Broadband all-optical modulation in hydrogenated-amorphous silicon waveguides

We demonstrate broadband all-optical modulation in low loss hydrogenated-amorphous silicon (a-Si: H) waveguides. Significant modulation (similar to 3 dB) occurs with a device of only 15 mu m without the need for cavity interference effects in stark contrast to an identical crystalline silicon waveguide. We attribute the enhanced modulation to the significantly larger free-carrier absorption effect of a-Si: H, estimated here to be Delta alpha = 1.63.10(-16).Delta N cm(-1). In addition, we measured the modulation time to be only tau(c) similar to 400 ps, which is comparable to the recombination rate measured in sub-micron crystalline silicon waveguides, illustrating the strong dominance of surface recombination in similar sized (460 nm x 250 nm) a-Si: H waveguides. Consequently, a-Si:H could serve as a high performance platform for backend integrated CMOS photonics. (C) 2010 Optical Society of America