Abstract
We have previously reported all-optical switching of picosecond pulses in a zero-gap directional coupler containing GaAs quantum wells.1 The intensity dependent refractive index causing the switch originates from the effect of photo-generated carriers on the position of the absorption edge and the screening of the excitons. The dynamics of the free carriers generated by the laser pulses that induce the switching therefore determine the speed of response. Since the generation of carriers is instantaneous, the rise time of the switch is of the order of the laser pulse width. However, the recovery time is dependent on the speed at which the carriers are relaxed usually by recombination between electrons and holes. In an earlier experiment,1 we measured the recovery time of a zero-gap directional coupler containing a single quantum well to be 1ns which indicated that lateral diffusion of the carriers was also contributing to the switch response. In this work we shall demonstrate the reduction in recovery time that is achieved by the application of an external reverse bias to sweep out the photo-generated carriers.
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