Measurement and Calculation of the Critical Pulsewidth for Gain Saturation in Semiconductor Optical Amplifiers

Active semiconductor optical waveguides are essential components in many recently proposed devices for high-speed optical signal processing. It is well known that ultrafast carrier dynamics, like carrier heating and spectral holeburning, lead to gain non-linearities, which restrict the modulation bandwidth of semiconductor lasers. In the case of pulse amplification, these non-linearities lead to a pulsewidth dependence of the gain saturation [1]. A critical pulsewidth can be defined [2], which separates two qualitatively different regimes: a long-pulse regime, where the gain is determined by the pulse energy only, and a short-pulse regime, where the gain also depends on the pulsewidth. Calculated critical pulsewidths are on the order of several picoseconds [1], which is getting in the range of pulses being explored for ultrafast optical signal processing. Experiments that we are aware of. however, do not investigate the detailed dependence of the saturation energy versus pulse duration, and subsequently do not allow extraction of the critical pulsewidth.