Transient analysis of microstrip lines with ferrite substrate by extended FD-TD method

In this paper, the wide band transient signal propagation characteristics along microstrip lines with ferrite substrate are presented. In the analysis how the frequency dependent media such as ferrite may be genearally fomulated by FD-TD method is described. the distortions of transient signal in Gaussian shape propagating along uniform or step junction microstrip are simulated by the extended FD-TD method. Results show the distinctive influence of applied DC magnetic field and magnetizaton on the dispersion of transient signal.     

反向交叉相位调制对NOLM开关特性影响

提出了NOLM中反向信号脉冲与控制脉冲耦合方程,研究了正、反向信号脉冲在传输过程中共同作用的非线性相移,分析了高斯脉冲和NRZ码在此情况下的开关特性,得到了有反向交叉相位调制时的第一最佳解复用长度、开关窗口和输出信号波形等对实际应用有价值的数据和波形.     

Transient response of microstrip step discontinuities on anisotropic substrate

In this paper, we present the numerical simulation of transient response of short pulse propagating through a microstrip step junction on anisotropic substrate having a tilted optical axis. In the simulation, the FD-TD method is extended to treat the cases having tilted optical axis expressed by a permittivity tensor with off-diagonal elements. The results show that the dispersion of transient signal caused by microstrip step discontinuities is quite significant and the dependence of transient characteristics of microstrip lines on the tilted angle of optical axis for anisotropic substrate can not be neglected.     

真空中线性啁啾时空高斯脉冲传输特性的分析

利用稳态相位点的方法研究了线性啁啾时空高斯脉冲传输过程中的相位特性，并在二阶近似的情况下讨论了其传输过程中的时空特性，两种方法从不同侧面得出了相同的结论，即：时空高斯脉冲在传输的过程中，在无穷远处交退化为球面波，或者在旁轴近似的情况下退化为平面波。     

高斯脉冲在半导体光放大器中传输的解析表征

采用解析方法,在考虑材料损耗和色散的情况下,详细研究了无啁啾高斯脉冲和啁啾高斯脉冲在半导体光放大器中传输的物理过程,分析了强度增益、脉冲宽度和频率啁啾与线宽增强因子、色散系数、小信号增益特征参数及初始啁啾之间的关系。结果表明:当输入变换极限的高斯脉冲时,色散会引起增益压缩,脉冲展宽和频率啁啾;同样情况下,线宽增强因子越大,脉宽加宽越明显,输出脉冲啁啾越大,且随着线宽增强因子的增大,输出脉冲啁啾极大值向特征参数值较小的一边移动。当输入啁啾高斯脉冲时,初始脉冲啁啾越大,增益压缩越明显,啁啾系数为正时,脉冲单纯展宽,输出啁啾随特征参数的增大而逐渐减小,啁啾系数为负时,初始啁啾与群速度色散导致的啁啾相互竞争,致使脉冲先被压缩后被展宽;脉冲最窄处对应的特征参数随线宽增强因子的增大而先增大后减小,输出啁啾随特征参数的增大而经历振荡后趋于平稳。     

基于BLT方程的微带线电磁耦合终端响应

为定量研究电磁波与微带线的耦合终端响应问题,提出一种基于BLT方程的电磁波与微带线耦合分析方法,相比传统方法计算效率高、占用内存少。将PCB板上微带线等效为有耗传输线模型,对辐照平面波进行矢量分析并求解等效激励源,运用BLT方程研究不同入射方式、脉冲波形对微带线终端的影响,并对入射波与终端响应进行了时域、频域分析。研究表明:当入射波频率与微带线长度满足一定关系式时对微带线的耦合最强,耦合电压峰值达2.4 mV;电场平行微带线入射比垂直PCB入射时的终端电压峰值大一倍;且同幅同脉宽的矩形脉冲较高斯脉冲和三角脉冲对微带线的耦合峰值电压大;不同波形的脉冲通过调节脉宽都可对微带线耦合终端电压达到mV量级。     

Spectrum Transformation of Gaussian Pulse in Waveguide by FDTD and Its Effect on Analysis of Discontinuity Problem

An interesting, surprising phenomenon, spectrum transformation of Gaussian pulse propagating in waveguide, is revealed in this paper. It is found that the spectrum power of zero frequency of Gaussian pulse is changed into the spectrum power of cut-off frequency of H₁₀ mode in rectangular waveguide when FDTD simulation is implemented in the absence of nonlinear material in waveguide. The cause of the spectrum transformation is explained based on the mode field structure at cut-off. Its effect on the correctness of analyzing waveguide discontinuity problem is presented too.     

Generation of an Electrostatic Pulse and a Second Harmonic EM Pulse in a Magnetoplasma

This paper presents an investigation of the generation of an electrostatic pulse by an EM pulse (Gaussian in space and time), propagating as a right/left-handed circularly polarized mode along the static magnetic field in a collisionless magnetoplasma. The generated electrostatic pulse, again interacting with an incident EM pulse, generates a second harmonic EM pulse. The effect of self-focusing of the incident EM pulse is seen to be significant on the generated pulses.     

Generalized Stokes parameters of stochastic spatially and spectrally partially coherent electromagnetic pulsed beams

The analytical expressions for the generalized (two-point) Stokes parameters of stochastic electromagnetic Gaussian Schell-model pulsed (GSMP) beams propagating in free space are obtained. The changes in the spectral Stokes parameters in free space propagation are studied. The dependence of on-axis and transverse spectral Stokes parameters of stochastic electromagnetic GSMP beams on the pulse parameters including pulse duration and temporal coherence length is stressed and illustrated numerically. The results are interpreted physically.     

Small-area ultrashort pulse propagation through a three-level medium

Propagation of an ultrashort, small-area (circularly polarized) pulse through a gas medium of three-level atoms near one-photon resonance is studied. The expression for the propagating pulse shape is obtained within the rotating wave and dipole approximations. Results are compared, both analytically and numerically, with those for two-level model. Sinusoidal and Gaussian shapes of input pulses are compared, and a high sensitivity of modulation of the light pulse for envelope to its input shape is revealed.     

高斯光脉冲在非线性增益介质中的孤子特性

本文从理论上分析了高斯光脉冲在非线性增益介质中的传播特性,从而解释高斯光脉冲的压缩及展宽和形成光孤子的机理。用计算机模拟了不同参数的高斯光脉冲在非线性增益介质中的传播过程,并获得了脉宽沿传播方向变化的定量关系。结果表明,以不同能量向增益介质中注入高斯脉冲,有可能产生各阶光孤子,但由于增益的存在,光孤子的传输距离受到限制。     

Soliton formation from a gaussian pulse in an optical fiber

Propagation of a frequency-modulated Gaussian pulse along an optical fiber with a gradient refractive index is studied. It is shown that, after propagating a certain distance, the pulse undergoes compression. If, at the point of maximum compression, the pulse intensity is exactly equal to the threshold intensity, then either a bright or dark vortex soliton can form.     

Mutual influence of the spectral components of perturbations on the modulation instability frequency interval in a cubic nonlinear medium

The influence of the shape of a Gaussian pulse propagating in a cubic nonlinear medium on the development of its modulation instability is analyzed, taking into account the time dispersion of the nonlinear response as well. Analytical dependences of the frequency interval of the perturbation development on the dispersion of the nonlinear response, the pulse duration, and the number of simultaneously acting perturbations, which affect each other due to the inhomogeneous pulse shape, are obtained. It is shown that, with increasing dispersion of nonlinear response, the frequency interval of the instability development initially narrows and then expands. Qualitative agreement between the analytical dependences and the results of computer simulation is demonstrated. The frequency interval of the modulation instability development in a medium without the nonlinear response dispersion that was previously determined by different authors under the assumption of “long” pulses is found to coincide with that obtained in this study for the Gaussian pulse under the assumption of the simultaneous action of a large number of perturbations.     

The Propagation of Transient Signals Along the Microstrip Using Wavelet Transformations

In this paper, we study the propagation property of the transient signals traveling along the microstrip using the method of the wavelet transform. This method has the advantages of improving the computation speed and localizing the waveform at any time and at any point along the transmission line to zoom in compared with the conventional Fourier transform. We give the dispersion of the Gaussian signal and the rectangle pulse signals on the microstrip. The results can be a reference in the study of the propagation of the ultra-high-speed and ultra-wide-band transient signals and in the design of MIC and MMIC.     

Development of the Microstrip Circulator with a Magnetized Ferrite Sphere in Millimeter Wave Band

In this paper, a novel microstrip circulator with a magnetized ferrite sphere is proposed for various millimeter wave communications. A three-dimensional Finite-Difference Time-Domain (FDTD) approach for the analysis of this ferrite sphere based microstrip circulator is first presented. The electromagnetic fields inside the ferrite junction are calculated using special updating equations derived from the equation of motion of the magnetization vector and Maxwell's curl equations in consistency. Frequency dependent insertion loss, isolation and reflection loss of circulator are calculated over a wide band of frequencies with a single FDTD run. Experimental results at Ka band are presented and compared with theoretical simulations. As a result, a good agreement is found between them.     

建筑物对不同体制电磁脉冲时域响应数值分析

 针对一般建筑物内空间电场强度时域变化特点,采用时域有限差分方法,数值模拟单极性高斯脉冲、双极性微分高斯脉冲以及窄带调制方波脉冲平面波在建筑物内传播、反射及透射过程;并对比分析不同脉冲参数对空间场强最大值及分布的影响。在一定脉冲宽度的微分高斯脉冲激励下,建筑物空间内最大场强变化范围值较高,为3．０~5.5 dB,其空间场强增强分布区域较大,并随脉宽增加而减小,但脉冲的最小重复频率相对要求最高。相应脉宽的高斯脉冲造成空间最大场强及分布区域范围最小,而脉冲的最小重复频率所需最低。当载频为房间谐振频率的窄带脉冲入射下,空间最大场强变化范围值相对最高,空间场强增强区域总体趋势随脉冲载频频率单调增加。     

Measuring temporal fluctuation on femtosecond scale in a random medium

We report an observation of femtosecond optical fluctuations of transmitted light when a coherent femtosecond pulse propagates through a random medium. They are a result of random interference among scattered waves coming from different trajectories in the time domain. Temporal fluctuations are measured by using cross-correlated frequency optical gating. It is shown that a femtosecond pulse will be broadened and distorted in pulse shape while it is propagating in random medium. The real and imaginary components of transmitted electric field are also distorted severely. The average of the fluctuated transmission pulses yields a smooth profile, probability functions show good agreement with Gaussian distribution.     

基于Fournier Forand体积散射函数的水中激光脉冲后向散射特性分析模型

基于Fournier Forand体积散射函数,建立了一种水中激光脉冲后向散射仿真模型.运用该模型可用Monte Carlo方法模拟光子在水中的传播过程,并得到光波后向散射的冲击响应.将初始激光脉冲与冲击响应进行卷积并求其傅里叶谱,即可得到激光脉冲后向散射信号的时域和频域特征.利用该模型分析了入射为高斯型激光脉冲时,水中散射体的尺度分布、散射体与纯水的相对折射率以及水体衰减系数对激光脉冲后向散射特性的影响.结果表明：随着小尺度散射体相对数量的增多、散射体与纯水相对折射率的增加、水体衰减系数的增大,激光脉冲后向散射信号能量增强,宽度增加,低频分量显著增大.     

Slow light with persistent spectral hole burning in waveguides

We model numerically the reshaping of a weak probe pulse propagating in an absorptive, optically dense, persistent spectral hole burning medium under conditions of slow group velocity. Saturated holes are burned in waveguide geometry by illumination in the transverse direction with low absorption, whereas the probing is carried out in longitudinal wave guiding directions with high absorption. We show that by choosing optimum hole spectrum, the Gaussian probe pulse may be delayed by several times its original duration, while overall pulse shape distortion is less than 1% and average energy loss is less than 10%.     

Propagation of ultrafast pulses in the anomalous-dispersion regime of silicon-on-insulator strip nanowaveguides

The dynamic evolution of ultrafast high-intensity pulses with a 100 fs half-width at 1/e intensity point based on the silicon-on-insulator (SOI) strip nanowaveguides is considered and investigated numerically under the condition of anomalous group-velocity dispersion (GVD) regime. For ultrafast high-intensity pulses propagating in millimeter-long SOI nanowaveguides, the interplay between the dispersion and nonlinear effects such as the two-photon absorption, free-carrier absorption, free-carrier dispersion, and self-phase modulation has to be taken into account, which results in the significant optical wave breaking phenomenon that occurs near the pulse leading edge for an unchirped Gaussian pulse in the anomalous GVD regime. However, when the input Gaussian pulse with linear up-chirp is introduced, the position of the optical wave breaking shifts from the leading pulse edge to its trailing edge along the several millimeters-long SOI nanowaveguides.