Design of the Optimum Holographic Optical Element Lens Using the Hologram Computer-Aided Design Tool

A hologram CAD (computer-aided design) tool capable of designing holographic optical element (HOE) is described. We have been developing this tool which is specialized for holograms. An optimum HOE lens with high diffraction efficiency and diffraction limited imaging characteristics is designed with the tool by applying a computer generated hologram (CGH) which generates an aspherical wave. The imaging characteristics of the HOE lens are experimentally verified and desirable results are obtained.This paper was originally presented at the 2nd International Conference on Optical Design and Fabrication, ODF2000 which was held on November 15-17, 2000 at the International Conference Center, Tokyo, Waseda University, Japan.     

基于谱线频率特征的调谐二极管激光吸收光谱参数分析

调谐激光二极管吸收光谱(TDLAS)技术因其高分辨率、高灵敏度和快速测量等优点在工业生产、环境污染监测等方面受到广泛应用。波长调制光谱（wavelength modulation spectrum, WMS）的二次谐波信号经常用作气体浓度反演的检测信号。TDLAS检测性能与系统参数,如锁相放大器的时间常数、扫描幅度、扫描频率、调制幅度、调制频率等的选取紧密相关,实际测量中各参数的选择多以谱线形态特征为依据,参数之间的关联性未能得到较好体现。由于信号的采样与处理均在频域对谱线产生作用,各参数之间的作用相互关联。然而很少有研究参数对谱线频域的影响,针对此问题,在一定的理论基础上通过实验分别观察各调制参数对二次谐波信号的影响。通过保持其他参数不变,只改变一个参数的方法,得出各个参数对信号线型、频率特征及噪声引入的影响规律,继而分析并验证了多参数联合变化对谱线频带的决定作用。与基于时域特征的传统方法相比,基于谱线频率特征分析一方面具有与谱线信号采集检测处理机理相近的优点,另一方面可以直观得到各参数对主频带的影响和不同频率信号的衰减趋势。总结出基于频率特征的各参数的基本选取方法,以谱线频带和截止频率相互关系为判定标准,截止频率的大小由锁相放大器时间常数决定。通过设置合适的时间常数和扫描参数使信号频带与截止频率相近但不相交,使谱线频带内频率分量不产生衰减,频带外噪声得到最大抑制;再根据锁相放大器的性能和信号信噪比来确定调制参数,使谱线主频幅度最大;最后根据系统需求确定采样率。单周期采样点不变时,低扫描频率时检测精度相对提高但耗时较长;反之,扫描频率提高,速度变快但检测精度下降。通过联合影响规律调整关联参数,减小硬件限制对参数最优值选取造成的影响。可在考虑系统检测需求与硬件条件限制的前提下,通过参数选择得到最优二次谐波信号,为此技术的实际应用提供了参数优化的实验依据与参考方法。     

过阻尼搓板势系统的随机共振

研究在周期信号和高斯白噪声共同作用下过阻尼搓板势系统的随机共振.由于用直接模拟法研究随机系统所用时间较多,考虑用半解析的方法对系统的随机共振现象进行研究.在弱周期信号极限下,结合线性响应理论和扰动展开法提出一种计算系统线性响应的矩方法.在此基础上,利用Floquet理论和非扰动展开法将矩方法扩展到系统非线性响应的计算.通过直接数值模拟结果和矩方法所得结果的比较展示了矩方法的有效性并采用均方差作为量化指标给出其适用的参数范围.研究结果表明,以系统的功率谱放大因子作为量化指标,发现在适当的参数条件下,系统的共振曲线有一个单峰出现,说明过阻尼搓板势系统存在随机共振现象.而且在一定范围内调节偏置参数时,共振曲线的峰值随偏置参数的增大而增大;在调节驱动幅值时,随机共振效应随驱动幅值的增大而增强.     

A Novel Fabrication Technique of Long Period Fiber Gratings Using a Holographic Optical Element

We develop a new flexible and precise ultraviolet exposure technique to fabricate a long period fiber grating using a computer-generated holographic optical element (HOE). The HOE can generate a striped beam pattern with about a 300 #x03BC;m period from a KrF excimer laser. This method offers (1) ease in varying the grating period and (2) grating period precision. We achieve a grating period within an accuracy of #x00B1;0.04 #x03BC;m. This means that the peak wavelength can be controlled within an accuracy of #x00B1;0.2nm with an operating wavelength of 1.55 #x03BC;m.This paper was originally presented at the 2nd International Conference on Optical Design and Fabrication, ODF2000 which was held on November 15-17, 2000 at the International Conference Center, Tokyo, Waseda University, Japan.     

基于平均吸收的太赫兹波振幅成像研究

提出了一种基于一定频率内平均吸收的太赫兹(THz)波振幅成像新方法。太赫兹波频率在0.1～10 THz之间,波段位于红外和微波之间。太赫兹波成像技术的一个显著特点是信息量大,如何对每个样品点的大量信息进行处理提取有用信息重构出样品的图像是一项关键技术。选用中间挖空有“THz”字样的白纸为样品作太赫兹波成像研究,首先探讨了时域和频域上几种常用太赫兹波振幅成像方法所反映的样品信息及其特点,进一步使用提出的基于一定频率内平均吸收的太赫兹波振幅成像新方法对样品进行图像重构。实验结果表明这种新方法可以很好的反映样品的真实信息,反映了样品在一定频率范围内由于吸收而引起的效果的综合,与吸收系数和厚度相关,离散效应得到了很好的消除,相对几种常用的太赫兹波振幅成像方法能够得到更清晰的图像。此新方法尤其适用于结构简单的样品,能够成为几种常用振幅成像方法的有力补充。     

相位调制激光多普勒频移测量方法的改进

本文对现有相位调制激光多普勒频移测量方法进行了改进,通过定义新的鉴频参量来同时利用相位调制信号直流和交流分量中的有用信息进行多普勒频移测量.由于相位调制信号直流分量中包含着调制信号光的Fabry-Perot干涉仪光强透过率,所以这一改进本质上是将基于Fabry-Perot干涉仪的边缘技术激光多普勒频移测量方法的优势引入到相位调制测量方法中,以提高其自身的性能.理论上证明改进后的相位调制激光多普勒频移测量方法无需对信号光的光强进行测量,所以可以进一步简化探测系统的结构和较少噪声混入的通道.另外,通过对改进前后鉴频和测量灵敏度曲线进行对比,还证明了其具有更高的测量灵敏度和动态范围.实验上对硬目标反射的频移可控信号光进行测量,不但证明了理论的正确性,而且证明了改进后的相位调制激光多普勒频移测量方法,测量动态范围提高约1倍,测量标准偏差降低约35%.     

Wavelength-Multiplexing Diffractive Phase Element with Quantized Phase Structure

We have reported on the design algorithm of the wavelength-multiplexing diffractive phase element (WMDPE) capable of generating independent spot patterns for more than two wavelengths. [J. Opt. Soc. Am. A 18 (2001) 1082] In this paper, the stepwise quantization method proposed by F. Wyrowski [J. Opt. Soc. Am. A 7 (1990) 961] is built into the algorithm to design the WMDPE with quantized phase structure. Validity of the method is verified by the WMDPE for 7 wavelengths with 9 phase levels. The optical experiment demonstrates that the fabricated WMDPE generates correct patterns for different wavelengths. Performance dependence of the WMDPE on the number of quantized phase levels is discussed based on the simulation results.This paper was originally presented at the 2nd International Conference on Optical Design and Fabrication, ODF2000 which was held on November 15-17, 2000 at the International Conference Center, Tokyo, Waseda University, Japan.     

Dependence of BOLD signal change on tactile stimulus intensity in SI of primates

Recently, we have demonstrated that the fine-digit topography (millimeter sized) previously identified in the primary somatosensory cortex (SI), using electrophysiology and intrinsic signal optical imaging, can also be mapped with submillimeter resolution using blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging at high field. In the present study, we have examined the dependence of BOLD signal response on stimulus intensity in two subregions of SI, Areas 3b and 1. In a region(s)-of-interest (ROI) analysis of Area 3b, BOLD signal amplitude increased linearly with increasing amplitude of an 8-Hz vibrotactile stimulus, and BOLD signal was sustained throughout the stimulation period. In contrast, in Area 1, a significant BOLD signal response was only observed with more intense stimuli, and ROI analysis of the dependence of BOLD response showed no significant dependence on stimulus intensity. In addition, activation was not sustained throughout the period of stimulation. Differing responses of Areas 3b and 1 suggest potentially divergent roles for subregions of SI cortices in vibrotactile intensity encoding. Moreover, this study underscores the importance of imaging at small spatial scales. In this case, such high-resolution imaging allows differentiation between area-specific roles in intensity encoding and identifies anatomic targets for detailed electrophysiological studies of somatosensory neuronal populations with different coding properties. These experiments illustrate the value of nonhuman primates for characterizing the dependence of the BOLD signal response on stimulus parameters and on underlying neural response properties.     

Elements of Cost-Based Tolerancing

One goal for optical design is to assign tolerances so that the as-built systems satisfy all required specifications and have the lowest fabrication and assembly expense. Tolerances affect not only the image quality, but also the production cost. Thus tolerance assignment is a critical step in the optical design process. In this paper we discuss the essential elements of a cost-based tolerancing method. The paper concludes with an example comparing results from a cost-based tolerancing procedure with results from a conventional approach.This paper was originally presented at the 2nd International Conference on Optical Design and Fabrication, ODF2000 which was held on November 15-17, 2000 at the International Conference Center, Tokyo, Waseda University, Japan.     

二值噪声驱动下二阶线性系统的随机共振

研究了二值噪声驱动下二阶线性系统的随机共振问题. 采用平均法推导出系统输出幅值增益的表达式,考察了幅值增益与系统频率、输入信号频率、噪声强度和噪声相关时间的关系,发现系统输出幅值增益随这些参量呈单峰共振变化. 另外,二值噪声的非对称性对共振峰值具有很大影响. 关键词： 随机共振 幅值增益 二值噪声 二阶线性系统     

Temperature dependent lineshape changes in solid H2 for low oH2 concentrations

The nmr lineshape due to unpaired oH₂ molecules in solid pH₂ changes significantly below 0.2 K. A deconvolution of lineshape based on a mitional narrowing model yields the relative amplitude of the part of the signal showing resolved structure as well as the temperature dependence of the frequency determining parameter. Both the relative amplitude of this signal and the temperature at which structure appears decrease with increasing oH₂ concentration.     

频域稀疏采样和激光成像方法

激光的单色性和自然图像频谱稀疏且集中在低频区间的特点,使图像频谱稀疏采样成像成为可能.基于小规模激光探测器,引入参考激光,本文提出了频域稀疏采样激光成像方法.介绍了频域稀疏采样激光成像的原理和成像系统结构,推导了激光回波重构复频谱的表达式,给出了重构频谱和复图像的仿真结果并分析了信号参数对重构效果的影响,同时采用相干系数、均方误差和结构相似度来评价其重构效果.规模为256×256的激光回波复图像仿真表明, 5个拼接1/4×1/4规模频域探测器组成的近似十字型稀疏采样结构,在约31.25%(5/16)的频域稀疏采样条件下,仍可获得较好的重构频谱和重构复图像.     

Reconstruction of holograms generated by using a combination of an iterative method and an error diffusion method

Two-level quantized phase holograms produced by using a combination of an iterative method and an error diffusion method are presented. By using a previously proposed iterative method, images reconstructed from two-level quantized phase holograms are rapidly improved with small amounts of iterative operations but further improvement of the image quality is difficult even if the iterations are greatly increased. Therefore, in order to exceed the improvement limitation of the image quality, the combination of the iterative method and an error diffusion method was used for the hologram-making process. Experimental results using the combination method showed better images than those obtained by the iterative method alone, when referred to results from synthesized holograms.     

三维物体多重菲涅耳计算全息水印与无干扰可控重建方法

提出了一种基于三维物体的多重菲涅耳计算全息水印方法.将水印信号作为虚拟三维物体的层面,首先结合分区复用层析法和菲涅耳双随机相位编码方法产生复噪声形式的水印信号;然后对水印信号的频谱作共轭对称处理实现实值编码;为减小对宿主全息图数字重建的影响,将水印信号的频谱设置于对宿主数字重建影响小的频谱非感兴趣区域;编码后的信号以一定强度叠加于宿主全息图,水印信号恢复无需原始宿主全息图信息,可实现盲提取,对宿主全息图重建像面的二维码可扫描识别.仿真测试结果表明,所提出的方法具有较好的透明性和稳健性,在宿主全息图遭受滤波、JPEG(联合图像专家小组)压缩、高斯噪声、剪切、旋转等各种攻击的情况下,不论对宿主还是水印信号仍具有良好的数字重建质量,对重建像面的二维码仍可扫描识别;而重建像面水印信号的无干扰可控重建后处理操作解决了不同层面水印信号之间的衍射干扰问题,提高了水印信号的重建质量.虚拟光学手段的应用丰富了水印信号设计方法并提升了算法的安全性.     

Controlling vibrational resonance in a multistable system by time delay

The phenomenon of vibrational resonance in a delayed multistable system that is excited by biharmonic signals is investigated in the present paper. Different from the former theory, the appearance and the disappearance of the vibrational resonance are controlled by adjusting the time delay parameter instead of modulating the amplitude of the high-frequency signal. The motion of the orbit within or between the different potential wells can also be controlled. Furthermore, based on both the methods of numerical simulation and analytical analysis, the behavior of delay-induced multiple vibrational resonance and its mechanism are investigated and discussed. The multiple vibrational resonance, which is quantified by the response amplitude at the low-frequency, is found to be periodic in the delay parameter with two periods, i.e., the periods of the two driven signals. The method used in this paper gives a new way for controlling vibrational resonance in a multistable system.     

On the dynamical properties of a Fermi accelerator model

In this paper we use discrete dynamical systems formalism to carefully investigate the effect of a time-dependent perturbation on a classical mechanical model. We present a study of a one-dimensional Fermi accelerator model and its parametric dependence on the amplitude of the movement of the wall. We focus on the low-energy region, in which the system may present chaotic behavior illustrated by orbits with stochastic behavior and sensitive dependence on initial conditions. Through numerical analysis, this behavior is quantitatively characterized by a positive Lyapunov exponent and by the position of the boundary of the observed ergodic component. Our results will be analyzed by comparing this model to a simplified version and to the Standard Map. These results indicate that the dynamics of the model is, in a certain sense, very weakly dependent of the parameter.     

改进的傅里叶域小波域联合去模糊算法

傅里叶域与小波域的联合去模糊算法在低噪声时具有优越的恢复效果,但是这种联合去模糊算法并不适用于含噪声的模糊图像.为了解决这一问题,本文将先验约束分别引入傅里叶域的去模糊步骤和小波域的去噪步骤.在傅里叶域,用矩阵形式表示目标函数.对目标函数添加平滑约束并且通过噪声水平和模糊图像高频信息计算得到平滑约束项的滤波系数.同样方式,在小波域对小波域目标函数添加能量约束,实现小波域目标函数的正则化过程.分析傅里叶域的噪声放大程度,通过傅里叶域的滤波系数计算得到小波域能量约束的滤波系数.傅里叶域的平滑约束可以抑制滤波过程中噪声的产生,小波域的能量约束可以提高小波域滤波的鲁棒性.仿真实验表明,改进的算法相比于原始算法具有更好的鲁棒性,可以有效提高图像的恢复质量.对于噪声标准差为0.010.1的模糊图像,改进算法恢复图像峰值信噪比比原始算法恢复图像的峰值信噪比高1左右.并且改进算法对于高斯型点扩散函数误差具有鲁棒性,当点扩散函数估计方差与实际方差相差0.4时,改进算法的恢复效果仍优于原始算法.     

Slow nonlinearity kinetics of the viscoelastic properties of oil during shear vibrations

Earlier we discovered the slow evolution of viscoelastic moduli of heavy crude oil. The shear modulus was measured at frequencies of 0.5, 5, and 50 Hz at different temperatures over 72 h. New studies of the dependence of the complex shear modulus on the strain amplitude revealed a logarithmic increase in the nonlinearity parameter as a function of time for this oil sample. It was experimentally established that the complex shear modulus is a linear function of the amplitude of shear perturbations. This is possible in the case of a linear dependence of values of the viscoelastic characteristics on the medium modulus of deformation.     

On the turbulent propagation of a flame in a closed volume

Regularities in the mutual variation of the velocity of propagation and electrical conductivity of a flame are investigated experimentally for turbulent combustion in a closed volume. An estimate proposed as a result of analysis of experimental data describes analytically the dependence of the velocity of propagation of the flame on the signal amplitude at ionization probes. In our opinion, the singularity observed on the approximate curve describing the dependence of the flame propagation velocity on the signal amplitude at ionization probes is responsible for the competition between generation and destruction of charged particles in the flame and corresponds to the conditions of quasi-stationary concentrations. The proposed method and established experimental facts can be used in the development of methods for diagnosing local intensity of burning in combustion chambers.     

Simulation of AE signals and signal analysis systems

A stochastic series is presented by which a typical AE signal detected by resonant transducer can be described. The series is then analysed numerically by a simulated system for AE amplitude distribution analysis. Comparison between the analytic distribution used in the generation of random series and the distribution obtained from the simulated system demonstrates how closely the measured parameter β corresponds to the parameter of source amplitude distribution b. The analysis shows that amplitude analysis gives better results when performed on ring-down bursts than on corresponding demodulated signals.