High-Q transparency band in all-dielectric metasurfaces induced by a quasi bound state in the continuum

TL;DR

This paper demonstrates how to induce ultra-narrow transparency bands in all-dielectric metasurfaces by exploiting quasi-bound states in the continuum, with theoretical analysis and microwave experiments confirming the phenomenon.

Contribution

It introduces a method to engineer high-Q transparency bands in dielectric metasurfaces by tuning array periodicity to overlap BICs with magnetic dipole resonances, supported by analytical and experimental validation.

Findings

Diverging Q-factors near BIC conditions lead to narrow transparency bands.

Analytical coupled dipole model accurately predicts the transparency phenomena.

Microwave experiments confirm the theoretical predictions.

Abstract

Bound states in the continuum (BICs) emerge throughout Physics as leaky/resonant modes that remain however highly localized. They have attracted much attention in Optics and Photonics, and especially in metasurfaces, i.e. planar arrays of sub-wavelength meta-atoms. One of their most outstanding feature is the arbitrarily large Q-factors they induce upon approaching the BIC condition, which we exploit here to achieve a narrow transparency band. We first show how to shift a canonical BIC in an all-dielectric metasurface, consisting of high-refractive disks exhibiting in- and out-of-plane magnetic dipole (MD) resonances, by tuning the periodicity of the array. By means of our coupled electric/magnetic dipole formulation, we show analytically that when the quasi-BIC overlaps with the broad (in-plane MD) resonance, a full transparency band emerges with diverging Q-factor upon approaching the BIC condition in parameter space. Finally, our experimental measurements in the microwave regime with a large array of high-refractive-index disks confirm the theoretical predictions. Our results reveal a simple mechanism to engineer an ultra-narrow BIC-induced transparency band that could be exploited throughout the electromagnetic spectrum with obvious applications in filtering and sensing.