From Fano resonances to bound states in the continuum in dipole arrays at THz frequencies

TL;DR

This paper demonstrates that in THz dipole arrays, Fano resonances evolve into bound states in the continuum (BICs) as the resonators become identical, offering pathways for ultrahigh-Q photonic applications.

Contribution

It provides experimental and theoretical evidence that Fano resonances in dipole arrays can be tuned into BICs, revealing a universal behavior in resonant dipole arrays.

Findings

High-Q Fano resonances observed at THz frequencies.

Fano resonances evolve into BICs with identical resonators.

Universal behavior in arrays of detuned dipoles.

Abstract

Fano resonances and bound states in the continuum (BICs) exhibit a rich phenomenology stemming from, respectively, their asymmetric line shapes and infinite quality factors. Here, we show experimentally and theoretically that rod dimer metasurfaces exhibit narrow (high-Q) Fano resonances at THz frequencies. These resonances evolve continuously into a BIC as the rods in each dimer become identical. We demonstrate analytically that this is a universal behavior occurring in arrays of dimers consisting of detuned resonant dipoles. Fano resonances arise as a result of the interference between broad and narrow lattice dipole resonances, with high-Q factors tending to infinity in the detuning parameter space as the narrow lattice resonance becomes a BIC for identical resonant dipoles. Similar configurations can be straightforwardly envisioned throughout the electromagnetic spectrum leading to ultrahigh-Q Fano resonances and BICs of interest in photonics applications such as sensing and lasing.