斜程大气传输光束孔径平滑到达角与像点起伏

像面到达角起伏、波面抖动和像点抖动通常是研究大气干扰情况下高分辨成像系统波前特性的重要方法之一。采用Rytov近似、包含湍流内外尺度影响的修正von Karmam近似谱和接收光学系统孔径滤波函数和传输权重函数中的Airy函数的高斯函数近似,研究了斜程湍流大气中传输束状波的波面抖动、像面到达角起伏和像点抖动规律,导出了圆孔接收系统测量到的包含湍流内外尺度影响的束状波孔径平滑波面抖动、像点抖动和像面到达角方差理论模型。     

大气相干长度的对比实验研究

大气相干长度是在激光大气传输和自适应光学研究中对大气湍流介质进行定量描述的重要参量。介绍了利用激光大气闪烁测量反演大气相干长度和利用差分像运动测量法(DIMM)测量光波到达角起伏方差来确定大气相干长度的两种不同测量方法，并根据光波到达角起伏和激光大气闪烁这两种不同方法测量大气相干长度的仪器，在相同的近地面传播路径上进行对比实验观测，两者测量结果有时存在一定的偏差，但其量级和时间变化趋势基本一致，这两种测量方法相互得到了验证。最后还对实验观测结果进行了讨论，分析了误差产生的原因。     

电离层模型反演问题的研究

利用修正的几何光学近似方法得到了电波以电离层的极限频率斜入射的情况下电波到达角度的涨落的统计特性与所描述的电离层介电常数不均匀性相关函数模型参数之间的函数关系。在此基础上指出了实验测量这些参数最佳方法。     

The impact of angle-of-arrival fluctuations of electromagnetic wave on the direction of maximum radiation of aperture antennas

Formlas were obtained for estimating the impact of angle-of-arrival fluctuations of electromagnetic wave on the direction of maximum radiation of aperture antennas. A model of slow and fast angle-of-arrival fluctuations was proposed that makes it possible separate the impact of large and small scales of atmospheric turbulences.     

利用闪烁和到达角起伏测量横向风速的对比研究

基于湍流冻结假说,利用时空相关函数分析了使用大气相干长度仪(DIMM)测量横向平均风速的原理,并通过闪烁和到达角起伏测量风速的路径权重函数确定风速传感器的安装位置。在弱湍流条件下,根据水平1 km传输实验测量的到达角起伏和光强起伏数据,分别计算横向风速并与风速传感器同时测量的参考风速对比,发现利用到达角起伏计算的风速与参考风速有一定的相关性。该实验拓展了大气相干长度仪的使用功能。     

全光纤保偏声光调制器的研究与应用

全光纤保偏声光调制器(PAOM)是光传感和光通信系统的重要组成部分.理论分析了全光纤保偏声光调制器两正交偏振轴的光能量转换机理及耦合效率,讨论了在扭转声波作用下,两种全光纤保偏声光调制器的结构和调制原理.最后讨论了这种调制器在温度、应变及气体检测中的应用,并讨论了其优缺点.     

自适应光学校正空地光通信到达角起伏的研究

介绍了用自适应光学来校正到达角起伏的方法.通过数值计算对这一校正效果进行了分析研究.仿真结果表明:自适应光学能够很好地校正由大气湍流引起的到达角起伏方差.同时也证明了自适应光学系统的补偿效果与激光传输的距离和收、发孔径的大小有关系.     

Weak scattering in random media, with applications to remote probing

A simple phase-screen technique has been used to derive statistical characterizations of the perturbations imposed upon a wave (plane, spherical, or beamed) propagating through a random medium. The method is essentially physical rather than mathematical; its application is limited only by the weak-scattering approximation, a limitation which is important only for long optical or acoustical paths. No other wavelength restriction is imposed. Situations treated include arbitrary path geometries, finite transmitting and receiving apertures, anisotropic or lossy media, and polarization effects. Results include, in addition to the usual statistical quantities, time-lagged functions, mixed functions involving phase and amplitude fluctuations, angle-of-arrival covariances, frequency covariance, and other higher order quantities.     

Polarization recovery for Polarization Shift Keying transmission based on analysis of torsion and curvature of three dimensional curve segments

A solution to the problem of recovering and tracking the signal configuration at the receiver side for digital optical transmission systems employing the modulation of polarization (POLSK) is proposed. The tracking algorithm for signal configuration is based on analysis of torsion and curvature of three dimensional curve segments. Impact of polarization effects on presented method is investigated. The only impairments considered in this paper are: frequency-independent birefringence and one lumped PDL element. The numerical simulations and experiments shows that the presented method is resistant to change of fiber optics birefringence; and is sensitive to depolarization effect and state of polarization location fluctuations which are equal or faster than the data rate.     

背景各向异性不均匀的随机起伏电离层中高频电波散射的几何光学近似

本文讨论了背景为各向异性、不均匀的随机起伏电离层中高频电波的传播和散射问题。在几何光学近似下，给出了电子浓度不均匀体散射引起的高频电波的相位与振幅的起伏，并在此基础上，讨论了起伏的统计特性。结果表明，由各向异性引起的侧向偏移与极化效应对高频电波波场的起伏有显著的影响，往往不能忽略。     

Line-of-sight wave propagation through the turbulent atmosphere

A review of the recent developments in the field of random fluctuations of an electromagnetic wave propagated over a line-of-sight path is presented. The major interest is in the optical to millimeter wavelength range where fluctuations in amplitude, phase, and angle-of-arrival are important system considerations. It is assumed that the fluctuations are the result of variations in the refractive index caused by turbulence in the atmosphere. The review concentrates on the major approximations involved in the theoretical developments, and in particular, attempts to put in perspective the arguments over Rytov's method. The paper includes a number of previously untranslated results from the Russian literature, and some previously unpublished results of the author's. A brief assessment of new theoretical approaches and a discussion of some extremely important experimental work are given.     

Soil Moisture Retrieval Using GNSS-R Techniques: Experimental Results Over a Bare Soil Field

This paper presents a new technique to retrieve soil moisture using global navigation satellite signals reflected over the soil surface using the measurement of the power fluctuations of the signal created by the interference between the direct GPS signal and the one reflected over the soil surface. As a function of the elevation angle, power fluctuations at vertical polarization pass through a notch, which is related to the soil moisture content, while horizontal polarization exhibits a very weak dependence. Experimental results of the measurements obtained over a bare soil field are presented and discussed.      

光栅成像位置传感器中的偏振调制技术

提出了一种用于光栅成像位置传感器的偏振调制技术,利用米勒矩阵对其调制原理进行了详细的分析。该偏振调制器主要由起偏器、萨伐尔板、两块1/4波片、光弹调制器和检偏器构成。起偏器、萨伐尔板置于探测光栅之前,在探测光栅位置上形成两个错位的偏振方向正交的像光栅。两块1/4波片、光弹调制器和检偏器置于探测光栅之后,实现对莫尔信号的高频调制。该偏振调制技术消除了光源光强波动和电路增益变化引入的测量误差,抑制了杂散光、探测器噪声对测量结果的影响。实验验证了该偏振调制技术的有效性,结果表明这一技术使光栅成像位移传感器获得了优于12 nm的重复测量精度。     

On a two-scatterer theory of sea echo

Results of visual observations and statistical analyses on the polarization dependence of fluctuations in radar echo are given. Some data are also given on relative power, as a function of polarization, contained in the two distinctly different fluctuation spectra observed. The fast fluctuations are from wind ripples, and the slower fluctuations are strongly dependent on the sea structure. The information on fluctuations is given as support of a two-scatterer concept for sea echo. The scatterers are: 1) a wind-dependent fine structure of the sea (ripples) interspersed with 2) smooth areas (facets) of the wave structure. The composite theory for rough surfaces developed recently in both the United States and the Soviet Union predicts that average radar cross section of sea echo for transmitting and receiving horizontal polarization never exceeds that for vertical polarization. However, measurements at near grazing incidence yield average HH cross sections that sometimes exceed average VV cross sections, and the observations reported herein suggest that reflection from facets is the cause. The composite theory includes the facets only in the sense of varying the slope of the waves on which the ripples are located. Therefore, the need is emphasized for a sea echo theory that is applicable to small incidence angles and includes the effects of the facets.     

一维各向异性掺杂光子晶体的缺陷模特性

利用传输矩阵的方法给出了光波在一维各向异性掺杂光子晶体中传播的透射率,研究了缺陷模的相关特性,经数值模拟计算得出:光通过一维各向异性掺杂光子晶体后,透射波中TE波和TM波存在明显的缺陷模,缺陷模的中心波长位置随光波入射角的改变而不同,两个缺陷模能完全分开;TE波的缺陷模中心波长位置随着光学厚度的增大向短波方向移动,TM...     

激光斜程湍流大气传输平均偏振起伏

运用光子密度分布函数和采用大气折射率起伏Von Karmam湍流谱、研究了相干激光通过斜程大气传输时的平均量子偏振起伏。通过唯象方法导出大气折射起伏对光场相位调制关系,从而建立了斜程大气光子密度分布函数模型。基于斜程湍流大气光子密度分布函数导出了平均＂量子偏振度＂的解析关系。结果指出：湍流大气导致光束偏振度起伏满足零均值高斯分布,大气湍流不影响光子偏振度统计平均值。     

多光束消偏振叠加对焦斑特性的影响

在惯性约束聚变(ICF)驱动器设计中,利用正交偏振板改变光束内部偏振态,实现靶面消相干叠加,以进一步改善靶面辐照均匀性。建立了正交偏振板的透过率函数,分别对单光束和多光束叠加两种情况下的焦斑偏振特性及均匀性进行数值模拟和分析。结果表明,利用正交偏振板能较好地实现光束消偏振叠加,焦斑在时间统计上表现为部分偏振光;采用正交偏振板互补组合方式时,消偏振效果随偏振板单元数的变化不敏感,因而可以选取单元数较少的正交偏振板,以降低对加工工艺的要求。     

Performance evaluation of waveguide phase modulators for coherent systems at 1.3 and 1.5 µm

This article describes the fabrication and performance evaluation ofX-cut andZ-cut Ti:LiNbO3traveling wave waveguide phase modulators designed for coherent systems applications at 1.3 and 1.5 μm. Details of device fabrication and measurements of phase shift as a function of optical wavelength, input polarization, modulation voltage, and modulation frequency are reported. Phase modulator performance in a 40-Mbit/s self-heterodyne coherent DPSK experiment is also discussed.     

Scattering by a conducting strip with a periodic edge

The electromagnetic field scattered by a conducting strip with a periodic edge consists of a finite number of radiating, generally depolarized, modes. The relative intensities are estimated by using the physical optics approximation for the induced current.     

Analysis of input-polarization-induced phase noise ininterferometric fiber-optic sensors and its reduction using polarizationscrambling

The dependence of the phase shift of an interferometric fiber sensor on the input state of polarization is analyzed, and it is shown that fluctuations in the input polarization to a fiber interferometer can lead to the generation of excess phase noise. The relationship between this effect and the variation in visibility with input polarization is described and theoretically confirmed. The use of depolarized source light to eliminate input-polarization-induced excess phase noise is theoretically and experimentally demonstrated