TM610高次模圆柱谐振腔的模拟研究

 根据电磁场理论设计了S波段TM610高次模圆柱谐振腔。运用HFSS，ISFELD3D， CST-MS及MAFIA软件计算了该谐振腔中TM₆₁₀及其附近模式的电磁场分布、谐振频率及模式间隔。计算表明：TM₆₁₀模式的电磁场集中在漂移管头周围的区域，谐振腔中心处无电磁场分布。根据TM₆₁₀模式的特点，采取了在腔中心放置铁氧体微波吸收材料的方法来抑制杂模。HFSS模拟表明：腔内吸收材料可消除TM₅₁₀模式外大部分杂模的影响。采用了在主谐振腔外加耦合吸收腔的方法来抑制TM₅₁₀模式，该吸收腔基模TM₀₁₀的谐振频率等于TM₅₁₀的谐振频率。模拟表明：TM₅₁₀模式的大部分能量可以被吸收腔内的铁氧体材料衰减掉，Q值从15 604下降到571。     

异步传输技术(ATM)综述

概述了异步传输模式(ATM)的产生、概念，并分析了ATM交换原理，在此基础上简单的介绍了ATM的应用。中心议题是异步传输的研究方向，因而又介绍了ATM的走向、ATM与IP的相互结合技术及MPLS、IPOA、ATM MPEG2等等ATM的最新研究进展。     

A Stabilized, Rationally Mode-Locked 10GHz Erbium Fiber Laser

A rationally mode-locked 10 GHz erbium fiber laser stabilized by a simple technique for extended time operation is described. The laser generates stable ~ 5 ps pulses that can be used in communications experiments. Back-to-back bit error rate (BER) measurements confirmed error-free operation for 6-8 hours, giving an error floor below 10 -14 . A receiver sensitivity of -19.7 dBm was achieved for BER of 10 -9 .     

Matrix-Based Analytical Model of Critical Coupling Length of Titanium In-Diffused Integrated-Optic Directional Coupler on Lithium Niobate Substrate

The critical coupling length Lc is the most important design parameter of an integrated-optic directional coupler, which is the basic building block of a variety of optical integrated circuits. The existing methods of estimating Lc of a Ti in-diffused waveguide directional coupler on LiNbO3 substrate are based on the beam propaga tion method (BPM), which requires huge computing time. A considerably simpler and computationally faster analytical method involving only multiplication of 2 x 2 matrices with no iterations is described in this article. A staircase type step-index profile is generated from the one-dimensional effective index profile in the lateral direction by partitioning the latter into a large number of thin sections of different refractive indices. The overall transfer matrix of the step-index layered structure so obtained may be computed by the progressive multiplication of individual transfer matrices (2 x 2) relating the field components in adjacent layers. Hence the wave amplitude in any layer may be computed as a function of the input wave amplitude for different angles of incidence. This method has been successfully employed to compute the propagation constants for symmetric and asymmetric guided modes in the coupled region of the directional coupler and hence compute the coupling length. The values of Lc computed for a variety of devices agree closely with the published experimental results reported by several research groups. The computer program implementing the model runs reasonably fast in an ordinary PC and is versatile enough to consider arbitrary waveguide dimensions. Ti film thickness, and diffusion parameters for any wavelength of input light and for both transverse electric and transverse magnetic polarizations.     

Hysteresis in Mode Competition in High Power 170?GHz Gyrotron for ITER

Hysteresis in mode competition in high power 170 GHz gyrotrons for ITER is studied. Specific examples of hysteresis with respect to variation of magnetic field, current, electron beam radius and beam voltage are given.     

A Mode Converter with Multi-waveguide Output from the TE01 Circular Waveguide Mode to the TE10 Rectangular Mode for Millimeter Wave Gyro-device Applications

A mode converter with multi-waveguide output for millimeter wave gyro-device applications is proposed in this article, which is used to convert the TE₀₁ circular waveguide mode into the TE₁₀ rectangular waveguide mode. Computer simulations with Ansoft HFSS code show that the energy transmission coefficient of larger than 95.96% may be reached in the frequency range from 34.094 GHz to 35.8 GHz (a bandwidth of 1.706 GHz) at a VSWR of lower than 1.5 for the input operating mode.     

螺旋波导TEm1-TE11模式转换器的设计

 基于耦合波理论，对螺旋波导(蛇形线微扰)94 GHz、6周期TE₀₁-TE₁₁模式转换器和10.24 GHz、4周期TE­31-TE11模式转换器进行了设计和数值分析。通过解耦合波方程得出模式转换器中各模式成分的比例关系，并对转换器的参数做进一步修正，然后利用电磁仿真软件进行模拟。两种转换器在中心频率处的模拟转换效率均达到98%以上，95%以上带宽超过2 GHz，仿真结果与理论分析吻合得较好。     

Study of bending loss and mode field diameter in depressed inner core triple-clad single-mode optical fibers

In this paper, the bending loss and the mode field diameter (MFD) of the R-type depressed inner core triple clad single-mode optical fibers are investigated. The effects of the optical and geometrical parameters on the bending loss and the MFD are examined in these fibers. The simulation results indicate that with increasing of the core radius (a), which is desired from manufacturing point of view, the bending loss and MFD coefficients are decreased. Consequently, the large core radius can be used to optimize the bending loss in the foregoing fibers. In the meantime, simulation outcomes show that the Δ and Q have considerable impact on the bending loss in the RI and RII fibers, respectively. The MFD and bending loss is decreased with increasing of Δ, but the case is inversed for Q. Based on the presented simulations, it is found out that the bending loss strongly depends on the distribution profile of the electric field in the cladding region for a given MFD. In other words, the field amplitude and damping rate in the cladding region determine the fiber bending loss.     

Laser-ultrasonic generation of Lamb waves in the reaction force range

The Laser-ultrasonic generation of Lamb waves in an elastic plate is investigated theoretically and experimentally for a laser source whose intensity is high enough to create reaction forces (normal tractions) on the illuminated surface of the specimen. The analytical solutions for transient waves are derived using the integral transform method first by considering an arbitrary source shape and time excitation function, and then specifically for circular and line source shapes. The simulation study allows us not only to predict the behavior of individual wave modes but also to construct the overall responses; thus it helps us better understand the wave excitation mechanisms. The dispersive and multi-modal nature of laser-generated Lamb waves is presented by showing the spatiotemporal Fourier transform of displacements obtained by the simulation study. The transform, displayed in the frequency-wave number domain, enunciates the characteristics of the propagating individual Lamb wave modes. The simulation results are then compared with the 2-D Fourier transform of a set of experimental data obtained by scanning an aluminum plate specimen.     

Mode Matching Analysis of Propagation Characteristics for Dielectric Ridge Guide with Triangular and Trapezoidal Profiles*

Leaky characteristics of dielectric ridge guide with triangular and trapezoidal cross section are analyzed by a method that combines the mode matching procedure with the staircase approximation and multimode microwave network theory. Our emphasis in this paper is on the parametric effects of cross section profile on leakage and propagation properties of the ridge guide. Some numeral results with their explanations are given for practical reference.*Supported by the National Natural Science Foundation of China (No. 60171019) and (No. 60371010)