Nonlinear optical glasses for ultrafast optical switches

In this paper we report degenerate four-wave-mixing measurements of the nonlinear coefficient of rutile and a number of optical glasses at 1.06 μm. We define a figure of merit which measures the suitability of a material for nonlinear waveguide switches and show that the best glasses have figures of merit substantially higher than any other material. We include a brief discussion of the types of switching elements that could be made with these materials.     

Provisioning algorithms for WDM optical networks

This paper concerns connection provisioning for optical networks employing wavelength division multiplexing. A heuristic algorithm is developed and numerically studied for routing and wavelength assignment of a set of static connection requests. The algorithm runs much faster than the optimum solution of this problem. An adaptation of the algorithm is proposed to design restorable networks which can handle a specified set of failures. The proposed algorithm is based on taking all failures into consideration simultaneously, and performs better than developing independent designs for each failure     

Scheduling algorithms for optical packet fabrics

Utilizing optical technologies to build packet fabrics for high-capacity switches and routers has several advantages in terms of scalability, power consumption, and cost. However, several technology related problems have to be overcome to be able to use such an approach. The reconfiguration times of optical crossbars are longer than those of electronic fabrics and end-to-end clock recovery in such systems add to the reconfiguration overheads. Both these problems can limit the efficiency of optical packet fabrics. In addition, existing work on input-buffered switches mostly assumes fixed size packets (referred as envelopes in this paper). When fixed size switching is used for Internet protocol networks where packets are of variable size, the incoming packets need to be fragmented to fit the fixed size envelopes. This fragmentation can lead to, possibly large loss of bandwidth and even instability. This paper addresses all of the above issues by presenting packetization and scheduling techniques that allow optical packet fabrics to be used within switches and routers. The proposed scheme aggregates multiple packets in a single envelope and when used in combination with proper scheduling algorithms, it can provide system stability as well as bandwidth and delay guarantees. As a result of the aggregation method, the reconfiguration frequency required from the optics is reduced, facilitating the use of optical technologies in implementing packet switch fabrics.     

Numerical study of multigrid implementations of some iterative image reconstruction algorithms

The numerical behavior of multigrid implementations of the Landweber, generalized Landweber, ART, and MLEM iterative image reconstruction algorithms is investigated. Comparisons between these algorithms, and with their single-grid implementations, are made on two small-scale synthetic PET systems, for phantom objects exhibiting different characteristics, and on one full-scale synthetic system, for a Shepp-Logan phantom. The authors also show analytically the effects of noise and initial condition on the generalized Landweber iteration, and note how to choose the shaping operator to filter out noise in the data, or to enhance features of interest in the reconstructed image. Original contributions include (1) numerical studies of the convergence rates of single-grid and multigrid implementations of the Landweber, generalized Landweber, ART, and MLEM iterations and (2) effects of noise and initial condition on the generalized Landweber iteration, with procedures for filtering out noise or enhancing image features     

Variational Bayesian Inference for a Nonlinear Forward Model

Variational Bayes (VB) has been proposed as a method to facilitate calculations of the posterior distributions for linear models, by providing a fast method for Bayesian inference by estimating the parameters of a factorized approximation to the posterior distribution. Here a VB method for nonlinear forward models with Gaussian additive noise is presented. In the case of noninformative priors the parameter estimates obtained from this VB approach are identical to those found via nonlinear least squares. However, the advantage of the VB method lies in its Bayesian formulation, which permits prior information to be included in a hierarchical structure and measures of uncertainty for all parameter estimates to be obtained via the posterior distribution. Unlike other Bayesian methods VB is only approximate in comparison with the sampling method of MCMC. However, the VB method is found to be comparable and the assumptions made about the form of the posterior distribution reasonable. Practically, the VB approach is substantially faster than MCMC as fewer calculations are required. Some of the advantages of the fully Bayesian nature of the method are demonstrated through the extension of the noise model and the inclusion of automatic relevance determination (ARD) within the VB algorithm.     

Multiresolution and hybrid Bayesian algorithms for automaticdetection of change points

Two methods for detection of step changes in noise corrupted piecewise-constant univariate datasets are presented. The aim is to determine automatically the number and position of any discontinuities in the mean. This problem is commonly known as the change-point problem. The multiresolution method presented involves performing a discrete wavelet transform. Shrinking the coefficients via soft thresholding, and then correlating across scales. Also Bayesian algorithms have long been available; they yield good results but they are impossible to apply in many cases due to the huge computational complexity. The technique is compared with previously published hybrid Bayesian algorithms. It is essential in any technique that the probability of false detections is low while retaining a sufficiently high probability of detection for correct change points. To this end the Student's t-test is introduced as a final stage after both methods. This eliminates most, if not all, false detections while retaining most correct ones. Simulation results are presented for each algorithm demonstrating that a good performance is obtained for datasets with different characteristics     

非线性贝叶斯滤波算法综述

滤波的目的是从序贯量测中在线、实时地估计和预测出动态系统的状态和误差的统计量。从递归贝叶斯估计的框架出发,对非线性滤波算法作了统一描述,并根据对后验概率密度的近似方法的不同,把非线性滤波划归为3类:基于函数近似的滤波方法、基于确定性采样的滤波方法和基于随机采样的滤波方法。对这些非线性滤波的原理、方法及特点做了分析和评述,最后介绍了非线性滤波研究的新动态,并对其发展作了展望。     

Nonlinear disordered media for broad-band optical limiting

We analyze broad-band limiting behavior in nonlinear structures that are, on average, periodic. Introduction of a controlled degree of randomness in layer thicknesses results in widening of the stopband. Light at all of the frequencies in this broadened effective stopband of the structure with randomly perturbed layer thicknesses exhibits true optical limiting-clamping of the transmitted intensity below a fixed level independent of incident intensity. We explore the impact of the degree of randomization and the strength of the nonlinear mechanism on the smoothness and regularity of the limiting spectrum and on the localization of the light within these cyclostationary media. Optical limiting in integrable devices is of interest in optical logic, signal processing, and personnel and sensor protection     

Nonlinear feedback preamplifier for optical trigger circuits

A nonlinear preamplifier system to improve the performance of a zero-crossover optical trigger circuit is presented. The network is based on a low-noise operational amplifier with a Zener diode feedback. It is proposed to exploit the nonlinear characteristic of this network to reduce timing measurement uncertainty. Accordingly the circuit has been developed and tested in operation.     

单模光纤非线性系数n2/Aeff的测量方法

通信距离的延长和WDM通道数的增加使光纤非线性效应日益显著，如何准确地测量非线性系数的大小成了人们关注的问题，文章介绍了几种非线性系数的测量方法，并对它们的优缺点进行了较全面的分析和比较。     

光流算法比较分析研究

运动目标检测是计算机视觉中重要的课题,运动目标的正确检测与正确分割影响着后续目标的跟踪与识别;光流法是运动目标检测和分析的重要方法,它能够在不知道任何预先场景情况下检测出独立的运动目标,并且可适用于动态场景的情况。首先介绍了光流的基本概念,然后介绍了常用的光流的四种算法;接着以智能交通中路口车辆视频为例,将这四种光流算法用于车辆检测,然后对四种光流算法的优缺点进行分析;最后对光流法在未来可能研究及改进的方向提出展望。     

Nonlinear optical susceptibility of AgI

We have measured the magnitude and absolute sign of the nonlinear optical coefficient in AgI to determine the importance of thed- electron contributions to the nonlinearity. The resultsd_{31} = +20.6 times 10^{-9}ESU andd_{33} = -41.1 times 10^{-9}ESU are in good agreement with theory.     

Parallelizable Bayesian tomography algorithms with rapid,guaranteed convergence

Bayesian tomographic reconstruction algorithms generally require the efficient optimization of a functional of many variables. In this setting, as well as in many other optimization tasks, functional substitution (FS) has been widely applied to simplify each step of the iterative process. The function to be minimized is replaced locally by an approximation having a more easily manipulated form, e.g., quadratic, but which maintains sufficient similarity to descend the true functional while computing only the substitute. We provide two new applications of FS methods in iterative coordinate descent for Bayesian tomography. The first is a modification of our coordinate descent algorithm with one-dimensional (1-D) Newton-Raphson approximations to an alternative quadratic which allows convergence to be proven easily. In simulations, we find essentially no difference in convergence speed between the two techniques. We also present a new algorithm which exploits the FS method to allow parallel updates of arbitrary sets of pixels using computations similar to iterative coordinate descent. The theoretical potential speed up of parallel implementations is nearly linear with the number of processors if communication costs are neglected.     

Nonlinear optical susceptibilities of solvents

We have measured the nonlinear optical susceptibility coefficient governing self-induced changes in the state of elliptical polarization of a monochromatic beam in 10 common solvents. These are the first such measurements at 1060 nm. We show how our results may be used to estimate self-focusing in these solvents and to clarify other non-linear optical properties.     

Nonlinear control in optical bistability

We study the influence of a small periodic modulation of the input field amplitude in dispersive optical bistability. When the system is initially near one of the two limit points in a stable state, the addition of a small periodic modulation may either stabilize or destabilize the system. We prove that destabilization occurs as a result of critical slowing down when the modulation frequency is decreased.     

Nonlinear optical pulse coupling dynamics

The pulse coupling dynamics in a nonlinear directional coupler (NLDC) is analyzed by using the new normalized coupled nonlinear Schro/spl uml/dinger equations. The operation of an NLDC can be divided into three regions according to L/sub D//spl kappa/: Region 1 (L/sub D//spl kappa//spl les/1), Region 2 (L/sub D//spl kappa/>50), and Region 3 (1相似文献   

Nonlinear fibers for signal processing using optical Kerr effects

This paper reviews nonlinear optical-fiber designs for signal processing using optical Kerr effects. The requirements for designing nonlinear fibers are described first. Then, the design concept is discussed and design examples are shown to illustrate the tradeoffs among the different fiber properties such as effective area, dispersion, and attenuation. Furthermore, fiber designs with distributed Brillouin frequency shift to mitigate the effect of simulated Brillouin scattering (SBS) in nonlinear fibers are discussed in detail. An SBS-threshold increase of 7 dB over conventional nonlinear fibers is experimentally demonstrated.     

Nonlinear optical devices based on suspended-core microstructured optical fibers

Suspended-core microstructured optical fibers are employed in lasers that generate ultrashort pulses and supercontinuum generators. It is demonstrated that a femtosecond fiber laser based on the ytterbium-doped microstructured fiber generates pulses with a duration of 95 fs at a wavelength of 1045 nm and a mean power of 5 mW in the absence of additional compression. Supercontinuum is generated in tapered microstructured fibers with suspended core in the wavelength interval 400–1400 nm. Suspended-core micro-structured fibers may serve as promising elements for nonlinear optical devices due to specific waveguide characteristics, relative simplicity of manufacturing, and variable optical properties.     

OBS网络数据信道调度算法性能比较与分析

光突发交换(0BS)网络中的数据信道调度算法是提高0BS网络性能的关键技术之一.首先介绍和分析了LAUC、LAUC-VF和0DBR基本原理和性能,结合国内外最新研究成果,介绍了四种支持QoS的数据信道调度算法,最后对其应用场合做出总结.