静磁表面波对高斯光脉冲的衍射特性研究

研究了磁光薄膜波导中线性啁啾高斯光脉冲与单频连续静磁波共线作用,给出了水平磁化时基于静磁表面波的磁光耦合方程.分别采用解析法和数值法计算了1310 nm和1550 nm两种光波长入射时衍射光的压缩特性,两种求解方法得到的结果一致.计算表明,衍射光脉冲的半峰全宽(FWHM)随相位失配因子的频率变化率和啁啾系数的增大而减小;在给定的计算参数下,与1310 nm波长对应的衍射光脉冲具有较大的峰值强度,但1550 nm波长输入时可以获得更窄的衍射光脉冲,因而1550 nm光脉冲更适于作为磁光脉冲压缩的脉冲源.文章还分析了磁损耗对衍射光脉冲的光强和输出脉宽的影响,对于普通的磁光薄膜,损耗基本上不影响光脉冲压缩效果.     

方波磁光调制测量在无机械连接的设备间方位传递中的应用

在航天、军事等领域往往需要传递无机械连接的设备之间的空间方位信息,而传统的方位测量系统测量范围小、测量精度低,难以满足系统高精度大范围传递的要求,为此改变传统方法中的调制方式,将方波磁光调制引入了方位测量系统,建立了基于方波磁光调制的方位测量模型。根据马吕斯定律,建立了方波磁光调制后的输出信号模型,并分析了调制后信号的特点。根据调制后信号的表达式与方位角的关系,推导、建立了调制后信号与方位角之间的关系方程,并利用调制后信号的增减性去除了方程的增根,结合调制前后信号的相位对比扩大了方位角的测量范围,最终得到了基于方波磁光调制的方位测量模型,实现了无机械连接的设备之间方位信息的传递。仿真结果表明,提出的基于方波调制的测量方法与传统方法比较,理论测量精度更高、测量范围更广,这为实现空间方位角高精度大范围测量提供了一种参考。     

基于矩形波信号的磁光调制偏振测量方法

建立并研究了基于矩形波磁光调制的检偏方法.运用计算机模拟,对矩形波磁光调制的利萨如图形进行了详细考察,研究了其检偏原理,并对其检偏精度进行了分析.研究表明.矩形波磁光调制的利萨如图形由几个离散点组成,通过观察离散点彼此之间是否重合,就可以判断检偏器是否处于消光位置.从而达到检偏的目的.同时,若用电子仪器监测输出信号是否为直流,即可以实现自动检偏.与基于正弦波磁光调制的倍频法相比,矩形波磁光调制方法的检偏精度有了明显提高,并且也容易实现自动测量.     

组合光调制中矢量分析方法

一般文献对光调制的分析方法为矩阵分析法,本文提出用矢量分析的新方法,并用此方法详细分析了电光调制和磁光调制的组合光调制中输出光强信号,得出了与矩阵方法一样的结果。     

正弦波与方波磁光调制的比较分析

基于正弦波磁光调制原理，同时利用利萨如图形方法，对正弦波磁光调制和方波磁光调制进行了计算机模拟．模拟结果表明，正弦波磁光调制具有磁光调制原理所描述的基本特性，并且其偏振角度检测准确度可达到0．001°；而方波磁光调制具有更好的应用特性，不存在波形失真问题，其氏取值不受小角度条件的限制，其偏振角度检测准确度可高于0．001°．对两种磁光调制进行的对比性实验研究，进一步支持了以上结论，表明方波磁光调制无论用于信号调制或用于偏振角度检测都具有独特的优势．另外，在实验中发现了两种磁光调制的限幅效应，并对其形成的原因进行了初步分析．     

内含光栏的光栅对展宽器式脉冲整形器的输出光束特性

在忽略空间衍射效应的情况下,研究了内含狭缝光栏的光栅对展宽器式脉冲整形器的输出光束的时间特性；通过与光束的空间传输特性类比解析了光栏宽度变化引起的脉宽变化以及脉冲轮廓出现时间衍射调制现象；讨论了空间衍射效应可忽略的条件；提出用光栏软边可消除这种调制。     

组合光调中矢量分析方法

一般文献对光调制的分析方法为矩阵分析法,本文提出用矢量的新方法,并用此方法详细分析了电光调制和磁光调制中输出光强信号,得出了与矩阵方法一样的结果     

基于两种静磁模的磁光压缩特性比较

将磁光效应作为微扰, 采用耦合模理论分析了磁光薄膜波导中微波静磁波对线性啁啾光脉冲的磁光Bragg衍射作用, 得到了传统磁化时磁光共线和非共线作用下的衍射光脉冲复振幅的解析表达式。在静磁波频率和波数相同的前提下, 通过对实际波导结构的计算表明, 基于静磁表面波的磁光共线作用比基于静磁正向体波的非共线作用更易于实现光脉冲压缩; 衍射光脉冲的半极大全宽度(FWHM)对失配斜率的依赖较为敏感。因此, 选用磁光共线作用和优化相位失配因子的频率变化率有助于改善磁光Bragg脉冲压缩器的性能。     

基于微波静磁波的并行磁光频谱分析研究

利用多个频率的微波静磁波同时与导波光的磁光作用可产生多级Bragg衍射光的原理可实现并行磁光频谱分析，即微波频率与衍射光在傅里叶透镜焦平面上的位置一一对应，而微波信号强度由多频静磁波对导波光的衍射效率确定。根据三频静磁波与导波光的磁光耦合方程，进行了仿真计算，结果表明，通过考虑多频磁光衍射中相位失配因素对衍射效率的影响可很好地恢复多频信号的相对强度。     

内含光栏的光栅以展宽器式脉冲整形器的输出光束特性

在忽略空间衍射效应的情况下，研究了内含狭缝光栏的光栅对展宽器式脉冲整形器的输出光束的时间特性。通过与光束的空间传输特性类比解析了光栏宽度变化引起的脉宽变化以及脉冲轮廓出现时间衍射调制现象；讨论了空间衍射效应可忽略的条件；提出用光栏软边可消除这种调制。     

Factorial correlators: angular scaling within QCD jets

Factorial correlators measure the amount of dynamical correlation in the multiplicity between two separated phase-space windows. We present the analytical derivation of factorial correlators for a QCD jet described at the double logarithmic (DL) accuracy. We obtain a new angular scaling property for properly normalized correlators between two solid-angle cells or two rings around the jet axis. Normalized QCD factorial correlators scale with the angular distance and are independent of the window size. Scaling violations are expected beyond the DL approximation, in particular from the subjet structure. Experimental tests are feasible, and thus would be welcome. Received: 12 January 2001 / Published online: 7 September 2001     

Signal preprocessing for digital correlators

The input format of fast digital correlators, such as used in photon correlation or recurrence rate correlation, is often exceeded by input signals, if high count rates coincide with sample times of the order of several hundred nanoseconds or more. Clipping, random clipping, and scaling are well known methods to reduce such signals appropriately. We discuss these procedures with special attention to noise performance possible errors introduced into the correlogram. Generalizations from single to multi-bit correlators are presented with a thorough discussion of random preset scaling, a new process suitable for multi-bit correlation of signals with arbitrary statistics. Furthermore we describe a new additional preprocessor which offers significant decrease of quantization noise, if constant background contributions are present in the signal. Though demonstrated on optical measurements, the methods treated in this paper generally apply, whenever the format of digital data has to be reduced prior to correlation.     

多频微波静磁波与导波光互作用研究

分析了磁光薄膜中同时激发的多个频率的静磁波对导波光的衍射作用过程,以三频为例推导了三级近似的耦合模方程,对于两频磁光作用的理论计算与实验基本一致.对于三频磁光作用,数值分析结果表明：对于主衍射效率（Principle Diffraction Efficiency,PDE）,小信号时只需考虑一级磁光作用.在超出小信号范围且PDE达到峰值之前,第三级磁光作用对PDE影响很小,只需考虑前两级磁光作用.小信号时,得到了PDE的近似解析表达式,在一定的频率间隔范围内与耦合方程的一级近似解较为符合.     

Discrimination of interaural phase differences in the envelopes of sinusoidally amplitude-modulated 4-kHz tones as a function of modulation depth

Psychometric functions were measured for the discrimination of the interaural phase difference (IPD) of the envelope of a sinusoidally amplitude-modulated (SAM) 4-kHz pure tone for modulation frequencies of 128 and 300 Hz and modulation depths (m) of 0.2, 0.6, 0.9, and 1.0. Contrary to recent modeling assumptions, it was found that a constant change in normalized interaural envelope correlation, with or without additional model stages to simulate peripheral auditory processing, did not produce a constant level of performance. Rather, in some cases, performance could range from chance to near perfect across modulation depths for a given change in normalized interaural envelope correlation. This was also true for the maximum change in normalized interaural envelope correlation computed across the cross-correlation functions for the stimuli to be discriminated. The change in the interaural time difference (ITD) computed from the IPD accounted for discriminability across modulation depths better than the change in normalized interaural envelope correlation, although ITD could not account for all the data, particularly those for lower values of m.     

GPS signal acquisition via compressive multichannel sampling

In this paper, we propose an efficient acquisition scheme for GPS receivers. It is shown that GPS signals can be effectively sampled and detected using a bank of randomized correlators with much fewer chip-matched filters than those used in existing GPS signal acquisition algorithms. The latter use correlations with all possible shifted replicas of the satellite-specific C/A code and an exhaustive search for peaking signals over the delay-Doppler space. Our scheme is based on the recently proposed analog compressed sensing framework, and consists of a multichannel sampling structure with far fewer correlators.The compressive multichannel sampler outputs are linear combinations of a vector whose support tends to be sparse; by detecting its support one can identify the strongest satellite signals in the field of view and pinpoint the correct code-phase and Doppler shifts for finer resolution during tracking. The analysis in this paper demonstrates that GPS signals can be detected and acquired via the proposed structure at a lower cost in terms of number of correlations that need to be computed in the coarse acquisition phase, which in current GPS technology scales like the product of the number of all possible delays and Doppler shifts. In contrast, the required number of correlators in our compressive multichannel scheme scales as the number of satellites in the field of view of the device times the logarithm of number of delay-Doppler bins explored, as is typical for compressed sensing methods.     

TFT construction of RCFT correlators IV:: Structure constants and correlation functions

We compute the fundamental correlation functions in two-dimensional rational conformal field theory, from which all other correlators can be obtained by sewing: the correlators of three bulk fields on the sphere, one bulk and one boundary field on the disk, three boundary fields on the disk, and one bulk field on the cross cap. We also consider conformal defects and calculate the correlators of three defect fields on the sphere and of one defect field on the cross cap.Each of these correlators is presented as the product of a structure constant and the appropriate conformal two- or three-point block. The structure constants are expressed as invariants of ribbon graphs in three-manifolds.     

基于绝对差度量的灰阶图像光学匹配运算

讨论了基于绝对差度量的灰阶图像识别问题;利用光学相关原理和循环编码方法实现了基于绝对差度量的灰阶图像快速匹配处理;基于差异度矩阵和λ截集的概念来描述匹配结果,提高了灰阶目标识别抵抗各种畸变干扰的稳定性。此方法可以适用于任何的相干光和非相干光相关系统,给出了实验示例。     

南中国海存在孤立子内波条件下的声场时间相关半径

在动态的海洋环境中,由于数据向量和拷贝场之间的失配,匹配场处理器的性能会发生退化。数据向量的时间相关半径是这种退化的一种量度。通过2001年ASIAEX南海实验中垂直阵上水听器接收到的声场数据求取了400 Hz窄带信号的声场时间相关。从实验数据处理结果观察到,伴随着传播路径上非线性内波的进入,声场的时间相关半径减小。同时利用一个二维的平流冻结海洋模型和传播路径上三个温度链的温度数据对声场进行了数值仿真,分析了不同频率下的声场时间相关半径。结果表明:实验结果与仿真的400 Hz信号的声场时间相关较为一致。可见,在时变的海洋环境下,声信道中存在孤立子内波将会使声场的时间相关半径大大缩短。      

Quantifying the effects of fast-acting compression on the envelope of speech

Fast-acting compression has several effects on the envelope of speech signals, especially when a target and a background are mixed together. Three measures of the envelope are described, which can be used to quantify these changes: (1) Within-signal modulation correlation or coherence, the degree of correlation (or coherence) of the envelope (on a dB scale) of a single source across different frequency regions, which is reduced by fast-acting compression; (2) fidelity of envelope shape, the degree to which the envelope shape of the target speech in different frequency channels is preserved following compression; and (3) across-signal modulation correlation or coherence (ASMC), the extent to which the target and background acquire a common component of modulation when they are compressed together, which becomes greater in absolute value (more negative) when the target and background are compressed together. Values of these measures are presented and compared with intelligibility scores obtained using stimuli processed (with a noise-vocoder) so as to preserve mainly envelope cues in a limited number of frequency channels. The results suggest that the dominant factor affecting intelligibility is ASMC.     

Quantum Harmonic Oscillator Systems with Disorder

We study many-body properties of quantum harmonic oscillator lattices with disorder. A sufficient condition for dynamical localization, expressed as a zero-velocity Lieb-Robinson bound, is formulated in terms of the decay of the eigenfunction correlators for an effective one-particle Hamiltonian. We show how state-of-the-art techniques for proving Anderson localization can be used to prove that these properties hold in a number of standard models. We also derive bounds on the static and dynamic correlation functions at both zero and positive temperature in terms of one-particle eigenfunction correlators. In particular, we show that static correlations decay exponentially fast if the corresponding effective one-particle Hamiltonian exhibits localization at low energies, regardless of whether there is a gap in the spectrum above the ground state or not. Our results apply to finite as well as to infinite oscillator systems. The eigenfunction correlators that appear are more general than those previously studied in the literature. In particular, we must allow for functions of the Hamiltonian that have a singularity at the bottom of the spectrum. We prove exponential bounds for such correlators for some of the standard models.