The response of a hybrid bistable optical device to step inputs of light was studied experimentally. The results confirm theoretical predictions concerning the dependence of switching time on the applied light increment. For the first time the phenomenon of ’’critical slowing down’’ is observed directly.
The influence of noise on an optical bistable system in the vicinity of one of the bifurcation points is investigated by studying the transient response to a step input of light. The experiment is performed under absorptive conditions in a sodium-filled nonlinear Fabry-Perot in the bad cavity limit. Alternatively, a bistable electronic circuit (Schmitt trigger) is shown to exhibit the same type of behavior while admitting more detailed studies. On the monostable side of the bifurcation point, we observe a transient bimodality as well as a shift of the average switching delay to shorter times with increasing noise. Both results are in accord with a recent prediction by Broggi and Lugiato. We also present indications that the average switching time is smoothly connected with the lifetime of the metastable state on the bistable side of the bifurcation point.
We analyze the main features of transient bimodality in optically bistable systems. This phenomenon is proved to exhibit a nonmonotonic behavior in its dependence on the noise level, because a decrease of noise first enhances and subsequently damps the transient bimodality. Hence we identify a range of noise levels which characterizes the phenomenon. In this range the most probable switching time exhibits a remarkably linear dependence on the logarithm of the noise parameter. We discuss the dependence of the phenomenon on the distance from the critical point, especially in connection with the experiments on critical slowing down. Our results show a very satisfactory qualitative agreement with the recent experiments on transient bimodality performed by Lange and collaborators. We argue that our picture holds in general for a large class of systems which exhibit the phenomenon of transient bimodality.
The switching dynamics of thermally induced optical bistability in ZnSe nonlinear interference filters is investigated experimentally and theoretically. The device, maintained on its low transmission level by a cw argon laser beam, is switched on its high transmission level by an external light pulse. Either a very fast switching or an important slowing down are obtained when the holding cw intensity or the switching pulse energy are well chosen. This variation of the switching times is analyzed theoretically and observed experimentally.