含特异材料光子晶体隧穿模的偏振特性

构造了由普通材料A(SiO₂)和电单负材料B组成的(AB)^N(BA)^N型一维光子晶体.数值计算表明原禁带的1907.3 nm处出现了一个十分尖锐的隧穿模. 入射角增加,该隧穿模的透射率和半峰全宽度均保持不变,但位置发生蓝移, 入射角在15°-65°的区间内,移动率的绝对值 |dλ/dθ| 较大.当B介质的磁导率μ_B 从5增加到10时,只是隧穿模的位置发生了红移. 介质的几何厚度增加时,隧穿模的透射率不变,但其位置红移明显,半峰全宽略有增加.     

四层单负材料一维光子晶体的透射谱特性

采用传输矩阵法研究四层单负材料一维光子晶体(AB)₂的透射谱特性,发现:透射谱中出现3个隧穿模,随着入射角的增大,3个隧穿模的位置几乎不随入射角变化;随着两种介质层厚度的增大,中央隧穿模的位置保持不变,左右两个隧穿模向中央隧穿模靠拢;随着电单负材料A的磁导率和磁单负材料B的介电常数的增大,3个隧穿模均向低频方向移动,相邻两个隧穿模之间的间隔在减小;三种情况中,3个隧穿模的半峰全宽最终均减小,品质因子均得到提高,其中介质层厚度的变化对隧穿模的半峰全宽和品质因子的影响最显著,入射角的变化影响最小。透射谱的这些特性,对设计新型光学器件具有一定的参考价值。     

一维三元光子晶体缺陷模的特性研究

在考虑色散关系的基础上,利用传输矩阵法讨论了一维三元光子晶体缺陷模的特征.结果表明:缺陷层几何厚度增加时,缺陷模中心红移,透射率下降,品质因子变小.三介质的几何厚度各自独立递增时,缺陷模都向长波方向移动,缺陷模的品质因子先增后降.入射角增大时,缺陷模中心蓝移,透射率不变,半峰全宽度变窄,品质因子变小.若忽略缺陷介质的色散,当其折射率减小时,缺陷模蓝移,透射率变大,半峰全宽度保持不变,品质因子增大.     

一维光子晶体缺陷模偏振特性的研究

利用一维光子晶体的透射率公式,计算出一维光子晶体掺杂后TE波和TM波缺陷模的波长随入射角的响应曲线、缺陷模透射峰随入射角的响应曲线、缺陷模透射峰随入射波长的响应曲线.研究发现,TE波和TM波的缺陷模透射峰均随入射角的增加而向短波方向移动；TE波缺陷模透射峰的半高宽度(FWHM)和峰值随入射角的增加而减小,而TM波缺陷模透射峰的半高宽度(FWHM)和峰值确随入射角的增加而增加；对TM波其波长为λ0的缺陷模也存在明显的“广义布儒斯特角”现象, TE波的缺陷模不存在“广义布儒斯特角”现象.     

一维光子晶体全反射隧穿的色散特性

利用介质材料的色散关系和特征矩阵法研究了一维光子晶体中TE波和TM波的全反射隧穿效应随色散的变化特征.TE波和TM波全反射隧穿导带的频率中心随色散强度的增加而降低,频率宽度随色散强度的增加而增大.TE波和TM波的全反射隧穿导带的频率中心随入射角的增加而升高,频率宽度随入射角的增加而减小.这些研究结果拓宽了对一维光子晶体中TE波和TM波波全反射隧穿效应的认识.     

单负材料一维光子晶体超窄带滤波特性研究

用传输矩阵法研究了单负材料一维光子晶体(ABD)m(CBA)n(ABD)m(CBA)n的透射谱。结果表明:当增加周期数m或D层介质厚度dD时,透射谱中的两个隧穿模越加锋锐,但所处频率位置不变;当增加周期数n或C层介质厚度dC时,透射谱中的两个隧穿模向中间靠拢趋于简并;当增加A层介质厚度dA时,透射谱中双隧穿模结构及位置无变化,而当增加B层介质厚度dB时,透射谱中的三模结构向低频方向移动,且逐渐消失;随着入射角θ的增大,透射谱中两隧穿模向禁带中心靠拢。利用单负材料光子晶体的透射谱特性可实现可调性和高品质的单、多通道超窄带滤波功能。     

由单负材料组成的一维对称型光子晶体中的隧穿模

由电单负材料A和磁单负材料B构成了一维对称型光子晶体,数值计算表明其带隙中出现了一隧穿模. 材料层数增加,隧穿模宽度急剧变窄,而其位置不变.隧穿模的位置和宽度对入射角的变化都不太敏感. 材料的几何厚度减小,隧穿模的位置蓝移,而其宽度不变. μ_A, ε_B增加,隧穿模的位置红移,宽度减小. 利用隧穿模的以上特性可以实现对电磁波传播的动态调控.     

含复折射率介质一维准周期光子晶体的透射特性

用Si和复折射率介质构成了(AB)N型一维准周期光子晶体,在考虑Si色散关系的基础上,利用传输矩阵法研究了其透射特性.数值计算表明其TE波的透射谱有如下特征:电磁波垂直入射时,在相对频率0～4的范围内存在4个等间距的尖锐的透射主峰,各主峰低频端相距0.148 (ω/ω0)处都有一透射副峰.入射角增加,主峰的透射率下降,副峰的透射率上升.周期数N增加,各主、副峰位置都有蓝移,但主峰透射率逐渐减小,而各副峰的半峰全宽度变小.当两介质厚度为定值时,从第一主峰到第四主峰,其透射率依次减小,两介质厚度增加时,各主峰的透射率下降.复折射率虚部增加时,各透射峰的位置保持不变,主峰的透射率变大,而副峰的透射率变小,反之亦然.     

含负折射率层的多层体系的反常光子隧穿

研究了多层体系含负折射率层的光学传输特性,通过传输矩阵方法,给出了体系透射率的一般表达式,并讨论了含负折射率层的四层结构在入射角大于临界角时的反常光子隧穿现象。当体系参量完全匹配时,对于任意入射光波长及大于临界角的入射,透射率均为1;仅衬底层不匹配时,对于给定的衬底参量,透射率和入射波长无关,仅和入射角相关。对于TM波,存在多层体系的布儒斯特角,使得透射率等于1。对于TE波则没有类似现象;在衬底不匹配的情况下,提高出射端的折射率将增加体系的透射率;中间层的厚度或者折射率不匹配时,透射率关于匹配位置对称分布且随着失谐的增加指数衰减,随着入射角的增加,衰减速度加快。     

各向异性光子晶体的全反射隧穿偏振特性

为了研究一维各向异性光子晶体的全反射隧穿偏振特性,利用传输矩阵法计算了TE波和TM波以大于全反射角入射一维各向异性光子晶体时的透射率,在透射波中发现了TE波和TM波的一、二级全反射隧穿带.得出了与一维各向同性光子晶体的全反射隧穿效应的不同点,即TE波和TM波的一、二级全反射隧穿带的频率中心和频率宽度存在着较大的差异,利用这个特性可以将两种偏振光进行频率分离,为设计优质偏振滤波器提供理论依据.     

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.