Recovery Of Noise-assisted Images In Nonlinear System Via Stochastic Resonance

In nonlinear science field,an important task is to study noise influence on the system output.Generally speaking,noise is often regarded as a negative factor which destroys the system output.However,noise can play a constructive role in regulating the output of nonlinear system under certain circumstances.This phenomenon is called stochastic resonance.In addition,it is well known that one cannot image directly through a nonlinear medium,as intensity-dependent phase changes distort signals as they propagate.Based on the above two problems,first,a photorefractive crystal was used as media for contributing a nonlinear image transmission system.Second,aiming at recovering the transmission image in nonlinear system,the achievements of the previous research of stochastic resonance and the photorefractive effect were introduced.The stochastic resonance effect was studied when the noise intensity and the properties of the photorefractive crystal were changed.In this part the noise-image was recovered.Then,starting from the Helmholtz equation,the perturbation wave equation of beam propagating in photorefractive media was deduced.Finally,to solve the perturbation wave equation the numerical simulation was carried out and compared with experimental results,verifying the occurrence of stochastic resonance in nonlinear systems.The experimental and theoretical results are of organic unification.The main contents of this paper are as follows:The first chapter summarized the research status of stochastic resonance theory.The theory of stochastic resonance and the signal-to-noise ratio were briefly introduced.The research of photorefractive materials was reviewed.The nonlinear optical properties,the physical mechanism of photorefractive effect,the characterization of photorefractive materials and the control principle of translational induction are introduced.The photorefractive properties of lithium niobate crystals were introduced emphatically.The second chapter studied the influence of noise on the linear system output to confirm the negative effect of noise on the image transmission system.The noise intensity of the nonlinear image transmission system was adjusted using the stochastic resonance theory so that the signal was recovered.Finally,changing the photorefractive properties of image transmission medium when the noise intensity is certain,the differences of the output images' quality were studied.The third chapter revised the theory of space charge field based on the experimental research theory,giving the specific expression of the space charge field,deducing the perturbation wave equation of the beam propagating in a given nonlinear medium,laying a foundation for the following numerical simulation.In the fourth chapter the influence of changing noise intensity and the photorefractive performance on the nonlinear system output were investigated by numerical simulation.The results of numerical simulation were coincide with experimental phenomena.The fifth chapter made a summary of the full text work,put forward the innovation point of the research and its future work.