过耦合结构超导铝共面波导谐振器温度特性研究

制备了基于超导铝膜的四分之一波长反射型共面波导谐振器,并利用矢量网络分析仪测量了该谐振器在低温超导状态下的传输特性。实验结果表明:对于拥有较大耦合电容的超导共面波导谐振器,在超导状态下随着环境温度的升高,超导薄膜的表面阻抗会增大,进而谐振器的中心谐振频率降低,谐振峰变宽。温度越高,谐振频率随温度升高而向低频偏移的速率越快。另一方面,随着环境温度升高,谐振器的外部耦合品质因数和负载品质因数也都会降低。温度越高,谐振器品质因数随温度升高而降低的速率越快。用二能级理论解释了实验现象,品质因数理论计算值与实验测量结果相接近。     

封面故事

正量子电容是电子填充费米面所引起的内禀电容效应,在低维材料中尤为显著,被广泛应用于电子态密度测量与电子多体效应的研究。南方科技大学电子与电气工程系陈晓龙、香港科技大学物理系王宁研究团队合作,基于单层石墨烯材料制备了新型量子电容器件,并构造了电致可调谐振电路,在2 V栅控电压下实现了电容值50%的改变与20%谐振频率的改变。     

一种基于交指电容裂环谐振器的差分微波传感器研究与设计（特邀）

提出了一种基于交指电容裂环谐振器的差分微波传感器。通过把交指电容结构嵌入到裂环谐振器的开口处以增强电场束缚效应,并且为了抑制外界环境因素的干扰,制作成差分结构。差分结构采用两个裂环谐振器分别分布于单根微带线两边的结构形式,谐振器与微带线呈磁耦合效应。该传感器结构可以克服传统微波传感器的低灵敏度和易受外界干扰的问题。在实验中,将一个谐振器作为参考单元,另一个谐振器作为测量单元,待检测液体样本放置于测量交指电容处,随着不同浓度的乙醇-水混合溶液的注入,测量单元的谐振频率相较于参考单元会发生明显的频率偏移和陷波幅值的偏差,由此可以拟合出复数介电常数与它们之间的关系以预测不同浓度的乙醇-水混合溶液的复数介电常数值。实验结果表明：所提出传感器的单位体积平均灵敏度可达3.630 8%/μL,比同类型的传感器提高了几倍至几十倍。     

可调频高功率宽谱微波的产生和辐射

 设计了一种可调谐频率的高功率宽谱微波辐射装置,装置由可调谐长度的1/4波长低阻同轴谐振器、环形开关、电容耦合器和宽谱辐射天线组成,中心频率调谐为200～400 MHz。低阻传输线与环形开关构成1/4波长短路谐振器,它产生的宽谱微波振荡通过耦合器耦合到宽谱辐射天线上辐射,而耦合器由集中电容与分布电感组成,实现宽谱微波在频率调谐范围内以较为一致的耦合度提取微波能量。通过转动螺杆滑动安装在同轴谐振器内芯上的环形开关,达到改变谐振频率的目的。最后,将可调频宽谱辐射装置与输出电压为500 kV的Tesla变压器脉冲功率源联试,得到200～400 MHz宽谱微波辐射,辐射因子为95～130 kV,频谱百分比带宽为10%～30%。     

SAW谐振器谐振频率微秒级快速检测方法

针对高速旋转环境下的谐振式声表面波(SAW)传感器信号快速检测,提出基于回波损耗测量原理的SAW谐振器谐振频率微妙级快速检测方法.对SAW谐振器进行线性扫频激励的过程中,将反射信号经功率检波与比较器转换为数字脉冲信号,使用计时器实时计算脉冲信号中心对应频率快速求得SAW传感器谐振频率.在8000 r/min转速范围内对...     

便携式谐振倍压电容充电电源的设计

对输入电压为24 V,输出电压3 kV的便携式谐振倍压电容充电电源进行了设计与验证。针对高变压比的特点,电源采用串联谐振拓扑与倍压整流相结合的拓扑结构,避免了高频变压器副边匝数过多、分布参数过大可能造成的不利影响。对高频变压器、谐振电容、开关器件等核心元件进行了设计和调试。最后采用该电源进行电容充电实验,其测试结果验证了设计的正确性。     

介质谐振器法测量超导薄膜微波表面阻抗

本文所用的测试方法为蓝宝石介质谐振器法,它采用一片超导薄膜替代谐振器的一端,通过测量微波介质谐振腔的品质因数和谐振频率随温度变化来确定超导薄膜的微波表面阻抗.本文设计和制作了一个工作于TE01δ模式,谐振频率在18.3GHz左右的蓝宝石介质谐振器,其无载品质因数在3K时可达到130000.用此方法可以对薄膜进行无损伤测量,测量后的薄膜还可继续使用.     

新型的高温超导薄膜梳齿谐振器

本文报导了一种新型结构的高温超导薄膜梳齿谐振器.我们通过改变谐振器梳齿的长度,使谐振器的谐振频率可以从800MHz到1300MHz左右,这正是我们研制的Hi-Tc rf SQUID所需要的两个频段.我们对这种新型谐振器的谐振频率与几何尺寸的关系进行了数值拟合.测试了使用该种新型谐振器的Hi-Tc rf SQUID的噪声.     

CDMA移动通信用高温超导滤波器的研制

本文提出了一种新型H型环带谐振器,具有结构紧凑,尺寸小,Q值高,非相邻耦合弱等优点.该谐振器在一侧设置了一个开口,改变开口位置,可以在较大范围内改变谐振器谐振频率,并且能够改变基频和二倍谐频之间的频率间隔.对于直连型馈线引入方式,H型环带谐振器容易实现外部Q值的匹配,同时对输入/输出端谐振器的谐振频率影响很小.本文还基于H型环带谐振器,采用2英寸双面YBCO高温超导薄膜设计并制作了用于CDMA移动通信系统的12节高温超导滤波器.该滤波器的中心频率为832MHz,相对带宽为1.6%.在70K温度下的测试结果显示滤波器的带内插入损耗低于0.28dB,反射损耗优于-15.5dB,带外抑制约为75dB,通带低频端带边陡峭度超过30dB/MHz,高频端带边陡峭度超过20dB/MHz.     

传输线法测量可调谐振器

在高阻硅基片上,我们制备了末端串联了dc-SQUID的λ/4谐振器,实现了可调超导共面波导谐振器.通过与谐振器耦合的传输线,我们测量了可调λ/4谐振器在外加磁通偏置下谐振频率的可调性,并将结果和理论值进行了比较和分析.     

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.     

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.     

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.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.     

Fiber Modal Index Measurements Based on Fiber Gratings

A novel method based on fiber gratings for measuring the effective indices of fiber modes is proposed. The effective index difference between the core mode and a cladding mode was obtained by analyzing the interference fringe of a pair of cascaded long-period fiber gratings. In order to extract the core mode index from the measured index difference, an index matching oil immersion method is proposed. By analyzing the interaction between the cladding mode and the oil applied on the cladding surface, the mode order and the effective index of the involved cladding mode might be calculated. Experimental results about the interference fringe shifts induced by the oil index and the oil-applied length are also presented.     

Optical Pulse Compression Schemes That Use Nonlinear Bragg Gratings

Nonlinear optical pulse compression of picosecond pulses typically requires long lengths of optical fiber and multiple components. Periodic structures, such as fiber Bragg gratings, are highly dispersive at wavelengths outside of the photonic bandgap. This implies that such gratings can be used as very short all-fiber compressors. In this paper a number of such compression schemes are reviewed involving uniform and nonuniform fiber Bragg gratings, relying on both soliton and nonsoliton compression principles. Experimental results supporting the corresponding underlying theory are also presented. Finally, an extension of one of the compression schemes is shown, which allows the generation of adjustable high-repetition rate soliton trains.