An inverse algorithm to calculate the refractive index profiles ofperiodically segmented waveguides from the measured near-fieldintensities

In this paper, the refractive index profiles of the periodically segmented waveguides (PSWs), which are fabricated in soda-lime glasses by the K⁺-Na⁺ ion-exchanged technique, are reconstructed from the measured transmitted near-field (NF) intensity combined with an inverse method. Through the proposed inverse method, the model Δn'=ηΔn, which characterizes the behavior of the PSWs, is also verified. In the numerical process, a finite-difference method is used to discretize the governing equation, and then a linear inverse model is constructed to identify the unknown refractive index profiles. The approach used is to rearrange the matrix form of the governing differential equation and estimate the unknown index profiles of the waveguides. Then, the linear least-squares error method is adopted to find the solutions. The results show that the accuracy of index determination can be accessed even when the measured noise is considered. In contrast to the traditional approach, the advantages of this method are that no prior information is needed on the functional form of the unknown index profiles, no initial guesses are required, no iterations in the calculating process are necessary, no intensity smoothing is required in advance, and the inverse problem can be solved in a linear domain. Furthermore, the existence and uniqueness of the solutions can easily be identified     

电波传播研究70年

对流层电波传播特性是影响无线电系统性能的重要因素,是电波传播研究的主要领域. 本文系统综述了近60年来中国电波传播研究所在无线电气象、地面无线电业务电波传播、空间无线电业务电波传播、电波传播效应对无线电系统影响评估等对流层电波传播不同方向开展的研究和取得的研究进展. 在此基础上,最后给出了对对流层电波传播研究的展望.     

一种改进的主动式近场毫米波成像算法

近年来在机场等公共场合屡屡发生恐怖袭击事件,一种安全有效的毫米波安检成像技术应运而生,但是该技术采用的传统波数域算法存在从加载后向散射数据到重建图像耗时较大,无法完全满足快速安检成像的要求。故提出一种改进的主动式近场毫米波成像算法,该算法对近场毫米波成像首先进行邻近聚焦再结合一致聚焦函数来代替传统的匹配滤波函数和插值部分,所提算法可提高成像效率,使其更具实用性。通过大量的仿真实验和实测实验证实了所提算法的高分辨率和图像保真度。     

棱镜型表面等离子体波传感器测量液体折射率的研究

对表面等离子体波共振现象产生的原理和激发条件进行了阐述。从电磁场理论和粒子振动的角度 ,分析了棱镜型表面等离子体波传感器产生共振的角度和待测液体折射率、介电常数的关系。通过自行设计的一套棱镜型表面离子体波传感器测试系统 ,测定了从 0 %～ 70 %的不同浓度甘油水溶液折射率与共振角度的关系 ,得到的实验结果具有较好的重复性并和理论分析相吻合。由此可以得到一种基于SPR现象的液体折射率测量方法     

A simplified procedure to calculate the power gain definitions ofFETs

A graphical method to easily derive the power gain definitions of field-effect transistors (FETs) is proposed in this paper. This method is applicable to MESFETs and high electron-mobility transistors described by the typical π model. A new set of simple expressions of the S-parameters, functions of the circuit elements of the FET complete model, is derived. These expressions are presented in graphic form to quickly compute the modules of the FET S-parameters and then the power gains. The accuracy of this approach has been proven by comparison with simulations of the FET complete model     

An improved sliding-load calibration procedure using asemiparametric circle-fitting procedure

Circle-fitting problems often occur in microwave engineering when dealing with variable delays, e.g., during calibration using a sliding load. This paper proposes an efficient semiparametric circle-fitting procedure, which takes into account the phase relationships over the frequencies. It produces more accurate results than the standard sliding-load calibration, requires only three positions on the sliding load for the whole frequency band, and is more robust to the settings of the positions of the sliding load. The proposed method also has the ability to detect whether or not the sliding load is defective or out of its specifications. This can be done by using only three positions on the sliding load. Optimal-position settings are then proposed. The performance of the proposed method is illustrated on sliding-load measurements up to 50 GHz, demonstrating the ability of detecting modeling errors and showing that the accuracy of the proposed method using three positions is comparable to the standard method with six positions     

An electrooptic intensity modulator with improved linearity

A highly linear electrooptic modulator has been designed, fabricated, and evaluated. The design of this modulator consists of only a simple modification to the directional coupler. Two-tone testing has demonstrated that, for an optical modulation depth of 30% per channel, the third-order intermodulation distortion is more than 30 dB lower than that of the conventional directional coupler or Mach-Zehnder modulators. This improvement was not observed to be accompanied by any increase in second harmonic distortion. Also included are results of two-tone computer simulations which predict the improvement in linearity of this device for a range of modulation depths.<>     

An approximate expression for the effective refractive index in symmetric DH lasers

Using a variational method and an approximate equation for the confinement factor, a simple expression for the effective refractive index of the TE0modes in a symmetric double heterostructure (DH) laser is obtained. The relative error is smaller than 1.2 percent. Its applications are discussed.     

液晶折射率与电压关系的研究

液晶的一个重要特性是：液晶的折射率会随所加于液晶上的电压的变化而变化。本文正是对这一规律进行了研究实验,并得出了实验结果。     

A stable procedure to calculate the transient scattering byconducting surfaces of arbitrary shape

A solution procedure to obtain the transient scattering by arbitrarily shaped conducting objects directly in the time-domain using the marching-on-in-time method is presented. The late-time oscillations are eliminated by a simple stabilization procedure which involves a negligible amount of extra computation. Numerical results for surface current density and far-scattered fields are given for various structures and compared with other methods     

中红外区基质折射率对碳化硅颗粒散射强度的影响

基于Mie散射理论,对不同基质中的碳化硅材料散射强度进行数值计算与理论分析,得到了中红外波段反常色散区和正常色散区中散射强度的分布特征,揭示了入射波长、基质折射率与散射强度分布的内在规律。研究结果为该材料在中红外区的开发和应用提供了理论依据。     

二次彩虹法高折射率玻璃微珠的折射率测量研究

通过对高折射率玻璃微珠在激光照明下形成的二次彩虹的实验研究,提出了一种激光照明下高折射率玻璃微珠二次彩虹条纹图的获取装置。以艾里的虹理论为基础,提出了一种由二次彩虹条纹图确定最小偏向角的方法,实现了高折射率玻璃微珠折射率的测量。实验证明,该方法的测量精度为0．4％,测量结果得到了V棱镜测试方法的证实。     

An improved method to correlate measured circuit speed withsimulation [CMOS gate arrays]

The relationship between the measured propagation delay of elementary circuits and the values obtained by circuit SPICE modeling was studied. Systematic and random variations of L_eff of the actual circuit from the modeled values L_eff, which were extracted from separate test devices, were identified as a major source of error. The error was significantly reduced by an improved method to obtain the values of L_eff within the logic circuits, thus permitting accurate circuit performance modeling and the required technology optimization     

Single mode fused couplers insensitive to external refractive index

Wavelength multiplexers produced using the fused taper technique have been fabricated to be insensitive to variations in the external refractive index, allowing them to be potted in silicone for environmental protection. The technique exploits two opposing dependencies by fabrication at a particular coupler cross-section     

An improved procedure for the design of periodic-permanent-magnet assemblies for traveling-wave tubes

A detailed analysis of the magnetic-field configurations in periodic focusing structures and new knowledge related to the design of permanent magnets which are to be used in the presence of fields of other magnets have led to the development of a new procedure for the design of periodic-permanent-magnet (ppm) focusing structures for traveling-wave tubes. With this new procedure, the ppm focusing structures can be designed very quickly, and the parameters of the structures produced will approximate the design predictions very closely. This paper describes the derivation and use of a set of design curves which have been used in the design of ppm focusing structures by the RCA Microwave Tube Operations Department for six years. It has been found that the peak axial fields of the structures produced on the basis of these design data are within five percent of the predicted values. Frequently, agreement between actual and predicted values within one percent has been observed. The design procedure requires only a few minutes time, and is applicable to any magnet material whose demagnetization curve is known. A section on the design of the soft-magnetic pole pieces ("shims") is also included.     

To the analyticity of the effective refractive index

The possibility to describe the plane-wave propagation in a periodic layered medium in terms of effective parameters is considered. It is shown that, for a finite system, the effective refractive index can be determined with the help of the amplitude transmission coefficient. The analyticity of the effective refractive index as a function of frequency is studied. It is shown that the effective refractive index is an analytic function of frequency, and the Kramers–Kronig relations, which connect the real and imaginary parts, are found.     

Stable and accelerated procedure to calculate transient scattering using electric field integral equation

A stable and accelerated procedure for the electric field integral equation (EFIE) is developed. The procedure employs an implicit method in conjunction with a time averaging scheme to solve EFIE with the second-order time derivatives. Two examples are provided to demonstrate the superior stability and efficiency of the proposed procedure.     

Fused couplers: condition for insensitivity to external refractive index

The condition necessary for fused tapered couplers to be insensitive to change in the external refractive index is derived. This condition depends critically on the shape of the coupler cross-section, e.g. it cannot occur in either the rectangular or in the elliptical cross-section.     

基于光纤位移测量的透明液体折射率测量方法

本文提出了一种基于光纤位移测量的液体折射率测量方法。首先,采用激光干涉法设计了 液体折射率测量的光学系统,并基于激光散斑消除理论,设计了针孔滤波器合理消除散斑, 提高了系统的抗干扰能力;其次,对测量系统中的位移测量方法进行分析和研究,提出了 一种光纤式位移测量方法,并设计应用反射式光纤位移传感器,取消传统的条纹计数,实 现了位移的高精度测量,其测量分辨力可达微米级;再次,采用机械位移驱动系统,驱动 光学系统元件移动来实现光程差的自动变化,其驱动分辨力可达纳米级;最后,搭建液体 折射率总体测量演示验证系统,以纯水、溶液为实验对象,其所需待测样品的容量少 于0.001ml。实验结果表明:纯水折射率 的测量精度可达1.5×10－3, 溶液折射率测量精度可达2.1×10－3,表明该测量方法可实现液体折射率的非接触、高精度 、智能测量。     

An improved method to estimate intrinsic small signal parameters of a GaAs MESFET from measured dc characteristics

This investigation offers a technique to predict the ac behavior of mm wavelength GaAs metal semiconductor field effect transistors by using dc characteristics. To predict the intrinsic equivalent circuit parameters of the device from dc data, the measured dc characteristics are first simulated by employing a nonlinear dc model. The effects of biasing on the device ac parameters are evaluated for its low-noise applications. An improvement greater than 10% in predicting the ac response of the device is observed. The concept of depletion layer modification caused by the transverse electric field inside the channel is introduced for accurate Miller's capacitor modeling. It is assumed that with increased device biasing there are more unbalanced positive charges in the gate depletion toward the drain-side of the Schottky barrier. The electric field lines originated by these uncompensated charges induce an opposite charge density in the gate electrode. This modifies the gate biasing and hence the Schottky barrier depletion. As a result, the values of intrinsic ac device parameters change. It is observed that an accurate dc modeling is key to predicting an accurate ac small signal equivalent circuit of a device.