Engineering bound states in the continuum at telecom wavelengths with non-Bravais lattices

TL;DR

This paper demonstrates how to engineer bound states in the continuum (BICs) at telecom wavelengths using non-Bravais lattices of dielectric nanoparticles, enabling tunable high-Q resonances for photonic applications.

Contribution

It introduces a method to tune BICs in non-Bravais nanoparticle lattices by detuning size and position, expanding control over optical resonances at telecom wavelengths.

Findings

BICs can be achieved by detuning size or position in non-Bravais lattices.

Surface lattice resonances exhibit a band gap of approximately 41 meV.

Tuning BICs is scalable to various frequencies and applicable to dielectric and plasmonic systems.

Abstract

Various optical phenomena can be induced in periodic arrays of nanoparticles by the radiative coupling of the local dipoles in each particle. Probably the most impressive example is bound states in the continuum (BICs), which are electromagnetic modes with a dispersion inside the light cone but infinite lifetime, i.e., modes that cannot leak to the continuum. Symmetry-protected BICs appear at highly symmetric points in the dispersion of periodic systems. Although the addition of nonequivalent lattice points in a unit cell is an easy and straightforward way of tuning the symmetry, BICs in such particle lattice, i.e., non-Bravais lattice, are less explored among periodic systems. Starting from a periodic square lattice of Si nanodisks, we have prepared three non-Bravais lattices by detuning size and position of the second disk in the unit cell. Diffraction-induced coupling excites magnetic/electric dipoles in each nanodisk, producing two surface lattice resonances at the $\Gamma$ point with a band gap in between. %of $\sim$ 41 meV. The high/low energy branch becomes a BIC for the size/position-detuned array, respectively, while both branches are bright (or leaky) when both size and position are detuned simultaneously. The role of magnetic and electric resonances in dielectric nanoparticles and the change of BIC to bright character of the modes is explained by the two different origins of BICs in the detuned arrays, which is further discussed with the aid of a coupled electric and magnetic dipole model. This study gives a simple way of tuning BICs at telecom wavelengths in non-Bravais lattices, including both plasmonic and dielectric systems, thus scalable to a wide range of frequencies.