三维高斯波束跟踪传播损耗预测改进模型

针对传统射线跟踪法需要考虑绕射并涉及接收球处理,从而算法复杂、计算量大等缺点,提出了一种基于三维高斯波束跟踪和二维网格加速的电波传播预测模型。该模型通过Gabor分解法将任意口径场分布展开为高斯型口径分布,直接实现了波场积分的离散化处理;高斯波束场采用复射线场模拟,并借助几何光学法加以复延拓,可处理反射、绕射和折射等复杂问题。相比传统射线跟踪法,本文模型无需考虑接收球处理和绕射,具有数学推导简单以及计算量小等优点。数值仿真结果表明,新模型预测精度与传统射线跟踪法基本相当,但预测效率可提高数十倍。     

光学组合半导体激光器输出光束特性研究

为了评价光学组合半导体激光器的输出光束性能,采用两种方法从理论上分析了光学组合半导体激光器的输出光束的光束传播因子.第1种方法与传统堆栈式半导体激光器的光束质量评价方法类似,通过几何光学得到光束束宽;第2种方法采用管芯光强分布的类高斯模型计算输出光束的二阶矩进而得到光束束宽,最后均得到输出光束的光束传播因子与激光条单元数及激光条包含管芯数的关系.进行了3个激光条组成的光学组合半导体激光器的实验,获得输出功率120W,功率密度209W/cm2,光束平均间距1.1mm,整体光束传播因子M2=197.对比了两种方法及实验结果.结果表明,这两种方法可以用来估算光学组合半导体激光器的输出光束质量.     

基模高斯光束轴向相干叠加柱波场的研究

运用标量光学理论,研究了纳米加工中的基模高斯光束轴向相干叠加光场的三维强度分布特征,导出了高斯驻波场的光强分布表达式。在此基础上通过数值计算方法,分析比较了正确波驻波场与高斯驻波场之间的异同点。     

温度对光伏光折变晶体中高斯光束自偏转的影响

基于扩散效应及暗辐射强度对温度的依赖关系,研究了温度对有偏压光伏光折变晶体中高斯光束自偏转特性的影响.将高斯光束作为入射类孤子波,采用数值方法求解含扩散项的波传播方程.结果表明,当晶体的温度在一定的范围内变化时,光束中心沿一抛物线轨迹偏转,并且光束中心偏转距离随温度的增加而增加,在一个特定温度处达到最大值,之后随温度的增加而减小.当温度发生足够大的变化时,高斯光束将不稳定甚至崩溃.通过调节晶体的温度能改变高斯光束的自偏转.     

温度对基于双光束耦合耗散晶体中高斯光束演化特性的影响

为了得到温度对高斯光束在耗散晶体中的孤子波演化的影响结果,基于温度对暗辐射强度和扩散场的影响,提出了双光束耦合强度和相位耦合系数的新模型,采用数值模拟的方法研究了高斯光束在双光束耦合光折变耗散系统中不同温度下的演化特性.结果表明,晶体的温度与高斯光束的稳定件密切相关.对于给定的耗散系统,若该系统能支持某一特定的全息屏蔽明孤子,可以找到与之匹配的高斯光束.在300～350 K温度范围内,高斯光束能在晶体中传播足够远的距离;而当晶体温度变化足够大时,高斯光束强度随传播距离增加而减小,入射的高斯光束不能以稳定的全息孤子态传播.     

宽角抛物方程的格林函数及其应用

基于分部傅立叶变换法,建立了宽角抛物方程在二维无界空间的格林函数.提出了计算宽角抛物方程初始场的格林函数法.在此基础上,用宽角抛物方程法计算了高斯电流源辐射在海平面上传播衰减情况,并与几何光学双射线模型以及格林函数本身的计算结果作了比较,验证了此格林函数的正确性,从而为建立求解抛物方程的新方法——辅助位函数法奠定了基础.     

利用复射线法分析腔体的散射场

利用基于几何光学和高斯波束法的复射线法分析了相对任意开口圆柱腔的后向散射场。该圆柱腔内部包含较复杂的中心锥，叶片等结构，计算了两种较复杂进气道模型的雷达截面，所得结果均与弹跳射线法结果进行了比较，二者吻合很好，该方法受计算机内存影响小，对电大腔体，复射线法精确高效。     

光在抛物型梯度折射率介质中传播特性的波动光学分析

本文从标量波动方程出发,在抛物线方程近似下得到高斯光束在抛物型梯度折射率介质中传播模的解析解;研究了高斯光束光斑半径、波面曲率半径以及强度分布的规律;并讨论了准几何光学近似条件。     

非球面伽利略扩束系统实现激光束空间整形

为实现高功率TEA CO2激光束空间整形,需要设计一套非球面伽利略型整形扩束系统,将束腰8mm的基模高斯光束整形扩束到直径25mm.根据基于几何光学原理导出的系统理论模型,采用龙贝格数值积分算法得到40组描述非球面的数据,非线性最小二乘法拟合数据,获得两个非球面矢高解析式.为验证所设计镜头的光束空间整形效果,用光学软件ZEMAX对束腰8mm的基模高斯光束进行了整形仿真,光线光路追迹结果与理论设计吻合.仿真整形结果表明,可以获得直径25mm的平顶光束,出射波面面形峰谷值误差25个波长,输出基本为平行光.这为进一步工程应用作了必要准备.     

利用伽利略扩束系统实现激光束空间整形

为实现高功率激光束空间整形,需要设计一套伽利略型整形扩束系统,根据P.W.Rhodes等人基于几何光学原理导出的系统理论模型,采用龙贝格数值积分算法得到40组描述非球面的数据,非线性最小二乘法拟合数据,获得两个非球面矢高解析式,并用光学软件对束腰8mm的入射基模高斯光束进行了空间整形仿真模拟,结果表明可以获得直径25mm的平顶光束输出。利用该镜头对不同束腰高斯光束进行整形仿真,结果表明当束腰大于8mm时,光束整形效果尚可;但当束腰小于8mm时,整形效果随束腰减小而变差。     

A hybrid (parabolic equation)-(Gaussian beam) algorithm for wavepropagation through large inhomogeneous regions

The wide-angle split-step parabolic equation (PE) algorithm is used to model electromagnetic wave propagation over general inhomogeneous terrain up to a height h. The PE-computed fields at h are then projected onto a complete Gabor basis from which we effect Gaussian beam propagation at altitudes greater than h. The Gaussian beams can be propagated through general inhomogeneous media, devoid of failures at caustics and shadow boundaries (as befalls ray tracing). The accuracy of the Gaussian beam algorithm is demonstrated via two realistic examples: (1) low-frequency (HF) ionospheric propagation with application to over-the-horizon radar and (2) near-grazing high-frequency propagation for communication or surveillance applications. In the context of these examples, we discuss relevant numerical issues associated with the hybrid algorithm from which general advantages and disadvantages are addressed     

Gaussian Fitting Parameters of the ESA PLANCK HFI Beams

We present Gaussian fitting parameters of simulated beams of the High Frequency Instrument (HFI) of the ESA PLANCK mission. This space probe is designed for measuring the anisotropy of temperature and polarization of the Cosmic Microwave Background (CMB). The six HFI spectral bands cover the frequency range 0.1 - 1 THz with 52 bolometers. Their beams are computed by multi-mode physical optics propagation of the source field from the apertures of the horns simulated by the scattering matrix approach. Computed power patterns are fitted by the elliptical Gaussian beams minimizing the peak difference between the two power distributions within the beam. This approximation is generally considered as acceptable from the scientific viewpoint, although we show that induced errors are far from negligible.     

A Comparison of Propagation Between Apertured Bessel and Gaussian beams

A true Bessel beam is a family of diffraction-free beams. Thus the most interesting and attractive characteristic of such beam is non-diffracting propagation. In optics, the comparisons of maximum propagation distance had been done between Bessel and Gaussian beams by Durnin and Sprangle, respectively. However, the results obtained by them are conflict due to the difference between their criteria. Because Bessel beams have many potential applications in millimeter wave bands, therefore, it is necessary and significant that the comparison is carried out at these bands. A new contrast criterion at millimeter wavelengths is proposed in our paper. Under this criterion, the numerical results are presented and a new conclusion is drawn.     

Quasi-optical techniques

The basic theory of quasi-optical Gaussian beam propagation and beam transformation by simple optical elements is summarized, and coupling to and between Gaussian beams is briefly discussed. Guidelines for Gaussian optics system design are reviewed, the most important being beam truncation and matching. Passive components in the terahertz frequency range based on quasi-optical propagation, including polarization processors, filters, diplexers, and ferrite devices, are examined. Some active quasi-optical devices, including multielement oscillators, frequency multipliers, and phase shifters, are described. Some specific applications of quasi-optical systems are briefly described     

高斯光束通过非线性梯度折射率透镜的传输特性

基于无像差自聚焦理论,使用ABCD定律导出了高斯光束在非线性梯度折射率介质中的解析传输公式。采用矩阵光学方法研究了高斯光束通过非线性梯度折射率透镜的传输特性。结果表明,介质的非线性性和非均匀性、激光功率及入射光束参数影响其传输特性。     

大气湍流对拉盖尔-高斯光束传播质量的影响

为了从系统的角度研究大气湍流对涡旋光束传播 质量的影响,根据广义惠更斯-菲涅尔积分和Kolmogorov湍流大气原理,利 用傅里叶光学分析方法和光束分步传播法对携带有轨道角动量(OAM)的 拉盖尔-高斯(LG)光束在湍流大气中的传播进行理论分析与数值仿真, 导出角谱形式的衍射模型及其对应的抽样限制条件。利用桶中功率(PIB,power in bucket)计算方法,分析湍流强度对不同OAM值的LG光束质量的 影响;引入高斯光束和点光源,对比评估典型光束的抗湍流能力。数值仿真结果表明:受大 气湍流影响,随着LG光束在湍流大气 中传播距离增加,光束会聚能力变弱有明显扩散;光束本身特有的环状光强分布及其相应的 相位分布都受到不同程度的破坏,损伤 程度与光束本身携带的OAM数有关;点光源对湍流的影响最为敏 感;高斯光束具有与小OAM值的LG光束相比拟的抗 湍流能力,且比大OAM数的LG光束有更强的抗湍流能力。     

Electromagnetic THz Radiation Modeling by DPSM

THz or T-ray imaging and spectroscopy are becoming increasingly popular nondestructive evaluation techniques for damage detection and characterization of materials. In order to understand the interaction between the T-ray electromagnetic waves and dielectric media a reliable model of electromagnetic wave propagation through dielectric materials must be developed. A recently developed semi-analytical method called the distributed point source method (DPSM) is extended to model electromagnetic wave propagation in THz range. Since T-ray signals generated by emitters or sources are close to Gaussian beams, the DPSM modeling is carried out for Gaussian beams generated by finite sized emitters. The DPSM generated results are compared with the analytical and experimental results. T-ray propagation in layered structures in absence of any anomaly and the interaction between the Gaussian beam and the spherical scatterer are also investigated.     

Gaussian beam launching for 3D physical modeling of propagation channels

Gaussian beam launching is proposed as an alternative to ray-based techniques for propagation channel modeling, and it is implemented and validated in the context of indoor propagation. A rigorous Gabor frame decomposition of source fields is used to represent a radiated field as a superposition of shifted and rotated Gaussian beams, conveniently expressed as complex rays. Beam tracking through multiple reflections and transmissions is straightforward, and fields can then be evaluated by summation of closed form expressions. The parameters of a given transformed Gaussian beam have to be calculated only once for all observation points, leading to easy implementation, and computationally efficient algorithms. Simulations of amplitude–delay profiles, mean excess delay, and RMS delay spread are performed in an indoor environment at 60 GHz and compared to measured and published results.     

涡旋光束的自适应光学波前校正技术

涡旋光束是一种具有螺旋波前的光束，其特点是其光强分布为环形，携带有与螺旋波前结构相关的轨道角动量。由于涡旋光束的角量子数可取任意整数，同时不同角量子数的光束之间相互正交，因此可提高光通信系统的信道容量。但涡旋光束在自由空间传输时会受到大气湍流的影响，进而产生波前畸变，因此需要采用自适应波前校正技术对畸变后的光束进行校正。文中对现有的涡旋光束波前校正技术进行了概述，重点介绍了笔者课题组提出的应用GS相位恢复算法和高斯光束探针相结合对涡旋光束波前畸变校正的技术及应用SPGD算法和泽尼克多项式对涡旋光束波前畸变校正的研究工作。     

Ray-density normalization for ray-optical wave propagation modelingin arbitrarily shaped tunnels

This work is concerned with the calculation of natural electromagnetic (EM) wave propagation and the determination of the propagation channel characteristics in highway or railway tunnels in the ultrahigh-frequency (UHF) range and above (>300 MHz). A novel ray-tracing technique based on geometrical optics (GO) is presented. Contrary to classical ray tracing, where the one ray representing a locally plane wave front is searched, the new method requires multiple representatives of each physical EM wave at a time. The contribution of each ray to the total field at the receiver is determined by the proposed ray-density normalization (RBN). This technique has the further advantage of overcoming one of the major disadvantages of GO, the failure at caustics. In contrast to existing techniques, the new approach does not use ray tubes or adaptive reception spheres. Consequently, it does not suffer their restrictions to planar geometries. Therefore, it allows one to predict the propagation of high-frequency EM waves in confined spaces with curved boundaries, like tunnels, with an adequate precision. The approach is verified theoretically with canonical examples and by various measurements at 120 GHz in scaled tunnel models