基于光纤组束激光的机载光电对抗方法

针对机载光电对抗平台受制于激光光源模块体积和重量的问题,结合光纤激光技术提出了新的基于光纤组束激光的机载光电对抗途径。详细分析了具体的激光组束方法,并明确了该型激光对抗的两种有效作用对象,详细论述了各种对象的作用机理及其关键因素。     

Excellent initial guess functions for simple shooting method in Yb3+-doped fiber lasers

Excellent initial guess functions, providing for setting suitable initial estimates for simple shooting method, are developed to solve high power Yb³⁺-doped fiber lasers model with boundary conditions. When the guess value of slope efficiency is greater than or equal to the critical guess value of slope efficiency, the initial guess values of the forward signal power and backward pump power, generating from the excellent initial guess functions, are good initial guess values for the simple shooting method. Then, comparing the simulation results using our simple shooting method and the number sequence transition method based on MATLAB BVP solvers (NSTM-BVPs), the difference of the simulation results are less than given absolute error tolerance for different fiber length. Finally, we can conclude that the critical guess value of slope efficiency is less than 0.3 for all the fiber length, Yb³⁺-doped concentration, signal reflectivity and pump power.     

Efficient low-threshold lasers based on an erbium-doped holey fiber

We report experimental results on the continuous-wave lasers based on a small core erbium-doped holey fiber. In a simple Fabry-Perot-type cavity with high output coupling, we demonstrate low-threshold (0.55 mw) high slope-efficiency (57.3%) operation confirming both the quality and exceptionally high gain efficiency of the fiber. In an all-fiber ring cavity where the cavity loss is reduced, we show that it is possible to achieve a low-threshold laser with extremely wide tunability (>100 nm around 1550 nm). Our results illustrate some of the unique opportunities provided by active small core holey fibers.     

一种基于拉格朗日松弛的时延约束多播路由算法

提出了一种基于拉格朗日松弛方法的时延约束最小代价多播路由算法(LR-DLMA)。该算法充分利用拉格朗日松弛方法的特点，通过构建封闭图，对封闭图进行拉格朗日松弛求得满足条件的多播树。仿真实验结果表明本算法性能稳定，其代价性能接近性能最好的BSMA算法，并具有快速、低时延的特点。     

A linewidth formula for semiconductor-optical fiber ring lasers

The authors derive a formula of linewidth for a semiconductor-optical-fiber ring laser by using coupled rate equations for the active and passive cavity. It is shown that the linewidth is not only the function of the two-cavity length ratio and time delay in fiber, but also the function of light intensity ratio of the two cavities and the phase shift introduced by junctions between the gain medium and the optical fiber     

一种基于L-M算法的组合神经网络模糊控制器

提出了一种基于L-M算法的神经网络模糊控制器。用两个相同的三层前向神经网络①和②来生成E和EC的隶属度,用三层前向神经网络③来实现模糊控制规则并生成控制输出,经过研究和对比选择了对于这3个网络来说最好的训练算法Levenberg-Marquardt算法。仿真结果表明了该控制器极好的控制性能。     

Modeling of multiwavelength Raman fiber lasers using a new and fast algorithm

We describe a numerical model for a multiwavelength Raman fiber laser. It uses an original algorithm which makes the model robust and fast. We show a comparison between simulated and measured Raman laser output powers, characterized by their slope efficiency and their threshold.     

A Lagrangean relaxation based near-optimal algorithm for advance lightpath reservation in WDM networks

Advance lightpath reservation is a new research topic for connecting high-speed computer servers in lambda grid applications and for dynamic lightpath provisioning in the future optical internet. In such networks, users make call requests in advance to reserve network resources for communications. The challenge of the problem comes from how to jointly determine call admission control, lightpath routing, and wavelength assignment. In this paper, we propose an efficient Lagrangean relaxation (LGR) approach to resolve advance lightpath reservation for multi-wavelength optical networks. The task is first formulated as a combinatorial optimization problem in which the revenue from accepting call requests is to be maximized. The LGR approach performs constraint relaxation and derives an upper-bound solution index according to a set of Lagrangean multipliers generated through subgradient-based iterations. In parallel, using the generated Lagrangean multipliers, the LGR approach employs a new heuristic algorithm to arrive at a near-optimal solution. By upper bounds, we assess the performance of LGR with respect to solution accuracy. We further draw comparisons between LGR and three heuristic algorithms—Greedy, First Come First Serve, and Deadline First, via experiments over the widely-used NSFNET network. Numerical results demonstrate that LGR outperforms the other three heuristic approaches in gaining more revenue by receiving more call requests.     

基于项目与用户的组合推荐算法研究

协同过滤技术是当前推荐系统中应用最广泛的推荐技术之一,随着系统用户规模的激增,传统的协同过滤技术存在实时性差、可扩展性差、数据稀疏性等问题。为了解决上述问题,提出了一种基于项目与用户的个性化组合推荐算法。首先,利用项目聚类对未评分项目进行评分预测,并填充用户-项目评分矩阵;再将项目聚类结果与用户行为特征相结合并对其进行用户聚类;最后,根据近邻相似性计算实现TOP-N推荐。实验表明,提出的组合推荐算法显著提高了推荐系统的准确性与实时性。     

光纤传感器用半导体激光器光频调制驱动电源

为了实现基于光频调制相位生成载波解调的干涉型光纤传感系统,需要对激光光源的频率进行调制.首先,文章根据直接电流调制原理设计井开发了一种半导体激光器光频调制驱动电源,主要由精密蕈准电压源、内部信号发生器,加法器、恒流源(电压电流转换、电流放大和电压负反馈)、慢启动电路、纹波抑制电路和过流保护电路等基本单元组成.接着,建立...     

Analytical model for rare-earth-doped fiber amplifiers and lasers

An analytical model for two-, three-, and four-level system rare-earth-doped fiber amplifiers and lasers is presented. The theory is applicable to dopants such as erbium, neodymium, thulium; praseodymium, and ytterbium. Fiber-amplifier gain is expressed in terms of attenuation coefficients, intrinsic saturation powers, and cross-saturation powers at the pump and signal wavelengths. These parameters can be directly determined from one- and two-beam fiber-transmission measurements. System-independent formulas are given for the slopes and thresholds of ring and linear fiber lasers. Good agreement between theory and experiment has been shown for erbium-doped fiber amplifiers and lasers and thulium-doped fiber lasers. Because of the finite-pump-level lifetime, three- and four-level models predict a flattening of the fiber laser slope at higher pumping powers when the fiber is shorter than the optimum length. Approximate system-independent solutions are also given for fiber amplifiers with excited-state absorption at either the pump or signal wavelengths. A novel technique, requiring only one tunable light source, is proposed for finding the best pump wavelength when pump ESA is present. The two-level analytical model recently developed for erbium-doped fibers is a special case of this theory     

锁模光纤激光器的研究进展

综述了锁模激光器的研究现状.详细阐述了近年来几种研究比较热门的锁模光纤激光器的原理、结构和发展.展望了光纤锁模激光器技术的发展前景.     

A fast algorithm for signature prediction and image formation usingthe shooting and bouncing ray technique

We present a fast simulation algorithm for generating the range profiles and inverse synthetic aperture radar (ISAR) images of complex targets using the shooting and bouncing ray (SBR) technique. Starting with the time-domain and image-domain ray-tube integration formulas we derived previously, we cast these formulas into a convolution form. The convolution consists of a nonuniformly sampled signal and a closed-form time-domain or image-domain ray spread function. Using a fast scheme proposed by Sullivan (1990), the nonuniformly sampled function is first interpolated onto a uniform grid before the convolution is performed by the fast Fourier transform (FFT) algorithm. Results for several complex targets are presented to demonstrate the tremendous computation time savings and excellent fidelity of the scheme. Using the fast scheme, a speed gain of a factor of 30 is achieved in performing the ray summation as compared to the direct convolution in range profile computation and a factor of 180 in ISAR image formation for a typical aircraft at S-band     

A new design approach for fiber DFB lasers with improved efficiency

The standard distributed feedback (DFB) laser optimization method is critically investigated and a new design approach based on the effective cavity length is presented. By applying this method in an erbium-ytterbium co-doped fiber, the pump-to-signal conversion ratio is increased by 40% for the same total device length and pumping conditions. The laser with the proposed design is produced and the theoretical results are verified by the experimental work.     

A reduced-complexity algorithm for combined equalization and decoding

This paper presents a new application of a suboptimal trellis decoding algorithm for combined equalization and decoding. The proposed algorithm can outperform the reduced-state sequence estimator (RSSE) of the same order of complexity. The algorithm, termed estimated future decision-feedback algorithm (EFDFA), was originally proposed for the problem of noncoherent decoding with multiple-symbol overlapped observations and is now reformulated for the problem of intersymbol interference inflicted channels. The EFDFA uses the RSSE as a building block. The performance improvement is achieved by using estimated future symbols in the decision process. The estimated future symbols are obtained by RSSE decoding time-reversed blocks of the input. The same technique can be used to greatly enhance the performance of the conventional decision-feedback equalizer. An analysis of the performance of the EFDFA based on the performance of the RSSE is described. The EFDFA can be configured as an adaptive equalizer capable of operating in a time-varying environment, and is shown to perform well in fading conditions. With only minor additional complexity, the EFDFA is also capable of producing soft outputs.     

A real-time exposure dose control algorithm for DUV excimer lasers

scan exposure model and analyzing the pulse-to-pulse energy fluctuation characteristics of DUV excimer lasers, a real-time dose regulation is implemented based on closed-loop feedback control, which especially focuses on reducing the effect of pulse energy overshot and pulse-to-pulse stochastic fluctuation. The experiment conducted on an ArF excimer laser with wavelength of 193 nm, repetition rate of 4 kHz, and pulse energy of 5 mJ confirms that such a real-time dose control algorithm is able to achieve a dose accuracy of above 0.89% even with only 20 pulses. It is fully expected that this algorithm will not only meet increasingly stringent dose accuracy requirements for sub-half-micron lithography, but also be helpful to improve lithography throughput as well as efficiency.     

基于对称逐步超松弛的低复杂度信道估计算法

随着大规模多输入多输出系统基站端天线数量的增大,系统的信道容量和频谱效率随之增加.传统的信道估计算法,如最小均方误差涉及到高维矩阵的求逆运算,特别在大规模多输入多输出系统中,导致系统复杂度过高.为降低大规模多输入多输出系统的计算复杂度,本文提出了一种基于对称逐步超松弛的低复杂度信道估计算法,该方法以迭代的形式有效避免高...     

城域光缆线路系统障碍和隐含断纤的查修

对城域光缆线路的系统障碍和隐含的断纤查修问题进行了详细的讨论，强调在具体的障碍查修过程中，应把技术手段和实践经验结合起来，灵活应用。     

A multiscale relaxation algorithm for SNR maximization innonorthogonal subband coding

Develops a technique for improving the applicability of complete, nonorthogonal, multiresolution transforms to image coding. As is well known, the L(2) norm of the quantization errors is not preserved by nonorthogonal transforms, so the L(2) reconstruction error may be unacceptably large. However, given the quantizers and synthesis filters, the authors show that this artifact can be eliminated by formulating the coding problem as that of minimizing the L(2) reconstruction error over the set of possible encoded images. With this new formulation, the coding problem becomes a high-dimensional, discrete optimization problem and features a coupling between the redundancy-removing and quantization operations. A practical solution to the optimization problem is presented in the form of a multiscale relaxation algorithm, using inter- and intrascale quantization noise feedback filters. Bounds on the coding gain over the standard coding technique are derived. A simple extension of the algorithm allows for the use of a weighted L(2) error criterion and deadband (non-MMSE) quantizers. Experiments using biorthogonal spline filter banks demonstrate appreciable SNR gains over the standard coding technique, and comparable visual improvements.     

Switching-induced perturbation and influence on actively Q-switched fiber lasers

Dynamic characteristics of typical actively Q-switched fiber lasers are numerically investigated by using the traveling-wave method. The multipeak phenomena of output pulses are analyzed, and the mechanism for these phenomena is detailed. In particular, the switching-induced perturbation and its influence are emphasized under different conditions. A quantitative analysis shows that under certain conditions of cavity, pump and switching, a split-pulse output can turn to a single-pulse output. Then how to realize the single-pulse output is systematically illustrated, and some experimental results are shown for comparison.