Full-wave Calculations Research Articles

First-Principles Study: The Optoelectronic Properties of the Wurtzite Alloy InGaN Based Solar Cells, within Modified Becke-Johnson (mBJ) Exchange Potential

Numerical simulation based on Full Potential-Linerazed Augmented Plane Wave calculations (FP-LAPW) is implemented in WIEN2K code to study the fundamental structural and optoelectronic properties of the Wurtzite ternary alloy structure InxGa1-xN (x = 0.125, 0.375, 0.625 and 0.875) matched on GaN substrate using a 16-atom supercell. The generalized gradient approximation of Wu and Cohen, the standard local density approach, and the Tran-Blaha modified Becke–Johnson potential were applied to improve the band structure and optical properties of the concerning compounds. Whenever conceivable, we compare the obtained results by experiments and computations performed with diverse computational schemes. In those alloys, the essential points in the optical spectra display the passage of electrons from the valance band to the unoccupied states in the conduction band. The results lead that Becke–Johnson potential will be a promising potential for the bandgaps engineering of III-V compounds which supplied that those materials had crucial absorption coefficients that lead to the application for optoelectronics components, especially solar cells.

Microwave metamaterial microstrip line with enhanced refractive index and its application to compact a Wilkinson power divider

A new microwave metamaterial microstrip line (meta-MSL) is studied by integrating planar mushroom metamaterial structures into a conventional MSL. The meta-MSL is featured with an enhanced effective refractive index than the conventional, extracted from numerical demonstrations using the S-parameter method. The extraordinarily increased refractive index is found to be associated with weak dispersion and low dissipation loss, making the meta-MSL particularly beneficial to compact a microwave Wilkinson power divider (WPD). One metamaterial WPD (meta-WPD) is built using new meta-MSLs. Full-wave numerical calculations reveal that the new meta-WPD has low insertion losses, low reflections, and high isolations between the output ports, working as a good substitute for the conventional WPD. However, the new meta-WPD is exceptional in its small size, which is particularly useful in mobile and wireless applications where compact microwave components are in critical demand.

A novel method for calculating broadband electrical performance of high-speed aircraft radome under thermo-mechanical-electrical coupling

The electrical performance of radomes on high-speed aircraft can be influenced by the thermal and mechanical loads produced during high-speed flight, which can affect the detection distance and accuracy of the guidance system. This paper presents a new method that uses the Finite Difference Time Domain (FDTD) method to calculate the electrical performance of radomes under Thermo-Mechanical-Electrical (TME) coupling. This method can accurately characterize the effects of material dielectric temperature drift and structural deformation on the electrical performance of the radome under flight conditions, enabling high-precision full-wave calculations of the broadband electrical performance of the radome. The method initiates by utilizing a Finite Element Grid Model (FE-GM) of the radome to sequentially acquire the radome’s response temperature field and structural deformation field through thermal and mechanical simulations. Subsequently, spatial mapping techniques are developed to accurately incorporate the dielectric temperature drift and structural deformation of the radome into its Yee grid Electromagnetic (EM) simulation model. A verification case was designed to test the proposed method, and the results confirmed its high computational accuracy. Additionally, the effectiveness and necessity of the method were further demonstrated by analyzing the electrical performance of a fused silica ceramic radome used on a high-speed aircraft.

Coupled mode theory for plasmonic couplers

Photonic integrated circuits play an increasingly important role in several emerging technologies. Their functionality arises from a combination of integrated components, e.g., couplers, splitters, polarization rotators, and wavelength selective filters. Efficient and accurate simulation of these components is crucial for circuit design and optimization. In dielectric systems, design procedures typically rely on coupled-mode theory (CMT) methods, which then guide subsequent refined full-wave calculations. Miniaturization to deep sub-wavelength scales requires the inclusion of lossy plasmonic (metal) components, making optimization more complicated by the interplay between coupling and absorption. Even though CMT is well developed, there is no consensus as to how to rigorously and quantitatively implement it for lossy systems. Here we present an intuitive coupled-mode theory framework for quantitative analysis of dielectric–plasmonic directional and adiabatic couplers, whose large-scale implementation in 3D is prohibitively slow with full-wave methods. This framework relies on adapting existing coupled mode theory approaches by including loss as a perturbation. This approach will be useful in designing dielectric–plasmonic circuits, providing a first reference point for anyone using techniques such as inverse design and deep learning optimization methods.

Scattering matrix for chiral harmonic generation and frequency mixing in nonlinear metasurfaces

We generalize the concept of optical scattering matrix (S-matrix) to characterize harmonic generation and frequency mixing in planar metasurfaces in the limit of undepleted pump approximation. We show that the symmetry properties of such nonlinear S-matrix are determined by the metasurface symmetries at the macroscopic and microscopic scale. We demonstrate that for description of degenerate frequency mixing processes such as optical harmonic generation, the multidimensional S-matrix can be replaced with a reduced two-dimensional S-matrix. We show that for metasurfaces possessing specific point group symmetries, the selection rules determining the transformation of the reduced nonlinear S-matrix are simplified substantially and can be expressed in a compact form. We apply the developed approach to analyze chiral harmonic generation in nonlinear metasurfaces with various symmetries including rotational, inversion, in-plane mirror, and out-of-plane mirror symmetries. For each of those symmetries, we confirm the results of the developed analysis by full-wave numerical calculations. We believe our results provide a new paradigm for engineering nonlinear optical properties of metasurfaces which may find applications in active and nonlinear optics, biosensing, and quantum information processing.

Rigorous full-wave calculation of optical forces on microparticles immersed in vector Pearcey beams.

We present the electromagnetic fields of vector Pearcey beams by employing the vector angular spectrum representation. The beams maintain the inherent properties of autofocusing performance and inversion effect. Based on the generalized Lorenz-Mie theory and Maxwell stress tensor approach, we derive the partial-wave expansion coefficients of arbitrary beams with different polarization and the rigorous solution to evaluate the optical forces. Furthermore, we investigate the optical forces experienced by a microsphere placed in vector Pearcey beams. We study the effects on the longitudinal optical force arising from the particle size, permittivity and permeability. This exotic curved trajectory transport of particles by vector Pearcey beams may find applications in the case where the transport path is partly blocked.

Design of an octagonal-shaped curved sensor antenna for dielectric characterization of liquids

In this study, an octagonal microstrip antenna with a 3D-printed curved-shaped substrate was proposed as a microwave sensor for measuring the dielectric constants of liquids. During the development of the sensor, an octagonal radiating plane was placed on the curved structure by adding an empty semi-cylindrical structure to the planar substrate. The 30 × 30 × 1 mm3 substrate was designed using PLA material with a dielectric constant of 2.41, and the conductive planes were formed using copper tape. The sensor was analyzed using full-wave electromagnetic computation software, and the reflection coefficients were obtained through simulations. Using simulation-obtained reflection coefficient data, the multi-layer perceptron (MLP) was utilized to estimate the dielectric constant. Then, the sensor was manufactured using a 3D printer, and the reflection coefficient measurements of the antenna were performed by filling the curved structure with liquids of varying characteristics. The MLP, which has an APE of 0.20 % for training and 1.52 % for testing, made predictions with an APE of 0.172 % for the simulation of the five materials considered and 1.524 % for the measurement data. It has been observed that the variable dielectric constant results in differences in the resonant frequency and amplitude. The good agreement between simulation and measurement results demonstrates that the proposed sensor can be utilized effectively for measuring the dielectric constants of liquids.

Efficient Computation of Electromagnetic Coupling From Various Types of Antennas Based on Reciprocity Theorem

In the design of complex electronic systems, such as electric vehicles, electromagnetic coupling between a specific component and an antenna should be quantitatively estimated according to the radiated emission (RE) and radiated immunity (RI) standards. However, full-wave electromagnetic simulations of complex systems and antennas in a large space take much time and effort. The decomposition method based on reciprocity and Huygens's principle, which enables the separate analysis of source and victim parts, has been previously proposed for efficient analysis of coupling to a lumped port of the victim antenna. In this article, the decomposition method along with the extraction of an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -parameter block is extended to handle the dominant transverse electric mode in a waveguide antenna. The proposed method removes the difficulty and uncertainty in the modeling process of a commercial waveguide antenna. Also, while applying the decomposition method, Huygens's principle is additionally applied to further reduce the full-wave simulation time of a large empty space. The proposed methods are validated with full-wave electromagnetic simulations, and also experimentally applied to RI estimation. The proposed time-efficient techniques can realize the full-wave computation of RE and RI for real complicated systems and commercial antennas.

In-Band Radar Cross Section Reduction and Enhancement of Gain for a Patch Antenna Array by Using a 1-D Periodic Metasurface Reflector

Abstract: Based on far-field cancellation, a low-profile metasurface (MS) for both x- and y-polarizations is created. This concept uses a 1-D MS instead of a typical MS with a low RCS that uses checkerboard architecture. The proposed MS can be integrated more freely in various applications because it does not require periodicity in two dimensions. A patch antenna array is proposed based on the proposed MS. Under normal incidence, full-wave calculations and measurements demonstrate that integrating the proposed MS reduces the scattering of the antenna array by more than 5 dB over the antenna working frequency band of 10.7 to 12 GHz (11.45 percent). Moreover, when the array radiates, parasitic radiation from the slots of the MS can be activated, increasing the array's boresight gain.

Optical pulling force on nanoparticle clusters with gain due to Fano-like resonance

We demonstrate that, in a simple linearly-polarized plane wave, the optical pulling forces on nanoparticle clusters with gain can be induced by the Fano-like resonance. The numerical results based on the full-wave calculation show that the optical pulling forces can be attributed to the recoil forces for the nanoparticle clusters composed of dipolar nanoparticles with three different configurations. Interestingly, the recoil forces giving rise to optical pulling forces are exactly dominated by the coupling term between the electric and magnetic dipoles excited in the nanoparticle clusters, while other higher-order terms have a negligible contribution. In addition, the optical pulling force can be tailored by modulating the Fano-like resonance via either the particle size or the gain magnitude, offering an alternative freedom degree for optical manipulations of particle clusters.

Threshold conditions for transversal modes of tunable plasmonic nanolasers shaped as single and twin graphene-covered circular quantum wires

We implement the lasing eigenvalue problem (LEP) approach to study the electromagnetic field in the presence of a circular quantum wire (QW) made of a gain material and wrapped in graphene cover and a dimer of two identical graphene-covered QWs, at the threshold of stationary emission. LEP delivers the mode-specific eigenvalue pairs, namely the frequencies and the threshold values of the QW gain index for the plasmon and the wire modes of such nanolasers. In our analysis, we use quantum Kubo formalism for the graphene conductivity and classical Maxwell boundary-value problem for the field functions. The technique involves the resistive boundary conditions, the separation of variables in the local coordinates, and, for the dimer, the addition theorem for the cylindrical functions. For single-wire plasmonic laser, we derive approximate engineering expressions for the lasing frequencies and threshold values of the gain index that complement the full-wave computations. For the dimer, we derive separate determinantal equations for four different classes of symmetry of the lasing supermodes and solve them numerically. Our investigation of the mode frequencies and thresholds versus the graphene and QW parameters shows that plasmon modes or, for the dimer, plasmon supermodes have lower frequencies and thresholds than the wire modes provided that the QW radius is smaller than 10 μm, however in thicker wires they are comparable. Only the plasmon-mode characteristics are well-tunable using the graphene chemical potential. In the dimer, all lasing supermodes form closely located quartets, however, they quickly approach the single-wire case if the inter-wire separation becomes comparable to the radius. These results open a way for building essentially single-mode plasmonic nanolasers and their arrays and suggest certain engineering rules for their design.

Axially Symmetric Source Field Penetration Through a Circular Aperture in a Thin Impedance Plate

The field penetration through a circular aperture in an infinite plane with a nonzero surface impedance excited by an axially symmetric source is analytically investigated. The problem is formulated in terms of an original dual-integral-equation approach and solved through the method of moments in the Hankel spectral domain. The proposed formulation is applied to the calculation of the axial magnetic field when the source is a current loop of finite radius coaxial with the aperture and it is shown that it is possible to separate the contributions of the aperture and of the nonzero impedance plate to the transmitted field. In the case of low frequencies and small apertures, closed-form expressions are also derived. Moreover, the approach is also applied to the case of a perfectly conducting plane giving rise to results that coincide with those recently presented in the literature. Finally, the accuracy of the proposed approach is validated through full-wave calculations.

Madelung Formalism for Electron Spill-Out in Nonlocal Nanoplasmonics.

Current multiscale plasmonic systems pose a modeling challenge. Classical macroscopic theories fail to capture quantum effects in such systems, whereas quantum electrodynamics is impractical given the total size of the experimentally relevant systems, as the number of interactions is too large to be addressed one by one. To tackle the challenge, in this paper we propose to use the Madelung form of the hydrodynamic Drude model, in which the quantum effect electron spill-out is incorporated by describing the metal–dielectric interface using a super-Gaussian function. The results for a two-dimensional nanoplasmonic wedge are correlated to those from nonlocal full-wave numerical calculations based on a linearized hydrodynamic Drude model commonly employed in the literature, showing good qualitative agreement. Additionally, a conformal transformation perspective is provided to explain qualitatively the findings. The methodology described here may be applied to understand, both numerically and theoretically, the modular inclusions of additional quantum effects, such as electron spill-out and nonlocality, that cannot be incorporated seamlessly by using other approaches.

Robustness Analysis of Metasurfaces: Perfect Structures Are Not Always the Best.

Optical metasurfaces rely on subwavelength scale nanostructures, which puts significant constraints on nanofabrication accuracies. These constraints are becoming increasingly important, as metasurfaces are maturing toward real applications that require the fabrication of very large area samples. Here, we focus on beam steering gradient metasurfaces and show that perfect nanofabrication does not necessarily equate with best performances: metasurfaces with missing elements can actually be more efficient than intact metasurfaces. Both plasmonic metasurfaces in reflection and dielectric metasurfaces in transmission are investigated. These findings are substantiated by experiments on purposely misfabricated metasurfaces and full-wave calculations. A very efficient quasi-analytical model is also introduced for the design and simulations of metasurfaces; it agrees very well with full-wave calculations. Our findings indicate that the substrate properties play a key role in the robustness of a metasurface and the smoothness of the approximated phase gradient controls the device efficiency.

Chiral quantum optics in broken-symmetry and topological photonic crystal waveguides

On-chip chiral quantum light-matter interfaces, which support directional interactions, provide a promising platform for efficient spin-photon coupling, nonreciprocal photonic elements, and quantum logic architectures. We present full-wave three-dimensional calculations to quantify the performance of conventional and topological photonic crystal waveguides as chiral emitter-photon interfaces. Specifically, the ability of these structures to support and enhance directional interactions while suppressing subsequent backscattering losses is quantified. Broken symmetry waveguides, such as the nontopological glide-plane waveguide and topological bearded interface waveguide are found to act as efficient chiral interfaces, with the topological waveguide modes allowing for operation at significantly higher Purcell enhancement factors. Finally, although all structures suffer from backscattering losses due to fabrication imperfections, these are found to be smaller at high enhancement factors for the topological waveguide. These reduced losses occur because the optical mode is pushed away from the air-dielectric interfaces where scattering occurs, and not because of any topological protection. These results are important to the understanding of light-matter interactions in topological photonic crystal and design of efficient, on-chip chiral quantum devices.

Utilizing interdigital and supershape geometries for the design of frequency selective surfaces with high angular and polarization stabilities

In this research article, the superformula is used to design the geometry of a frequency selective surface (FSS) unit cell, which resembles the shapes found in nature. The designed shape of unit cell is like petals, which may take different form by varying the values of six parameters. The proposed FSS unit cell has both angular and polarization stabilities of incident wave. For the miniaturization of FSS and decrease of resonance frequency, interdigital capacitances (IDCs) are devised in the FSS structure, which do not deteriorate angular and polarization stabilities. The dimensions of the unit cell are 10 mm × 10 mm and the resonance frequency is specified as 3.5 GHz. An equivalent circuit is derived for the unit cell to evaluate its frequency responses. Its performance as the transmission coefficient is obtained by the equivalent circuit and full-wave simulation. The effects of variations of the geometrical dimensions of the FSS unit cell on its performance are studied. A prototype model of proposed FSS is fabricated and measured. The performance of its equivalent circuit, full-wave computer simulation results and measured data are compared and are shown to be in good agreement.

Plasmonic Nanocavity Induced Coupling and Boost of Dark Excitons in Monolayer WSe2 at Room Temperature.

Spin-forbidden excitons in monolayer transition metal dichalcogenides are optically inactive at room temperature. Probing and manipulating these dark excitons are essential for understanding exciton spin relaxation and valley coherence of these 2D materials. Here, we show that the coupling of dark excitons to a metal nanoparticle-on-mirror cavity leads to plasmon-induced resonant emission with the intensity comparable to that of the spin-allowed bright excitons. A three-state quantum model combined with full-wave electrodynamic calculations reveals that the radiative decay rate of the dark excitons can be enhanced by nearly 6 orders of magnitude through the Purcell effect, therefore compensating its intrinsic nature of weak radiation. Our nanocavity approach provides a useful paradigm for understanding the room-temperature dynamics of dark excitons, potentially paving the road for employing dark exciton in quantum computing and nanoscale optoelectronics.

Эффективное описание влияния рефракции, применимое при интерпретации интерферометрических измерений плотности плазмы в малом токамаке

It was shown that the assumption of straight-line probing beams, which is usually used in reconstructing the plasma density profile from interferometric measurements, leads to unacceptably large errors in the case of a dense plasma. A fast method based on the assumptions of geometric optics is proposed for calculating the interferometric signal. This method takes into account the refraction of the probe wave and can be used in reconstruction of the plasma density profile. The method correctness is confirmed by comparison with the results of full-wave calculations.

Design of frequency selective surface based on Minkowski fractal and interdigital capacitance

In this paper, the Minkowski fractal is used to design the geometry of a frequency selective surface (FSS) unit cell, which resembles the shapes found in nature. The proposed FSS unit cell has both angular and polarization stabilities of incident wave. For the miniaturization of FSS and decrease of resonance frequency, interdigital capacitances (IDCs) are devised in the FSS structure, which do not eliminate angular and polarization stabilities. The dimensions of the unit cell are 5 mm × 5 mm and miniaturized 0.095λ0×0.095λ0. The resonance frequency is specified as 5.75 GHz with 155 MHz bandwidth. An equivalent circuit is derived for the unit cell to evaluate its frequency responses. The effects of variations of the geometrical dimensions of the FSS unit cell on its performance are studied. A prototype model of proposed FSS is fabricated and measured. The performance of its full-wave computer simulation results and measured data are compared and are shown to be in good agreement.

Switchable electromagnetic shield based on seawater

Abstract In this paper, we propose a concept of switchable electromagnetic shield based on seawater. The shield is designed to be a multilayer structure consisting of one chamber layer filled with free space or seawater and three dielectric layers to match with the communication wave signal. At low-power signal for communication purpose, the shield with the chamber layer filled with free space can make the wave signal transparently propagate through. At high-power interference microwave signal impinging onto the shield, the structure with the chamber layer filled with seawater can reflect and absorb the microwave energy. Transparency state for communication signal is designed based on the theory of transmission line, where a key indicator for communication signal transmission is the input impedance of the shield. Shielding state is theoretically calculated under different seawater parameters in a wide frequency band. Both the transparency and shielding states are validated by full-wave numerical calculations, and the results are in good agreement.