Azimuthally uniform surface-plasma modes in thin metalliccylindrical shells

The pure transverse-magnetic (TM)-polarized surface-plasma bound modes of a thin metallic right circular cylindrical shell imbedded in dielectric materials are studied. Two modes are generally found to be supported by the structure. They are analogous to the two modes of the corresponding planar structure of a thin metallic film bound by dielectrics. One of the modes is shown to have sufficiently small loss to make it of potential application in fiber optics. The transcendental equation of the modes generalizes that of the planar geometry by having the cylinder radius as a parameter. The equation is solved exactly in the complex domain for all cases considered     

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     

The effects of covering on complex wave propagation in gyromagneticslotlines

The evolution of complex leaky waves in partially open gyromagnetic slotlines into complex modes in a shielded slotline is presented. Given a particular stratified gyromagnetic slotline with two sidewalls present, four types (Types I-IV) of guided structures are defined and investigated, depending upon the four possible combinations of top and bottom covers. The behavior of the complex solutions is discussed for the partially open gyromagnetic slotlines. Initially, the slotline of Type I, which lacks both top and bottom covers, shows that no coupling exists among various pairs of leaky waves. By adding only a top cover into Type I, the resultant slotline of Type II exhibits certain coupling between different sets of leaky waves. Similarly, by adding only a bottom cover into Type I, the resultant slotline of Type III shows that certain strong leaky waves of Types I and II now become weak leaky waves. From these numerical experiments, we deduce that the complex modes supported by Type IV, which is completely shielded, can be the result of the mode coupling of the two previously found leaky waves in Types II and III waveguides, respectively. Therefore, the formation of complex modes in shielded slotline is related to the effects of covering on mode coupling of the various leaky waves of the partially open slotlines     

Coupling between gaussian and guided modes at the input and output of oversized circular waveguides

The coupling between a gaussian TEMoo bearn with HE 1m modes for dielectric waveguides and TE1m and TM1m modes for metallic waveguides is analytically studied. An optimization method allows to know HE11 or TE11 modes create gaussian TEMmm bearns at the output of the waveguide.     

A complete set of normal modes in three-layered electron waveguides

Mathematical expressions are given for guided and radiation modes including nonpropagating parts in three-layered electron waveguides, in addition to gaining a clear understanding of the difference between electron and optical waveguides in terms of normal modes. According to the dispersion diagrams, it is shown that a complete set of normal modes for electron waveguides depends on the electron's total energy and that in the quantum-well-type waveguide the discrete modes and the continuous modes radiating to one side of the film are reduced to nonpropagating modes in a certain energy range, whereas a complete set of normal modes for optical waveguides always consists of three types of modes: guided modes, substrate radiation modes, and substrate-cover radiation modes. In addition, the discrete modes and the continuous modes radiating to one side of the film are not reduced to nonpropagating modes in the entire range of frequencies. Also, it is shown that the guided modes always exist in electron waveguides composed of arbitrarily different Al-concentration ratios in the film, substrate, and cover regions, and a new waveguiding quantum-step-type structure, which utilizes the total reflection at both the potential rise and drop is proposed, whereas in optical waveguides, the guided modes exist only in the structure in which the refractive index of the film is higher than those of the substrate and of the cover     

On the mode-coupling formation of complex modes in a nonreciprocalfinline

This paper studies and models the mechanism for forming the complex modes commonly found in boxed quasi-planar or planar guided-wave structures. To illustrate the fact that the mode-coupling among the various forms of modes is closely related to the formation of complex modes, the dispersion characteristics of the complex propagation constants (or the so-called mode spectrum) of a nonreciprocal unilateral finline are obtained by the rigorous full-wave SDA (spectral-domain approach). It is found that in the mode spectrum of the nonreciprocal finline, a forward wave and a backward wave interact to produce a pair of complex modes. The interactions between two forward (backward) traveling waves, between a forward wave and a backward wave, and between two complex waves (modes) are modeled by applying the mode-coupling theory. The concept of hypothetical modes is introduced in the model. These hypothetical modes are obtained by applying mode-coupling theory to the mode spectrum previously obtained. The approximate values obtained for the propagation constants of the three types of wave interactions using the model presented in the paper are in close agreement with those given by the full-wave SDA     

基于局部表面等离子体激元的共振增强超材料吸收器的吸收性质

提出了一种在150～165 THz区域内的具有单峰吸收特性的高性能超材料吸收器。设计的吸波器包含两个阵列:双金属颗粒阵列和双空气孔阵列。金属层的阻尼常数在模拟中被优化。发现在模拟中使用2. 3倍的阻尼常数时,可以获得最大吸收率96%。吸收峰由局域表面等离子体(LSP)模式共振激发。为了揭示共振电磁机理,进行了两组模拟,研究结构参数变化对共振吸收峰的影响。发现随着垂直距离V的增加,吸收峰被增强,当V=160 nm时,获得新的吸收带。在第二次模拟中,对于水平距离H的增加,吸收峰也增强,并且当H=190 nm时获得另一个新的吸收带。电场强度分布结果表明LSP模式的激发和LSP模式之间的耦合效应导致吸收峰增强现象。     

Complex modes in shielded suspended coupled microstrip lines

The existence of complex modes in electrically shielded suspended coupled microstrip lines has been studied extensively, and the results are presented. A rigorous full-wave spectral-domain approach (SDA) with a newly proposed and tested set of basis functions can efficiently and accurately determine the propagation characteristics of the dominant, higher-order, and complex modes for planar or quasi-planar transmission lines. These basis functions are validated by comparing the convergence study of field solutions with those obtained by various sets of preconditioned bases and by the unconditioned subdomain ones. Excellent agreement is obtained for the propagation constants and the normalized complex longitudinal and transverse current distributions on conducting strips for the strongly coupled microstrip lines. For all the particular case studies discussed, it is shown that the complex modes may exist in all the shielded suspended coupled microstrip lines, even when the substrate dielectric constant is low. Theoretical results for the fundamental, higher-order, evanescent, and complex modes are presented for suspended coupled microstrip lines     

Suppression of waveguide modes in strip transmission lines

Undesired waveguide modes can be excited in a strip transmission line shielded in a wide metallic channel. A mode suppressor which suppresses selectively the waveguide modes over a certain frequency range is described. This technique allows a substantial increase of the channel and dielectric substrate dimensions.     

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.     

LP modes and ideal modes on optical fibers

The transformation from coupled-mode equations for LP modes to those for ideal modes and the expressions of one set of modes in terms of linear combinations of the other set of modes are studied, using the coupled-mode theory. The expressions (including higher-order corrections) of modal fields and propagation constants for ideal modes are given in terms of those for LP modes in three different cases. Thus, cases where a LP mode can or cannot directly replace a corresponding ideal mode are made clear.     

Computation of proper and improper modes in multilayeredbianisotropic waveguides

An efficient numerical method is presented to determine the loci of both the proper and complex improper modes of a multilayered bianisotropic planar waveguide. The propagation constants of the waveguide modes are expressed in terms of the zeros of a specific analytic function. The use of appropriate integration zero-searching methods is proposed since information about the possible number of complex improper modes cannot be previously extracted. The general formulation presented here has been applied to the study of the complex improper modes of single and two-layer structures containing magnetized ferrites. It has been found that the transition from physical proper to complex improper modes is made throughout a nonphysical real improper mode     

Characteristic modes for dielectric and magnetic bodies

A theory of characteristic modes for material bodies, both with and without losses, is developed. For loss-free bodies, the modes consist of a set of real characteristic sources which diagonalize the generalized network matrix for the body, and a set of characteristic fields which diagonalize the scattering matrix. Most of the properties of these modes remain the same as those of the corresponding modes for perfectly conducting bodies. For lossy bodies, the corresponding modes have complex characteristic sources. However, in the lossy case there also exists a set of real characteristic sources which diagonalize the generalized network matrix, but their fields do not diagonalize the scattering matrix.     

An organic multilevel non-volatile memory device based on multiple independent switching modes

The demand for higher data density memory structures is greater today than ever before. Multilevel resistive organic memory devices (OMD) provide an ideal solution, in being easily fabricated, cost-effective and at the same time promising high storage capacity. However, conventional methods for multilevel OMDs impose demanding requirements on material properties and attain only limited performance. We hereby provide an alternative design concept that combines multiple switching modes in one device to realize multilevel function. The device possesses a simple structure by using a ferroelectric phase-separated blend as the active layer. Two switching modes, the ferroelectric switching and the metallic filament switching, are realized simultaneously in this device, and enable a ternary storage function. The cross-section scanning electron microscope (SEM) images provide a strong evidence of the formation and annihilation of the metallic filament.     

Complex modes in boxed microstrip

A method is described for obtaining the propagation coefficients and field patterns of a large number of modes for microstrip with a minimum of computational effort. The method uses a discrete space-domain formulation to calculate a large number of higher-order modes in a way which leads to their fast location and which ensures that node modes are missed. This includes those pairs of modes with complex conjugate propagation constants of the type reported for finline, as well as the normal evanescent modes. In addition, the characteristic impedance of microstrip is efficiently calculated. The results presented are obtained using the generally accepted power-current definition and are in agreement with other published results     

Higher-order evanescent modes on slow-wave structures

By employing suitable mathematical models, the higher-order evanescent modes on two common slow-wave systems are discussed. It is shown that these closely resemble corresponding modes on related plane-waveguide or coaxial-line structures.     

Network-theoretical model of the gyrotron oscillator part I: Empty cavity oscillation modes

A network-theoretical model of the gyrotron has been elaborated which is both conspicious and rigorous. The problem of self-consistently representing the field in the presence of the electron beam is attacked by expansion into the empty structure oscillation modes. In this first part, a method is presented to determine the empty gyrotron cavity oscillation modes, i.e. theQ factors, resonance frequencies, and field distributions in axisymmetric, but otherwise quite general cavities. It is based on the field representation in terms of local normal waveguide modes. Matrix equations in these modes for different type of cavity sections (building blocks) are formulated. Along with the open resonator boundary conditions, these equations form a nonstandard eigenvalue problem; the eigenvalues are the complex eigenfrequencies, the eigenvectors correspond to the field distributions. By way of example, the method is applied to a simple and a complex cavity.     

Investigations of optically pumped submillimeter wave laser modes

A complete theory for waveguide laser modes for oversized metallic and dielectric waveguides with circular cross section has been developed for the submm wavelength region. The experimental investigations have been done by a submm heterodyne technique for the first stage using a Schottky barrier diode in an open structure mixer.     

Resonant frequencies of dielectric resonators containing guidedcomplex modes

It is shown that unless complex modes are included in the mode-matching analysis to determine the resonant frequencies of dielectric-loaded resonators, some resonant frequencies could be missed. Field distributions, mode charts, and mode coefficients of dielectric-loaded resonators in which complex modes exist are presented. Experimental measurements for the verification of the computed results are presented and show good agreement with theory     

Excitation and propagation of modes of a multilayer fibre

The excitation and propagation characteristics of the lowest-order modes of a glass-fibre waveguide are determined without recourse to approximations concerning the core or cladding radii. Although under unfavourable circumstances higher modes may be strongly excited, by applying a lossy coating to the exterior surface of the fibre, these modes may be strongly attenuated. However, the layer has negligible influence on the attenuation of the dominant mode.