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Fabrication of integrated structures for coupling VCSEL to fibre

Fabrication of integrated structures for coupling VCSEL to fibre. Denis Wohlfeld, K.-H. Brenner Chair of Optoelectronics, University of Mannheim. Outline. Motivation: Coupling VCSEL to fibre Negative photoresist SU-8 SU-8 bevelled structures - problems & solutions Results Conclusion.

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Fabrication of integrated structures for coupling VCSEL to fibre

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

  2. Outline • Motivation: Coupling VCSEL to fibre • Negative photoresist SU-8 • SU-8 bevelled structures - problems & solutions • Results • Conclusion

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

  4. Outline Motivation: Coupling VCSEL to fibre Negative photoresist SU-8 SU-8 bevelled structures - problems & solutions Results Conclusion

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

  6. Outline Motivation: Coupling VCSEL to fibre Negative photoresist SU-8 SU-8 bevelled structures - problems & solutions Results Conclusion

  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 1 Bevelled SU-8 structures

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

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

  10. SU-8 bevelled structures - problems & solutions Reflections from index boundaries - our approach • IM1, IM2, IM3 index matching layers • H2O „bath“ to achieve index matching • H2O: n = 1.33, almost neutral to SU-8 • Total transmission: 84.1% Quartz IM1 Mask IM2 SU-8 Substrate IM3 Layer model

  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

  12. SU-8 bevelled structures - problems & solutions Problem: non-planar resist-surface Spin coated (130m) Prebake SU-8 surface 130m - 230m Mask diffraction

  13. SU-8 bevelled structures - problems & solutions Mask z = 0m Diffraction pattern z = 100m Diffraction Calculation - Rayleigh, Sommerfeld 100m

  14. SU-8 bevelled structures - problems & solutions Possible approaches: Polishing Reduction of mask size Mask diffraction

  15. Outline Motivation: Coupling VCSEL to fibre Negative photoresist SU-8 SU-8 bevelled structures - problems & solutions Results Conclusion

  16. Results Standard mask size Reduced mask size Quality of structure - Mask diffraction 150m 150m

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

  18. Results Top view Bottom view Deflection at the mirror

  19. Results Motivation: Coupling VCSEL to fibre Negative photoresist SU-8 SU-8 bevelled structures - problems & solutions Results Conclusion

  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

  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-2004-506078).

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