采用仿射变换的红外与可见光图像配准方法

图像配准是图像融合技术的基本环节和首要问题。针对红外和可见光图像的配准问题,分析了两者配准的特点。引入6参数的仿射变换模型来描述3D空间中的目标,分析了通常采用的4参数模型的不完备性。利用模型计算配准参数,并用最小二乘法达到用多个配准点拟合出最优参数解的目的。实验结果表明,此方法可以很好地消除红外和可见光图像之间的差异。     

Versatile generation of optical vortices based on paraxial mode expansion

We demonstrate a simple and versatile method for generating various configurations of optical vortices from a Gaussian light beam by using glass plates and an astigmatic mode converter (AMC). The glass plates are inserted into the Gaussian beam to imprint nodal lines along the edges, and the AMC then transforms the beam with the nodes into a vortex beam. The procedures are discussed in terms of a transverse-mode expansion of the paraxial light beam, in which each Hermite-Gaussian mode is converted into the corresponding Laguerre-Gaussian mode by the AMC. We generated several vortex configurations, and the results show good agreement with the theoretical predictions.     

Random number generation based on the time of arrival of single photons

We report the demonstration of a new type of true random number generator based on the random distribution of the time interval between photons from a single-photon-like source. The experimental setup is simple and robust against mechanical and temperature disturbances. With improved detector resolution and efficiency, the random number bit rate could be increased by more than an order of magnitude to satisfy practical requirements.     

Extended pseudorandom sequences and two-dimensional coding collimators based on them

A new extensive class of one-dimensional binary sequences, called extended pseudorandom sequences, is proposed which enables a radiation-physics experiment to be optimized more completely and enables problems of planar emission tomography to be solved effectively using integral-code measuring systems. __________ Translated from Izmeritel’naya Tekhnika, No. 6, pp. 66–71, June, 2007.     

基于数字希尔伯特变换的OCT信号处理与系统实现

信号处理方法的选择是光学相干层析(OpticalCoherenceTomography,OCT)系统研制的重要环节,直接决定着OCT系统的硬件构建和实现。应用硬件实现OCT信号处理的方法虽然速度快,但存在硬件开销大,系统配置可调节性差等缺点。进而采用了基于数字希尔伯特变换的软件方法来处理OCT信号。该数字处理方法对探测得到的离散干涉实信号进行解析拓展,得到同时具有振幅信息和相位信息的复信号,其中的振幅信息被用于OCT的图像重建。介绍了研制的光纤OCT系统和各驱动单元的同步时序控制,最后给出了人体皮肤和洋葱的OCT高清晰层析图。     

Model updating based on an affine scaling interior optimization algorithm

Finite element model updating is usually considered as an optimization process. Affine scaling interior algorithms are powerful optimization algorithms that have been developed over the past few years. A new finite element model updating method based on an affine scaling interior algorithm and a minimization of modal residuals is proposed in this article, and a general finite element model updating program is developed based on the proposed method. The performance of the proposed method is studied through numerical simulation and experimental investigation using the developed program. The results of the numerical simulation verified the validity of the method. Subsequently, the natural frequencies obtained experimentally from a three-dimensional truss model were used to update a finite element model using the developed program. After updating, the natural frequencies of the truss and finite element model matched well.     

Approaches to achieve broadband optical transformation devices with transmuted singularity

Many optical instruments with dielectric singularities cannot be manufactured directly. Their singularities can be transmuted through optical transformation, and equivalent physical media can be built to perform the same optical behaviors. The transformed physical media are usually anisotropic and inhomogeneous and, therefore, difficult to fabricate. In this work, several mathematical approaches are proposed to produce a transformed lens with all the elements of the material tensors to be no less than unity. This increases the ease of implementation, as natural materials may be used, which substantially widens the bandwidth of the transformed devices. Although we focus on an omnidirectional retroreflection lens as an example, the approaches developed here are universal and applicable to a wide class of devices with dielectric singularities.     

Improved numerical solver for Kansa''s method based on affine space decomposition

Radial Basis functions (RBFs) have been successfully developed as a truly mesh-free method to find the numerical solutions of partial differential equations (PDEs). In particular, the asymmetric RBF collocation method (Kansa's method) is one of the most frequently used methods due to its ease of implementation. To achieve high accuracy, the resultant system of RBF–PDE problem usually becomes badly conditioned. We propose in this paper an improved solution method based on an affine space decomposition that decouples the influence between the interior and boundary collocations. Numerical examples are given to compare the proposed method with several direct methods.     

Tunable optical frequency comb generation in a periodically poled lithium niobate waveguide based on stimulated Brillouin scattering

We propose and demonstrate a technique for the generation of an optical frequency comb (OFC) in a periodically poled lithium niobate (PPLN) waveguide based on stimulated Brillouin scattering. A single continuous wave laser is sent to a multi-wavelength Brillouin erbium fibre laser for generating a set of coherent and phase-locked multi-wavelength spectral lines. They are injected into a PPLN waveguide to obtain an OFC. We investigate the influence of the cavity structure on the OFC property in our two different schemes. The number of comb lines is affected by the 980 pump current and Brillouin pump power. The OFCs are tunable in a large range by changing their central wavelength.     

Supercontinuum generation in a single-mode optical fiber with novel dispersion profile

A novel dispersion model different from the conventional one is introduced to enhance supercontinuum generation in dispersion-flattened/decreasing fiber. The results show that supercontinuum spectrum generated in this fiber is by far wider than that in the conventional one,whose flat width can be nearly 1000 nm. The results further show that both the fiber parameters such as peak chromatic dispersion, dispersion differential constant and dispersion decreasing coefficient and the pump pulse parameters including pulse width, soliton order, frequency chirp are crucial to the flat ultra-wideband supercontinuum spectrum generated in this fiber.     

基于多项扩展式局部方向张量的仿射不变兴趣点检测算子

针对基于立体视觉的移动机器人导航中摄像机视角及光线亮度的变化会使所获得的场景环境图像发生一定的仿射变换,为了选取稳定的图像局部特征点,提出了一种具有仿射不变的兴趣点检测算法--多项局部方向张量(polynomial local orientation tensors,PLOT)算子.PLOT算子是基于图像多项扩展式局部...     

基于盲数的螺栓可靠性计算

基于未确知理论中盲数的概念和运算规则,建立了盲数强度应力可靠度计算模型,并用LabVIEW语言编写了相应的计算程序．通过对螺栓的实际可靠度计算,并与传统可靠度设计进行了对比分析,验证了模型的有效性和实用性．     

Directional laser generation and detection of ultrasound with arrays of optical fibers

Some aspects of the generation and detection of ultrasound with laser beams are presented. The objective of the study is (1) to present some experimental results on the generation of ultrasound with an array of optical fibers, (2) to discuss the possibility of generating directional surface waves with acousto-optic scanning in a very narrow frequency band, thus increasing the signal-to-noise ratio, and (3) to discuss the feasibility of the directional detection of ultrasound by using an array of optical fibers as a receiver, also with the goal of increasing the signal-to-noise ratio.     

High-throughput optical processors based on semiconductor nanostructures for incoherent-light optical analog computers with parallel image processing

Fast-response optical recording media based on semiconductor nanostructures (CdTe, GaAs) have been developed for image recording and processing at a speed of up to 10⁶ cps, which is 2–3 orders of magnitude higher than the speed of well-known media based on liquid crystals (MIS-LC). The new media are characterized by a photosensitivity of 10^?2 W/cm² and a spatial resolution of 5–10 lines/mm. Methods for the readout of images recorded in the nanostructures are developed and high-speed incoherent-light optical processors based on these structures are created. The possibility of using these processors for building optical analog computers and image correlators is demonstrated.     

Multiple-wavelength quasi-phase-matching for efficient idler generation in MgO:LiNbO3 based nanosecond optical parametric oscillator

We present numerical results for optimization of the overall idler conversion efficiency of a nanosecond optical parametric oscillator (OPO), wherein the signal generated in the OPO process is also used as the pump for a difference frequency generation (DFG) process in a quasi-periodic MgO:LiNbO(3) crystal. The phase-matching conditions are considered such that the generated idler frequencies in both the processes (i.e., OPO and DFG) coincide. Optimization for the idler generation has been performed with respect to the different parameters, such as input pump power, pump pulse duration, and the output coupler reflectivity, for quasi-phase-matched interaction in MgO:LiNbO(3). Wavelength of the pump, signal, and idler waves considered in the optimization are 1.064 μm, 1.456 μm, and 3.95 μm, respectively. A maximum overall idler generation efficiency of ≈33% could be obtained in the simultaneous OPO+DFG process for a pump pulse duration of 72 ns and output coupler reflectivity (R(s)) of 90%, whereas for the stand-alone OPO process, the maximum idler generation efficiency was found to be ≈15%. The optimization has been illustrated for an average pump power of 8 W at a pulse repetition frequency (PRF) of 10 kHz. This approach of simultaneous OPO+DFG process can be employed to significantly enhance the idler generation efficiency of nanosecond OPOs.     

Direct control of fractal pattern generation on an optical fractal synthesizer

We propose a method for direct control of position, rotation, and scaling of fractal patterns generated on an optical fractal synthesizer. In this method we introduce an iterated-function-system mother function to produce control parameters for arbitrary fractal patterns. We implemented the method experimentally and verified the effectiveness of the method.     

Tissue characterization based on scatterer number density estimation

The authors propose a robust model for characterizing the statistical nature of signals obtained from ultrasonic backscatter processes. The model can accommodate frequency-dependent attenuation, spatially varying media statistics, arbitrary beam geometries, and arbitrary pulse shapes. On the basis of this model, statistical schemes are proposed for estimating the scatterer number density (SND) of tissues. The algorithm for estimating the scatterer number incorporates measurements of both the statistical moments of the backscattered signals and the point spread function of the acoustic system. The number density algorithm has been applied to waveforms obtained from ultrasonic phantoms with known number densities and in vitro mammalian tissues. There is an excellent agreement among theoretical, histological, and experimental results. The application of this technique for noninvasive clinical tissue characterization is discussed.     

Low-cost optical amplitude modulator based on a tapered single-mode optical fiber

A new, to our knowledge, modulator based on a tapered single-mode optical fiber is introduced. The electro-optic device consists of a tapered optical fiber placed on a resonator made of a piezoelectric material. An electrical signal applied to the piezoelectric material makes the taper bend, and that displacement produces a modulation in the intensity of the optical signal traveling through the fiber. This device is very easy to build and is low in cost. Because of its nature, this new device might be very useful in optical fiber sensors. Its performance is analyzed, and the results are discussed.     

基于希尔伯特黄变换的刀具磨损特征提取

概述了希尔伯特黄变换(HHT)的基本理论和算法,对信号经过经验模态分解(EMD)后得到的固有模态函数(IMF)求取振幅均值,差值筛选出与刀具磨损相关的IMF分量,并对单分量固有模态函数求取边际谱,获取边际谱最大幅值点,建立他们与刀具磨损之间的映射关系,进行特征提取,将其作为神经网络的输入特征向量,结合希尔伯特三维时频谱进行刀具磨损状态的判断。研究结果证明,该方法可以作为刀具磨损监测中信号特征提取的一种简单和可靠的方法。     

基于S变换的心音信号特征提取

为了准确获得心音信号生理、病理信息,在对比研究各种时频分析方法的基础上,采用具有良好时频分辨率的S变换提取心音信号特征,实现心脏病辅助诊断。首先对心音信号进行包络提取、第一心音定位及心音分段,然后对一个周期信号进行S变换,最后提取变换后矩阵的统计学特征,并将该特征作为区别不同心音信号的特征向量。通过相关评价可知该方法可以有效识别不同心音信号。