# Bound States in the Continuum and Fano Resonances in the Dirac Cone Spectrum

## TL;DR

This paper investigates how bound states in the continuum (BIC) and Fano resonances manifest in the scattering spectra of high-index dielectric spheres arranged in a triangular lattice, revealing complex spectral features linked to Dirac cone physics.

## Contribution

It introduces a coupled mode theory framework to explain Fano resonances and BICs in a Dirac cone spectrum within a 2D dielectric array, highlighting new spectral phenomena.

## Key findings

- Observation of extremely narrow Fano resonances at triple degeneracy points.
- Identification of ring of off-Gamma BICs induced by in-Gamma BICs.
- Quantitative spectral theory for BICs and Fano resonances in Dirac cone systems.

## 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 Fan 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.