Waveguides with a bulk semiconductor guide and grating coupler have been designed to operate as all-optical switches as they are easy to grow and to optimize. Investigation of the linear optical properties of a GaAs sample grown on a Bragg mirror has shown discrepancies between its nominal and real parameters. Nonlinear operation of such a non-optimized device exhibits fast and well contrasted switchings but no bistability. Modelling the optical linear and nonlinear properties of the film allows us to describe observations and suggest improvements: observed switchings are mainly due to thermal phenomena, which could be reduced by preserving the nonlinear film quality during the grating etching process, by reducing the incident beam spot-size and by improving the thermal conductivity currently limited by the Bragge reflector. Such an optimized device should be a competitive all-optical switch.
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