Frequency conversion in external cavity semiconductor lasers exposed to optical injection

We have investigated experimentally and theoretically the phenomenon of frequency conversion in a semiconductor laser subjected simultaneously to delayed feedback and optical injection. We report observations of frequency conversion in the nearly degenerate detuning range, even with the production of a cascade of higher harmonics, through the process of multiwave mixing. We demonstrate that the external feedback exerts a strong influence on the conversion process, by narrowing the linewidth of the converted signal and, mainly, by affecting the conversion efficiency. Maxima in the efficiency occur whenever the frequency of the injected signal fulfils the phase conditions imposed by the external cavity; moreover, the choice of the feedback parameters controls the detuning range within which frequency conversion is allowed.