POLARIZATION-DEPENDENT OPTICAL NONLINEARITIES OF MULTI-QUANTUM-WELL LASER-AMPLIFIERS STUDIED BY 4-WAVE-MIXING

We present a detailed study of the polarization properties of four-wav e mixing in multiquantum-well (MQW) semiconductor optical amplifiers ( SOA's). In particular, the polarization selection rules relevant to al l processes contributing to the generation of the four-wave mixing sig nal are rigorously derived and discussed. We then show the importance of these results in applications where four-wave mixing is used as a s pectroscopic tool to study the optical nonlinearities of semiconductor gain media. For illustration, we demonstrate two novel applications o f polarization-resolved four-wave mixing. The first is a new technique for measuring the recombination lifetime in SOA's, based on mixing of a pump wave with polarized amplified spontaneous emission noise. In t he second, we use the same polarization selection rules to measure the interwell transport lifetime in alternating-strain MQW amplifiers. Fi nally, we also discuss the possibility of studying the dynamics of the optically induced phase coherence between spin-degenerate states.