High nonlinear figure-of-merit amorphous silicon waveguides

The nonlinear response of amorphous silicon waveguides is reported and compared to silicon-on-insulator (SOI) samples. The real part of the nonlinear coefficient gamma is measured by four-wave-mixing and the imaginary part of gamma is characterized by measuring the nonlinear loss at different peak powers. The combination of both results yields a two-photon-absorption figure of merit of 4.9, which is more than 7 times higher than for the SOI samples. Time-resolved measurements and simulations confirm the measured nonlinear coefficient $\gamma$ and show the absence of slow free-carrier effects versus ns free-carrier lifetimes in the SOI samples.