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. 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

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 e- Parallel connector Silicon Substrate
Parallel waveguides
Digital input hn e-
Optical fibre ribbon
Coupling
optics
wires
Integrated circuit
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
Cladding Layer
Silicon Substrate
Guiding Layer

8. 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

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. Hybrid UV-Patternable Sol-Gels
Photoinitiator UV
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. 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

23. Tx module with connector
Waveguide array
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. 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

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. 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-G ).

28. Thank you for your attention