行波光电二极管级联阵列输出功率合成研究

针对未来光载无线通信所需的高功率、大带宽的光电探测器,提出了一种行波光电二极管级联阵列功率合成电路.先将行波光电二极管级联,再按照阵列式结构将多组级联的光电二极管组合起来,实现射频功率合成,以获得高功率、大带宽的射频信号.采用EDA工具,对该光电转换射频功率合成电路进行仿真模拟.仿真结果表明,该功率合成电路可以有效地将各光电二极管的射频输出信号进行功率合成,功率合成后的信号带宽显著增加,仿真结果与理论分析完全一致.此外,电路分析表明,增加该功率合成电路中的高阻微带线的特性阻抗可以有效提高其输出射频信号的带宽.     

L型阵列探测器合成功率研究与设计

针对行波探测器阵列只能合成输出功率而不能同时提高工作带宽的现状,基于m推演型滤波电路原理,提出了一种新的L型阵列探测器,即通过在光电二极管之间串联电容减少结电容对截止频率的影响,再与两个电感串联形成单个阵列单元,然后将单个阵列单元级联构成全新的L型滤波器电路结构。结果表明,L型探测器阵列能够对射频输出信号进行功率合成,同时工作带宽提高至67 GHz,相较于传统光电探测器,工作带宽提高两倍。通过增加级联光电二极管的数量,可以持续增大输出功率,同时L型探测器阵列的推演方法可根据实际需求灵活设计出期望的光电探测器,为未来大带宽、高功率的光电探测器设计提供理论基础。     

多元T型阵列探测器原理与性能

针对行波探测器阵列只合成多个光电二极管的输出功率而不能提高工作带宽的问题,提出了一种多元T型电路结构的阵列探测器.通过在各个光电二极管支路串联电容降低等效电容,减小结电容对探测器截止频率的影响,再用电感连接各个光电二极管支路构成T型滤波器电路结构,在合成多个光电二极管输出功率的同时增加了工作带宽.仿真结果表明,在光电二极管支路串联与光电二极管结电容相等大小的电容时,四元T型阵列探测器相比四元行波探测器阵列输出功率减少了一半,但工作带宽提高了一倍,而相比于传统探测器则在输出功率和工作带宽上都提高了一倍,此外八元T型阵列探测器与四元行波探测器阵列输出功率相同,工作带宽提高了一倍.     

叉状光电探测器阵列电极的设计与优化

针对行波光电探测器阵列(TW-PDA)的传输时延导致各路电信号在输出终端产生相位失配,影响整体频率响应的问题,提出了一种叉状光电探测器阵列(F-PDA)的电极结构.该电极采用对称连接结构代替TW-PDA的逐级连接结构的方法,使得各路光电探测器单元与信号输出终端的距离保持一致,从而克服传统结构中由于传输时延带来的一系列问题.电极的结构参数经HFSS进行设计并优化后,在100GHz内的最大插入损耗不超过1.5dB,特征阻抗稳定于50Ω左右.实验结果表明,制备的TW-PDA在40GHz下的插入损耗约2.5dB,3dB带宽约6.9GHz;而F-PDA对应的测试结果分别约1.36dB以及13.8GHz.相比而言,本文提出的结构存在明显的性能提升.     

共振腔增强型光电探测器

共振腔增强型光电探测器是近十年发展起来的新型探测器。它是在探测器内制备微共振腔并在中间插入激活层构成的。在这种结构中,由于共振腔对非共振波长的抑制及对共振光场的放大作用,使探测器的量子效率在共振波长处被增强,带宽－量子效率之积比传统的光电二极管提高了近３倍。由于它同时具备对波长的选择作用和高频响应特性,因而是光通信理想的探测器件。     

PIN光电二极管探测器响应特性测试

介绍了PIN光电二极管探测器的工作原理及基本结构,设计了探测器的测试系统,说明了测试系统中各个组成部分的结构和功能.利用该系统对PIN管光探测器电路的电特性进行了测试,测试结果表明PIN光电二极管探测器的响应特性符合技术要求.     

方环结构的宽频可调超材料滤波器

采用微控制电路加载技术控制超材料的等效介电常数和等效磁导率在不同时间的空间分布形式,实现空间滤波器中心频率的可调.设计了一种方环缝隙结构超材料滤波器,单元结构尺寸为18.5mm×18.5mm,通过在单元结构上加载变容二极管实现X波段内的连续可调.当变容二极管电容值从0.15pF增大到0.70pF时,仿真结果表明滤波器的中心频率从11.8GHz逐渐减小到10.5GHz,工作带宽为16.3%(10.2~12.0GHz),通带内的回波损耗最小值为22dB,插入损耗最大值为0.6dB.测试结果表明滤波器的中心频率从11.7GHz逐渐减小到10.3GHz,工作带宽为17.2%(10.1~12.0GHz),且通带内的回波损耗最小值为25dB,插入损耗最大值为0.5dB.     

量子光学实验中宽带低噪声光电探测器的研制

针对量子光学实验的特殊要求,通过设计优化宽带低噪声放大电路,研制出宽带低噪声光电探测器.我们重点分析了影响光电探测器增益、带宽和噪声的因素,通过选择合适的光电二极管、取样电阻、反馈电阻和输出电容,获得了宽带低噪声光电探测器.该光电探测器的带宽为2～50 MHz,能够用于输入功率达15 mW光场的噪声测量,适用于包括平衡零拍探测、差拍探测等量子光学实验.考虑到在量子光学实验中需要一对平衡的光电探测器,我们制作了一对2 MHz～31 MHz带宽内共模抑制比大于30 dB的平衡光电探测器,并用于1064 nm激光和1550 nm激光的强度噪声测量和散粒噪声基准的校准.     

InP基矩形马赫-曾德高速电光调制器行波电极设计与测试

提出了一种由新型沟槽耦合器和90°弯曲波导构成的InGaAsP/InP基矩形马赫-曾德电光调制器,对该调制器的L型波导相移臂设计了T型类微带行波电极.首先利用电极的等效电路估算带宽上限,进而在考虑阻抗匹配、回波损耗以及带宽等性能的基础上,使用有限元方法对电极的传输、输入/输出以及过渡区的结构参量进行优化.仿真结果表明由于受到电极输入及过渡区的性能限制,设计的整体行波电极匹配阻抗大于42Ω,回波损耗小于-15dB,带宽可达65GHz.测试制备的Ti/Au行波电极,得到回波损耗为-12dB和带宽为20GHz的最优性能.     

窄带有机光电探测器的优化设计

针对基于无机材料的光电探测器需要借助滤光器或棱镜耦合实现窄带响应,提出了一种通过有机材料制备窄带光电探测器并提高吸收峰值和降低半高全宽的方法和结构。该器件由分布布拉格反射器和有机光电二极管构成。有机光电二极管的顶电极和底电极之间构成光学微腔。采用传输矩阵法,详细分析了分布布拉格反射器的中心波长、有机光电二极管透明顶电极和光敏感层的厚度对有机光电探测器吸收性能的影响。研究结果表明,Tamm等离激元共振波长接近光敏感层的光学带隙时,可获得半高全宽小于20 nm的窄带响应,并且吸收峰值在70%以上。基于PTB7∶PC~(71)BM和PTB7-Th∶IEICO-4F的有机光电探测器分别可用于探测红光和近红外光。该研究从基本物理机制出发,结合材料和器件结构可将有机光电探测器的响应窗口从可见光拓展至近红外光。     

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.     

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.     

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.     

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.     

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.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.