Switching Experiments with a Mach-Zehnder-type All-Optical Device Based on the Band-Filling Nonlinearity in a GaAs Waveguide and Reduction in Its Relaxation Time

We examine switching characteristics of an all-optical device in Mach-Zehnder configuration, that is based on the band-filling nonlinearity in a GaAs waveguide. Switching waveforms corresponding to π (full switching), 2π, and 2.7π have been obtained and they were compared with theoretical curves. Good agreement has been observed between experimental and theoretical results. The control light pulse energy required for full switching is estimated to be approximately 6 pJ. The switching speed of the above device is limited by the slow relaxation time of photogenerated carriers. In order to reduce the switch-off time determined by the carrier relaxation, we investigated a method which involves application of a DC electric field across the thin core layer of the waveguide in order to sweep photogenerated carriers away from the light-guiding region and effectively reduce the relaxation time. With this technique, the usual switching speed of approximately 1 ns was reduced to approximately 24 ps.