We investigate the influence of noise present in the periodic input signal of a passive optically bistable element. The thermally induced absorption nonlinearity of CdS crystals is used to achieve optically bi- stable behavior. By measuring the signal-to-noise ratio (S/N) of the noisy modulated input signal and of the output signal the phenomenon of stochastic resonance is found: With increasing noise strength the S/N increases up to a maximum value corresponding to the above resonance and then decreases again. The S/N of a noisy input can be enhanced by up to approximately 6 dB with this system. Furthermore, the cases of sinusoidal and rectangular modulation of the bistable element are compared.

• Received 25 October 1993

DOI:https://doi.org/10.1103/PhysRevA.49.2199