用于圆形口径光学元件的功率谱密度检测

光学元件加工质量的检测和评价是保证整个光学系统安全、正常运行的关键.波前功率谱密度(Power Spectral Density,PSD)能给出光学表面的空间频谱分布,反映高精度光学元件加工质量的特殊要求.在总结现有功率谱密度指标基础上,提出由于圆形口径的旋转对称性,可以采用径向波前功率谱密度来表征圆形口径光学元件波前频谱分布特征的方法,并给出了采用三坐标仪作为测试仪器测量圆形口径光学元件的波前功率谱密度时相应的数值计算方法.     

基于功率谱AR模型估计的序列图像复原算法研究

在分析信号复原过程的基础上,提出基于功率谱AR模型估计的序列图像复原算法.对分段信号的功率谱进行估计,在保持图像整体信息良好的前提下,得到幅值谱的补偿滤波器,从而实现序列图像复原.利用所建模型对风洞试验图像进行实验研究,复原图像信噪比得到提高,复原以后的图像误差得到很大程度的减小,恢复效果明显.研究表明,采用功率谱AR模型估计的复原方法,可以有效地应用于气动光学效应序列图像复原.     

小波在基于功率谱密度特征曲线评价中的应用

为了解决功率谱密度仅仅是一种强激光条件下光学元件表面质量评价指标,无法对通过加工来消除某频段误差进行确定性指导这一问题,采用小波理论对光学元件表面误差进行了分析和试验验证,在利用功率谱密度特征曲线找到表面误差不合格频率带的基础上,利用二维连续小波变换得到了能作为加工过程反馈的不合格频率带的对应区域.结果表明,利用此方法能有效地找到特定误差频段对应的区域,从而指导加工,提高加工的效率.     

部分响应信号功率谱密度的计算

提出了一个基于维纳－辛钦定理的求部分响应功率谱密度的有效方法，分析了部分响应信号功率谱密度对于信号传输特性的影响。     

激光波前功率谱密度与焦斑旁瓣的关系

基于波前功率谱密度(PSD)的定义,分析了采用功率谱密度方法研究中频波前畸变与焦斑旁瓣关系的可行性。由于任意形状的波前畸变都可以由不同空间频率的正弦函数叠加组成,以正弦函数波前为例进行功率谱密度分析和远场分析。分析表明,当中频波前畸变的幅度满足一定条件时,远场二级以上的衍射非常低,可以忽略不计,此时波前功率谱密度与焦斑旁瓣具有非常好的相似性,并且这种相似性仅与中频波前畸变的幅度有关,与空间频率无关。最后还用数值模拟的方法验证了这个结论对叠加后的结果仍然成立。研究结果可以用于设计满足惯性约束聚变(ICF)驱动器打靶对焦斑旁瓣要求的光学元件中频段波前畸变指标。     

信号功率谱密度的物理基础

借助于信号对简谐振子和简谐振子阵列的作用,定义了信号的瞬时能量谱密度,进一步引入了信号的瞬时能量、功率谱密度、功率、能量谱密度及总能量等基本物理量,给出了功率谱密度的主要性质以及功率谱密度与其它各物理量之间的关系。     

PCC-OFDM功率谱密度及系统性能分析

针对多项式相消编码正交频分复用（PCC-OFDM）信号的功率谱密度以及循环前缀对PCC-OFDM功率谱密度的影响进行了理论分析与计算机仿真,研究了循环前缀长度（Cyclic Prefix,CP）与带外功率大小的关系,结果表明在同样长度的循环前缀下,PCC-OFDM比普通OFDM具有较低的带外功率。在不同信道条件下,对PCC-OFDM性能进行仿真,并与普通的OFDM系统进行比较,表明PCC-OFDM具有较高的性能和实用价值。     

光学表面功率谱密度的表征

以硅基板镀制单层HfO2薄膜前后的表面微观形貌的变化为例,开展了光学表面功率谱密度的计算及表征研究。首先给出了一维功率谱密度(PSD1D)、二维功率谱密度(PSD2D)以及各向同性功率谱密度(PSDISO)的计算方法和具体步骤。然后使用原子力显微镜测量了硅基板镀膜前后在1 m1 m、5 m5 m、10 m10 m、20 m20 m四种扫描尺寸下的表面轮廓。在此基础上使用MATLAB编程计算得到这四种扫描尺寸下的PSDISO,对这些PSDISO使用几何平均算法拼接得到具有足够大频率范围的PSDISO-Combined。结果显示,硅基板镀膜前后的PSDISO-Combined在低频段基本相同,中高频段出现了明显差异。分析指出这是由镀膜后表面柱状晶体结构引起的。提出了对PSDISO在频域上积分得到表面均方根粗糙度ISO,再同由定义式计算得到的STD作对比的方法。计算得到的ISO与STD基本相同,验证了PSDISO计算方法的准确性。     

压控振荡器功率谱密度的研究

本文在分析计算了压控振荡器电路中的输出功率谱密度的基础上,针对控制电压涨落的情况,求解了振荡频率随机时的朗之万（Ｌａｎｇｅｖｉｎ）方程,获得了振荡频率涨落的均方根（ｒｍｓ）值,给出了涨落－耗散定理的一种表述,这使我们能更好地研究功率谱密度的线宽和有关噪声的起源。     

Butterworth Window for Power Spectral Density Estimation

The power spectral density of a signal can be estimated most accurately by using a window with a narrow bandwidth and large sidelobe attenuation. Conventional windows generally control these characteristics by only one parameter, so there is a trade-off problem: if the bandwidth is reduced, the sidelobe attenuation is also reduced. To overcome this problem, we propose using a Butterworth window with two control parameters for power spectral density estimation and analyze its characteristics. Simulation results demonstrate that the sidelobe attenuation and the 3 dB bandwidth can be controlled independently. Thus, the trade-off problem between resolution and spectral leakage in the estimated power spectral density can be overcome.     

子孔径拼接干涉测量一大口径双曲面

为了无需辅助元件就能够实现对大口径非球面的检测,将子孔径拼接技术与干涉技术相结合,提出了一种利用子孔径拼接干涉检测非球面的新方法.分析了该技术的基本原理,并基于齐次坐标变换、最小二乘拟合建立了一种综合优化的拼接模型,在此基础上初步设计和搭建了子孔径拼接干涉检测装备.利用该方法对一口径为350 mm的双曲面进行了5个子孔径的拼接检测,得到拼接后的全口径面形误差的PV值为0.319λ,RMS值为0.044λ(=632.8 nm).为了对比和验证,对该非球面进行了零位补偿检测,两种方法测量所得的全口径面形分布是一致的,其PV值和RMS值的偏差分别为0.032λ和0.004λ.实验结果表明:该数学模型和拼接算法是准确可行的,从而提供了一种非零补偿测试大口径非球面的手段.     

箔条回波的统计特性

讨论了箔条回波的功率谱密度的两个极化用射分量的互相关系数。在箔条偶极子速度分布服从麦克斯威尔分布的条件下，证明了箔条回波功率谱密度具有高斯函数形式。箔条的两个极化散射分量间的互相关特性对于研究极化抗箔条干扰有重大意义。     

激光标线器非球面柱透镜设计

针对基模能量高斯分布造成的激光标线器线斑能量分布不均匀的问题,提出了一种非球面柱透镜的解决方法。该方法不同于传统的旋转对称整形系统的设计,属于非对称整形系统的设计范畴。根据光束传输的能量分配守恒法则和折射定律建立方程组,通过数学软件数值求解方程组,解得非球面矢高表达式。光学软件模拟表明,所设计的非球面柱透镜能使线斑能量均匀分布,工作距离范围宽,不仅适用于准直入射高斯光束,而且适用于会聚入射高斯光束。     

Steady-state analysis of a complex adaptive notch filter using modified gradient algorithm

Based on power spectral density (PSD) analytical technique, mean square error (MSE) (or variance) of the frequency estimate of a first-order complex adaptive IIR notch filter (ANF) using modified complex plain gradient (MCPG) algorithm is investigated in this paper. The steady-state expression for MSE is derived in closed form. A quantitative analysis for the estimation MSE has been carried out. It has been revealed that the MSE of frequency estimate is independent of an input frequency of a complex sinusoid. In addition, computer simulations are treated to corroborate the theoretical analysis and the relationships between MSE and system parameters are shown.     

Blind source separation for convolutive mixtures based on the joint diagonalization of power spectral density matrices

This paper studies the problem of blind separation of convolutively mixed source signals on the basis of the joint diagonalization (JD) of power spectral density matrices (PSDMs) observed at the output of the separation system. Firstly, a general framework of JD-based blind source separation (BSS) is reviewed and summarized. Special emphasis is put on the separability conditions of sources and mixing system. Secondly, the JD-based BSS is generalized to the separation of convolutive mixtures. The definition of a time and frequency dependent characteristic matrix of sources allows us to state the conditions under which the separation of convolutive mixtures is possible. Lastly, a frequency-domain approach is proposed for convolutive mixture separation. The proposed approach exploits objective functions based on a set of PSDMs. These objective functions are defined in the frequency domain, but are jointly optimized with respect to the time-domain coefficients of the unmixing system. The local permutation ambiguity problems, which are inherent to most frequency-domain approaches, are effectively avoided with the proposed algorithm. Simulation results show that the proposed algorithm is valid for the separation of both simulated and real-word recorded convolutive mixtures.     

EVALUATION OF POWER SPECTRAL DENSITY OF PASSIVE INTERMODULATION DISTORTION IN HIGH-POWER COMMUNICATION SATELLITE SYSTEMS

In order to analyze the deleterious effects of Passive InterModulation (PIM) on high power communication satellite systems, the basic concept of PIM is introduced, and an equation for the power spectral density of the n-th order PIM distortion insuch systems is derived by applying fiat signal-power spectrum assumption and Fourier transform method~ It is indicated that PIM level generally decreases with order and the lowest frequency receive channel in the receive band is the channel of most affected by PIM interference.     

光神经网络与光神经芯片

简要介绍了用于光神经网络的光神经器件的基本结构与工作原理。     

Prognostic methodology for remaining useful life estimation of retention loss in nanoscale resistive switching memory

Noise is a key indicator of the physical phenomenon underlying device operation, defect density and degradation trends. The analysis of noise in the frequency domain and the exponent (value of slope, α on logarithmic scale) of the power spectral density (PSD) can provide useful insight on the operating and failure mechanism of any device/system. We shall use this noise as a prognostic indicator to detect the instant at which the retention loss of a non-volatile memory device begins to occur. A qualitative perspective to prognostic management of a resistive random access memory (RRAM) device is provided in this work. Our method of detecting retention loss involves the unique observation of a slope of α = 3/2, which arises due to diffusion or ionic migration phenomenon.