Semiconductor lasers are extremely sensitive to optical feedback, which can cause power dropout events (often called low-frequency fluctuations (LFF)) near the solitary laser threshold. In this phenomenon, the laser power suddenly drops to almost zero and then recovers in a stepwise manner to its original power level, only to drop out again at irregular time intervals. Previous attempts to explain the origin of these power dropout events employed either solely deterministic or stochastic models. However, power dropout events occur near the solitary laser threshold, where stochastic fluctuations due to spontaneous emission noise typically have a large influence on the dynamical behavior of a laser. In this paper, we have therefore included both deterministic and stochastic mechanisms in our numerical computations to provide a comprehensive model for the dropout events. We show numerically that in some parameter regimes, spontaneous emission noise qualitatively influences the nature and statistics of the dropouts. Experimental measurements of the mean time between dropout events and its dependence on feedback strength agree well with analytic predictions made by Henry and Kazarinov (1986) based on the assumption that spontaneous emission noise induces these dropout events.
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