用于光导板的亚微米光栅透射衍射特性分析

提出了利用亚微米光棚制作光导板的方法,用严格耦合波理论博分析了亚微米光栅从光密介质到光疏介质的1级透射衍射效率与光栅槽深的关系,讨论在满足基底全反射条件的入射角下,对应于红、绿、蓝(红光700mn,绿光555nm,蓝光465nm)三色光的亚微米光栅(0.651μm、0.516μm、0.433μm)在导波条件下的光场衍射特性,并用实验证明在导波条件下1级衍射效率与光栅槽深关系的可靠性,给出亚微米光栅型光导板的初始结构,进行误差分析.     

Time-domain analysis of the Sommerfeld VMD problem based on theexact image theory

A novel time-domain solution of the Sommerfeld half-space problem is constructed through the exact image theory. The radiation from a vertical magnetic dipole (VMD) above the planar interface of two lossless and dispersionless dielectric media is analyzed. The reflection field is given as a Laplace transform when the refraction index of the lower medium is greater. The converse case of refraction indexes is also studied, and the reflection field is written as originating from an image source located in homogeneous space. The present theory is seen to lead to a numerically efficient result, which is demonstrated with examples     

光电晶体中光折变空间孤子传输的数值模拟

给出了描述光折变光电晶体中空间孤子的非线性薛定鄂方程,利用分步傅里叶变换法研究了光电晶体的光折变空间孤子的传输特性.数值模拟结果表明:在忽略光电晶体的克尔效应时,晶体中传输的光束失去了空间孤子的传输特性;在考虑晶体的克尔效应可以与外调制光强度相比拟时,随着外加光强的增加,空间孤子的形状可能发生变形,甚至失去其传输的稳定性;在考虑晶体克尔效应非常强时,空间孤子可以在光电晶体中稳定地、不变形的传输,具有理想信息载体的传输特性.     

反常涡旋光束锥形折射特性分析

为了分析反常涡旋光束的锥形折射,利用锥形折射衍射理论,给出了反常涡旋光束通过双轴晶体光场的表达式。通过数值模拟,分析了锥形折射的环半径和光束束腰半径的比值、光束阶数、拓扑荷数和传播距离等参数对传输特性的影响。结果表明:当锥形折射的环半径远大于光束束腰半径时,在焦像面处,反常涡旋光束的锥形折射光场与高斯光束的双环结构不同,其光场是多环结构;随着拓扑荷数的增加,在焦像面处的亮环数也会增加;光场进一步传输时,光场从多环结构转换成双环结构,且内外环结构特征也会发生变化。     

时间平均流场对星图影响的仿真研究

针对高超飞行器在飞行过程中产生的高速流场光学传输效应对星图的影响,运用雷诺平均法对飞行器边界湍流流场参数进行了计算,采用光线追迹法计算了星光在高速流场中的传输路径,应用物理光学法计算得到时间平均流场的光学传递函数,最后对气动光学效应退化星图进行了模拟。仿真结果表明．时间平均流场使得星光传输发生偏移和模糊,导致畸变星图中...     

光波在含特异材料的环形腔内的传输特性

基于光线传输矩阵理论,研究了含特异材料环形腔内光波光斑半径和相对光强的分布特性.结果表明:以负折射率材料内部作为起始位置,光波传输一周后,子午面和弧矢面光斑半径均较大,中心光强较弱.当光波离开负材料后,光斑半径迅速减小,由于凹面镜的影响,在其表面又达到极大值,但较负材料内部光斑半径小很多.当光波传输起始点远离凹面镜后,光斑半径依次减小,在两平面镜中心达到最小值,此时中心光强最大.在此基础上,分析了负材料长度和介质折射率对光波束腰半径的影响.研究发现,介质长度对环形腔内子午面和弧矢面的束腰半径影响较小,但介质折射率对负材料内部束腰半径的影响较大.     

圆偏振光在手征负折射材料表面的反射和极化特性研究

从理论上分析了圆偏振光入射到手征负折射材料表面的反射与透射特性,给出了归一化反射透射功率与入射角的关系曲线以及布儒斯特角与手征参数之间的关系曲线.当入射角大于两个本征波的临界角时,全内反射现象发生.由于手征负折射介质中的一个本征波发生了负折射,右旋或左旋圆偏振光入射时反射波的极化态有着与常规介质完全不同的特性,以布儒斯特角入射时反射光都为线偏振波但极化方向并不相同.     

Propagation of the light generated by quasi-homogeneous sources through quasi-homogeneous media

The spectral density of the quasi-homogeneous (QH) light has been known when it scatters on QH media or propagates in free space. The case that QH sources are surrounded by QH media is proposed in this paper. Under the paraxial approximation, the spectral density of the QH light propagating through QH media is derived. A modified scaling law for the propagation of the QH light through QH media is also obtained. This law also holds true in the far field beyond the paraxial approximation.     

Focusing of a light beam of Gaussian field distribution in continuous and periodic lens-like media

The behavior of a light beam traveling in continuous or periodic lens-like media is considered. The light beam is assumed to be launched with a Hermite-Gaussian or Laguerre-Gaussian field distribution. Under suitable conditions and for most focusing media we find that the beam center follows a paraxial ray, and an independent equation determines the motion of the beam radius. The form of the field distribution does not change. In a continuous inhomogeneous focusing medium, the beam cross section varies periodically in distance with a period half of that of the oscillatory motion of the beam center. In periodic media, a particular solution is found for the case when the beam propagates with a nearly constant cross section. Discussions include an acoustic lens-guide and a lens-guide using heat diffusion in a gas.     

平面光波在电介质表面的反射特性仿真研究

文中根据麦克斯韦电磁理论,利用电矢量和磁矢量来分析光波在两介质表面的反射特性,把平面光波的入射波、反射波和折射波的电矢量分成两个分量:一个平行于入射角,另一个垂直于入射角,对平面光波在电介质表面的反射和折射进行分析,推导了菲涅尔公式,并结合MATLAB研究光波从光疏介质进入光密介质,以及光波从光密介质进入光疏介质时的反射率、透射率、相位等随入射角度的变换关系。同时对光波在不同介质中传播时的特性变化进行仿真研究,根据仿真结果分析了布鲁斯特角、全反射现象及相位变化的特点。有关各量的平行分量与垂直分量依次用指标p和s来表示,s分量、p分量和传播方向三者构成右螺旋关系。     

折射式起偏器的密勒矩阵表示及偏振度分析

为了研究折射式起偏器的密勒矩阵表达式,以矩阵光学中关于斯托克斯矢量和密勒矩阵的有关理论为基础,通过理论运算导出了折射式起偏器的密勒矩阵的一般表达式;探讨了自然光以任意角度入射折射式起偏器的情况下透射光的斯托克斯矢量表示及偏振度所满足的公式;绘制了以布儒斯特角入射时透射光偏振度与介质折射率及介质层数的关系曲线。结果表明,在以布氏角入射折射式起偏器的前提下,增大介质的折射率和介质层数更容易获得较高的偏振度。这一研究结果对多层介质膜器件同样适用,具有一定的现实参考意义。     

Sizing emboli in blood using pulse Doppler ultrasound. II. Effectsof beam refraction

For pt.I see ibid., vol.43, no.6, p.572-80 (1996). A theoretical and numerical study of the acoustic field intensity within a curved flow conduit having (1) diameter similar to the wavelength of the interrogating frequency and (2) speed of sound mismatch with the surrounding medium is presented. The field intensity is shown to vary significantly and in a monotonic fashion across the flow conduit. The resulting insonation of emboli transiting through the Doppler sample volume is explored with a Monte Carlo study of the behavior of the embolus to blood power ratio (EBR). The numerical simulation findings are shown to be in good agreement with previously reported experimental results. A method is explored for estimating embolus diameter when this refraction artifact is present, and shown to yield excellent results when applied to experimental data. Further work toward clinical application of these results is discussed     

Plane-wave characterization of antennas close to a planar interface

The plane-wave scattering matrix is used to characterize antennas that are located just above a planar interface that separates two media. The plane-wave transmitting spectrum for the field radiated downward into the lower medium is expressed directly in terms of the current distribution of the transmitting antenna. The transmitting spectrum for a reciprocal antenna determines the plane-wave receiving spectrum for the field that propagates upward in the lower medium. A measurement procedure is discussed for determining the plane-wave transmitting and receiving spectra from measurements with a probe that is located in the lower medium.     

The snell and fresnel relationships for electromagnetic waves with the constant linear polarization

General conditions for the existence of plane electromagnetic waves with a single nonzero electric-field component (TE waves) in an anisotropic medium are established. A transformation that makes it possible to derive similar formulas for TM waves (plane electromagnetic waves with a single nonzero magnetic-field component) from the formulas expressing the properties of TE waves is considered. A general numerical algorithm is developed for calculating the amplitudes (with allowance for phases) of the TE waves formed when an external TE wave propagates through a system of plane-parallel plates consisting of media supporting TE waves. Formulas are obtained for the solution of the particular problem on the transmission of a TE wave through a plane interface between two media supporting TE waves. A series of relationships that can be interpreted as generalizations of the Snell and Fresnel relationships for media of the considered type are derived. Formulas for the transmission, reflection, and refraction coefficients are obtained. The existence conditions for TE (TM) surface waves are derived. A numerical method is proposed for computing the spectra of such surface waves formed on the interface between two media. For isotropic media, analytic expressions for the spectra of surface waves are derived. It is shown that the obtained formulas are similar to the known formulas for surface TM waves in dielectrics but, in addition, make it possible to take into account both the permittivities and permeabilities of the media.     

双光楔可控扫描一维轨迹分析

根据几何光学和光的标量衍射理论,对双光楔的折射特性进行了数学分析.研究发现,以相反旋向相同转速旋转的双光楔对光的折射作用等效于一个折射角随2个光楔转角变化的单光楔.在此基础上,对通过双光楔的光束在像面上的衍射光场分布作了理论分析,得到了在夫琅禾费衍射下,光束经转动双光楔在像平面上的衍射光斑随时间变化的规律,从而为一维扫描的可控操作提供了理论指导.     

含曲面介质结构复杂目标电磁散射计算的射线追踪方法

针对含曲面介质结构的电大复杂目标电磁散射计算问题, 提出一种基于平面元网格模型曲率重构与射线密度归一化概念相结合的快速射线追踪方法.该方法通过曲率重构计算复杂目标表面的主曲率半径, 考虑从光疏介质到光密介质和从光密介质到光疏介质时电磁波照射凹凸曲面所具有的不同扩散或聚焦效应, 并利用射线密度归一化计算射线追踪过程中每一根射线对总散射场的贡献.当射线与介质表面的碰撞点位于焦散处时, 通过引入功率追踪成功克服了传统几何射线管在焦散处的奇异性.仿真结果验证了该方法的正确性和高效性.     

基于F-P腔的干涉/强度调制型光纤温度传感器

介绍了一种基于非本征F P腔的干涉/强度调制型光纤温度传感器。宽谱光源发光二极管(LED)发出的光经过2×2耦合器C1 传给F P传感头,传感头返回光信号再次经过耦合器C1 及C2 后分成两路,一路直接传给光电探测器D1,另一路经过窄带滤光片再传给D2,光信号经光电转换及放大后由计算机采集处理。给出了采用不同谱宽的两路光信号进行自补偿运算和温度测量的理论模型,并简单分析了影响这一温度传感器长期稳定性的原因。实验中利用Levenberg Marquardt非线性拟合得到与理论模型符合很好的温度定标曲线。该传感器在 20~200℃量程内,温度变化最小分辨率达到0 .1℃,长期测量精度达到±0. 2℃。     

Optically variable watermark (OVW) microstructures for transparent substrates

We report on the novel fabrication of optically variable watermarks (OVW) in a transparent substrate. The OVW is incorporated into the substrate via an embossing process. The master embossing die is produced by a combination of electron beam lithography, greytone photolithography, and precision electroplating techniques. The micro-embossing into polypropylene film is performed at 130 °C and 100 kN, a similar pressure to that used in intaglio printing. The optical effect produced by the device corresponds to a switch from one image to another as the device is observed in transmission when held in front of a light source and moved up and down. The image switching mechanism is a result of the refraction of the incident light through the embossed interlaced rows of micro-prisms, with the two different images corresponding to opposite prism slopes. Specific results reported here include an OVW image switch from a “$” to a “50” symbol and a second test image corresponding to an image switch from a portrait to a logo style image. Applications of the OVW technology include anti-counterfeiting protection for polymer banknotes, identity cards with transparent regions and labels attached to brand name products.     

Propagation of EM pulses excited by an electric dipole in aconducting medium

Exact solutions are given for the transient electromagnetic (EM) fields excited by an electric dipole antenna with an impulsive current in a conducting medium. There exists an optimum waveform for the antenna current which can generate an EM pulse with a maximum intensity at a particular distance from the antenna. It is found that the EM fields of an EM pulse excited by an antenna in a conducting medium can be divided into two parts. The first part is an impulse wave which propagates with the speed of light (1/√(μϵ)) and decays exponentially. The second part builds up gradually and propagates slowly, and more importantly this part attenuates as an inverse power of distance which is a much slower rate than an exponential decay     

Linear, or "Small-signal," theory for the Gunn effect

A model wherein the density of free carriers in the conduction band of a semiconductor is dependent on the electric field and decreases at high fields is considered. The growth and phase velocity of an RF wave of small amplitude which propagates through the medium are evaluated. From these properties the threshold electric field and the frequency tuning characteristics vs. electric field for an oscillating sample are calculated. In high-resistivity samples are predicted 1) the threshold field to increase with increasing resistivity, and 2) the oscillating frequency to decrease when the field is increased above threshold. Experimental data which are consistent with both of these predictions are presented.