Study On The Technology Of Weak Optical Signal Reconstruction Via Stochastic Resonance

The detection of weak light signal plays an important role in the fields of defense technologies,optical remote sensing,communication and engineering techniques.The existence of noise in the detection process is always regard as a negative and uncontrollable interference,which leads to the decrease of system performance.Filtering noise is an effective method to improve signal quality,however,it is inoperative when the signal frequency band is overlapping with the noise using the traditional technologies.Stochastic resonance is a nonlinear phenomenon that has attracted much attention recently.Broadly speaking,stochastic resonance means that performances of the system,such as the response to periodic signals,can be enhanced by the noise and be made optimal at certain noise levels.This phenomenon is rather counter-intuitive,but the mechanism lies in the complex interplay between nonlinearity and stochasticity.In this thesis,the recovery of light pulse signals lost in noise background via stochastic resonance in all-optic bistable systems is investigated,and the main content are shown as follows:1.The traditional methods of noise signal processing are introduced and its technological developments on the basis of the existent scientific questions.The overview of stochastic resonance and its application on signal enhancement are expound in detail.The unique advantage to deal with noise signal via stochastic resonance are also demonstrated.2.The theoretical basis of stochastic resonance base on bistable system is introduced,containing the output properties of optical bistability and the Langevin equation which is used to describe the nonlinear motion of the particles.The transition properties of the double-well potential with period signal and noise forcing are analyzed.The output characteristic of bistable system is depicted through numerical simulation,which is measured quantitatively by the cross correlation function.3.A theoretical model used to recover weak pulse signal buried in noise via stochastic resonance in silicon-on-insulator(SOI)waveguide resonator is proposed.We analyze the influences of bistable system parameters containing the mirror reflectivity of the resonator and the free-carrier lifetime on the output properties of stochastic resonance by measuring the cross-correlation between the output signals and the input signals.The system performances to detect signals with different power levels and fixed signal-to-noise ratio are also investigated by calculating the cross-correlation gain with variable free-carrier lifetimes.The influence of system parameters on the stochastic resonance is quantitatively analyzed by calculating the cross-correlation coefficient between the input and output signals.4.A novel scheme is proposed to restore weak pulse signals immersed in noise via stochastic resonance based on photothermal effects induced optical bistability in buckled dome microcavity.The bistable properties of dome microcavity are analyzed with different initial detuning wavelengths and effective cavity lengths.A theoretical model is derived to interpret the nonlinear process of pulse signals recovery through double-well potential theory.