Trapezoidal index single-mode fibers for the 1.55 µm band

An analytical study is made of single-mode fibers with a trapezoidal index of refraction profile for low dispersion operation in the 1.55-μm band using Ge doped silica core and pure silica cladding. It is found that certain trapezoid proportions give a fiber with a combination of less Ge doping, larger core diameter, faster decay of the field in the radial direction within the cladding, and smaller rate of change of dispersion with wavelength than is simultaneously possible with either the step index or triangular profiles.     

Substructure formation and texture in electrodeposits

The author’s work on electrodeposit substructure in relation to the texture is reviewed. Addressed are substructure anisotropy in electrodeposits and the axial and the random components of their texture, periodicity of the substructure with increasing nuclear charge of constituent atoms, regular variation in the substructure with increasing supercooling in the electrodeposition, and occurrence of an amorphous state during electrocrystallization of metals. Interrelation between the substructure and the texture in electrodeposits, and the influence of structure on electrodeposit properties are also discussed.     

Propagation properties of a cylindrically polarized vector beam

A general expression for the electric field of a cylindrically polarized vector beam propagating in free space is derived on the basis of the exact fully vectorial solution of Maxwell equations in transverse Fourier space,which indicates that a cylindrical polarization can be regarded as the combination of radial and azimuthal polarizations, and the electric field retains cylindrical symmetry under the propagation. The simulation results denote that the longitudinal electric field depends on the ratio of the waist width to wavelength and the angle between the electrical vector and the radial direction; in particular, when this angle is 24.5°, a flattop intensity distribution is obtained at the plane z=0.     

Electrooptic polarization modulation in [110]-oriented GaAs-InGaAsmultiple quantum wells

An electrooptic modulator that is sensitive to the polarization state of transmitted light is demonstrated by using the intrinsic optical anisotropy of biaxially strained [110]-oriented GaAs-In_y Ga_1-xAs multiple quantum wells. The ellipticity and the direction of polarization of a linearly polarized input pulse are modulated by a change in the in-plane dichroism and birefringence produced by a change in the voltage applied across the p-i-n region containing the quantum wells. Sensitive ellipsometric measurements are used to directly measure the anisotropy in the complex index of refraction between the two principal in-plane axes of the sample as a function of wavelength for selected voltages. The latter information is then used to determine the operating wavelength, the contrast ratio, the optical bandwidth, and the tunability of the modulator. This structure requires only standard elementary post-growth processing     

形状双折射金属表面等离激元的特征长度

针对p偏振,研究形状双折射金属和常规介电材料界面的表面等离激元(SPP)。基于形状双折射金属介电常数的双轴各向异性和SPP的色散关系,分别在X方向和Y方向讨论SPP波长、传播距离以及在两种介质中的穿透深度等特征长度的变化规律。另外,分别讨论形状双折射金属的3个结构参数对SPP特征长度的影响,发现X方向的结构周期变化只影响Y方向的SPP特征长度,Y方向的结构周期变化只影响X方向的SPP特征长度,纳米孔半径的变化同时影响X方向和Y方向的SPP特征长度。     

多脉冲激光辐照皮肤组织的光热效应实验研究

通过实验测定了离体乳猪皮肤组织在多脉冲Nd:YAG激光辐照下径向和轴向不同位置的温度分布,重点研究了激光辐照能量密度、脉冲重复频率以及波长对皮肤组织温升分布的影响.研究结果表明:皮肤组织中的温度分布与探测位置、激光辐照能量密度、脉冲激光的重复频率以及波长密切相关;在激光辐照时间为40 s的情况下,同一波长同一频率时组织温度随能量密度的增加而增大,波长1064 nm、霞复频率10 Hz时的安全光剂量阈值为1118.19 mJ/cm2;同一波长同一能量密度时,组织温度随脉冲激光重复频率的增加面增大;同一能量密度同一频率时,波长为1 064 nm的多脉冲激光辐照皮肤组织时的光热效应较532 nm波长明显.     

Opening of Hybrid Bandgaps in Two-Dimensional Photonic Crystals of Pb(Mg$_{1/3}$Nb$_{1/3}$ )O$_{3}$–PbTiO $_{3}$ Having Very Low Refractive Index Contrast

The effect of anisotropy on two-dimensional photonic crystals of hexagonally arranged Pb(Mg_1/3Nb_1/3)O₃-PbTiO₃ (PMNT) rods in air background was analyzed using a finite-difference time-domain method. The refractive index contrast between PMNT (n = 2.47) and air is low compared to conventional semiconductor-air photonic crystals. Yet, hybrid (polarization-independent) photonic bandgaps were achieved for anisotropic PMNT rods by adjusting the structural parameters and the anisotropy. The maximum bandwidth found was 20 nm. It was possible to engineer the center wavelength of this bandgap to 980, 1300, and 1550 nm, for potential applications as switches, electrooptic filters, and modulators in this region.     

折射率和粒子尺度对大气气溶胶光散射特性的影响

采用Mie散射方法计算了小尺度范围内,0.65 m波长大气气溶胶粒子光学特性与折射率、粒子尺度参数的关系,并分析了折射率虚部对气溶胶粒子散射相函数的影响。结果表明:在小尺度范围内,气溶胶粒子散射特性受折射率、尺度参数影响较大,折射率实部和尺度参数对消光效率因子等非散射角散射参量的影响存在一定程度的对称性。同时还发现,在特殊散射角位置,无论对于单粒子还是对于多分散粒子群系统,气溶胶粒子（群）的散射相函数与折射率虚部基本无关,不同折射率虚部的散射相函数在前向散射方向存在交点,交点位置随粒子尺度参数的变化基本为高斯分布。随着粒子尺度参数的增大,交点位置向前向小角方向移动,并逐步趋于离散。这一结论对了解大气气溶胶粒子的散射效应具有一定的参考意义。     

海洋湍流下波长分集无线光通信系统性能分析

由于海水的吸收、散射衰减以及海洋湍流效应会引起水下无线光通信（Underwater wireless optical communication,UWOC）系统接收端光信号的闪烁,导致UWOC系统传输性能下降。基于Gamma-gamma分布的海洋湍流信道模型,根据海洋湍流参数和各向异性因子表示的等效结构参数,推导出波长分集UWOC系统中断概率（Outage probability,OP）与平均误码率（Bit error rate,BER）封闭表达式。研究分析随着各向异性因子的增加,具有不同波长分集阶的水下无线光通信系统中断概率与平均误码率的变化,比较接收端使用最佳组合（Optimal combining,OC）与等增益组合（Equal gain combining,EGC）技术的水下无线光通信系统平均误码率,并仿真不同海洋湍流参数、传输距离对波长分集UWOC系统性能的影响。数值结果表明,随着各向异性因子的增加,海洋湍流对水下无线光通信系统产生的影响逐渐减弱,使用波长分集技术的UWOC系统比无波长分集技术的UWOC系统中断概率与平均误码率明显改善。     

一维各向异性掺杂光子晶体的缺陷模特性

利用传输矩阵的方法给出了光波在一维各向异性掺杂光子晶体中传播的透射率,研究了缺陷模的相关特性,经数值模拟计算得出:光通过一维各向异性掺杂光子晶体后,透射波中TE波和TM波存在明显的缺陷模,缺陷模的中心波长位置随光波入射角的改变而不同,两个缺陷模能完全分开;TE波的缺陷模中心波长位置随着光学厚度的增大向短波方向移动,TM...     

圆迹变换及图像纹理分析

针对迹变换提取的特征对于含圆弧形纹理图像描述欠佳的问题,提出了圆迹变换及其纹理特征提取方法.圆迹变换使用圆迹线来跟踪图像,并将圆迹线上的泛函结果映射到由半径、长度和角度三个参数生成的空间上,对该结果继续做泛函积分,能得到图像四重圆迹空间特征.在圆迹线上使用不同的泛函能得到不同的圆迹变换结果,不同的泛函组合能获得不同的圆迹变换特征,能表示图像不同的纹理性质和更深层次的图像信息,产生多维的圆迹变换纹理特征信息.在Coil-20对象图库及Brodatz纹理库上对含圆弧形图像的分类实验表明,在训练样本较少的情况下,利用圆迹变换提取的纹理特征,其识别能力比迹变换都有明显提升,对于包含圆形、弧线形纹理的图像具备了更好的分辨能力.     

An Integrated Segmentation and Analysis Approach for QCT of the Knee to Determine Subchondral Bone Mineral Density and Texture

We have developed a new integrated approach for quantitative computed tomography of the knee in order to quantify bone mineral density (BMD) and subchondral bone structure. The present framework consists of image acquisition and reconstruction, 3-D segmentation, determination of anatomic coordinate systems, and reproducible positioning of analysis volumes of interest (VOI). Novel segmentation algorithms were developed to identify growth plates of the tibia and femur and the joint space with high reproducibility. Five different VOIs with varying distance to the articular surface are defined in the epiphysis. Each VOI is further subdivided into a medial and a lateral part. In each VOI, BMD is determined. In addition, a texture analysis is performed on a high-resolution computed tomography (CT) reconstruction of the same CT scan in order to quantify subchondral bone structure. Local and global homogeneity, as well as local and global anisotropy were measured in all VOIs. Overall short-term precision of the technique was evaluated using double measurements of 20 osteoarthritic cadaveric human knees. Precision errors for volume were about 2-3% in the femur and 3-5% in the tibia. Precision errors for BMD were about 1-2% lower. Homogeneity parameters showed precision errors up to about 2% and anisotropy parameters up to about 4%.     

一种缓变结构一维光子晶体的缺陷模研究

利用传输矩阵方法,研究了单折射率层缓变准周期结构一维光子晶体存在不同缺陷时的缺陷模。结果表明,当该准周期结构中存在缺陷时,引入了缺陷模,且缺陷模与缺陷层的位置和结构参数相关。缺陷层不同,缺陷模的位置及共振透射峰也不同。随着缺陷层光学厚度的增大,缺陷模波长向长波方向移动。     

The influence of the AlN film texture on the wet chemical etching

The influence of the aluminum nitride (AlN) film texture on the chemical etching in KOH solution was invested. The AlN films with the different texture and crystal quality were prepared by sputtering. It is found that the chemical etching behaviors, including the etch rate, the activation energy, the surface morphology and the anisotropy, are strongly dependent on the film texture. There is a faster etching in the case of mixed (1 0 0) and (0 0 2) texture and a lower rate in the case of only (0 0 2) texture. The etch rate also decreases with the crystal quality. The sample with the only (0 0 2) texture forms discontinuous column structure after etching and exhibits lower porosity compared to that of the mixed (1 0 0) and (0 0 2) texture. Due to the strong anisotropy of the AlN wurtzite structure, the morphology of the film deposited at 700 °C shows the homogeneous pyramid shape after etching. The cross-section micrographs of etching patterns indicate that the anisotropy of the chemical etching is improved with the improving of the crystal quality.     

Structure of Bi<Subscript>2</Subscript>Se<Subscript>0.3</Subscript>Te<Subscript>2.7</Subscript> alloy plates obtained by crystallization in a flat cavity by the Bridgman method

The property anisotropy in Bi₂Se_0.3Te_2.7 alloy is analyzed by constructing index surfaces for the thermoelectric figure of merit and thermal expansion coefficient. Texture is an important factor forming the property anisotropy and technological applicability of an ingot for fabricating modules. The property anisotropy is analyzed based on studying the texture in ingots produced by the modified Bridgman method (thermoelectric plate growth in a flat cavity). Analysis of the texture shows that not only the crystallization rate, but also the crystallization cavity design is an important factor for the proposed crystallization method, affecting the formation of the thermoelectric-material structure. As the plate thickness is decreased by changing the heat removal conditions in a thin gap, a more perfect structure can be obtained.     

电化学刻蚀半导体的结构分析

结合多孔硅(Si)、多孔砷化镓(GaAs)以及多孔磷化铟(InP)的不同孔形貌,综合分析了元素半导体硅及Ⅲ-Ⅴ族化合物半导体GaAs、InP的刻蚀结构,系统地阐述了晶体结构在电化学刻蚀中的作用。化合物半导体由于存在晶格极化和各向异性,使得不同晶面的溶解速率或钝化速率不同,导致孔沿着溶解速率较大的方向生长,钝化速率较大的晶面成为孔壁,在一定程度上影响了孔的形状、大小及周期性排列等特征。用电流控制模型对不同孔的生长过程进行了较好的解释,进一步证明了晶体的结构特征对其产生的重要影响。     

Periodicity Perturbed Grounded Frequency Selective Surface Arrays as Millimeter Wave Random Phase Coherence Destroying Diffusers

This paper presents the design, construction and testing of perturbed periodicity slot type grounded Frequency Selective Surface (FSS) array as millimeter wave (mm-wave) random phase diffusers to eliminate speckle in active mm-wave imaging. To create a random phase diffuser for destroying the coherence of mm-wave sources we proposed FSS based diffusers arrays where the periodicities between the elements are different thought the slot of the cells are similar. The impacts of periodicity variations of both TM and TE field directions have been investigated. The periodicity of an FSS is the main design parameter used to optimize the phase shifting properties of the arrays. The critical parameters of the diffuser arrays design, such as phase relation with periodicity and optimum designed consideration are discussed. We designed the FSS arrays with Finite Integral Technique, fabricated by using etching technique and characterized the S-parameters with a free space Millimeter Wave Vector Network Analyzer (MVNA).     

原位背散射电子衍射研究压缩变形过程中AZ31合金的微观组织演变

本文采用原位背散射电子衍射(原位-EBSD)方法研究了AZ31合金在压缩应力下的微观组织演变.结果表明{ 10-12}[-1011]孪生是主要的变形模式.该孪生模式导致了变形后晶体取向发生了明显的转变,由原始取向为其C轴垂直于挤压方向ED的丝织构,转变为其C轴平行于ED及压缩应力方向.同时位错滑移也提供了一定的变形量....     

Modes in s.a.w. grating resonators

It is shown that s.a.w. gratings on the surface of an isotropic medium may support modes that are confined underneath the grating. The 3-dimensional resonant-mode patterns are derived for the Rayleigh wave in a high-Q-factor resonator consisting of two gratings separated by ?/2, where ? is the grating periodicity, in the limit when the grating width is large compared with a wavelength. The resonance frequencies of the different modes are presented.