应用Zoom FFT方法提高相干测风激光雷达频谱分辨率

脉冲相干测风激光雷达距离门内的回波具有中频高、频带宽、采样点稀疏等特点。采用传统的信号处理方法, 雷达频谱分辨率很难提高。在研究无线电雷达信号频谱细化技术的基础上, 采用Zoom FFT 频谱细化结合数字滤波器组的方法, 通过仿真研究验证了该方法对提高脉冲相干激光测风雷达的频谱分辨率具有良好效果。文章介绍了Zoom FFT 算法和数字滤波器组的原理,对模拟低频和高频信号进行了仿真,并且利用真实风场数据进行了验证,充分证明了该算法对于提高脉冲相干激光测风雷达的频谱分辨率的有效性。     

机载激光多普勒测风雷达技术及其应用

为了加快发展我国机载测风雷达技术,对机载激光多普勒测风雷达的研究及应用情况进行了介绍,对机载激光多普勒测风雷达的基本工作原理、系统组成、应用方式及领域等进行了分析,并对光纤激光器在机载雷达系统中的应用进行了预测.结果表明,采用全光纤相干结构的机载测风雷达具有测量精度高、结果稳定可靠、响应速度快、系统结构紧凑、环境适应能...     

1550 nm相干激光测风雷达微弱回波信号处理

针对激光测风雷达回波信号极其微弱,直接快速傅里叶变换(FFT)后无法得到回波信号频域幅值的问题,该文提出了嵌入现场可编程门阵列(FPGA)的数字中频信号处理方法,有效地提取了回波信号频域幅值.激光测风雷达的回波信号是相干激光脉冲信号经过空气中气溶胶后向散射的信号,由于空气中气溶胶浓度小以及激光发射功率限制,回波信号微弱...     

基于GPS照射源的天地双基地雷达探测系统

研究了GPS卫星作为照射源,接收机在地面的天地收发分置的双基地雷达探测系统.该系统通过测量目标双基地距离和与目标双基地多普勒频率来实现对目标的探测.通过对回波信号进行多普勒补偿之后再进行相干积累和非相干积累,获得较大的处理增益,从而实现对微弱目标信号的检测.     

全光纤相干多普勒激光雷达非线性最小二乘风速反演方法及实验研究

研制了一套人眼安全的全光纤相干多普勒激光测风雷达系统。系统采用1550 nm全光纤单频保偏激光器作为激光发射光源,激光器单脉冲能量0.2 m J,重复频率10 k Hz,脉冲半高全宽400 ns,线宽小于1 MHz。激光雷达接收望远镜和扫描器口径100 mm,采用速度方位显示(VAD)扫描模式对不同方位的视线风速进行测量,使用平衡探测器接收回波相干信号,通过1 G/s的模拟数字(AD)采集卡对相干探测信号进行采集,在现场可编程门阵列(FPGA)数字信号处理器中进行1024点快速傅里叶变换(FFT)得到不同距离门回波信号功率谱信息。对于获得的各方位视线风速,研究采用非线性最小二乘法对激光雷达测量的风速剖面矢量进行反演。激光雷达与风廓线雷达测量的风速进行了对比,两者测量的水平风速,风向和竖直风速相关系数分别为0.988,0.941和0.966。     

相干激光测风雷达高分辨距离门自适应技术研究

脉冲相干激光测风雷达的信号处理通常采用固定长度距离门来划分时域信号,并对每个距离门做频谱计算得到风速度信息。固定距离门的时域信号划分存在中频信号的非整周期截断问题,导致频谱计算时出现频谱泄露而产生误差,使信噪比降低。文中提出一种基于整周期搜索的自适应距离门划分方法,距离门长度与中频信号频率自适应,可实现对信号的整周期分割,避免了频谱处理中的频谱泄漏问题,提高频率估计精度。采用加噪信号对两种处理方法进行仿真分析,结果表明:自适应距离门方法可实现距离门长度与中频信号的自适应,在信噪比小于1 dB时,该方法得到的中频估计误差是固定距离门方法的38%~62%。应用自适应距离门方法处理激光测风雷达系统获取的转盘和风场回波信号,与使用固定距离门方法的激光测风雷达测量结果进行对比。结果表明:自适应距离门划分方法对转盘速度测量的均方根误差为0.19 m/s,大气风速度测量的距离分辨率在7~11 m之间变化,均优于固定距离门方法,实现了激光测风雷达的距离分辨率和测量精度的提升。     

UWS冲激雷达时域多普勒测速算法研究

超宽谱(UWS)冲激雷达是一种新体制的无载波雷达,不能通过载波多普勒频率对目标速度进行测量,因此需要采用新的测速方式.文章首先对UWS冲激雷达时域多普勒测速原理进行了研究,并对测速精度进行分析,指出其影响因素.提高回波信号信噪比和测速精度的关键在于对动目标回波信号进行有效的相干积累,因此本文提出了回波时间预估的目标回波信号积累方法.最后,通过仿真实验表明,该方法能够很好的对回波信号进行积累,有效提高信号信噪比和测速精度.     

滤波器组在相干激光测风雷达信号处理中的应用

首先简要介绍了相干激光测风雷达和数字滤波器组的工作原理,然后重点分析了余弦调制滤波器组。余弦调制滤波器组具有实现简单、占用资源少等特点。信号通过滤波器组后可分解成若干个窄带子信号,目标的多普勒频率将落入其中一个子带信号中,针对这一子信号进行处理可获得较高的信噪比。利用Matlab设计出了8通道余弦调制滤波器组,然后对回波信号进行处理,从仿真结果和实测信号处理结果可以看出:该方法可以判断并抽取出多普勒频率所在的子带信号。     

激光雷达测风系统信号采集处理研究

为满足风场对风速测量的需求,研制了基于FPGA的激光雷达测风系统高速信号采集处理模块,负责对激光雷达回波信号采集、快速傅里叶变换(FFT)及频谱数据累加平均运算.将采集到的1024点回波数据通过流模式、块浮点结构FFT运算,分别得到单次频谱数据和1024次累加平均频谱数据,并利用数据传输模块可靠传输至上位机进行显示与分析.通过搭建工作波长为1550 nm的连续相干激光雷达测风系统,对信号采集处理模块进行指标测试和累加平均滤波算法验证.测试结果表明:该采集处理模块能够在100 MHz时钟下对回波信号实时采集处理,频谱分辨率达到97.66 kHz,将风速测量精度提升至7.57cm/s.     

基于相干激光雷达气象多要素探测EI北大核心CSCD

相干激光测风雷达具有体积小、探测效率高、信噪比强等特点,在气象、航空保障以及风电等行业得到了广泛的应用,但是目前雷达数据产品大多是利用回波多普勒频移信息反演的风场数据产品,未对雷达回波信号强度信息进行数据挖掘。针对当前相干激光测风雷达数据产品开发不足的问题,介绍了一种新型基于相干探测的激光雷达数据产品生成技术,该技术在探测风场的同时,实现云高、消光系数及能见度等多种气象要素数据产品的生成。首先,通过分析回波信号特性,推导出雷达回波信号功率的计算方法,获取探测范围内各距离位置的回波信号强度信息。在此基础上,利用阈值法和微分零叉法反演出云底高度,同时采用改进型Klett算法实现大气消光系数的反演,继而实现能见度的测量。最后,与气象站能见度仪、激光云高仪以及532 nm气溶胶激光雷达进行数据对比验证试验,试验数据结果显示:云高对比精度可达5.0%,能见度对比精度可达12.2%,消光系数对比有较好的一致性,并可长期在多种气象环境下连续测量。     

Resolution Enhancement Technology:Integrated Process Solutions using OPC

DUV lithography, using the 248 nm wavelength, is a viable manufacturing option for devices with features at 130 nm and less. Given the low kl value of the lithography, integrated process development is a necessary method for achieving acceptable process latitude. The application of assist features for rule based OPC requires the simultaneous optimization of the mask, illumination optics and the resist.Described in this paper are the details involved in optimizing each of these aspects for line and space imaging.A reference pitch is first chosen to determine how the optics will be set. The ideal sigma setting is determined by a simple geometrically derived expression. The inner and outer machine settings are determined, in turn,with the simulation of a figure of merit. The maximum value of the response surface of this FOM occurs at the optimal sigma settings. Experimental confirmation of this is shown in the paper.Assist features are used to modify the aerial image of the more isolated images on the mask. The effect that the diffraction of the scattering bars (SBs) has on the image intensity distribution is explained. Rules for determining the size and placement of SBs are also given.Resist is optimized for use with off-axis illumination and assist features. A general explanation of the material' s effect is discussed along with the affect on the through-pitch bias. The paper culminates with the showing of the lithographic results from the fully optimized system.     

Cost-effective test solutions for smart card and other integrated flash applications

From its emergence in the late 1980s as a lower cost alternative to early EEPROM technologies, flash memory has evolved to higher densities and speedsand rapidly growing acceptance in mobile applications.In the process, flash memory devices have placed increased test requirements on manufacturers. Today, as flash device test grows in importance in China, manufacturers face growing pressure for reduced cost-oftest, increased throughput and greater return on investment for test equipment. At the same time, the move to integrated flash packages for contactless smart card applications adds a significant further challenge to manufacturers seeking rapid, low-cost test.     

An improved parallel thinning algorithm with two subiterations

The parallel thinning algorithm with two subiterations is improved in this paper. By analyzing the notions of connected components and passes, a conclusion is drawn that the number of passes and the number of eight-connected components are equal. Then the expression of the number of eight-connected components is obtained which replaces the old one in the algorithm. And a reserving condition is proposed by experiments, which alleviates the excess deletion where a diagonal line and a beeline intersect. The experimental results demonstrate that the thinned curve is almost located in the middle of the original curve connectivelv with single pixel width and the processing speed is high.     

Theoretical analysis of the relationship between the Brillouin gain coefficient and the strain in the optical-fiber sensors

The relation between the power of the Brillouin signal and the strain is one of the bases of the distributed fiber sensors of temperature and strain. The coefficient of the Bfillouin gain can be changed by the temperature and the strain that will affect the power of the Brillouin scattering. The relation between the change of the Brillouin gain coefficient and the strain is thought to be linear by many researchers. However, it is not always linear based on the theoretical analysis and numerical simulation. Therefore, errors will be caused if the relation between the change of the Brillouin gain coefficient and the strain is regarded as to be linear approximately for measuring the temperature and the strain. For this reason, the influence of the parameters on the Brillouin gain coefficient is proposed through theoretical analysis and numerical simulation.     

Novel fiber-optical interferometer with miniaturized probe for in-hole measurements

Today, micro-system technology and the development of new MEMS （Micro-Electro-Mechanical Systems） are emerging rapidly. In order for this development to become a success in the long run, measurement systems have to ensure product quality. Most often, MEMS have to be tested by means of functionality or destructive tests. One reason for this is that there are no suitable systems or sensing probes available which can be used for the measurement of quasi inaccessible features like small holes or cavities. We present a measurement system that could be used for these kinds of measurements. The system combines a fiber optical, miniaturized sensing probe with low-coherence interferometry, so that absolute distance measurements with nanometer accuracy are possible.     

Development of the readout system for waveguide multilayer optical card

Waveguide multilayer optical card （WMOC） is a novel storage device of three-dimensional optical information. An advanced readout system fitting for the WMOC is introduced in this paper. The hardware mainly consists of the light source for reading, WMOC, motorized stages addressing unit, microscope imaging unit, CCD detecting unit and PC controlling ＆ processing unit. The movement of the precision motorized stage is controlled by the computer through Visual Basic （VB） language in software. A control panel is also designed to get the layer address and the page address through which the position of the motorized stages can be changed. The WMOC readout system is easy to manage and the readout result is directly displayed on computer monitor.     

Study of waveguide coupling efficiency in hybrid silicon lasers

This paper presents a new method to increase the waveguide coupling efficiency in hybrid silicon lasers. We find that the propagation constant of the InGaAsP emitting layer can be equal to that of the Si resonant layer through improving the design size of the InP waveguide. The coupling power achieves 42% of the total power in the hybrid lasers when the thickness of the bonding layer is 100 nm. Our result is very close to 50% of the total power reported by Intel when the thickness of the thin bonding layer is less than 5 nm. Therefore, our invariable coupling power technique is simpler than Intel＇s.     

A method for calculating the center position of collimated light

It is a key problem to accurately calculate beam spots＇ center of measuring the warp by using a collimated laser. A new method, named double geometrical center method （DGCM）, is put forward for the first time. In this method, a plane wave perpendicularly irradiates an aperture stop, and a charge couple device （CCD） is employed to receive the diffraction-beam spots, then the geometrical centers of the fast and the second diffraction-beam spots are calculated respectively, and their mean value is regarded as the center of datum beam. In face of such adverse instances as laser intension distributing defectively, part of the image being saturated, this method can still work well. What＇s more, this method can detect whether an unacceptable error exits in the courses of image receiving, processing and calculating. The experimental results indicate the precision of this method is high.     

Collinear phase-matching study of terahertz-wave generation via difference frequency mixed in GaAs and Inp

The collinearly phase-matching condition of terahertz-wave generation via difference frequency mixed in GaAs and InP is theoretically studied. In collinear phase-matching, the optimum phase-matching wave hands of these two crystals are calculated. The optimum phase-matching wave bands in GaAs and lnP are 0.95-1.38μm and 0.7-0.96μm respectively. The influence of the wavelength choice of the pump wave on the coherent length in THz-wave tuning is also discussed. The influence of the temperature alteration on the phase-matching and the temperature tuning properties in GaAs crystal are calculated and analyzed. It can serve for the following experiments as a theoretical evidence and a reference as well.     

Effects of the alloy compositions on the phonon-polaritons in ternary mixed crystals

Composition dependence of bulk and surface phonon-polaritons in ternary mixed crystals are studied in the framework of the modified random-element-isodisplacement model and the Bom-Huang approximation. The numerical results for Several Ⅱ - Ⅵ and Ⅲ- Ⅴ compound systems are performed, and the polariton frequencies as functions of the compositions for ternary mixed crystals AlxGa1-xAs, GaPxAS1-x, ZnSxSe1-x, GaAsxSb1-x, GaxIn1-xP, and ZnxCd1-xS as examples are given and discussed. The results show that the dependence of the energies of two branches of bulk phonon-polaritons which have phonon-like characteristics, and surface phonon-polaritons on the compositions of ternary mixed crystals are nonlinear and different from those of the corresponding binary systems.