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Optical pulse compression using a nonlinear optical loop mirror constructed from dispersion decreasing fiber

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science china(Technological sciences) 2004年第1期47卷 33-50页

作者： CAO Wenhua & LIU SonghaoSchool of information, Wuyi university, Jiangmen 529020, china School for information and optoelectronic science and engineering, south china normal university, guangzhou 510631, china 1. School of information Wuyi University 529020 Jiangmen China 2. School for information and optoelectronic science and engineering South China Normal University 510631 Guangzhou China

A novel scheme to compress optical pulses is proposed and demonstrated numerically, which is based on a nonlinear optical loop mirror constructed from dispersion decreasing fiber (DDF). We show that, in contrast to the conventional soliton-effect pulse compression in which compressed pulses are always accompanied by pedestals and frequency chirps owning to nonlinear effects, the proposed scheme can completely suppress pulse pedestals and frequency chirps. Unlike the adiabatic compression technique in which DDF length must increase exponentially with input pulsewidth, the proposed scheme does not require adiabatic condition and therefore can be used to compress long pulses by using reasonable fiber lengths. For input pulses with peak powers higher than a threshold value, the compressed pulses can propagate like fundamental solitons. Furthermore, the scheme is fairly insensitive to small variations in the loop length and is more robust to higher-order nonlinear effects and initial frequency chirps than the adiabatic compression technique.

关键词： dispersion decreasing fiber (DDF), optical pulse compression, optical solitons.

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Imaging theory of nonlinear second harmonic and third harmonic generations in confocal microscopy

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science china(Physics,Mechanics & Astronomy) 2004年第1期47卷 8-16页

作者： TANG Zhilie1, XING Da2 & LIU Songhao2 1. Department of Physics, south china normal university, guangzhou 510631, china 2. School for information and optoelectronic science and engineering, south china normal university, guangzhou 510631, china Correspondence should be addressed to Tang Zhilie (email: tangzhl@***) Received April 23, 2003 1. Department of Physics South China Normal University 510631 Guangzhou China 2. School for information and optoelectronic science and engineering South China Normal University 510631 Guangzhou China

The imaging theory of nonlinear second harmonic generation (SHG) and third harmonic generation (THG) in confocal microscopy is presented in this paper. The nonlinear effect of SHG and THG on the imaging properties of confocal microscopy has been analyzed in detail by the imaging theory. It is proved that the imaging process of SHG and THG in confocal microscopy, which is different from conventional coherent imaging or incoherent imaging, can be divided into two different processes of coherent imaging. The three-dimensional point spread functions (3D-PSF) of SHG and THG confocal microscopy are derived based on the nonlinear principles of SHG and THG. The imaging properties of SHG and THG confocal microscopy are discussed in detail according to its 3D-PSF. It is shown that the resolution of SHG and THG confocal microscopy is higher than that of single- and two-photon confocal microscopy.

关键词： second harmonic generation, third harmonic generation, confocal microscopy, three-dimensional point spread function.

维普期刊数据库

A note for preconditioning nonsymmetric matrices

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Applied Mathematics(A Journal of Chinese Universities) 2010年第1期25卷 93-100页

作者： CHEN Xiao-shan LI Wen School of Mathematics, south china normal university, guangzhou 510631, china School of Mathematics South China Normal University Guangzhou China

In this paper, we consider preconditioners for generalized saddle point systems with a nonsymmetric coefficient matrix. A constraint preconditioner for this systems is constructed, and some spectral properties of the ... 详细信息

关键词： Preconditioner saddle point matrix minimal polynomial Schilder's factorization.

维普期刊数据库

Enhanced Compression of Fundamental Solitons in Dispersion Decreasing Fibers with Negative Third-order Dispersion Ⅱ. Effects of Fiber Characteristics and Initial Soliton Width

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Chinese Journal of Lasers 2001年第6期10卷 66-72页

作者： CAO Wenhua (Department of Electronic \%&\% information engineering, Wuyi university, Jiangmen 529020, china) GUO Qi LIU Songhao (Institute of Quantum Electronics, south china normal university, guangzhou 510631, china) 五邑大学电子与信息工程系广东江门 529020 华南师范大学量子电子学所广东广州 510631

Previous work have shown that the combined effects of negative third-order dispersion (TOD) and Raman self-scattering (RSS) can significantly enhance soliton compression in dispersion decreasing fibers (DDFs). In this paper, the effects of the negative TOD coefficient and the effective amplification of DDF′s on the performance of soliton compression are investigated. It is shown that for a given initial soliton width and a given effective amplification, there exists an optimum value of the negative TOD coefficient of the DDF at which the enhancement in soliton compression is maximum. It is also shown that the compression enhancement saturates when the effective amplification exceeds a certain value, which has been explained as a compromise between the higher-order effects induced increase of the ratio of input to output group-velocity dispersion coefficients of the DDF and the TOD induced non-adiabatic compression characteristics. The dependence of the compression enhancement on the initial soliton width have also be studied and the scheme is found works well for solitons with initial widths less than 3 ps.

关键词： fundamental solitons pulse compression dispersion decreasing fibers third-order dispersion Raman self-scattering

Efficient CRT-based residue-to-binary converter for the arbitrary moduli set

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science china(information sciences) 2011年第1期54卷 70-78页

作者： CHEN JianWen & YAO RuoHe School of Electronic and information engineering.south china university of Technology, guangzhou 510640,china 1. School of Electronic and information engineering South China University of Technology Guangzhou 510640 China

The conversion from residue to weighted binary representation plays an important role in the residue number *** on Chinese Remainder Theorem,a new residue-to-binary converter using arbitrary moduli set is *** new converter uses the difference-correction algorithm for the conversion output and eliminates the modulo M operation,where M is the dynamic range of the residue number *** sizes of the multipliers and modular multipliers in the new converter are small,thereby reducing the area and delay of the proposed *** and synthesis results indicate that the new converter is more area-time effcient than the published converters based on Chinese Remainder Theorem.

关键词： RNS Chinese Remainder Theorem difference correction modular arithmetic residue-to-binary arbitrary moduli set

Estimation of underdetermined mixing matrix based on support vector machine

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Progress in Natural science:Materials International 2007年第11期17卷 1363-1367页

作者： Yang Zuyuan and Xie Shengli(School of Electrics & information engineering, south china university of Technology, guangzhou 510641, china) School of Electrics & information engineering South China University of Technology Guangzhou 510641 China

In underdetermined blind source separation (BSS), a novel algorithm based on extended support vector machine (SVM) is proposed to estimate the mixing matrix in this paper, including the number of the active sources. Instead of traditional clustering algorithms, it mainly takes the modulus of observations and the number in each direction of arrival, without any prior knowledge about the sources except for sparsity, and it is not sensitive to the initial values. Simulations are given to illustrate availability and robustness of our algorithm.

关键词： underdetermined BSS SVM clustering

Linearly time-varying channel estimation and training power allocation for OFDM/MIMO systems using superimposed training

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science china(information sciences) 2011年第7期54卷 1456-1470页

作者： ZHANG Han 1,DAI XianHua 2 & Pan DaRu 1 1 School of Physics and Telecommunication engineering.south china normal university,guangzhou 510006,china 2 Department of information science and Technology,SUN Yat-sen university,guangzhou 510026,china 1. School of Physics and Telecommunication engineering South China Normal University Guangzhou 510006 China2. Department of Information Science and Technology SUN Yat-sen University Guangzhou 510026 China

We address the problem of estimating the linearly time-varying (LTV) channel of orthogonal frequency division multiplexing (OFDM)/multiple-input multiple-output (MIMO) systems using superimposed training (ST).The LTV channel is modeled by truncated discrete Fourier *** on this model,a two-step approach is adopted to estimate the LTV channel over multiple OFDM *** also present performance analysis of the channel estimation and derive a closed-form expression for the channel estimation *** is shown that the estimation variances,unlike that of the conventional ST-based schemes,approach to a fixed lower-bound as the training length increases,which is directly proportional to information-pilot power *** wireless communication systems with a limited transmission power,we optimize the ST power allocation by maximizing the lower bound of the average channel *** results show that the proposed approach outperforms the frequency-division multiplexed training schemes.

关键词： OFDM/MIMO systems linearly time-varying channel estimation superimposed training training power allocation

RBF neural network and active circles based algorithm for contours extraction

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Progress in Natural science:Materials International 2007年第6期17卷 681-686页

作者： Zhou Zhiheng, Zeng Delu and Xie Shengli(College of Electronic & information engineering, south china university of Technology, guangzhou 510640, china) College of Electronic and information engineering South China University of Technology Guangzhou 510640 China

For the contours extraction from the images, active contour model and self-organizing map based approach are popular nowadays. But they are still confronted with the problems that the optimization of energy function will trap in local minimums and the contour evolutions greatly depend on the initial contour selection. Addressing to these problems, a contours extraction algorithm based on RBF neural network is proposed here. A series of circles with adaptive radius and center is firstly used to search image feature points that are scattered enough. After the feature points are clustered, a group of radial basis functions are constructed. Using the pixels’ intensities and gradients as the input vector, the final object contour can be obtained by the predicting ability of the neural network. The RBF neural network based algorithm is tested on three kinds of images, such as changing topology, complicated background, and blurring or noisy boundary. Simulation results show that the proposed algorithm performs contours extraction greatly.

关键词： contours extraction RBF neural network dynamic clustering.

Vector bundle constraint for particle swarm optimization and its application to active contour modeling

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Progress in Natural science:Materials International 2007年第10期17卷 1220-1225页

作者： Zeng Delu, Zhou Zhiheng and Xie Shengli(College of Electronic and information engineering, south china university of Technology, guangzhou 510641, china) College of Electronic and information engineering South China University of Technology Guangzhou 510641 China

Active contour modeling (ACM) has been shown to be a powerful method in object boundary extraction. In this paper, a new ACM based on vector bundle constraint for particle swarm optimization (VBCPSO-ACM) is proposed. Different from the traditional particle swarm optimization (PSO), in the process of velocity update, a vector bundle is predefined for each particle and velocity update of the particle is restricted to its bundle. Applying this idea to ACM, control points on the contour are treated as particles in PSO and the evolution of the contour is driven by the particles. Meanwhile, global searching is shifted to local searching in ACM by decreasing the number of neighbors and inertia. In addition, the addition and deletion of particles on the active contour make this new model possible for representing the real boundaries more precisely. The proposed VBCPSO-ACM can avoid self-intersection during contour evolving and also extract inhomogeneous boundaries. The simulation results proved its great performance in performing contour extraction.

关键词： boundary extraction active contour modeling particle swarm optimization velocity update vector bundle.