TE-polarized Waves Research Articles

Численный метод решения задачи о распространении ТЕ-поляризованных волн в многослойном неоднородном волноводе кругового сечения, заполненном метаматериалом

Численный метод решения задачи о распространении ТЕ-поляризованных волн в многослойном неоднородном волноводе кругового сечения, заполненном метаматериалом

Porous Gold Nanolayer Coated Halide Metal Perovskite-Based Broadband Metamaterial Absorber in the Visible and Near-IR Regime

Investigation of the optical response of metal-perovskite configuration-based hyperbolic metamaterials (HMMs) was made toward achieving nearly-perfect absorption in the 300-900 nm wavelength span. More precisely, the HMM structure comprised of periodically arranged gold (Au) and methyl ammonium lead iodide (MAPbI3) nanolayers was taken. The results were derived by exploiting the effective medium theory and transfer matrix method. The proposed HMM was found to exhibit nearly-perfect absorption in a regime of 400-800 nm. In order to achieve better uniformity in the wideband absorption, the structure was also modified by replacing the top Au-nanolayer with a porous Au-nanolayer. The analyses of the modified configuration revealed perfect absorption (>99%) for a wide range of incidence angles corresponding to the TM-polarized incidence excitations in the UV and visible regimes. However, the spectra corresponding to the TE-polarized waves exhibited over 70% absorption only. It is expected that this configuration would find potentials in solar energy harvesting, biosensing and active photonic devices.

Step-wise homogeneous passive coatings for reduction of electromagnetic scattering from cylindrical metallic bodies

The total scattering cross section (or width) of strongly scattering metallic objects can be reduced by using various cloaks, which are complex structures with a limited frequency bandwidth. In many applications, however, dramatic reduction of total scattering is not always required, for instance, when backscattering reduction is the critical parameter. Moreover, the direction of illumination is sometimes known and scattering reduction for other illumination directions is not required. In these scenarios, it is possible to achieve the desired scattering reduction using much simpler manufactured devices. In this paper, we explore possibilities to reduce backscattering and forward scattering from cylindrical bodies for plane-wave illumination from a certain direction. The proposed scattering-reduction device is a shell formed by several sectors of different uniform dielectric materials. We compare the requirements on the material cover which are needed to reduce backscattering and forward scattering widths and outline the corresponding design approaches. We show that all-dielectric and easily realizable structures can effectively reduce total scattering without using active materials or non-uniform anisotropic materials. We develop and numerically test the method for TE-polarized incident waves, since this polarization is more critical for considered applications.

Influence of Graphene Coating of the Elements in a Two-Dimensional Parabolic Mirror Consisting of Parallel Cylinders on Radio Wave Focusing

We model the diffraction of a plane TE-polarized electromagnetic wave by a parabolic structure consisting of N parallel circular cylinders, where N ∼ 50. The problem of diffraction of a plane wave by a cylinder with arbitrary coordinates of its center is solved. The coupling of individual structural elements is not allowed for in the performed calculations. The field behavior in the vicinity of the focus of the considered parabolic antenna is studied for cylinders made of a dielectric, a dielectric with a graphene monolayer, and perfectly conducting cylinders. It is found that a layer of graphene can lead to an almost twofold increase in the maximum amplitude of the field in the focus, which makes the focusing properties of the dielectric antenna rather close to those of an antenna consisting of perfectly conducting cylinders. It is shown that the field amplitude in the focus oscillates strongly as the frequency increases, and the focus itself moves slightly off the center of the reflector system. The size of the focal spot is studied as a function of the incident-field frequency, cylinder radii, and the distance between the individual reflectors. It is shown that the field in the vicinity of the considered structure has certain features, such as slow and fast oscillations of the field amplitude, which occur as the frequency of the incident wave varies.

Copying a Plasmonic Signal From an Optical Signal

We propose a plasmonic signal copier (PSC) composed of a gapped surface plasmon polariton waveguide (SPPW) and an optical waveguide laid across the gap. The interaction between an SPP and an optical signal around the gap edge is demonstrated experimentally and numerically with polarizations of the incident optical wave. A plasmonic signal is invertedly copied from a TE-polarized optical signal incident to the optical waveguide. The symmetrically distributed charges induced from the TE-polarized optical waves on the metal gap edges of input/output SPPWs were determined to be an essential trigger of the copied plasmonic signal. The characteristics of the PSC enable creation of a plasmonic-based circuit system that is compatible with an optical-based circuit system.

Complex Waves in Dielectric Layer

The propagation of monochromatic TE-polarized waves in a partially shielded dielectric layer is considered. The existence of infinitely many complex leaky waves is proved as well as the absence of complex surface waves.

Design of an ultra-broadband near-perfect bilayer grating metamaterial absorber based on genetic algorithm

An ultra-broadband metamaterial absorber, consisting of 2D SiO2-Ti square bilayer grating on SiO2 film and Ti substrate, is proposed and designed by rigorous coupled wave analysis (RCWA) and genetic algorithm (GA) methods. The optimized structure shows an average absorption of 98.3% in the wavelength range of 300 nm to 2100 nm. Moreover, the metamaterial absorber is polarization-independent and also insensitive to incidence angle for both TM- and TE-polarized waves. The physical mechanisms responsible for nearly perfect broadband absorption, including the Wood's anomaly (WA), cavity resonance (CR), surface plasmon polaritons (SPPs) and the resonance of magnetic polaritons (MPs), have been analyzed clearly by finite-difference time-domain (FDTD) method and the inductor-capacitor (LC) circuit model. Overall, the proposed metamaterial absorber is a promising candidate in solar applications.

On the Existence of an Infinite Number of Leaky Complex Waves in a Dielectric Layer

The problem of propagation of TE-polarized electromagnetic waves in a dielectric layer is considered. The waves existing in the structure under study are classified. It is rigorously proved that, in the dielectric layer, there are no surface complex TE waves, but there are infinitely many complex leaky TE waves.

Application of Subspace-Based Distorted-Born Iteration Method in Imaging Biaxial Anisotropic Scatterer

Various natural and artificial materials are anisotropic. The inverse scattering problem of anisotropic scatterers is widely involved in oil detection, nondestructive evaluation of composite materials and microscopic imaging of biological tissue. In this contribution, the two-dimensional inverse scattering problem of biaxial anisotropic scatterers illuminated by the TE-polarized incident wave is investigated. Since the biaxial anisotropic scatterer has different permittivity components along different transverse directions, the problem faced with is more complex than in the scalar TM-polarized case. The subspace-based distorted-Born iteration method (S-DBIM) is employed. Only one regularization term is involved in the inversion, which is proven to be quite robust against noise and flexible to be chosen. Both synthetic and experimental results are given to prove the validity of the proposed method. The results illustrate that as the interaction between the incident electric field and the scatterer induces a directional scattered field, the images constructed appear clear into the strongly scattered directions, but blurred into weakly ones. Overall, S-DBIM is shown to yield super-resolved images for the biaxial anisotropic scatterers, while being quite robust with respect to noise.

Effective Medium Model of Periodic Nanolayered Transparent Shields

An innovative effective medium model based on the transfer matrix method is proposed for the simulation of 1D-periodic subwavelength metal–dielectric laminated structures excited by TM- or TE-polarized plane wave with oblique incidence angles. The homogeneous medium of each period is characterized by TM or TE complex effective permeability and conductivity. The resulting effective single layer (ESL), having the same total thickness of the multilayer laminate, is represented by a transfer matrix given by the product of the transmission matrices of the periods composing the structure. Notice that this model allows the homogenization of n -layer periods, while the effective medium approximation method is formulated for only two-layer periods. The ESL is used to compute the transmission and reflection coefficients and the shielding effectiveness of 1D-periodic nanolayered transparent coatings made by alternating layers of silver, zinc oxide, or titanium dioxide films, in the frequency range from 100 MHz up to 10 THz. The propagating wave performances of the ESL are compared with the ones given by the rigorous multilayer model. Finally, two different screens made of transparent coatings over glass are proposed and analyzed.

Highly birefringent metamaterial structure as a tunable partial polarizer.

We consider a highly anisotropic metamaterial structure, composed of parallel metal nanostripes, and show that a thin layer of the material can be used as a tunable partial polarizer. The transmittance of the structure for TE-polarized waves depends strongly on the incidence angle, while for TM-polarized waves, it stays high and essentially constant. In particular, using the structure, the degree of polarization of a partially polarized or unpolarized light can be tuned by changing the incidence angle. The TE-wave transmittance drops from, c.a., 1 to 0 when the incidence angle increases by 5 deg only, owing to the presence of an unusual higher-order odd-symmetric TM mode that we have revealed in the structure. The tuning can be made smoother by introducing another layer of a similar metal-nanostripe structure on top of the first one. The new design allows the TE-wave transmittance to decrease gradually towards 0 with the incidence angle increasing from 0 to about 30 deg. Our structures serve as an essential optical component for studies involving partially polarized light.

Effective-Medium Characteristics of Reflective Metasurface: A Quasi-One-Port Network Theory

Reflective metasurfaces are utilized as a bridge linking propagating waves and surface waves. However, the effective constitutive parameters (permittivity and permeability) cannot be retrieved by conventional theory without transmission coefficients. In this paper, an innovative method based on a quasi-one-port network model is proposed to robustly retrieve the effective electromagnetic parameters ( $\varepsilon _{\mathrm {eff}}$ , $\mu _{\mathrm {eff}}$ , $n_{\mathrm {eff}}$ , and $z_{\mathrm {eff}}$ ) for reflective metasurfaces with isotropic unit cells. The validity of the method is demonstrated by imping TE-polarized terahertz waves normally and obliquely (10°) on the multiple-layer unit cells. The effective boundary of the multiple-layer cells is determined by minimizing the deviation of the effective refractive indices from 0.1018 to 0.0260 using a genetic algorithm, which increases the consistency of the retrieval results. The sensitivity of the effective constitutive parameters to the accuracy of reflection coefficients and nonzero incident angle $\theta _{i}$ is also discussed. This method is beneficial for the design of reflective metasurfaces or multichannel reflectors, the coupling of spoof space plasmon polaritons, and other applications of anomalous reflection.

On the existence of the nonlinear leaky TE-polarized waves in a metal–dielectric cylindrical waveguide

We consider propagation of leaky waves in the Goubau line (a perfectly conducting cylinder covered by a concentric dielectric layer) filled with nonlinear inhomogeneous medium. The problem is reduced to the analysis of a nonlinear integral equation with a kernel in the form of the Green’s function of an auxiliary boundary value problem on an interval. The existence of propagating nonlinear leaky waves for the chosen nonlinearity (Kerr law) is proved using the method of contraction. Conditions under which a finite number of waves can propagate are obtained and the intervals of localization of the corresponding propagation constants are determined. For the numerical solution, a method based on solving an auxiliary Cauchy problem (a version of the shooting method) is proposed. In numerical experiments, two types of nonlinearities are considered and compared: Kerr nonlinearity and nonlinearity with saturation. New propagation regimes are discovered.

Radiation force and torque on perfect electrically–conducting (PEC) corrugated circular and elliptical cylinders in TE or TM polarized plane progressive waves with arbitrary incidence

In this work, theoretical modeling and numerical computations for the electromagnetic (EM) radiation force and torque (per-length) on perfect electrically conducting (PEC) cylinders of corrugated circular and elliptical geometrical cross-sections are developed and presented. A TE-polarized or TM-polarized plane progressive wave illumination with arbitrary incidence (in the polar plane) is assumed at normal incidence with respect to the axis of the cylindrical particle. The multipole expansion method in cylindrical coordinates is used and the scattering coefficients of the object of arbitrary shape (in 2D) are determined by imposing appropriate boundary conditions and solving numerically a linear system of equations by matrix inversion. Numerical computations are performed for the non-dimensional longitudinal and transverse radiation force functions as well as the axial radiation torque function. Suitable convergence plots confirm the validity of the multipole expansion approach to evaluate the radiation force and torque with no limitation to a particular frequency range (i.e. Rayleigh, Mie or geometrical optics regimes can be considered using the presented formalism). Particular emphases are given on the shape of the particle (i.e., circular or elliptical), its non-dimensional size, the corrugation/waviness characteristic of its surface, the polarization of the incident plane wave field, and the angle of incidence in the polar plane. The numerical predictions show that the longitudinal and transverse components of the radiation force vector are positive regardless of particle shape, size, corrugation properties, polarization and incidence angle [0 ≤ α ≤ 90°], while the axial torque component reverses sign at particular values of these parameters. The results are predominantly relevant in understanding the fundamentals of the optical/EM radiation force and torque theories and possible applications dealing with the interactions of EM waves with elongated tubular particles with circular or noncircular ribbed surfaces in particle manipulation and other areas. The acoustical analogue is also noted, which shows the universal characteristic of the radiation force and torque phenomena.

Propagation of electromagnetic waves through non-uniform dielectric layers

The propagation of TE- and TM-polarized electromagnetic (EM) waves through a dielectric layer with spatial variation of the refractive index is reported in this paper. The relative permittivity of the layer is assumed to be graded along the thickness direction, and its spatial variation is described by a quartic polynomial. The corresponding mode equations are Helmholtz equations with variable coefficients that can be transformed to a triconfluent Heun equation, a local exact solution of which is expressed in terms of triconfluent Heun functions. The solutions cover many particular cases owing to a variability of four optional parameters (coefficients) of the quartic polynomial. The general local solution for a TE-polarized EM wave is employed for the calculation of transmission properties of a periodic one-dimensional photonic crystal using the Floquet theory.

Nonlinear hydrodynamic effects in dense microplasmas interacting with microwaves

Plasmas respond nonlinearly to GHz electromagnetic waves, owing to nonlinear interactions described by the electron momentum equation. These nonlinearities are especially important in high field regions of the plasma as is common in resonant structures that generate plasma discharges with intense localized amplification of the incident field. Most models treat the plasma as a linear Drude material that does not capture the nonlinear polarization terms of a plasma. In this work, we couple the nonlinear electron momentum equation to electromagnetic wave simulation in order to explore the nonlinear behavior. We develop a theoretical foundation via perturbation analysis to guide our expectations from numerical simulation. Through numerical simulation of 2D TE-polarized waves incident on a cylindrical plasma, we show that in the presence of electrical field strengths of ∼MV/m and higher, dense microplasmas have second harmonic power conversion efficiency approaching 10−6 at low pressures. The generated harmonic power is shown to arise mostly from the inertial term in the electron momentum equation. Therefore, a significant portion of the harmonic current density is generated at the surfaces of critical electron density for the fundamental frequency.

Metal-Coated -Cut GaAs Coupled to Tapered Parallel-Plate Waveguide for Cherenkov-Phase-Matched Terahertz Detection: Influence of Crystal Thickness

The influence of crystal thickness of metal-coated -cut GaAs (M-G-M) on Cherenkov-phase-matched terahertz (THz) pulse detection was studied. The M-G-M detectors were utilized in conjunction with a metallic tapered parallel-plate waveguide (TPPWG). Polarization-sensitive measurements were carried out to exemplify the efficacy of GaAs in detecting transverse magnetic (TM)- and transverse electric (TE)-polarized THz waves. The reduction of GaAs’ thickness increased the THz amplitude spectra of the detected TM-polarized THz electro-optic (EO) signal due to enhanced electric field associated with a more tightly-focused and well-concentrated THz radiation on the thinner M-G-M. The higher-fluence THz beam coupled to the thinner M-G-M improved the integrated intensity of the detected THz amplitude spectrum. This trend was not observed for TE-polarized THz waves, wherein the integrated intensities were almost comparable. Nevertheless, good agreement of spectral line shapes of the superposed TM- and TE-polarized THz-EO signals with that of elliptically polarized THz-EO signal demonstrates excellent polarization-resolved detection capabilities of M-G-M via Cherenkov-phase-matched EO sampling technique.

Membrane-type polarization-controlled color filters on silicon substrate

Two polarization-controlled color filters (CF), named CF-I and CF-II, are designed and implemented on an HfO2-on-silicon platform. The devices are with a 200-nm-thick membrane structure realized by etching the silicon substrate beneath the grating patterns away. The spectral responses are characterized by a micro-reflection measurement system. CF-I outputs blue and green colors and CF-II generates yellow and red colors, for normal incident TM- and TE-polarized waves, respectively. Detailed results and analyses on them are also provided both theoretically and experimentally. Particularly, the achieved membrane-type color filters have the potential of being transferred from the silicon substrate to other foreign platforms by breaking off the support beams mechanically, and thus may be applied in several fields such as image sensors, display elements, and even wearable devices.

A Tunable Polarization-Dependent Terahertz Metamaterial Absorber Based on Liquid Crystal

In this paper, a tunable polarization-dependent terahertz (THz) metamaterial absorber based on liquid crystal (LC) is presented. The measurement results show that absorption peak is at 239.5 GHz for a TE-polarized wave and 306.6 GHz for a TM-polarized wave, without exerting the bias voltage on the LC layer. An increase in bias voltage affects the orientation of LC molecules and causes redshifted resonant frequencies. By adjusting the bias voltage from 0 to 10 V, frequency tunabilities of 4.7% and 4.1% for TE- and TM-polarized waves, respectively, were experimentally demonstrated. Surface current and power loss distribution was analyzed to explain the physical mechanism of the absorber, while the absorption dependence on geometrical parameters and incident angles was also studied in detail. According to the obtained results, the proposed absorber is shown here to be capable of achieving tunable polarization-dependent absorption, and to have potential application in terahertz polarization imaging, terahertz sensing, and polarization multiplexing.

Engineered Metasurface of Gold Funnels for Terahertz Wave Filtering

Surface plasmon polariton (SPP) excitation of the coupled light at small contact area of chromium pillars as the interface of metastructured gold funnel layer and silica medium can be enhanced locally in the gold meta-funnel-structured filter. In the present investigation, the filter is comprised of three layers, namely gold meta-funnels, nano-sized chromium pillars, and silica as the substrate. The incoming infrared (IR) waves, coupled with the excited plasmons at the first and second layers, form an excitation, known as deformed plasmon polariton. Asymmetric distribution of localized SPPs takes place owing to the inherent converging plasmonic feature of the gold funnel structure. The formation of reflection peaks with different magnitudes at different incidence angles of the polarized wave in the spectral characteristics makes the structure prominent for filtering the IR waves. Moreover, the gold meta-funnel-structured filter possesses the additional feature of distinguishing the type of polarized incidence wave. It was found that the transmission remains maximum corresponding to the normal incidence of the TE-polarized waves, whereas the TM-polarized waves over the same wavelength range are almost blocked for any value of incidence angle. The existence of transmission peaks corresponding to the TE waves demonstrates another application of this device as metastructured polarizer filter.