Новые публикации

Evolution of the resonances of two parallel dielectric cylinders with distance between them

Bulgakov, E. N.; Pichugin, K. N.; Sadreev, A. F. Source: PHYSICAL REVIEW A, 100 (4):10.1103/PhysRevA.100.043806 OCT 8 2019

We study evolution of resonant modes by traversing over the distance between two parallel dielectric cylinders. The processes of mutual scattering of Mie resonant modes by cylinders result in an interaction between the cylinders which lifts a degeneracy of resonances of the isolated cylinders. There are two basic scenarios of evolution. For strong interaction of cylinders resonances bypass the Mie resonances with increase of the distance. That scenario is typical for low-lying resonances (monopole and dipole). For weak interaction of cylinders the resonances are bound around the Mie resonances of isolated cylinders that form the second scenario. Both scenarios demonstrate a significant enhancement of the Q factor compared to the case of an isolated cylinder

Interaction between coaxial dielectric disks enhances the Q factor

Pichugin, K. N.; Sadreev, A. F. Source: JOURNAL OF APPLIED PHYSICS, 126 (9):10.1063/1.5094188 SEP 7 2019

We study the behavior of resonant modes under variation of the distance between two coaxial dielectric disks and show an avoided crossing of resonances because of the interaction between the disks. Owing to coaxial arrangement of disks, the resonant modes are specified by the azimuthal index m=0,1,2,. In the present paper, we consider the case m=0. At a long enough distance, the modes are symmetric and antisymmetric hybridizations of the resonant modes of the isolated disk. With decreasing the distance, the interaction becomes stronger, giving rise to avoided crossings of different resonances of the isolated disk. This in turn enhances the Q factor of the two disks by one order in magnitude compared to the Q factor of the isolated disk.

Multi-channel bound states in the continuum in coaxial cylindrical waveguide

Pilipchuk, A. S.; Pilipchuk, A. A.; Sadreev, A. F. Source: PHYSICA SCRIPTA, 94 (11):10.1088/1402-4896/ab1e9b NOV 2019

Bound states in the continuum (BICs) or embedded trapped modes are widely studied in different physical systems. The studies are restricted to a single open scattering channel. In the present paper we consider BICs embedded into several continua in a cylindrical resonator opened by two coaxially attached cylindrical waveguides with different radii. We demonstrate that engineering the BICs requires a degeneracy of three eigenmodeds of the closed resonator. That is achieved by variation of both the length and the radius of the resonator.

Experimental observation of a symmetry-protected bound state in the continuum in a chain of dielectric disks

Sadrieva, Z. F.; Belyakov, M. A.; Balezin, M. A.; Kapitanova, P. V.; Nenasheva, E. A.; Sadreev, A. F.; Bogdanov, A. A. Source: PHYSICAL REVIEW A, 99 (5):10.1103/PhysRevA.99.053804 MAY 2 2019

The existence of bound states in the continuum (BIC) manifests a general wave phenomenon first predicted in quantum mechanics by John von Neumann and Eugene Wigner [J. von Neumann and E. Wigner, Phys. Z. 30, 465 (1929)]. Today it is being actively explored in photonics, radiophysics, acoustics, and hydrodynamics. We report an experimental observation of an electromagnetic bound state in the radiation continuum in a one-dimensional array of dielectric particles. By measurement of the transmission spectra of the ceramic disk chain at GHz frequencies, we demonstrate how a resonant state in the vicinity of the center of the Brillouin zone turns into a symmetry-protected BIC with increase in the number of the disks. We estimate a number of the disks when the radiation losses become negligible in comparison to material absorption and, therefore, the chain could be considered practically as infinite. The presented analysis is supplemented by measurements of the near fields of the symmetry-protected BIC. All measurements are in a good agreement with the results of the numerical simulation and analytical model based on a tight-binding approximation. The obtained results provide useful guidelines for practical implementations of structures with bound states in the continuum that opens up horizons for the development of optical and radio-frequency metadevices.

High-Q resonant modes in a finite array of dielectric particles

Bulgakov, Evgeny N.; Sadreev, Almas F. Source: PHYSICAL REVIEW A, 99 (3):10.1103/PhysRevA.99.033851 MAR 26 2019

We trace the Q factor of the resonant modes which are limited to bound states in the continuum (BICs) for N= in the finite array of N dielectric spheres and disks. For the symmetry-protected BICs we observe the quadratic dependence of the Q factor on N for high-refractive-index particles, while for low-refractive-index particles there is an interplay between the quadratic and cubic dependencies. The Q factor of accidental BICs grows cubically with N. We show that a plane wave can excite these quasi-BICs for tuning of the angle of incidence.

Bound states with orbital angular momentum in the continuum of cylindrical non-axisymmetric waveguide

Lyapina, A. A.; Pilipchuk, A. S.; Sadreev, A. F. Source: ANNALS OF PHYSICS, 396 56-70; 10.1016/j.aop.2018.05.020 SEP 2018

We consider acoustic wave transmission in a non-axisymmetric waveguide which consists of a cylindrical resonator of radius and length and two cylindrical waveguides of radius whose axes are shifted relative to the axis of the resonator and relative to each other by azimuthal angle . We find multiple bound states in the continuum (trapped modes) with nonzero orbital angular momentum under variation of due to full destructive interference of resonant modes leaking into waveguides. For we find the degenerate bound states in the continuum whose contribution into the scattering wave function is complex and supports giant vortical acoustic intensity spinning inside the resonator.

Goos-Hanchen and Imbert-Fedorov shifts of higher-order Laguerre-Gaussian beams reflected from a dielectric slab

Pichugin, Konstantin N.; Maksimov, Dmitrii N.; Sadreev, Almas F. Source: JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION, 35 (8):1324-1329; 10.1364/JOSAA.35.001324 AUG 1 2018

We consider reflection of the Laguerre–Gaussian light beams by a dielectric slab. In view of the unified operator approach, the higher-order Laguerre–Gaussian beams represent a parametric family with the transverse beam profile given by an arbitrary generating parameter. Relying on the Fourier expansion in the focal plane of the beam, we compute the Goos–Hänchen and the Imbert–Fedorov shifts for light beams with non-zero order and azimuthal index. It is demonstrated that both shifts exhibit resonant behavior as functions of the angle of incidence due to the interference between the waves reflected from the upper and lower interfaces. The centroid shifts strongly depend on the order and azimuthal index of the beam. Most interestingly, it is found that the generating parameter of the higher-order beam families strongly affects the shifts. Thus, reshaping of the incident wavefront with fixed order and azimuthal index changes the linear Goos–Hänchen shift up to one half of the beam radius, both negative and positive.

Fibers based on propagating bound states in the continuum

Bulgakov, Evgeny; Sadreev, Almas Source: PHYSICAL REVIEW B, 98 (8):10.1103/PhysRevB.98.085301 AUG 1 2018

We show that a circular periodic array of silicon dielectric cylinders supports nearly bound states in the continuum (BICs) propagating along the cylinders. These propagating nearly BICs with extremely large-Q factors are surrounded by resonant modes weakly leaking into the radiation continuum. We present leaky zones in the form of dispersion curves for complex eigenfrequencies dependent on propagation constant kz, with the wave vector directed along the cylinders in the vicinity of different types of BICs. Symmetry-protected nearly BICs have the resonant width proportional to squared propagation constant Γk2z; the widths of non-symmetry-protected nearly BICs behave as Γ(kzkc)2, where kc and non-symmetry-protected nearly BICs have the resonant width proportional to k4z. The latter propagating nearly BICs can serve for the transmission of a electromagnetic signal paving a way to a different type of optical fiber. We also demonstrate weakly leaking resonant modes which carry orbital angular momentum.

Scattering plane waves by a dielectric cylinder with periodically modulated permittivity at oblique incidence

Bulgakov, Evgeny N.; Sadreev, Almas F. Source: PHYSICAL REVIEW A, 97 (6):10.1103/PhysRevA.97.063856 JUN 28 2018

For scattering of electromagnetic waves by a dielectric cylinder with periodically modulated permittivity we focus on the vicinity of the frequency of the wave with regard to the eigenfrequencies of bound states in the continuum. Then response of the cylinder becomes extremely sensitive to the angle of incidence and polarization of the plane wave. The cross section of the scattering of electromagnetic waves with mixed polarization undergoes crucial change from the Bragg shape to the Fano shape by rotation of the polarization that paves a way to tuning of Fano resonances by an external source.

Trapped modes in a non-axisymmetric cylindrical waveguide

Lyapina, A. A.; Pilipchuk, A. S.; Sadreev, A. F. JOURNAL OF SOUND AND VIBRATION, 421 48-60; 10.1016/j.jsv.2018.01.056 MAY 12 2018

We consider acoustic wave transmission in a non-axisymmetric waveguide which consists of a cylindrical resonator and two cylindrical waveguides whose axes are shifted relatively to each other by an azimuthal angle . Under variation of the resonator's length and fixed we find bound states in the continuum (trapped modes) due to full destructive interference of resonant modes leaking into the waveguides. Rotation of the waveguide adds complex phases to the coupling strengths of the resonator eigenmodes with the propagating modes of the waveguides tuning Fano resonances to give rise to a wave faucet. Under variation of with fixed resonator's length we find symmetry protected trapped modes. For these trapped modes contribute to the scattering function supporting high vortical acoustic intensity spinning inside the resonator. The waveguide rotation brings an important feature to the scattering and provides an instrument for control of acoustic transmittance and wave trapping.

Optical defect mode with tunable Q factor in a one-dimensional anisotropic photonic crystal

Timofeev, Ivan V.; Maksimov, Dmitrii N.; Sadreev, Almas F. PHYSICAL REVIEW B, 97 (2):10.1103/PhysRevB.97.024306 JAN 22 2018

We consider a one-dimensional photonic crystal composed of alternating layers of isotropic and anisotropic dielectric materials. Such a system has different band structures for different polarizations of light. We demonstrate that if a defect layer is inserted into the structure, the crystal can support a polarized optical defect mode that is a bound state in the continuum (BIC). In the case of an anisotropic defect layer, by tilting the principle dielectric axes of the defect layer relative to those of the photonic crystal the BIC is transformed to a quasi-BIC. We derive an analytical expression for the decay rate of the resonance. An experimental setup with a liquid crystal defect layer is proposed to tune the Q factor of the quasi-BIC through applying an external electric field. We speculate that the setup provides a simple and robust platform for observing optical bound states in the continuum in the form of resonances with tunable Q factor.

Propagating Bloch bound states with orbital angular momentum above the light line in the array of dielectric spheres

Bulgakov, Evgeny N.; Sadreev, Almas F. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION, 34 (6):949-952; Doi: 10.1364/JOSAA.34.000949 JUN 1 2017

We present propagating Bloch bound states in the radiation continuum with orbital angular momentum in an infinite linear periodical array of dielectric spheres. The bound states in the continuum demonstrate a giant Poynting vector spiraling around the array. They can be excited by a plane wave with incident linear polarization with a small tilt relative to the axis of the array.

Tuning of Fano resonances by rotation of continuum: Wave faucet

Sadreev, Almas F.; Pilipchuk, Artem S.; Lyapina, Alina A. EPL, 117 (5): Doi: 10.1209/0295-5075/117/50011 MAR 2017

We consider wave transmission in a non-axisymmetric waveguide which consists of cylindrical resonator and two semi-infinite cylindrical waveguides whose axes are shifted relative to each other by azimuthal angle Δphgr. Although rotation by Δphgr does not change the eigenfrequency spectrum of the resonator, it effectively tunes the Fano resonances and respectively gives rise to an analog of a faucet opening and closing wave flux under rotation. Moreover, under the rotation of the waveguide and variation of the length of resonator, numerous events of the Fano resonance collapse occur to argue for the bound states in the continuum. In the nearest vicinity of the bound states scattering wave function with orbital angular momentum shows phase dislocations with giant vortical acoustic flows around.

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