Stochastic resonance in a bistable ring laser

Stochastic resonance was recently observed in a bistable ring laser. It is a phenomenon in which the response of a bistable system to a periodic modulation is enhanced by the injection of noise along with the modulation. So far, comparisons of the experimental observations with theory have been made only for models that are much simplified compared with the more realistic two-mode equations that describe the ring laser. We report here the results of numerical simulations of the stochastic differential equations for the laser with periodic modulation of the asymmetry between the two modes and injected noise. The simulations reveal the phenomenon of stochastic resonance in a manner closely resembling the experimental observations. The appearance of second-harmonic frequencies in the output power spectrum and the role of the colored nature of the pump laser noise are studied. Finally, we discuss the relation of the recent experimental measurements of hysteresis in a ring dye laser by Gage and Mandel J. Opt. Soc. Am. B (to be published) to the observation of stochastic resonance.