Measurement and calculation of the critical pulsewidth for gain saturation in semiconductor optical amplifiers

The nonlinear gain response of InGaAsP bulk optical amplifiers under ultrafast optical excitation at 1.53 mu m is investigated. In particular, the dependence of the gain saturation energy on the pulse duration is measured in the range of pulse durations from 150 fs to 11 ps, for different bias currents and lengths of the amplifier. By comparison with a theoretical model, a critical pulsewidth is inferred below which nonlinear carrier dynamics Like carrier heating and spectral hole burning dominate the gain saturation.