大焦深成像系统仿真实验研究

如何增大非相干光学成像系统的焦深是应用光学研究领域的热点问题.本文对采用高次非球面光学掩模板与图像处理相结合增大成像光学系统焦深的新方法进行了深入分析,建立了大焦深成像系统仿真实验模型,并进行了大焦深成像系统仿真实验.实验结果证明了该方法在维持原相对孔径的同时使光学系统在较大的离焦范围内有好的成像质量.实际应用中还要综合考虑模板参量、信噪比等关键因素.     

基于调制传递函数的光学低通滤波器评价模型与实验研究

为了量化评价光学低通滤波器(optical low pass filter,OLPF),利用调制传递函数(modulation transfer function, MTF)建立了一个包含OLPF的二维数字光学成像系统模型,并以此模型为基础构建了OLPF的评价函数.应用该评价函数,计算三种典型OLPF的滤波特性,计算结果表明随着理想光学系统空间截止频率的增大,三种OLPF的滤波性能均有先微弱增强,后迅速减弱的趋势;当光学系统F数大于44时,采用嵌入“两层四点”式OLPF的数字成像系统的低通 关键词： 光学低通滤波器 调制传递函数 评价函数 空间频率     

基于信噪比通道宽度的光电成像系统匹配方法的研究

将光电成像系统中的光学系统和探测器视为线性系统,应用匹配滤波和等效平方带宽理论,综合考虑了系统的信噪比和带宽,建立了基于信噪比通道宽度的系统性能评价模型。利用评价模型进行计算机仿真。根据仿真结果分析,得出了光学系统与探测器的匹配特性和最佳匹配条件。     

高质量数字全息波面重建系统研究

基于阿贝成像理论对数字全息波面重建系统进行研究. 结果表明,利用成像系统对物光场进行变换,可以让物光场的高频角谱分量到达电荷耦合器件（CCD）探测器.为研究重建物光场质量,导出了CCD在光学系统后任意位置波面重建的计算公式,研究了物光通过傍轴光学系统到达CCD时波面重建系统的脉冲响应. 理论及实验研究表明,将CCD平面置于物光场像平面附近可以对物光场进行高质量重建. 关键词： 信息光学 数字全息 波面重建     

基于互信息的干涉成像采样系统性能分析

为了优化干涉采样成像系统的设计,采用端到端的互信息量评价系统的性能.建立了基于互信息的干涉采样成像系统数学模型.利用该模型得到了互信息量最大时光学成像系统和CCD的匹配条件:相干成像光学系统的截止频率等于CCD的Nyquist频率.分析了物体频谱分布、噪声、光源相干性和光学成像系统像差对互信息量的影响.结果表明,它们不影响光学成像系统和CCD的匹配条件.     

基于像差选择性校正的光学-数字联合设计

提出面向成像系统的光学和数字图像处理联合优化设计.根据泽尼克多项式模型分析了每种像差对成像清晰度的影响;在变分贝叶斯框架下,提出了基于加权双向差分先验模型的像差数字校正算法;将像差分为易于数字校正和不易于数字校正两类,建立基于像差选择性校正策略的光学-数字处理联合设计方法.采用联合设计方法设计了三镜片大像差光学系统,其奈奎斯特频率处的MTF值约为0.50,采用传统方法设计的六镜片光学系统MTF值约为0.53,两系统成像质量相当,本文方法可降低系统复杂度.     

光电子技术与器件 光电成像与器件

TH703 2005032098 基于信噪比通道宽度的光电成像系统匹配方法的研究= Study on matching design methods based on signal to noise ratio bandwidth in photoelectric imaging system[刊,中]／ 张超岳(山东大学信息科学与工程学院.山东,济南 (250100)),吴福田∥光学技术．-2004,30(5). -554-557 将光电成像系统中的光学系统和探测器视为线性系 统,应用匹配滤波和等效平方带宽理论,综合考虑了系统 的信噪比和带宽,建立了基于信噪比通道宽度的系统性能 评价模型。利用评价模型进行计算机仿真。根据仿真结     

弹载卡式红外光学系统消热差设计

为了消除环境温度变化对弹载红外光学系统成像质量的影响,设计了一种在3.7μm～4.8 μm波段工作的弹载卡塞格林式红外消热差光学系统.利用ANSYS软件分析了整流罩在大气中的受热变形对光学系统成像质量的影响,采用光学被动式消热差法对光学系统在-40℃～+65℃范围内进行了温度补偿.设计结果表明,系统MTF在20 lp/mm时轴外可达0.41以上,不同视场下的弥散斑直径小于一个像元尺寸且系统结构简单.该设计可保证光学系统的像面稳定性,有效提高火控系统对目标探测与识别能力.     

大口径红外离轴三反光学系统设计及公差分析

在空间光学领域中,光学系统的发展趋势为长焦距、大视场、轻量化、大相对孔径、高成像质量等。为适应该发展趋势,对大口径反射式光学系统进行研究,在共轴三反系统的成像理论基础上,为避免中心遮拦,提高成像质量,采用视场离轴方式,设计了一款大口径离轴三反式光学系统。该光学系统在奈奎斯特空间频率17 lp/mm处,光学传递函数MTF大于0.75,成像质量接近衍射极限。此外,光学系统公差的合理分配是影响相机总体性能的主要因素,运用公差灵敏度分析和反转灵敏度分析,计算各公差对光学系统成像质量的影响,给出了合适的公差分配,经过模拟分析,按照给定的公差加工装调,系统光学传递函数大于0.55。     

稀疏孔径光学系统成像恢复算法研究

分析了传统小波阈值去噪方法,给出改进去噪算法.先对稀疏孔径光学系统含噪成像,通过改进小波阈值去噪,提高信噪比,最大程度得到较为理想成像结果,参考修正维纳滤波方法,对去噪结果经过修正维纳滤波实现成像恢复.在实验中,考虑结构非冗余性,利用光学设计软件ZEMAX设计Golay6结构不同填充因子的稀疏孔径光学系统,以本算法进行成像恢复.实验结果表明本文算法优于单独使用维纳滤波或修正维纳滤波方法.     

Stochastic resonance in a monostable system driven by square-wave signal and dichotomous noise

<正>This paper investigates the stochastic resonance in a monostable system driven by square-wave signal,asymmetric dichotomous noise as well as by multiplicative and additive white noise.By the use of the properties of the dichotomous noise,it obtains the expressions of the signal-to-noise ratio under the adiabatic approximation condition.It finds that the signal-to-noise ratio is a non-monotonic function of the asymmetry of the dichotomous noise,and which varies non-monotonously with the intensity of the multiplicative and additive noise as well as the system parameters.Moreover, the signal-to-noise ratio depends on the correlation rate and intensity of the dichotomous noise.     

Stochastic resonance in a time-delayed mono-stable system with correlated multiplicative and additive white noise

This paper considers the stochastic resonance for a time-delayed mono-stable system, driven by correlated multiplicative and additive white noise. It finds that the output signal-to-noise ratio (SNR) varies non-monotonically with the delayed times. The SNR varies non-monotonically with the increase of the intensities of the multiplicative and additive noise, with the increase of the correlation strength between the two noises, as well as with the system parameter.     

Stochastic resonance in an asymmetric bistable system driven by coloured correlated multiplicative and additive noise

This paper investigates the stochastic resonance （SR） phenomenon in an asymmetric system with coupling between multiplicative and additive noise when the coupling between two noise terms is coloured. The approximate expression of signal-to-noise ratio has been obtained by applying the two-state theory and SR exhibits in the bistable system. Moreover, the potential asymmetry r and cross-correlation strength λ can weaken the SR phenomenon, while the cross-correlation time r can strengthen the SR phenomenon.     

非高斯噪声激励下FitzHugh-Nagumo神经元系统的随机共振

研究了乘性非高斯噪声和加性高斯白噪声共同激励下FitzHugh-Nagumo(FHN) 神经元系统的随机共振问题. 利用路径积分法和两态模型理论, 推导出系统信噪比的表达式. 研究结果表明: 系统参数在不同的取值条件下, FHN神经元模型出现了随机共振和双重随机共振现象. 此外, 非高斯参数q在不同的取值条件下, 乘性噪声强度和加性噪声强度对信噪比的影响是不同的. 非高斯噪声的加入有利于增强FHN神经元系统的信号响应.     

Theory of noise in a kilo-Hz cascaded high-energy Yb-doped nanosecond pulsed fiber amplifier

A theoretical analysis of noise in a high-power cascaded fiber amplifier is presented. Unlike the noise theory in low power communication, the noise of a high power system is redefined as the leaked output energy between pulses with coherent beat noise uncounted. This definition is more appropriate for high power usage in which the pulse energy receives more attention than the pulse shape integrity. Then the low power pre-amplifying stages are considered as linear amplification and analyzed by linear theory. In the high-power amplification stages, the inversion is assumed to recover linearly in the time interval between pulses. The time shape of the output pulse is different from that of the input signal because of different gains at the front and back ends of the pulse. Then, a criterion is provided to distinguish the nonlinear and linear amplifications based on the signal-to-noise ratio （SNR） analysis. Then, an experiment that shows that the output SNR actually drops off in nonlinear amplification is performed. The change in the noise factor can be well evaluated by pulse shape distortion.     

Application of the bispectrum for detection of small nonlinearities excited sinusoidally

The nonlinear behaviour of damaged systems excited by vibration or ultrasound offers potential as a technique for damage detection in machine condition monitoring and non-destructive testing applications. The bispectrum, a third-order spectrum, has properties that lend themselves to the measurement of nonlinearities in systems. The properties of interest are insensitivity to Gaussian noise and ability to detect quadratic phase coupling. However, thus far analysis of the statistics of bispectrum estimation has been mainly aimed at stochastic systems. Many applications to vibration and ultrasound involve primarily deterministic, periodic excitations in the presence of stochastic noise. This paper considers the properties of a bispectrum estimate when applied to a system with weak quadratic nonlinearity excited by the superposition of two sinusoids in the presence of additive Gaussian noise. This is compared, using signal-to-noise ratios, to the powerspectrum, with the results validated using numerical data. Also addressed is the effect of quadratic phase coupling on such a system (in the absence of noise).     

Stochastic resonance in an asymmetric bistable system driven by multiplicative and additive Gaussian noise and its application in bearing fault detection

The phenomenon of stochastic resonance (SR) in a new asymmetric bistable model is investigated. Firstly, a new asymmetric bistable model with an asymmetric term is proposed based on traditional bistable model and the influence of system parameters on the asymmetric bistable potential function is studied. Secondly, the signal-to-noise ratio (SNR) as the index of evaluating the model are researched. Thirdly, Applying the two-state theory and the adiabatic approximation theory, the analytical expressions of SNR is derived for the asymmetric bistable system driven by a periodic signal, unrelated multiplicative and additive Gaussian noise. Finally, the asymmetric bistable stochastic resonance (ABSR) is applied to the bearing fault detection and compared with classical bistable stochastic resonance (CBSR) and classical tri-stable stochastic resonance (CTSR). The numerical computations results show that:(1) the curve of SNR as a function of the additive Gaussian noise and multiplicative Gaussian noise first increased and then decreased with the different influence of the parameters a, b, r and A; This demonstrates that the phenomenon of SR can be induced by system parameters; (2) by parameter compensation method, the ABSR performs better in bearing fault detection than the CBSR and CTSR with merits of higher output SNR, better anti-noise and frequency response capability.     

Signal detection based on recurrence matrix statistics

This work considers the problem of detecting signals in noise in the absence of a well-defined signal model. Specifically, we compare detectors based on recurrence plots to one of the more commonly used detection strategies. Results indicate improvements are possible using the recurrence-based detectors for certain signal-to-noise ratios.     

Stochastic resonance in a time-delayed asymmetric bistable system with mixed periodic signal

This paper studies the phenomenon of stochastic resonance in an asymmetric bistable system with time-delayed feedback and mixed periodic signal by using the theory of signal-to-noise ratio in the adiabatic limit. A general approximate Fokker--Planck equation and the expression of the signal-to-noise ratio are derived through the small time delay approximation at both fundamental harmonics and mixed harmonics. The effects of the additive noise intensity $Q$, multiplicative noise intensity $D$, static asymmetry $r$ and delay time $\tau$ on the signal-to-noise ratio are discussed. It is found that the higher mixed harmonics and the static asymmetry $r$ can restrain stochastic resonance, and the delay time $\tau $ can enhance stochastic resonance. Moreover, the longer the delay time $\tau $ is, the larger the additive noise intensity $Q$ and the multiplicative noise intensity $D$ are, when the stochastic resonance appears.     

基于最大熵原理的小波去噪方法

小波变换去噪中最关键的问题是如何确定小波系数的阈值,使其能够将与噪声和信号相对应的小波系数合理地区分开来。根据概率论的基本原理可以推断,随机序列的细节小波变换系数符合正态分布。基于此结论,可以利用最大熵原理确定一个阈值,使得绝对值小于此阈值的小波系数组成的序列符合正态分布。该阈值在统计意义下能够最佳地区分信号与噪声的小波系数。采用光谱数据的仿真分析以及与其他方法的对比实验证明,这种最大熵小波去噪方法不仅在提高信噪比方面显示出了其优势,而且去噪效果不易受信噪比变化的影响。