Dynamical origin of low frequency fluctuations in external cavity semiconductor lasers

Low-frequency fluctuations (LLFS) in semiconductor lasers subject to time-delayed optical feedback from external reflectors have been experimentally observed and theoretically studied for the past two decades. Yet recently a question has come into focus: whether these fluctuations are only a transient phenomenon. This Letter addresses this issue from the viewpoint of deterministic chaotic transitions. In particular, we investigate the single-mode single-delay Lang-Kobayashi equations by constructing a scheme that allows for a detailed bifurcation analysis and, consequently, an understanding of the coexistence of LFFs and stable emission on the maximum gain mode, the latter's being the subject of recent experiments [Phys. Rev. A 60 (1999) 634]. Our computations suggest that LFFs can be either transient or sustained, depending on the dynamical interplay between the maximum gain mode and a chaotic set. (C) 2000 Elsevier Science B.V.