Brewster quasi bound states in the continuum in all-dielectric metasurfaces from single magnetic-dipole resonance meta-atoms

TL;DR

This paper demonstrates how to engineer Brewster quasi-BICs in all-dielectric metasurfaces using single magnetic-dipole meta-atoms, enabling tunable high-Q resonances with potential applications across the electromagnetic spectrum.

Contribution

It introduces a novel scheme to create Brewster quasi-BICs by adjusting magnetic-dipole orientations, simplifying the tuning process in metasurfaces.

Findings

Experimental validation in microwave regime

Achieved high Q-factors at normal incidence

Demonstrated tunability of resonances with magnetic-dipole orientation

Abstract

Bound states in the continuum (BICs) are ubiquitous in many areas of physics, attracting especial interest for their ability to confine waves with infinite lifetimes. Metasurfaces provide a suitable platform to realize them in photonics; such BICs are remarkably robust, being however complex to tune in frequency-wavevector space.Here we propose a scheme to engineer BICs and quasi-BICs with single magnetic-dipole resonance meta-atoms. Upon changing the orientation of the magnetic-dipole resonances, we show that the resulting quasi-BICs,emerging from the symmetry-protected BIC at normal incidence, become transparent for plane-wave illumination exactly at the magnetic-dipole angle, due to a Brewster-like effect. While yielding infinite Q-factors at normalincidence(canonical BIC), these are termed Brewster quasi-BICs since a transmission channel is always allowed that slightly widens resonances at oblique incidences. This is demonstrated experimentally through reflectance measurements in the microwave regime with high-refractive-index mm-disk metasurfaces. Such Brewster-inspired configuration is a plausible scenario to achieve quasi-BICs throughout the electromagnetic spectrum inaccessible through plane-wave illumination at given angles, which could be extrapolated to other kind of waves.