1.55 um silicon-based reflection-type waveguide-integrated thermo-optic 2 ×2 switch

In this work a waveguide-integrated 2 ×2 switch operating at the infrared communication wavelength of 1550 nm is proposed and theoretically discussed. The device is based on the total internal reflection (TIR) phenomenon and the thermo-optic effect (TOE) in hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si). It takes advantage of a bandgap-engineered a-Si:H layer to explore the properties of an optical interface between materials showing similar refractive indexes but different thermo-optic coefficients. In particular, thanks to modern plasma-enhanced chemical vapour deposition (PECVD) techniques, the refractive index of the amorphous film can be properly tailored to match that of c-Si at a given temperature. TIR may be therefore achieved at the interface by acting on the temperature. The device is integrated in a 4 m-wide and 3 m-thick single-mode rib waveguide. The substrate is a silicon-oninsulator (SOI) wafer with an oxide thickness of 500 nm. We calculated an output crosstalk always better than 24 dB and insertion losses as low as 3.5 dB.