Stochastic Resonance in an Optical Bistable System

随机共振(SR)是通过在输入相干信号中加入随机噪声来提高输出信噪比的一种协同现象。尽管它看起来很奇怪，但它出现在不同的系统中。考虑到加噪控制信噪比的能力，它有望应用于信号处理，特别是光信号处理中，谐振信号的特性取决于输入噪声的相关时间和强度分布。该系统由LiNbO_3晶体和偏振器组成，其输出电反馈给晶体。该系统具有工作稳定、光频范围宽、光功率低等特点。在实验中，将指数相关的高斯噪声和正弦信号应用到系统中。实验结果表明，噪声相关时间越小，信噪比峰值越大，共振宽度越窄，产生峰值信噪比的噪声强度越小，并利用应用范围较广的SIMPLE模型进行了数值模拟。仿真中使用的方程是具有双稳电势、正弦输入和指数相关高斯噪声的过阻尼系统的朗之万方程。仿真结果与实验结果具有相同的特点。所用方程的应用范围并不局限于本系统，因此本研究结果也适用于其他类型的双稳系统中的SR现象。

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.