19 research outputs found
Multipolar origin of bound states in the continuum
Metasurfaces based on resonant subwavelength photonic structures enable novel
ways of wavefront control and light focusing, underpinning a new generation of
flat-optics devices. Recently emerged all-dielectric metasurfaces exhibit
high-quality resonances underpinned by the physics of bound states in the
continuum that drives many interesting concepts in photonics. Here we suggest a
novel approach to explain the physics of bound photonic states embedded into
the radiation continuum. We study dielectric metasurfaces composed of planar
periodic arrays of Mie-resonant nanoparticles ("meta-atoms") which support both
symmetry protected and accidental bound states in the continuum and employ the
multipole decomposition approach to reveal the physical mechanism of the
formation of such nonradiating states in terms of multipolar modes generated by
isolated meta-atoms. Based on the symmetry of the vector spherical harmonics,
we identify the conditions for the existence of bound states in the continuum
originating from the symmetries of both the lattice and the unit cell. Using
this formalism we predict that metasurfaces with strongly suppressed spatial
dispersion can support the bound states in the continuum with the wavevectors
forming a line in the reciprocal space. Our results provide a new way of
designing high-quality resonant photonic systems based on the physics of bound
states in the continuum.Comment: 13 pages, 7 figures, 2 table
Light-matter interaction between photonic bound states in the continuum and bright excitons in transition metal dichalcogenides
Being motivated by recent achievements in the rapidly developing fields of optical bound states in the continuum (BICs) and excitons in monolayers of transition metal dichalcogenides, we analyze strong coupling between BICs in Ta2O5 periodic photonic structures and excitons in WSe2 monolayers. We demonstrate that giant radiative lifetime of BICs allow to engineer the exciton-polariton lifetime enhancing it three orders of magnitude compared to a bare exciton.The work has been supported by the Ministry of Education and Science of the Russian Federation
(3.1668.2017/4.6), the Russian Foundation for Basic Research (16-37-60064) and the President
of Russian Federation (Grant MK-403.2018.2)
Strong coupling between excitons in transition metal dichalcogenides and optical bound states in the continuum
Being motivated by recent achievements in the rapidly developing fields of optical bound states in the continuum (BICs) and excitons in monolayers of transition metal dichalcogenides, we analyze strong coupling between BICs in Ta 2 O 5 periodic photonic structures and excitons in WSe 2 monolayers. We demonstrate that giant radiative lifetime of BICs allows to engineer the exciton-polariton lifetime enhancing it three orders of magnitude compared to a bare exciton. We show that maximal lifetime of hybrid light-matter state can be achieved at any point of k-space by shaping the geometry of the photonic structure.This work was supported by the Russian Foundation for Basic Research (16-37-60064, 17-02-
01234), the Ministry of Education and Science of the Russian Federation (3.1668.2017/4.6), the
President of Rus- sian Federation (MK-403.2018.2
Engineering of high- states via collective mode coupling in chains of Mie resonators
Efficient trapping of light in nanostructures is essential for the
development of optical devices that are based on the interaction between light
and matter. In this work, we show theoretically and experimentally that
one-dimensional arrays of subwavelength dielectric Mie-resonant particles can
support collective resonances with increased -factors. We demonstrate that
the increase of the -factor can be explained by interaction between the
collective electric and magnetic dipole modes of the chain resulting in
appearance of the inflection point at the band edge. The considered effect is
studied experimentally in the chain of high-index ceramic cylinders in the
microwave spectral range.Comment: 11 pages, 8 figure
Bound states in the continuum and Fano resonances in the strong mode coupling regime
The study of resonant dielectric nanostructures with a high refractive index is a new research direction in the nanoscale optics and metamaterial-inspired nanophotonics. Because of the unique optically induced electric and magnetic Mie resonances, high-index nanoscale structures are expected to complement or even replace different plasmonic components in a range of potential applications. We study a strong coupling between modes of a single subwavelength high-index dielectric resonator and analyze the mode transformation and Fano resonances when the resonator’s aspect ratio varies. We demonstrate that strong mode coupling results in resonances with high-quality factors, which are related to the physics of bound states in the continuum when the radiative losses are almost suppressed due to the Friedrich–Wintgen scenario of destructive interference. We explain the physics of these states in terms of multipole decomposition, and show that their appearance is accompanied by a drastic change in the far-field radiation pattern. We reveal a fundamental link between the formation of the high-quality resonances and peculiarities of the Fano parameter in the scattering cross-section spectra. Our theoretical findings are confirmed by microwave experiments for the scattering of high-index cylindrical resonators with a tunable aspect ratio. The proposed mechanism of the strong mode coupling in single subwavelength high-index resonators accompanied by resonances with high-quality factors helps to extend substantially functionalities of all-dielectric nanophotonics, which opens horizons for active and passive nanoscale metadevices.The numerical calculations were performed with
support from the Ministry of Education and Science of
the Russian Federation (Project 3.1500.2017/4.6) and the
Australian Research Council. The experimental study of the cylinder SCS in the microwave frequency range was supported by
the Russian Science Foundation (17-79-20379). The analytical
calculations with resonant-state expansion method were performed with support from the Russian Science Foundation
(17-12-01581). A. A. B., K. L. K. and Z. F. S. acknowledge
support from the Foundation for the Advancement of
Theoretical Physics and Mathematics “BASIS” (Russia)
High-Q Supercavity Modes in Subwavelength Dielectric Resonators
Recent progress in nanoscale optical physics is associated with the development of a new branch of nanophotonics exploring strong Mie resonances in dielectric nanoparticles with a high refractive index. The high-index resonant dielectric nanostructures form building blocks for novel photonic metadevices with low losses and advanced functionalities. However, unlike extensively studied cavities in photonic crystals, such dielectric resonators demonstrate low quality factors (Q factors). Here, we uncover a novel mechanism for achieving giant Q factors of subwavelength nanoscale resonators by realizing the regime of bound states in the continuum. In contrast to the previously suggested multilayer structures with zero permittivity, we reveal strong mode coupling and Fano resonances in homogeneous high-index dielectric finite-length nanorods resulting in high-Q factors at the nanoscale. Thus, high-index dielectric resonators represent the simplest example of nanophotonic supercavities, expanding substantially the range of applications of all-dielectric resonant nanophotonics and meta-optics.Theoretical studies have been supported by the Ministry
of Education and Science of the Russian Federation
(3.1500.2017/4.6), the Russian Foundation for Basic
Research (16-02-00461), and the Australian Research
Council. Simulations of complex eigenmodes have
been supported by the Russian Science Foundation
(17-12-01581)
Bound states in the continuum in photonic structures
Bound states in the continuum provide a remarkable example of how a simple
problem solved about a century ago in quantum mechanics can drive the research
on a whole spectrum of resonant phenomena in wave physics. Due to their huge
radiative lifetime, bound states in the continuum have found multiple
applications in various areas of physics devoted to wave processes, including
hydrodynamics, atomic physics, and acoustics. In this review paper, we present
a comprehensive description of bound states in the continuum and related
effects, focusing mainly on photonic dielectric structures. We review the
history of this area, basic physical mechanisms in the formation of bound
states in the continuum, and specific examples of structures supporting such
states. We also discuss their possible applications in optics, photonics, and
radiophysics.Comment: 80 pages, 21 figure
Strong Mode Coupling and High-Q Supercavity Modes in Subwavelength Dielectric Resonators
We reveal that isolated subwavelength dielectric resonators support states with giant Q-factors similar to bound states in the continuum formed via destructive interference between strongly coupled eigenmodes and characterized by singularities of the Fano parameters