The perfectly matched layer boundary condition for modal analysis of optical waveguides: leaky mode calculations

The perfectly matched layer (PML) boundary condition is applied to modal analysis for optical waveguides. It is demonstrated that the PML is suitable and effective in computation of leaky modes.     

On the modal expansion of resonator field in the source region

Two field expansions for the electromagnetic field radiated by electric and magnetic currents in a cavity resonator are presented. The first utilizes the cavity resonant modes only, while the other utilizes, in addition, the irrotational modes. The first expansion is shown to be more suitable if the exciting currents have volume distributions. On the other hand, the second expansion is more suitable if the resonator contains surface or filamentary current distributions. Typical examples are given to demonstrate the convergence behavior of the two expansions near and within the source region     

MEMS tunable resonant leaky mode filters

A tunable double-grating resonant leaky mode microelectromechanical-type element is introduced. A significant level of tunability is demonstrated by adjusting mechanically the structural symmetry of the grating profile. Tuning is also possible by variation of the thickness of the resonant layer. For a particular example silicon-on-insulator structure treated, it is shown that the resonance wavelength can be shifted by /spl sim/300 nm with a horizontal movement of /spl sim/120 nm within the 1.4-1.7-/spl mu/m wavelength band. Additionally, the reflectance can be varied from /spl sim/10/sup -3/ to 1 at central wavelength of 1.55 /spl mu/m with a vertical movement of /spl sim/200 nm. These results demonstrate new possibilities in design of tunable optical devices.     

Vector wave expansion method for leaky modes of microstructured optical fibers

A new method for calculating the confinement loss of leaky modes in arbitrary microstructured optical fibers is presented. The full vector algorithm is based on a polar coordinate Fourier decomposition method with adjustable boundary conditions, capable of accurately determining the outward radiating fields of the waveguide. Example waveguides with circular and elliptical hole shapes and their leaky mode solutions are presented and discussed.     

Uncertainties of the leaky mode correction for near-square-law optical fibres

It is shown that the leaky-mode correction as used, for example, for the near-field scanning technique, becomes uncertain for near-square-law fibres if they deviate from perfect circular symmetry. Results for the transition of the leaky-mode behaviour are presented.     

Analysis of approximations for the mode dispersion in monomode fibres

A number of recent papers have discussed the mode dispersion in step-index, monomode fibres using formulae based on accurate approximations for the modal propagation constant. It is shown here that, since dispersion depends on the first and second derivatives of the propagation constant, the use of such formulae may often be invalid and that a different type of approximation may be more useful     

Beamwidth approximations for the fundamental mode in symmetric double-heterojunction lasers

The beamwidth for the fundamental TE0mode in symmetric DH lasers is approximated within 4 percent by analytical formulas covering wide ranges of cavity thickness and refractive index steps. By using a Gaussian approximation for near-field distributions, and numerically calculated beamwidth curves, we find a Gaussian beam-like expression for the beamwidth, over the range1.5 < D < 6, whereDis the normalized guide thickness. In the nonGaussian region0 < D < 1.5, the beamwidth is estimated by using a corrected Dumke-like asymptotic approximation.     

Analysis of metal-interlaced-grating vertical-cavitysurface-emitting lasers using the modal method by modal expansion

It is analyzed by the modal method by modal expansion (MMME) that the strong polarization discrimination of a vertical-cavity surface-emitting laser (VCSEL) can be effectively obtained by using the metal-interlaced grating on the topmost layer of the VCSEL. The MMME is used to overcome the problems coming from the large permittivity discontinuities at GaAs-Al-air-Al interfaces. The analyses predict the correct direction of dominant polarization and the mode-suppression ratio. The calculated transmission efficiencies explain the characteristics of the VCSEL's below threshold. It is found that the difference in phase and amplitude between the two orthogonal polarization generated by the grating plays important roles for the selection of a dominant polarization through mirror reflectivities and mirror losses. In addition, the influence of various thin metal layers on polarization stabilization is demonstrated     

Analysis of guided modes in multilayer/multiconductor structures bythe “boundary integral-resonant mode expansion method”

This paper describes a new method for the analysis of modes propagating in shielded waveguides consisting of many dielectric and perfectly conducting layers of different widths. The eigenvalue problem inherent to the mode determination is formulated subdividing the structure into layered elementary wave-guides EWGs and matching the fields generated in adjacent EWGs by unknown equivalent sources placed at the interfaces. The special representation of the EWG field, consisting of boundary integrals and mode expansions, leads to a linear matrix eigenvalue problem involving a limited number of variables. Thanks to this peculiarity the method permits one to determine many modes in short computing times. The method was implemented in a flexible and fully automatic computer code, whose reliability and efficiency has been confirmed by many tests     

辐射模缝隙馈源激励的2GHz无线电波在室内的传播

本文给出了用辐射模缝隙馈源作为发射天线时，2GHz窄带和宽带无线电波在室内传播特性的测量结果。对于窄带信号，主要测量了传播过程中的衰减，测量结果表明，沿缝隙馈源方向，接收信号电平按指数规律衰减，在垂直于电缆方向上，接收信号电平的衰减较慢，损耗指数较小：在平行和垂直于馈源方向上慢衰落基本服从正态分布，而快衰落分别服从Rayleigh和Rician分布。对于宽带信号，测量了多径脉冲相应，得到了均方根时延扩展及其概率分布。     

A scalar variational analysis of rectangular dielectric waveguidesusing Hermite-Gaussian modal approximations

A scalar variational analysis of rectangular dielectric waveguides using Hermite-Gaussian modal approximations is presented. The technique analyzes waveguides by finding a closed-form, approximate solution to the given problem. We begin with an assumed, closed-form field solution, with unknown parameters which can be chosen to best match the assumed field to the actual field solution using variational principles. The values of the unknown parameters of the assumed field are determined by solving a set of simultaneous equations, not by a search method. As a result, this analysis method is computationally fast. Another benefit is that this method gives best-fit, closed-form modal approximations     

Characteristics of guided and leaky waves on multilayer thin-filmstructures with planar material gratings

This paper presents the characteristics of guided (surface) waves and leaky waves on multilayer structures with planar implanted periodic dielectric blocks. A three-dimensional (3-D) integral-equation formulation in conjunction with the method of moments (MoM's) is used to find the propagation constants of the surface-wave and leaky-wave modes. The analysis deals with layered structures with irregular implants. Photonic band-gaps of both guided waves and leaky waves for rectangular air-implants are identified. Anisotropic properties of the surface waves and leaky waves are investigated. The design of leaky-wave antennas with the information of mode characteristics is discussed. The analysis is validated through the comparison with a low-frequency effective-medium approach and results for linear gratings     

Role of controlled mode conversion in leaky feeder mine communication systems

Using an idealized model, we consider VHF wave transmission in a straight mine tunnel that contains a braided coaxial cable. The controlled interchange of energy between the propagation modes can be used to optimize the communication range and allow for coupling to and from portable hand-held antennas. In particular, we show that the optimum lengths for maximum transmission through the leaky cable sections or mode converters predicted here are compatible to those predicted by approximate coupled mode theory.     

Compressed-width leaky EH/sub 1/ mode PBG antenna

The recently developed electric-magnetic-electric (EME) microstrip is successfully used to design a compact leaky-mode antenna with fan beam radiation patterns. The EME microstrip consists of composite metals paralleling the electric and magnetic surfaces, where the magnetic surface is made of an array of coupled inductors. The frequency scanning behavior, experimentally and theoretically confirmed by matrix-pencil analyses, indicates that the line width can be reduced by 20%, compared to that of the conventional microstrip with the identical radiation angle of the first higher order (EH/sub 1/) mode at the same frequency.     

A modal analysis of TEM mode in circular-rectangular coaxialwaveguides

A modal analysis of transverse electromagnetic (TEM) mode in a circular-rectangular coaxial waveguide is presented in this paper. The analysis is based on the modal-expansion technique. Analytic expressions for the characteristic impedance and attenuation coefficient are derived from the solution of the TEM mode. The calculated results are compared with those of the finite-element method, as well as published data. Excellent agreement is observed     

Simple approximations for chromatic dispersion in single- mode fibers with various index profiles

Simple approximate formulas of chromatic dispersion and zero-chromatic dispersion wavelength are empirically derived for single-mode fibers with various index profiles having the deformations such as a central dip, hump, and/or tailing at a core cladding interface. These profiles are typical which are commonly obtained in current single-mode fibers. The approximation is based on the exact solution of vector-wave equation. These accuracies are better than 0.3 and 0.03 percent for the chromatic dispersion and zero-chromatic dispersion wavelength, respectively. With the aid of the simple approximations, the properties of chromaric dispersion and zero-chromatic dispersion wavelength for practical single-mode fibers are discussed. The relation between the chromatic dispersion and basic fiber parameters of single-mode fibers, effective cutoff wavelength of the LP11mode, and the spot-size of the LP01mode, are clarified.     

Electrooptic beam deflection using the leaky mode of a planar waveguide

Electrooptic beam deflection using the leaky mode of a TiO/sub 2/ thin-film waveguide in optical contact with a LiNbO/sub 3/ crystal is discussed. Initial measurements yielded a deflection efficiency of 0.34 mrad/kV and suggest potential for more than an order of magnitude improvement. By depositing the waveguide directly onto the electrooptical crystal, a rugged miniature device that has the potential for high-speed operation and an angular deflection efficiency equal to or higher than that of currently available bulk devices can be fabricated. In addition to the strict tolerances on the coating thickness, the deposited films must have extremely low losses, a high refractive index, and be resistant to environmental effects.<>     

Non reciprocal single mode conversion in multilayer magnetooptical waveguides

Multilayer structures are of great interest in the fabrication of single mode devices for Integrated Optics. this work it is shown that a multilayer structure allows not only single-mode behaviour but it enhaces the non-reci procity of the quide.     

Analysis of slots in nonradiating dielectric waveguide using the modal expansion method

A modal expansion method is used with the reciprocity and Poynting theorems to derive the admittance of inclined slots cut in the metal wall of a nonradiating dielectric (NRD) waveguide. Theoretical values of normalised conductance and susceptance are compared with previously reported experimental results and are found to be in good agreement.<>     

漏泄同轴电缆辐射模式分析及高次模抑制

本文从Ｆｌｏｑｕｅｔ定理出发,详细分析了漏泄同轴电缆的辐射模式,给出了辐射模式的存在条件,讨论了单模辐射的频带宽度。在此基础上进一步研究了高次模的抑制方法及其在电缆结构上的实现,目的是扩展单模辐射的频带宽度。本文理论是根据频带宽度的要求设计漏泄同轴电缆外导体上缝隙排列方式的基础。