ANALYSIS OF ORIGIN OF NONLINEAR GAIN IN 1.5 MU-M SEMICONDUCTOR ACTIVELAYERS BY HIGHLY NONDEGENERATE 4-WAVE-MIXING

The origin of the nonlinear gain effect in 1.5 mu m semiconductor acti ve layers is investigated by using highly nondegenerate four-wave mixi ng, where the pump-probe detuning is extended up to 2 THz. From the si gnal intensity measured as a function of the detuning frequency we fin d that both the spectral hole burning and the dynamic carrier heating contribute to the four-wave mixing. The dynamic carrier heating, howev er, creates the index grating rather than the gain grating, and hence, the spectral hole burning is the main origin of the nonlinear gain ef fect.