Nano- and Micro-Optics on integrated circuit boards

Ray T. ChenCHEN@ECE.UTEXAS.EDU

WWW.MRC.UTEXAS.EDU/CHEN.HTML

Nanophotonics and Optical Interconnects LabElectrical and Computer Engineering

The University of TexasAustin, TX 78758

Typical Metro DWDM Link

Current individual optical components are too costly, bulky and add to system design

complexities.

Lasers

Amplifiers Amplifiers

Switches

Receivers

Switch

VOA’sMUX

DeMUXMUX

DeMUX VOA’s VOA’s

Chip Based MUX w/ VOA

Chip Based DeMUX w/ VOA

Amplifiers Amplifiers

Add Drop

Receivers

Chip Based ROADM

Lasers

Add Drop

Multi functional OIC’s reduce cost and greatly simplify system

design.

Introduction:Projection of Bandwidth

�Optical backplane

�Optical PC Board

�Passive Waveguide Components

Potential Markets for UT’s IP Portfolio

Components

�Active Optical Components

�Optical Biosensor

Source IBM

Materials for Guided Wave Optics

Feature\Material Polymer III-V Compound LiNbO3 SiO2/Si

Loss at 1.55 µµµµm 0.1dB/cm ~0.5dB/cm 0.1dB/cm 0.1dB/cm

EO Effect Better medium Good Almost None

Volume Hologram

& Moldability Yes No No No

Interconnect Size unlimited ~10 inches ~6 inches 12 inchesInterconnect Size unlimited ~10 inches ~6 inches 12 inches

Substrate Any III-V Compound LiNbO3 Si

∆∆∆∆n/∆∆∆∆T Large Small Small Small

Amplifier Yes Yes Yes Yes

Tg for Si CMOS ? good good good

Reliability ? Highest High MediumCost Lowest Highest High Medium

: Advantage :Disadvantage :Neutral

Fully Embedded Board Level Fully Embedded Board Level Optical InterconnectionOptical Interconnection

Cu Trace

� Unique Architecture for Optical PWB (Printed Writing Board)

; All the optical components are interposed inside the PCB

Solve the package problem / Reduce Cost Effects

Micro-via

45° micro-mirror

VCSEL array

Optical PCB

1x12 PIN

Photodiode

12-channel Polymer

Waveguide [109 cm ]

1x12 VCSEL

R. T. Chen, et al, Invited Paper to

Proc. IEEE 88, 780 (2000).

Lamination of Optical Waveguide FilmLamination of Optical Waveguide Film& Integration of Thin Film VCSEL& Integration of Thin Film VCSEL

� 12-Channel Polymer Waveguide

& 45o Micro-Mirror

Optical Layer (~170 µm)

PSA (Pressure Sensitive Adhesive) Film

(100 / 200 µm)

250µm

� Cross Section View

of Laminated Optical Layer

2 mm

PCB Substrate

� Cu Transmission Lines for VCSEL (or PD) Integration

PCB Sub

PCB Sub

Cu Trans. Lines

(thickness = ~ 10 µm)

PSA film

Optical layer

VCSEL

Optical Layer

Optical Layer

VCSEL

Bottom Emitting VCSEL

Top Emitting VCSEL

- PSA (Pressure Sensitive Adhesive) Film : 100 / 200 µm

- Optical Waveguide Film Layer = ~ 170 µm

via

Optical Signal Distribution in a Network CardOptical Signal Distribution in a Network Card

Substrate Removed 1 X 12 GaAs VCSEL Array

� Flatten Optical Layer to Facilitate Embedded Structure

� ~ 10 µµµµm Thickness VCSEL Formation

- Mechanical Lapping : ~ 50 µµµµm

- Chemical Wet-etching (Citric Acid : H2O2 ) : ~ 10 µµµµm

X 50 X 50

200µm

~ 10 µm

Original VCSEL

on GaAs Substrate

Substrate Removed

VCSEL (~ 10 µm)

GaAs Sub

X 50 X 50

Integration of VCSEL and PIN Photodiode with Optical Waveguide Film

� Photolithography UV-Aligner

� UV-Curable Adhesive

1x12 VCSEL 1 x 12 PIN

Photodiode12-channel Polymer

Waveguide [109 cm ]

Speed Measurement of Substrate Removed 850 nm Wavelength VCSEL

� Eye-diagram � BER/Q-factor/Jitter RMS[ Vbias = 2.0 V / Ibias = 5.0 mA ]

25

30

-log[BER] / Q-factor / Jitter RMS

Q-factor

Vbias = 2.0 V

Ibias = 5.0 mA

Ampl = 0.5 V

Offs = 0 V

Freq.= 10 Gb

NRZ mode

PRBS = 231-1

Jitter RMS = 4.6 ps

Q-factor = 5.18

Eye width = 71.7 ps

2 4 6 8 10 120

5

10

15

20

25

-log[BER] / Q-factor / Jitter RMS

Frequency [GHz]

Q-factor

-log[BER]

Jitter RMS

1xN Beam Splitter for Fiber to the Home

(FTTH) applications using PON

Polyimide Based 1-to-48 Fanout H-tree

Optical Waveguide on Si-Substrate

(c) (d)

Optical Bandwidth Measurement of

the 51 cm Long Waveguide

The 3-dB optical bandwidth is determined to be 150GHz for the 51cm long waveguide

Schematic of Fully Embedded External Modulator

Using %anophotonic Devices

Photonic Crystal WG ModulatorVias

Photonic Crystal Laser Beam Router

CW Laser DiodeDriving Electrode

Photonic crystal structure in nature

Opal, the best known periodical

structure in nature.

• In-plane structure: Photonic crystal waveguide

• High dispersion enhances modulation efficiency,

Fully-Embedded Silicon Thin Film Nano-

Photonic Crystal Waveguide Modulator

• High dispersion enhances modulation efficiency, up to 100 times

Conventional

Mach-Zehnder

Modulator

Proposed Si PCW

Modulator

Improvement

Factor

Size ~ 4mm ~ 40 um 100 X reduction

Key Performance Improvement

Size ~ 4mm ~ 40 um 100 X reduction

Power

consumption ~ 0.3 W ~ 0.01 W

10X to100X

reduction

Integration No integration

potential

Potential for high

density integration N/A

* Conventional Mach-Zehnder modulator performance represents typical specifications.

2-D Image 3-D Image

High smoothness,

exact round shape

JEOL JBX-6000FS/E E-Beam Nano-Lithography

SEM Micrographs & Key Facilities

Rough

sidewall

without

post-

etching

oxidation

Focus Ion Beam (FIB)

nano-polished endface

FEI Strata DB235

Dual Beam SEM/FIB

Nano-characterization System

Plama-Therm 790 Si

and SiO2 Reactive

Ion Etching (RIE)

PCW

100µm

PCW

100µmair-trenches

Photonic Crystal MZI Modulator

Micrographs of Mach-Zehnder(MZ)

modulator: electrodes, pads, and

photonic crystal waveguides (in

lighter color)

Y-junction of the MZ modulator, the rib

waveguide splits as it extends up. Two 4µm

wide air-trenches (etched through the entire

upper silicon layer) separate the rib

waveguides from the surrounding silicon.

electrodeselectrodes

Electrode

Electro-padElectrodes

PCW

Rib waveguide

Photonic Crystal MZI Modulator

- more SEM micrographs

ElectrodeElectro-pad

-80 -60 -40 -20 0 20 40 60 80-6

-4

-2

0

2

4

6

Cu

rren

t (m

A)

Voltage (V)

Switching characteristics : Modulation traces

1 Gbit/sec

Operating wavelength: λ =1541 nm

Applied voltage: Von = 2 V, Voff = -1 Vλ = 1541 nm and Iπ = 7.1 mA

Modulation depth = 92 %

22

Two dimensional design – compact mode splitter

• Essentially randomly add and/or subtract cylinders within a region to try to get desired function, iteratively

• Successfully designed

Multimode inputSingle mode

outputs

23

• Successfully designed possibly smallest mode splitter ever designed

� After ~10000 search steps (48 hours on a Pentium III computer)

� Negligible intuition to how can we know how good we could make it?

Engineer precise mode splitting with

positioning of dielectric columns

Simulation of The Final Structure

)1,0,0(2

0 −=λ

πG )239.1914,-0.9-0.3314,-0(

21

λ

π=G )391914,-0.920.3314,-0.(

22

λ

π=G )0.92390,0.3827,-(

23

λ

π=GThe individual beam

iiietrGiErrv

*)exp(* ω−• )0 , ,0 1(0 =e )7055,-0.3380.9409,0.0(1 =e )70055,0.3380.9409,-0.(2 =e )0,0,1(3 =e

24

Simulation of the final structure without

considering the absorption during the

holography process.

Simulation of the final structure considering

the absorption during the holography

process. The lower portion receives less

dosage

(111) in-plane and perpendicular lattice spacing for the FCC-type photonic crystal

are 0.63 and 2.10µm for SU8

Fabricated devices

25

(a) The cleaved 3D photonic crystal on SU8. The upper-left corner inset shows the

cm2 size photonic crystal. The lower-right corner inset shows the FCC-type (111)

diffraction pattern. (b) SEM image of the (111) plane structure of AZ 4620.

The lower-right corner inset shows the FCC-type (111) diffraction pattern.

Bandgap Measurement for SU8 based structure Using FTIR

26

Bandgap in [111] direction for C-band and

S-band.

Match of the simulated gap and the

measured gap.