Experimental and theoretical study of filtered optical feedback ina semiconductor laser

We report on the systematical investigation of the steady-state regime and the dynamical behavior of a semiconductor laser subject to delayed filtered optical feedback. We study a Fabry-Perot (FP) interferometer type of filter placed in the external feedback loop of a diode laser. The effects of the filter on the locking of the diode laser frequency to the external cavity modes are described. We report and observe hysteresis, bistability, and multistability and show that all these are well described by a set of rate equations for the coupled laser and FP cavity system. We also present an experimental stability diagram that summarizes the dynamical behavior of the system     

一种基于数字电视地面广播照射源的外辐射源雷达快速杂波相消算法

为了减小外辐射源雷达系统中常规杂波相消算法的运算量,该文利用数字电视地面广播(DTTB)照射源中的PN序列,提出了一种快速杂波相消算法。该算法基于PN序列良好的自相关特性,并考虑到DTTB信号对载频频偏(CFO)很敏感,提出2-D信道和CFO估计来提高估计精度;然后,利用估计的信道和CFO进行直达波重构和杂波相消,剩余目标回波和噪声。相比于传统的杂波相消算法,该方法运算量比较小,并且所有处理都基于预警天线,不需要参考天线,简化了系统模型。最后仿真实验验证了算法的有效性。     

A New Transmission Line Microcavity Model for Vertical Cavity Surface Emitting Lasers

In this paper we present a new transmission line microcavity model for vertical cavity surface emitting lasers (VCSEL). The model is based on optical wave equations and implemented with state-space techniques to predict the lasing modes and analyze the decay properties of the Fabry-Perot (FP) cavities. The model is used to analyze microcavities in both time and frequency domains in terms of material and physical parameters of the lasers, and provide a simple and fast way to optimize the cavity length, reflective mirror and active region of the lasers.     

Virtual reality treatment of flying phobia

Flying phobia (FP) might become a very incapacitating and disturbing problem in a person's social, working, and private areas. Psychological interventions based on exposure therapy have proved to be effective, but given the particular nature of this disorder they bear important limitations. Exposure therapy for FP might be excessively costly in terms of time, money, and efforts. Virtual reality (VR) overcomes these difficulties as different significant environments might be created, where the patient can interact with what he or she fears while in a totally safe and protected environment, the therapist's consulting room. This paper intends, on one hand, to show the different scenarios designed by our team for the VR treatment of FP, and on the other, to present the first results supporting the effectiveness of this new tool for the treatment of FP in a multiple baseline study.     

A new method for resynchronization attack

This paper presents a new method for resynchronization attack, which is the combination of the differential cryptanalysis and algebraic attack. By using the new method one gets a system of linear equations or low-degree equations about initial keys, and the solution of the system of equations results in the recovery of the initial keys. This method has a lower computational complexity and better performance of attack in contrast to the known methods. Accordingly, the design of the resynchronization stream generators should be reconsidered to make them strong enough to avoid our attacks. When implemented to the Toyocrypt, our method gains the computational complexity of O（2^17）, and that of 0（2^67） for LILI-128.     

测量光伏探测器PN结品质因子与反向饱和电流的方法

由于制造工艺和生产条件的不同,光伏探测器的特征参量结品质因子和反向饱和电流有很大差别。提出一种PN结特征参量的间接测量方法,并对该测量方法所用的数值计算方法的收敛性进行数学证明。提出了两个使用开路电压和短路电流计算光电池PN结品质因子和反向饱和电流的简化解析计算公式。与迭代法的计算结果相比,使用简化解析计算公式得到的结品质因子和反向饱和电流的相对误差分别为0.03%和0.25%;与实验结果相比,使用迭代法计算结果的开路电压值的相对误差不小于0.3%。     

Modified Fabry–Perot and Rate Equation Methods for the Nonlinear Dynamics of an Optically Injected Semiconductor Laser

Modifications have been introduced to the Fabry– Perot (FP) and the rate equation methods to improve the accuracy of the analysis of the nonlinear dynamics of a laser with external optical injection. Comparison between the modified methods and the more accurate transmission-line laser model (TLLM) shows good agreement, while the computational time of the latter is larger by two or three orders of magnitude. In the FP method, the stimulated recombination term in the carrier density evolution equation is modified to include the backward propagating wave and the exponential longitudinal dependence of the electromagnetic field. In the rate equation method, the optical injection term is modified to account for the contribution of the amplification and losses of the injected light inside the cavity to the average photon density. The derivation explaining the validity of these changes and the mathematical relationship between the two methods is presented. Improved stability maps for different values of the injected optical power and frequency detuning are demonstrated and compared with those obtained by the TLLM. The gain compression effect is included in the FP model, and its effect on the stability properties is discussed.      

Phase noise approximation analysis for the OFDM system

The influence of phase noise (PN) present at the access point (AP) and mobile terminator (MT) may degrade the performance in orthogonal frequency division multiplexing (OFDM) system, because the OFDM system is sensitive to the PN.The method of PN approximation based on the PN power spectrum was proposed to combat the influence of the PN present.The idea of the PN cancellation is the PN is approximated for the sum of the different frequency between the AP and the MT as well as Doppler shift supposing that the fixed different frequency during several OFDM symbols are identical, so the variable phase may be considered as the combination of the fixed partition and the random partition.The approximation method is utilized to remove the fixed and the random phase partition so that the signal-to-noise ratio (SNR) may be improved.The analysis and the simulation proposed show that the method may effectively improve the performance of the OFDM system.     

基于Haar小波变换的直扩信号伪码盲同步方法

为了解决非合作条件下短码直接序列扩频信号的盲同步问题,提出了一种基于Haar小波变换的伪码同步方法。该方法不需要事先知道扩频序列,先将直扩信号进行延迟相乘和低通滤波处理,计算其Haar小波变换,再按照伪码周期分段进行累加,搜索幅度累计平均的峰值,即可估计出直扩信号的伪码同步时间。理论分析和仿真实验表明在低信噪比下,该方法仍具有较好的性能,而且计算量较小、数值稳定性好,易于工程实现。     

A method for progressive optimization of pump power and wavelengths for Raman amplification

We present a method for progressive optimization of pump power and wavelengths for Raman amplification, which allows for selective compensation of the relevant nonlinear interactions. This method first allows for a rapid one-step assessment of gain performance for a given set of wavelengths without determining pump powers in a novel approach which completely avoids the numeric solution of the Raman equations, thereby enabling ideal performance prediction while significantly reducing computational effort. The method then provides a technique to selectively compensate for pump-pump, pump-signal, and amplified signal-signal interactions, enabling one to control how much computational effort is expended determining pump powers based on the level of accuracy desired, which varies widely in practice. Lastly, the method is independent of solution techniques for the Raman equations, thereby eliminating the need to recast the Raman equations with separate, typically restrictive assumptions (such as ignoring amplified spontaneous emission and Rayleigh backscattering).     

BTT导弹增广比例导引律研究

比例导引规律相比于直接追踪法,跟踪精度有所提高,但是在目标机动性加大的情况下,传统比例导引规律制导精度仍不理想.因此,给出了三维空间导弹-目标追逃运动的空间矢量方程,建立了三维空间导弹-目标追逃运动模型,并基于李雅普诺夫稳定性理论,设计增广比例导引律(APNG).即在比例制导规律基础上,引入目标加速度补偿项来克服目标加速度对制导精度的影响.将该方法运用于机动目标的跟踪,仿真结果表明了增广比例导引律相比于传统比例导引律,制导精度高,脱靶量低,制导飞行时间短,制导性能有极大的提高.     

Modeling second-order nonlinear effects in optical waveguides usinga parallel-processing beam propagation method

In this work, we present a simple efficient numerical solution for the three-dimensional coupled wave equations containing a second-order nonlinearity, using an explicit finite difference beam propagation method (EFD BPM). The linear EFD-BPM is known to be very efficient and to gain large speed up when implemented on parallel computers. The new nonlinear version of the EFD-BPM has the same features of the linear counterpart in using two separate computational windows, one for the fundamental field and the other for the second-harmonic field. We demonstrate the implementation and discuss the application of this method to a nonlinear rib waveguide using the quasi-phase-matching technique     

基于奇异值分解的直扩信号伪码序列及信息序列盲估计方法

针对非合作扩频通信中直扩信号伪码序列的盲估计问题,在已知码片速率和伪码周期的前提下,该文提出一种基于奇异值分解的直扩信号伪码序列及信息序列的盲估计方法。该方法对接收信号构成的观测矩阵进行奇异值分解,通过左奇异向量实现伪码序列估计的盲估计。同时,通过右奇异向量可以在信号序列未同步和伪码序列未知的情况下实现信息序列的盲估计。仿真实验结果表明该算法具有精确度高、稳定性高、计算量小和观测时间短等优点。     

Fast and stable least-squares approach for the design of linearphase FIR filters

We present a new numerical algorithm for solving the normal equations associated with the least-squares design of linear phase FIR filters. The usual solution methods have a computational complexity of O(N³). Moreover, solving the normal equations with Gaussian elimination commonly yields numerical errors, especially when the filter is long. Here, we convert a least-squares method into the problem of constructing a system of orthonormal functions. The proposed design algorithm needs only O(N²) computations, and numerical errors can be reduced. Some examples are given to show the performance of the algorithm     

圆锥浸没透镜电子光学系统的研究

本文研究利用边界元素法计算圆锥透镜场分布，用曲傍轴轨迹方程组、实际轨迹方程组追迹计算各种初条件的带电粒子轨迹，确定电子光学参量。其计算结果Ｓ．Ｙａ．Ｙａｖｏｒ等采用渐近解析方法的结果相符。     

Some new algorithms for recursive estimation in constant linear systems

Recursive least-squares estimates for processes that can be generated from finite-dimensional linear systems are usually obtained via ann times nmatrix Riccati differential equation, wherenis the dimension of the state space. In general, this requires the solution ofn(n + 1)/2simultaneous nonlinear differential equations. For constant parameter systems, we present some new algorithms that in several cases require only the solution of less than2nporn(m + p)simultaneous nonlinear differential equations, wheremandpare the dimensions of the input and observation processes, respectively. These differential equations are said to be of Chandrasekhar type, because they are similar to certain equations introduced in 1948 by the astrophysicist S. Chandrasekhar, to solve finite-interval Wiener-Hopf equations arising in radiative transfer. Our algorithms yield the gain matrix for the Kalman filter directly without having to solve separately for the error-covariance matrix and potentially have other computational benefits. The simple method used to derive them also suggests various extensions, for example, to the solution of nonsymmetric Riccati equations.     

Efficient computational methods for strongly coupled cardiac electromechanics

Strongly coupled cardiac electromechanical models can further our understanding of the relative importance of feedback mechanisms in the heart, but computational challenges currently remain a major obstacle, which limit their widespread use. To address this issue, we present a set of efficient computational methods including an efficient adaptive cell model integration scheme and a solution method for the monodomain equations that maintains high conduction velocity for time steps greater than 0.1 ms. We also present a novel method for increasing the efficiency of simulating electromechanical coupling, which shows a significant reduction in computational cost of the mechanical component on a personalized left ventricular geometry with an active contraction cell model reparametrized for human cells.     

基于合作形成的认知无线网络频谱共享策略

当具备不同利益的多个主网络竞争为单个次级网络提供频谱接入机会时,它们可以通过基于重复博弈模型的频谱共享机制实现对授权通信频段的合作垄断,从而最大化它们的整体数据传输效用。然而当某个主网络对未来传输效用不够重视时,它会为了获得比垄断效用更高的传输效用而偏离当前的合作垄断,从而降低了其他主网络的当前和未来数据传输效用。为此,2种新的频谱共享策略被提出以促使所有主网络形成更为灵活和可靠的频谱共享合作垄断。数值仿真表明,相比现有的触发策略,这2种新策略能够为所有主网络获得更优的整体数据传输效用。     

Blind adaptive multiuser detection for DS/SSMA communications withgeneralized random spreading

A new spreading scheme and an accompanying blind adaptive receiver structure are proposed for direct-sequence spread-spectrum multiple-access communications in a slowly-varying, frequency-selective fading channel. Each user's spreading sequence is given by the Kronecker product of a long-period pseudonoise (PN) sequence, which is accurately modeled by a random sequence, and a short-length deterministic signature code. This spreading scheme bridges the gap between pure PN spreading and pure short-code spreading schemes. It is shown that with this spreading scheme, the channel response to the desired signal component is easily estimated without relying on the spectral decomposition of the signal correlation matrix. With the estimate of the channel response, the receiver suppresses interference based on the maximum signal-to-interference ratio criterion. The blind adaptive receiver requires only coarse timing information and a priori knowledge of the desired user's PN sequence for adaptation. Numerical results show that the adaptive receiver significantly suppresses interference by successfully estimating the channel response and the interference statistics with a low computational complexity. An extension to spatio-temporal processing using an array antenna is also discussed