Gain compression and recovery in semiconductor optical amplifiers

A recently reported theory of gain recovery in semiconductor optical amplifiers (SOAs) is extended to develop approximate expressions for the gain compression and recovery time in terms of probe wavelength, unsaturated gain and device length. These results indicate (1) that the gain recovery time should be approximately inversely proportional to the transmission gain spectrum, and (2) that the wavelength dependence of the gain compression caused by the pump pulse will be dominated by the spectrum of the SOA gain at the probe wavelength. These predictions are tested against pump-probe measurements of gain compression and recovery in a series of four semiconductor optical amplifiers of different lengths but otherwise identical structures. A continuous wave probe beam from a tunable laser is used to measure the wavelength dependence of gain compression and recovery times. Spectral features are used to verify the correlations between these quantities and their dependence on device length.