arXiv subjects

Vladimir R. Tuz

Publications and source records attributed to Vladimir R. Tuz.

At least 19 recordsLinked to original sources

arXiv2024

Analytical model of metasurfaces comprising meta-atoms with anisotropic polarizabilities

A general analytical approach to the study of electromagnetic resonances of metasurfaces consisting of meta-atoms with anisotropic electric and magnetic dipole polarizabilities and irradiated with obliquely incident light is developed in the direct dipole-moment representation. The presented approach allows us to clearly trace and explain the features of the electromagnetic coupling between electric and magnetic dipole moments in the metasurface and to identify its role in the formation of optical resonances. For these purposes, the dependence of the dipole lattice sums on the angle of illumination is also presented. Expressions for the transmittance and reflectivity corresponding to the specular reflectance are presented with explicit inclusion of the dipole moments of particles in the array, which allows using these expressions for multipole analysis of purely numerical results concerning the optical response of metasurfaces. The developed analytical method is tested to characterize the spectral resonances of dielectric metasurfaces composed of rectangular silicon nanoprisms. In addition, we discuss the relationship and similarity between the results of coupled dipole and coupled dipole-quadrupole methods. Our analytical representation of electromagnetic dipole coupling is an insightful and fast method for the characterization of collective resonances in metasurfaces under illumination at oblique incidence. It could be especially useful for designing planar nanophotonic devices consisting of arbitrary-shaped building blocks and operating under special irradiation conditions.

physics.optics↗

arXiv2023

Transition between radial and toroidal orders in a trimer-based magnetic metasurface

The change in the arrangement of magnetic dipole moments in a magnetic metasurface, due to the influence of an external static magnetic field, is discussed. Each meta-atom of the metasurface is composed of three identical disk-shaped resonators (trimer) made of magnetically saturated ferrite. To provide physical insight, full-wave numerical simulations of the near-fields and transmission characteristics of the metasurface are complemented by the theoretical description based on the multipole decomposition method. With these methods, the study of eigenmodes and scattering conditions of a single magnetic resonator, trimer, and their array forming the metasurface is performed. It is found that the magnetic dipole-based collective hybrid mode of the trimer can be gradually transformed from the radial (pseudomonopole) to azimuthal (toroidal) order and vice versa by varying the bias magnetic field strength. This is because the magnetic dipole moment of each individual disk constituting the trimer undergoes rotation as the bias magnetic field strength changes. This transition between two orders is accompanied by various patterns of localization of the electric field inside the meta-atoms. Due to the unique field configuration of these modes, the proposed metasurface can be considered for designing magnetic field sensors and nonreciprocal devices.

physics.app-ph↗

arXiv2023

Trapped mode control in metasurfaces composed of particles with the form birefringence property

Progress in developing advanced photonic devices relies on introducing new materials, discovered physical principles, and optimal designs when constructing their components. Optical systems operating on the principles of excitation of extremely high-quality factor trapped modes (also known as the bound states in the continuum, BICs) are of great interest since they allow the implementation of laser and sensor devices with outstanding characteristics. In this paper, we discuss how one can utilize the anisotropic properties of novel materials (transition metal dichalcogenides, TMDs), particularly, the bulk molybdenum disulfide (MoS2), to realize the excitation of trapped modes in dielectric metasurfaces. The bulk MoS2 is a thin-film structure in which the light wave behaves the same way as that in the uniaxial anisotropic material with the form birefringence property. Our metasurface is composed of an array of disk-shaped nanoparticles (resonators) made of the MoS2 material under the assumption that the anisotropy axis of MoS2 can be tilted to the rotation axis of the disks. We perform a detailed analysis of eigenwaves and scattering properties of such anisotropic resonators as well as the spectral features of the metasurface revealing dependence of the excitation conditions of the trapped mode on the anisotropy axis orientation of the MoS2 material used.

physics.optics↗

arXiv2022

Trapped-mode excitation in all-dielectric metamaterials with loss and gain

Non-Hermitian photonics based on combining loss and gain media within a single optical system provides a number of approaches to control and generate the flow of light. In this paper, we show that by introducing non-Hermitian perturbation into the system with loss and gain constituents, the high-quality resonances known as trapped modes can be excited without the need to change the symmetry of the unit cell geometry. To demonstrate this idea, we consider a widely used all-dielectric planar metamaterial whose unit cell consists of a pair of rectangular nanoantennas made of ordinal (with loss) and doped (with gain) silicon. Since the quality factor of the trapped-mode resonance can be controlled by changing both spatial symmetry and non-Hermiticity, varying loss and gain allows us to compensate for the influence of asymmetry and restore the quality factor of the localized mode. The results obtained suggest new ways to achieve high-quality resonances in non-Hermitian metamaterials promising for many practical applications in nanophotonics.

physics.optics↗

arXiv2022

Reconfigurable topological states in arrays of bianisotropic particles

Topological photonics promotes a novel approach to resilient light manipulation by exploiting spatio-temporal symmetries of the system and dual symmetry of electromagnetic field. Various prospective device applications pose the need to flexibly control robust field localization associated with topological modes. Here we design a topological array of resonant dielectric meta-atoms with bianisotropic response induced by a spatial symmetry reduction. Mutual orientation of the designed meta-atoms encodes a staggered bianisotropy pattern capable of trapping topological states in a one-dimensional array containing a small number of particles. We show that the topological interface state can be tailored by the rotation of coaxial bianisotropic particles arranged in an equidistant lattice. Our experimental implementation based on ceramic horseshoe-shaped disks demonstrates remarkable reconfigurability of electromagnetic topological states.

physics.app-ph↗

arXiv2021

Superscattering Empowered by Bound States in the Continuum

We uncover a novel mechanism for superscattering of subwavelength resonators closely associated with the physics of bound states in the continuum. We demonstrate that superscattering occurs as a consequence of constructive interference driven by the Friedrich-Wintgen mechanism, and it may exceed the currently established limits for the cross-section of a single open scattering channel, within the channel itself. We develop a non-Hermitian model to describe interfering resonances of quasi-normal modes to show that this effect can only occur for scatterers violating the spherical symmetry, and therefore it cannot be predicted with the classical Mie solutions. Our results reveal unusual physics of non-Hermitian systems having important implications for functional metadevices.

physics.optics↗

arXiv2021

Multimode parity-time and loss-compensation symmetries in coupled waveguides with loss and gain

Loss compensation via inserting gain is of fundamental importance in different branches of photonics, nanoplasmonics, and metamaterial science. This effect has found an impressive implementation in the parity-time symmetric (PT-symmetric) structures possessing balanced distribution of loss and gain. In this work, we generalize this phenomenon to the asymmetric systems demonstrating loss compensation in the coupled multi-mode loss-gain dielectric waveguides of different radii. We show that similar to the PT-symmetric coupled single-mode waveguides of identical radii, the asymmetric systems support the exceptional points called here the loss compensation (LC) thresholds where the frequency spectrum undergoes a transition from complex to real values. Moreover, the LC-symmetry thresholds can be obtained for dissimilar modes excited in the waveguides providing an additional degree of freedom to control the system response. In particular, changing loss and gain of asymmetric coupled waveguides, we observe loss compensation for TM and TE modes as well as for the hybrid HE and EH modes.

physics.optics↗

arXiv2021

Toroidic and antitoroidic orders in hexagonal arrays of dielectric trimers: magnetic group approach

Herein, we investigate the symmetry-protected toroidal dipole resonances and conditions of their excitation in a new type of electromagnetic metamaterials. These metamaterials are all-dielectric planar periodic arrays of dielectric disks disposed on a dielectric substrate. The elementary building blocks of the array are trimers which are distributed in hexagonal unit supercells. The highest geometrical symmetry of the unit supercell is C6v. The analysis is fulfilled by using the representation theory of groups with the application of the magnetic group theory, which is a new approach in solving such problems. We have shown that to get access to the toroidal supermodes of the array, the unit supercell symmetry must be broken twice: firstly, the C3v symmetry of the trimer, and secondly, the C6v symmetry of the unit supercell needs to be reduced. Selection rules for the symmetric and antisymmetric orders of the toroidal dipole moments in the arrays are defined. In particular, we have shown that with the reduction of the unit supercell symmetry to the C2v group, the array exhibits the toroidal dipole resonance with an antitoroidic order. The arrays with the lower Cs symmetry can provide the resonances with both toroidic and antitoroidic orders. It is also shown that these arrays are always polarization sensitive. Full-wave simulations and experiments confirm the theoretical predictions. The suggested metamaterials can provide an enhanced light-matter interaction due to the spatially and temporally confined light in resonant systems with very high quality factors.

physics.optics↗

arXiv2020

Symmetry analysis of trimer-based all-dielectric metasurfaces with toroidal dipole modes

Herein, we discuss the conditions for excitation of symmetry-protected toroidal dipole modes in all-dielectric metasurfaces composed of trimer or twin-trimer clusters of dielectric disks. Such metasurfaces permit enhanced light-matter interaction due to spatially confined light in resonant systems with a high-quality factor. To describe characteristics of toroidal modes existing in the clusters, we use the magnetic dipole moments approximation, group-theoretical methods, group representation theory, symmetry-adapted linear combination method, and circuit theory. To validate the obtained theoretical results, we fulfill both full-wave numerical simulations and microwave experiments. In particular, we have shown that the toroidal dipole mode appears as a quasi-dark state of the trimer. It can be excited in the metasurface by the field of a linearly polarized wave, providing the symmetry of the trimer is properly reduced. In the metasurface, the properties of the toroidal dipole mode are determined primarily by the parameters of a single trimer and are not a consequence of the periodicity of the array. The coupling of the toroidal dipole modes in the twin-trimers can appear in both bonding and anti-bonding fashion resulting in different orders of the net toroidal dipole moment. Due to the unique field configuration of these modes, the proposed metasurfaces can be considered as a platform for efficient light-matter interaction for enhanced absorption, nonlinear switching, and sensing.

physics.app-ph↗

arXiv2020

Loss compensation symmetry of unequally sized dielectric cylinders with gain and loss

A rigorous analytical approach is applied to solve the eigenvalue problem for a pair of circular dielectric cylinders with complex permittivity. This approach relies on field expansion in terms of two sets of orthogonal azimuthal modes, which are coupled due to finite distance between the cylinders. We investigate the ability of a gain-dielectric cylinder operated in the fundamental TM mode to compensate material losses of a larger cylinder operated in the higher-order radial TM mode. To achieve such a loss compensation phenomenon, a simple design strategy is developed. It is shown that this phenomenon can be achieved for a certain distance between the cylinders, which is associated with the exceptional point of the system. For smaller distances, the adverse impact of high-order azimuthal (hybrid) modes are found to be essential. The results obtained are validated against full-wave simulations.

physics.optics↗

arXiv2020

Magnetically induced topological transitions of hyperbolic dispersion in biaxial gyrotropic media

Magnetically induced topological transitions of isofrequency surfaces of bulk waves propagating through an unbounded biaxial gyrotropic medium are studied. The medium is constructed from a two-component superlattice composed of magnetized ferrite and semiconductor layers. To derive the constitutive parameters of the gyrotropic medium, a homogenization procedure from the effective medium theory is applied. The study is carried out in the frequency range near the frequency of ferromagnetic resonance, where the magnetic subsystem possesses the properties of natural hyperbolic dispersion. The topological transitions from an open type-I hyperboloid to several intricate hyperbolic-like forms are demonstrated for the extraordinary waves. We reveal how realistic material losses change the form of isofrequency surface characterizing hyperbolic dispersion. The obtained results broaden our knowledge on the possible topologies of isofrequency surfaces that can appear in gyrotropic media influenced by an external static magnetic field.

cond-mat.mes-hall↗

arXiv2020

Magnetic dipole ordering in resonant dielectric metasurfaces

Artificial magnetism at optical frequencies can be realized in metamaterials composed of periodic arrays of subwavelength elements, also called "meta-atoms". Optically-induced magnetic moments can be arranged in both unstaggered structures, naturally associated with ferromagnetic (FM) order, or staggered structures, linked correspondingly to antiferromagnetic (AFM) order. Here we demonstrate that such magnetic dipole orders of the lattices of meta-atoms can appear in low-symmetry Mie-resonant metasurfaces where each asymmetric dielectric (non-magnetic) meta-atom supports a localized trapped mode. We reveal that these all-dielectric resonant metasurfaces possess not only strong optical magnetic response but also they demonstrate a significant polarization rotation of the propagating electromagnetic waves at both FM and AFM resonances. We confirm these findings experimentally by measuring directly the spectral characteristics of different modes excited in all-dielectric metasurfaces, and mapping near-field patterns of the electromagnetic fields at the microwave frequencies.

physics.class-ph↗

arXiv2019

Superscattering from subwavelength corrugated cylinders

Wave scattering from a cylinder with a tensor impedance surface is investigated based on the Lorentz-Mie theory. A practical example of such a cylinder is a subwavelength metallic rod with helical dielectric-filled corrugations. The investigation is performed with the aim to maximize scattering cross-section by tailoring the surface impedance of cylindrical scatterers. For the normally incident TEz and TMz waves the required surface impedance of a subwavelength cylinder can be produced by longitudinal (axial) and transverse (circumferential) corrugations, respectively. It is shown that such corrugations induce superscattering at multiple frequencies, which can be widely tuned with either or both the size and permittivity of dielectric-filled corrugations. In the microwave band, this effect is demonstrated to be robust to material losses and is validated against the full-wave simulations and experiment. For the TEz waves the enhanced scattering from the cylinder is found to have a broad frequency bandwidth, provided that the relative permittivity of corrugations is low or equal unity. In the latter case, the corrugated cylinder acts as an all-metal superscatterer. For such cylinders the near-field measurements are implemented and provide the first experimental evidence of the superscattering phenomenon for all-metal objects. In addition to multifrequency superscattering, the dielectric-filled corrugations are shown to provide multifrequency cloaking of the cylinder under the incidence of the TMz waves. Simultaneous superscattering and cloaking at multiple frequencies distinguishes corrugated cylinders from other known practicable scatterers for potential applications in antenna designing, sensing, and energy harvesting.

physics.app-ph↗

arXiv2019

Homogeneous enhancement of electric near-field in all-dielectric metasurfaces composed of cluster-based unit cells

In order to construct a dielectric analog of spaser, we study theoretically and experimentally several configurations of cluster-based unit cells for an all-dielectric metasurface characterized by resonant conditions of the trapped mode excitation. Excitation of the trapped mode is realized by either specific displacement of particles in the cluster, or perturbation of the equidistantly spaced particles by off-centered round holes or coaxial-sector notches. It turns out that the latter approach is more advantageous for enhancement of electric near-field with homogeneous distribution in-plane of the structure and its strong localization outside the high-refractive-index dielectric particles. This feature opens prospects for realization of highly desirable subwavelength flat lasing structures based on strong near-field interaction with substances exhibiting pronounced nonlinear characteristics and properties of gain media.

physics.app-ph↗

arXiv2019

Chiral metasurface formed by 3D-printed square helices: A flexible tool to manipulate wave polarization

The transmission of linearly and circularly polarized waves are studied both theoretically and experimentally for chiral metasurfaces formed by arrays of metallic square helices. The helical particles of the metasurfaces are constructed of rectangular bars manufactured by direct three-dimensional printing in solid metal. The transmittance of the metasurface is found to depend critically on the number of bars forming the square helical particles. In the case of an even number of bars, the chiral metasurface exhibits identical co-polarized transmittance of orthogonal linearly polarized waves, which are characterized by a dual-band asymmetric transmission. For an odd number of bars, the metasurface provides the same cross-polarization conversion for any polarization orientation of the incident field and thus serves as a polarization-independent twist polarizer. Finally, the transmittance of this polarizer is investigated with respect to the dimensions of the square helices. The investigated chiral metasurfaces are characterized by strong broadband circular dichroism regardless of the number of bars in the helical particles. The wide variety of transmission properties observed in the metasurfaces makes them particularly attractive for use in polarization conversion and separation devices.

physics.class-ph↗

arXiv2019

Metasurface engineering through bound states in the continuum

Metasurfaces have attracted a lot of attention in recent years due to novel ways they provide for the efficient wavefront control and engineering of the resonant transmission. We discuss an approach allowing effectively control appearance of the sharp Fano resonances in metasurfaces associated with the {\it bound states in the continuum}. We demonstrate that by breaking the symmetry transversely, in the direction perpendicular to a metasurface with a complex unit cell, we can control the number, frequency, and type of high-$Q$ resonances originating from bound states in the continuum. As example, we demonstrate experimentally the metasurfaces with magnetic dipole and toroidal dipole responses governed by the physics of multipolar bound states.

physics.optics↗

arXiv2019

Invisibility and perfect absorption of all-dielectric metasurfaces originated from the transverse Kerker effect

Dielectric metasurfaces perform unique photonics effects and serve as the engine of nowadays light-matter technologies. Here, we suggest theoretically and demonstrate experimentally the realization of a high transparency effect in a novel type of all-dielectric metasurface, where each constituting meta-atom of the lattice presents the so-called transverse Kerker effect. In contrast to Huygens' metasurfaces, both phase and amplitude of the incoming wave remain unperturbed at the resonant frequency and, consequently, our metasurface totally operates in the invisibility regime. We prove experimentally, for the microwave frequency range, that both phase and amplitude of the transmitted wave from the metasurface remain almost unaffected. Finally, we demonstrate both numerically and experimentally and explain theoretically in detail a novel mechanism to achieve perfect absorption of the incident light enabled by the resonant response of the dielectric metasurfaces placed in the vicinity of a conducting substrate. In the subdiffractive limit, we show the aforementioned effects are mainly determined by the optical response of the constituting meta-atoms rather than the collective lattice contributions. With the spectrum scalability, our findings can be incorporated in engineering devices for energy harvesting, nonlinear phenomena and filters applications.

physics.optics↗

arXiv2019

Dual-polarized all-angle cloaking of a dielectric nanowire by helical graphene ribbons

Scattering from a dielectric nanowire coated by helical graphene strips (nanoribbons) is investigated for dual-polarized wave at oblique incidence. In the long-wavelength approximation, the helical strips are treated as a homogeneous layer with averaged tensor conductivity. It is shown that performance of well-known surface cloaks in the form of graphene monolayer, axial and azimuthal graphene strips can be deteriorated in a wide range of incidence angles. To overcome this problem, helical graphene strips are proposed as an advanced metasurface for dual-polarized all-angle cloaking of dielectric nanowire in the terahertz band. It is found that such metasurface suppresses scattering from nanowire more effectively as compared to graphene monolayer, regardless of the angle of wave incidence. Moreover, dual-polarized all-angle cloaking of dielectric nanowire can be broadly tuned in frequency with parameters of helical graphene strips.

physics.optics↗