Stochastic Resonance in an Optical Bistable System

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Stochastic resonance (SR) is a cooperative phenomenon that the output signal-to-noise ratio (SNR) is enhanced by adding random noise to the input coherent signal. In spite of its strange appearance, it occurs in various systems. In view of the ability of controlling SNR by adding noise, it is expected to be applied to signal processing, especially to optical signal processing.The characteristics of the resonance signal depends on the correlation time and the intensity distribution of the input noise.In the present study, SR experiments in an optical bistable system were performed. The system is composed of a LiNbO_3 crystal and a polarizer, and its output is fed back to the crystal electrically. The system has features of stable operation and working in wide optical frequency range and with low optical power. In the experiment, exponentially correlated Gaussian noise and a sinusoidal signal are applied to the system. The experimental results show that, with smaller noise correlation time, the peak value of the SNR is larger, the width of the resonance is narrower, and the noise intensity which gives the peak SNR is smaller.Numerical simulations were also performed using simple model which has wide application field. The equation used in the simuilation is a Langevin equation for an overdamped system which has a bistable potential, a sinusoidal input, and the exponentially correlated Gaussian noise. The simulation results have the same characteristics with those of the experiments. The application field of the used equation is not limited to the present system, so that the results of the present study can also be applied to SR phenomena in other types of bistable systems.