Optical feedback on self-pulsating semiconductor lasers

Weak optical-feedback effects on the statistical properties of self-pulsations in narrow-stripe semiconductor lasers are analyzed using Lang-Kobayashi-type equations. The self-pulsation features are compared with the characteristics of excited relaxation oscillations. We determine the operating regime in which the randomizing effect of spontaneous-emission noise destroys pulse coherence. In this regime, only phase-insensitive effects of optical feedback are possible, and optimum jitter reduction is achieved with delay times of the order of an integer-odd multiple of the free-running pulsation period. In the high-pump operating regime, interpulse coherence is retained and the optical-feedback phase is shown to be instrumental for pulse-jitter control. Our results show that for cavity lengths up to 10 cm, variations on the order of half an optical wavelength induce jitter variations of one order of magnitude.