Impact of input profile, absorption coefficients, and chirp on modulational instability of femtosecond pulses in silicon waveguides under fourth-order dispersion

Abstract

We report the modulational instability (MI) analysis in silicon-on-insulator waveguides under fourth-order dispersion. The two-photon absorption (TPA) generates four symmetric optimum frequencies in the MI gain spectrum. The free-carrier absorption is found to enhance the value of the central MI gain. The chirp amplifies the intensity of the main pulse train peaks, leading to input profile independence. It shifts the occurrence of these peaks at short propagation distances. The absorption coefficients counteract the chirp, creating a pump dependence, and the high values of TPA destroy drastically the spontaneous breakup mechanism, leading to pump depletion.