Slow dynamics in semiconductor multi-longitudinal-mode laser transients governed by a master mode

Abstract

We examine the response to the sudden switch of the pump parameter in a multimode semiconductor laser with intensity coupling on a model whose validity has been successfully compared to experimental results. We find the existence of a very slow modal evolution governed by a master mode, which reaches its steady state on a time scale that is a couple of orders of magnitude longer than that of the total intensity. The practical consequences for applications are examined, such as the temporal evolution of the spectral width of the laser emission and the time at which its steady state is attained. Issues related to modeling choices, such as the number of modes and their placement with respect to line center, are discussed.

Fast dynamics and spectral properties of a multilongitudinal-mode semiconductor laser: evolution of an ensemble of driven, globally coupled nonlinear modes

“…This regime, which displays the characteristic damped oscillations both in the carrier number and in the total intensity, connects the belowthreshold dynamics with the slow modal one previously reported [19]. In particular, its final state -corresponding to the disappearance of oscillations in the carrier density and in the total laser intensity -is responsible for the ensuing, hidden modal dynamics [19]. The paper concludes with the analysis of the characteristics of the frequency spectrum emitted by the laser during the fast transient (Section IV).…”

“…This detailed analysis paves the way for the central point of the paper: the analysis of the strongly coupled (multimode) transient in the oscillatory regime (Section III C). This regime, which displays the characteristic damped oscillations both in the carrier number and in the total intensity, connects the belowthreshold dynamics with the slow modal one previously reported [19]. In particular, its final state -corresponding to the disappearance of oscillations in the carrier density and in the total laser intensity -is responsible for the ensuing, hidden modal dynamics [19].…”

“…The results are non-trivial and show the existence of multiple time scales and of collective dynamics which contribute to a fast evolution (studied in this paper), which precedes the slow, hidden dynamics already presented elsewhere [19]. The discussion is entirely cast in terms of laser physics, but, making abstraction from the direct physical meaning of the variables -i.e., identifying the carrier number as a global coupling field and the laser modes as oscillators nonlinearly coupled to that (mean) field -, the results can be transposed to a generic dynamical system consisting of a large number of oscillators each individually coupled to a global field.…”

“…For these latter devices, we have recently shown [19] that a realistic model for a multimode semiconductor laser, with experimentally matched parameters [17], predicts a slow, hidden dynamical mode-evolution governed by a master mode. An overall agreement exists between our recent predictions and a wealth of experimental data (e.g.…”

“…In this paper, we analyze the deterministic dynamics of the multimode laser transient and determine the modal intensity distribution at the end of the fast transient starting from a below-threshold condition and leading into the slow dynamics [19] with the characteristic oscillations of a Class-B laser [23]. The apparent equilibrium solution, taking place at the end of the fast transient, in reality amounts to an inherent out-of-equilibrium one, when analyzed in terms of modal intensity distribution.…”