Small-signal IM response of grating-terminated external cavity semiconductor lasers

The small-signal intensity modulation response and the CW noise spectrum of a semiconductor laser coupled to an external cavity are known to be enhanced in narrow peaks centered around the harmonics of the cavity resonance frequency. We have previously shown that each resonance peak of the response exhibits an amplitude discontinuity near the harmonics of cavity resonance frequency. In this paper, we show that each peak of the noise spectrum is bifurcated into a pair of closely spaced peaks of different amplitudes and bandwidths. A comprehensive analytical model is developed to investigate the discontinuity of response peaks and to study the effect of various parameters on their bandwidth and modulation efficiency. It is shown that strong optical feedback, strong gain compression and dc bias above threshold reduce the modulation efficiency but increase the modulation bandwidth