Enhanced optical nonlinearity in amorphous silicon and its application to waveguide devices

We present the first measurements of optical nonlinearity due to free carrier effects in amorphous silicon films using z-scan technique, demonstrating enhanced nonlinearity due to existence of midgap localized states. We also introduce, fabricate and experimentally characterized a new composite waveguide structure consisting of amorphous and crystalline silicon. The fabricated composite rib waveguide confirms to have enhanced free-carrier nonlinearity at the estimated value of 4cm/GW, i.e., seven times larger than that of a crystalline silicon waveguide. Due to existence of the midgap localized states in amorphous silicon, the measured free-carrier lifetime in the composite rib waveguide was about similar to 300ps which is shorter than the values reported in the literature for similar geometries made of silicon. (c) 2008 Optical Society of America.