Chair of Optoelectronics DGAO Wroclaw 1 Fabrication of integrated structures for coupling VCSEL to fibre Denis Wohlfeld, K.-H. Brenner Chair of Optoelectronics, University of Mannheim

Chair of Optoelectronics DGAO Wroclaw 2 Outline Motivation: Coupling VCSEL to fibre Negative photoresist SU-8 SU-8 bevelled structures - problems & solutions Results Conclusion

Chair of Optoelectronics DGAO Wroclaw 3 Motivation 45° mirror + fibre alignment element Index matching between fibre and mirror (depending on final material) Multimode fibre Ø 125  m VCSEL diameter ~ 30  m Coupling VCSEL to fibre Glass GaAs Chip SU-8 strucutre + fibre Current Top Mirror Laser Cavity Botton Mirror Gain Region Setup for optical couplingVertical Cavity Surface Emitting Laser 10  m

Chair of Optoelectronics DGAO Wroclaw 4 Outline Motivation: Coupling VCSEL to fibre Negative photoresist SU-8 SU-8 bevelled structures - problems & solutions Results Conclusion

Chair of Optoelectronics DGAO Wroclaw 5 SU-8 Negative Photoresist Epoxy based negative photoresist UV-exposure ~365nm- 400nm Refractive index of n = 1.69 Exposure Development Structure SU-8 molecule

Chair of Optoelectronics DGAO Wroclaw 6 Outline Motivation: Coupling VCSEL to fibre Negative photoresist SU-8 SU-8 bevelled structures - problems & solutions Results Conclusion

Chair of Optoelectronics DGAO Wroclaw 7 SU-8 bevelled structures - problems & solutions Limitation of exposure angle due to refraction - problem Angle of bevelled resist-structures limited by refraction ( α < 36° ) SU-8 Exposure Setup 1Bevelled SU-8 structures

Chair of Optoelectronics DGAO Wroclaw 8 SU-8 bevelled structures - problems & solutions Limitation of exposure angle due to refraction - our approach Coupling prism for larger angles Exposure Setup 2

Chair of Optoelectronics DGAO Wroclaw 9 SU-8 bevelled structures - problems & solutions Reflections from index boundaries - problem Total reflection at up to 4 boundaries ( ) Fresnel Equations: Layer model Quartz Air Mask Air SU-8 Air IM3

Chair of Optoelectronics DGAO Wroclaw 10 SU-8 bevelled structures - problems & solutions Reflections from index boundaries - our approach IM1, IM2, IM3 index matching layers H 2 O „bath“ to achieve index matching H 2 O: n = 1.33, almost neutral to SU-8 Total transmission: 84.1% Layer model Quartz IM1 Mask IM2 SU-8 Substrate IM3

Chair of Optoelectronics DGAO Wroclaw 11 SU-8 bevelled structures - problems & solutions Slanted arrangement Flexible angle adjustment Index matching at all layers Reflections from index boundaries - our approach Adjustment screw

Chair of Optoelectronics DGAO Wroclaw 12 SU-8 bevelled structures - problems & solutions Problem: non-planar resist-surface Spin coated (130  m) Prebake SU-8 surface 130  m  m Mask diffraction

Chair of Optoelectronics DGAO Wroclaw 13 SU-8 bevelled structures - problems & solutions Mask z = 0  mDiffraction pattern z = 100  m Diffraction Calculation - Rayleigh, Sommerfeld 100  m

Chair of Optoelectronics DGAO Wroclaw 14 SU-8 bevelled structures - problems & solutions Possible approaches: Polishing Reduction of mask size Mask diffraction

Chair of Optoelectronics DGAO Wroclaw 15 Outline Motivation: Coupling VCSEL to fibre Negative photoresist SU-8 SU-8 bevelled structures - problems & solutions Results Conclusion

Chair of Optoelectronics DGAO Wroclaw  m Quality of structure - Mask diffraction Results Standard mask sizeReduced mask size

Chair of Optoelectronics DGAO Wroclaw 17 Quality of structure - Angle Results Angle 45° ± 1.0° Bevelled SU-8 structure: side view 100  m Mirror element: side view

Chair of Optoelectronics DGAO Wroclaw 18 Deflection at the mirror Results Top viewBottom view

Chair of Optoelectronics DGAO Wroclaw 19 Results Motivation: Coupling VCSEL to fibre Negative photoresist SU-8 SU-8 bevelled structures - problems & solutions Results Conclusion

Chair of Optoelectronics DGAO Wroclaw 20 Conclusion Bevelled SU-8 structures with UV possible Angle 45° ± 1.0° SU-8 structures can be used as masters for injection molding Next step: Final integration chip to fibre

Chair of Optoelectronics DGAO Wroclaw 21 Acknowledgment We acknowledge the support of the European Community- Research Infrastructure Activity under the FP6 "Structuring the European Research Area" programme (HadronPhysics, contract number RII3-CT ).