Dielectric Cylinder Research Articles

Dual-band all-dielectric chiral photonic crystal

We present an all-dielectric chiral photonic crystal that guides the propagation of electromagnetic waves without backscattering for dual bands. The chiral photonic crystal unit cell is composed of four dielectric cylinders with increasing inner diameter clockwise or anticlockwise, which leads to chirality. It is demonstrated that the proposed chiral photonic crystal can generate dual band gaps in the gigahertz frequency range and has two types of edge states, which is similar to topologically protected edge states. Hence, the interface formed by the proposed 2D chiral photonic crystal can guide the propagation of electromagnetic waves without backscattering, and this complete propagation is immune to defects (position disorder or frequency disorder). To illustrate the applicability of the findings in communication systems, we report a duplexer and a power divider based on the presented all-dielectric chiral photonic crystal.

ELECTROMAGNETIC RADIATION SCATTERING BY LINEAR LOW-PARTICLE AGGREGATES OF FINITE DIELECTRIC CYLINDERS

A numerical simulation of functions of the angular distribution of the scattering intensity for dimers and thrimers of finite dielectric cylinders is made using the formalism of the volume integral equation. The function of the angular distribution of the scattering intensity dependence on the optical and geometric parameters of single finite cylinders and their mutual location is studied. It is shown that the electrodynamic interaction between the cylinders leads to a strong change of the angular distribution of intensity of the radiation scattered by this system in comparison with that for two cylinders without electrodynamic coupling.

DCT-Based Deep Learning of Polarimetric Scattering From a Dielectric Cylinder

Electromagnetic wave interaction with cylindrical structures plays an important role in numerous research fields. For the efficient analysis of electromagnetic scattering by cylindrical components, we previously proposed a deep learning scheme which verified that with increased abstraction capability by deep neural network (DNN), it was able to handle the highly oscillatory scattering patterns to an acceptable degree. In this letter, we extend by focusing on more efficient data structural exploration by eliminating the redundancy inherent in the bistatic scattering pattern. Two schemes based on discrete cosine transform (DCT) compression are identified with increasing complexity from 2-D to 3-D DCT, realizing compression ratios of around 26 and 58, respectively, and correspondingly training is about 11 and 14 times more efficient than our previous work on equivalent graphics processing unit (GPU) requirements. Both compression-based schemes have shown good learning capabilities in terms of accuracy and generalization potential, as demonstrated by their predictions of the complicated polarimetric bistatic scattering patterns within and outside the entire dataset and by the extremely high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R^{2}$ </tex-math></inline-formula> values and low root mean square errors (RMSEs) in the scatter plots. The physical considerations of reciprocity are achieved automatically. It is expected that the proposed compression-based deep learning schemes be useful in the design of future physically based inversion algorithms.

Polarimetric Airborne Radar Sounding as an Approach to Characterizing Subglacial Röthlisberger Channels

Conventional airborne radar sounding techniques are well suited to the detection and characterization of flat-lying, specular subglacial water bodies. However, topographically positive, diffusively scattering Rthlisberger (R-)channels are more difficult to image, while also exerting substantial control on basal friction and ice dynamics. As subglacial R-channels share geometrical similarities with targets of interest in polarimetric ground-penetrating radar studies (i.e., cylindrical pipes), in this study we investigate whether similar concepts can be adapted to detect and characterize R-channels. While closed form analytical solutions exist for the scattering widths of perfect electrically conducting (PEC) and dielectric circular cylinders, the insight they provide for the polarimetric response of half-cylinder R-channels is limited. As such, a series of modeling experiments have been performed to characterize the scattering widths of half cylinders. Our results demonstrate that scattering from subglacial R-channels depends on numerous factors including the polarization and frequency of the incident radar wave, the size of the R-channel, and the relative orientation of the R-channel to a pair of orthogonally oriented, linearly polarized radar antennas. The results imply that patterns in the like-polarized echo powers across the signal bandwidth may be useful in inferring R-channel existence and possibly estimate R-channel size. However, as differences in scattering width are small and decrease with increasing misalignment between the acquisition system antennas and R-channel strike, achieving a high degree of radiometric resolution and stability should be a driving factor in polarimetric radar system design.

Volumetric integro-differential equations in diffraction and eigenvalue problems (r e v i e w)

Volumetric integral and integro-differential equations are considered that describe problems of diffraction by three-dimensional bodies with given macroscopic permittivity and magnetic permeability, as well as problems on free vibrations of such bodies. Similar equations are obtained for waveguide structures: hollow shielded waveguides with dielectric filling, dielectric waveguides (optical beamguides), photonic-crystal waveguides. Dominantly stationary linear electromagnetic problems are considered. Non-stationary and nonlinear problems are mentioned casually. Numerical results are given for oscillations H01delta and H011 of a cylindrical dielectric resonator, for waves of a rectangular dielectric waveguide and a plasmonic waveguide, dispersion in a photonic crystal, and diffraction by a rectangular dielectric cylinder. Keywords: ...

Dual Band Second‐Order Topological Corner States in 2D Valley‐Hall Hexagonal Photonic Crystals

Second‐order topological corner states are of great importance in the field of topological photonics. In particular, for realizing disorder‐immune coherent nanosources based on nonlinear processes one needs multiband topological corner states. This work reports dual band second‐order topological corner states in the structure of valley‐Hall hexagonal photonic crystals. When the ratio between the radii of dielectric cylinders in the unit cells continuously increases, bulk gap opening, appearance of edge states, edge gap opening, and generation of second‐order corner states successively occur in the first and third bandgaps. By changing the structural parameters, the eigenfrequencies of the corner states in both edge gaps can be flexibly adjusted. Compared with square‐lattice valley‐Hall systems, large difference of eigenfrequencies of corner states in dual bandgaps can be obtained with hexagonal photonic crystals, which is the key advantage of the proposed systems for applications in nonlinear coherent generations such as second‐harmonic generation. The numerical results show that the dual band second‐order corner states clearly exhibit robustness against structural defects, significantly distinguished from the defect states. The results presented in this work pave the way toward topologically protected coherent nanosources by nonlinear frequency conversion which are robust against structural disorder or defects.

Effect of a perfectly conducting corner space on the PAFs for an absorptive dielectric circular cylinder

The photophoretic asymmetry factors (PAFs) for an absorptive dielectric circular cylinder, located near a perfectly conducting and totally reflecting corner space are derived and computed. The method used in this analysis relies on the modal expansion method in cylindrical coordinates, the classical method of images, and the translational addition theorem of cylindrical wave functions. Initially, the components of the internal electric field vector are obtained stemming from an analysis of the scattering. Subsequently, the solution is used to integrate to the normalized intensity function over the cylinder’s volume to obtain the longitudinal (L) and transverse (T) PAFs. Both TM- and TE-polarized plane progressive waves with arbitrary incidence (in the polar plane) are considered. Attention is given to varying the dimensionless size parameter of the cylinder, the angle of incidence of the incoming waves, and the dimensionless distance parameters from the corner space. Numerical examples illustrate the analysis and demonstrate the net effect of the totally reflecting corner space on the L- and T-PAFs, where negative, positive, and neutral values have been predicted. The results are relevant in applications related to the emergence of the photophoretic force and torque on an absorptive particle located near surfaces and topics in electromagnetic/optical scattering, particle manipulation and assembly, optically bound matter, light–matter interactions, and photopheresis.

Microwave Studies of Three Chiral Ensembles in Chains of Coupled Dielectric Resonators

Random matrix theory has proven very successful in the understanding of the spectra of chaotic systems. Depending on symmetry with respect to time reversal and the presence or absence of a spin 1/2 there are three ensembles, the Gaussian orthogonal (GOE), Gaussian unitary (GUE), and Gaussian symplectic (GSE) one. With a further particle-antiparticle symmetry the chiral variants of these ensembles, the chiral orthogonal, unitary, and symplectic ensembles (the BDI, AIII, and CII in Cartan's notation) appear which are the main point of interest in this paper. Following a recently published work on chiral random matrix ensembles and their experimental realizations (Rehemanjiang et al., PRL 124, 116801 (2020)), this is achieved by using dielectric cylinders placed between two parallel aluminium plates. These cylinders act as microwave resonators which are used to create tight-binding chains of finite length up to N=5. The different ensembles are achieved by using different types of couplings: For the orthogonal case spatial proximity is used, for the unitary case microwave circulators are used, and for the symplectic case a combination of circulators and cables is used to create the necessary symmetry. In all cases the predicted repulsion behavior between positive and negative eigenvalues for energies close to zero are verified by a comparison with theory taking the finite size of the systems into account. We will show that the difference to the expected universal behavior is given by logarithmic corrections only. These corrections stem from the Hamiltonians having zero entries in their off-diagonal blocks.

Photophoretic asymmetry factors for an absorptive dielectric cylinder near a reflecting planar boundary

The effect of a perfectly reflecting boundary (i.e., planar wall) on the photophoretic asymmetry factors (PAFs) for an absorptive dielectric cylinder is investigated. The expression for the normalized intensity function for the electric field internal to the cylinder is used in conjunction with the multiple scattering theory of waves, the translational addition theorem in cylindrical coordinates, and the method of images to derive analytically and compute numerically the longitudinal (L) and transverse (T) PAFs for the cylinder as well as the internal dimensionless intensity function. Both TM- and TE-polarized plane progressive waves with arbitrary incidence (in the polar plane) are considered. Particular emphases are given on the dimensionless size parameter of the cylinder, the incidence angle of the illuminating field, and the dimensionless distance parameter from the flat surface. The results show that the net effect of the planar wall increases or decreases the amplitudes of the PAFs (thus, the photophoretic force and torque), depending on the particle-wall distance, incidence angle, particle size, and the polarization of the incident field. The results of this analysis are useful in applications related to electromagnetic/optical scattering, particle manipulations, optically bound matter, and photophoresis.

Investigation of directivity of the nanoantenna by its inherent resonant states

We present a quasinormal mode (QNM) approach for modeling the nanoantenna and describe the response of localized dielectric cylinder resonators. The inherent resonant states of the dielectric cylinder nanocavity are investigated for modified and reduced geometrical symmetry. We find some modes contributing mainly to the directivity and have a high-quality factor. The variation of the eigenmodes with cylinder height and substrate refractive index has also been investigated.

Are there bound states in the continuum in a dielectric ring?

Trapping and confining electromagnetic waves is important in both basic research and a variety of applications. For these purposes, various physical mechanisms are exploited including bound states in the continuum, which have been actively investigated recently. Bound states in the continuum have been observed in various objects consisting of both one and a number of dielectric structures. In particular, these photonic states were observed in high-contrast dielectric cylinders in the regime of strong eigenmode coupling, which leads to destructive interference in the far-field zone. In this article, we present the results of a study of bound states in a continuum in a dielectric ring, i.e. cylinder with coaxial air hole. The dependence of the quality factor Q on the normalized diameter of the hole is discussed.

Leaky-Wave Radiation From 2-D Dielectric Lattices Excited by an Embedded Electric Line Source

This article presents an analytical and numerical investigation of the radiation features of an interesting class of electromagnetic bandgap (EBG) structures excited by an electric line source. The radiation from 2-D lattices made with lossless dielectric cylinders, typically optimized by using the Bloch analysis of the corresponding 2-D photonic crystals, is originally investigated in terms of leaky waves. A thorough modal analysis of open waveguides, composed of a finite number of periodic chains of circular dielectric rods, is presented, which shows a multiplicity of bound and leaky modes. Two radiation windows are identified and the relevant directive features are described in terms of properly excited dominant leaky modes. The possible excitation of higher order leaky modes and guided modes has been carefully considered, by also capturing the relevant residue contributions in a nonspectral representation of the excited fields. The final results on radiated fields by realistic truncated structures, obtained by <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ad hoc</i> software as well as full-wave EM simulators, are in excellent agreement with those predicted by the proposed leaky-wave approach.

Ultrawideband Terahertz Absorber with Dielectric Cylinders Loaded Patterned Graphene Structure.

In this paper, we theoretically designed and numerically analyzed an ultrabroadband meta-absorber with near unity absorptivity that works in terahertz spectrum. A wideband meta-absorber composed of bilayer patterned graphene and dielectric cylinder array with high symmetry was proposed. The wideband absorption mechanism benefited from two aspects. The first one was enhanced surface plasmons based on bilayer patterned graphene. And the second one was the coupling of continuous resonant modes within Fabry-Perot cavities to the enhanced surface plasmons in the graphene. An ultrawide bandwidth with absorptivity over were obtained from THz to THz. Simulated results showed that the proposed ultra-wideband absorbing structure also possessed high performance of polarization independence, flexible tunability, large incident angle insensitivity, and compact fabrication.

Resonance frequencies of arbitrarily shaped dielectric cylinders

ABSTRACT We consider eigenvalue problems for dielectric cylindrical scatterers of arbitrary cross with generalized conditions at infinity that enable one to take into account complex eigenvalues. The existence of resonance (scattering) frequencies associated with these eigenvalues is proved. The technique involves the determination of characteristic numbers (CNs) of the Fredholm operator-valued functions of the problems constructed using Green's potentials. Separating principal parts in the form of meromorphic operator pencils, we apply the operator generalization of Rouché's theorem to verify the occurrence of CNs in close proximities of the pencil poles. The results are illustrated in detail using the case of a dielectric cylinder of circular cross section.

Excitation of the Round Infinite Impedance Cylinder by Internal Extrinsic Current: Far-Field Radiation

The paper considers the method of solving the problem of excitation a circular infinite impedance cylinder by means of extrinsic current with an arbitrary spatial orientation. The formal solution of the problem is based on the method of expanding the fields in a complete system of eigenfunctions. Arbitrary distribution of extrinsic currents is taken into account factors excitation. An approximate solution of the problem in the far field is presented. The effect of a dielectric cylinder on the directional diagram of an axial electric dipole is studied.

Optimized design for illusion device by genetic algorithm

The illusion device developed from the scattering cancellation employs very simple homogeneous and isotropic materials, but this device is only valid for electrically small objects. In this paper, we prove that the illusion device optimized by genetic algorithm can be applied to large-scale occasions. For an electrically small target, an optimized core–shell illusion device can achieve better illusion effect than the analytical design based on the scattering cancellation. With the increase of the device size, the ability of the single-layered shell to manipulate the scattering is very limited. For a moderate-size target, two optimized multi-layered examples are presented: one is to make a dielectric cylinder appear as another dielectric target, and the other is to make a conducting cylinder behave like a double-negative-material target. The full-wave simulations are carried out to visualize the similar field distributions of the target and the optimized multi-layered design. This optimized design greatly widens the size application range of the illusion device and can also improve the illusion performance with simple material parameters.

Rough layer scattering filled by elliptical cylinders from the method of moments combined with the characteristic basis function method and the Kirchoff approximation.

In this paper, the electromagnetic field scattered by several 2D scatterers of any shape is calculated rigorously from the boundary integral equations discretized by the method of moments with the point matching method and pulse basis functions. In addition, the resulting linear system is efficiently solved from the domain decomposition method named the characteristic basis function method. To accelerate the computation of the primary basis functions, which requires solving sublinear systems, the Kirchoff approximation is applied for metallic and dielectric objects. The efficiency of the method is tested on several applications met in practice: stack of rough interfaces separating homogeneous media, collection of metallic and dielectric elliptical cylinders, collection of coated elliptical cylinders, and a combination of the previous scenarios.

Analytical theory for three-wave mixing processes in a slightly deformed nanowire

The second order optical response of centrosymmetric materials manifests itself mostly at their surface, being strongly suppressed in their bulk. However, the overall surface response is also suppressed in nanoparticles with a centrosymmetric geometry subjected to homogeneous fields. Nevertheless, nanoparticles with a noncentrosymmetric geometry do exhibit second order optical properties. We develop an analytical theory to investigate the second order optical response of a noncentrosymmetric thin cylinder with a slightly deformed cross-section made up of a centrosymmetric material subjected to two monochromatic fields. We calculate the linear and nonlinear near fields perturbatively using the extent of the deformation away from a circular cross-section as the perturbation parameter. We obtain expressions for the quadratic hyperpolarizabilities in terms of the linear response evaluated at the three frequencies involved. We analyze the spectral features of the nonlinear response functions and explore their resonant structure for a model dielectric cylinder. Furthermore, we evaluate the second order radiated fields, the radiation patterns and efficiency of the different quadratic processes. We obtain a strong competition between electric dipolar, magnetic dipolar and electric quadrupolar contributions even for very small deformations.

The total optical force exerted on black phosphorus coated dielectric cylinder pairs enhanced by localized surface plasmon

Non-invasive manipulation and trapping of nanoparticles, molecules, and cells are essential in a variety of fields. The total optical force and near-field enhancement via localized surface plasmon resonance in the dielectric cylinder pairs coated with black phosphorus (DCPs-BP) are studied analytically and numerically in this work. In the DCPs-BP structure, the total optical force between the two cylinders can reach over 1000 pN/(mW μm). Specifically for the polystyrene particle captured in the center of the DCPs-BP structure, the optical trapping force up to 4000 pN/(mW μm) can be achieved. These results provide new avenues for the successful manipulation and capture of nanoscale particles.

Bound states in the continuum in strong-coupling and weak-coupling regimes under the cylinder – ring transition

Abstract Bound states in the continuum (BIC) have been at the forefront of research in optics and photonics over the past decade. It is of great interest to study the effects associated with quasi-BICs in the simplest structures, where quasi-BICs are very pronounced. An example is a dielectric cylinder, and in a number of works, quasi-BICs have been studied both in single cylinders and in structures composed of cylinders. In this work, we studied the properties of quasi-BICs during the transition from a homogeneous dielectric cylinder in an air environment to a ring with narrow walls while increasing the diameter of the inner air cylinder gradually. The results demonstrate the quasi-BIC crossover from the strong-coupling to the weak-coupling regime, which manifests itself in the transition from the avoided crossing of branches to their intersection with the quasi-BIC being preserved on only one straight branch. In the regime of strong-coupling and quasi-BIC, three waves interfere in the far-field zone: two waves corresponding to the resonant modes of the structure and the wave scattered by the structure as a whole. The validity of the Fano resonance concept is discussed since it describes the interference of only two waves under weak coupling conditions.