Research On Effects Of Noise In A Laser And Optical Bistable Systems

Recently, with the new discovery of various noise induced phase transition phenomena in different subject,more and more people come to realize the important role of noise. In the nonlinear conditions, random fluctuation can decide the evolution of the system, and even cause the system macroscopic phase transition. This dissertation mainly studies the noise effects in single-mode laser and optical bistable system, the main research achievements are as follows:(1) The physical essence of the phenomenon of stochastic resonance (SR) in single mode laser is investigated from the points of the type of input signal and the way of coupling for signal and noise. First, the output signal-to-noise ratio (SNR) of single-mode laser system with square wave signal input is calculated. It is found that the adjustment of the duty cycle of square wave signal and the noise correlation coefficient can significantly affect the resonance and suppression of the system. Only when the noise correlation coefficient is less than zero, the system will appear the phenomenon of SR. The curve of SNR versus signal period increases monotonously. The SNR of the system is increased with the increase of duty cycle. When the duty cycle of square wave signal is the maximum value of1, the square wave periodic signal falls back into a continuous periodic signal, that is, a continuous periodic signal is just a special case of the model of this paper, and the model of this paper has wider significance. At the same time, the phenomena of stochastic resonance of the noise and signal in different coupling mode are also studied. It is found that, only when the external noise is modulated by pulse period signal, the curve of the output SNR of the system with the signal period can exhibit resonance and suppression coexisting phenomenon, namely the SR in a broad sense.(2) The effects of a new correlation style:the cross-correlation between the real part and imaginary part of pump noise on the statistical properties and the characteristics of laser dynamics are studied. A new laser amplitude equation which contains the correlation coefficient between the real part and imaginary part of pump noise is founded. The correlation coefficient affects the steady state, the transient state and dynamical characteristic of laser significantly. The curves of various type for single-mode laser are showing a quasi "repeate phase transformation" phenomena with the increasing of the correlation coefficient. When the correlation coefficient equals to0.707, the output power is at is maximum, but the fluctuation of laser is also at its maximum. Stochastic multiresonance appears in the curve of SNR as a function of correlation coefficient between the real and imaginary parts of the pump noise. The phase locked of laser is induced by the cross-correlation between the real and imaginary parts of quantum noise. However, the change of phase locked arises from the cross-correlation between the real and imaginary parts of pump noise or quantum noise.(3) The noise effects in optical bistable system are investigated from two aspects: the correlation intensity between multiplicative and additive moises and self-correlation time of multiplicative noise, respectively. It was found that the area of optical bistability with positive correlation between noises expands in comparison with the deterministic case, and a significant decreasing of the bistable threshold. When the cooperativity parameter C approaches zero, noise still can induce optical bistability. Increasing the self-correlation time of multiplicative noise can evidently expends the area of optical bistability in the case of positive correlation between noises.However, the self-correlation time of multiplicative noise has little effect in optical bistability in the case of negative correlation between noises.