detailed mathematical expressions of some fiberparameters may be different. If not stated otherwise, the remainder of this document will referto step-index fibers, which is appropriate for an application-oriented specification of importantparameters.

2.1 Physical parameters

2.1.1 Dimensions

Core/cladding diameter: The core diameter, dco, is twice the radial distance from the fiberaxis to the point where the index of refraction takes on the value it has in the cladding.The cladding diameter, dcl > dco, is twice the radial distance from the fiber axis to thepoint where the index of refraction becomes different from that in the cladding. Bothparameters are usually given in µm.

Index-of-refraction-profile: The radial profile of the index of refraction determines thewaveguiding properties of the fiber. In order to obtain wave guidance, the index ofrefraction in the core, nco, usually has to be higher than the index of refraction in thecladding, ncl. The index-of-refraction-profile for step-index fibers as a function of theradius r reads

n ={

nco : 0 < r < dco/2ncl : dco/2 < r < dcl/2

. (2.1)

The ratio

∆ =n2

co − n2cl

2n2co

(2.2)

is known as the relative refraction index difference.

If single-mode operation is aimed at, the upper bound for the core diameter is

dco <λV

π

1√n2

co − n2cl

, (2.3)

with a normalized frequency V = 2.405.

6

CHAPTER 2. IDENTIFICATION OF FIBER PARAMETERS 7

Core-cladding concentricity error: The radial distance between the geometric center ofthe core and the cladding is defined as core-cladding concentricity error.

Maximum fiber length: The maximum length of fiber, Lmax, which can be produced in onepiece is limited. Especially for infrared fibers, this length can be quite short (e.g. a fewmeters).

2.1.2 Mechanical parameters

Hardness: The hardness measures the resistance of the fibers’s material to indentation. Itcan be measured on the Moh’s and Vicker’s scale. The latter is a more quantitativemeasure, which measures the impression made using a pyramid-shaped diamond forcedinto the surface of a material. The result is given as the Vickers hardness number

VHN = 1854P

d2(2.4)

in kg/mm2, where P is the load in grams and d is the mean length of the indentation inmicrons. Moh’s scale characterizes the scratch resistance through the ability of a hardermaterial to scratch a softer. On this scale quartz (SiO2) has a hardness of 7, whereasdiamond (C) has a hardness of 10.

Hardness of a fiber material comes into play when preparing a fiber facet: In general,with a hard material it is easier to prepare a well-defined, smooth surface by polishing.It is also more scratch-resistant.

Tensile strength: The tensile strength of a fiber is the maximum amount of tensile stressthat it can be subjected to before it breaks. Tensile strength is measured in units offorce per unit area, i.e. Newton per square meter ([N/m2] or [Pa]).

Coefficient of elasticity: The relative elongation when subjected to an axial force (providedthe material is in the elastic region) is described by the coefficient of elasticity Young’smodulus E,

∆L

L=

1E

F

A, (2.5)

where ∆L is the absolute elongation, L is the fiber length, F is the applied force, and Ais the cross sectional area of the fiber. The coefficient of elasticity is therefore given inN/m2.

Minimum bending radius: When bending a fiber with less than the minimum bendingradius, it breaks.

2.1.3 Thermal parameters

Operating temperature range: The operating temperature range defines lower and uppertemperature limits within which the fiber can be operated.

Thermal expansion coefficient: The thermal expansion coefficient α gives the relativeelongation per temperature unit of a fiber,

∆L

L= α ∆T , (2.6)


where ∆L is the absolute elongation, L is the fiber length, and ∆T is the temperaturechange. The thermal expansion coefficient is given in K−1.

Thermo-optic coefficient: The thermo-optic coefficient (given in K−1) describes the changeof the index of refraction of a material due to a temperature change, dn/dT . This effectalso depends on the wavelength and on the absolute temperature. If light of high intensityis transmitted via the fiber, the thermo-optic effect can lead to self-focusing and thereforeto an additional intensity increase. This may lead to thermal damage of the fiber.

Temperature coefficient of optical length: The parameter 1L

d(nL)dT describes the temper-

ature dependence of the optical length, which is the product of the refractive index ofthe fiber’s material n and the geometrical length L of the fiber.

Thermal conductivity: The thermal conductivity of a fiber is equivalent to the quantity ofheat that passes in unit time through unit area of unit length of fiber, when its oppositefaces are subject to unit temperature gradient. Thermal conductivity is measured in[Wm−1K−1].

Laser damage threshold: The maximum light intensity (given in W/m2) which can betransported over a fiber without damaging it is defined by the laser damage threshold.

2.2 Waveguiding parameters

2.2.1 Transmission parameters

Mode field radius: The mode field radius w0 is the radial dimension, where the intensityof the fundamental mode drops to 1/e2 = 0.135 of its peak value. Close to single-modecutoff, the modefield radius is only slightly larger than the core radius. Two octavesabove the cutoff wavelength it increases substantially [8].

Fiber attenuation vs. bending radius: Generally, the fiber attenuation increases with de-creasing bending radius. The bend loss coefficient αB for the fundamental mode LP01,given in dB/m, as depending on the bend radius R is given by [9, 10]

αB =10

ln 102√

π(n2co − n2

cl(1 + b∆)2)γ3/2d2

co(n2co − n2

cl)√

RK21 (dcoγ/2)

exp(− 2γ3R

3k2n2cl(1 + b∆)2

), (2.7)

where k = 2π/λ is the wave number, b is the ratio of the integrated field in the core tothe total integrated field of the LP01 mode, K1 is a modified Hankel function, and withthe abbreviation

γ =√

n2clk

2b2∆2(1 + 2/b∆) . (2.8)

The total attenuation of a fiber is then

αtotal = α + αB , (2.9)

where α is the attenuation coefficient of the straight fiber. Figure 2.1 shows αB over Rfor a fiber with dco = 9.3 µm, ∆ = 0.4% at λ = 1550 nm.


Figure 2.1: Bending loss coefficient αB as a function of bending radius R.

Birefringence: Imperfections of the fiber geometry or mechanical stress cause unintendedbirefringence. However, birefringence can also be a desired fiber property, e.g. for po-larizing or polarization maintaining fibers. In a birefringent fiber, two principal axesfor linear polarized eigenmodes exist, allowing for propagation of decoupled waves atdifferent velocities.

Beat length: The beat length LB of a fiber is defined as the distance after which two com-ponents of a field polarized parallel and normal to the optical axis, and therefore expe-riencing different propagation constants due to birefringence, have a phase shift of 2π.After a length of ∆L the phase shift amounts to

∆ϕ = 2π∆L

LB. (2.10)

The beat length depends on the wavelength and on the refractive indices of the twoprincipal axes,

LB =λ

|ne − no|, (2.11)

where ne and no are the indices of refraction parallel and normal to the optical axis ofthe birefringent fiber. The beat length of a standard fiber may be in the range of severalmeters.

2.2.2 Wavelength parameters

Cut-off wavelength: Every mode of a fiber except the fundamental mode experiences acertain wavelength above which it can not propagate. The cut-off wavelength of a fiber,


λc, is defined as the wavelength above which only one mode – the fundamental mode –represents a valid solution for the wave equation. The cut-off wavelength for a step-indexfiber is given by

λc =dcoπ

V

√n2

co − n2cl , (2.12)

with a normalized frequency of V = 2.405.Since in practice the transition from single-mode to multi-mode operation is not abrupt,experimenters define the cut-off wavelength as that wavelength where the power propa-gating in the fiber is by 0.1 dB higher than the power of the fundamental mode.

Fiber attenuation vs. wavelength: To determine the wavelength range of a fiber, the fiberattenuation α(λ), usually given in dB/km, is presented in a diagram as a function of thewavelength. The shape of this curve depends on the fiber geometry and material.

Normalized frequency: The normalized frequency of a fiber is defined by

V =dcoπ

λ

√n2

co − n2cl. (2.13)

For single-mode operation, the normalized frequency must not be higher than 2.405. Thedesign criterion for a step-index fiber to be solely single-mode above a desired wavelengthλc is

dco

√n2

co − n2cl ≤ 0.766λc . (2.14)

2.2.3 Fiber coupling

Acceptance angle: When coupling into a fiber, the angle between incident light beams andthe fiber axis must be lower than

Θ = arcsin√

n2co − n2

cl (2.15)

in order to provide wave-guiding due to total reflection at the core-cladding boundary.

Numerical aperture: The numerical aperture is the sine of the acceptance angle,

NA =√

n2co − n2

cl . (2.16)

Effective numerical aperture: Due to imperfections during the manufacturing of the fiber,the actual numerical aperture may be slightly different from the theoretical one. In thiscase it is called effective numerical aperture.

Reflective loss: When coupling light into or out of a fiber, losses occur due to reflectionsat the fiber facet as a consequence of index-of-refraction differences of the propagationmedia within and outside the fiber (so-called Fresnel losses). The reflectivity of a beamentering the fiber parallel to the fiber axis is given by

R =(nm − nco)2

(nm + nco)2, (2.17)

where nm and nco are the indices of refraction of the medium outside the fiber and thefiber core, respectively.


Coupling efficiency: When coupling into a fiber (be it from free-space or from anotherfiber) the ratio of guided light power to total available light power is called couplingefficiency. The easiest way to couple a free-space beam into a fiber is to use a lens as afocussing element. In a breadboard setup with an approximately Gaussian input beamoptimum coupling is obtained, if the lens matches the modefield radius w0 of the beamin the focal plane to the modefield radius of the field propagating in the fiber [11, 12].For fixed lens and waveguide parameters, the coupling efficiency changes significantlywith changing wavelength. The maximum coupling efficiency can be obtained at single-mode cutoff, i.e. for V = 2.405, [13]. This theoretical maximum coupling efficiency1

between the LP01 mode propagating in the fiber and an Airy function at the input planeof the fiber amounts to η = 0.786 [14]. Additional reflective loss, due to the Fresnelreflection (2.17) at the fiber facet (see above), reduces this coupling efficiency unless anantireflective coating is used.

Output divergence angle: Optical waves exiting a single-mode fiber will experience diffrac-tion, depending on the mode field radius and the wavelength. Assuming a Gaussianintensity profile within the single-mode fiber, the full output divergence angle reads

ε =2λ

πw0. (2.18)

In case of a multi-mode fiber the output divergence angle is best characterized via thefiber’s numerical aperture. It is just twice the acceptance angle (see above).

2.2.4 Dispersion

Dispersion: The velocity of waves in a fiber depends on the wavelength. This leads to arelative delay of signal components at different wavelengths, corresponding to a temporalspread of the signal. This effect, called dispersion, compounds of chromatic dispersion(wavelength-dependent index of refraction and radial extension of the field in the fiber)and mode dispersion (due to propagation velocity differences of different modes).

Dispersion vs. wavelength: The chromatic dispersion coefficient, given in ps/(km·nm), ispresented in a diagram as a function of the wavelength.

Zero dispersion wavelength: The zero dispersion wavelength is the wavelength for whichthe chromatic dispersion coefficient vanishes.

1For calculating this coupling efficiency not an approximation but the exact field was used for the fiber’sfundamental mode.

Chapter 3

Market survey

From November 2004 to January 2005 I performed a thorough market survey concerning opticalfibers in the mid-infrared spectral range, with emphasis on the wavelength range from 2 to12 µm. Manufacturers and distributors for various types of fibers were contacted and askedfor offers and detailed specifications. While the focus was the European market, I eventuallyperformed a world-wide survey.

As outlined in Chapter 1, I distinguish between solid-core fibers, hollow waveguides, andphotonic crystal fibers.

The major information sources for my search were the Internet, the Laser Focus WorldBuyers Guide [15], and personal knowledge.

3.1 Fibers offered

Table 3.1 gives an overview of the IR fibers offered and provides main parameters as well asthe price and delivery time. From some companies offering several types of fibers (e.g. fiberswith different dimensions) I only asked for exemplary offers. To allow a comparison withthe characteristics of standard fibers, I added information provided by three representativemanufacturers of telecom fibers.

12

CHAPTER 3. MARKET SURVEY 13ty

pe

mate

rial

pro

duct

core

/cl

addin

gw

avel

ength

ven

dor

pri

cedel

iver

ydata

shee

tdia

met

erra

nge

tim

e[µ

m]

[µm

]E

UR

/m

[wee

ks]

solid-c

ore

fiber

Chalc

ogen

ide

C1

100/−

to1000/−

2−

10

Am

orp

hous

Mate

rials

96

3A

.7C

2100/−

to1000/−

d0.7−

7A

morp

hous

Mate

rials

A.7

CIR

fiber

250/300

2−

6A

RT

photo

nic

s85

2−

6A

.3C

IRfiber

340/400

2−

6A

RT

photo

nic

s105

2−

6A

.3C

IRfiber

400/440

2−

6A

RT

photo

nic

s115

2−

6A

.3C

IRfiber

500/550

2−

6A

RT

photo

nic

s135

2−

6A

.3IR

T-S

U50/170

to700/800

2−

5C

orA

ctiv

e2680f

2−

4A

.10

IRT

-SE

50/170

to700/800

2−

9C

orA

ctiv

eA

.10

Bej

ing

fiber

150/400

1−

6B

eijing

S-F

iber

Tec

hn.

A.6

Bej

ing

fiber

250/600

2−

12

Bei

jing

S-F

iber

Tec

hn.

A.6

Bej

ing

fiber

3100/600

2−

12

Bei

jing

S-F

iber

Tec

hn.

A.6

Bej

ing

fiber

450/400

2−

11

Bei

jing

S-F

iber

Tec

hn.

A.6

Flu

ori

de

SM

fluori

de

8.5

/122

0.5−

3.7

Fib

erLabs

153

1A

.15

MM

fluori

de

TFF

190/200

0.7−

2.5

Fib

erLabs

46

A.1

6M

Mfluori

de

GFF

140/200

to400/530

0.5−

4Fib

erLabs

46e

A.1

6SG

fiber

100/−

to700/−

0.4

5−

5In

frare

dFib

erSyst

ems

A.1

4M

IDIR

MM

fiber

50/−

to1000/−

0.3−

4.5

IRphoto

nic

sA

.2M

IDIR

SM

fiber

9/125

0.3−

4.5

IRphoto

nic

s226

8−

10

A.1

6.5

/125

Le

Ver

reFlo

ure

1325

<1

Ger

manate

HP

fiber

150/−

1−

3a

Infr

are

dFib

erSyst

ems

23–38c

A.1

3H

Pfiber

250/−

1−

3a

Infr

are

dFib

erSyst

ems

306

A.1

3H

Pfiber

450/−

1−

3a

Infr

are

dFib

erSyst

ems

421

A.1

3H

Pfiber

700/−

1−

3a

Infr

are

dFib

erSyst

ems

230–383j

A.1

3poly

cryst

allin

e-

Optr

an

MIR

200/300

to860/1000

4−

16

Cer

am

Opte

cA

.5si

lver

halide

Optr

an

MIR

300−

1000b

4−

16

Cer

am

Opte

cA

.5si

lver

halide◦

900/1000

3−

18

Infr

are

dFib

erSen

sors

745

4A

.12

silv

erhalide

�750×

750,1000×

1000i

2−

18

Infr

are

dFib

erSen

sors

A.1

2P

IRfiber

450/500

4−

18

ART

photo

nic

s190

2−

6A

.4P

IRfiber

630/700

4−

18

ART

photo

nic

s230

2−

6A

.4P

IRfiber

900/1000

4−

18

ART

photo

nic

s270

2−

6A

.4si

ngle

-cry

stal-

sapphir

e150−

425b

0.3−

3P

hotr

an

506h

2−

3A

.11

hollow

waveg

uid

eH

itach

ifiber

700

3−

12

Hitach

iC

able

A.9

HW

EA

/H

WC

A300−

1000

2.9−

12

Poly

mic

roTec

hnolo

gie

s387g

1−

2A

.8photo

nic

cryst

alfiber

Silic

aH

C-1

550-0

210.9

1.4

5−

1.6

5C

ryst

alFib

reA

/S

tele

com

fiber

Silic

aSM

F-2

8e

9/125

Corn

ing

0.0

3SM

09/125

9/125

j-fiber

0.0

26

<1

AllW

aveF

iber

9/125

ofs

0.0

44k

aacc

ord

ing

todia

gra

min

data

shee

tbno

claddin

gcm

inim

um

purc

hase

length

100

mdnot

available

bef

ore

mid

2005

eoffer

for

fiber

wit

hco

redia

met

er160

µm

f offer

for

fiber

wit

hco

re/cl

addin

gdia

met

er50/170

µm

incl

udin

gco

nnec

tors

and

coati

ng

gH

WE

Afiber

,opti

miz

edfo

rE

r:Y

AG

,offer

by

Optr

onis

Gm

bH

hoffer

for

fiber

wit

hco

redia

met

er250

µm

i square

wav

eguid

ej m

inim

um

purc

hase

length

10

mkoffer

from

Matt

ig-S

chauer

(Aust

ria)

Table 3.1: Overview of all fiber offers resulting from the market survey performed.

CHAPTER 3. MARKET SURVEY 14

3.2 Fiber vendors

Tables 3.2 and 3.3 present detailed contact information on fiber manufacturers and vendors,while Table 3.4 contains information on companies where I was unable to make contact.

Chalcogenide fibers with dimensions 400/500 µm, produced by ARTphotonics, are offeredby JT Ingram Sales & Marketing Co. for the price of 333 EUR for 2 m, including SMA con-nectors and protective tubing.

Photran single-crystal sapphire fibers with a core diameter of 250µm and PTFE (Poly-tetrafluoroethylene) buffer are offered by Laser Components (Germany) for the price of 823EUR/m.

Polycrystalline fibers with dimensions 400/500 µm and 630/700 µm, produced by ARTpho-tonics, are offered by JT Ingram Sales & Marketing Co. for the price of 449 EUR and 525EUR for 2 m, respectively, including SMA connectors and protective tubing. ARTphotonicsadditionally offers square PIR fibers with core/cladding dimensions from (450/500 µm)2 forthe price of 240 EUR/m to (900/1000 µm)2 for 240 EUR/m and bare core PIR fibers withdiameters from 500 µm to 1000 µm, for 130 EUR/m to 210 EUR/m. ARTphotonics fibers areadditionally offered by FiberWare.

The prices of all PIR fibers offered apply for products with moderate quality of core/claddingboundary, corresponding to an attenuation of 0.2− 0.8 dB/m at a wavelength of 10.6 µm.

I could not get in contact with Beijing S-Fiber Technology (China) who, on their homepage,claim to produce chalcogenide fibers. It is neither possible to send an email to the addressesposted on the homepage nor to get in contact by phone. Autex (Japan) did not respond to mymails. It is probably a distributor for Polymicro’s (USA) hollow fibers. I also did not succeedto get in contact with OmniGuide Communications Inc. (USA), probably a manufacturer ofhollow core photonic bandgap fibers.

In the search for photonic crystal fibers designed for the mid-infrared, I also contactedCrystal Fibre A/S (Denmark) but they responded that they only work with silica. The dis-tributor Oxford Electronics (UK) has a chalcogenide fiber in his program but cannot offer itat this time.

The fiber section of Saphikon (France) was moved to Photran (USA). BlazePhotonics Ltd.(UK) is now owned by Crystal Fibre A/S (Denmark).


com

pany

addre

ssco

untr

yphone

fax

UR

Le-

mail

Am

orp

hous

Mate

rials

Inc.

3130

Ben

ton

Garl

and,Tex

as

75042

USA

phone:

fax:

+1-9

72-4

94-5

624

(G.W

hale

y)

+1-9

72-2

72-7

971

(G.W

hale

y)

ww

w.a

morp

housm

ate

rials

.com

GregW

hale

y@

am

orphousm

ateria

ls.c

om

RayH

ilto

njr

@am

orp

housm

ate

rials

.com

ART

photo

nic

sG

mbH

Sch

warz

schildst

r.6

D-1

2489

Ber

lin

Ger

many

phone:

fax:

+49-3

0-6

789-4

153

+49-3

0-6

789-4

156

ww

w.a

rtphoto

nic

s.de

info

@art

photo

nic

s.de

Cer

am

Opte

cIn

dust

ries

Inc.

515A

Shaker

Rd.

East

Longm

eadow

,M

A01028

USA

phone:

fax:

+1-8

00-9

34-2

377

+1-8

60-7

47-4

487

(C.Sm

ith)

+1-4

13-5

25-1

112

+1-8

60-7

93-4

909

(C.Sm

ith)

ww

w.c

eram

opte

c.co

mSale

sEngin

eeri

ng@

Cer

am

Opte

c.co

mcheryl.sm

ith@

ceram

opte

c.c

om

Cer

am

Opte

cG

mbH

Sie

men

sstr

.44

53121

Bonn

Ger

many

phone:

fax:

+49-2

28-9

79670

+49-2

28-9

796799

CorA

ctiv

eH

igh-T

ech

Inc.

2700,Jea

n-P

erri

n,Suite

121

Queb

ec(Q

C)

Canada,G

2C

1S9

Canada

phone:

fax:

+1-4

18-8

45-2

466-2

19

(D.B

eik

o)

+1-4

18-8

45-2

609

(D.B

eik

o)

ww

w.c

ora

ctiv

e.co

msa

les@

cora

ctiv

e.co

min

fo@

cora

ctiv

e.co

mdavid

.beik

o@

coractive.c

om

Corn

ing

Inc.

One

Riv

erfr

ont

Pla

zaC

orn

ing,N

Y14831

USA

phone:

fax:

+1-6

07-7

86-8

125

+1-6

07-7

86-8

344

ww

w.c

orn

ing.c

om

/optica

lfiber

Cry

stalFib

reA

/S

Blo

kken

84,D

K-3

460

Bir

ker

ød

Den

mark

phone:

fax:

+45-4

348-2

800

(Gen

eral)

+45-4

348-2

820

(R.K

ris

tianse

n)

+45-4

348-2

801

(R.K

ris

tianse

n)

ww

w.c

ryst

al-fibre

.com

conta

ct@

cryst

al-fibre

.com

rek@

cryst

al-fibre.c

om

Fib

erLabs

Inc.

2-1

-15

Ohara

,K

am

ifukuoka,Saitam

a,

356-8

502

Japan

Japan

phone:

fax:

+81-4

9-2

78-7

829

(B.In

oue)

+81-4

9-2

63-9

328

(B.In

oue)

ww

w.fi

ber

labs.

co.jp

info

@fiber

labs.

co.jp

inoue@

fiberla

bs.

co.jp

Hitach

iC

able

,Ltd

.1-6

-1O

hte

mach

i,C

hiy

odaku,

Tokyo

100-8

166

Japan

Japan

phone:

fax:

+81-2

94-2

5-3

837

(A.H

ongo)

+81-2

94-4

3-7

487

(A.H

ongo)

ww

w.h

itach

i-ca

ble

.co.jp

hongo.a

kih

ito@

hit

achi-cable

.co.jp

Infr

are

dFib

erSen

sors

ImG

ille

sbach

tal33

52066

Aach

enG

erm

any

phone:

fax:

+49-2

41-6

5609

(L.K

uepper)

+49-2

41-6

5617

(L.K

uepper)

ww

w.ifs

-aach

en.d

e/42.0

.htm

lkuepper.ifs

@t-

online.d

eIn

frare

dFib

erSyst

ems

Inc.

2301-A

Bro

adbir

chD

r.,

Silver

Spri

ng,

MD

20904

USA

phone:

fax:

+1-3

01-6

22-9

546

+1-3

01-6

22-7

131

(A.T

chap)

+1-3

01-6

22-7

135

ww

w.infr

are

dfiber

syst

ems.

com

info

@in

frare

dfiber

syst

ems.

com

ale

xtchap@

infr

aredfibersystem

s.c

om

IRphoto

nic

sIn

c.248

Rue

Coro

tSuit

e212

Ile

des

Soeu

rs(V

erdun)

Montr

eal,

Canada,H

3E

-1K

9

Canada

phone:

fax:

+1-5

14-5

78-5

060

(E.G

eoffri

on)

+1-5

14-5

78-0

177

ww

w.irp

hoto

nic

s.co

min

fo@

irphoto

nic

s.co

megeoffrio

n@

irphoto

nic

s.com

Table 3.2: Contact information for fiber vendors. Telephone numbers and email addresses ofpersons with whom a personal contact was established are printed in bold face.


com

pany

addre

ssco

untr

yphone

fax

UR

Le-

mail

j-fiber

Gm

bH

ImSem

mic

ht

1D

-07751

Jen

aG

erm

any

phone:

fax:

+49-3

641-3

52-1

00

+49-3

641-3

52-1

01

ww

w.j-fi

ber

.com

info

@j-fiber

.com

Le

Ver

reFlo

ure

Cam

pus

Ker

Lann

F-3

5170

Bru

z,B

ritt

any

Fra

nce

phone:

fax:

+33-2

-9905-3

130

(G.M

aze)

+33-2

-9905-9

53

(G.M

aze)

lever

refluore

.com

info

@le

ver

refluore

.com

sale

s@le

ver

refluore

.com

ofs

2000

Nort

hea

stE

xpre

ssw

ay

Norc

ross

,G

eorg

iaU

SA

phone:

+1-8

88-3

42-3

743

+1-7

70-7

98-5

555

ww

w.o

fsoptics

.com

ofs

@ofs

optics

.com

Photr

an

LLC

13446

Pow

ay

Road,P

MB

#150

Pow

ay,

CA

92064

USA

phone:

fax:

+1-8

58-7

48-0

850

+1-6

19-5

07-4

455

(L.R

oth

rock)

+1-8

58-7

48-0

854

(L.R

oth

rock)

ww

w.p

hotr

an.c

om

sale

s@photr

an.c

om

roth

rock@

znet.

com

Poly

mic

roTec

hnolo

gie

s,LLC

.18019

N.25th

Aven

ue.

Phoen

ix,A

rizo

na

85023-1

200

USA

USA

phone:

fax:

+1-6

02-3

75-4

100

+1-6

02-3

75-4

110

ww

w.p

oly

mic

ro.c

om

fiber

ware

Gm

bH

Born

hei

mer

Str

.4

09648

Mit

twei

da

Ger

many

phone:

fax:

+49-3

727-6

13335

+49-3

727-6

13336

ww

w.fi

ber

ware

.de

offi

ce@

fiber

ware

.de

JT

Ingra

mSale

s&

Mark

et-

ing

Co.

316

Harl

equin

Ct,

Ovie

do,Fl32765

USA

phone:

fax:

+1-5

61-5

73-6

533

+1-2

53-6

63-2

608

ww

w.jtingra

m.c

om

/Jim

@jt

ingra

m.c

om

Lase

rC

om

ponen

tsG

mbH

Wer

ner

-von-S

iem

ens-

Str

.15

82140

Olc

hin

gG

erm

any

phone:

fax:

+49-8

142-2

864-0

+49-8

142-2

864-1

1w

ww

.lase

rcom

ponen

ts.c

om

info

@la

serc

om

ponen

ts.c

om

Matt

ig-S

chauer

Gm

bH

Matz

ner

gass

e34

1140

Wie

nA

ust

ria

phone:

fax:

+43-1

-984-8

383-6

2(R

.B

inder)

+43-1

-984-8

383-5

0(R

.B

inder)

ww

w.m

att

ig-s

chauer

.at

r.b

inder@

matt

ig-s

chauer.a

tO

ptr

onis

Gm

bH

Honse

llst

r.8

D-

77694

Keh

lG

erm

any

phone:

fax:

+49-7

8-5

19126-3

4(D

.Schoch)

+49-7

8-5

19126-1

0(D

.Schoch)

ww

w.o

ptr

onis

.com

schoch@

optr

onis

.com

Oxfo

rdE

lect

ronic

sLtd

Pyra

mid

House

,59

Win

ches

ter

Road,

Four

Mark

s,H

am

psh

ire

GU

34

5H

RU

Kphone:

fax:

+44-1

420-5

61200

+44-1

420-5

61300

ww

w.o

xfo

rd-e

lect

ronic

s.co

msa

les@

oxfo

rd-e

lect

ronic

s.co

m

Table 3.3: Contact information for fiber vendors, continued. Telephone numbers and emailaddresses of persons with whom a personal contact was established are printed in bold face.Distributors are listed below manufacturers, separated by an empty line.


com

pany

addre

ssco

untr

yphone

fax

UR

Le-

mail

Aute

x16-5

Tom

ihis

a-c

ho,Shin

jyuku

Tokyo

162-0

067,Japan

Japan

phone:

fax:

+81-3

-3226-6

321

+81-3

-3226-6

290

ww

w.a

ute

x-inc.

co.jp

[sale

s32@

aute

x-inc.

co.jp]

Bei

jing

S-F

iber

Tec

hnolo

gy

A#

1006,T

ianyuan

Apart

men

tN

o.3

6,

South

GuangA

nM

enR

oad,

Xuanw

uD

istr

ict,

Bei

jing,Post

Code:

100054

Chin

aphone:

fax:

[+86-1

0-8

3522482]

[+86-1

0-6

3586031]

ww

w.s

-fiber

.com

.cn

[sfiber

@so

hu.c

om

][s

unhuim

ail@

vip

.sin

a.c

om

]O

mniG

uid

eC

om

munic

a-

tions

Inc.

One

Ken

dall

Square

Buildin

g100,3rd

Flo

or

Cam

bri

dge,

MA

02139

USA

phone:

fax:

+1-6

17-5

51-8

444

+1-6

17-5

51-8

445

ww

w.o

mni-guid

e.co

min

form

ation@

om

ni-guid

e.co

m

Table 3.4: Contact information for fiber manufacturers and vendors I failed to get in touchwith.


3.3 Comparison of fibers offered

In the following more detailed information on the fibers listed in Table 3.1 is presented [2].Figure 3.1 shows the attenuation of the different fibers for three representative wavelengths,Fig. 3.2 provides an overview of the corresponding useful wavelength ranges. In the subsectionsto follow I list the detailed properties as extracted from the data sheets copied in AppendixA.

6

α[d

B/m

]

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

C1

C2

CIR

fiber

IRT-SU

IRT-SE

Beijin

gFibe

r1

Beijin

gFibe

r2

Beijin

gFibe

r3

Beijin

gFibe

r4

SMFluo

ride

fiber

MM

Fluo

ride

TFF

MM

Fluo

ride

GFF

SGfib

er

mid

IRMM

fiber

mid

IRSM

fiber

PIR

fiber

Opt

ranMIR

core/c

lad

silver

halid

efib

er�

silver

halid

efib

er◦

germ

anateHP

fiber

sing

lecrystal fi

ber

HW

EA

HW

CA

Hitachi

fiber�

��

��

��

��

��

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��

��

��

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��

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��

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��

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��

��

��

��

��

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��

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��

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��

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��

��

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��-�chalcogenide

-�fluoride

-�polycrystalline

-�other

u

u

u uu u

u u u

u uu

u

u. . . 3 µm. . . 5 µm. . . 10.6 µm

w

Figure 3.1: Attenuation coefficient α for different wavelengths of the fibers offered.

CHAPTER 3. MARKET SURVEY 19C

1

C2

CIR

fiber

IRT

-SU

IRT

-SE

Bei

jing

Fib

er1

Bei

jing

Fib

er2

Bei

jing

Fib

er3

Bei

jing

Fib

er4

SMFlu

orid

efib

er

MM

Flu

orid

eT

FF

MM

Flu

orid

eG

FF

SGfib

er

mid

IRM

Mfib

er

mid

IRSM

fiber

PIR

fiber

Opt

ran

MIR

silv

erha

lide

fiber

�

silv

erha

lide

fiber◦

germ

anat

eH

Pfib

er

sing

lecr

ysta

lfib

er

HW

EA

HW

CA

Hit

achi

fiber

-

01

23

45

67

89

1011

1213

1415

1617

18

λ[µ

m]

6 ?other6 ?

polycrystalline

6 ?flouride6 ?

chalcogenide

Figure 3.2: Wavelength ranges of the mid-infrared fibers offered.


3.3.1 Chalcogenide Fibers

pro

duct

C1

C2

CIR

Fib

erIR

T-S

UIR

T-S

E

mate

rial

As-

Se-

Te

As 2

S3

As 2

S3/A

s-S

Sulp

hid

eSel

enid

eco

mpany

Am

orp

hous

Mate

rials

Am

orp

hous

Mate

rials

ART

photo

nic

sC

orA

ctiv

eC

orA

ctiv

e

data

shee

tin

subse

ctio

nA

.7A

.7A

.3A

.10

A.1

0st

ruct

ure

core

/cl

ad

core

/cl

ad

core

/cl

ad

core

/cl

ad

core

/cl

ad

wavel

ength

range

[µm

]2−

10

0.7−

71.5−

62−

52−

9cu

t-off

wavel

ength

[µm

]co

re/cl

addin

gdia

met

er[µ

m]

100/−

to1000/−

100/−

to1000/−

200/250

to700/800

50/170

to700/800

50/170

to700/800

core

refr

act

ion

index

2.8

2.4

2.4

2.4

2.7

coating

mate

rial

double

poly

mer

dualco

at

acr

yla

tedualco

at

acr

yla

tem

inim

um

ben

din

gra

diu

s@

fiber

dia

met

er[m

m]@

[µm

]1

@100a

8@

500a

10

@750a

40

@1000a

1@

100a

17

@500a

30

@750a

40

@1000a

oper

ating

tem

per

atu

rera

nge

[◦C

]7

to127

ther

malex

pansi

on

coeffi

cien

t[1

0−

7/K

]235

241

ther

mo-o

pti

cco

effici

ent

[10−

5/K

]3

±0.9

tensi

lest

rength

[MPa]

916

@100a

483

@500a

469

@750a

427

@1000a

841

@100a

386

@500a

310

@750a

303

@1000a

lase

rdam

age

thre

shold

[W]

5100

@5.2

5µm

num

eric

alaper

ture

0.3

0.2

60.3

0fiber

att

enuation

@w

avel

ength

s[d

B/m

]@

[µm

]0.2−

0.4

@5.2

50.2−

0.4

@9.2

74−

5@

10.6

0.2−

0.4

@5.2

50.2

@(2−

4)

<0.2

<0.5

aco

redia

met

er


pro

duct

Bei

jing

Fib

er1

Bei

jing

Fib

er2

Bei

jing

Fib

er3

Bei

jing

Fib

er4

mate

rial

As-

S/A

s-S

As-

Se-

Te/

As-

Se-

Te

GeS

eTe/

Ge-

As-

Se-

Te

As-

Se/

As-

Se

com

pany

Bei

jing

S-F

iber

Tec

hnolo

gy

Bei

jing

S-F

iber

Tec

hnolo

gy

Bei

jing

S-F

iber

Tec

hnolo

gy

Bei

jing

S-F

iber

Tec

hnolo

gy

data

shee

tin

subse

ctio

nA

.6A

.6A

.6A

.6st

ruct

ure

core

/cl

ad

core

/cl

ad

core

/cl

ad

core

/cl

ad

wavel

ength

range

[µm

]1−

62−

12

2−

12

2−

11

cut-

off

wavel

ength

[µm

]co

re/cl

addin

gdia

met

er[µ

m]

50/400

50/600

100/600

50/400

core

refr

act

ion

index

coating

mate

rial

min

imum

ben

din

gra

diu

s@

fiber

dia

met

er[m

m]@

[µm

]

oper

ating

tem

per

atu

rera

nge

[◦C

]th

erm

alex

pansi

on

coeffi

cien

t[1

0−

7/K

]th

erm

o-o

pti

cco

effici

ent

[10−

5/K

]te

nsi

lest

rength

[MPa]

lase

rdam

age

thre

shold

num

eric

alaper

ture

0.5

0.5

0.5

0.5

fiber

att

enuation

@w

avel

ength

s[d

B/m

]@

[µm

]0.2

@2.4

<0.5

@(1

.8−

3.7

)a

<1

@(4

.5−

6)a

<0.5

@8

<1

@(3

.7−

5.7

)a

<1.5

@(7−

10)a

3@

10.6

<1

@4

aacc

ord

ing

toth

edia

gra

min

the

data

shee

t


3.3.2 Flouride

pro

duct

single

mode

Flu

ori

de

fiber

mult

imode

Flu

ori

de

fiber

TFF

mult

imode

Flu

ori

de

fiber

GFF

SG

fiber

mate

rial

HM

FG

-ZB

LA

NH

MFG

HM

FG

HM

FG

com

pany

Fib

erLabs

Inc.

Fib

erLabs

Inc.

Fib

erLabs

Inc.

Infr

are

dFib

erSyst

ems

data

shee

tin

subse

ctio

nA

.15

A.1

6A

.16

A.1

4st

ruct

ure

core

/cl

ad

core

/cl

ad

core

/cl

ad

core

/cl

ad

wavel

ength

range

[µm

]0.5−

3.7

b0.7−

2.5

0.5−

40.4

5−

5cu

t-off

wavel

ength

[µm

]2.3

c

core

/cl

addin

gdia

met

er[µ

m]

8.5

/122

190/200

140/200

to400/530

100/−

to700/−

core

refr

act

ion

index

coating

mate

rial

UV

cura

ble

resi

nja

cket

UV

cura

ble

resi

nja

cket

poly

mer

icbuffer

coating

min

imum

ben

din

gra

diu

s@

fiber

dia

met

er[m

m]@

[µm

]20

@190a

20

@150a

5@

100a

10

@200a

40

@400a

oper

ating

tem

per

atu

rera

nge

[◦C

]≤

250

ther

malex

pansi

on

coeffi

cien

t[1

0−

7/K

]th

erm

o-o

pti

cco

effici

ent

[10−

5/K

]te

nsi

lest

rength

[MPa]

lase

rdam

age

thre

shold

num

eric

alaper

ture

0.2

10.6

50.2

80.2

2

fiber

att

enuation

@w

avel

ength

s[d

B/m

]@

[µm

]<

0.0

3@

(0.5−

2.6

)b

<0.0

6@

(2.5−

3.5

)b

<0.5

@(3

.5−

4.1

)b

<0.0

3@

(0.7−

2.6

)b

<0.0

5@

(2.6−

3.5

)b

<0.5

@(3

.5−

4.2

)b

<0.0

5@

(1.5−

2.5

)b

<0.2

@(2

.5−

2.8

)b0.0

5@

2.5

aco

redia

met

erbacc

ord

ing

toth

edia

gra

min

the

data

shee

tcca

lcula

ted

from

fiber

dia

met

erand

num

eric

alaper

ture


pro

duct

mid

infr

are

dm

ult

imode

fiber

mid

infr

are

dsi

ngle

mode

fiber

mate

rial

HM

FG

HM

FG

-ZB

LA

NH

MFG

com

pany

IRphoto

nic

sIR

photo

nic

sLe

Ver

reFlo

ure

data

shee

tin

subse

ctio

nA

.2A

.1st

ruct

ure

core

/cl

ad

core

/cl

ad

core

/cl

ad

wavel

ength

range

[µm

]0.3−

4.5

0.3−

4.5

cut-

off

wavel

ength

[µm

]≤

3.5

c2.5

core

/cl

addin

gdia

met

er[µ

m]

50/−

to1000/−

9/125

6.5

/125

core

refr

act

ion

index

coating

mate

rial

UV

cure

d,

dualacr

yla

te,

oth

er

UV

cure

d,

dualacr

yla

te,

oth

erm

inim

um

ben

din

gra

diu

s@

fiber

dia

met

er[m

m]@

[µm

]4

@125

4@

125

oper

ating

tem

per

atu

rera

nge

[◦C

]−

20

to80

−20

to80

ther

malex

pansi

on

coeffi

cien

t[1

0−

7/K

]100−

250

100−

250

ther

mo-o

pti

cco

effici

ent

[10−

5/K

]te

nsi

lest

rength

[MPa]

≥480

≥480

lase

rdam

age

thre

shold

num

eric

alaper

ture

≤0.3

≤0.3

0.3

fiber

att

enuation

@w

avel

ength

s[d

B/m

]@

[µm

]≤

0.5

@(2

.94,2.7

8,2.0

7,2.8

)≤

0.5

@(0

.5−

4.5

)

aco

redia

met

erbacc

ord

ing

toth

edia

gra

min

the

data

shee

tcca

lcula

ted

from

fiber

dia

met

erand

num

eric

alaper

ture


3.3.3 Polycrystalline

pro

duct

PIR

fiber

Optr

an

MIR

Optr

an

MIR

Spec

tralG

rade

Silver

Halide

Fib

ers

Spec

tralG

rade

Silver

Halide

Fib

ers

mate

rial

silv

erhalide:

AgC

l:A

gB

rsi

lver

halide:

AgC

l:A

gB

rsi

lver

halide:

AgC

l:A

gB

rsi

lver

halide

silv

erhalide:

AgC

l:A

gB

rco

mpany

ART

photo

nic

sC

eram

Opte

cC

eram

Opte

cIn

frare

dFib

erSen

sors

Infr

are

dFib

erSen

sors

data

shee

tin

subse

ctio

nA

.4A

.5A

.5A

.12

A.1

2st

ruct

ure

core

/cl

ad

core

/cl

ad

core

core

core

/cl

ad

wavel

ength

range

[µm

]4−

18

4−

16

4−

16

2−

18

3−

18

cut-

off

wavel

ength

[µm

]co

re/cl

addin

gdia

met

er[µ

m]

300/500

to900/1000

200/300

to860/1000

300−

1000

750×

750a

1000×

1000a

900/1000

core

refr

act

ion

index

2.1

52.1

02.1

02.2

02.2

0co

ating

mate

rial

PE

EK

(Poly

Eth

erE

ther

Ket

one)

poly

carb

onate

or

Tef

zel

poly

carb

onate

or

Tef

zel

min

imum

ben

din

gra

diu

s10×

FD

b100×

FD

b100×

FD

b10×

FD

b10×

FD

b

oper

ating

tem

per

atu

rera

nge

[◦C

]−

270

to140

−60

to110

−60

to110

ther

malex

pansi

on

coeffi

cien

t[1

0−

7/K

]th

erm

o-o

pti

cco

effici

ent

[10−

5/K

]te

nsi

lest

rength

[MPa]

>100

100

100

>110

>110

lase

rdam

age

thre

shold

[kW

/cm

2]

12d

10d

10d

12d

num

eric

alaper

ture

0.2

5e

0.1

3−

0.3

5e

0.5

e<

0.4

2c

<0.2

6c

fiber

att

enuation

@w

avel

ength

s[d

B/m

]@

[µm

]0.1−

0.5

@10.6

<0.5

@(9−

12.5

)f

<1

@(5−

13)f

<0.6

@3.5

<0.3

@5

<0.2

@10.6

<1

@3.5

<0.6

@5

0.1−

0.3

@10.6

asq

uare

bFD

...fi

ber

dia

met

ercif

fiber

length

isgre

ate

rth

an

2m

dcw

CO

2Lase

reeff

ecti

ve

NA

f acc

ord

ing

todia

gra

min

data

shee

t


3.3.4 Other IR fibersty

pe

Ger

manate

single

cryst

alfiber

hollow

waveg

uid

ehollow

waveg

uid

ehollow

waveg

uid

epro

duct

HP

Fib

ersa

pphir

eopti

cal

fiber

HW

EA

HW

CA

Hitach

ifiber

mate

rial

GeO

2Sapphir

ehollow

silica

waveg

uid

eE

rYA

Ghollow

silica

waveg

uid

eC

O2

hollow

silica

waveg

uid

eco

mpany

Infr

are

dFib

erSyst

ems

Photr

an

LLC

Poly

mic

roTec

hnolo

gie

sPoly

mic

roTec

hnolo

gie

sH

itach

iC

able

data

shee

tin

subse

ctio

nA

.13

A.1

1A

.8A

.8A

.9st

ruct

ure

core

/cl

ad

core

hollow

hollow

hollow

wavel

ength

range

[µm

]1−

3b

0.3−

32.9−

12

2.9−

12

3−

12

cut-

off

wavel

ength

[µm

]

core

/cl

addin

gdia

met

er[µ

m]

150/−

to700/−

150−

425

300−

1000

d300−

1000

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pro

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Chapter 4

Measurement methods

In this chapter measurement methods for the following fiber-parameters are described:

• Attenuation vs. wavelength

• Attenuation vs. bending radius

• Minimum bending radius

• Cut-off wavelength

• Mode field diameter

• Effective numerical aperture

• Output divergence angle

• Coupling efficiency

• Chromatic dispersion

• Temperature coefficient of optical length

• Coefficient of elasticity

When selecting measurement methods I paid special attention to the feasibility of performingthe experiments with the equipment available in the optical labaratory of the Institute ofCommunications and Radio-Frequency Engineering.

4.1 Attenuation vs. wavelength

Attenuation of fibers can be characterized by the attenuation-coefficient α(λ), which gives theattenuation per unit length [dB/m], as:

P (z) = P (0) 10−αz

10 , (4.1)

where P (0) is the power directly at the beginning of the fiber and P (z) is the power at thelength z of the fiber.

27

CHAPTER 4. MEASUREMENT METHODS 28

The attenuation coefficient α is not defined for the total transmitted power, but for thepower carried by a certain mode. In general, different modes experience different attenuationcoefficients. Therefore, and due to mode-coupling, the attenuation coefficient depends onthe fiber-length z. However, after a certain fiber-length, a steady-state or equilibrium modedistribution (EMD) is established, which means that the ratio of power carried by the eachmode relative to a reference mode, no longer depends on the fiber-length z.

Provided such an EMD can be obtained, the loss-coefficient α of the total transmittedpower can be measured [16]. A steady-state distribution emerges after a certain fiber-length,either when the power carried by higher order modes is attenuated to a negligible extent(because of the higher α for these modes) or due to mode coupling, if present in considerablestrength. Since the test fibers are very short (a few meters), this is not feasible. There aretwo methods for obtaining an EMD in short fiber pieces:

• In the mechanical method an EMD is established by enforcing strong mode-coupling withmode-scramblers or by using mode filters.

• The optical method is based on a limited launch numerical aperture, which means tocreate an input-beam, which fills only 70% of the core diameter and 70% of the numericalaperture of the fiber, so that the excitation of higher-order modes, leaky modes, andcladding modes is avoided.

The optical method suits best for the measurement of, usually short, IR-fibers, due tocertain limitations of the mechanical method in measurement of short fibers.

Attenuation measurement of singlemode fibers can be done by the well known cut-backtechnique, whereas the attenuation coefficient of multimode fibers can be measured best bythe taper based technique, where a hollow glass taper is used to create an EMD in the fiberunder test.

4.1.1 Cut-back technique

The cut-back technique is the reference test method for attenuation measurement recom-mended by the ITU [17]. It is preferable for attenuation measurement of singlemode fibers.

First step is to measure the output-power of the fiber P2. Then the fiber is cut to thecut-back point (which could be 2m from the launching point, for instance), and the output-power P1 at the cut-back point is measured, without changing the launching conditions. Sothe measurement is independent from the launching conditions. The attenuation coefficient αcan then be calculated as

α =10z

logP1

P2, (4.2)

where z is the length fiber piece cut off. The measurement can be done either for some specificwavelengths or over a wavelength-range. Figure 4.1 shows a measurement-setup for measuringα over a wavelength-range. The wavelength is selected by a monochromator. The signal ismodulated and a chopper is used, together with a lock-in amplifier, to improve the signal tonoise ratio. By coupling with a fiber or by a suitable system of optics it can be assured thatonly the fundamental mode is excited in the fiber. The propagation of higher-order modesthrough the cut-back length, is prevented by by a mode filter (higher-order modes can beremoved by a bend of the fiber, for example), while cladding modes are removed by a claddingmode stripper. The measurement should be done at the same temperature for all wavelengths.


Figure 4.1: Measurement setup for the cut-back method (from [17]).

4.1.2 Taper-based technique

The following is based on the article: “Attenuation Measurement of Infrared Optical Fibersby Use of a Hollow-Taper-Based Coupling Method” by Ilko K. Ilev et. al. [18]. In the measure-

Figure 4.2: Measurement setup for the taper-based technique (from [18]).

ment setup shown in Figure 4.2, the optical method is used to create an EMD-state and theattenuation coefficient is determined through power measurements in front of the input-endand behind the output-end of the fiber. In this setup a hollow taper is used, due to certainadvantages, as explained in the following.

The taper is made of Pyrex-glass with 3.5 mm input diameter, and 250µm output diam-eter, and a length of 120 mm. This ensures a cone angle of less than 1◦, so that grazingincidence is achieved. Therefore, reflectance coefficients are very high (close to 100%), andalso wavelength-independent, so that measurements can be performed over a wide wavelength-range. In contrast to a conventional lens there are no problems in finding the optimum point


for coupling in.

Figure 4.3: Intensity distribution at the input (a) and at the output (b) of the taper (from [18]).

The taper has a very low output numerical aperture (about 0.033) and its output diametershould be chosen smaller than the fiber core, to satisfy the conditions for a limited launchnumerical aperture. Furthermore, the taper forms a smooth, Gaussian-shaped, laser beamprofile (inside the taper occurs an intensive conversion of higher order modes into leaky modesbecause of the grazing incidence). Figure 4.3 shows the measured intensity distribution at theinput and at the output of the taper.

Altogether, the use of the taper ensures that lower-order modes are excited predominately,and thus a proper EMD-state is achieved. In order to confirm this, Figure 4.4 shows thefar-field intensity distributions measured after a 1m hollow fiber, using taper-to-fiber couplingand lens-to-fiber coupling. The output-intensity after taper-to-fiber coupling shows low-ordermodes around the fiber-axis, while the output-intensity after fiber-to-lens coupling is strongmultimodal.

Figure 4.4: Far-field intensity distributions measured after a 1 m hollow fiber, using taper-to-fiber coupling (a) and lens-to-fiber coupling (CaF2-lens, focal length f=100 mm) (b) (from [18]).

The attenuation coefficient can be calculated after measuring the power P0 at the taperoutput, and the power at the fiber output P1, as:

α =10z

logP0

P1(4.3)

A broadband, tunable laser-source has to be used to measure the attenuation coefficient independence on the wavelength. If the attenuation of solid-core fibers is measured, a correction


for the Fresnel-reflections R at both fiber-ends has to be done. For that purpose the Fresnel-relation (see Section 2.2.3) can be used (n gives the index of refraction of the fiber):

R =(

n− 1n + 1

)2

(4.4)

If the fiber is sufficient long, a cut-back measurement can be done instead of this correction.For measurements made with a fluoride-glass fiber with a core diameter 250 µm, a length

of 1 m, and an attenuation of about 1 dB/m, the difference of the attenuation-coefficient mea-sured with the conventional cutback-method, and the attenuation-coefficient measured withthe taper-based method was as low as 0.05 dB/m.

4.2 Attenuation vs. bending radius

The bending-induced attenuation can be determined as follows: First the power P1 at theoutput-end of the straight fiber is measured. Then a part of the fiber with the length Lw iswound up on a cylinder with the radius r0 and the power P2 is measured at the output-end ofthe fiber. The bending-induced attenuation in [dB/m] is then

αB(r0) =10Lw

logP1

P2. (4.5)

A diagram attenuation vs. bending can be obtained by using several cylinders with differentdiameters and measuring αB for each value of r0.

4.3 Minimum bending radius

The minimum bending radius of a fiber can be determined using the setup shown in Figure4.5. The distance D, between the two face-plates, is slowly decreased, until the fiber breaks.The breaking-point Dbreak could be determined by use of an acoustic sensor. Since the fiber is

Figure 4.5: Schematic diagramm of the bending technique for breaking fibers (from [19]).


not bent to a semi-circle by this device, the bending radius at the breaking-point Rbreak (thispoint is exact between the two face-plates, at D/2), is less than Dbreak/2. It can be calculatedfrom [19].

Rbreak =1

1.198Dbreak − d

2, (4.6)

where d is the overall fiber diameter (including any coating material). Because the strengthof the fiber is not distributed uniformly over the fiber-length (due to material imperfections),a series of measurements should be done, followed by a statistical evaluation of the obtainedresults.

4.4 Cut-off wavelength

The cut-off wavelength λc depends not only on fiber geometry and refractive indices of coreand cladding, but also on length, bending, and mechanical stress of the fiber. With respectto these facts, cut-off wavelength is defined as the wavelength, where the power propagatingthrough the fiber is by 0.1 dB higher than the power transported by the fundamental mode, ifthe fiber is 2 m long and has a loop with a radius of some 140 mm [17].

4.4.1 Transmitted power technique

Assuming that the same power of the LP01 mode and of the LP11 mode is coupled into afiber, the power Ptest(λ), measured at the output of this fiber, will decrease significantly if thewavelength of the light goes beyond λc, because the LP11 mode can only propagate for λ ≤ λc.In the transmitted power technique the cut-off wavelength is determined from that change ofPtest(λ).

In order to remove the influence of the wavelength-dependent attenuation of the fiber onthe determination of λc, the power Ptest(λ), measured at the output-end of the fiber undertest, is referred to the power Pref(λ), measured at the output-end of a reference fiber, as

R(λ) =Ptest(λ)Pref(λ)

. (4.7)

The testfiber should have a length of 2 m, and a loop with a radius of 140 mm. As areference fiber either the same fiber with an additional loop (single bend attenuation), or amultimode fiber (power-step) can be used (see Figure 4.6).

Single bend attenuation

Within the single bend attenuation method the reference power Pref(λ) is measured as afunction of the wavelength at the output-end of the testfiber, in which an additional loop wasinserted. The radius r of this loop has to be small enough to ensure, that the power intensitytransmitted by the LP11 mode is radiated off, so that only the fundamental mode LP01 canpropagate in the reference fiber. At wavelengths near λc, R(λ) gives the ratio of the powertransmitted over the testfiber (i.e. the power transmitted by the LP01 mode for λ > λc, andby the LP01 mode and the LP11 mode for λ ≤ λc) to the power transmitted over the referencefiber (that is the power transmitted by the fundamental mode LP01). The cut-off wavelengthcan then be determined as the lowest wavelength, for which R(λ) = 0.1 dB (see Figure 4.7).Figure 4.8 shows that the exact value of the loop radius r does not affect the determinationof λc.


claddingmode stripper

launching system PD

testP

refP

refP


launching system PD

(b)

multimode fiber


launching system PD

loopadditional

(a)testfiber

testfiber

Figure 4.6: Measurement setup: Single bend attenuation (a), power step (b) (from [20]).

The measurement of a Fluoride fiber is reported in [22]. The intensity P1 has been measuredfrom the straight fiber, and Pref has been measured from the same fiber having a loop withr = 40mm.

The advantage of the single bend attenuation method is that there is no change in couplingbetween the two measurements.

Power step

In the power step method Pref(λ) is measured at the output-end of a multimode fiber, in orderthat both, the LP01 mode and the LP11 mode can propagate in the reference fiber [21]. Thespectral attenuation characteristic of this fiber should be similar to that of the testfiber. Atwavelengths near λc, R(λ) gives the ratio of the power transmitted over the testfiber (i.e. thepower transmitted by the LP01 mode for λ > λc, and by the LP01 mode and the LP11 modefor λ ≤ λc) to the power transmitted over the reference fiber (that is the power transmittedby the LP01 mode and the LP11 mode). Cut-off wavelength can then be determined as thelowest wavelength, where R(λ) is 0.1 dB above its minimum value (see Figure 4.9) [17].

Measurement setup

The wavelength-range of the light source has to be large enough for cut-off wavelength deter-mination, and the linewidth should not extend 10 nm (FWHM). The signal to noise ratio canbe improved by modulating the source in combination with a lock-in amplifier. The couplingshould ensure that the same amount of power is carried by the LP01 mode and the LP11 mode.This could be done by coupling in with a multimode fiber, or by coupling in with a large spotsize and numerical aperture [17]. If the power step method is used, leaky modes should beavoided, because they can induce ripples in R(λ), and thus complicate the determination ofthe cut-off wavelength.


Figure 4.7: R(λ) for r = 30mm (from [21]).

Figure 4.8: R(λ) for r=10, 20, 30, 50mm (from [21]).

4.5 Mode field diameter

The mode field diameter (MFD) characterizes propagation properties of singlemode fibers,as are, e.g., loss due to macrobendings, microbendings, or connectors. Additionally, cut-offwavelength or chromatic dispersion can be determined if the spectral behavior of the MFD isknown. The mode field diameter can be determined from a scan of the near-field or far-field,of the light exciting the fiber, or from several measurements of the far-field power behind acircular aperture (located behind the output-end of the fiber) with different diameters at eachmeasurement (variable aperture technique).

4.5.1 Theoretical background

The MFD can be determined either in the near-field or in the far-field (see Figure 4.10). The


Figure 4.9: Power Step Method: R(λ) (from [17]).

R

0

P

0’r

near−field planefar−field plane

zθ

Figure 4.10: Near- and far-field geometries (from [23]).

near-field MFD, dn, can be calculated according to the Petermann I definition

dn = 2√

2

√√√√√√√∞∫0

r3 dr

∞∫0

E2(r) r dr

, (4.8)

where E2(r) gives the radial intensity distribution in the near-field, whereas the far-field MFD,df, can be calculated using Petermann II definition

df =2√

2wff

, with wff =

√√√√√√√∞∫0

F 2(p) p3 dp

∞∫0

F 2(p) p dp

, (4.9)


where p = k sin(θ) with k = 2πλ , and F 2(p) gives the intensity distribution in the far-field [23].

The far-field MFD can be calculated from F 2(θ), after substituting p in (4.9):

df = 2√

2π

λ

√√√√√√√√√π2∫0

F 2(θ) sin3(θ) cos(θ)dθ

π2∫0

F 2(θ) sin(θ) cos(θ)dθ

. (4.10)

The intensity in the far-field F 2(p) can be derived from the near-field intensity E2(r) byuse of the Hankel transform1. Therefore, the near-field MFD can be calculated from theintensity-distribution in the far-field (4.11), and the far-field MFD can be calculated from theintensity-distribution in the near-field (4.12).

dn = 2√

2

√√√√√√√∞∫0

[dF (p)

dp

]2p dp

∞∫0

F 2(p) p dp

(4.11) df = 2√

2

√√√√√√√∞∫0

E2(r) r dr

∞∫0

[dE(r)

dr

]2r dr

(4.12)

The near-field MFD is at least equal the far-field MFD: df ≤ dn. For Gaussian intensitydistributions2 both MFD definitions are equal df = dn = 2

√2w, and at r = dn

2 the intensitydrops to 1

e2 of its maximum [23].It is important for the measurement of the MFD, that only the fundamental-mode is

propagating inside the fiber. This can be guaranteed by a mode-filter, or by a sufficient smallloop of the fiber.

4.5.2 Far-field scan

The far-field intensity F 2(θ) as a function of θ is scanned by a flexible detector (see Figure4.11), and the MFD can then be calculated using (4.10). The detector should be moved in

��

��

LD

filtercladding modefiber

R

θ

photodiode

Figure 4.11: Measurement setup: Far-field scan (from [23]).

fixed steps not greater than 0.5◦ and the dynamic range of the measurement has to be at least1F (p) =

∫∞0

E(r)J0(rp)rdr = 1√2π

H{E}(p)

2E(r, w) = Ae− r2

2w2 .


50 dB. The angular region in the far-field, covered by the active area of the detector, must notbe too large. That can be assured by placing the detector at a distance R from the fiber endgreater than 40 d b

λ , where d is the expected MFD, and b is the diameter of the active area ofthe detector [17].

4.5.3 Near-field scan

The near-field intensity E2(r) at the output-end of the fiber is magnified by a suitable lens,and then scanned by a flexible detector (see Figure 4.12). The far-field MFD can be calculatedthrough (4.12). The active area of the detector must not be too large and the detector has tobe adjustable precisely. Furthermore, the aperture of the lens should be at least 0.5 to avoidspatial cutoffs [17].

��

��

��

��

LED

modestripper

fibreunder

test

40 xOBJ Scanning

fibre

detector

Figure 4.12: Measurement setup: Near-field scan (from [23]).

4.5.4 Variable aperture technique

In the variable aperture technique the far-field power P (θ ≤ θ0) of the light exiting the fiberis measured for the circular area θ ≤ θ0, where θ is the angle between the light-beam and thefiber axis (see Figure 4.13). The measurement of P (θ ≤ θ0) is performed by placing a circular

��

��

��

��

��

��

��

��

��

��

��

� � �

��

D 0

P

x

zθ 0

Figure 4.13: Variable Aperture Technique (from [23]).

aperture with the radius x = D tan θ0 in the distance D from the output-end of the fiber, and


focusing the light passing the aperture onto a detector (see Figure 4.13). The center of theaperture has to be located on the fiber-axis z.

The measurement is performed for at least 12 different apertures corresponding to anglesin the range of 0.02 ≤ sin θ0 ≤ 0.25 (≤ 0.4 for dispersion shifted fibers). It is not necessary toperform measurements for higher values of θ0, since the intensity of the light is very low forhigher values of θ.

The MFD can then be calculated as

df =λ

πD

{∫ ∞

0

[1− P (x)

Pmax

]x

(x2 + D2)2dx

}− 12

, (4.13)

where P (x) = P (θ ≤ θ0) and Pmax is the power measured from the setup with the largestaperture used in the measurements. Equation (4.13) can be obtained by integrating (4.10)and assuming small angles θ [17].

4.6 Effective numerical aperture

The effective numerical aperture NA is defined as the sine of the angle θ, at which the far-field intensity of the light exciting the fiber has dropped to 5% of its maximum value (seeFigure 4.14). It can be determined by the far-field method. First step is to aquire the far-field

Figure 4.14: Determination of the numerical aperture from far-field radiation pattern (from[24]).

intensity pattern I(θ) of the fiber output end as a function of θ (see Section 4.5.2). The fibershould be 2 m long, and excited by an overfilled launch in order excite all possible guidedmodes. This means, that the launch spot intensity is uniformly distributed over the core, andthe launch numerical aperture exceeds the numerical aperture of the fiber [24]. The numericalaperture can then be calculated as

NA = sin∆θ

2, (4.14)

where ∆θ is the angular region where the output intensity is higher than 5% of its maximumvalue (see Figure 4.14).

The theoretical numerical aperture could also be determined from the measured index ofrefraction profile of the fiber, as described in [24].


4.7 Output divergence angle

The output divergence angle ε characterizes the diffraction of light leaving a fiber. The outputdivergence angle of a singlemode fiber can be determined as follows: The radial distances r1

and r2, at which the light-intensity drops to 1/e2 of its maximum value, are measured at the

fiberε

r 2

r 1

L2

L1

Figure 4.15: Measurement of the output divergence angle.

distances L1 and L2 from the fiber-end, using the results of a far-field scan (see section 4.5.2).Then the output divergence angle ε can be calculated from

tan ε =r2 − r1

L2 − L1. (4.15)

It is essential that only the fundamental mode propagates in the fiber. This can be realizedby means of a fiber loop.

If the mode field diameter df is known, only one measurement (r1 at the distance L1 fromthe fiber-end) has to be performed, and ε can be calculated from

tan ε =r1 −

df

2

L1. (4.16)

The output divergence angle of a multimode fiber can be calculated from the numericalaperture NA of the fiber (see Section 4.6), as

ε = arcsin(NA) . (4.17)

4.8 Coupling efficiency

The coupling efficiency can be determined by making two measurements: First the power P1

of the light (this can be a free space beam or light guided in a fiber) that should be coupledin, is measured. Then the light is coupled into the fiber and the power P2 at the output-endof this fiber is measured. It has to be assured that neither cladding modes nor leaky modescan propagate as far as to the output-end of the fiber. This could be done by a cladding


mode stripper and a fiber loop (with a diameter small enough to remove leaky modes andlarge enough not to increase the fiber’s attenuation). When taking the influence of the fiberattenuation α, given in [dB/m], into account, the coupling efficiency reads

η = 10αLfib/10 P2

P1, (4.18)

where Lfib is the length of the fiber. In order to keep this influence small the piece of fiberused for this measurement should be as short as possible. Since the coupling efficiency changessignificantly with wavelength, the measurements have to be performed separately for desiredspecific wavelengths or, more general, over a wavelength-range.

4.9 Chromatic dispersion

Method Principledirect techniques turning point analysis

non-Fourier-transform center wavelength against air-path lengthmethods indirect techniques shift of center wavelength for increase of op-

tical path-lengthFourier-transform Fourier-transformation of the interferogrammethods

Table 4.1: Overview of measurement techniques of chromatic dispersion [25,26]

Chromatic dispersion of fibers can be measured with various methods. However, interfer-ometric methods, where the fiber is in one the arms of the interferometer, have to be used toobtain accurate results if only very short pieces of fiber are available (e.g. a few meter), as itis the case for most of the fibers designed for transmitting light with wavelengths above 2 µm.These methods can be divided into non-Fourier-transform methods and Fourier-transformmethods (see Table 4.9). In non-Fourier-transform methods the output-intensity of the in-terferometer is measured at several wavelengths, either at constant or at variable differencesbetween air-path-length and fiber-path-length. A tunable laser source or a monochromatoris necessary to perform wavelength dependent measurements. In Fourier-transform methods,measurements are done over a broad spectral range, without selecting discrete wavelengths,for varying differences between air-path-length and fiber-path-length.

Chromatic dispersion D(λ) and dispersion slope S(λ) coefficients of the fiber can be deter-mined from the effective group index of the fiber ng(λ), from the effective index of refractionof the fiber n(λ), as well as from the group propagation time τfib(λ) in the fiber, as [27,25]:

D(λ) =dng(λ)c dλ

=1lfib

dτfib(λ)dλ

= −λ

c

d2n(λ)dλ2

, (4.19)

S(λ) =dD(λ)

dλ= −λ

c

d3n(λ)dλ3

+1λ

D(λ) . (4.20)

4.9.1 Non-Fourier-transform methods

The following text is based on the article “Interferometric Chromatic Dispersion Measurementson Short Lengths of Monomode Optical Fiber” by P. A. Merritt et al. [25].


Within this measurement method the light of a source is split-up into two beams, whichthen propagate either through the air-arm or through the fiber-arm of a Mach-Zehnder in-terferometer (see Figure 4.16). After superimposing the two beams, the intensity Iout(λ) isobtained at the detector. It is significantly depending on the wavelength of the light, as wellas on the difference in optical path length between the air-arm and the fiber-arm. Figure4.17 shows Iout(λ) at a certain optical path length difference as a function of the wavelength.Chromatic dispersion can be extracted from measurements of Iout(λ), either at a constantoptical path length difference (direct techniques), or at varying optical path length differences(indirect techniques).

Theoretical background

The principle configuration of the interferometer is shown in Figure 4.16. One arm of theinterferometer contains the device under test, i. e. a short fiber piece with length lfib about1 m, of which the chromatic dispersion is measured, while the other path leads through air.

The interference fringes shown in Figure 4.17, from which the chromatic dispersion willbe extracted, are a consequence of different propagation properties in the air and in the fiber.There are also air-paths in the fiber-arm, lair, fiber-arm, which have to be subtracted from thelength of the air-arm, in order to obtain the path-length, corresponding to the fiber-pathlength, and therefore, contributing to the interference fringes:

lair = lair-arm − lair, fiber-arm . (4.21)

The difference in optical length between the fiber-path and the air-path, OPD (optical pathlength difference), is then

OPD = lair − n(λ) lfib . (4.22)

At a fixed wavelength λ, a change in air-path length of ∆L, leads to a change in optical pathlength difference of ∆OPD.

fibercoupler

variableair path

��

��

��

��

��

��

detectorbroadbandsource

mono−chromatortestfiber

air−arm

fiber−arm

Figure 4.16: Simplified measurement setup with a Mach-Zehnder Interferometer [25].

The light emitted by the source is split up by a beamsplitter, then propagates throughthe two arms, and is finally combined by a second beamsplitter. Superimposing the intensityof the fiber-path Ifib(λ) and of the air-path Iair(λ), we obtain the output-intensity of theinterferometer

Iout(λ) = Iair(λ) + Ifib(λ)− 2√

Iair(λ) Ifib(λ) cos[2π

λ(lair − lfib n(λ))

]. (4.23)


Expanding for the effective index of refraction of the fiber a taylor series around λ

n(λ) = n + (λ− λ)dn

dλ

∣∣∣∣λ

+(λ− λ)2

2!d2n

dλ2

∣∣∣∣λ

+(λ− λ)3

3!d3n

dλ3

∣∣∣∣λ

+ . . . , (4.24)

we get

Iout(λ) = Iair(λ) + Ifib(λ)− 2√

Iair(λ) Ifib(λ) cos

[2π

λ

(lair − lfib

(n− λ

dn

dλ

∣∣∣∣λ

))−

−2π lfib

(dn

dλ

∣∣∣∣λ

+(λ− λ)2

2!λd2n

dλ2

∣∣∣∣λ

+(λ− λ)3

3!λd3n

dλ3

∣∣∣∣λ

+ . . .

)]. (4.25)

Here λ is the so called center-wavelength, at which the group propagation time τ is equalin both arms of the interferometer. This is equivalent to setting zero the first term inside thecosine-function of (4.25):

τair − τfib = lair1c− lfib

1c

(n− λ

dn

dλ

∣∣∣∣λ

)︸︷︷︸

ng(λ)

= 0 , (4.26)

where c is the velocity of light in vacuum. Around this wavelength, Iout(λ) is cosinusoidalwith decreasing cycle duration, moving both above and below λ. A schematic representationis shown in Figure 4.17. The envelope of this function is due to the spectral characteristic ofthe source. Techniques for extracting dispersion coefficient and slope coefficient from these

λ1 λ2 λ λ3 λ4

I out

λ

Figure 4.17: Schematic representation of Iout around λ (from [25]).

interferometric fringes can be divided into direct and indirect techniques. Direct techniques usedata measured at a constant optical path length difference (OPD), whereas indirect techniquesrequire data measured at varying optical path length differences.

Direct techniques

Chromatic dispersion can be obtained by determining two wavelengths λ1 and λ2 of minimaof Iout(λ), which are separated by M intensity cycles of Iout(λ), and which are located on the


same side of λ (turning point analysis; see Figure 4.17). Consequently, 2πM is added to theargument of the cosine in (4.25), and (4.27) can be obtained by subtracting the argument ofthe cosine in Iout(λ2) from the argument of the cosine in Iout(λ1)3:[

(λ1 − λ)2

λ1− (λ2 − λ)2

λ2

]12!

d2n

dλ2

∣∣∣∣λ︸︷︷︸

A

+

[(λ1 − λ)3

λ1− (λ2 − λ)3

λ2

]13!

d3n

dλ3

∣∣∣∣λ︸︷︷︸

B

=2πM

lfib. (4.27)

Chromatic fiber dispersion is characterized by (4.19) and part A of (4.27). It can be calculatedeither directly from (4.27) by neglecting part B, and thus assuming S(λ)|

λ� D(λ)|

λ, or more

accurate by determining another two wavelengths of minima of Iout(λ), which yields anotherequation of the form of (4.27). We then obtain two equations with two unknown variables,from which D(λ) and S(λ) can be calculated by employing (4.19) and (4.20).

To determine the wavelengths of the minima of Iout(λ) the wavelength-spectra should besmoothed to remove noise, and then differentiated.

Indirect techniques

• Chromatic fiber dispersion can be determined by measuring the center-wavelength λ asthe air-path length is varied (l′air = lair +∆lair). Following (4.26), the group propagationtime in the fiber τfib at the wavelength λ = λ reads

τfib(λ) = τair =1c(lair + ∆lair) . (4.28)

The chromatic dispersion coefficient of the fiber can be calculated as (cf. (4.19))

D(λ) =1lfib

dτfib(λ)

dλ. (4.29)

• The chromatic dispersion coefficient can be obtained for a specific wavelength (λ =λ0 + ∆λ/2), by measuring the shift of the center-wavelength λ, after an incrementalincrease of the optical path length difference ∆OPD. Since the change of the grouppropagation time of the fiber τfib = ∆OPD/c, the chromatic dispersion coefficient of thefiber is given by (see (4.19))

D

(λ0 +

∆λ

2

)=

1lfib

∆τ

∆λ=

1lfib

∆OPD

c ∆λ. (4.30)

Resolution

The following resolutions can be obtained by extrapolating the values of fiber-pieces of 1mlength: Using the indirect technique of differentiating group delay data leads to a resolutionvalue of 2 ps/(nm·km). More accurate results are obtained using direct techniques. Turningpoint analysis gives a resolution of 0.8 ps/(nm·km).

Measurement setup

The setup is based on the Mach-Zehnder interferometer shown in Figure 4.16. Some additionalcomponents are necessary to allow for automatic measurements. The complete measurementsetup as suggested in [25] is shown in Figure 4.18.

3Here we assumed that the Taylor expansion is confined to the first three terms.


Figure 4.18: Measurement setup (from [25]). (P. . . polarizer, λ/4. . . quarter-waveplate,λ/2. . . half-waveplate, MS. . . mirror, BS. . . beamsplitter, GT. . . Glan-Thompson polarizer,IF. . . interference filter, OS. . . optical shutter, PZTM. . . piezoelectric translated mirror,APD. . . avalanche photodiode detector, SF. . . spatial filter, TF. . . test fiber)

A LED with full width half maximum bandwidth of 50 nm is used as a broadband lightsource. The output beam is spatially filtered by a singlemode fiber before entering the interfer-ometer. The beam exiting the interferometer passes a monochromator where the wavelengthis selected in 0.2 nm steps, and then the intensity is measured by an avalanche photodiode.Due to the low light level after the input fiber, synchronous detection is used to increase thesignal to noise ratio.

A HeNe-Laser beam is aligned coaxially to the LED beam for path-length stabilization,which is done by piezoelectric controlled mirror movement. An additional mirror togetherwith a shutter is used to measure the spectral profile of the LED simultaneously.

The measurement is performed over a wavelength range from 780−910 µm in 0.2 nm steps.

4.9.2 Fourier-transform methods

The description of the following method is based on the article: “Three Ways to Implement In-terferencial Techniques: Application to Measurements of Chromatic Dispersion, Birefringence,and Nonlinear Susceptibilities” by P.-L. Francois et al. [26].

The output-intensity, obtained by the experiment described in section 4.9.1, depends on thewavelength λ and the air-path length lair. In the following method, the intensity is measuredover the whole wavelength-range of the broadband source at once. From the measured interfer-ograms the chromatic dispersion of the fiber can be extracted by use of Fourier-transformation.

By integrating (4.23) over the whole frequency spectrum we obtain the proportion

Iout(lair) ∝∫ ∞

0R(ω) cos

[2π

λ(lair − lfib n(λ))

]dω . (4.31)

Source characteristic and transfer functions of the fiber-path and of the air-path are combined


in the real valued function R(ω). After substituting the argument of the cosine-function

2π

λ[lfib n(λ)− lair] = β(ω)lfib −

2π

λlair = β(ω)lfib −

ω

clair , (4.32)

where c is the velocity of light in vacuum and β = 2πλ n(λ) is the propagation constant of the

fundamental-mode in the fiber, we obtain


0R(ω) cos

[β(ω)lfib −

ω

clair

]dω . (4.33)

Eventually, the phase of the cosine-function is also changed by effects like abberation. If thesephase-changes are not negligible, the substitution β(ω)lfib := β(ω)lfib + Φ(ω) has to be done4.

Since the fields arriving at the detector are real quantities, R(ω) is a symmetric functionand β(−ω) = −β∗(ω). Therefore, (4.33) can be written as


−∞R(ω) ej[β(ω)lfib−ω

clair] dω , (4.34)

which is equivalent to the inverse Fourier-transform:

Iout(lair) ∝ F−1

{R(ω) ejβ(ω)lfib

}(lairc

). (4.35)

Therefore β(ω)lfib can be determined from the Fourier-transform of Iout(lair/c) up to an ad-ditive constant. The variations of the effective index of refraction n(λ) can then be obtainedfrom n(λ) = λ

2πβ(λ), and chromatic dispersion can be calculated as (of (4.19))

D(λ) = −λ

c

d2n(λ)dλ2

= −λ

c

d2

dλ2

[λ

2πβ

]= − λ

2πc

d2(λβ)dλ2

= (4.36)

= − λ

2πc

d

dλ

(β + λ

dβ

dλ

)= − λ

2πc

(2dβ

dλ+ λ

d2β

dλ2

).

Zero-dispersion wavelength corresponds to the inflexion point of the variations of the effectiveindex of refraction.

Measurement technique

The measurement setup is shown in Figure 4.19. The broadband source is realized by ahalogen lamp, and the subsequent filter ensures λ > 1.2 µm. A lock-in amplifier togetherwith a chopper is used to improve the signal-to-noise ratio. Lead-in fiber and mixing fiberare singlemode fibers. Even if several modes are transmitted over the test fiber, only thefundamental LP01 mode contributes to the interferences, because there is little transfer fromhigher order modes in the testfiber to the LP01 mode in the mixing fiber.

Iout(lair) is measured, while lair is changed in steps of 0.2 µm. Figure 4.20 shows measuredinterferograms for different types of fibers5.

The amplitude of the Fourier-transform of Iout(lair), and the variations of the effectiveindex of refraction, which is derived from the phase of the Fourier-transform of Iout(lair), areshown in Figure 4.21. The wavelength-region of interferences, and thus the region in which


amplifierlock−incomputer

��

��

��

��

��

��

detectorfiber

mixing halogen lamp

testfiberlead−infiber

chopper

couplerfiber

variableair path

Figure 4.19: Measurement setup [26].

0 50 100 150 200 0 200 400 600 800

SEGCOR fiber

0 200 400 600 800 1000

QC Fiber fluoride glass fiber

Variation of lair [ µm]

Figure 4.20: Measured interferograms of QC fiber, SEQCOR fiber, and fluoride glass fiber(from [26]).

1.6 1.8 2.01.80

4

8−5

effe

ctiv

e in

dex

0

2

4

0

2

4

6

1.31.3

Am

plitu

de

1.5 1.7

vari

atio

ns (1

0 )−5

1.5 1.7

Am

plitu

de

1.3 1.5 1.7

effe

ctiv

e in

dex

vari

atio

ns (1

0 )−5

1.3 1.5 1.7

Am

plitu

de

1.6 2.0

effe

ctiv

e in

dex

vari

atio

ns (1

0 )6

(c)Wavelength [µm]

-5

0

2

4

6

1.3

Wavelength [µm](b)

Wavelength [µm](a)

Figure 4.21: Amplitudes of the Fourier-transform of Iout(lair) and variations of the effectiveindex of refraction, derived from the phase of the Fourier-transform of Iout(lair), of QC fiber(a), SEQCOR fiber (b), and fluoride glass fiber (c) (from [26]).

chromatic dispersion can be determined, can be seen from these diagrams. A comparisonof the dispersion-spectra obtained with the Fourier-transform method, and the dispersion-spectra obtained from measurements with non-Fourier-transform methods (see [26]), is shownin Figure 4.22.

4The effects of aberrations of the optics on the phase are represented by Φ(ω); this substitution has to bedone in the functions derived from (4.33) too.

5dispersion-flattened (quadruply-clad) QC fiber, dispersion-shifted (segmented core) SEQCOR fiber, and afluoride glass fiber


1.4 1.6 1.8 2.0

fluoride fiberSEGCOR

QC

−20

−10

0

10

Dis

per

sion[ p

skm

nm

]

Wavelength [µm]

Figure 4.22: Comparison of the dispersion-spectra obtained with the Fourier-transform method(thick lines) and the dispersion-spectra obtained with mode delay measurements from theinterferogram-envelopes (thin lines) (from [26]).

A different measurement-setup for Fourier-transform measurements using fiber-couplersinstead of bulk optics is presented in [28].

4.10 Temperature coefficient of optical length

The following is based on the article: “Heterodyne Interferometric Measurement of the Thermo-Optic Coefficient of Single Mode Fiber” by S. Chang et al. [29].

In the described method the temperature of a fiber Fabry-Perot interferometer (FFPI),built up from the test-fiber, is varied, in order to determine the temperature coefficient ofoptical length 1

Ld(nL)

dT , from the temperature dependent output-signal and the wavelength ofthe source.

The authors of the article claim that measurements with the common used method of theangle of minimum deviation (AMD) [30] are only accurate to the order of 10−4 K−1, whereastemperature coefficients of optical length of fibers are about one or two decades lower, so thatthe described method has to be used in order to obtain accurate results.

The interferometer is fabricated from the fiber, of which the temperature coefficient ofoptical length shall be determined. Its length is 12 mm and the end-faces are coated withsingle layer TiO2, with a reflectivity of 3 − 4%. The interferometer is surrounded by a tube,in contact with a thermo-electric cooler for temperature control.

Figure 4.23 shows the measurement-setup. The light-source is a strained layer quantumwell DFB diode laser module, providing a stable output wavelength (1558 nm) with 0.8MHzline width. There is also an isolator integrated in this module. The laser is modulated by a veryweak rf-current, with a modulation frequency of ωm = 280 MHz, which yields a modulationindex β � 1. The spectrum of the obtained signal contains three components, which are thecarrier frequency ω0, and two side-band frequencies ω0 + ωm, and ω0 − ωm. The optical field


Figure 4.23: Setup for interferometric measurement of the thermo-optic coefficient (from [29]).

at the output of the laser diode is

E(t) ≈ E0

{J0(β)ejω0t + J1(β)ej(ω0+ωm)t + J−1(β)ej(ω0−ωm)t

}, (4.37)

where Jk(β) with k ε {0,±1} is the Bessel function. The signal propagates through a 2 × 2coupler, with 50% coupling ratio, into a Fabry-Perot interferometer sensor. Index matchingoil at the other output-end of the coupler ensures, that no light is reflected back from thatend-face.

The effect of the resonator on the signal is represented by the complex reflection functions

Tk(ωk) = e−δk−jϕk with ωk = ω0 + kωm, k = 0,±1 , (4.38)

where δk is the amplitude attenuation and ϕk is the optical phase shift at ωk. For β � 1 thesignal leaving the interferometer is

Er(t) ≈ E0

{T0(ω0)ejω0t + T1(ω1)

β

2ejω1t − T−1(ω−1)

β

2ejω−1t

}. (4.39)

Via the coupler the signal arrives at the photodetector, where the intensity is given by

I(t) ≈ E20eδ0β

{[e−δ1 cos(ϕ0 − ϕ1)− e−δ−1 cos(ϕ−1 − ϕ0)

]cos(ωmt)

+[e−δ−1 sin(ϕ−1 − ϕ0)− e−δ1 sin(ϕ0 − ϕ1)

]sin(ωmt)

}. (4.40)

The output of the photodetector is amplified, and filtered by a bandpass with center frequencyωm. Afterwards it is mixed with the signal modulating the source. The signal at the outputof the mixer is

V (t) ∝ E20eδ0β

{[e−δ1 cos(ϕ0 − ϕ1)− e−δ−1 cos(ϕ−1 − ϕ0)

]cos(ωmt) sin(ωmt)

+[e−δ−1 sin(ϕ−1 − ϕ0)− e−δ1 sin(ϕ0 − ϕ1)

]sin2(ωmt)

}. (4.41)


It is then filtered by a lowpass in order to obtain dc-signal related to the phase shift differencebetween the carrier and the side bands

V (ϕk, δk) ∝12E2

0 eδ0β[e−δ−1 sin(ϕ−1 − ϕ0)− e−δ1 sin(ϕ0 − ϕ1)

]. (4.42)

The amplitude attenuation and the phase shift caused by the interferometer are

e−δk =r√

(1− cos θk)2 + sin2 θk√(1− r2 cos θk)2 + (r2 sin θk)2

and (4.43)

ϕk = arctan[

sin θk

1− cos θk

]+ arctan

[r2 sin θk

1− r2 cos θk

]. (4.44)

The output signal V (ϕk, δk) becomes zero, if δ−1 = δ1 and sin(ϕ−1 − ϕ0) = sin(ϕ0 − ϕ1).This is the case, if the resonators resonance frequency is equal to the carrier frequency ω0.The phase shift θ of the signal after a round-trip in the resonator, and thus the resonancefrequency of the resonator, can be modified by changing the resonator temperature T , becausethe refractive index n as well as the resonator length L/2 is depending on the temperature:

θ =nLω

c= 2π

nL

λ. (4.45)

Both simulation and experimental results show that the output signal oscillates periodicallywith the temperature (see Figure 4.24). Differences between simulation and experimental

Figure 4.24: Output signal V (ϕk, δk) vs. temperature: The results of the theoretical simulationare shown by the line, and the experimental results are shown by dots (from [29]).

results arise from doping material differences in the simulation model and the measured fiber.During one oscillation period ∆T , the signal in the resonator experiences a 2π phase change,so that together with (4.45) the following equation is obtained:

d(nL)dT

∆T = λ0 . (4.46)

The obtained results have to be related to L, in order to make them independent of the usedresonator length and the temperature coefficient of optical length is

1L

d(nL)dT

∆T =1L

λ0 . (4.47)


The temperature coefficient of optical length can be calculated from the oscillation period ∆Tand the wavelength of the carrier λ0.

With a measured oscillation period of ∆T = 6.51 ◦C the temperature coefficient of opticallength is 9.92 · 10−6 K−1 for a Corning singlemode fiber with n = 1.4488. The temperaturecoefficient of optical length of a Amorphous Materials chalcogenide glass fiber, calculated fromdata provided by the manufacturer, is 9.58 · 10−5 K−1, and of a sapphire fiber, calculated fromdata from [3], is 2.3 · 10−5 K−1.

For measurements at higher wavelengths, as it is necessary for infrared fibers, the coatingof the resonator has to be changed.

4.11 Coeffiecient of elasticity

The coefficient of elasticity (Young’s modulus E) can be determined by a tensile test. Thetensile stress σ = F

A0, applied to fiber in axial direction, is continuously increased until the

fiber breaks, while the elongation ∆L of the fiber the fiber is measured. With the strain

ε =l − l0

l0=

∆l

l0(4.48)

of a fiber, a stress-strain diagram as shown in Figure 4.25 can be obtained [31]. The forceapplied to the fiber is given by F , while A0 and l0 are the original cross sectional area andlength of the fiber. If the applied stress is less than σE , it is proportional to the strain of the

Figure 4.25: Stress-strain curve (from [31])

fiber by the factor of E. Therefore Young‘s modulus can be calculated from the linear part ofthe diagram as

E =FA∆ll0

. (4.49)

Some coefficients of elasticity of infrared fibers are: ESapphire = 430 GPa, EFluoride =54 GPa, Echalcogenide = 21.5 GPa, and Esilver-halide = 0.14 GPa [3]. Therefore, applying 25% of


its tensile strength to a 1 m chalcogenide fiber (see Section 3.3.1) would result in an elongationof

∆l =25 MPa21.5 GPa

· 1 m = 0, 0012 m . (4.50)

Chapter 5

Outlook

With the data obtained from the market survey (see Chapter 3), the fibers which fit best tothe requirements of the applications described in Chapter 1 have been selected, and samplesof a few meter of each of those fibers have been bought.

The next step will be the verification of the characteristics provided by the vendors inthe datasheets and the measurement of the parameters which have not been specified by thevendors, using the measurement methods described in Chapter 4.

As a first measurement, the transmission and the output intensity distribution of a hollowglass taper for attenuation measurement of multimode fibers, as described in Section 4.1.2,has been determined.

52

Appendix A

Data sheets

A.1 IR Photonics: MID-infrared single mode fiber

53

APPENDIX A. DATA SHEETS 54

A.2 IR Photonics: MID-infrared multi mode fiber


A.3 ARTPhotonics: CIR fiber

2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,00

200

400

600

800

1000

Atte

nuat

ion,

dB

/km

Wavelength, µm

CIR-fiber Chalcogenide IR-glass fiber

remote IR spectroscopy 1.5 - 6µm

flexible pyrometry & IR-imaging

Er:YAG-laser power delivery

Chalcogenide InfraRed (CIR-) glasses based on As-S-composition are the best for fiber optic in 2 – 6 µm range of spectra. Thereby CIR-fibers transmit IR-radiation in the gap between silica glass fibers (0.2 – 2.4µm) and Polycrystalline InfraRed (PIR-) fibers (4 – 18µm). CIR-Fibers are drawn in core-clad structure with double polymer coating and characterized by a low optical losses and high flexibility. The innovative glass purification process provides the attenuation spectra free from OH- absorption band at 3µm and thus it enables CIR-fibers to be used for Er:YAG laser power delivery

FEATURES •..... high transmittance from 2 µm up to 6 µm •..... suitable for Er:YAG - laser power delivery •..... optical losses 0.2 dB/m at 2 - 4 µm •..... double polymer coating for high flexibility •..... durable cables with SMA-connectors

APPLICATIONS Flexible delivery for Er:YAG - laser flexible IR-imaging systems remote non-contact pyrometry in the 200-600K range fiber probes for remote process IR - spectroscopy

FIBER SPECIFICATION Transmission range .................................1.5 - 6 µm Core/Clad structure .................................As2S3/As-S Core/Clad diameter .................................200-700 / 300-800 µm Numerical Aperture………………………..0.3 Core refractive index ...............................2.4 Protective coating ....................................Double polymer Ambient temperature range.....................280 – 400 K

Advanced Research &

Technology in


A.4 ARTPhotonics: PIR fiber

€F® PIR - fibers Polycrystalline Core/Clad fiber for Mid-infrared spectrum (4-18µm) from a Silver Halide solid solution The development of specialty fibers for the Mid-Infrared region has resulted in a unique product – Core / Clad Polycrystalline Infra-Red (PIR-) fibers. PIR fibers are non-toxic, very flexible, transparent across a broad spectral region 4 –18 µm and capable of operating over the wide temperature range of −270 °C up to +140 °C. They are manufactured in a core/clad structure of superior quality from pure AgCl: AgBr solid solution crystals using an innovative vacuum extrusion method. They possess by no aging effect compared to an alternative bare core fiber. The range of €F®-PIR-fiber cables are available with a durable PEEK polymer jacket and terminations using either an SMA – type connector with a Ti or polymer ferrule or special one, manufactured on customer request. A wide variety of different optical coupling units can also be designed & fabricated for specialized customer requirements.

High transmittance from 4 µm up to 18 µm. 50 W.

st).

Suitable for CO2 - laser power delivery up to

4,0 6,0 8,0 10,0 12,0 14,0 16,00

500

1000

1500

2000

2500

Wavelength, µm

Atte

nuat

ion,

dB

/km

Low Attenuation at 10.6 µm (0.1-0.5 dB/m). Fiber diameters from 0.3 to 1.0 mm (on requeFiber lengths up to 20 m (for 0.5 mm diameter). No aging effect

Flexible delivery system for CO and CO2 laser. Flexible IR-imaging systems.

range. , in-vivo and process IR - spectroscopy.

Remote non-contact pyrometry in the 100-600KFiber probes for remote in-line

Fiber diameter (standard) ................................... 400/500, 630/700, 900/1000 µm ................................. 4-18 µm

0.1-0.5 dB/m

MPa meter]

ber Diameter]

Transmission range............Attenuation at 10.6 µm.......................................Refractive index ................................................. 2.15 Effective NA....................................................... 0.25 Laser Damage Threshold for cw CO2-laser........ >12 kW/cm²

Melting point ...................................................... 415°CTensile strength .................................................. >100 Minimum Bending Radius (fixed)...................... 10×[Fiber DiaMinimum Elastic Bending Radius...................... 100×[Fi


€F® PIR - cables

CABLE SPECIFICATIONS • Core/clad PIR-fibers are protected by a loose PEEK-jacket (PolyEtherEther-

Ketone) to provide stiff, flexible and hermetic protection against mechanical, photoinduced and chemical damage over a wide temperature range (up to 250°C)

• Standard fiber/cable diameters are listed below. Other fiber diameters in 0.3 –

1.5mm range are also available upon the request for special fabrication:

Fiber core/cladding diameter *) (µm) Jacket’s inner/outer diameter (µm) 400 / 500 750 / 1590 630 / 700 1400 / 3175

900 / 1000 1400 / 3175 *) other diameter are available in 300 – 1000 µm range on request (10m min order)

• Cable termination with a special Ti-ferrule SMA-connector:

for low power (spectroscopy & radiometry) applications for high laser power delivery – free standing fiber end standard cable length – 1m & 2m

• PIR-fiber end-surface treatment: Cutting.....................low cost, high performance - standard Polishing..................for special application, including AR-coating – on request SMART...................for reduced reflection of high CO2-laser intensity – on request

OPTIONS

- accessory kits for remote spectroscopy with FTIR, QCL and TDL-spectrometers - pig-tailing of IR-detectors: TE- & LN-cooled MCT, PbSe, thermopiles, etc.

1 – PIR 400/500 after 2.5 year storing (red) 2 – PIR 600/700 after 2.5 year storing (purple) 3 – PIR 400/500 after 1 month storing (green)

PIR 600/700

PIR 400/500

Attenuation at 10.6µm in core/clad PIR-fibers measured within 28 months storage after extrusion


A.5 CeramOptec: Optran MIR

CeramOptec is unique in its ability to manufacture fiber optic CO2 laser delivery systems and MIRoptical fiber commercially. CeramOptec’s flexible fiber optic delivery systems for CO2 lasers offer anadvantage over articulated arms—the typical delivery system for CO2 lasers—which are often rigidand cumbersome. Optran MIR optical fibers are the finest quality laser fibers for everything frommedical treatments to FT-IR spectroscopy (4 – 16 µm).

Features

■ Optimized for CO and CO2 lasers■ Low attenuation in the MIR region■ Non-brittle and very flexible■ Non-hygroscopical material■ High numerical aperture■ Reliable coupling accessories available■ Core/Clad or Bare Core design

Applications■ Medical

CO2 Laser Delivery■ Industrial/Scientific

FT-IR spectroscopy PyrometryLaser marking Remote, non-contact, temperature controlIR imagingLaser surface treatment

Physical PropertiesCrystal of solid solution: AgCl : AgBrSpecific weight: 6.39 g/cm3

Melting point: 412˚Tensile strength: 100 MPaWork temperature: -60˚ to +110˚CMinimum bend radius: R = 100 x Ø fiber

Optical PropertiesTransmission range: 4 to 16 µmRefractive index (core): 2.1Practical NA: 0.5 (bare core)

0.35 (core/clad)0.25 (core/clad)0.13 (core/clad)

Damage threshold (CO2 CW): 10 kW/cm2

Reflective loss (l = 10.6 µm) 25%

Innovative Fiber Optics...Every Step of the Way™

OPTRAN® MIR FIBERS

Transmission 80%

90%

3 4 5 6 7 8 9 10 11 12 130.0

0.5

1.0

1.5

2.0

2.5

3.0

Wavelength (um)

Atte

nuat

ion

(dB

/m)

Optran MIR


Please contact our Sales Engineering representatives:North AmericaCeramOptec Industries, Inc.515A Shaker Road; East Longmeadow, MA 01028Tel: 800-934-2377

413-525-0600Fax: 413-525-1112Email: [email protected] Coast OfficeTel: 408-362-0100Fax: 408-629-1657Email: [email protected] GmbHSiemensstr. 44; 53121 Bonn, GermanyTel: +49 (0) 228-979670Fax: +49 (0) 228-9796799Email: [email protected]

Innovative Fiber Optics...Every Step of the WayCeramOptec was founded in 1986 and today is a global leader in the production of stock and custom silica / silica, plastic-clad silica, and hard polymer-clad silica optical fibers; fused capillary tubing; DPSS lasers; diode modules; and low loss bundles and assemblies for UV, VIS, and IR transmission, medical laser delivery, sensors, plasma fusion, and spectroscopy. With several facilities worldwide, we are able to provide our customers with local, prompt, and reliable service and products. By maintaining complete control over the entire manufacturing process—from preformmanufacturing to finished fiber product—we are able to provide the highest quality control, custom solutions, and competitive pricing to our customers.Please visit http://www.ceramoptec.com for more information.CeramOptec is a subsidiary of biolitec™ AG.Please visit http://www.biolitec.com for more information.

Bare Core

Product Code Ø Core (µm) ± 2% Ø Loose Tube (µm) ± 2% Max. Length (m)MIR 300 300 700 20MIR 500 500 1000 10MIR 700 700 1500 10MIR 1000 1000 2000 10

Product Code Ø Core (µm) ± 2% Ø Clad (µm) ± 2% Ø Jacket (µm) ± 5% Max. Length (m)MIR 200/300 BPLC 200 300 400 10MIR 400/500 BPLC 400 500 700 10MIR 600/700 BPLC 600 700 900 10MIR 860/1000 BPLC 860 1000 1300 5

ML-127 REV. A (05/03)©2003 CeramOptec Industries, Inc.

Optran MIR—Bare Core Design

Mixed Silver Halide

Surrounding Air Functions as Cladding

Loose Polymer Tube(Polycarbonate or Tefzel®)

Optran MIR—Core/Clad Design

Mixed Silver Halide

Mixed Silver Halide

Loose Polymer Tube(Polycarbonate or Tefzel®)

Core/Clad

Notes:

NA is measured at the 95% intensity angle.

CeramOptec strives to ensure the accuracy of all information provided; however, we imply no warranties and disclaim any liability in connection with the use of this information.

Tefzel® is a registered DuPont product.


A.6 Beijing S-Fiber Technology: Infrared Fiber


A.7 Amorphous Materials: C1, C2

IR Fibers

containing ultra violet.

TABLE 1 PROPERTIES OF AMI CORE GLASSES AND FIBERS

CORE GLASS As-Se-Te (Cl) As2S3 (C2)

Glass Transition Temperature °C 136 180

Softening Point °C 170 208

Thermal Expansion ∆L/Lx106/ºC 23.5 21.4

Refractive Index @ 4 µm

@ 10 µm

Value 2.82

2.81

Value 2.41

2.38

Thermal Change in Index xl05/°C +3 ± 0.9

Fiber Absorption From Transmission / Maximum Laser Power Transmitted.

@ 5.25 µm, db/m 0.2-0.4 5<10 w 0.2-0.4 > 100 w

@ 9.27 µm, db/m 0.2-0.4 5<10 w ----

@ l0.6 µm, db/m 4-5 5 w ----

Bend To Break Radius (cm) / Tensile Strength (psi) @ 40 Mpa/s Strain Rate

lOOO µm Core 4 62,000 4 44,000

750 µm Core 1 68,000 3 45,000

500 µm Core 0.8 70,000 1.7 56,000

<l00 µm Core 0.1 133,000 0.1 122,000

( Measurements courtesy of Tom Loretz of CES)

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APPENDIX A. DATA SHEETS 63IR Fibers

Numerical Aperture* 0.6-0.7 (± 40-50°) O.5-O.6 (± 35-40°)

(Measured at the 90 % point using variable iris while detecting energy from a heated surface. Large value results because of Fresnel reflection I refraction at oblique angles of incidence by the high refractive index core glass.)


IR Fibers

SPOOLED FIBER FIBER CONNECTOR

GLASS CLAD IR FIBER PRICE LIST PRICE, DOLLARS PER METER



A.8 Polymicro: HWCA, HWEA

Polymicro Technologies > Products and Technologies > Optical Fibers > HOLLOW SILICA Waveguide, IR Applications

Products > Optical Fibers > HOLLOW SILICA Waveguide (HSW™), IR Applications

HOLLOW SILICA Waveguide (HSW™)- IR Applications HW

Hollow Silica Waveguide: Usage Guide and Test Process Overview

Characteristics

❍ Wavelength Range 2.9 µm past 10.6µm ❍ High Laser Damage Threshold: > 1000W of 10.6µm ❍ Strong and Flexible ❍ Non-Toxic: Sterilizable * ❍ Low Insertion Loss ❍ No End Reflection ❍ Transmission Optimized for CO2 or Er:YAG wavelengths

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



Polymicro Technologies > Products and Technologies > Optical Fibers > HOLLOW SILICA Waveguide, IR Applications

Terminations Available

Poly-Lok™:

❍ Removable, reusable connectors, ideal for prototyping ❍ SMA (905), SMA (906), STII, and FC (STII and FC not available for 1000µm bore) ❍ Not for permanent installations

Permanent SMA (905), SMA (906), STII, and FC:

❍ Waveguide protrudes 1 to 2 mm from connector endface

This product is licensed and manufactured under the following patents: US: 5,440,664; 5,567,471; 4,930,863; 5,497,440; and 5,605,716; Israel: 86296; 105956; and 111904; Europe: 0344478.

LEGAL NOTICES | PRIVACY POLICYWed, 26 May 2004 15:35:28 GMT

Copyright © Polymicro Technologies, LLC. 1995 - 2003. All Rights Reserved18019 N. 25th Avenue.

Phoenix, Arizona 85023-1200 USA 602-375-4100 Main602-375-4110 Fax



A.9 Hitachi: hollow fiber

Lamp Monochromator Detector(HgCdTe)

controller Lock-in Amp

Chopper

Computer Plotter

ZnSe Lensf=1”

ZnSe Lensf=1.5”

2 4 6 8 10 120

5

10

15

Wavelength (μm)

Tran

smis

sion

Los

s (dB

)

Infrared spectral attenuation of the hollow fiber


A.10 CoreActive: IRT-SU, IRT-SE

Mid-Infrared Transmission Optical Fiber

CorActive delivers a full range of Infrared Transmission (IRT) optical fibers to address the beam delivery requirements for wavelengths in the mid-Infrared spectrum from 2.0 to 9.0 µm. CorActive’s family of Infrared Transmission Fiber products have been designed specifically to provide ultra low loss optical transmission in the mid-Infrared spectrum. The high optical quality and low loss characteristics of CorActive’s IRT optical fibers will enable performance enhancements of many existing applications that have relied on free space optics, low quality fiber or other beam delivery methods. A proprietary optical fiber manufacturing method ensures that fiber impurities and optical defects are removed prior to fiber drawing. This ensures the lowest loss and highest quality optical transmission of mid-IR wavelengths in the 2.0 to 9.0 µm range.

Ultra Low Loss High Power Capacity High Nonlinearity Bend/Polarization Insensitive

Robust Mechanical Properties Rare Earth Doping Available Designed for Military Applications by the U.S. Naval Research Laboratory

CorActive IRT Product Features and Benefits

IRT Product Features Customer Benefits Superior Beam Quality World leading fiber quality enables new fiber based mid-IR applications Proprietary Manufacturing Process Ensures highest optical quality by eliminating impurities and defects High Power Capacity Enables high power beam delivery of mid-IR wavelengths Consistent Reproducibility Reduces manufacturing costs and increases production yield Broad Product Family Ensures the most effective fiber choice for your application IRT Fiber Applications CorActive’s IRT optical fiber has been designed for high performance and demanding applications such as: - Infrared Counter Measure (IRCM) - IR Imaging Fiber Bundle (FLIR) - Er:YAG Laser Beam Delivery (3.0 µm) - IR Spectroscopy

Leading Low Loss IR Fiber Superior High Power Handling

Spectral Attenuation

012345678

1 3 5 7 9 11

Wavelength (um)

Atte

nuat

ion

(dB/

m) IRT-Se

IRT-Su

Peak Power Density: 1.1 GW/cm2 (27kW)

0

0.5

1

1.5

2

0 0.5 1 1.5 2 2.5 3

Pin (W)

Pout

(W)


Mid-InfraredTransmission Optical Fiber

Fiber Specifications

IR Transmission Fiber IRT-SU IRT-SE

Core/Clad Structure Materials Sulphide Selenide

Optical Properties

Transmission Wavelength Range (µm) 2-5 2-9 Core Refractive Index 2.4 2.7 Numerical Aperture (nominal) 0.26 0.30 Nominal Attenuation (dB/m) <0.2 <0.5

Physical & Geometric Properties

Core Diameter (µm) 4-700 ± 3% Cladding Diameter (µm) 80-800 ± 3% Cladding Non-circularity (%) <2 Core/Clad Concentricity Error (µm) <5 Protective Coating Composition Dual Coat Acrylate

Environmental Properties

Chemical Insensitivity Insoluble in water, concentrated hydrochloric acid, non-oxidizing acids, gasoline, toluol, alcohol and acetone

Advanced Cable Manufacturing Process Advanced Cable Manufacturing Process

In our continuing effort to bring our customers the best service possible, CorActive utilizes a proprietary cable manufacturing process, which ensures optimal Anti-Reflective coating application. In our continuing effort to bring our customers the best service possible, CorActive utilizes a proprietary cable manufacturing process, which ensures optimal Anti-Reflective coating application.

IRT Cable Sheathing FC High Reliability Connector

Printed in Canada Copyright© 2004 CorActive High-Tech Inc. All rights reserved


A.11 Photran LLC: Sapphire optical fiber

Sapphire Fiber Specifications

The Sapphire Fiber Advantage

● Biocompatiable, nontoxic, USP Class VI approved - passes both implant and elution test protocols

● High transmission from visible to beyond 3 micron wavelength.

● Flexible - bend radius as low as 20mm for 150 micron fiber diameter.

● High Strength - 400,000 psi/2.8 GPa - use of PTFE buffer further improves durability and handling.

● High laser damage threshold (1200 J/em2) and high melting point (2053ºC) enable high repetition rates and average power.

Sapphire Optical Fiber Specifications

(Typical Specifications)

Fiber Core Diameter (microns) 150 250 325 425

Buffer Diameter (microns) 400 450 650 750

Effective NA 0.12 0.12 0.12 0.12

Transmission (per meter) 80% 80% 80% 80%

Minimum Bend Radius (mm) 20 30 60 80

Length-Maximum Standard 2 meters 2 meters 2 meters 2 meters

Length-Maximum Special Order 4 meters 4 meters 4 meters 4 meters

file:///E|/projects/phasecap/TN3/Faserdatenblaetter/f14.html (1 of 2)18.01.2005 15:38:50


A.12 Infrared Fiber Sensors: Spectral grade Silverhalide fibers

Core/Clad Fibers

Fiber diameter 900/1000µm (other diameters on request)Transmission range 3− 18 µmAttenuation at 10.6 µm 0.1− 0.3 dB/mAttenuation at 5µm < 0.6 dB/mAttenuation at 3.5 µm < 1 dB/mEffective NA (L>2 m) < 0.26Laser Damage Threshold for cw CO2-laser 12 kW/cm2

No ageing

Core Only Fibers

Fiber diameter 750 µm × 750 µm and 1 mm × 1 mm(other diameters on request)

Transmission range 2− 18 µmAttenuation at 10.6 µm < 0.2 dB/mAttenuation at 5µm < 0.3 dB/mAttenuation at 3.5 µm < 0.6 dB/mEffective NA (L>2m) 0.42No ageing

Refractive index (core) 2.2Melting point 420 ◦CTensile strength >110 MPaMinimum Inelastic Bending Radius 10 × Fiber DiameterMinimum Elastic Bending Radius 100 × Fiber Diameter


A.13 Infrared Fiber Systems: HP fiber

IFS, Inc. Product 1

Applications:

• Dentistry

• Dermatology

• Ophthalmology

• General Surgery

• Orthopedics

Features:

• GeO2 – based glass

• High Power Handling

• Excellent Flexibility and Strength

• Glass Clad – No Bending Loss

• Low Optical Loss

• Non-Toxic

A key component to the Er:YAG, YSGG or Ho:YAG mid-infrared laser system is the optical fiber, which is used to transmit the laser power from the laser to the patient. Since conventional silica glass fibers cannot transmit in the infrared, a special fiber (HPTM fiber) made from Germanium Oxide (GeO2) – based glass was

developed by IFS, Inc. Fiber can handle up to 20 Watts of laser power for applications in dermatology, dentistry, ophthalmology, orthopedics and general surgery and is being sold worldwide to numerous laser companies. There are no other reliable fibers on the market for these types of applications and with today’s production volumes, IFS is a leading supplier of specialty HPTM fiber for mid-infrared medical lasers.

[ Home ] [ Up ] [ HP Fiber Specs ]

Infrared Fiber Systems, Inc. * Phone: (301)-622-9546 * Fax: (301)-622-7135 * [email protected]

file:///E|/projects/phasecap/TN3/Faserdatenblaetter/f16a.htm18.01.2005 17:05:55


IFS, Inc. Product 1

Typical Specifications

Input Power @10 Hz 20.0 W (at least)

Loss at 2.94 µm 0.70 dB/m

Loss in visible region 1.00 dB/m (or less)

Output NA 0.12 (@ input NA=0.08)

Max acceptance NA 0.25

Available Core sizes 100 – 700 µm

Toxicity Passes Agar Overlay cytotoxicity and Dermal Sensitization tests

Core Size

Minimum Bend Radius

150 µm 0.5 cm

400 µm 2.5 cm

500 µm 4.0 cm

[ Home ] [ Up ]


file:///E|/projects/phasecap/TN3/Faserdatenblaetter/f16b.htm18.01.2005 17:06:24


A.14 Infrared Fiber Systems: SG fiber

Features:

• Low Optical Loss

• Multispectral Transmission

• Good Flexibility and Strength

• Glass Clad – No Bending Loss

• Perfect Matrix for Rare-Earth Doping

Applications:

• IR Imaging

• Fiber Lasers

• Fiber Amplifiers

• Temperature Sensing

• Remote Spectroscopy

IFS offers Heavy Metal Fluoride glass fibers (SGTM fiber) for use in a variety of industrialand scientific sensor systems such as temperature sensing and remote chemical analysis. Thesefibers transmit from the ultraviolet through 5µm in the mid-infrared. They can be furnishedas single fibers, cables or bundles. Infrared imaging bundles have been supplied to the Navyand to NASA as well as to the private companies. We have also developed fiber optic probesfor use with our AOTF spectrometer for remote and in-situ sensing applications.


IFS, Inc. Product 2

Typical Specifications

Optimal Transmission Range 0.45 µm to 5.0 µm

Minimum Loss at 2.5 µm 0.05 dB/m

Max Operating Temperature 250 oC

Output NA 0.22

Available Core sizes 100 – 700 µm

Core Size

Minimum Bend Radius

100 mm 0.5 cm

200 µm 1.0 cm

400 µm 4.0 cm

[ Home ] [ Up ]


file:///E|/projects/phasecap/TN3/Faserdatenblaetter/f17b.htm18.01.2005 17:09:05


A.15 FiberLabs Inc.: SMFF

Fluoride Fiber SMFF

EnglishJapanese

Fluoride Glass Fiber - SMFF(Single Mode Fluoride Fiber) & Fiber-Module

=> SMFF(Single Mode Fluoride Fiber)

Rare earth doped SMFF enable to get high efficiency emissions easily, and are used for fiber lasers, optical amplifiers, and so on. Fiber module with pig-tail of silica fibers are also available.

Loss Spectra & Wavelength of Emission

SMFF Typical Fiber Parameters

DopantConcentration

ppm molNA

CoreDiameter

um

CladdingDiameter

um

Custom Fiber Price(US$)

Pr,Nd,Ho,Er,Tm,Yb, etc.

500 ~ 30,0000.150.200.27

2 ~ 12 123+/-3$8,000~

$20,000 /lot

Fluoride Fiber in Stock

=> Fluoride Fiber Module

Fiber module with pig-tail of silica fibers can be easily connected to other silica fibers. The hermetic sealed module can be used under the condition of high temperature and high humidity.

Insertion Loss Return Loss Output Fiber Size(mm)Operating

Temperature

Less than 1.5dB Less than -50dB SMF 15(H)X150(W)X100(D) -10 ~ 45 C

Request Sheet (Information, Quotation, Order, etc.)

HOME / Products / About FiberLabs / R&D / Information / Site-Map

Copyright(C) FiberLabs Inc. All Rights Reserved.

file:///E|/projects/phasecap/TN3/Faserdatenblaetter/f20.htm18.01.2005 16:54:21


A.16 FiberLas Inc.: MMFF

Fluoride Fiber MMFF

EnglishJapanese

Fluoride Glass Fiber - MMFF(Multi Mode Fluoride Fiber)

=> MMFF(Multi Mode Fluoride Fiber)

MMFF have a broad transmission wavelength range from visible to infrared rays. There are two types of MMFF, depending on the applications. GFF series, which have longer transmission wavelength up to 4.0um, are suitable for IR spectrum guides. TFF with higher NA are appropriate for NIR spectrum transmission.In addition to the form of resin jacket fibers, single core and bundled cables are also available.

Loss spectra GFF-xxx*500nm to 4.0 um transmission range*20mm bend radius for GFF-150(proof test)*Custom-made fibers available

TFF-190*700nm to 2.5um transmission range*20mm bend radius(proof test)*Customized fiber bundles available

DCFF Typical Fiber Parameters

Part #Core Diameter

(um)Cladding Diameter

(um)Buffer(um)

NA JacketPrice(US$)

GFF-160/200-450 160 200 450 +/-10%

0.28UV

CurableResinJacket

$60.00/m

GFF-240/300-450 240 300 450 +/-10% $125.00/m

GFF-320/400-550 320 400 550 +/-10% $200.00/m

GFF-400/500-650 400 500 650 +/-10% $300.00/m

TFF-190/200-450 190 200 450 +/-10% 0.65 $60.00/m

Fluoride Fiber in Stock


Bibliography

[1] M. Pfennigbauer, F. Fidler, W. Leeb, and U. Johann, “TN1: Survey of instrument op-portunities, Contract ESA/ESTEC/18514/04/NL/PA, Technical Note 1,” 30.11.2004.

[2] M. Pfennigbauer, F. Fidler, W. Leeb, and M. Dirnwoeber, “TN3: Market survey, ContractESA/ESTEC/18514/04/NL/PA, Technical Note 3,” 2004.

[3] J. A. Harrington, “Infrared fiber optics,” Handbook of Optics, Vol.3, ed. M. Bass, NewYork: McGraw-Hill, 2000.

[4] J. A. Harrington, “Hollow-glass waveguides have unique properties,” Laser Focus World,pp. S8–S10, August 2004.

[5] Crystal Fibre A/S. (2005, March). [Online]. Available: http://www.crystal-fibre.com/products/airguide.shtm

[6] Crystal Fibre A/S. (2005, March). [Online]. Available: http://www.crystal-fibre.com/products/nonlinear.shtm

[7] J. Eichenholz, “Photonic-crastal fibers have many uses,” Laser Focus World, pp. S5–S7,August 2004.

[8] O. Wallner, W. R. Leeb, and R. Flatscher, Design of spatial and modal filters for nullinginterferometers, Proceedings of SPIE, Vol. 4838, 668-679, 2003.

[9] D. Marcuse, Curvature loss formula for optical fibers, Journal of Optical Society of Amer-ica, Vol. 66, pp. 216-220, 1976.

[10] A. J. Harris and P. F. Castle, “Bend loss measurements on high numerical aperture single-mode fibers as a function of wavelength and bend radius,” J. Lightwave Technol., vol. 4,no. 1, pp. 34–40, 1986.

[11] W. D. Heacox and P. Connes, “Optical fibers in astronomical instruments,” The Astron-omy and Astrophysics Review, Vol.3, pp. 169-199, Springer-Verlag, 1992.

[12] M. Nisoli, S. Stagira, S. D. Silvestri, O. Svelto, S. Sartania, Z. Cheng, G. Tempea, C. Spiel-mann, and F. Krausz, Toward a Terawatt-Scale Sub-10-fs Laser Technology, IEEE Journalof Selected Topics in Quantum Electronics, Vol. 4, No. 2, pp. 414-420, 1998.

[13] O. Wallner, “Modal filtering of optical waves,” Doctoral Thesis, Institute of Communica-tions and Radio-Frequency-Engineering, Vienna University of Technology, 2004.

[14] O. Guyon. (2002) Wide field interferometric imaging with single-mode fibers. [Online].Available: http://www.edpsciences.org/articles/aa/abs/2002/19/aa2299/aa2299.html

77

http://www.crystal-fibre.com/products/airguide.shtm

http://www.crystal-fibre.com/products/airguide.shtm

http://www.crystal-fibre.com/products/nonlinear.shtm

http://www.crystal-fibre.com/products/nonlinear.shtm

http://www.edpsciences.org/articles/aa/abs/2002/19/aa2299/aa2299.html

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[15] Optoelectronics Industry Sourcebook 2004 Buyers Guide. Nashua, New Hampshire USA:LaserFocusWorld, 2004.

[16] D. Marcuse, Principles of Optical Fiber Measurements, 1st ed. New York, New YorkUSA: Academic Press, Inc., 1981.

[17] ITU-T G.650.1: Definitions and test methods for linear, deterministic attributes of single-mode fibre and cable, Prepublished Recommendation, International TelecommunicationUnion, 2004.

[18] I. K. Ilev, R. W. Waynant, and M. A. Bonaguidi, “Attenuation measurement of infraredoptical fibers by use of a hollow-taper-based coupling method,” Applied Optics, vol. 39,no. 19, pp. 3192–3196, July 2000.

[19] M. J. Matthewson, C. R. Kurkjian, and S. T. Gulati, “Strength measurement of opticalfibers by bending,” Journal of the American Ceramic Society, vol. 69, no. 11, pp. 815–821,November 1986.

[20] G. Cancellieri, Single-Mode Optical Fiber Measurement: Characterization and Sensing,1st ed. Norwood, Massachusetts USA: Artech House, Inc., 1993.

[21] D. L. Franzen, “Determining the effective cutoff wavelength of single-mode fibers: Aninterlaboratory comparison,” Journal of Lightwave Technology, vol. LT-3, no. 1, pp. 128–134, February 1985.

[22] Y. Ohishi, S. Mitachi, and S. Takahashi, “Fabrication of fluoride glass single-mode fibers,”Journal of Lightwave Technology, vol. LT-2, no. 5, pp. 593–596, October 1984.

[23] M. Artiglia, G. Coppa, P. di Vita, M. Potenza, and A. Sharma, “Mode field diametermeasurements in single-mode optical fibers,” Applied Optics, vol. 7, no. 8, pp. 1139–1152,August 1989.

[24] D. L. Franzen, M. Young, A. H. Cherin, E. D. Head, M. J. Hackert, K. W. Raine, andJ. G. N. Baines, “Numerical aperture of multimode fibers by several methods: Resolvingdifferences,” Journal of Lightwave Technology, vol. 7, no. 6, pp. 896–901, June 1989.

[25] P. A. Merritt, R. P. Tatam, and D. A. Jackson, “Interferometric chromatic dispersionmeasurements on short lengths of monomode optical fiber,” Journal of Lightwave Tech-nology, vol. 7, pp. 703–716, 1989.

[26] P.-L. Francois, M. Monerie, C. Vassallo, Y. Durteste, and F. R. Alard, “Three ways to im-plement interferencial techniques: Application to measurements of chromatic dispersion,birefringence, and nonlinear susceptibilities,” Journal of Lightwave Technology, vol. 7,no. 3, pp. 500–513, March 1989.

[27] G. P. Agrawal, Fiber-Optic Communication Systems, 3rd ed. New York USA: John Wiley& Sons, Inc., 2002.

[28] Y. Noh, D. Kim, S. Oh, and U. Pack, “Lasers and electro-optics, 1999. cleo/pacific rim’99. the pacific rim conference on,” vol. 3, 1999, pp. 599–600.

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[29] S. Chang, C.-C. Hsu, T.-H. Huang, W.-C. Chuang, Y.-S. Tsai, J.-Y. Shieh1, and C.-Y.Leung, “Heterodyne interferometric measurement of the thermo-optic coefficient of singlemode fiber,” Chinese Journal of Physics, vol. 38, no. 3, pp. 437–442, June 2000.

[30] D. Gettemy, W. Harker, G. Lindholm, and N. Barnes, “Some optical properties of KTP,LiIO3, and LiNbO3,” Journal of Quantum Electronics, vol. 24, no. 11, pp. 2231–2237,November 1988.

[31] G. Fasching, Werkstoffe fuer die Elektrotechnik, 3rd ed. Vienna Austria: Springer-VerlagWien New York, 1994.

characterization of optical fibers

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comprehensive