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Scattering of light by metal-coated dielectric nanocylinders periodically distributed along a cylindrical surface is investigated both theoretically and numerically. The structure is under the authors' interest because of its practical application in design and fabrication of plasmonic devices such as plasmonic ring resonators, Plasmonic Crystals and THz waveguides. The method is based on the T-matrix approach and the field expansion into the cylindrical Floquet modes. The method is rigorous, straightforward and can be easily applied to various cylindrical configurations with different types and locations of the excitation sources. Scattering cross section and absorption cross section of three and four silver (Ag) coated-dielectric nanocylinders periodically situated along a cylindrical surface are studied. Near field distributions are investigated at particular wavelengths corresponding to the resonance wavelengths in the spectral responses. Special attention is paid to the unique and interesting phenomena characterizing the cylindrical structure composed of the metal-coated nanocylinders such as: a ) localization of the field at the outer and inner interfaces of the metal-coated nanocylinders; b) excitement of the field in the gap region between the nanocylinders through the coupled plasmon resonance and c) strong confinement of the field inside the cylindrical structure. Detailed investigations have shown that unique phenomena characterizing the cylindrical configurations of the nanocylinders can be realized using a relatively simple structure composed of three nanocylinders and there is no need to further increase a number of the scatterers (nanocylinders).

Two simple single layer single feed cross slot patch antennas with air dielectric (er = 1) substrate providing multiple frequency operation is proposed.At first a cross slot rectangular patch antenna providing quad frequency operation is proposed and experimentally studied. The measured quad frequencies are 1.93, 2.57, 3.18, and 3.56 GHz. Another cross slot trapezium patch antenna providing quad frequency operation is proposed and experimentally studied. The measured quad frequencies are at 1.43, 1.81, 2.97, and 3.58 GHz. Trapezium patch antenna is found to be more compact in size and as well as reduction in resonant frequency compared to rectangular patch antenna. Measured values are in good agreement with simulated results. The measured radiation patterns at each measured resonant frequency are also shown. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:612–615, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25765

Directivity of radiation from a localized source coupled to electromagnetic crystals is investigated theoretically using a two-dimensional model. The closed form expression for the far field of radiation is derived and used to examine two primary factors governing the directivity. It is shown that the directivity is uniquely characterized by the transmission windows of the electromagnetic crystals in the frequency and angular spectral domains and the Fabry-Perot resonance condition for the radiated field in the space surrounding the source.

The Fourier series expansion method is a useful tool to approach the problems of discontinuities in optical waveguides, and it applies to analyze the Floquet-modes of photonic crystal waveguides. This paper shows that the Floquet-mode calculation with large truncation order is limited and explains the reason. Furthermore, two techniques of the formulation are presented to relieve this limitation. One of them is a use of the symmetric properties of the Floquet-modes, and another is a use of the Rayleigh quotients to improve accuracy of eigenvalue calculation. They are validated by numerical experiments.

A theoretical analysis of the cladding modes is presented for an asymmetric dual-core fiber that consists of a primary core near the fiber axis and a secondary core. Numerical examples are given to demonstrate that the approximation of a two-layer fiber geometry is inadequate to describe the accurate modal properties of the cladding modes. It is shown that the field distributions of the cladding modes are dependent on the azimuthal angle under the presence of two cores. The maximum field intensities are located away from the fiber axis with a shift in the local maxima in the primary core toward the secondary core. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 507–510, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24066

A problem of coupling between conventional dielectric waveguides and a two-dimensional photonic crystal waveguide is analyzed, using the Fourier series expansion method combined with the absorbing boundary condition of a perfectly matched layer (PML). A novel structure for the input and output ends of the photonic crystal waveguide is proposed to increase the coupling efficiency. Numerical examples are demonstrated and discussed to validate the effectiveness of the proposed structure.

This study presents theoretical and experimental investigations on novel, compact, single layer and single probe-fed rectangular microstrip patch antennas for dual and multi frequency operation. The novel design is achieved by cutting two rectangular slots at one side of the patch antenna. Compared with the conventional rectangular patch antenna, our antenna can achieve reduction in patch size up to 85%. Dual frequency operation has also been achieved effectively by just adjusting the feed position of a conventional rectangular patch antenna. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 961–965, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23255

A novel formulation of radiation from a localized line source placed in two-dimensional photonic crystals consisting of layered periodic arrays of parallel circular cylinders is presented. The method employs the spectral domain approach. The spectral response of the photonic crystals to the line source excitation is calculated using the lattice sums, the T-matrix of a circular cylinder, and the generalized reflection and transmission matrices of the layered system. The far-zone radiated field is obtained using the conventional asymptotic method to the spectral response. The radiation patterns of the localized line source sandwiched by two photonic crystals are numerically studied.

We analyzed the frequency and quality factor of microcavities on a two-dimensional photonic crystal, using a Fourier series expansion method combined with perfectly matched layers (PMLs). Numerical examples are demonstrated and discussed to show that the resonant frequency and the quality factor Q values can be calculated by the present method using PMLs.

—This paper proposes the pseudo-periodic Fourier transform to analyze the electromagnetic scattering from periodic structures with non-plane wave incidence. The pseudo-periodic Fourier transform converts arbitrary field components into pseudo-periodic functions and the conventional grating theories based on the Floquet theorem become applicable. The inverse transform is given by integrating with respect to the transform parameter over a finite interval and the near field analysis requires numerical integration. Some application examples are numerically examined and the results show good convergence.

A rigorous electromagnetic theory is developed to analyze multiport waveguide junctions with artificial inclusions formed of the conducting strips and dielectric layers. The method is based on the Fourier transform technique combined with the mode matching method technique that takes into account the edge conditions in vicinity of the strip edges. The scattering characteristics of a 3-port junction are discussed with the numerical examples for the SWR maps, the power reflection and transmission coefficients, and the 2D plots of near fields distributions inside the junction area. A strategy of optimize matching properties of the 3-port waveguide junctions is also presented.

A full-wave method for modal analysis of two-dimensional photonic-crystal waveguides consisting of layered arrays of rectangular cylinders is presented. The mode propagation constants and the mode field profiles can be derived by an improved Fourier series method, which is of very simple form, and is always suitable for all the arrays of arbitrary profiles, any depth, and any permittivity. The dispersion equation is expressed by using the generalized reflection matrices for space harmonic waves. The validity of the proposed method has been confirmed by comparison with other methods. Numerical examples of the dispersion characteristics and field distributions are presented for the lowest TE and TM modes of several waveguides in different structures. This method can analyze not only the propagation properties of waveguides, but also their loss natures.

Electromagnetic scattering from two-dimensional photonic crystals with two-dimensionally periodic defects is analyzed using a model of multilayered periodic arrays of parallel circular cylinders. The reflectance of the photonic crystals of finite thickness, which are free-standing or embedded in a dielectric slab, is obtained in terms of the lattice-sums, the T-matrix of a circular cylinder, and the generalized reflection matrix for a layered system. Numerical examples demonstrate that the refection and transmission bands of the crystals are reformed by introducing the periodic defects and their band natures are very sensitive to the polarization of excitation and the relative position of the defect element within a unit cell.

A rigorous and simple method of analyzing scattering and absorbing characteristics of multilayered gratings embedded in a dielectric slab has been proposed. The method combines a generalized scattering matrix with a lattice sums matrix and a T-matrix of an isolated single cylinder instead of the aggregate T-matrix. The validity of the present method has been confirmed by several numerical experiments and comparisons with other published results. Numerical examples show that the absorbing characteristics become very complex and are not linear with the decreasing of cylinders’ conductivity, when the arrays are stacked to a multilayered structure and are embedded in a dielectric slab.

Leaky characteristics of dielectric ridge guide with triangular and trapezoidal cross section are analyzed by a method that combines the mode matching procedure with the staircase approximation and multimode microwave network theory. Our emphasis in this paper is on the parametric effects of cross section profile on leakage and propagation properties of the ridge guide. Some numeral results with their explanations are given for practical reference.

Loss and dispersion characteristics of groove guide are two practically important factors in the design for millimeter wave system consisting of groove guide. In this paper, a new method is presented for analyzing loss and dispersion characteristics of the groove guides with arbitrary groove cross-sections. The method is based on the combination of an equivalent active transmission line equation and the staircase approximation. Numerical results of dispersion and attenuation properties for some groove guides with different groove profiles are given. The effectiveness and practicality of the present analysis are confirmed by the data given in the literature.

A very efficient and simple formulation for analyzing 2D photonic crystals with periodic defects is presented. This method is a combination of lattice sums' matrices and a T-matrix of an isolated cylinder. The numerical examples show the convergence is very fast and the computing accuracy is very high. The scattering properties by three kinds of photonic crystals with periodic defects are investigated, and the propagating nature of a coupled-cavity waveguide are discussed. The validity and usefulness of this formulation is confirmed by the numerical experiments. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 256–261, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21140

is shown in Figure 12. Again, it is found that the error sharply increases when the segments with both large size and large radius are used. CONCLUSION This paper has investigated the accuracy of a wire-grid model using MoM computation. The mixed-potential electric-field integral equation (MPIE) is formulated to analyze electromagnetic scattering of the PEC bodies with the wire-grid model, where the triangular basis function and the sinusoidal basis function used in NEC2 are implemented, respectively. The accuracy of the model is explored via error evaluation of the calculated near-zone scattering electric field in the analysis of the sphere and plate scattering, where the error function takes the error from the magnitude, phase, and polarization of the calculated fields into account. The results indicate that the wire-grid model in combination with the MoM algorithm with the triangular basis function can accurately analyze electromagnetic problems. This model was optimized and the minimum error was reached when the coefficient of the radius was about 0.9, regardless of the size of the segments. The slight change of the radius near the optimal radius hardly influenced the accuracy of this model. However, the wire-grid model combined with the MoM with the sinusoidal basis function used in NEC2 resulted in sufficiently high error such that the EM problem cannot be simulated with it.

A new formula has been proposed for analyzing arbitrary shaped-gratings. The formula is in very simple form, is always suitable for all the gratings of arbitrary profiles, any depth, and any permittivity. The new formula has a character of satisfying rigorously the energy-flux conservation. The effectiveness and its characters have been confirmed by numerical examples. The numerical examples have shown that the new formula is superior to the classical formulas with Fourier series technique in convergence, computing precision, and stability.

A rigorous and simple method for analyzing a rectan- gular-groove guide using a Fourier-transform technique, which takes the field singularities at the edge of the guide into consideration, is presented. The convergence of the solutions is very fast and the ac- curacy improves significantly. It is shown that a mode-propagation constant with five-figure accuracy is obtained by solving a 7 7 matrix equation. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 388 -392, 2004; Published online in Wiley Inter- Science (www.interscience.wiley.com). DOI 10.1002/mop.20148

—Rigorous and fast convergent analysis of a coupler slotted in common wall between two dissimilar rectangular waveguides is described by a mode-matching method combined with Fourier transform technique and consideration of the singularity of electromagnetic field around edges. Comparing with a conventional mode-matching method, the present method has two advantages. One is that it can avoid the usage of the dyadic Green’s function, the other is that it can overcome the relative convergence problem. The consideration of the field singularity has greatly improved the convergence and the calculated accuracy of a solution. This analysis is rigorous and the computer cost is very low.

The Fourier series expansion method is applied to realize an accurate full-vectorial analysis of the problem of a step-index optical fiber connected to an inhomogeneous embedded optical waveguide with rectangular cross section, using periodic boundary conditions in both transverse directions. Using this method, the Maxwell's equations in the waveguide system are reduced to a simple eigenvalue problem of a linear system for the Fourier coefficients. Then the behavior of the transmitted and reflected powers of the guided and radiation modes is clarified for each gap distance and transverse shift between the two waveguides, and compared with the cases of the homogeneous embedded waveguide and different transverse refractive index variations. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 14–18, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11272

A simple and direct method to the problem of two- dimensional electromagnetic scattering from a dielectric cylinder with multiple eccentric cylindrical inclusions is proposed. The method is based on the T-matrix approach. An aggregate T-matrix of the external cylinder for TM-wave and TE-wave excitations is derived in terms of the T-matrices of individual cylinders isolated in the host medium. The backscattering and differential scattering cross- sections of the host cylinder are easily obtained by matrix calculations for the aggregate T-matrix. Numerical investigation is presented for the case where all cylinders have circular cross-sections. Numerical examples for up to three inclusions demonstrate that the scattering characteristics are significantly influenced by the internal asymmetry and inhomogeneity pertinent to the locations and material of the inclusions.

A numerical approach for transition problems in optical waveguides is presented, with the use of the Fourier-series expansion method combined with the absorbing boundary condition by a perfectly matched layer (PML). The optical propagation along a transition is described by a simple matrix algebra. The numerical examples demonstrate that the radiation modes with wider propagation angle are strongly attenuated in the presence of PML, and hence unwanted interference of the boundary-reflected radiation field to the guided wave field is suppressed. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 422–426, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10482

This study reports the design and analysis of a plasmonic sensor based on a heavily doped silicon and metallic grating structure working in the mid-infrared region. The numerical results show that the reflection spectrum of the phosphorous-doped Si grating structure with a dopant concentration of 1 × 2020 has a sharp asymmetric Fano resonance dip, which is strongly dependent on the refractive index change in the surroundings. It yields a sensitivity of 8000 nm/RIU (refractive index unit) and 950 nm/RIU working in the air and water media, respectively, very high values compared with that of existing devices. Moreover, the Fano resonance caused by coupling of the Wood–Rayleigh anomaly and surface plasmon resonances is demonstrated by calculating the magnetic field and Poynting vector patterns. Further, a feasible and easy fabrication process of the sensor featuring high performance is represented.

A fast and efficient method for analyzing an inset dielectric guide is presented using the Fourier transform technique with a modified perfectly matched boundary. In order to deal with an open region, a novel idea, modified perfectly matched boundary condition (PMB), has been proposed. By introducing the modified PMB, the numerical integral has been avoided and the accuracy of the numerical solution has been improved. Moreover, the singular behavior of the fields at metal edge is taken into account in the analysis. The numerical examples are shown that the convergence of the solution is very fast and the relative error less than 0.07% is attained even if only the first term is considered in the field expansion of the guide. The numerical results of the propagation constants for single- and double-layered inset dielectric guides agree well with those of literatures.

The formalism of Rokushima and Yamakita [J. Opt. Soc. Am. 73 (1983) 901] treating the diffraction on planar multilayered 1D anisotropic gratings is extended to the diffraction on anisotropic 2D multilayer grating structures bi-periodic in the plane parallel to the interfaces. In addition to the oblique incidence of plane waves, the case of normal incidence is also treated. The goal of the paper is to provide a basis for the formal analysis of 2D patterned multilayers with natural or induced anisotropies. For example, such structures are of interest in the design of new magnetic and magneto-optic devices. In view of the fact that the anisotropies have often a negligible effect on the energy distribution among diffracted modes with respect to the isotropic case the optical response is alternatively expressed in terms of the ellipsometric parameters of diffracted waves. The present analysis represents generalization of the problem of electromagnetic wave interactions in planar multilayers consisting of layers characterized by a general permittivity tensor treated by Yeh [J. Opt. Soc. Am. 69 (1979) 742].

An optically controlled nonlinear directional coupler (NLDC) to be useful in optical integrated circuits has been analyzed. The optical control is achieved through the interactions between a laser beam and surrounding semiconductor medium. The effect of plasma density, laser beam wavelength and waveguide with on the performance of the coupler including critical power has been thoroughly investigated. A far better performance compared to a simple NLDC has been achieved.

A coupled-mode formulation for an NRD-guide coupler is presented using the singular perturbation technique. The first-order and second-order perturbations are taken into account in the analysis and the coupled-mode equations based on the eigenmodes of each waveguide in isolation are derived. The propagation constants obtained by these equations are compared with those by the exact theory, conventional coupled-mode theory, and improved coupled-mode theory. The numerical results of present formulation are in good agreement with the exact theory and superior to those of the other formulations.

A rigorous and efficient method for characterizing rectangular waveguide junctions is presented. Using the image theory, in this method, the junction problem is transformed into an aperture problem in a uniform rectangular waveguide. The fields in the cavity region expressed by Fourier integrals are matched to those on apertures expanded by the normal modes of arm-waveguides. Then a system of linear equations with very fast convergence is obtained to determine scattering parameters of the junction. The scattering parameters are calculated for right-angle corner bends, symmetric E- and H-plane T-junctions, asymmetric E- and H-plane T-junctions, and asymmetric series E-plane T-junctions, which agree very well with literatures.

A novel coupled-mode formulation for multilayered and multiconductor transmission lines is developed. In this formulation, the solutions to the original multiconductor system are approximated by a linear combination of eigenmode solutions associated with the isolated single conductor line located in an appropriate reference dielectric medium. The reciprocity theorem is used to derive the coupled-mode equations. The coupling coefficients are expressed in terms of the simple overlap integrals between the eigenmode fields and currents of the individual conductor lines. As a basic application, the dispersion characteristics of two identical coupled-microstrip lines are analyzed using the proposed coupled-mode theory. It is shown that the results are in very close agreement with those obtained by the direct Galerkin's moment method over a broad range of weak to strong coupling.

The power-transfer characteristics of a three-waveguide nonlinear directional coupler (NLDC) are investigated with the beam-propagation method based on the finite-difference scheme. The coupler consists of two outer linear waveguides and a center waveguide with a nonlinear Kerrlike medium. It is shown that the three-waveguide NLDC is useful for constructing a power-dependent power divider, a power-dependent power combiner, and an optical logic element. © 1995 John wiley & Sons, Inc.

A new coupled-mode formulation for parallel dielectric waveguides is presented by using a singular perturbation technique. The theory is applied to two parallel, planar dielectric waveguides and the coupled-mode equations that are asymptotically correct are obtained.

An optical coupler composed of three-channel waveguides with different core sizes is analyzed numerically. Dispersion relations and field distributions are presented for the lowest three modes in the coupler. It is shown that the geometric parameter of the coupler can be optimized so as to satisfy the condition for a maximum power transfer efficiency.

A very efficient and simple formulation for analyzing electromagnetic crystal waveguides consisting of magnetized ferrite materials has been described. This method is a combination of lattice sums' matrices, a T-matrix of an isolated cylinder, and generalized scattering matrices. The numerical experiments have confirmed that the convergence is very fast and the computing precision is very high. The guiding modes of several electromagnetic crystal waveguides consisting of magnetized ferrite including hole type and pillar type have been discussed. We also investigated the effect of the internal magnetic field to their propagation constant.

A rigorous approach to modal analysis of a dielectric guide surrounded by two dimensional photonic crystals consisting of a periodic lattice of circular rods is presented using the lattice sums technique combined with the T-matrix approach.