Negligible nonlinear absorption in hydrogenated amorphous silicon at 1.55μm for ultra-fast nonlinear signal processing

Three-photon absorption (3PA) has been observed as the dominant mechanism for nonlinear absorption in wide-bandgap hydrogenated amorphous silicon (a-Si: H-W) at 1.55 mu m. The nonlinear index n(2) and 3PA coefficient were measured to be 22 x 10(-17)m(2)/W and 5.0 x 10(-26) m(3)/W-2 respectively at 1.55 mu m by using the z-scan method. This indicates that the figure of merit (FOM) of this material is intensity dependent. A value FOM>60 is predicted at intensities below 0.5 GW/cm(2) which is the maximum practical intensity for high-bit-rate (>160GB/s) all-optical signal processing. The nonlinear phase change in a-Si: H-W has been compared with other common nonlinear materials (c-Si, As2S3, Ge11.5As24Se64.5) for a 2cm long waveguide with a-Si: H-W showing the greatest potential for integrated devices for all-optical processing with a high nonlinear index and negligible nonlinear absorption at intensities <0.5GW/cm(2). (C) 2014 Optical Society of America