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Communications in Theoretical Physics

Influence of Signal and Noise on Statistical Fluctuation of Single-Mode Laser System

Dahai Xu, Cheng Qing-Hua, Cao Li, Wu Da-Jin

Published Nov 1, 2006• 1 citation
Publisher

Abstract

On the basis of calculating the steady-state mean normalized intensity fluctuation of a signal-mode laser system driven by both colored pump noise with signal modulation and the quantum noise with cross-correlation between its real and imaginary parts, we analyze the influence of modulation signal, noise, and its correlation form on the statistical fluctuation of the laser system. We have found that when the amplitude of modulation signal weakens and its frequency quickens, the statistical fluctuation will reduce rapidly. The statistical fluctuation of the laser system can be restrained by reducing the intensity of pump noise and quantum noise. Moreover, with prolonging of colored cross-correlation time, the statistical fluctuation of laser system experiences a repeated changing process, that is, from decreasing to augmenting, then to decreasing, and finally to augmenting again. With the decreasing of the value of cross-correlation coefficient, the statistical fluctuation will decrease too. When the cross-correlation form between the real part and imaginary part of quantum noise is zero correlation, the statistical fluctuation of laser system has a minimum. Compared with the influence of intensity of pump noise, the influence of intensity of quantum noise on the statistical fluctuation is smaller.

DOI
10.1088/0253-6102/46/5/023

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Using the linear approximation method,we have studied the time vevolution of intensity correlation function C(t) in a single-mode laser driven by the colored pump noise with signal modulation and the quantum noise with cross-correlation between the real and imaginary parts.When pump noise self-correlation time τ changes,we have found that,the time evolution of the C(t) will exhibit various change forms:that is,monotonous descending;monotonous rise;the appearance of a maximum;periodically surging with descending envelope.Furthermore,when the τ is a certain value,the value of the C(t) will lessen with the between the real and imaginary parts of quantum noise correlative increases,but when quantum noise intensity Q increases,the value will increase,and when pump noise intensity P increases,the descending of the C(t) with time has been delayed.
Using the linear approximation method, we have studied how the correlation function C ( t ) of the laser intensity changes with time in the loss-noise model of the single-mode laser driven by the colored pump noise with signal modulation and the quantum noise with cross-correlation between the real and imaginary parts. We have found that when the pump noise self-correlation time τ changes, (i) in the case of τ ≪ 1, the C ( t ) vs. t curve experiences a changing process from the monotonous descending to monotonous rise, and finally to the appearance of a maximum; (ii) in the case of τ≫ 1, the curve only exhibits periodically surging with descending envelope. When τ ≪ 1 and τ does not change, with the increase of the pump noise intensity P , the curve experiences a repeated changing process, that is, from the monotonous descending to the appearance of a maximum, then to monotonous rise, and finally to the appearance of a maximum again. With the increase of the quantum noise intensity Q , the curve experiences a changing process from the monotonous rise to the appearance of a maximum, and finally to the monotonous descending. The increase of the quantum noise with cross-correlation between the real and imaginary parts will lead to the fall of the whole curve, but not affect the form of the time evolution of C ( t ).
Using the linear approximation method, we calculated the steady-state mean normalized intensity fluctuation for a loss-noise model of a single-mode laser driven by a pump noise and a quantum noise, whose real part and imaginary part are cross-correlated. We analyzed the valid range for the linear approximation method by studying the influences on the steady-state mean normalized intensity fluctuation by the cross-correlation coefficient, the intensities of the quantum and pump noise, the net gain, and the amplitude and frequency of the input signal, and we found that the valid range becomes wider when the cross-correlation between the real and imaginary part of quantum noise is weaker, the noise intensities of quantum and pump are weaker, the laser system is far from the threshold and the signal has smaller amplitude and higher frequency.
The influences of the two forms of modulated noises, i.e. the bias signal-modulated noise and the direct signal-modulated noise, on the normalized intensity fluctuation (NIF) are investigated, and the results of the two forms of modulation are compared in detail. We find that a minimum for the case of the bias signal modulation appears in the curve of the dependence of the NIF upon the quantum and pump noise intensities when the correlation coefficient between the quantum noise and the pump noise is negative. However, the NIF for the case of the direct signal modulation is independent of the correlation coefficient between the two noises. Moreover, at the same parameter region, the NIF for the bias signal modulation is only one-eighth as much as that for the direct signal modulation.
Using the linear approximation, we have studied the time evolution of intensity correlation function C ( t ) in a single-mode laser driven by both the coloured pump noise with signal modulation and the quantum noise with cross-correlation between its real and imaginary parts. In the case of the pump noise with self-correlation time τ<<1, we find that the time evolution of C ( t ) varies with modulation signal frequency Ω , amplitude B and net gain a 0 . (i) As Ω increases, the time evolution of C ( t ) changes from monotonically descending to flat descending and finally to damply oscillating; (ii) as B increases, it changes from monotonically descending to maximal; (iii) as net gain a 0 increases, it changes repeatedly from monotonically descending to monotonically ascending and to maximal, finally to monotonically descending again. However, in the case of τ>>1, the time evolution of C ( t ) only exhibits a form of damping oscillation.