Electromagnetic Resonances of Free Dielectric Spheres

A systematic study is made of electromagnetic resonances of a spherical, free, and isotropic sample supposed to be without dielectric loss. The characteristic equation which is both complex and transcendant has been resolved with a computer. The results for the first modes (frequency and Q factor for /spl epsi/ varying between 1 and 100) are presented. The Q factor that is calculated represents the comparison between the energy stored by the resonance system and energy radiated per cycle; this is the theoretical maximum Q in the case of nonlossy materials. The different modes are classed in TE/sub nmr/ and TM/sub nmr/ modes which comprise exterior and interior modes. It is shown that for n >or= r the energy is concentrated in all directions near the surface; these are known as surface modes. This systematic study is confirmed by experiments in which numerous modes have been observed and identified.     

超声物料输送的微摩擦驱动力实验研究

提出一种沿长度方向突变的变截面直梁压电振子结构,该振子能保证输送工作台面上各质点振幅均匀一致.由于振子具有结构对称性,可在空间上实现两个互相垂直的同阶弯曲模态(近似同频),这两个模态的叠加使工作面上各质点做可更改运动参数的椭圆运动.应用悬臂梁结构研制了一个毫牛最级的微力测试装置,完成输送振子微小摩擦驱动力的测试.对微摩擦驱动力的主要影响因素进行了实验分析.实验结果表明,工作面质点椭圆运动轨迹的长轴在水平面上比在铅垂面上时更有利于物料的超声振动输送.振子振幅增大时,振子对试件的摩擦驱动力也相应增大;当振子两个方向振动的速度相位差从0°～90°增大时,摩擦驱动力呈增大趋势.     

The Transmission of TE/sub 01/ Wave in Helix Waveguides

Relations are investigated between the transmission characteristics of a helix waveguide and its surface impedance in regions where any simple approximate formulas are not available because of the magnitude of the surface impedance. The numericaf calculations show that, for any given value of the surface impedance and the angular mode index, there exist an infinite number of different modes which are distinguishable from each other by different values of the radial propagation content. Selecting a mode with minimum attenuation for each given surface impedance, we can draw the equiattenuation lines, connecting these points of equal attenuation on the complex surface impedance plane. At some point on the complex surface impedance plane, a maximum value of the minimum attenuation is found. For the TM/sub 0/ mode supported by a helix waveguide 50 mm in diameter, used at a frequency of 50 kmc, this minimax value of the attenuation constant is about 8 neper per meter, and the corresponding value of the surface impedance is about 57.6-j28.8 ohms. The attenuation constants of all the TM/sub 0/ modes corresponding to this optimum value of the surface impedance cannot be smaller than this minimax value. The same kind of calculations are also performed for the two lowest hybrid modes. Physical structures giving the best value of the surface impedance are also suggested.     

TE Mode Excitation on Dielectric Loaded Parallel Plane and Trough Waveguides

A theoretical and experimental study of the launching of TE surface wave modes on dielectric loaded parallel plane and trough waveguides has been performed. The source is a linear transverse current filament perpendicular to and extending across the space between the parallel side walls. Families of curves are presented, which show the bidirectional Iaunchlng efficiencies for the dominant TE modes of these two transmission lines as a function of dielectric constant, dielectric slab thickness, and current filament location. Measured bidirectional efficiencies are compared to the theoretically predicted values. Measured unidirectional launching efficiencies as high as 97 per cent were obtained for the case where a short circuit is located on one side of the current filament.     

Designing air-core photonic-bandgap fibers free of surface modes

It is known that the coupling of core modes to surface modes in air-core photonic-bandgap fiber (PBF) can give rise to large propagation losses. Using computer simulations, we analyze the relationship between the air-core geometry and the presence or absence of the surface modes in air-core PBFs with a triangular hole pattern. We identify ranges of core radii for which the fiber supports no surface modes over the entire wavelength range of the bandgap, i.e., only core modes are present. In particular, for a hole radius /spl rho/=0.47/spl Lambda/, where /spl Lambda/ is the hole spacing, the core supports a single mode and no surface modes for core radii between 0.8/spl Lambda/ and 1.1/spl Lambda/. The absence of surface modes suggests that fibers within this range of configurations should exhibit a very low propagation loss. We also show that the existence of surface modes can be predicted quite simply from a study of the bulk modes alone, which is much simpler and faster than carrying out a full analysis of the defect modes.     

Dual mode and stacked concentric ring patch antenna arrays

A dual mode concentric ring patch antenna is discussed which is suitable for vehicles operating with mobile satellite communication systems. It is operated at two modes, the TM/sub 21/ and TM/sub 41/ modes, which possess conical radiated beams. Switching between these modes provides omnidirectional azimuth coverage with elevation beam steering.<>     

The control of polarization of laser diodes

The mode-competition phenomena are studied through three experiments. At first, in double-heterostructure laser diodes with thick active layers, TE and TM modes tend to coexist and the mode competition between these two modes is observed from the correlation of the light outputs of these two modes where the increase of light output of one mode tends to decrease the light output of other mode. In a laser diode operating with an external reflector, the increase of light output for the TE mode leads to the decrease of light output for the TM mode. In case the external reflector is set to deviate from the parallel plane to the cleaved surface of the laser diode, the TM-mode component tends to its magnitude, even if the inherent mode of this diode is TE. In the experiment of external light-beam irradiation onto a laser diode, the light intensity of one mode is decreased by an incidence of light beam having another mode from the other laser diode. In this experiment, the significance of a gap distance between the two laser diodes is confirmed clearly, where the two laser diodes interact with each other through the light beam.     

Influence of surface metallisation on magnetoelastic surface wave

The surface-wave coupling which obtains between an elastic bulk shear wave and two magnetostatic modes (one of which is a bulk wave and the other a surface wave) is discussed in the context of a metallised semi-infinite ferrite geometry.     

A mixed spectral-domain approach for dispersion analysis ofsuspended planar transmission lines with pedestals

A mixed spectral-domain analysis is used to derive dispersion characteristics of domain modes in a class of planar transmission lines with a pedestal. Equivalent structures are constructed in which magnetic surface currents are identified as the unknowns at the aperture separating two different regions. Spectral dyadic Green's functions are derived for these structures using the spectral-domain immittance approach. The characteristic equations resulting from the application of the spectral Galerkin method involve mixing two different spectral domains, which exist on the two sides of the pedestal support. The present method allows one to retain the simplicity and numerical efficiency of the conventional spectral-domain immittance approach, which cannot be applied directly to the present structures. Numerical data are provided for the dispersion characteristics of dominant modes in a pedestal-supported stripline and finline     

Mode Chart for E-Plane Circulators (Correspondence)

The mode chart of the E-plane junction circulator is given. The geometry considered consists of two ferrite disks placed against the narrow walls at the plane of symmetry of a symmetrical 3-port E-plane waveguide junction. It is experimentally found to exhibit two modes. One of these modes has a resonant frequency which increases with the spacing between the two ferrite disks. The other mode has a resonant frequency which decreases with the spacing between the disks. Both modes are independent of the disk spacing when the spacing is large. It is also found that the frequency of both modes is proportional to the thickness of the ferrite disks. Finally, circulators obtained by magnetizing each of the two modes circulate in opposite directions. Experimental results on a circulator obtained in this way are included.     

TM-polarized surface-plasma modes on metal-coated dielectriccylinders

TM-polarized surface plasma modes on a thin metallic cylindrical shell embedded in dielectric media are investigated. The dispersion characteristics of both bound modes and leaky waves are obtained for two sets of material parameters, the first corresponding to an optical fiber in which the metallic shell occupies a region between the core and the cladding and the second corresponding to a metal coated cylindrical rod in vacuum     

Experimental Demonstration of Local Quasi-TEM Gap Modes in Single-Hard-Wall Waveguides

This letter reports an experimental study of a gap waveguide which is able to support a plurality of degenerate local quasi-TEM modes. No sidewalls are needed to separate these modes, which is a very useful property in the upper microwave and millimeter-wave bands. The waveguiding media is formed in the gap between a conducting plate and a hard surface. The working principle is described first. Next a practical realization is explained and tested experimentally.      

双空芯光子晶体光纤表面模控制方法

表面模与纤芯基模耦合是使双空芯光子晶体光纤产生无耦合点的根本原因。为进一步探究双空芯光子晶体光纤中表面模的产生及控制机理,采用平面波展开和全矢量有限元法,分析了纤芯周围石英环相对厚度和纤芯的截切半径对表面模和无耦合点的影响。结果表明,纤芯截切半径固定时,随着石英环相对厚度的增大,无耦合点向长波长方向移动;石英环相对厚度固定为1时,纤芯最佳截切半径为0.9～1.0,可以较好地抑制表面模。这为新型双空芯光子晶体光纤的结构设计和现实应用提供了理论依据。     

Orthogonal waves on electron beams

The propagation of slow electrokinetic waves on finite electron beams which fill a conducting tunnel is discussed for modes of axial symmetry. In addition to the familiar space-charge modes, a pair of modes exists which are related to the vortex frequency (omega_{upsilon} = omega_{c} - 2theta_{0}). The finite magnetic field introduces a coupling between these modes. A set of four orthogonal modes can be derived by the use of matrix transformations, thus eliminating the necessity of solving a complicated characteristic equation. For infinitely high magnetic fields, the two additional modes disappear and the four modes reduce to the fast and slow space-charge waves.     

Mode Coupling Between Surface Wave Transmission Lines

The eigenvalue equation describing the mode coupling between two Goubau surface wave lines is derived utilizing the point matching method for solutions of boundary value problems. Excellent agreement is obtained between theoretical and experimental results. A method for obtaining the hybrid wavenumbers of coupled surface wave lines is proposed for a finite set of TE and TM modes.     

无源谐振腔的谐振频率偏移效应

无源谐振腔的有效谐振频率（被测得谐振频率）偏移作为参考的基模谐振频率的效应是谐振腔中存在的高阶横模所引起的。由光探测器光接收孔径的有限性或表面的不均匀性而导致各阶横模的空间不正交性，是引起谐振频率偏移效应的主要原因。对此作了详细研究，并对计算结果进行了讨论，总结出谐振频率偏移与谐振腔各参量的相互关系，从而提出减小这种效应的有效措施。     

金属纳米二聚体结构的局域表面等离子体激元共振特性研究

将金属纳米粒子二聚体结构作为光学谐振腔,采用 时域有限差分(FDTD)法仿真模拟了一种新型局域表面等离子体激光器(SPASER)。 使用洛伦兹复介电常数模型研究二聚体的增益介质特性,探讨了二聚体结构中 两个纳米局域表面等离子体激元共振(LSPR)以及相互作用机制,进一步研究了 LSPR相互作用对SPASER的局域场增强的影响。 模拟结果表明,相比较单纳米颗粒SPASER,LSPR的相互作用使得二聚体SPASER的局域电场显著 增强,增强因子最 大可以相差27倍。本文研究为纳米光学器件尤其是激光器件的设计提 供了依据。LSPR效应的 研究可以用于探索一些光与物质相互作用的极限效 应,从而为有源光子线路、生物传感以及量子信息处理等研究开辟道路。     

原子与双模腔相互作用系统中光场的量子特性

研究双模间存在耦合情况下,二能级原子与双模腔场相互作用系统中光场的压缩效应、反聚束效应和亚泊松分布等量子特性。通过对两模间耦合系数取不同值时Mandel Q函数演化曲线的比较,讨论了两模间耦合系数对光子统计分布的影响。研究结果表明,光场呈现出反聚束效应和亚泊松分布,以及两模间呈现反关联等量子特性,但光场不呈现压缩效应;另一方面,随两模间耦合系数的增大,光场的亚泊松分布效应减弱。     

Numerical modeling and electromagnetic resonant modes in complex grating structures and optoelectronic device applications

An extended surface impedance boundary condition algorithm is developed that allows for the optical properties of a wide variety of complex one-dimensional periodic grating structures to be modeled. Wood-Rayleigh anomalies, diffraction, and electromagnetic resonance modes including horizontally oriented surface plasmons and vertical surface resonances are identified and described as well as analyzing their structural and geometrical dependencies. Methods to combine these modes to produce hybrid modes that channel and localize light are described. Application of these modes to metal-semiconductor-metal photodetectors (MSM-PD) is discussed and an example silicon-based MSM-PD with over 30 GHz bandwidth and 0.3 A/W responsivity is described.     

Design of a Quasi-Optical Mode Converter for a Frequency Step-Tunable Gyrotron

The quasi-optical mode converter for a frequency step-tunable gyrotron which consists of a dimpled-wall antenna (Denisov-type launcher) and a beam-forming mirror system has been optimized for 9 modes from TE_17,6 at 105 GHz to TE_23,8 at 143 GHz. The first mirror is a large quasi-elliptical focusing one; the second and third are phase-correcting mirrors with a non-quadratic shape of the surface. The results of calculations show that for these modes the Denisov-type launcher has a well-focused beam with low diffraction losses, and the radiation pattern presents an almost identical field shape for all modes considered. A multi-mode optimization of the phase-correcting mirrors with two different methods has been tested. The simulations show that the phase-correcting mirrors can be used for broadband operation in the frequency range from 105 GHz up to 143 GHz in the various design modes. This quasi-optical mode converter can achieve efficiencies of 94%-98% for converting the rotating high-order cylindrical cavity modes into the usable fundamental Gaussian mode.