Bound states in the continuum and Fano resonances in the Dirac cone spectrum

Abstract

We consider light scattering by two dimensional arrays of high-index dielectric spheres arranged into the triangular lattice. It is demonstrated that in the case a triple degeneracy of resonant leaky modes in the Gamma-point the scattering spectra exhibit a complicated picture of Fano resonances with extremely narrow line-width. The Fano features are explained through coupled mode theory for a Dirac cone spectrum as a signature of optical bound states in the continuum (BIC). It is found that the standing wave in-Gamma BIC induces a ring of off-Gamma BICs due to different scaling laws for real and imaginary parts of the resonant eigenfrequencies in the Dirac cone spectrum. A quantitative theory of the spectra is proposed.

Bound States in the Continuum in Multipolar Lattices

“…One should mention that as we consider the lattice consisting of the multipoles with the rotational symmetry (m = 0), the nodal lines are actually nodal surfaces (cones). Thus, the off-Γ BICs form a closed continues line [36,[49][50][51]. As the band is nearly flat the BICs form nearly circles in the k-space.…”

A Quasi-Bound States in the Continuum Dielectric Metasurface-Based Antenna–Reactor Photocatalyst

“…Metasurfaces have garnered significant attention in recent years as new platforms due to their exceptional thermal conversion, electromagnetic manipulation, and acoustic wave control. − Metamaterials, by definition, provide functionalities not available in natural materials such as negative indices of refraction and extremely high photon densities of states: metasurfaces are designed to possess these properties in a 2D format. Their unique features enable new ways to control and concentrate the flow of electromagnetic (EM) energy, by manipulating effective electric permittivities and magnetic permeabilities, also in the ultrafast regime. − A recent type of metasurface that has shown extraordinary potential is a quasi-Bound States in the Continuum (quasi-BIC) metasurface, which exploits nonradiative optical states for enhancing light–matter interactions. − Quasi-BIC states first appeared in the context of the developing field of quantum mechanics; however, they were later described more generally as arising from the destructive interference between a pair of resonances. This effect occurs when the coupling constants of all radiating waves disappear by appropriate tuning of the geometrical parameters of a system (known as the Friedrich–Wintgen scenario, 1985) .…”

“…Our building block for the quasi-BIC metasurface is a meta-atom with broken in-plane inversion symmetry, chosen for its simplicity and sharp resonant spectral features. , The polarization-sensitive design and geometrical parameters of the meta-atom are shown in Figure a, with the height of the nanopillars set to 180 nm. By shortening the length of one of the nanopillars, the in-plane inversion symmetry of the silicon nitride (Si 3 N 4 )-based structure was broken, enabling the excitation of a sharp quasi-BIC resonance due to distortion of the symmetry-protected BIC (Figure a–c).…”