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 O’Dwyer, 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. overcladding Undercladding Core waveguide SiO2/GeO2 SiO2 Si or SiO2 Consolidation Photolithography and Reactive Ion Etching Flame Hydrolysis Deposition and Consolidation 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. hn e- Objectives: Tx module Parallel connector Silicon Substrate Parallel waveguides Digital input Optical fibre ribbon Coupling optics wires Integrated circuit VCSEL array

7. Cladding Layer Guiding Layer Cladding Layer Silicon Substrate 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. Catalyst 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

9. 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)

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

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

12. 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

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

14. 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

15. UV Hybrid UV-Patternable Sol-Gels Photoinitiator MAPTMS

16. Photolithography Standard Mask-Aligner

17. 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

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

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

20. 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

21. 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. 32.34 mm 35.16 mm 250 mm 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

23. Tx module with connector Connector Waveguidearray Silicon Signal out Signal in Silicon Fibre Ribbon Laser array driving electronics VCSEL array 850 nm Alignment Pin

24. 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 perdevice

26. 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

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

28. Thank you for your attention