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

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

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...

Introduction Current technology: silica-on-silicon technology expensive steps labour intensive refractive index range limitations Flame Hydrolysis Deposition / Chemical Vapour Deposition Undercladding Flame Hydrolysis Deposition and Consolidation Photolithography and Reactive Ion Etching Core overcladding waveguide Consolidation Si or SiO2 SiO2 SiO2/GeO2

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)

Objectives: Tx module e- Parallel connector Silicon Substrate Parallel waveguides Digital input hn e- Optical fibre ribbon Coupling optics wires Integrated circuit VCSEL array

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 Cladding Layer Silicon Substrate Guiding Layer

Zirconia used for refractive index tuning 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 + R’OH Zirconia used for refractive index tuning Catalyst

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)

Refractive Index Tuning Dn = 0.01 for a 35 % concentration variation TEOS MAPTMS

Refractive Index Tuning Dn = 0.01 for a 6 % concentration variation Zr propoxide

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

Hybrid UV-Patternable Sol-Gels MAPTMS or 3-(methoxysilyl)propyl methacrylate Resulting structure with a non-hydrolysable group as obtained with such precursors

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

Hybrid UV-Patternable Sol-Gels Photoinitiator UV MAPTMS

Photolithography Standard Mask-Aligner

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

Refractive Index Tuning UV-patterning step Parameters: Intensity, Duration, Wavelength Effect of the UV exposure on the refractive index of the guiding layer materials

Waveguide Array Fabrication Rinsing step Picture of ridge waveguides 3D-Map of ridge waveguides Acquisition with Dektak V 200 Si surface profiler

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

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

Optical Testing End view of two waveguides, light injected at the other ends 250 mm 35.16 mm 32.34 mm Optical Loss = 0.79 dB/cm (measured at 840 nm by butt-coupling) Length of waveguides = ~1 cm

Tx module with connector Waveguide array Silicon Signal out Signal in Silicon Fibre Ribbon Laser array driving electronics VCSEL array 850 nm Alignment Pin

Tx module with connector Optical interface sub-module Fibre ribbon polished and metallized facet MT-ferrule VCSELs OE-component sub-assembly

overall transmission rate: 20 Gbit/s per device POI Tx module testing Transmission tested at 2.5 Gbit/s/channel overall transmission rate: 20 Gbit/s per device

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

Acknowledgements 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).

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