Control of nearly degenerate four-wave mixing in a distributed feedback semiconductor laser amplifier via coherent electrical modulation

Synchronous current modulation is investigated theoretically and experimentally as a method for enhancing or suppressing nearly degenerate four-wave mixing in a distributed feedback semiconductor laser amplifier. For modulation depths of 3% an enhancement of 200-300% in phase conjugate signal is observed. Expressions for the current modulation depth required to compensate the optical beat modulation are derived in the saturated and unsaturated case. Also, to enable experimental verification, the average intracavity intensity of the DFB amplifier for given input intensity is calculated. In the unsaturated case the square of the compensating modulation depth is seen to vary linearly with the product of intracavity intensities in accordance with theory