空气背衬芯轴型光纤水听器加速度性能研究

对用于水声探测的光纤水听器,加速度相移灵敏度是一个重要的参数。本文采用有限元法对空气背衬芯轴型光纤水听器的加速度相移灵敏度进行了理论分析,并通过实验验证,得到了空气背衬芯轴型光纤水听器加速度相移灵敏度的优化规律,提高芯轴壳体的硬度可有效降低光纤水听器的加速度相移灵敏度,而改变芯轴壳体的厚度对水听器加速度灵敏度影响不大。     

MEMS压电水听器和矢量水听器研究进展*

基于微电子机械系统制造技术的MEMS压电水听器和矢量水听器具有小型化、低功耗、低成本、易成阵、无源、噪音低等优点。对基于ZnO薄膜的MEMS水听器和矢量水听器进行了研究,测试结果表明,硅微压电水听器的灵敏度为-192 d B(ref.1 V/μPa),基本达到实用化的要求。MEMS压电矢量水听器等效声压灵敏度为-229.5 d B(ref.1 V/μPa),比同类型压阻式MEMS矢量水听器的灵敏度高17 d B,但还未达到实用化要求。为了进一步提高MEMS矢量水听器的灵敏度,设计了具有U形槽的压电复合悬臂梁结构和电极串联结构,采用具有更高压电系数的掺钒ZnO薄膜作为压电层,并对MEMS制备工艺进行了改进,有望显著提高MEMS矢量水听器的灵敏度。     

双套筒式PVDF聚合物薄膜水听器

本文提出一种采用PVDF聚合物薄膜压电材料的双套筒式水听器结构,并通过静态分析方法给出了水听器的低频电声灵敏度公式.理论优化值及该结构式水听器的一例实测结果均表明,这种结构具有乐观的应用前景.     

F-P型光纤水听器温度特性研究

温度漂移对水听器系统输出的影响是其实用化进程中的关键技术障碍。这主要表现在温度变化引起水听器探头背衬材料的胀缩和光纤折射率的变化。首先从弹性力学轴对称问题的准静态理论出发分析了背衬材料的应力特性，并用光弹理论及热应力理论分析了温度改变对光纤相位常数的影响，得出了温度影响干涉式光纤水听器光学相位输出的数学表达式。给出了温度变化对水听器光学相位输出影响的实验测量结果，得出了光学相位随温度变化的线性关系图，与理论计算结果吻合。     

一种用于大坝混凝土声层析成像的水听器线阵

声层析成像技术可以用图像的方式精确完整地反映层析面上检测体内部质量,是一种有效的无损检测手段,在大坝混凝土的安全隐患检测中发挥着越来越重要的作用。本研究旨在研制成像用的接收声波的水听器线阵,该水听器线阵由12个水听器阵元组成,阵元间隔2 m,水听器由直径40 mm的接收型压电圆管和前置放大器组成。水听器在低于20 k Hz的频率范围内,自由场接收电压灵敏度为-173±3 d B,在2 MPa静水压力下灵敏度下降不超过2 d B。制作了2例具有清晰接收波形、一致性和可靠性好的水听器线阵,最终为客户在现场实地获得了高质量的层析图像。     

薄膜材料横向热扩散率的热辐射检测

利用薄膜材料横向尺寸远大于其厚度的特点，通过测量横向传播热波的幅值和相位来确定薄膜的热扩散率是可行的，本文介绍带有背衬的薄膜的横向热扩散率的检测理论，以及利用非接触的热辐射技术对金刚石－硅复合膜的检测结果。     

一种用于大坝混凝土声层析成像用水听器线阵

声层析成像技术可以用图像的方式精确完整地反映层析面上检测体内部质量,是一种有效的无损检测手段。在大坝混凝土的安全隐患检测中发挥着越来越重要的作用,本研究旨在研制成像用的接收声波的水听器线阵,水听器线阵由12个水听器阵元组成,阵元间隔2m,水听器由直径40mm的接收型压电园管和前置放大器组成,水听器在低于20kHz的频率范围内,自由场接收电压灵敏度为-173±-3dB,在2MPa静水压力下灵敏度下降不超过2dB。制作了二例了具有清晰接收波形、一致性和可靠性好的水听器线阵,最终为客户在现场实地获得了高质量的层析图像。     

表面热透镜技术应用于薄膜微弱吸收测量的理论和实验

由薄膜表面光热形变简化理论和表面热透镜衍射理论导出表面热透镜信号表达式，从理论上证明了表面热透镜信号和薄膜吸收率的线性关系. 应用表面热透镜技术研制了薄膜吸收测量仪，测量结果表明其吸收率测量灵敏度和精度均达10^-6量级. 关键词： 吸收测量 表面热透镜 光热形变 薄膜     

表面热透镜薄膜吸收测量灵敏度提高方法

为提高表面热透镜薄膜吸收测量仪的灵敏度，在表面热透镜衍射理论基础上，通过数值模拟给出了探测激光腰斑半径、探测激光腰斑到样品表面距离、样品到探测光纤端面距离等仪器参数的优化方法. 经优化调整后该仪器能达到优于0.1ppm量级的薄膜吸收率测量灵敏度. 关键词： 吸收测量 表面热透镜 光热形变 薄膜     

用于矢量水听器的弯曲圆盘型声压水听器

针对在同振型矢量水听器中有效地复合声压通道的问题,提出一种采用压电双迭片结构的弯曲圆盘型声压水听器。压电双迭片由中心开孔的压电圆片和金属背衬组成,采用弯曲振动工作模式。为提高声压水听器的灵敏度,分别通过理论计算和有限元仿真的方法对双迭片结构进行了分析与优化设计,并制作了一只声压水听器样机用于实验验证。测试结果表明,声压水听器的灵敏度为-157 dB(0 dB re 1 V/μPa),在25 Hz~1000 Hz频带内分布平坦,并具有全指向性的特点。综合理论研究与实验室测试结果,这种弯曲圆盘型声压水听器成功满足了低频宽带声信号接收的需要,达到了复合同振型矢量水听器对声压通道的设计要求。     

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.