Analysis of a Metal-Coated Planar Dielectric Waveguide with Chiral Cladding

The propagation characteristics of a metal-coated planar waveguide with chiral media filled in the cladding are presented. The effects of chirality on cutoff, dispersion characteristics and field distributions of the waveguide are studied. The results show that cladding chirality brings phase chopping to the transverse electric field component of those modes with odd mode numbers.     

Continuous Mode Spectrum of a Circular Dielectric Rod

The continuous modes for a circular dielectric rod are derived. These modes are identified with the fields due to the scattering of a plane wave at oblique incidence from a dielectric rod, thus providing insight into their behavior. This identification suggests that the modes be classified as incident transverse magnetic (ITM) modes when the incident plane-wave portion of H/sub z/ is zero and as incident transverse electric (ITE) modes when the incident plane-wave portion of E/sub z/ is zero. The transition region from discrete to continuous modes is analyzed in detail. Very simple approximate modes are derived for use in optical waveguide studies.     

Comparison of Q-Factors Between TE and TM Modes in 3-D Microsquares by FDTD Simulation

Mode characteristics of three-dimensional (3-D) microsquare resonators are investigated by finite-difference time-domain (FDTD) simulation for the transverse electric (TE)-like and the transverse magnetic (TM)-like modes. For a pillar microsquare with a side length of 2 mum in air, we have Q-factors about 5 times 10³ for TM-like modes at the wavelength of 1550 nm, which are one order larger than those of TE-like modes, as vertical refractive index distribution is 3.17/3.4/3.17 and the corresponding center layer thickness is 0.2 mum. The mode field patterns show that TM-like modes have much weaker vertical radiation coupling loss than TE-like modes. TM-like modes can have high Q-factors in a microsquare with weak vertical field confinement.     

Fundamental and Higher Mode Inversion of Dispersed GPR Waves Propagating in an Ice Layer

Dispersion of ground-penetrating radar (GPR) waves can occur when they are trapped in a layer. In this paper, we analyze the modal propagation of GPR pulses through a layer of ice that is overlying water. Dispersed transverse electric (TE) waves that are trapped in the waveguide have larger amplitudes than the critically refracted waves that travel through air, whereas the transverse magnetic (TM) critically refracted waves traveling through air are more dominant than the trapped dispersed TM waves. This can be explained by the leaky waveguide behavior of the ice layer. The reflection coefficients for the waves incident on the ice-water interface show that the TM modes are more leaky than the TE modes. Still, clear dispersion is observed in both cases, which depends on the permittivity and thickness of the ice. Similar to inversion of dispersed Rayleigh waves, these parameters can be estimated by calculating phase-velocity spectra, picking dispersion curves, and inverting the dispersion curves using a combined local and global minimization procedure. Synthetic data show several higher order modes of which separate and combined inversions return the input modeling parameters accurately. Experimental data acquired on a frozen lake show strong dispersion for the TE and TM modes. The phase-velocity spectra of the field data show three TE and four TM modes of which separate and combined inversion of different modes return similar values for the ice thickness and known permittivity of ice. Due to the more leaky behavior of the TM modes, the TE inversion is better constrained and more suitable for inversion.     

Investigation of Bragg gratings on planar InGaAsP/InP waveguides atnormal and oblique incidence

The polarization-dependent mode coupling of Bragg gratings on planar InGaAsP/InP waveguides is investigated by transmittance and reflectance measurements at normal and oblique incidence in the 1.5-μm wavelength region. Strong coupling between TE (transverse electric) and TM (transverse magnetic) modes is observed at oblique incident, whereas the TE-TE coupling vanishes at an incidence angle of 45°. The behavior of the near field close to the Bragg wavelength and the effects of radiation into the substrate are analyzed. It is experimentally shown that small deformations of the phase fronts on the input side lead to strong interference effects on the output side     

Analysis of Wave Propagation in Anisotropic Film Waveguides with Bent Optical Axes

We present an analytical method for studying the wave propagation in anisotropic planar optical waveguides where the oblique angle between the optical axis and the propagation axis changes arbitrarily in the film surface along the propagation length. The analysis is based on the coupled-mode theory, where the coupling between a guided mode and radiation modes is regarded to be of major importance. We apply a hypothetical boundary method to quantize the continuum of radiation modes, and replace the continuously changing oblique angle by a step approximation. It is shown that these approximations do not degrade the computational accuracy. To exemplify the wave-propagation properties, we deal with a waveguide consisting of LiNbO/sub 3/ and let the oblique angle change linearly along the propagation length. It is found that the incident guided TE mode leaks its power primarily in a very narrow region centered on the critical oblique angle, and that TE radiation modes play an important role in the power conversion, even though they carry far less power than the TM radiation modes.     

Analysis of discontinuities in an asymmetric dielectric slabwaveguide by combination of finite and boundary elements

An approach that combines the finite-element, and boundary-element methods is extended to the analysis of discontinuities in an asymmetric slab waveguide. The discontinuity region is divided into three regions. One is a finite region with arbitrary inhomogeneities, and the others are semi-infinite and homogeneous regions. The finite-element and boundary-element methods are applied to the former and latter regions, respectively. For uniform waveguide regions connected to discontinuities, analytical solutions are used, in which all the eigenmodes, namely, guided modes, substrate radiation modes, and substrate-cladding radiation modes, are taken into account. To show the validity and usefulness of this approach, computed results are given for three kinds of step-discontinuities with transverse electric (TE) and transverse magnetic (TM) mode incidences     

Analysis of Circular Dielectric Waveguide with Chiral Cladding

The propagation characteristics of a circular dielectric waveguide with chiral media filled in the cladding are investigated. The relation between the cutoff frequency and the chiral admittance, the dispersion curves for some modes with different angular mode numbers and the transverse distribution of fields are presented. Some new features different from the ordinary circular dielectric waveguide are resulted. The results show that the cladding chirality may lead to a single-mode operation in the circular dielectric waveguide.     

Mode Coupling and Vertical Radiation Loss for Whispering-Gallery Modes in 3-D Microcavities

The characteristics of whispering-gallery modes (WGMs) in 3-D cylindrical, square, and triangular microcavities with vertical optical confinement of semiconductors are numerically investigated by the finite-difference time-domain (FDTD) technique. For a microcylinder with a vertical refractive index 3.17/3.4/3.17 and a center layer thickness 0.2 mum, Q-factors of transverse electric (TE) WGMs around wavelength 1550 nm are smaller than 10³, as the radius R < 4 mum and reach the orders of 10⁴ and 10⁶ as R = 5 and 6 mum, respectively. However, the Q-factor of transverse magnetic (TM) WGMs at wavelength 1.659 mum reaches 7.5 times 10⁵ as R = 1 mum. The mode coupling between the WGMs and vertical radiation modes in the cladding layer results in vertical radiation loss for the WGMs. In the microcylinder, the mode wavelength of TM WGM is larger than the cutoff wavelength of the vertical radiation mode with the same mode numbers, so TM WGMs cannot couple with the vertical radiation mode and have high Q -factor. In contrast, TE WGMs can couple with the corresponding vertical radiation mode in the 3-D microcylinder as R < 5 mum. However, the mode wavelength of the TE WGM approaches (is larger than) the cutoff wavelength of the corresponding radiation modes at R = 5 mum (6 mum), so TE WGMs have high Q-factors in such microcylinders too. The results show that a critical lateral size is required for obtaining high Q-factor TE WGMs in the 3-D microcylinder. For 3-D square and triangular microcavities, we also find that the Q-factor of TM WGM is larger than that of TE WGM.     

Radiation by a straight thin-wire antenna embedded in an isotropicchiral medium

Radiation characteristics of a straight thin-wire antenna embedded in an isotropic chiral medium are explored. The radiation field contains both left-circularly polarized (LCP) and right-circularly polarized (RCP) components. The radiation pattern is found to be symmetric about the plane &thetas;=π/2, azimuthally isotropic, and TEM (transverse electromagnetic) in nature; however, all three of these features are found as well for isotropic achiral media. Some specific features of the radiation field on certain constant spherical surfaces are also examined. If the antenna is reduced to a point dipole, it is shown that the radiation resistance is enhanced by the presence of chirality in the embedding medium, and the antenna LCP gain differs from the RCP gain     

Leaky modes of optical waveguides with varied refractive index for microchip optical interconnect applications – Asymptotic solutions

In two-dimensional optical waveguides with the varied refractive index, approximate analytic solutions of the leaky modes are derived by using an asymptotic analysis for both transverse electric (TE) and transverse magnetic (TM) modes. Numerical simulations show that the asymptotic solutions of the leaky modes are quite close to the exact ones. The results are useful in the eigenmode method, where the leaky modes appear if a perfectly matched layer (PML) is used to terminate the transverse directions of optical waveguides.     

Diffraction from an abruptly terminated dielectric slab waveguide in the presence of a cylindrical scatterer

The efficiency of using an adaptor lens in front of an abruptly terminated symmetric slab optical waveguide is examined analytically in this paper. The adaptor lens is assumed to be of cylindrical shape with a constant refractive index. The coupling of the modes propagating inside the slab guide into radiation waves in the presence of the lens is treated by integral equation methods. In the first step an integral equation is derived for the Green's functionG(r/r')of an abruptly terminated slab waveguide. The integral equation is solved approximately by an iterative procedure giving accurate results when the difference of the refractive indices between the slab waveguide and substrate-cover regions is small. The Green's function is then used to formulate another integral equation for the unknown field inside the adaptor lens. The latter integral equation for the cylindrical lens cross section area is solved by adopting a cylindrical partial wave expansion for the unknown interior field. After determining this field, the reflection-coupling coefficients for the guided modes propagating in the opposite direction of the incident wave, are computed by using the Green's functionG(r/r'). Radiation patterns are also derived in the far field region for an incident slab guided mode. Numerical results are computed and presented for several guide dimensions, lens radii, and refractive indices.     

手征介质圆波导中阶梯不连续性的散射和辐射特性研究

采用多模网络与严格模匹配相结合的方法，对开放型手征介质圆波导中的二种阶梯不连续性的散射和辐射特性进行分析和求解，仔细讨论了手征参数和几何尺寸对散射和辐射特性的影响．给出的结果对手征介质元器件的研究有实际的参考意义．     

Transverse-leaky-mode characteristics of ARROW VCSELs

Transverse-leaky-mode characteristics of antiresonant-reflecting-optical-waveguide (ARROW) vertical-cavity surface-emitting lasers (VCSELs) are studied. It is found that the suppression of high-order transverse leaky modes in ARROW VCSELs can be deteriorated by the influence of spatial hole burning and thermal lensing effects. On the other hand, a new design rule is proposed to deduce the optimum dimensions of ARROW so that the suppression of high-order transverse leaky modes can be enhanced. Furthermore, the turn-on transient response of ARROW VCSELs is investigated. It is found that the radiation loss has significant influence on the built-up time of the first-order transverse leaky mode.     

Intrinsic modes of radiation in ferrite patch antennas

We have found two types of radiation modes for patch antennas loaded with ferrite materials. Each mode of radiation is a linear combination of normal modes of propagation in parallel plate waveguide separated by a slab of ferrite material. We have introduced new boundary conditions in which only TE modes of oscillation in the patch antenna cavity result. According to different propagation directions relative to the applied DC field these TE modes are distinguished as transverse modes and longitudinal modes, and they possess mutually perpendicular radiation polarizations. While the longitudinal TE modes are found to form discrete modes in the frequency domain, the radiation frequency of a transverse TE mode can be continuously tuned over a wide frequency range by varying the biasing magnetic field. Circularly polarized radiations may result from simultaneous excitations of these two modes. Ferrite patch antennas of square geometry have been fabricated and tested. The measured resonant frequencies compared very well with our theory     

基于一维缺陷光子晶体的角度测量仪的设计

提出用一维缺陷光子晶体来测量角度特别是小的角度变化的设计方案。用Si薄膜和SiO2薄膜组成一维缺陷光子晶体,用特征矩阵法研究该光子晶体的禁带中的缺陷模的波长和强度随入射角缓慢变化而变化的规律,由此提出根据缺陷模的波长、强度、偏振性与入射角的关系进行角度测量的原理。本设计特别适用于极小的角度变化的测量。     

手征介质填充双平板中导模的反射和透射特性

用多模网络与严格模匹配相结合的方法,对纵向填充一层、两层和多层手征介质的双平板中导模的反射和透射特性进行了分析和求解.分析中在横截面采用等效传输线,在纵向采用多模传输线方法,并且利用结构的对称性使得问题简化.对各种不同情形进行了数值计算,讨论了手征参数和波导结构的尺寸对反射和透射特性的影响.     

Power Reflection and Transmission Coefficients for Meander‐Line Polarizers with a Chiral Slab

This paper presents a theoretical investigation of power reflection and transmission coefficients for a meander‐line polarizer placed periodically on a chiral slab. It is assumed that a linearly polarized transverse magnetic wave is incident on a chiral slab from the air region. In the analysis, we derive the electric and magnetic fields in the modal form in the air and chiral regions. We obtain power reflection and transmission coefficients in a straightforward manner after matching the tangential components of the electric and magnetic fields at the boundaries. We present numerical results for the power reflection and transmission coefficients versus frequency and incident angle for different values of the chirality admittance. A meander‐line polarizer placed on a dielectric slab can convert a linearly polarized wave to a circularly polarized wave. The design parameters for a meander‐line polarizer are the dimensions of the meander‐line and the values of the dielectric slab. Replacing a dielectric slab with a chiral slab introduces a new independent parameter which controls the wave polarization.     

Spectral analysis considerations relevant to radiation and leakymodes of open-boundary microstrip transmission line

The continuous radiation spectrum of an open microstrip transmission line and its nonspectral leaky modes are conceptualized through a transform-domain integral-operator formulation and relevant spectral analysis. The radiation spectrum is identified with branch cuts in the axial wavenumber plane, which constrain the migration of branch-point singularities in the transverse wavenumber plane. Leaky-wave modes occur only when the branch cuts in the axial wavenumber plane are violated. The relationship among spectral radiation modes, nonspectral leaky-wave modes, and branch cuts in the axial wavenumber plane is discussed. The influence of branch cuts in the axial wavenumber plane upon the location of branch points in the transverse wavenumber plane is detailed, and a rationale is offered for the choice branch cuts in the latter plane. The formulation is applicable to a wide class of open conducting or dielectric waveguides     

相对论电子在周期磁场中的辐射频谱

分析了相对论电子在空间周期磁场中的运动轨迹.在一定条件下,电子在垂直原始入射方向上的运动是简谐的,利用谐振子模型求出了它的辐射频谱和频宽;最后讨论了运动的非谐性.得到辐射频谱分布将是与电子的初速度、磁场强度有关.