23 September 2015 Waveguide-coupling to be used in a micro optical laser gyroscope
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Abstract
A new concept for the realization of a micro optical laser gyroscope was developed. This new concept involves a passive free space ring resonator in which the light is circulating by reflections at three double mirrors and an external light source to activate the resonator. To couple the light in and out of the resonator waveguide-couplers are employed. This paper reports on the simulation of waveguide-coupler structures and on experimental investigation of coupling efficiency using micro fabricated SU-8 coupler structures. The modeled coupler structures consist of two parallel waveguides. The waveguides with rectangular profile are in close proximity i.e. separated only by a narrow gap over a certain path length Waveguide-coupler structures with similar geometries have been micro fabricated and optically characterized. It has been found that as a consequence of the lithographic formation of SU-8 high aspect ratio waveguides residual SU- 8 material remains between the waveguides as the gaps become very small (below 5 μm). In these structures a parasitic connection between the two parallel waveguides could be identified. No coupling effect was observed in the micro fabricated devices with perfect gap separation. From comparison of simulations and experiments we can conclude that there is a coupling mechanism based on the residual SU-8 material bridging the separation gap. Bridging allows coupling light at gaps even larger than 1 μm. Such residual material coupling can be achieved with SU8 lithographic high aspect ratio structuring (height 30 μm x width 50 μm or height 30 μm x width 20 μm) in which sub μm-gaps are almost impossible to produce with standard technologies.
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Ingmar Leber, Thalke Niesel, Andreas Dietzel, "Waveguide-coupling to be used in a micro optical laser gyroscope", Proc. SPIE 9577, Optical Modeling and Performance Predictions VII, 95770O (23 September 2015); doi: 10.1117/12.2189522; https://doi.org/10.1117/12.2189522
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