Planar Optical Integrated Circuits Based on UV-Patternable Sol-Gel Technology

1
Planar Optical Integrated Circuits Based on
UV-Patternable Sol-Gel Technology

• Jean-Marc Sabattié, Brian D. MacCraith, Karen
  Mongey,
• Jérôme Charmet, Kieran ODwyer,
• School of Physical Sciences, National Centre for
  Sensor Research, Dublin City University
• Mathias Pez, Francois Quentel,Thierry Dean
• THALES Research Technology France

2
Plan

• Introduction
• Objectives
• Sol-Gel Technology
• Materials Preparation
• UV-Patternable Sol-Gel Technology
• Waveguide Fabrication Process
• Parallel Optical Interconnects Assembly

3
Introduction

• 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...

4
Introduction

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

Flame Hydrolysis Deposition / Chemical Vapour
Deposition
5
Objectives

• 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)

6
Objectives Tx module
Parallel connector
Silicon Substrate
Parallel waveguides
Digital input
Optical fibre ribbon
Coupling optics
Integrated circuit
wires
VCSEL array
7
Waveguide Structure Targets

• 8-waveguides array sub-module to be integrated
  into a transmitter chip
• Constraints
• refractive indices are to match silica optical
  fibre parameters
• ? D (refractive index core - refractive index
  cladding) 0.02

8
Sol-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 ROH
• Zirconia used for refractive index tuning

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Refractive 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)

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Refractive Index Tuning
Dn 0.01 for a 35 concentration variation
TEOS
MAPTMS
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Refractive Index Tuning
Dn 0.01 for a 6 concentration variation
Zr propoxide
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Refractive Index Tuning

• 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 (Dn) tuned by
  adjusting the Zirconium content

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Hybrid UV-Patternable Sol-Gels

• MAPTMS or
• 3-(methoxysilyl)propyl methacrylate
• Resulting structure with a non-hydrolysable group
• as obtained with such precursors

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Hybrid UV-Patternable Sol-Gels

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

non soluble in a wide range of solvents
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Hybrid UV-Patternable Sol-Gels
Photoinitiator
MAPTMS
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Photolithography

• Standard Mask-Aligner

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Waveguide Preparation Process
Spin-Coating cladding layer
Spin-Coating cladding layer
Thermal treatment
Thermal treatment
Spin-Coating guiding layer
Dicing Waveguides
UV-patterning
Polishing facets
Solvent wash
Optical testing
Thermal treatment
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Refractive Index Tuning

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

Effect of the UV exposure on the refractive index
of the guiding layer materials
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Waveguide Array Fabrication

• Rinsing step

Picture of ridge waveguides
3D-Map of ridge waveguides
Acquisition with Dektak V 200 Si surface profiler
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Waveguide structures

• Characterisation of the waveguides

Ridge profile of a ridge waveguide
Cross-section picture of a waveguide
Acquisition with Dektak V 200 Si surface profiler
Acquisition with optical microscope
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Waveguide Array Fabrication Conclusions

• Compromise between
• Refractive Index changes from
• Precursors
• UV-patterning
• Thermal treatments
• Hardness (for dicing, polishing)
• Temperature resistance (for electronics bonding)

22
Optical Testing
End view of two waveguides, light injected at the
other ends
Optical Loss 0.79 dB/cm (measured at 840 nm by
butt-coupling) Length of waveguides 1 cm
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Tx module with connector
Connector
Waveguide array
Silicon
Signal out
Signal in
Silicon
Fibre Ribbon
Laser array driving electronics
VCSEL array 850 nm
Alignment Pin
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Tx module with connector
Optical interface sub-module
Fibre ribbon
polished and metallized facet
MT-ferrule
VCSELs
OE-component sub-assembly
25
POI Tx module testing

• Transmission tested at 2.5 Gbit/s/channel

overall transmission rate 20 Gbit/s per device
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Conclusions

• 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

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Acknowledgements

• Brian D. MacCraith,
• Karen Mongey,
• Jérôme Charmet,
• Kieran ODwyer
• 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).
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• Thank you for your attention