光子晶体光纤中交叉相位调制光谱展宽特性研究

实验研究了超高速时分复用信号与探测光同向传输,在色散平坦高非线性光子晶体光纤中的交叉相位调制光谱展宽特性,从光谱学的角度分析了信号光波长漂移,泵浦光与信号光总功率及功率比,二者偏振态失配对交叉相位调制光谱展宽效应的影响,探讨了实现偏振不敏感交叉相位调制效应的可行性。研究发现,在36 nm波长范围,总功率大于23 dBm,泵浦光与信号光功率比合理,二者偏振态匹配时交叉相位调制效果最好,交叉相位调制的偏振相关性为11 dB,指出利用色散平坦高非线性光子晶体光纤中的残余双折射,调节泵浦光与光纤双折射主轴成45°,可以实现偏振不敏感交叉相位调制效应,随后的理论模拟和实验结果相一致。研究结果为实现基于交叉相位调制原理工作的超快全光信号处理器件作了充分准备。     

基于相位调制-解调的光纤激光相位噪声检测方法研究

在主动相位控制相干合成中,常用的光纤激光主动相位控制方法主要有外差法、多抖动法和随机并行梯度下降算法等. 基于多抖动法和外差法的原理,提出了一种新型的基于相位调制-解调的相位检测与控制方法. 该方法利用周期信号对参考光进行相位调制,将调制后的参考光与待检测信号光进行相干检测,通过对相干光强信号和相位调制信号的融合处理,实现相位噪声的检测和控制. 对该方法进行了数值模拟和实验研究. 实验结果表明,对于频率为2 kHz,噪声范围为[0,2π)的正弦噪声,相位检测精度优于λ/50,控制精度可达 关键词： 光纤激光 相干合成 相位噪声检测 调制-解调     

非线性相位噪声对DQPSK调制系统性能影响研究

为了研究非线性相位噪声对差分正交相移键控（DQPSK）调制系统性能的影响,在理论推导非线性相位噪声数学模型的基础上,通过固定接收端信噪比不变,仿真分析了40Gb/s速率时DQPSK调制系统误码率随输入信噪比的变化情况。结果表明:与二进制差分相移键控（DPSK）调制相比,DQPSK调制对非线性相位噪声的影响更为敏感,当非线性效应较大时,非线性相位噪声将使系统误码率显著增大,严重影响系统通信质量。因此,当采用DQPSK调制时,必须考虑非线性相位噪声对系统性能的影响。     

激光输入光纤环形腔内相位调制输出功率谱分析

从理论上详细分析了光纤环形腔有内相位调制时的输出光电流功率谱密度函数，该理论对任意相干长度的输入激光光源都是有效的。理论结果和实验数据表明，过快的相位调制能够平坦光电流功率谱上由于环形腔谐振特性而形成的周期性小峰，而弱相位调制对环形腔输出功率谱则影响不大。     

光源相位噪声对高斯玻色采样的影响

高斯玻色采样是实现量子计算优势的主要途径之一,同时也有望应用于加速稠密子图、量子化学等问题.然而,实验中必不可少的噪声却可能阻碍高斯玻色采样的量子优势.此前的研究主要关注于光子损失和光子非全同噪声.本文通过数值模拟研究了另一种噪声——光源相位噪声对高斯玻色采样的影响.采用蒙特卡罗方法近似计算相位噪声下高斯玻色采样的输出概率分布,发现随着探测光子数的增加,相位噪声带来的误差逐渐加大.同时,相位噪声会导致采样出大概率样本的能力,即HOG (heavy output generation)值显著降低.最后发现,在输入平均光子数相同时,有光子损失的高斯玻色采样相比无损失情形对于相位噪声有更大的容忍性.本文的研究有助于大规模高斯玻色采样中更好地抑制相位噪声.     

相位调制锁定光学谐振腔

通过对单频激光的相位调制，利用光学谐振腔的色散曲线得到鉴频信号，将一个环形谐振腔和一个驻波揩振腔锁定在激光的频率上。     

激光的相位噪声特性以及抑制方法研究

回顾了到目前为止激光相位噪声的研究成果,阐述了由经典模型和弛豫振荡导致的在线宽展宽影响下的激光线宽。提出了自发辐射放大会对激光谱线产生进一步影响的问题。在噪声的抑制方面,分析了电子介入系统锁相方案的锁相效果。通过比较已锁相激光和未锁相激光与理想激光之间的互相关函数,结果表明,成功的锁相会使锁相激光的相干长度扩展到无限长。     

高斯白噪声对神经元二维映射模型动力学的影响

从神经元二维映射模型出发，用高斯白噪声模拟了神经元的噪声环境，进而研究了高斯白噪声对参数空间相图的影响.研究发现，噪声可以提高系统的可兴奋性.通过数值模拟研究了噪声引起的相干共振现象.结果表明，只有当系统参数选取在静息区域且接近连续点火和静息状态分界线时才可以得到相干共振现象. 关键词： 高斯白噪声 神经元二维映射模型 相图 相干共振     

可调谐窄线宽钛宝石激光脉冲的放大和频率展宽

在频域上进行了光参变激光器对钛宝石激光脉冲作选取放大并频率扩展的理论分析和数值模拟。实验上实现了用BBO光学参变振荡器作钛宝石激光脉冲选取、频率展宽为120nm的连续可调谐窄线宽（小于0.02nm）激光输出。     

Global Pressure of One-Dimensional Polydisperse Granular Gases Driven by Gaussian White Noise

We study the global pressure of a one-dimensional polydisperse granular gases system for the first time, in which the size distribution of particles has the fractal characteristic and the inhomogeneity is described by a fractal dimension D. The particles are driven by Gaussian white noise and subject to inelastic mutual collisions. We define the global pressure P of the system as the impulse transferred across a surface in a unit of time, which has two contributions, one from the translational motion of particles and the other from the collisions. Explicit expression for the global pressure in the steady state is derived. By molecular dynamics simulations, we investigate how the inelasticity of collisions and the inhomogeneity of the particles influence the global pressure. The simulation results indicate that the restitution coefficient e and the fractal dimension D have significant effect on the pressure.     

Global Pressure of One-Dimensional Polydisperse Granular Gases Driven by Gaussian White Noise

We study the global pressure of a one-dimensional polydisperse granular gases system for the first time,in which the size distribution of particles has the fractal characteristic and the inhomogeneity is described by a fractal dimension D. The particles are driven by Gaussian white noise and subject to inelastic mutual collisions. We define the global pressure P of the system as the impulse transferred across a surface in a unit of time, which has two contributions,one from the translational motion of particles and the other from the collisions. Explicit expression for the global pressure in the steady state is derived. By molecular dynamics simulations, we investigate how the inelasticity of collisions and the inhomogeneity of the particles influence the global pressure. The simulation results indicate that the restitution coefficient e and the fractal dimension D have significant effect on the pressure.     

有源光纤自相位调制的频谱展宽估计

有源光纤的两种非性效应－非线性极化和增益饱和效应都引起光信号频谱展宽。增益饱和导致包络失真，同时也影响到由非线性极化所造成的自相位调制。这种影响可用一个函数ｆ（ｚ）表示。     

Flux in the Case of Gaussian White Noises

The transport of a spatially periodic system driven by additive and multiplicative Gaussian white noises (between which there is a correlation function) is investigated. The probability current (flux) shows .that the correlation function between the additive and multiplicative noises, and the spatial asymmetry are ingredients for the flux of particles. It is a new phenomenon that the correlation function between the additive and multiplicative noises can cause transport.     

Universal Character of Stochastic Resonance and a Constructive Role of White Noise

It is shown that, in spite of claims put forward in the literature, the stochastic resonance (SR) appears even in linear systems—both overdamped and inertial—driven by Gaussian white noise, and even after averaging the asymptotics over the initial phase of the input signal. This supports recent suggestions that SR is a universal effect present in every stochastic process modulated by external signals. It is also shown that the noise may sustain the output signal which otherwise would vanish exponentially in the course of time.     

Stochastic Analysis of Predator–Prey Models under Combined Gaussian and Poisson White Noise via Stochastic Averaging Method

In the present paper, the statistical responses of two-special prey–predator type ecosystem models excited by combined Gaussian and Poisson white noise are investigated by generalizing the stochastic averaging method. First, we unify the deterministic models for the two cases where preys are abundant and the predator population is large, respectively. Then, under some natural assumptions of small perturbations and system parameters, the stochastic models are introduced. The stochastic averaging method is generalized to compute the statistical responses described by stationary probability density functions (PDFs) and moments for population densities in the ecosystems using a perturbation technique. Based on these statistical responses, the effects of ecosystem parameters and the noise parameters on the stationary PDFs and moments are discussed. Additionally, we also calculate the Gaussian approximate solution to illustrate the effectiveness of the perturbation results. The results show that the larger the mean arrival rate, the smaller the difference between the perturbation solution and Gaussian approximation solution. In addition, direct Monte Carlo simulation is performed to validate the above results.     

Blind Additive Gaussian White Noise Level Estimation from a Single Image by Employing Chi-Square Distribution

The additive Gaussian white noise (AGWN) level in real-life images is usually unknown, for which the empirical setting will make the denoising methods over-smooth fine structures or remove noise incompletely. The previous noise level estimation methods are easily lost in accurately estimating them from images with complicated structures. To cope with this issue, we propose a novel noise level estimation scheme based on Chi-square distribution, including the following key points: First, a degraded image is divided into many image patches through a sliding window. Then, flat patches are selected by using a patch selection strategy on the gradient maps of those image patches. Next, the initial noise level is calculated by employing Chi-square distribution on the selected flat patches. Finally, the stable noise level is optimized by an iterative strategy. Quantitative, with association, to qualitative results of experiments on synthetic real-life images validate that the proposed noise level estimation method is effective and even superior to the state-of-the-art methods. Extensive experiments on noise removal using BM3D further illustrate that the proposed noise level estimation method is more beneficial for achieving favorable denoising performance with detail preservation.     

基于电光调制提高静态傅里叶干涉具光谱分辨率的研究

在静态干涉系统中,采用电光调制可变折射率晶体LiNbO₃做静态傅里叶干涉具的材料,两侧分别加载相位相反的调制信号,从而在不改变静态傅里叶干涉具尺寸的条件下提高光谱分辨率。通过推导光程差函数与折射率调制度的函数关系,计算得在折射率调制度为0.030的条件下,比同尺寸干涉具光谱分辨率提高了16.7倍,达到2.836 cm-1。仿真结果表明折射率调制度会因波长增大而减小,光程差函数会随干涉位置的增大而产生偏大的现象。实际探测过程中,由于光谱范围500～1 100 nm相对较窄,波长变化造成的光谱探测失真不大,可以通过标定补偿,所以应用该方法可以有效地提高静态干涉系统的光谱分辨率。     

激光线宽对原子相干效应的影响

该文在λ型三能级原子系统中分别讨论了耦合场和探针场线宽对电磁诱导透明(EIT)的影响,通过实验观测探针光和耦合光线宽变化时EIT的透明窗口的变化,得出耦合光对EIT的影响大于探针光线宽的影响,这一结果将为原子存储时间的提高具有一定意义.     

多勒普加宽斯塔克效应调制分析

用半经典理论分析了含多勒普加宽的斯塔克效应调制，使用密度矩阵近似，导出了吸收线附近ＮＨ３分子的吸收系数和调制度表达式，实验研究了１０．７８４μｍ波长的斯塔克效应调制特性，调制频率１ＭＨｚ时，调制度达到３３％。