Nonlinear Optics and Optical Switching in GaLAs and GaAs Near Half Band Gap

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In the last decade the nonlinear optical properties of semiconductors, especially GaAs and A1GaAs have been studied extensively near their bandgap, and have been applied with limited success to all-optical switching. However little is known about the physics and applications of semiconductors near half their gap. Our preliminary results on a nonlinear directional coupler have shown the potential for classical all-optical waveguide switching below half the band gap. Based on this preliminary result, it is proposed to investigate the third order nonlinear properties of bulk and MQW samples of GaAs and A1GaAs near half their band gap, that is to: 1) measure the spectral dependence of both the nonlinearity n2 and two photon absorption coefficient B2, looking for enhancements due to gap states, excitons ets; 2) use the below half band gap nonlinearities to demonstrate all-optical switching devices; 3) investigate spatial soliton propagation, and its potential application to logic devices in A1GaAs; 4) study whether the cascading of second order nonlinearities can lead to large third order nonlinearities.