OPTICAL BISTABILITY IN SEMICONDUCTOR PERIODIC STRUCTURES

We report on a theoretical demonstration of optical bistability in periodic layered media, particularly in long-period GaAs-AlAs superlattices. The proposed structure consists of a periodic multilayer system, as opposed to previously demonstrated nonlinear bistable devices which employed Fabry-Perot etalons. The optical resonance effect which is essential for bistable devices is, in our case, induced by a refractive index modulation. The nonlinear active medium is distributed in the whole structure rather than placed between the two mirrors of a Fabry-Perot cavity. It is shown by a complete calculation of wave propagation in the periodic nonlinear medium that a multiple valued feature appears in the structure's nonlinear reflectivity spectrum. The input/output characteristics of the structure exhibit bistable hysteresis similar to that of a nonlinear Fabry-Perot etalon. Both the reflection and the transmission modes are analyzed. The intensity threshold for bistability is shown to be as low as 9 kW/cm2 for a 30-period GaAs-AlAs superlattice of a thickness of about 4-mu-m. The characteristics of this type of device are discussed and compared to those based on Fabry-Perot etalons.