DESIGN OF A NEW TYPE OF ELECTRO-OPTIC POLYMER WAVEGUIDE MODULATOR WITH ULTRAHIGH BANDWIDTH

In this article, rectangle, trapezoidal and T type microstrip lines embedded into up cladding of the waveguide are designed. By the analysis of the finite element method (FEM), this embedded microstrip line has perfect velocity matching between the electric signal and lightwave carrier and at the same time, conductor loss of the trapezoidal and T type microstrip lines also reduce. Thus the modulator’s bandwidth increases greatly. Calculations show that, comparing with one of non-embedded rectangle microstrip line which is the most familiar configuration of polymer modulator, the optical 3-dB bandwidths of embedded trapezoidal and T type microstrip increase 264% and 339% respectively under the condition of impedance matching.     

Improved dispersion tolerance of a Mach-Zehnder modulator by optimizing the modulator voltage and time delay

We present a method for improving the dispersion tolerance of a dual-arm Mach-Zehnder modulator by independently optimizing the applied voltage on each arm and the time delay between them. We found a significant improvement in the dispersion tolerance. Using the negative chirp effect and the time delay, it was possible to extend the transmission distance of 10 Gbit/s optical nonreturn-to-zero signals without any additional electrical or optical components.     

Research on time division multiplexing modulation approach applied in three-axis digital closed-loop fiber optic gyroscope

In this paper, the structure and the fundamental principle of a three-axis Time Division Multiplexing (TDM) fiber optic gyroscope system are presented. The design of TDM fiber-optic gyroscope system is mathematically analyzed. An effective modulation approach is developed, the bias stability compared with that of a normal fiber-optic gyroscope is theoretically given and the system dynamic character is presented. In order to test the correctness of the approach, the dynamic simplified model is introduced and the simulation is conducted. The experimental result matches the simulation, indicating that the TDM modulation approach is feasible.     

抛物型初边值问题的有限元与边界积分耦合的离散化及其误差分析

1．引言边界元方法是近二十几年来迅速发展起来的一类新的偏微分方程的数值方法．它的独特之处是将空间的维数降低一维,从而倍受工程技术人员的青睐,并在工程技术与计算数学领域得到越来越广泛的重视和研究．对椭圆型问题,边界元方法的理论与应用研究已取得丰硕成果;对发展型问题,近年来在理论方面的研究也已取得重要进展［6－11］．但边界元方法难以处理非均质问题,而有限元对各类问题及各种区域具有较好的适应性,将两者结合起来可充分发挥各自的优点．文山提出了一种抛物方程初边值问题的有限元与边界积分的耦合方法,其主要思想是…     

CO和CO2的1.58μm波段可调谐二极管激光吸收光谱的二次谐波检测研究

红外可调谐二极管激光吸收光谱技术作为新的痕量气体监测分析方法,在大气化学研究和污染气体监测中得到了应用.文章介绍利用可调谐二极管激光吸收光谱学(TDLAS)技术对常压下的CO和CO2的近红外波段光谱静态测量研究和洛伦兹线型下的CO2二次谐波光谱与调制度的关系.     

ILUS: An incomplete LU preconditioner in sparse skyline format

Incomplete LU factorizations are among the most effective preconditioners for solving general large, sparse linear systems arising from practical engineering problems. This paper shows how an ILU factorization may be easily computed in sparse skyline storage format, as opposed to traditional row-by-row schemes. This organization of the factorization has many advantages, including its amenability when the original matrix is in skyline format, the ability to dynamically monitor the stability of the factorization and the fact that factorizations may be produced with symmetric structure. Numerical results are presented for Galerkin finite element matrices arising from the standard square lid-driven cavity problem. © 1997 John Wiley & Sons, Ltd.     

Absence of nonradiative recombination centers in modulation-doped quantum wells revealed by two-wavelength excited photoluminescence

Absence of nonradiative recombination (NRR) centers inside GaAs wells and at GaAs/Al_0.2Ga_0.8As hetero-interfaces in a Si modulation-doped GaAs/Al_0.2Ga_0.8As multiple quantum well (MQW) structure became clear for the first time by an improved two-wavelength excited photoluminescence (PL). The NRR parameters of modulation and uniform-doped MQWs were determined self-consistently by combining the analysis of the PL intensity change due to the below-gap excitation with the internal quantum efficiency and the recombination lifetime. These results showed the superiority of modulation-doping scheme over that of uniform-doping for light emitting devices.     

用于核磁共振的直接数字合成频率源

直接数字频率源的使用可以简化核磁共振谱仪的设计,降低核磁共振谱仪设计的成本. 文中介绍一种采用Analog Device公司的AD7008芯片设计的基于PC机的直接数字合成频率源,它可实现频率和相位的高速切换,频率分辨率为0.01Hz,相位分辨率为0.09°,最后给出核磁共振实验结果.     

基于调制度分析的加权最小二乘相位展开方法(英文)

介绍了光学相位展开的加权最小二乘法,采用调制度分析方法确定其权值.模拟和实际的相位展开例子都说明了其有效性.     

可用于建筑结构检测的分布式光纤形变片

本文在光时域反射计(OTDR)和光纤形变片的基础上,提出了一种分布式光纤传感器-分布式光纤形变片.该检测方法属于OTDR的损耗调制法,即通过测量粘贴于光纤形变片上的光纤弯曲损耗来获取测量点的应变量或位移量.作者分别在微位移架和悬臂梁进行了位移检测和应变检测,结果表明该分布式光纤形变片提供了一种可检测应变量与位移量的检测方法.值得注意的是,该分布式光纤形变片的传感网络采用时分复用的总线拓扑,能在一根光纤上同时检测多个检测点的变化.