Intensity dependence of the transparency current in InGaAsP semiconductor optical amplifiers

Summary form only given. Recently there has been considerable interest in ultrafast gain and refractive index nonlinearities in InGaAsP semiconductor amplifiers at wavelengths around 1.5 /spl mu/m. In particular, when an amplifier is biased at transparency such that a pulse propagating through it experiences no net gain or absorption, a large non-linearity having a recovery time of a few picoseconds has been measured. In this paper measurements of the transparency using the pump-probe method were compared to the optoelectronic signal method. Some discrepancies were observed and these are discussed together with the implications of the intensity-dependent transparency current for all-optical switching.