Broadband all-optical modulation in hydrogenated-amorphous silicon waveguides

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Abstract
We demonstrate broadband all-optical modulation in low loss hydrogenated-amorphous silicon (a-Si:H) waveguides. Significant modulation (~3 dB) occurs with a device of only 15 µm 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 ∆α = 1.63∙10−16∙∆N cm−1. In addition, we measured the modulation time to be only τc ~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.