Amorphous silicon waveguides for microphotonics

Amorphous silicon a-Si was made by ion irradiation of crystalline silicon with 1x10(15) Xe ions cm(-2) at 77 K in the 1-4 MeV energy range. Thermal relaxation of the amorphous network at 500 degreesC for 1 h leads to an amorphous layer with a refractive index of n=3.73, significantly higher than that of crystalline silicon (n=3.45 at lambda=1.55 mum). a-Si can thus serve as a waveguide core in Si based optical waveguides. Channel waveguides were made by anisotropic etching of a 1.5 mum silicon-on-insulator structure that was partly amorphized. Transmission measurements of these waveguides as function of the amorphous silicon length show that the a-Si part of the waveguides exhibit a modal propagation loss of 70 cm(-1) (0.03 dB mum(-1)) and a bulk propagation loss of 115 cm(-1) (0.05 dB mum(-1)). Losses due to sidewall roughness are estimated, and are negligible compared to the modal loss. (C) 2002 American Institute of Physics.