Optical nonlinearities and applications of semiconductors near half the band gap.

Abstract

The nonlinear optical properties of bulk and quantum well semiconductor waveguides were measured as well as their time response near half the band gap. Experiments were performed on different semiconductors including the following bulk semiconductors GaAs, AlGaAs, InGaAlAs, and on GaAs/AlGaAs quantum well samples, to measure the two and three photon absorption, the free carrier cross section, and the nonlinear index of refraction. Also all-optical switching was demonstrated in a nonlinear directional coupler, and for the first time in a nonlinear X-switch. The switching exhibited high throughput, and the switching time is shorter than the 400 femtosecond pulses used in the experiment. A three photon figure of merit including the influence of nonlinear index, waveguide parameters, and three photon absorption was developed for a nonlinear directional coupler. This new figure of merit as well as the other figures of merit developed for all-optical switching are shown to be satisfied in AlGaAs when used below half the band gap.