Investigation of pulsed coherent injection locking of a mode-locked laser

Pulsed coherent injection locking of a mode-locked laser was investigated. This method combines optically-driven mode-locking with coherent injection locking to produce pulsed light which is both synchronized and optically coherent with an injected signal. A high quality pulse train from a commercial laser was injected into a monolithic mode-locked laser fabricated at the Laboratory for Physical Sciences. A coherent output was achieved when the repetition rate was matched and the longitudinal modes were tuned correctly. Under these conditions we observed a dip in the reflected injecting signal, indicating destructive interference with the monolithic laser output. While this serves as a simple monitor for coherent injection, the coherently locked output spectrum was significantly broader than that of the injected signal and a small change in mode detuning produced a large spectral change. The variations of temporal and spectral characteristics of the monolithic laser were qualitatively explained with a simple theoretical model.