Chaotic transitions and low - frequency uctuations in semiconductor lasers withoptical feedback

This paper examines the dynamical origin of low-frequency uctuations in semiconductor lasers subject to time-delayed optical feedback. In particular, we study chaotic transitions in these lasers by numerical integration of Lang-Kobayashi equations for the laser pumped near threshold. In order to classify these transitions we compute bifurcation diagrams in parameter regimes covering a wide range of feedback levels. Numerical computations suggest: (1) at moderate feedback levels, the system evolves around the remains of attractors which are rst created in place of a cascade of external cavity modes and then merged together in a sequence of chaotic transitions; and (2) depending on the feedback strength, the highest gain mode can remain stable and is either unattainable by the system or can be reached after a chaotic transient. These results suggest that low-frequency uctuations in semiconductor lasers can be either transient or sustained. The dynamical mechanism for both transient and sustained LFFs is elucidated.