Statistical distribution of trajectories in the time-intensity plane during semiconductor-laser gain switching

We show that a semiconductor laser switched from below to above threshold by a gradual increase of the optical gain, which follows a stepwise change of the injected current (gain switching), exhibits, besides a random distribution of the turn-on times, peculiar features in the time-intensity evolution. In particular, we find that the switching trajectories in the time-intensity plane cluster under a line at a nonzero angle off the time axis. This new effect can be used to discriminate transient fluctuations due to spontaneous emission against those arising from other effects.