TRC路径特征及其对时间反演信噪比的影响

时间反演具有时空聚焦特征，在许多方面有着潜在的应用。其中，基于时间反演腔的系统是一种主要的反演系统，可用于脉冲压缩、波束成形、微扰探测等。时间反演腔通常是一个电大的微波混沌腔，内部电磁波的传播具有明显的多径特征，即时间色散特征。因此，在时间反演过程中，反演腔可对反演信号进行相位补偿，重构出初始信号，从而在初始位置形成脉冲的时间压缩和空间聚焦。为了拓展时间反演腔的实际应用，本文基于多径信道模型研究腔体参数对反演性能的影响，重点分析路径的衰减特征、串扰特征和叠加特征对反演信噪比的影响，并总结给出影响反演信噪比的主要参数以及基本规律。     

时间反演脉冲电磁波在双负材料中传播特性研究

利用全时域电磁仿真技术, 对比研究了时间反演脉冲电磁波和脉冲电磁波透过Smith结构双负材料后的时域波形、脉宽压缩以及材料内部空间电场峰值强度分布等时域传播特性. 结果表明：时间反演脉冲电磁波在透过双负材料后, 在初始源激励处表现出良好的时间和空间聚焦特性. 更重要的是, 在双负材料内部, 观测到了电场峰值强度减弱、截面电场峰值强度趋向均衡分布等新型的物理现象. 这些物理现象对发展能够承受大功率新型的双负材料电子器件及其应用系统很有参考研究价值.     

基于信道处理的时间反演幅度可调控多目标聚焦方法

在微波无线输能领域中,如何实现多目标点的电磁波可调控聚焦是一个值得关注的问题.本文提出了一种基于时间反演多径环境下的多目标电磁波聚焦的新方法.该方法基于多个输出之间的信道相关性,将输入和输出节点之间的信道信息进行提取、筛选、加权和重构后在单个发送端上重建反演信号,利用时间反演的空间选择特性实现均衡的电磁波聚焦.基于这种方法,设计了两组在多径环境下的实验.实验结果表明,通过这种方法可以使弱相关模型下不同输出端口获得均衡稳定的聚焦峰,在强相关模型下使不同输出端口的分辨效果进一步提升.此外,6个额外的实验验证了所提出的方法可以在弱相关或强相关的单输入多输出信道模型下,通过改变不同的权值灵活地调整不同接收端的输出峰值电压比.     

时间反演镜对时间反演电磁波聚焦特性影响因素的研究

时间反演电磁波聚焦特性的主要影响因素来自于时间反演镜(time reversal mirror,TRM).利用电磁仿真工具,对各种影响因素进行分析,给出了改善时间反演电磁波聚焦特性的方法.最后,通过实验对改善方法的有效性进行了验证. 关键词： 时间反演镜 时间反演电磁波 聚焦特性 影响因素     

基于时间反演电磁波的微结构天线的单频点超分辨力聚焦研究

提出了在时间反演技术条件下单频的电磁波信号可以实现超分辨力聚焦这一思路,并基于信道理论推导了该思路的可行性;基于传统的同轴探针结构建立了间距为1/4波长的微结构模型,仿真结果证实了该模型结合时间反演技术在单频信号和宽带信号激励时均可以表现出超分辨力聚焦特性,理论分析和仿真结果为单频以及多频带天线的超分辨力聚焦特性的研究提供了重要的指导作用。     

一种用于时间反演通信的亚波长天线阵列设计

基于时间反演电磁波的远场超分辨聚焦特性, 设计了一种亚波长天线阵列, 其天线单元刻蚀有微结构、单元间距为1/20工作波长且信道相互独立. 在保证相似的辐射特性的条件下, 该亚波长天线阵列对比于其他微结构刻蚀所组成的亚波长天线阵列, 具有较好的远场超分辨率聚焦特性. 为基于时间反演的高速率、高质量多天线通信提供了一种有效的终端天线阵列.     

时间反演电磁波超分辨率特性

时间反演电磁波在特定的远场环境下具有超分辨率特性.结合时间反演技术构建具有超分辨率特性的模型进行仿真,对结果分析后筛选出能够实现超分辨率特性的关键因素,可为实用的小型化、多天线无线通信系统的设计提供指导. 关键词： 时间反演电磁波 时间反演技术 超分辨率     

惯性约束聚变装置中靶面光场特性的统计表征方法

在激光驱动的惯性约束聚变装置中,常采用多种束匀滑手段对焦斑的时空特性进行调控.光传输链路中涉及的光学元件众多、传输变换复杂,往往导致光传输模型复杂,且在运用衍射光学方法分析焦斑形态和特征时面临大量的数据处理和计算,致使出现计算量大、计算效率低等问题,亟需寻求快速而简便的新方法来描述焦斑的统计特征.本文利用光场特性的统计表征方法对靶面光场进行表征,采用圆型复数高斯随机变量直接描述靶面光场的统计特征,并基于典型焦斑评价参数对衍射光学方法和统计表征方法得到的远场焦斑进行了对比和分析.结果表明,采用衍射光学方法和统计表征方法获得的焦斑的瞬时特征基本一致,其时间积分的远场焦斑有所不同,但仍可进一步采用相关系数来表征其远场焦斑的时间变化特征.     

亚波长金属线阵中一维时间反演电磁波的聚焦机理研究

基于周期金属线阵的等效电介质模型, 并使用传输线理论方法, 得到了金属线阵中时间反演电磁波的解析表达式. 接着, 在等效电介质模型的适用范围内, 讨论了金属线半径、金属线阵周期、金属线阵周期数对时间反演电磁波聚焦的影响. 从而在理论上证实, 这种结构可以实现远场时间反演电磁波聚焦, 同时, 也为时间反演技术提供了工程参考.     

基于远场时间反演的亚波长天线阵列研究

基于远场时间反演, 从信号处理角度对亚波长阵列的超分辨率聚焦特性进行了理论分析. 提出了一种新型的微结构刻蚀亚波长阵列, 通过时间反演聚焦实验表明, 该阵列具有远场超分辨聚焦特性, 各单元间信道相互独立. 将这种亚波长阵列应用在时间反演镜天线上, 通过实验验证了可以获得更好的超分辨率聚焦效果. 所提出的亚波长天线阵列对多天线超宽带无线通信具有潜在的应用价值. 关键词： 时间反演 亚波长 天线阵列 超分辨率     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Retrieval of ultraviolet skylight radiances and O3 slant column densities from balloon-borne limb spectrometer

With a novel light-weight and absolutely calibrated ultraviolet （UV） spectrometer, UV skylight radiances and O3 slant column densities are measured by balloon-borne limb measurements in Xinjiang area, China. UV skylight radiances measured at the height of 31 km are compared with the results from Modtran in the wavelength range from 290 to 420 nm. O3 slant column densities are derived from radiance spectra in the Huggins bands （320 - 335 nm） using differential optical absorption spectroscopy method. And the parameter exhibits a good correlation with the same value simulated by radiative transfer model （Tracy）. The O3 profile simultaneously measured by an O3 sonde is used as input in Tracy calculations. The O3 sonde is launched on the same balloon.     

Design optimization of highly sensitive LSPR enhanced surface plasmon resonance biosensors with nanoholes

For breaking through the sensitivity limitation of conventional surface plasmon resonance (SPR) biosensors, novel highly sensitive SPR biosensors with Au nanoparticles and nanogratings enhancement have been proposed recently.But in practice, these structures have obvious disadvantages.In this study, a nanohole based sensitivity enhancement SPR biosensor is proposed and the influence of different structural parameters on the performance is investigated by using rigorous coupled wave analysis (RCWA).Electromagnetic field distributions around the nanohole are also given out to directly explain the performance difference for various structural parameters.The results indicate that significant sensitivity increase is associated with localized surface plasmons (LSPs) excitation mediated by nanoholes.Except to outcome the weakness of other LSP based biosensors, larger resonance angle shift, reflectance amplitude, and sharper SPR curves' width are obtained simultaneously under optimized structural parameters.     

Polymer gratings based on photopolymerization for low-order distributed feedback polymer lasers

Novel polymer distributed feedback(DFB)gratings are fabricated based on photopolymerization to reduce lasing threshold of polymer lasers.A photopolymer formulation sensitive to 355-nm ultraviolet(UV)light is proposed for the fabrication of polymer gratings and it can be used to form polymer films by spin-coating process.A very low surface-relief depth ranging from 12.5 to about 1.0 nm has been demonstrated with a refractive-index modulation of about 0.012.The experimental results indicate that such polymer gratings have promising potentials for the fabrication of low-order DFB organic semiconductor lasers.     

A novel methodology for photometric compensation of projection display on patterned screen

We propose a novel methodology based on the projector-camera (ProCam) system to address the photometric compensation issue for the projection display on the patterned screen.The patterned screen is treated as the combination of a perfect white screen and a color modulator.The perfect white screen is used to automatically and accurately characterize the ProCam system offline using the polynomial model,and the parameters of the color modulator can be efficiently recovered by employing only two gray images based on the linear reflectance model.The experimental results show that the color artifacts of the display image can be greatly improved with this methodology,which demonstrates its feasibility and validity in the photometric compensation.