SiO2纳米微球表面结构在可见光波段的减反特性

研究了不同尺寸SiO2胶体微球形成纳米结构薄膜的光学传输特性和光子带隙。通过在玻璃基底上自组装透光的SiO2胶体微球形成胶体晶体薄膜, 依据布拉格定律,分析微球尺寸对胶体晶体光子带隙的影响。为实现可见光波段的全方位减反射,提出通过改变胶体粒径将胶体晶体带隙位置移动至紫外波段,理论计算得出当粒径为112 nm,占空比为0.45时能实现可见光波段0.5%的平均反射率。实验结果表明,玻璃基底在400~800 nm间的平均反射率从4.3%降低至0.7%,最小反射率达0.3%。通过控制微球粒径移动光子带隙位置,优化晶体结构参数实现了可见光波段的减反射,有效提高了光学组件对可见光的利用率。     

级联一维光子晶体全方位反射器的带宽最大化

理论研究了由级联一维光子晶体构成的光子异质结构的全方位透射(反射)特性.其中各级联光子晶体的高低折射率介质相同、光学厚度比不同.以两个光子晶体级联的结构为对象,利用传输矩阵方法系统研究了不同偏振态光在不同入射角时光子帯隙的变化,得出实现全方位光子带隙的最大展宽条件,即前一光子晶体的帯隙上限要和后一光子晶体的带隙下限在最大入射角时重合.分别给出了满足和不满足该最大展宽条件的级联结构的全方位带隙参量,通过对全方位带隙宽度的比较说明了满足最大展宽条件的级联结构具有最大的全方位带隙宽度.     

一维三元异质结构光子晶体反射特性

利用传输矩阵法对一维三元光子晶体异质结构的光学特性进行了研究,讨论了介质层厚无序度对三元结构光子禁带的影响.研究表明,将具有相互交叠光子禁带的一维光子晶体叠加构成异质结,可以有效地增大全角度反射的频率范围,当入射角从0°增大到89°,该结构均可实现从0.410 w/w0到0.654 w/w0宽频波段的全反射;相对于二元结构,三元结构可以减小在实际制作过程中随机误差引起的介质层厚无序对光子带隙的影响.该研究结果可为实现可见光及红外光波段大角度反射器的制备及应用提供理论支持.     

一维光子晶体带隙结构研究

在考虑介质色散的基础上,研究了介质层厚度对光子晶体带隙结构的影响.利用传输矩阵法,计算了以LiF和Si两种材料组成的一维光子晶体带隙结构.结果表明,介质层厚度的增加会引起禁带的红移,厚度减小会引起蓝移.分析了含空气缺陷层、金属缺陷层的光子晶体结构,发现空气缺陷层对带隙结构的高反射区域变化不大,而在低反射区域,反射系数为零的波带之间出现了两边反射系数增加,中间反射系数减小的情况.在金属缺陷层的带隙结构中,金属对整个波长范围光的吸收作用不同,金属对低反射区1.6 μm、1.85 μm处透射率较大的透射光吸收作用明显,而在1.28~1.38 μm处透射率波长区间,几乎无吸收.     

可见光波段SiO2/CdSe一维光子晶体及缺陷模的研究究

采用SiO2/CdSe构建了可见光波段一维光子晶体结构,并在其中引入LiTaO3缺陷层。利用传输矩阵法,分析了电磁波在无缺陷与含LiTaO3缺陷层两种光子晶体中的带隙结构,系统地研究了缺陷层参数对光子晶体可见光波段带隙结构的影响规律。计算结果表明：LiTaO3的引入,有利于带隙宽度的增加,调整缺陷层结构参数,缺陷模的位置可在不同颜色区域出现,如红光、黄光等缺陷模。该结构有望用于制作可见光波段的滤波器。     

含超导材料Thue-Morse序列一维光子晶体传输特性研究

超导光子晶体是一类重要的带隙可调谐的光子晶体.利用传输矩阵法研究了含超导材料的Thue -Morse序列准周期结构—维光子晶体在可见光波段的传输特性.数值结果表明在正入射时,光子带隙宽度和位置基本不随序列项数的增加而改变;准周期超导光子晶体的传输特性可以通过改变传统电介质材料的结构参数和环境温度等来进行调节.     

可见光波段SiO_2/CdSe一维光子晶体及缺陷模的研究

采用SiO_2/CdSe构建了可见光波段一维光子晶体结构,并在其中引入LiTaO_3缺陷层。利用传输矩阵法,分析了电磁波在无缺陷与含LiTaO_3缺陷层两种光子晶体中的带隙结构,研究了缺陷层参量对光子晶体可见光波段带隙结构的影响规律。计算结果表明:LiTaO_3的引入,有利于带隙宽度的增加,调整缺陷层结构参量,缺陷模的位置可在不同颜色区域出现,如红光、黄光等缺陷模。该结构有望用于制作可见光波段的滤波器。     

Ge基二维正方晶格光子晶体带隙优化设计

采用平面波展开法模拟二维光子晶体在E极化和H极化下的能带结构,研究Ge基二维正方晶格光子晶体的填充比以及晶格排列结构对最大禁带宽度的影响。结果表明：在空气背景材料中填充Ge柱的介质柱结构中,可产生TE、TM带隙,且各方向完全带隙出现在r/a=0.19~0.47范围内,最大完全帯隙禁带宽度可以达到0.064（归一化频率）;在选取Ge为背景材料的空气孔型结构中,同样可产生TE、TM带隙,且各方向完全带隙出现在r/a=0.46~0.49范围内,最大完全帯隙禁带宽度可以达到0.051（归一化频率）。同时,不论在介质柱型还是空气孔型结构中,带隙宽度都随着r/a的增大呈先增大后减小的趋势。     

含负磁导率或双负材料的一维光子晶体的全方位带隙中波的反射相位特性

运用传输矩阵法研究了含负磁导率或双负材料的一维光子晶体结构在全方位光子禁带中波的反射相位谱.研究发现"负磁导率材料-正折射率材料"光子晶体和"双负材料-正折射率材料"光子晶体,在所述带隙中,对TE波而言,反射相位随入射角的增大而增大;对TM波而言,禁带频率范围内波的反射相位随入射角的增大而减小;TE波和TM波,两种结构的反射位相均随介质层的厚度缩放因子增大而增大,且都与周期数无关.     

二维光子晶体禁带特性研究

采用平面波展开法对二维光子晶体分别在E和H极化下的带隙进行了计算. 考虑了填充比、晶格结构、介电常数对最大绝对帯隙的影响. 结果表明,不论是正方晶格还是三角晶格,TM模在介质柱型光子晶体中更容易形成带隙;TE模在空气孔型光子晶体中更容易形成带隙. 填充比一定,最大绝对帯隙宽度并非随着介电常数增大总是增大,而是存在一个峰值. 相对介电常数一定,最大绝对帯隙宽度随填充比的变化也存在一个峰值. 不论空气孔型还是介质柱型结构,三角晶格比正方晶格更容易形成帯隙. 关键词： 平面波展开法 TE模 TM模 最大绝对帯隙     

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.     

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.     

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.