Analysis of Optical Waveguide Consisting of a Square-Law Lenslike Medium and its Analogies to Circular TE/sub 01/ waveguide

Propagation behavior of light beams along sinusoidal and serpentine bends as well as circular bends and linearly tapered bends of optical waveguides consisting of a square-law Ienslike medium is investigated in detail, both theoretically and numerically, on the basis of the approximate wave theory. A new design method of the circular bend for removing the effects of the bend is proposed and numerical results are presented. The divergence phenomena of the beam trajectory in both the sinusoidal and serpentine bends of the optical waveguide are discussed in comparison with mode-conversion phenomena occurring in the circular TE/sub 01/ waveguide with the same bends. Several design conditions to eliminate undulations of the beam trajectory and/or the spot size which would occur at a circnlar bend of the optical waveguide are also studied, and interesting analogies to the design conditions proposed so far to prevent mode-conversion losses at a circular bend of the TE/sub 01/ waveguide are shown.     

Ka波段TE01模椭圆弯波导的设计

根据椭圆波导中电磁波的传播理论与耦合波理论,基于CST仿真软件,采用了有限积分法设计出了高功率、宽带宽、高效率的TE01模900过模椭圆弯波导。CST设计仿真表明在中心频率在30．5GHz处的传输效率为98．8％。传榆效率在98％以上的带宽大于2GHz。     

Circular Bends in Dielectric Frame Beam Waveguides (Short Papers)

An investigation is described on circular bends in beam waveguides constituted by dielectric frames. A uniform bending of the guide axis is obtained by tilting each frame by a small angle; however, due to the phase correction performed by the dielectric frame, the losses introduced by the bending can be made lower than those of an analogously bent iris waveguide. A numerical analysis is performed on the basis of the analogy between beam waveguides and open resonators which permits the assessment, in a number of cases, of the maximum permissible amount of tilting and the corresponding optimum frame dimensions in view of acceptable losses. The losses due to mode conversion are also evaluated when considering the connection between a straight and a curved section of the waveguide.     

Azimuthally periodic electrostatically focused electron ribbon beams

Methods of enhancing transmission of ribbon-shaped electron beams undergoing circular motion in azimuthally periodic cylindrical electrostatic lenses are treated. Lens forces add to the naturally occurring curvature focusing to achieve this increase in beam transmission. Three basic configurations, differing only in the method of applying lens voltages, are treated: symmetrical focusing, deflection focusing, and asymmetric focusing (including inner and outer electrode segmentation). Expressions for beam perveance and rippling are derived from the paraxial-ray equation for thin electron ribbons advancing along a two-dimensional curved optical axis. The stiffness of azimuthally periodic electrostatically focused electron ribbons (i.e., the immunity of the beam to transverse disturbing forces) also receives attention. Mathematical extensions of the analysis to ribbon beams undergoing helical motion are discussed, and numerical results applicable to selected values of lens parameters are presented. Experimental results for an azimuthally periodic lens, constructed to test the analysis, are discussed in light of the theory developed.     

Study of WDM polymer planar curved waveguide couplers

A wavelength division multiplexer based on curved polymer planar waveguide is proposed. According to the coupled modetheory and the waveguide structure, the performance of the curved waveguide coupler (CWC) is analyzed. The results showthat CWC can accommodate wider multiplexing bandwidth than parallel straight waveguide coupler (SWC) due to thecompensation effect of the effective coupling length. The two variables, curvature radius and minimum spacing, increasethe design flexibility of the waveguide device. A 4-channel wavelength division multiplexing (WDM) system based onCWC is designed. The deviation of the center wavelength, due to the errors of curvature radius and minimum spacingduring fabrication process, is investigated. The smaller the curvature radius and the minimum spacing are, the larger thecentral wavelength deviation caused by the error of the curvature radius and the minimum spacing is, which provides someuseful theoretical basis for the design and the fabrication of polymer waveguide devices.     

A rigorous and efficient method of moments solution for curvedwaveguide bends

An accurate and computationally efficient method of moments solution together with a mode-matching technique for the analysis of curved bends in a general parallel-plate waveguide is presented. In order to exemplify the techniques, the method is applied to study the transmission characteristics of single and cascaded curved E- and H-plane bends in a rectangular waveguide. It is shown that the effect of the orientation of cascaded bends on the transmission properties can be significant, and examples to demonstrate this effect are included. Results of the convergence with increasing number of expansion functions illustrate that only a few terms need to be considered for accurate evaluation of the transmission characteristics of structures with single and multiple bends. Comparison with measurements for single and cascaded curved H-plane bends in a WR-90 waveguide show good agreement with the predicted result     

自由曲面透镜白光LED光束整形技术

为了获得高均匀性、对称性及一些特殊形状强度分布的白光发光二极管(LED)光束以满足某些特定的需求,基于白光LED光源为朗伯光源的特性,运用自由曲面透镜的方法对LED光束进行了光束整形,分别采用单一自由曲面透镜以及全内反射(TIR)透镜与微透镜阵列组合两种不同的整形结构,进行了加工工艺和原理理论分析,并通过了实验验证.结...     

非线性梯度折射率棒透镜高斯光束的色差

本文首次研究了高斯光束通过非线性梯度拆射率棒透镜的色差特性。导出了色差公式。结果表明，色差特性强烈依赖入射高斯光束的正规化光束功率和束腰。这在线性情形以及几何光学近似中没有相似的性质。     

A Light Beam Waveguide Using Hyperbolic-Type Gas Lenses

This paper is concerned with the optimum design of a light beam waveguide constructed with a proposed lens-like medium, namely, a hyperbolic-type gas lens which has a hyperbolic temperature distribution on its transverse cross section. In such a medium, the temperature distribution is ideally quadratic in the transverse directions, and so the mode conversion due to the higher order variation of the dielectric constant can be minimized. Moreover, this guide has the following merits; the design procedure is simple, the mode matching at the input part is easy, and it is possible to construct a waveguide using ordinary air as the lens medium. And this consideration can be easily extended to the guide with curved configuration. It was shown that the experimental convergency of this gas lens was in agreement with the theoretical one.     

色散透镜系统中宽带厄米-高斯光束的焦移

为了了解带宽对厄米-高斯光束的聚焦特性和焦移的影响，采用衍射积分推导了TEM₁₁模和TEM₂₂模厄米-高斯光束通过受光阑限制色散透镜的传输公式，并利用数值计算对聚焦光强分布进行了研究，分析了带宽对两种模式焦移的影响。结果表明，TEM₁₁模和TEM₂₂模厄米-高斯光束的焦移量都会随带宽增大而增大，但两者的大小依赖相对带宽；当相对带宽小于0.25时，TEM₂₂模焦移量大于TEM₁₁模焦移量，然而相对带宽大于0.25时，后者会稍大于前者；带宽变化使TEM₂₂模轴上光强主极大和次极大发生消长，从而引起轴上光强极大位置发生跃变。该研究结果对宽带厄米-高斯光束的应用具有一定的参考价值。     

Gaussian beam transformation with cylindrical lenses

We develop formulas for Gaussian beam transformation with fixed total distance between beamwaists, and consider the use of cylindrical lenses or mirrors to produce beams which are not symmetric about the axis of propagation. For antenna feeds, it is necessary that the beam waists for both planes perpendicular to the axis of propagation be coincident. This requirement is analyzed, and appropriate transformation formulas obtained. The far-field patterns of a scalar feed born cylindrical lens combination operating at a frequency of 94 GHz have been measured and found to be in quite good agreement with the elliptical patterns predicted by the transformation formulas.     

Generation of millimeter wave Gaussian beams and their propagation in a dielectric waveguide

Linearly polarized fundamental mode Gaussian beams were generated and coupled to a hollow circular oversized dielectric waveguide by placing the waist of the beam at the guide entrance. The transmission properties of the waveguide were characterized as a function of frequency for a variety of coupling conditions. These conditions included changes in the input beam waist radius, angle of incidence, and displacement perpendicular and parallel to the guide axis. It has been found that: 1.) power transmission is maximized when the waist of the input beam is centered at the guide input, injected normally, and has a radius of 0.43 times the waveguide radius, 2.) power transmission decreases rapidly with increasing angle of incidence and the rate of that loss increases with frequency, 3.) the waveguide preserves the linear polarization of the input beam, 4.) power transmission in the fundamental waveguide mode is not greatly affected by moderate displacements in the input beam position, and 5.) upon exit from the waveguide the launched EH₁₁ mode propagates as a fundamental mode Gaussian beam in the quasi-far field. The results compare favorably to the transmission theory of Belland and Crenn and approximately to the near and far field mode pattern theory of Degnan.     

Photonic-Crystal Heterostructure Waveguides

Photonic crystals (PC) are periodic dielectric structures that, if suitably designed, prohibit light propagation within a frequency band even though the constituent materials may be transparent in this range. One of the remarkable applications of such artificial photonic materials has been to provide guiding of light. Ultimately, to guide light in directions other than straight lines, PC waveguide (PCW) bends are needed, and thus are expected to be essential building blocks of photonic integrated circuits. While bending light through large angles is possible with conventional waveguides, the corner radii of such bends cannot typically be reduced to the electromagnetic wavelength, which hinders the realization of extremely compact devices. And though sharp two-dimensional (2-D) PCW bends have been proposed, the transmission is typically low and/or narrow band. Here we focus on PCWs obtained by introducing line defects in otherwise period 2-D PCs with the aims of enhancing the typical poor and low-bandwidth transmission through tight bends. We show how PCW bends occurring at heterojunctions between different PCs may enable unprecedented flexibility in meeting these aims. The deformation introduced to the usual PC lattice lifted off the angle constraint and resulted in the power transmission greater than 90% over in the 95-nm bandwidth     

非对称共面波导弯曲结构传输损耗的研究

针对共面波导弯曲结构传输损耗较大的问题,对直角、45毅斜角和圆角非对称共面波导弯曲结构进行 了分析。结合使用频域和时域的有限差分方法计算了3 种弯曲结构的模式转换性能。在理论分析的基础上,提出了 一种测试装置,克服了矢量网络分析仪无法直接测量模式间能量转换的问题。理论分析和测试结果表明:在较高频 段3 种ACPW 弯曲结构的传输损耗均小于相应结构的CPW 弯曲结构的传输损耗,并且3 种结构的ACPW 弯曲结构 中,圆角弯曲结构的传输损耗最小。     

用轴棱锥实现可改变的局域空心光束

理论和实验研究了利用轴棱锥-透镜系统产生的局域空心光束，分析了局域空心光束的演变过程，由简单的几何光学结构和近轴光线追迹的方法进行模拟。研究结果表明，局域空心光束的暗中空区域不仅与聚焦透镜的焦距有关，而且与光阑半径以及聚焦透镜到轴棱锥间的距离有关；对于给定的轴棱锥，局域空心光束的横向暗斑尺寸与焦距成正比，并且其纵向暗斑尺寸与聚焦透镜到轴棱锥间的距离以及光阑半径成反比。这些结果表明，改变聚焦透镜的焦距和聚焦透镜到轴棱锥间的距离以及光阑半径，可有效地改变局域空心光束的暗中空区域。     

不同空间分布光束通过聚焦光学系统传输特性的比较

基于柯林斯公式和ABCD传输矩阵理论，在相同激光功率和初始束宽下，研究了不同空间分布光束通过聚焦光学系统的传输特性，结果表明，入口处不同阶次的超高斯光束在距离光学系统焦点一半的位置（z=f/2)，光强分布的差别很大，轴上光强随着阶次的增加，先增加，然后减小至固定值；聚焦光学系统入口处超高斯光束的阶次越大，即光强分布越均匀，在光学系统的焦点位置（z=f)，光轴上激光强度越大，直至趋于固定值，但光强分布的差别不大。     

光阑偏心对数字散斑干涉空间频谱的影响研究

光阑在空间域内对成像光束起到限制的作用,在光学系统中的应用十分广泛。在数字散斑干涉测量系统中,通常采用光阑对物光空间频率进行限制,便于针对待测目标完成后续的信号解调。理想情况下,光阑的中心位置应与光轴重合、且表面与光轴垂直,但在实际过程中,经常由于调整精度问题使得光阑中心偏离光轴,或者由于结构设计问题采用偏心光阑。本文以空间光束的傅里叶变换特性为基础,研究了光阑中心偏离光轴位置对物光和数字散斑干涉空间频谱的影响,并进行了实验验证,理论与实验结果一致。本文对数字散斑干涉系统关键参数设计,具有理论指导意义。     

全固化激光器中的耦合系统—透镜导管的简化设计

用几何光学的方法计算了竭地管的慢轴和快轴方法的光束分布，结果表明，用于固体激光器泵浦的高功率激光二极管阵列的连续分布的激光束通过透镜导后可以获得平滑面均匀的光场分布，基于这种分布，我们设计了两种结构的透镜导管，用激光二极管阵列实验测得未镀抗反膜的透镜导管的耦合效率高达８４％。     

Integrated magnetooptic Bragg cell modulator in yttrium irongarnet-gadolinium gallium garnet taper waveguide and applications

An integrated magnetooptic (MO) device which consists of an ion-milled collimation-focusing lens pair and a guided-wave MO Bragg cell modulator in a yttrium iron garnet-gadolinium gallium garnet (YIG-GGG) taper waveguide substrate with dimensions of 6.0×16.0 mm ² has been realized for the first time. Performance characteristics of the waveguide lenses including the focal spot size, sidelobe level and throughput, and that of the integrated MO Bragg cell modulator using the magnetostatic forward volume wave (MSFVW) at X-band carrier frequency including the bandwidth, diffraction efficiency, dynamic range, and frequency resolution have been measured at the optical wavelength of 1.303 μm. Scanning of the focused diffracted light beam by varying the carrier frequency of the MSFVW and RF spectral analysis by simultaneous application of multiple microwave frequencies have been demonstrated