Simultaneous CW operation of shared angular dispersive element WDMlasers

We show that when more than two channels operate continuous-wave (CW) simultaneously in shared dispersive element wavelength-division-multiplexing (WDM) lasers, χ⁽³⁾ in the passive shared waveguide can cause spontaneous fluctuations in frequency and power. We propose the simple cure of making the shared waveguide extremely short. We obtain a value for the nonlinear-index coefficient of our InGaAsP waveguides of +0.9×10^-12 cm ²/W     

Analytical angular correlation function in mode-stirred reverberation chamber

A new closed-form expression for the autocorrelation function of the electric field as a function of the rotation angle of the stirrer is proposed. It allows the quantification of the influence of the stirrer radius on the stirring efficiency. A comparison between theoretical and experimental results is also given.     

Approximations to complementary error function by method of least squares

A few simple approximations are derived for erfc (x) by method of least squares (MLS). The detailed error profiles are presented. It is shown how these approximations are useful in extracting the inverse of erfc(x). Finally a simple approximation with overall relative root mean square error (RRMS) of less than one percent is presented.     

SDH网元的原子功能组成

现代传输网节点将由功能更强的SDH网元取代传统的ADM或DXC，文章介绍了SDH网元的主要功能及设备的原子功能构成。     

功能梯度薄膜的脉冲激光沉积研究进展

介绍了功能梯度薄膜材料的特点和应用 ;比较了功能梯度薄膜常用制备方法 ;概括了功能梯度薄膜制备中的掺杂技术并给出了脉冲激光沉积功能梯度薄膜的模型 ;论述了脉冲激光沉积技术在制备功能梯度薄膜材料方面的应用与最新进展     

Top-emitting organic light-emitting diodes integrated with thermally evaporated scattering film for reducing angular dependence of emission spectra

A scattering film is obtained by thermally evaporating tetraphenylethene (TPE) onto the substrate. The TPE molecules self-crystallize themselves as microsheet on reaching the substrate. The resultant TPE films exhibit strong light scattering effect because of the random distribution of the crystallized sheets. The scattering films, being able to be deposited by thermal evaporation, can thus integrate with top-emitting organic light-emitting diodes (OLEDs) directly. As a result, the top-emitting OLEDs exhibit reduced angular dependence of emission spectra; for example, the color coordinates is only slightly shifted from (0.2891, 0.6001) to (0.2735, 0.5617) when the viewing angle increases from 0° to 80°.     

Intramodal part of the transfer function for an optical fiber

Intramodal contributions in measurements of optical-fiber bandwidth are investigated theoretically and experimentally in the quasimonochromatic case. A relation is established between the intramodal transfer function and a possibly non-Gaussian source spectrum, which may also vary with modulation frequency. By considering the latter variation in particular, we are able to predict the intramodal length dependence and show how it may deviate from that of a conventional approach.     

Cu掺杂量对Zn-Cu共掺TiO2薄膜光学带隙的影响

采用溶胶-凝胶旋涂法,分别以钛酸四丁酯(Ti(O C₄H₉)₄)为钛源、硝酸锌(Zn(NO₃)₂·6H₂O)为锌源、硝酸铜(Cu(NO₃)₂·3H₂O)为铜源制备了不同掺杂量的Zn、Cu共掺TiO₂薄膜。分别采用X射线衍射仪(XRD )、薄膜测厚仪、紫外-可见分光光度计(UV-Vis)对所制备的样品进行表征。结果表明 :与本征TiO₂和2.0 at%Zn²⁺-TiO₂相比,Cu²⁺的掺 杂减小了样品的晶面间距及晶粒尺寸、增加了样品的半高宽及比表面积,进而提高了薄膜的 光催化活性能。随着Cu²⁺掺杂量的增加,样品沿(101)晶面择优取向先增强后减弱 ,薄膜的吸光度呈现先升高后降低的趋势,TiO₂的 带隙值由3.424 eV减小到3.325 eV。与本征TiO₂和2.0 at%Zn²⁺-TiO₂相比 ,2.0at%Zn²⁺－1.0 at%Cu²⁺-Ti O₂的样品结晶度最好,(101)晶面择优取向最佳,薄膜表面的缺陷较少、较为均匀平整 且吸光度更好,光学带隙值最小为3.325 eV。     

Estimation of the spatial correlation function and angular spectrum by using a multiantenna system

A closed formula based on representing the angular spectrum in the Fourier basis was obtained for computing the correlation coefficients of signal fadings in elements of the multiantenna system. The method of estimating the expansion coefficients of the angular spectrum with subsequent evaluation of the spatial correlation function was proposed.     

Comparison of the linear least squares and nonlinear least squares spheres

Two important, to scientists and engineers, sphere fitting procedures, namely the linear least squares (LLS) and the non-linear least squares (NLLS) methods and their general random-error analysis are described. The first-order random errors of the center coordinates and the radius of the fitted sphere using the above mentioned procedures are derived in detail under the assumption that the variance-covariance matrix exists for the random error vector. With the additional trivariate normal error distribution assumption, the Maximum Likelihood (ML) estimators and their standard deviations are also derived. The effectiveness of these procedures are studied through computer stimulation.     

Finding the approximate angular probability density function of wave arrival by using a directional antenna

The first-order approximate angular probability density function of wave arrival can be obtained by plotting the mean-square value of signal level versus the pointing angle of a mobile radio directional antenna during an entire test run. The accuracy of this first-order approximation is dependent on the beamwidth of the antenna. As the beamwidth of the antenna becomes narrower, the approximate density function becomes more accurate. There are also higher order approximations for obtaining a more accurate angular probability density function without narrowing the directional antenna beamwidth. These higher order approximations are related to the moments of the signal strength received by the same directional antenna used in obtaining the first-order approximation. All of these are theoretical predictions. An experimental verification using a first-order approximate angular probability density function in finding theoretical level crossing rates of a mobile radio signal is given. The theoretical level crossing rates are in fairly good agreement with the experimental ones as long as the angular probability density function is not far from a uniform distribution.     

粗糙基底上涂层的极化双向反射分布函数

为了有效检测光学基底和镀膜后的光学元件质量,根据微面元电磁散射理论建立了一阶极化光散射模型,推导求解出其极化双向反射分布函数,获得了极化双向反射分布函数PP项与散射角和方位角的三维关系。数值模拟分析了入射角、基底粗糙度及不同涂层厚度对极化双向反射分布函数的影响。数值结果表明:极化双向反射分布函数与入射角、相关长度、均方根高度及涂层厚度均成反比。P极化入射产生的P极化双向反射分布函数强烈依赖于入射角、散射角和方位角。布鲁斯特角的位置随着入射角的增加逐渐向散射方位角小的方向移动。     

Experiment-based estimation of point spread function in electron-beam lithography: Forward-scattering part

The point spread function (PSF) plays an important role in electron beam (e-beam) lithography, e.g., estimation of resist profile, proximity effect correction, etc. One of the essential tasks is how to estimate the PSF with accuracy and efficiency. Conventional approaches include estimation of PSF’s based on certain functions or through a Monte Carlo simulation. A new approach to estimating PSF’s based on experimental data is proposed to provide an alternative to the conventional approaches. It utilizes the relationship between a PSF and a line spread function (LSF), and that between a LSF and the remaining resist profile. Since effects of all phenomena and processes involved in the exposure step are reflected in experimental results, the proposed approach has a good potential to generate realistic PSF’s for any substrates and e-beam tools as long as experiments can be carried out. In this paper, the implementation of the new approach for estimation of the forward scattering part of PSF is described along with the simulation and experiment results.     

PCB用层间绝缘膜和高功能玻纤布

概述了PCB使用的层间绝缘膜和高功能玻璃布。     

Partial-fraction expansion: part 3 [rational function numerical analysis]

This series of articles has been discussing means of obtaining partial-fraction expansions (PFEs) of rational functions numerically. In parts 1 and 2 we presented the background on Chin and Steiglitz' algorithm (IEEE Trans. Circuits Syst., pp.42-45, 1977) for determining the PFE coefficients associated with the proper rational function H(s), which may contain multiple poles. We now continue with Chin and Steiglitz' algorithm, laying out the particulars of forming the PFE coefficients. The analysis leads to a very straightforward algorithm that requires only a few lines of code to implement.     

Model selection through a statistical analysis of the globalminimum of a weighted nonlinear least squares cost function

This paper presents a model selection algorithm for the identification of parametric models that are linear in the measurements. It is based on the mean and variance expressions of the global minimum of a weighted nonlinear least squares cost function. The method requires the knowledge of the noise covariance matrix but does not assume that the true model belongs to the model set. Unlike the traditional order estimation methods available in literature, the presented technique allows to detect undermodeling. The theory is illustrated by simulations on signal modeling and system identification problems and by one real measurement example     

The receive voltage transmission function of a phased array antenna element

A general method has been developed for determining the voltage response of a phased array element to an incoming electric field. The incident field may arrive from any scan angle, and mutual coupling effects are accounted for in terms of the array element active reflection coefficient. The method defines a receive voltage transmission functionbar{T}(theta, phi, f)as a term whose product with the incident electric fieldE_{i}(theta, phi, f) results in the array element voltage response. The derivation ofbar{T}(theta, phi, f)is obtained by treating each phased array antenna element as a receiving aperture, having an active impedance related to the mutual coupling in the array. The element effective length is formulated using an array element receive equivalent circuit, and the transmission functionbar{T}(theta, phi, f)is obtained using this effective length formulation. The usefulness of the transmission function for studying the response of a phased array element to particular radar signal waveforms is suggested, and an experimental evaluation ofbar{T}(theta phi, f)is described using mutual coupling measurements on a 37-element crossed dipole test array.     

Studies of the angular correlation function of scattering by randomrough surfaces with and without a buried object

The discrimination of the scattered wave from an object buried in shallow ground from that of the rough surface is a difficult task with present ground penetrating radar (GPR) systems. Recently, a new approach for this classical problem has been proposed and its effectiveness has been verified. This new method is based on the angular correlation function (ACF) of the scattered wave observed at two or more different incident and scattered angle combinations. It has been shown that the angular memory signatures of rough surfaces are substantially different from those of typical man-made targets and by choosing the appropriate incident and scattered angles, the surface scattering can be minimized whereas the scattering from the target is almost unchanged. The authors present detailed numerical studies of the ACF of the scattered wave from rough surfaces with and without a buried object. To obtain the ACF, the three averaging methods: realization, frequency and angular averaging, are tested numerically. It is shown that a single random rough surface of moderate extent can exhibit memory effect by using frequency averaging. Frequency averaging with a wide bandwidth is also effective for suppressing fluctuation in ACF and is most useful for practical applications. Numerical simulations indicate that even when the ratio of scattered intensities with and without the buried object is close to unity, the corresponding ratio of ACF magnitude can be more than 10 dB. Thus, using the ACF is superior to using the radar cross section (RCS) in the detection of buried objects