Propagating bound states in the continuum in dielectric gratings

TL;DR

This paper investigates propagating bound states in dielectric gratings, demonstrating their stability under certain symmetries and identifying geometries that support these states using Fourier modal analysis.

Contribution

It introduces a method to identify geometries supporting stable propagating bound states in dielectric gratings, emphasizing the role of mirror and glide symmetries.

Findings

Bound states exist in specific grating geometries.

Symmetries ensure stability of bound states against parameter variations.

Fourier modal approach effectively identifies leaky zones and bound states.

Abstract

We consider propagating bound states in the continuum in dielectric gratings. The gratings consist of a slab with ridges periodically arranged ether on top or on the both sides of the slab. Based on the Fourier modal approach we recover the leaky zones above the line of light to identify the geometries of the gratings supporting Bloch bound states propagating in the direction perpendicular to the ridges. Most importantly, it is demonstrated that if a two-side grating possesses either mirror or glide symmetry the Bloch bound states are stable to variation of parameters as far as the above symmetries are preserved.