26 March 1999 Grating couplers using silicon-on-insulator
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Abstract
In integrated optics, grating couplers are used when conventional end-fire methods are cumbersome and less efficient in coupling light in and out of thin-film waveguides. Our aim is to fabricate a high efficiency grating coupler for integrated optics applications at infra-red wavelengths and for thin-film waveguides which can be used for sensor applications. In this paper, theoretical output efficiencies of silicon (Si) rectangular, ideal right-angled blazed and non-ideal trapezoidal gratings are presented. Using perturbation theory, Si rectangular gratings with optimum grating heights exhibit a maximum predicted output efficiency towards the surface at the order of 80% and Si right-angled blazed gratings have predicted efficiencies approaching 100%. The fabrication method consists of using electron beam lithography and reactive ion etching. Ion beam milling is also considered with the aim of creating blazed profiles by tilting the silicon-on-insulator (SOI) wafer. In our work, smart cut SOI Unibond wafers are used as the base material for fabricating the grating couplers as they offer good flexibility in choosing the guiding layer and buried layer thickness'. These waveguides are chosen to have an Si film thickness of 0.92 micrometer and an SiO2 buried layer thickness of 0.67 micrometer in order to use the transverse resonance effect to improve the output coupling efficiency. Si rectangular with various grating heights, designed at the first order of diffraction, were fabricated and characterized. The highest efficiency grating yet reported in SOI was produced, having the coupling efficiency in excess of 70%.
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Martin Tze Wei Ang, Martin Tze Wei Ang, Graham T. Reed, Graham T. Reed, Adrian P. Vonsovici, Adrian P. Vonsovici, Alan G. R. Evans, Alan G. R. Evans, Paul R. Routley, Paul R. Routley, Tony Blackburn, Tony Blackburn, Mike R. Josey, Mike R. Josey, } "Grating couplers using silicon-on-insulator", Proc. SPIE 3620, Integrated Optics Devices III, (26 March 1999); doi: 10.1117/12.343717; https://doi.org/10.1117/12.343717
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