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Graphene, a two-dimensional monatomic layer of carbon material, has demonstrated as a good candidate for applications of ultrafast photodetectors, transistors, transparent electrodes, and biosensors. Recently, many studies have shown that using metallic deep gratings could enhance the absorptance of graphene of 2.3% up to 80% in the near infrared region for applications in photon detection. This paper presents utilizing a nanograting structure, namely, a compound metallic grating could greatly enhance the absorptance of graphene up to 98% and widen its spectral bandwidth to 0.6 μm, which are greater than those of previous work. The study also showed that the absorptance spectrum is insensitive to angles of incidence. Furthermore, the proposed graphene-covered compound grating might bring a lot of benefits for graphene designs-based optical and optoelectronic devices.

A full-wave numerical approach for the analysis of bounded and leaky modes in periodic chain composed of both lossless and lossy 2-D cylindrical inclusions is proposed. An effective method based on the lattice sums technique is adapted to the analysis of modes with complex propagation wavenumbers, thus allowing for the appropriate choice of the spectral determination for each spatial harmonic. Periodic chains of both dielectric and silver nanocylinders are studied and the relevant modal phase and attenuation constants are rigorously calculated in all the different propagation regimes, including bound and radiative regions as well as plasmonic behaviors.

An efficient and rigorous approach to analyze the radiation from an electric dipole placed in 3-D woodpile electromagnetic bandgap material (EBG) structures consisting of layered periodic arrays of circular cylinders is presented. The response in the spectral domain of the woodpile EBGs excited by a dipole source is calculated using one-dimensional lattice sums, the 3-D transition matrix of a circular cylinder, and the generalized reflection and transmission matrices of the layered system. The closed-form expression of the radiated field is rigorously obtained by a finite integral of the spectral response. Comparisons with the far fields calculated using reciprocity both with the present approach and with a fully independent commercial EM software package are presented showing excellent agreement with the proposed method and demonstrating the high computational efficiency of the semianalytical formalism.

Functional post-wall waveguides that are formed by periodically distributed dielectric posts are numerically analyzed. In this preliminary study, the propagation constant and attenuation constant of the dielectric post-wall waveguide is rigorously calculated using our originally developed numerical method. The developed formulation is accurate and numerically very fast. Structural parameters of the dielectric post-wall waveguide are properly chosen in order to achieve the confinement of the field in the guiding region as strong as possible even in case of one-layered dielectric structure. The final goal of our investigations is to realize the functional dielectric post-wall waveguide-based filters, which are expected to have a practical application in THz region, where the metallic (PEC) rods are losing their properties.

CA Jandieri Functional post-wall waveguides and waveguide based compact passive circuits - namely bandpass filters - that are formed by introducing additional metallic or dielectric posts inside the post-wall waveguide are analyzed. Scattering parameters (S-parameters) of the waveguide-based bandpass filters are calculated using the method of images combined with the lattice sums technique. The developed formulation is numerically very fast, hence it can be considered as one of the best-suited approaches for the analysis of multiple scattering in post-wall waveguides and for numerical structural optimization. A breeder genetic algorithm is employed as a global search heuristic in order to track down the optimal geometrical parameters for the introduced posts yielding a bandpass filter characteristic in the desired frequency bands. Comparison with other references validates the correctness and utility of our formalism. Different configurations for the specifications of post-wall waveguide-based bandpass filters are discussed.

Purpose The purpose of this paper is to develop a rigorous self-contained formulation for analyzing electromagnetic scattering by grating of plasmonic nanorods. The authors investigate this structure from the viewpoint of the practical application as a refractive index plasmonic sensor. The presented rigorous formulation is accompanied with a neat implementation providing a high computation efficiency and could be considered as an important tool for designing and optimizing compact sensors. Design/methodology/approach Scattering of an incident plane wave by grating made of a periodic arrangement of metal-coated dielectric nanocylinders on a dielectric slab is rigorously investigated using the recursive algorithm combined with the lattice sums technique. As a dielectric slab, the authors consider glass material, which is widely used in experiments, whereas silver (Ag) is used as a low loss metal suitable to excite plasmon resonances. The main advantage of the developed self-contained formulation is that first the authors extract the reflection and transmission matrices of a single planar array from a separate analysis of the grating and the slab and then obtain the scattering characteristics of the whole structure by using a recursive formula. The method is computationally fast. Findings Dependence of the surface plasmon resonance wavelength on the refractive index of the surrounding medium is carefully investigated. The resonance peaks are red-shifted with respect to an increasing refractive index of surrounding medium showing an almost linear behavior. Near field distributions are analyzed at the resonance wavelengths of the spectral responses. Special attention is paid to the formation of the dual-absorption bands because of the excitation of the localized surface plasmons. The authors give physical insight to the coupling between grating and the glass slab. The authors found that a strong enhancement of the field inside the slab occurs when the scattered wave of the grating is phase-matched to the guided modes supported by the slab. Originality/value In the authors’ formulation, they do not use any approximation and it is rigorous and accurate. The authors use their original method. The method is based on the lattice sums technique and uses the recursive algorithm to calculate the generalized reflection and transmission characteristics by grating. Such fast and accurate method is an effective tool apt for designing and optimizing tailored sensors, for e.g. advanced biomedical applications.

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).

Functional post-wall waveguide (PWW) based passive circuits are formed by introducing specific arrangements of additional posts into the PWW structure. Each arrangement represents a circuit element and consists of a circular array of cylindrical posts periodically distributed on the circumference of the corresponding ring. The circular arrays (i.e. the circuit elements) provide enough degrees of freedom to tailor the spectral response in the framework of an ultra-compact planar filter topology. The PWW circuit is analyzed using image theory in combination with the lattice sums technique yielding a highly-efficient semi-analytical computational scheme that is perfectly suitable for the numerical structural optimization of mm-wave band-pass filters. Along an exemplary study we demonstrate the feasibility of steep skirt selectivity within a device footprint of around 0.75A2.

Modal analysis of infinite periodic chain composed of a square scatterer within the unit cell has been analyzed using the Fourier series expansion method combined with PML. Phase constant and attenuation constant associated with the guiding and leaky modes, respectively have been efficiently calculated.

A rigorous self-contained formulation for analyzing electromagnetic scattering by a grating of plasmonic nanorods (Ag) coupled to a magneto-optical slab is presented. Bi-substituted gadolinium iron garnet is considered as the magneto-optical material. We measured the dielectric permittivity of the iron garnet and utilized the experimental data in our analyses. The method uses the Lattice Sums technique combined with the generalized reflection matrix approach. Using the method, the spectral response in reflectance as well as near-field distributions at resonance wavelengths have been numerical studied. Special attention has been paid to the coupling mechanism between the plasmonic grating and the magneto-optical slab. Physical insight is given to the strong field enhancement inside the magneto-optical material due to coupling with the plasmonic grating. Generalization of the method to the multilayered sandwiched structures, where the metal layer supporting surface plasmons is in contact with a layer possessing magnetically induced anisotropy, is straightforward. Such a combination enables one to achieve a multifold increase in sensitivity when compared with a system having just one nonmagnetic metal layer.

The scattering of TE polarized plane wave by metal-coated dielectric nanocylinders is investigated with a particular emphasis on the enhancement of the near fields. If the wavelength of illumination is properly chosen, two unique near field distributions can be excited through the surface plasmon resonances. The enhanced near fields are localized along the inner or outer interface of the coating metal, being dependent on the wavelengths. It is shown that the scattering cross-section of the nanocylinders is also enhanced when the illuminating field resonates to the surface plasmons of the structures.

Doubled-sided grating structures including two identical single-layered metal gratings separated by a dielectric layer exhibit enhanced optical transmission in the visible region for transverse magnetic polarized light. The maximum transmission (71%) is attributed to a resonance of magnetic polaritons while the minimum one (5%) is found to be caused by surface plasmons between metal and dielectric layers. The transmission resonance of the grating structures is analyzed by varying their geometrical parameters and materials in order to evaluate different potential applications such as tunable optical filters, polarizers, and self-suspended-type plasmonic sensors.

During the last few decades, an extensive research effort has been aimed at studying and developing novel structures based on the photonic crystals composed of the multilayered arrays of periodically distributed circular rods. A photonic crystal with a complete bandgap has been used to localize electromagnetic waves to specific arrays and to guide the propagation of electromagnetic waves along certain directions at restricted frequencies. After this discovery, photonic crystals have inspired great interest because of their novel scientific and engineering applications in guiding devices for controlling the propagation of light. Various analytical and numerical methods have been developed to analyze the photonic crystal waveguides made by removing a row of either air columns or dielectric rods that result in multimode guiding [1, 2]. Recently, scientific attention has been paid to the possibility to efficiently guide electromagnetic waves along a chain formed by periodically distributed scattering elements (a simple single-layered structure) [3, 4]. A simplicity of design and fabrication could be considered as the main advantage of this structure. However, in order to validate its good guiding properties, detailed theoretical and numerical studies are needed. In this regard, we propose a Fourier series expansion method as an efficient method to study the guiding modes and leaky modes of infinite chain of periodically distributed circular rods [5]. In the proposed method a fictitious periodicity in the transverse direction (in the upper and lower regions of the guiding structure) is introduced and the original waveguide is approximated by one period of the periodic waveguide array. The electric and magnetic fields are expanded in a Fourier series and the problem is reduced to the set of linear equations for the Fourier coefficients. Based on the Fourier series expansion method we have numerically calculated the real and imaginary values of the propagation constant associated with the guiding and leaky modes, respectively. The results for the real value of the propagation constant has been compared with the results obtained based on the Lattice Sums technique and the excellent agreement has been observed between these two methods. Several numerical results have proofed the accuracy and validity of the propose formulation. Although in our studies we consider the circular rods to be the pure dielectric (without intrinsic loss), the problem can be easily generalized to study the structure composed of the periodically distributed plasmonic nanocylinders having a complex dielectric permittivity.

Interaction of light with the metallic nanostructures gives rise to various novel effects in photonics and optoelectronics [1]. Research of surface plasmons and their excitation by light is of particular interest in the studies of metamaterials, optical antennas, plasmonic sensors, and plasmonic crystals. The enhanced surface plasmon resonance in noble metallic systems at optical frequencies is expected to be a promising issue for realizing excellent scatterers and absorbers of the visible light. The surface plasmons characterize the unique response in collective motions of electrons on a metal-dielectric interface, which is allowed when the permittivity of the metal is negative for the wavelength of excitation. Recently, much attention has been paid to the light scattering from periodic nanowires coupled to a layered dielectric structure [2] for their applications to optical sensors, imaging, and integrated devices.

Light scattering by a grating made of the Ag nanocylinders onto a dielectric substrate is investigated using an accurate and rigorous formalism based on a recursive algorithm combined with the lattice sums technique. Physical insight is given to the localization of the field along the interfaces of the Ag nanocylinders, to the strong reflected field by the grating and the field enhancement at the surface of the dielectric substrate. The accuracy of the numerical analysis has been validated based on the principle of the energy conservation.

A semi-analytical approach for a periodic planar array formed by a finite number of circular cylinders is presented using a model of layered cylindrical arrays. The method consists in extracting the reflection and transmission matrices of a cylindrically periodic array of circular cylinders and then obtaining the characteristics of layered structures by using a recursive formula.

A semi-analytical approach for analyzing two-dimensional electromagnetic scattering by layered cylindrical arrays of circular rods periodically distributed along concentrically layered circular rings is presented. The method uses the T-matrix of a circular rod in isolation, the reflection and transmission matrices of a cylindrical array expressed in terms of the cylindrical harmonic waves as the basis and the generalized reflection and transmission matrices for a layered cylindrical structure. Using the method, the scattering of plane waves impinging on the cylindrical arrays from the exterior region and the radiation from a line source located inside the cylindrical arrays are numerically investigated. Numerical examples demonstrate that the layered cylindrical arrays are effective for forming a directed beam in the scattered and radiated fields.

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

A semi-analytical approach for analyzing the electromagnetic radiation of a line source in cylindrical electromagnetic bandgap (EBG) structure is presented. The cylindrical structure is composed of circular rods periodically distributed along concentrically layered circular rings. The method uses the T-matrix of a circular rod in isolation, the reflection and transmission matrices of a cylindrical array expressed in terms of the cylindrical waves as the basis, and the generalized reflection and transmission matrices for a layered cylindrical structure. Using the proposed method, the radiated field from a line source placed inside a three-layered cylindrical EBG structure with defects is investigated. The defects are created by removing the particular circular rods from each circular ring. The structure is prominent from the viewpoint of flexible design of the directive antennas. Numerical examples demonstrate that the cylindrical EBG structures are very effective at forming and controlling the directed beam in the radiated fields.

Many software engineering problems can be viewed as a large multidimensional searching problem. This paper presents an enhancement of conventional Genetic Algorithms (GA) for more efficient multi-variable or multi-dimensional searches. The concept relies upon expressing chromosomes as vectors in the required multidimensional frame of reference. Usual GA operators are also defined as vector operators. Comparison with conventional genetic algorithm is made to illustrate its superior performance.

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.

A semi-analytical approach for a specific microstructured fiber, which is formed by layered cylindrical arrays of circular rods in a homogeneous background medium, is presented. The M circular rods are symmetrically distributed on each of the N -concentric circular cylindrical surfaces The method uses the T -matrix of a circular rod in isolation, the reflection and transmission matrices for a cylindrical array, and the generalized reflection and transmission matrices for a cylindrically layered structure.

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.