The spatial dependence of SOA nonlinearities relevant to all-optical switching

Counter-propagating pump-probe measurements in a semiconductor optical amplifier (SOA) are reported. As well as providing information on the device temporal dynamics these also show the signature of spatially localised effects, namely, gain depletion and saturation along the waveguide. In switching configurations with co-propagating control and data pulses, only the control pulse duration dictates the sharpness of the switching window edge. However, counter-propagating schemes exhibit slow switch on/off, due to the device finite length. Since the results in the counter-propagating geometry relate to the shape of the switching window in the mentioned schemes, the measurements reported in this work demonstrate how the systems operation could be optimised by adjusting parameters such as electrical bias and pump pulse energy. This may provide a method of overcoming some of the limitation imposed by device length.