CONTROL OF NEARLY DEGENERATE 4-WAVE-MIXING IN A DISTRIBUTED-FEEDBACK SEMICONDUCTOR-LASER AMPLIFIER VIA COHERENT ELECTRICAL MODULATION

Synchronous current modulation is investigated theoretically and exper imentally as a method for enhancing or suppressing nearly degenerate f our-wave mixing in a distributed feedback semiconductor laser amplifie r. For modulation depths of 3% an enhancement of 200-300% in phase con jugate signal is observed. Expressions for the current modulation dept h required to compensate the optical beat modulation are derived in th e saturated and unsaturated case. Also, to enable experimental verific ation, the average intracavity intensity of the DFB amplifier for give n input intensity is calculated. In the unsaturated case the square of the compensating modulation depth is seen to vary linearly with the p roduct of intracavity intensities in accordance with theory.