Influences of quantum noises on direct-modulated properties of 1.3-μm InGaAsP/InP laser diodes

Due to the zero dispersion point at 1.3μm in optical fibres, 1.3-μm InGaAsP/InP laser diodes have become main light sources in fibre communication systems recently. Influences of quantum noises on direct-modulated properties of single-mode 1.3-μm InGaAsP/InP laser diodes are investigated in this article. Considering the carrier and photon noises and the cross-correlation between the two noises, the power spectrum of the photon density and the signal-to-noise ratio (SNR) of the direct-modulated single-mode laser system are calculated using the linear approximation method. We find that the stochastic resonance (SR) always appears in the dependence of the SNR on the bias current density, and is strongly affected by the cross-correlation coefficient between the carrier and photon noises, the frequency of modulation signal, and the photon lifetime in the laser cavity. Hence, it is promising to use the SR mechanism to enhance the SNR of direct-modulated InGaAsP/InP laser diodes and improve the quality of optical fibre communication systems.     

Delay-induced state transition and resonance in periodically driven tumor model with immune surveillance

The phenomenon of stochastic resonance (SR) in a tumor growth model under the presence of immune surveillance is investigated. Time delay and cross-correlation between multiplicative and additive noises are considered in the system. The signal-to-noise ratio (SNR) is calculated when periodic signal is introduced multiplicatively. Our results show that: (i) the time delay can accelerate the transition from the state of stable tumor to that of extinction, however the correlation between two noises can accelerate the transition from the state of extinction to that of stable tumor; (ii) the time delay and correlation between two noises can lead to a transition between SR and double SR in the curve of SNR as a function of additive noise intensity, however for the curve of SNR as a function of multiplicative noise intensity, the time delay can cause the SR phenomenon to disappear, and the cross-correlation between two noises can lead to a transition from SR to stochastic reverse-resonance. Finally, we compare the SR phenomenon for the multiplicative periodic signal with that for additive periodic signal in the tumor growth model with immune surveillance.     

Theoretical investigations of impulsive synchronization on semiconductor laser chaotic systems

The impulsive synchronization problem for semiconductor laser (SL) chaotic systems is studied. SL systems can be described by the rate equations governing photon density and carrier density. Because the carrier density is not easy to observe or measure, only photon density is used to design the impulsive controller. Several sufficient conditions for the synchronization of SL chaotic systems via impulsive control are derived. Numerical simulations are presented to show the effectiveness of the proposed method.     

Stochastic Resonance in a Bacterium Growth System Subjected to Colored Noises

We present the logistic growth model to study the stochastic resonance (SR) in a bacterium growth system under the simultaneous action of two externalmultiplicative cross-correlation noises and periodic external forcing. The expression of the signal-to-noise ratio (SNR) for a bacterium growth system is derived by using the theory of SNR in the adiabatic limit. Based on SNR, we discuss the effects of self-correlation time τ₁ and τ₂, cross-correlationtime τ₃ and cross-correlation strength λ on the SNR. It is found that the self-correlation time τ₁ and τ₂, and cross-correlation strength λ enhance the SR of the bacterium growth system, while cross-correlation time τ₃ weakens the SR of the bacterium growth system.     

Stochastic Resonance in Linear Region of a Single-Mode Laser： Effects of Amplitude Modulation of Signal

A single-mode laser noise model driven by quadratic colored pump noise and amplitude modulation signal is proposed. The real and imaginary parts of the pump noise are assumed to be cross-correlation. The effect of cross-correlation of noise and amplitude modulation of signal on laser statistical properties is studied by using the linearized approximation. The analytic expression of signal-to-noise ratio (SNR) is calculated. It is found that the phenomena of stochastic resonance (SR) respectively exist in the curves of the SNR versus the noise cross-correlation coefficient λ and the SNR versus the pump parameter a, as well as the SNR versus the signal frequency ω in our model. It is shown that there are three different typies of SR in the model: the conventional form of SR, the SR in the broad sense, and the bona fide SR.     

色噪声驱动下调幅波的单模激光随机共振

对单模激光增益模型的光强方程加入调幅波，用线性化近似方法计算了以e指数形式关联的两色噪声驱动下光强的输出功率谱及信噪比. 结果表明噪声间互关联时间及互关联程度对随机共振影响很大，信噪比随着载波信号频率ω和调制信号频率Ω的变化也和白噪声的变化曲线有很大不同. 关键词： 色噪声 单模激光 随机共振 调幅波     

噪声交叉关联强度的时间周期调制对线性过阻尼系统的随机共振的影响

针对由加性、乘性噪声和周期信号共同作用的线性过阻尼系统, 在噪声交叉关联强度受到时间周期调制的情况下,利用随机平均法推导了系统响应的信噪比的解析表达式. 研究发现这类系统比噪声间互不相关或噪声交叉关联强度为常数的线性系统具有更丰富的动力学特性, 系统响应的信噪比随交叉关联调制频率的变化出现周期振荡型随机共振, 噪声的交叉关联参数导致随机共振现象的多样化.噪声交叉关联强度的时间周期调制的引入有利于提高对微弱周期信号检测的灵敏度和实现对周期信号的频率估计. 关键词： 随机共振 周期振荡型共振 噪声交叉关联强度 信噪比     

Stochastic resonance of bias signal-modulated noise in a single-mode laser＊

Stochastic resonance (SR) for bias signal modulation is studied in a single-mode laser system. By investigating a gain-noise model driven by correlated pump noise and quantum noise, we find that, whether the correlation coefficient between both the noises is positive or negative, SR always appears in the dependence of signal-to-noise ratio (SNR) upon the noise correlation time and the frequency of the modulation signal. However, only when the correlation coefficient between both noises is negative can SR occur in the dependence of SNR upon the quantum noise intensity and pump noise intensity, while when the correlation coefficient between both noises is positive, it shows monotonically.     

Influence of the net gain on characteristic of stochastic resonance in a single-mode laser system

The phenomenon of stochastic resonance (SR) is found in a single-mode laser system driven by the colored pump noise with signal modulation and the quantum noise with cross-correlation between the real and imaginary parts. When the net gain a0 changes, it is found that, 1) the shape of the curve of the signal-tonoise ratio (SNR) versus the pump noise self-correlation time T exhibits a changing process of multiform SR, from single-peak SR to simultaneous existence of resonances and suppressions; 2) the curve of SNR versus signal frequency Ω experiences a complicated changing process from the monotonous descending to the simultaneous appearances of a maximum and a minimum, and finally to monotonous descending; 3)the curve of SNR versus cross-correlation coefficient between the real and imaginary parts of the quantum noise λq appears an acute single-peak SR. Therefore, the net gain a0 greatly influences the characteristic of SR of laser system.     

Studying the Mode－Spectra Characteristics of An Above－Threshold Biased Semiconductor Laser

ＳｔｕｄｙｉｎｇｔｈｅＭｏｄｅ－ＳｐｅｃｔｒａＣｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆＡｎＡｂｏｖｅ－ＴｈｒｅｓｈｏｌｄＢｉａｓｅｄＳｅｍｉｃｏｎｄｕｃｔｏｒＬａｓｅｒ￥ＸＩＡＧｕａｎｇｑｉｏｎｇ；ＷＵＺｈｅｎｇｍａｏ；ＣＨＥＮＪｉａｎｇｕｏ；ＬＵＹｕｃｕ...     

光学双稳系统中的随机共振

运用绝热近似理论，研究了由加性噪声和乘性噪声及周期信号驱动的光学双稳系统的随机共振现象. 发现该模型中输出信噪比R～随着加性噪声强度D_a的变化曲线中会出现随机共振现象，而信噪比R～随着乘性噪声强度D_m的变化曲线是单调减小的，信噪比曲线中没有出现随机共振现象. 因此，加性噪声和乘性噪声对输出信噪比的影响是不同的. 关键词： 随机共振 信噪比 乘性噪声 加性噪声     

具有色关联的色噪声驱动下单模激光线性模型的随机共振

研究了具有指数形式关联的两色噪声驱动下单模激光线性模型受信号调制后其输出信噪比，发现了随机共振现象.根据计算结果讨论了噪声（即噪声强度、噪声间互关联程度和关联时间）和信号（信号频率和信号振幅）对信噪比的影响. 关键词： 随机共振 噪声关联时间 信噪比     

An improved transmission line laser model for multimode laser diodes incorporating thermal effects

An improved transmission line model to study the thermal effects in semiconductor laser diodes is reported in this paper. The temperature effects in the laser characteristics are obtained by incorporating temperature dependent gain and carrier density equations for the laser cavity. These primary factors are introduced in the regular transmission line laser model to estimate the static and dynamic characteristics of an 1.3μm InGaAsP double heterostructure laser diode. The results show good agreement with the experimental observation and solution of rate equations referred in the literature. The key feature of this model is that it provides the laser spectra at various temperatures. Based on the model, time dependent evolution of optical spectrum, temperature dependent optical output and frequency chirp are evaluated. Further the distribution of photon and electron density within the cavity is also determined.     

外腔反馈对半导体激光器振荡特性的影响

通过有效反射系数的引入，根据激光谐振腔的自再现条件和对腔内光子密度、载流子密度方程的求解，分析了外腔反馈对半导体激光器的阈值增益、振荡频率和输出功率等振荡特性的影响，并通过实验进行了验证.外腔反馈后，半导体激光器的阈值电流从420mA降为370mA，输出功率的斜率效率获得了提高，理论计算的输出功率曲线与实验结果符合的很好. 关键词： 半导体激光器 外腔反馈 振荡特性     

相关多普勒光学层析成像

提出了基于互相关的多普勒OCT(correlated Doppler optical coherence tomography, CD-OCT)方法, 能够有效的抑制噪声, 实现低信噪比条件下的流速探测. 对CD-OCT算法进行了详细的推导, 分析了噪声的相关性对该算法结果的影响, 最后基于谱域和时域联合探测方法(joint spectral and time domain optical coherence tomography, STD-OCT)以及CD-OCT算法的对比实验证明了该算法能够进一步实现信噪比的提高, 使测量的结果更为稳定.     

Influences of noise correlation and time delay on stochastic resonance induced by multiplicative signal in a cancer growth system

This paper investigates the stochastic resonance (SR) phenomenon induced by the multiplicative periodic signal in a cancer growth system with the cross-correlated noises and time delay. To describe the periodic change of the birth rate due to the periodic treatment, a multiplicative periodic signal is added to the system. Under the condition of small delay time, the analytical expression of the signal-to-noise ratio R_{\rm SNR} is derived in the adiabatic limit. By numerical calculation, the effects of the cross-correlation strength \lambda and the delay time \tau on R_{\rm SNR} are respectively discussed. The existence of a peak in the curves of R_{\rm SNR} as a function of the noise intensities indicates the occurrence of the SR phenomenon. It is found that \lambda and \tau play opposite role on the SR phenomenon, i.e., the SR is suppressed by increasing \lambda whereas it is enhanced with the increase of \tau, which is different from the case where the periodic signal is additive.     

Circuit model for absorption grating gain-coupled distributed feedback semiconductor lasers

A circuit model for absorption grating (AG) gain-coupled (GC) distributed feedback (DFB) semiconductor laser diodes (LD) is presented, based on the rate equations of carrier densities in active region and absorption grating, as well as the photon density. The relation of photon lifetime to cavity loss and facet loss, and the relation of light power to average photon density are derived. As an example, self-pulsation in AG–GC–DFB–LD is studied.     

Stochastic resonance in a gain--noise model of a single-mode laser driven by pump noise and quantum noise with cross-correlation between real and imaginary parts under direct signal modulation

Stochastic resonance (SR) is studied in a gain--noise model of a single-mode laser driven by a coloured pump noise and a quantum noise with cross-correlation between real and imaginary parts under a direct signal modulation. By using a linear approximation method, we find that the SR appears during the variation of signal-to-noise ratio (SNR) separately with the pump noise self-correlation time \tau , the noise correlation coefficient between the real part and the imaginary part of the quantum noise \lambda_q , the attenuation coefficient \gamma and the deterministic steady-state intensity I_0 . In addition, it is found that the SR can be characterized not only by the dependence of SNR on the noise variables of \tau and \lambda_q, but also by the dependence of SNR on the laser system variables of \gamma and I₀. Thus our investigation extends the characteristic quantity of SR proposed before.     

Frequency dynamics of semiconductor lasers with atomic absorbers: theory and experiments

In this paper we discuss the spectral behavior of monomode semiconductor laser systems whose output amplitude is constant, but whose frequency may be bistable, multistable, locked or present instabilities. The explored configurations are: (i) a laser diode (Fabry-Pérot) under orthogonal filtered optical feedback; and (ii) an extended-cavity diode laser with an intracavity strongly-saturated resonant vapor. Starting from rate equations for the carrier density and for the radiation field oscillating in the cavity of these systems we describe spectral features which are in very good quantitative agreement with experimental observations.