外鼓式热敏CTP制版机光学系统设计

为了解决外鼓式热敏计算机直接制版(CTP)设备的制版镜头因畸变、场曲过大而导致制版质量不良问题, 采用ZEMAX光学仿真软件, 设计了一款低畸变、低场曲的制版镜头光学系统, 并对其进行了公差分析和实验验证。结果表明, 该光学系统由6片透镜组成, 工作波长为830 nm, 场曲小于1 μm, 畸变小于0.1%, 调制传递函数在全视场200 lp/mm处大于0.7, 并且镜片都采用标准球面设计, 制版效果良好。该系统能够满足实际制版生产需求, 具有一定的市场前景。     

群时延对混合扩频信号接收的影响分析

针对信道群时延失真对直扩/跳频混合扩频信号接收性能的影响难以量化的问题,文中从混合扩频信号相关特性的角度出发,推导了存在群时延失真时的相关特性表达式,并通过数值积分的方式计算了不同群时延失真类型下的相关峰损失及其位置偏移情况,以此量化了群时延失真对混合扩频信号接收性能的影响。计算结果表明,随着群时延失真的逐渐恶化,相关峰值会不断降低;与此同时,群时延失真还会造成相关峰的裂变和位置的偏移,从而对混合扩频信号应用于测量系统带来不利影响。     

Joint optimization of VQ codebooks and QAM signal constellationsfor AWGN channels

A joint design scheme has been proposed to optimize the source encoder and the modulation signal constellation based on the minimization of the end-to-end distortion including both the quantization error and channel distortion. The proposed scheme first optimizes the vector quantization (VQ) codebook for a fixed modulation signal set, and then the modulation signals for the fixed VQ codebook. These two steps are iteratively repeated until they reach a local optimum solution. It has been shown that the performance of the proposed system can be enhanced by employing a new efficient mapping scheme between codevectors and modulation signals. Simulation results show that a jointly optimized system based on the proposed algorithms outperforms the conventional system based on a conventional quadrature amplitude modulation signal set and the VQ codebook designed for a noiseless channel     

利用曲率分析的三维网格质量评估方法

由于顶点的曲率能够很好地反映3维网格的视觉特征,该文提出了一种利用曲率分析的3维网格质量评估方法。该方法首先估算各顶点的曲率,然后在每个顶点的邻域内构建一个曲率矩阵,并根据原始网格和失真网格对应曲率矩阵的奇异值差异评估顶点位置的失真,最后通过对这些局部失真的加权联合得到网格的整体失真。实验结果表明,相比于其他方法,该文提出的方法不但能够更准确地评估3维网格的质量,而且具有更好的鲁棒性。     

Distortion of OFDM Signals on Radio-Over-Fiber Links Integrated With an RF Amplifier and Active/Passive Electroabsorption Modulators

The integration of orthogonal frequency division multiplexing (OFDM) and radio-over-fiber (RoF) techniques have made cost-effective and high-data-rate mobile wireless Internet networks possible, such as wireless broadband networks. This paper describes the distortion effects of OFDM signals fed via an RF amplifier integrated with an RoF link employing active and passive electroabsorption modulators (EAM) for chiefly broadband in-building network applications. First, peak-to-average power ratio was investigated for RoF links. Second, the adjacent channel power ratio, which estimates the degree of spectral re- growth due to the in-band and out-of-band interference resulting from distortion effects from nonlinear amplification, error vector magnitude, and system distortion effects, was also observed for the proposed system. In this study, we considered a combined Volterra-series and impulse response-based analytical model for WiBro systems and compared it to the observed measurements. We analyzed the different nonlinear distortion effects for OFDM signals driven via an RF amplifier that was integrated with an RoF link employing a distributed feedback laser as a transmitter and an active and passive InP EAM as a receiver. The results show significant agreement between the suggested analytical model and the measurement case. This study is unique in that it examines the distortion effects of RoF links with active and passive EAMs as an access point for OFDM-based wireless access networks.     

OFDM系统中基于压缩感知的非线性失真恢复研究

正交频分复用系统(OFDM)的高峰均比(PAPR)问题降低了系统传输效率,增加了解调难度,使高功率放大器(HPA)满负载工作。该文针对削波与HPA引入的非线性失真问题,提出在接收端采取基于泰勒级数的预处理方式对非线性干扰进行处理,最小化信号畸变影响。在发送端通过削波降低信号的PAPR,并利用削波噪声在时域上的稀疏性特性,将传输过程作为整体考虑,最后利用正交匹配追踪算法(OMP)恢复总的非线性失真信号。仿真结果表明,该文所提方法能够有效抑制系统的干扰信号,减少了有用信号受到的非线性影响,验证了该方案的正确性。     

Process-induced distortion in silicon wafers

As the packing density of integrated circuits increases so does the need for increasingly accurate registration between lithographic steps. In-plane wafer distortion between such steps can limit this accuracy depending on the lithographic technique used and on the nature of the distortion. The in-plane distortion of 3-in silicon wafers at different stages of a simulated n-MOS process sequence was measured directly using the Bell Laboratories Electron-Beam Exposure System (EBES). The results indicate that the in-plane wafer distortion was linear (to within the overall EBES reading noise of ± ⅛ µm per axis). The radius of curvature of each wafer was measured independently. The wafer distortion is correlated to the change in curvature induced by the films grown or deposited on the wafer. After these films were removed, the wafers reverted to their original dimensions. Since the wafer diameter is at least two orders of magnitude smaller than the radius of curvature, a linear correction is still a good approximation. Therefore, even though the process-induced changes in vector lengths were as high as 1 µm over 50 mm, the three-point alignment strategy employed by EBES is sufficient to achieve a maximum registration error on the wafers of ¼ µm or less.     

Nonlinearity modelling of an on-board microwave photonics system based on Mach-Zehnder modulator

For the nonlinearity distortion problem of Mach-Zehnder modulator(MZM)applied in the on-board microwave photonics system,the situation for two input radio frequency(RF)signals with different frequencies and phases is discussed,and an exact analytical solution is derived with the method of expanding Bessel series and Graf addition theory.According to the analytical expression,the nonlinearity characteristics of the modulator can be precisely predicted,and the system performance can be optimized.The correctness of the analytical solution is approved by simulation results.Analytical results indicate that the nonlinearity distortion is suppressed as the decrease of modulation index,the increase of direct current bias phase shift and phase difference between two input RF signals.When the phase difference equals zero orπand the direct current bias phase shift isπ/2,there are only odd-order distortion terms.When the phase difference equals zero orπand the direct current bias phase shift isπ,there are only even-order distortion terms.     

Detection of nonlinear distortion in audio signals

Nonlinear distortion of a signal passing through a system may be caused by a number of factors. One of those factors, a limiter like transfer function, is considered. The nonlinear distortion causes a change in the probability density function (PDF) of the signal. The PDF of the signal can be characterized by the coefficients of a fifth-order polynomial fitted to the PDF curve. The coefficients are used as a vector input to an artificial neural network trained to classify the vector as belonging to a distorted or undistorted audio signal. Results show that the artificial neural network is able to classify signals, with PDFs indicating the presence of significant high amplitude components, into distorted or undistorted. A low amplitude signal will not be distorted during its passage through a nonlinear system and therefore the output will be classified as "not distorted". This gives rise to, what seem to be, errors in the classification of signals. However, the technique developed identifies distortion in the signal and not in the system through which the signal has passed.     

基于Sagnac型的双光路平衡探测光纤声传感器

为解决传统声电传声器易腐蚀、易受电磁干扰等问题,提出了一种用光纤提取声音的声光换能器结构。该传感器以Sagnac干涉仪为原型,利用声压作用于感应光纤产生的光弹效应实现光波相位的调制,采用3 × 3耦合器构建双光路平衡探测系统,通过干涉实现语音信号的解调,将光电转换后得到的幅值相等的两路信号进行差分处理,消除共模干扰信号和降低光源噪声。实验测试表明,系统性能稳定,波形失真小,在300~3 400 Hz范围内实现声音信号的提取与还原。     

The design of the shifting section of an intensifier silicon target pick-up tube

The principle for designing the shifting image section of an intensifier silicon target pick-up tube is given. An electrostatic electron-optical system with a photocathode having an effective diameter of 40mm and a system magnification of 0.65 has been designed. Experiments show that when the electron image of the photocathode is transferred to the silicon target, the geometric distortion is 2%, and the field curvature is 2mm. The astigmatism is less than 0.32 mm at 80 percent of the viewing field and the resolution is over 50 Ip/mm. It shows that the design of the electron-optical system is good and reasonable.     

基于子孔径波前振幅调制的斜率和曲率信号提取算法

斜率和曲率混合型波前传感技术将子孔径内波前的一阶和二阶导数信息全部利用起来,能够实现高阶像差的精密测量,是区域型波前传感技术的一个重要发展方向。在利用子孔径波前振幅调制的斜率和曲率混合型波前传感器的基础上,提出了一种基于质心探测的斜率和曲率信号提取算法,实现各个子孔径内待测波前斜率、拉普拉斯曲率以及扭转曲率的直接测量。仿真结果表明,在理想条件下,单一子孔径内斜率和曲率信号的检测精度均在0.02（=632.8 nm）以内;噪声水平小于10%时,斜率和曲率信号的检测精度均在0.08以内。该算法具有较高的检测精度及良好的抗噪性。     

旋转对称电子光学系统的五级几何像差分析

本文旋转对称电子光学系统五级几何像差按边界条件分成球有效期左、亚像散和场曲、亚彗差、像散和场曲、畸变等六类,并分析各类像差在高斯像平面上的图像。     

一种新型微光夜视仪目镜系统设计

为解决传统微光夜视仪目镜系统高性能与轻量化之间的矛盾,提出了一种新型的折射/衍射混合自由曲面微光夜视仪目镜结构,以传统艾菲尔目镜为基础,应用Zemax 软件设计了新型微光夜视仪目镜系统,系统由三片透镜组成,都采用K9 玻璃,将设计结果与传统艾菲尔目镜的光学性能进行了比较,结果表明,新型目镜系统不仅在垂轴像差、垂轴色差、畸变、场曲等光学性能上大大优于传统目镜系统,而且在重量和总长方面也得到了较大的改善,满足现代微光夜视仪目镜小畸变、轻量化、高像质的实际需求,为微光夜视仪目镜的轻小型设计提供了一种新的思路。     

Automatic Cancellation Method of Multipath Echo Distortion in FM Broadcasting Receivers

An automatic canceling method of multipath echo distortion in FM broadcasting receiver is proposed. The cancelling system is composed of two additional parts to the conventional receiver: a programable transversal filter operating at linear IF stage and a microcomputer. The microcomputer calculates echo parameters (relative echo amplitudes, delay times and phase differences between direct wave and echoes at the carrier frequency), from the amplitude-frequency characteristics between sending station and IF stage of the receiver, which is obtained from both outputs of an IF signal envelope detector and FM demodulator. The microcomputer sends control signals to the weighting circuits of the transversal filter. The output signal of the transversal filter is fed back and added to the incoming signal. Tap weighting adjustment is continued until a flat amplitude-frequency characteristics is obtained. The results of computer simulation show this method works well for various echo conditions and the distortion can be completely eliminated.     

Applications of cumulant based inverse filter criteria to deconvolution of seismic signals and speech signals

The well-known (minimum phase) prediction error filter, which is based on correlation function (second-order statistics), has been popularly used to deconvolve seismic signals as well as speech signals. However, it is found that there remains phase distortion in the predictive deconvolved signals since the source wavelet and the vocal track filter can be non-minimum phase. In this paper, we apply two cumulant (higher-order statistics) based inverse filter criteria, which can simultaneously remove the amplitude distortion and the phase distortion of non-minimum phase system, to deconvolving seismic signals and speech signals. Some simulation results and experimental results with real speech data are provided to demonstrate these two criteria.     

基于深度学习的抗窄带干扰MSK非相干接收机

窄带干扰(Narrowband Interference,NBI),作为一种敌意的频域干扰,会严重地恶化最小频移键控(Min-imum Shift Keying,MSK)非相干检测的误码率(Bit Error Rate,BER)性能.为降低窄带干扰对BER性能的影响,MSK非相干接收机一般首先对接收信号进行干扰抑制.然...     

基于最小统计量和掩蔽效应的单通道语音增强

利用人耳感知的掩蔽特性，并结合含噪语音能量的最小统计量估计，提出了一种低信噪比下的单通道语音增强算法。该算法对原始语音在Bark频带能量的最小统计量进行估计，从而准确估计含噪语音信噪比，再从感知的角度，在时域和Bark频域上合理调整增强系数，以实现语音增强的目的。实验表明，该增强算法能够在减小语音失真的同时，很好地抑制背景噪声和残余音乐噪声。     

Propagation-medium matched direct-sequence (PM-MDS) spread-spectrumsignals

The distortion of high-data-rate digital radio signals, such as direct-sequence-spread-spectrum (DS-SS) signals, when transmitted through dispersive media greatly degrades the system performance. The design of propagation-medium matched direct-sequence signals that overcome the performance degradation caused by the medium dispersion is described. The performance of PM-MDS signals in multipath dispersive media is evaluated and compared with the corresponding performance when randomly selected (unmatched) DS signals are used. The results show the advantages of PM-MDS transmission. The proposed PM-MDS signals do not require the use of sophisticated signal processing at the receiving ends, and are thus most suited for secure communication systems using one central transmitting station and numerous receiving units     

Mean curvature mapping for detection of corneal shape abnormality

Corneal topography is used to measure the anterior surface of the cornea. It is conventionally represented as radial slope, radial curvature, and elevation. In this paper, we introduce the application of mean curvature mapping as an alternative representation of the corneal topography. The purpose is to improve the detection of keratoconus and other diseases characterized by local increase in corneal curvature. Both simulated keratoconic cornea and real keratoconus data exported from the corneal topography system were analyzed. Four representations of corneal topography were generated and compared. It was found that mean curvature mapping provided the most precise cone location in simulated keratoconus. In both actual and simulated keratoconus cases, the appearance of the cone-like distortion is more consistent on mean curvature maps. Mean curvature mapping may improve the detection and localization of corneal shape abnormalities.