Chirped pulse propagation in saturated traveling wave semiconductor amplifiers

The gain saturation behavior of optical amplifiers is of increasing importance in the operation of many photonic devices. Saturation has been viewed as a phenomenon limiting the performance of traveling wave amplifiers (TWA) and has been studied using models based on very simple carrier density and frequency dependent gain. We are exploring the use of gain saturation in spatially inhomogeneous amplifiers as a means to provide spectral equalization in optical A to D converters and possibly in DWDM systems. In the paper we examine analytically the characteristics of saturated spatially inhomogeneous amplifiers for the A to D converter application. In the application a chirped and equalized pulse is modulated by the signal to be converted and then time stretched by dispersion in a fiber. The signal is spectrally demultiplexed to digitize the signal. In the paper, we analyze TWA performance in the saturated gain regime during chirped pulse propagation. Detailed gain and spontaneous emission functions were derived using first principles. The band structure of the InGaAsP MQW was obtained from the k.p formalism