National Centre for Sensor Research Planar Optical Integrated Circuits Based on UV-Patternable Sol-Gel Technology Jean-Marc Sabattié, Brian D. MacCraith,

National Centre for Sensor ResearchNational Centre for Sensor Research

Planar Optical Integrated Circuits Planar Optical Integrated Circuits

Based on UV-Patternable Sol-Gel Based on UV-Patternable Sol-Gel

TechnologyTechnology

Jean-Marc Sabattié, Brian D. MacCraith, Karen Mongey,

Jérôme Charmet, Kieran O’Dwyer, School of Physical Sciences, National Centre for Sensor Research, Dublin City University

Mathias Pez, Francois Quentel,Thierry Dean

THALES Research & Technology France


PlanPlan• Introduction

• Objectives

• Sol-Gel Technology

• Materials Preparation

• UV-Patternable Sol-Gel Technology

• Waveguide Fabrication Process

• Parallel Optical Interconnects Assembly


IntroductionIntroduction

• Increase in communications traffic larger capacity networks

• Planar Lightwave Circuits (PLCs) as the future of optical communications:– Passive devices: Parallel Optical

Interconnects (POI), Splitters, Couplers...– Active devices: Variable Optical Amplifiers...


IntroductionIntroduction

Flame Hydrolysis Deposition / Chemical Vapour Deposition

Undercladding

Flame Hydrolysis Deposition

and Consolidation

Photolithography and

Reactive Ion Etching

Core

overcladding

waveguide

ConsolidationSi or SiO2

SiO2

SiO2/GeO2

Current technology:

silica-on-silicon technology– expensive steps– labour intensive– refractive index range limitations


ObjectivesObjectives

• Demonstration of the UV-patternable silica sol-gels technology for the manufacture of PLCs– at room temperature– at low cost

• Example: parallel optical interconnects transmitter chip (POI Tx)


Objectives: Tx moduleObjectives: Tx module

Digital input

Coupling optics

VCSEL array

Optical fibre

ribbon

Parallel waveguides

Parallel connector

Integrated circuit

e- h

wires

Silicon Substrate


Waveguide Structure TargetsWaveguide Structure Targets

8-waveguides array sub-module to be integrated into a transmitter chip

Constraints: – refractive indices are to match silica optical fibre parameters

(refractive index core - refractive index cladding) = 0.02

Cladding Layer

Cladding Layer

Silicon Substrate

Guiding Layer


Sol-Gel TechnologySol-Gel Technology

• Silica/zirconia are made via the sol-gel process from Alkoxide Precursors

Si(OR)4 + 2 H2O SiO2 + ROH

Zr(OR’)4 + 2 H2O ZrO2 + R’OH

Zirconia used for refractive index tuning

Catalyst


Refractive Index TuningRefractive Index Tuning

• Precursors for Cladding and Guiding Layers:– Tetrathyl orthosilicate (TEOS)– 3-(methoxysilyl)propyl methacrylate (MAPTMS)– Zirconium Propoxide

– Irgacure 1800 (photoinitiator)

– Methacrylic acid (complexing agent for Zr propoxide)



50 60 70 80 90 100

1.478

1.480

1.482

1.484

1.486

1.488

1.490

1.492

1.494

MAPTMS content (% of total SiO2)

Re

fra

ctiv

e I

nd

ex

OEt

SiEtO

OEt

OEt

CH3

O

O

Si

H

H

OMe

OMe OMe

TEOS

MAPTMS

n = 0.01 for a 35 % concentration variation



Zr

(C3H7)OOC3H7

OC3H7

OC3H7

Zr propoxide

2 4 6 8 101.470

1.475

1.480

1.485

1.490

1.495

Zirconium content (% of SiO2)

Re

fra

ctiv

e i

nd

ex

n = 0.01 for a 6 % concentration variation



Cladding and guiding materials preparation:– Same amount of TEOS and MAPTMS in both

materials• to promote adhesion between layers• to obtain materials with similar thermal expansion

coefficients

– Refractive index difference (n) tuned by adjusting the Zirconium content


Hybrid UV-Patternable Sol-GelsHybrid UV-Patternable Sol-Gels

MAPTMS or

3-(methoxysilyl)propyl methacrylate

Resulting structure with a non-hydrolysable group

as obtained with such precursors

CH3

O

O

Si

H

H

OMe

OMe OMe

Si

O

O

O

R Si

O

O

O

SiR O

O

R

Zr

Si

O

RO

O

O

O



Aim: to create an organic network in parallel to the inorganic silica network by radical polymerisation

Si

O

O

O

SiR O

O

R

Zr

Si

O

RO

O

O

O

non soluble in a wide range of

solvents



O

OH

O

.OH .

UV

.CH3

O

O

Si(OCH3)3

H

CH3

O

O

Si(OCH3)3

CH2

Photoinitiator

MAPTMS

CH2

CH3

O

O

Si(OCH3)3O

.


PhotolithographyPhotolithography

Standard Mask-Aligner


Waveguide Preparation ProcessWaveguide Preparation Process

Spin-Coating cladding layer

Thermal treatment

Spin-Coating guiding layer

UV-patterning

Solvent wash

Thermal treatment

Spin-Coating cladding layer

Thermal treatment

Dicing Waveguides

Polishing facets

Optical testing



• UV-patterning step– Parameters: Intensity, Duration, Wavelength

0 10 20 30 40 50 60 70 800.000

0.001

0.002

0.003

0.004

0.005

0.006

at max 375 nm, 320 - 400 nm,

10 mWatt cm-2

Ref

ract

ive

index

incr

ease

UV exposure (min)

Effect of the UV exposure on the

refractive index of the guiding layer materials


Waveguide Array FabricationWaveguide Array Fabrication

• Rinsing step

Picture of ridge waveguides 3D-Map of ridge waveguides

Acquisition with Dektak V 200 Si surface profiler


Waveguide structuresWaveguide structures

• Characterisation of the waveguides

Cross-section picture of a waveguideRidge profile of a ridge waveguide

Acquisition with Dektak V 200 Si surface profiler

Acquisition with optical microscope


Waveguide Array Fabrication Waveguide Array Fabrication ConclusionsConclusions

• Compromise between – Refractive Index changes from

• Precursors • UV-patterning• Thermal treatments

– Hardness (for dicing, polishing)– Temperature resistance (for electronics

bonding)


Optical TestingOptical Testing

Optical Loss = 0.79 dB/cm(measured at 840 nm by butt-coupling)

Length of waveguides = ~1 cm

End view of two waveguides, light injected at the other ends

250 m

35.16 m32.34 m


Tx module with connectorTx module with connector

VCSEL array850 nm

Fibre Ribbon

ConnectorWaveguide array

Alignment Pin

Signal in

Laser array driving electronics

Silicon

Silicon

Signal out


Tx module with connectorTx module with connector

VCSELs

polished and metallized

facet

OE-component sub-assembly

Optical interface sub-module

MT-ferrule

Fibre ribbon


POI Tx module testingPOI Tx module testing

Transmission tested at 2.5 Gbit/s/channel

overall transmission rate: 20 Gbit/s per device


ConclusionsConclusions

• Parallel Optical Interconnect demonstrator

• UV-patternable sol-gel materials technology for PLC

applications demonstrated

• Tunability of the materials for various applications

(patterns, refractive index)

• Compatibility with electronics industry methods


AcknowledgementsAcknowledgements• Brian D. MacCraith,• Karen Mongey,• Jérôme Charmet,• Kieran O’Dwyer

NCSR / School of Physical Sciences,

Dublin City University

Ireland

• Mathias Pez,

• Francois Quentel,

• Thierry Dean

THALES Research & Technology France,

Domaine de Corbeville,

France

European Commission Brite-Euram Programme (Project number: BRPR-G98-0777).


Thank you for your attention

Documents

National Centre for Sensor Research Planar Optical Integrated Circuits Based on UV-Patternable Sol-Gel Technology Jean-Marc Sabattié, Brian D. MacCraith,