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

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)

High-Q resonances with low azimuthal indices in all-dielectric high-index nanoparticles

Recently, a novel class of high-Q optical resonators based on all-dielectric subwavelength nanoparticles with high refractive index has been proposed [M. V. Rybin, et al, arXiv:1706.02099, 2017]. Here we study a complex spectrum of such nanoscale resonators by means of the resonant-state expansion, treating the problem as a nonHermitian eigenproblem. We show that the high-Q features can be described within the mechanism of external coupling of open channels via the continuum. For ceramic resonators with permittivity = 40, we demonstrate that the quality factor of a trapped mode with a low azimuthal index could reach the value Q = 104.This work has been supported by the Ministry of Education and Science of the Russian Federation (3.1668.2017/4.6) and the Russian Foundation for Basic Research (16-02-00461, 16-37-60064, 17-02-01234)

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

High-Q Supercavity States in High-Index Subwavelength All-Dielectric Resonators

We study strong coupling between eigenmodes of a single subwavelength high-index dielectric resonator and analyse the mode transformation and Fano resonances by varying resonators aspect ratio. We demonstrate that the strong mode coupling is associated with formation of states with giant Q-factors similar 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 confirm our theoretical findings with microwave experiments by using a high-index cylindrical resonator with tunable aspect ratio.This work was financially supported by the Russian Science Foundation (17-12-01581)

Transition from Optical Bound States in the Continuum to Leaky Resonances: Role of Substrate and Roughness

Optical bound states in the continuum (BIC) are localized states with energy lying above the light line and having infinite lifetime. Any losses taking place in real systems result in transformation of the bound states into resonant states with finite lifetime. In this Letter, we analyze properties of BIC in CMOS-compatible one-dimensional photonic structure based on silicon-on-insulator wafer at telecommunication wavelengths, where the absorption of silicon is negligible. We reveal that a high-index substrate could destroy both off-Γ BIC and in-plane symmetry protected at-Γ BIC turning them into resonant states due to leakage into the diffraction channels opening in the substrate. We show how two concurrent loss mechanisms, scattering due to surface roughness and leakage into substrate, contribute to the suppression of the resonance lifetime and specify the condition when one of the mechanisms becomes dominant. The obtained results provide useful guidelines for practical implementations of structures supporting optical bound states in the continuum