BIC in waveguide arrays within a symmetry classification scheme

TL;DR

This paper investigates bound states in the continuum (BIC) in a photonic waveguide array, classifying eigenmodes by symmetry, and analyzing spectral properties and Fano resonances using coupled mode theory.

Contribution

It introduces a symmetry classification scheme for BICs in waveguide arrays and links spectral features to eigenmode symmetries and interference effects.

Findings

Established conditions for BIC existence based on symmetry

Linked Fano resonances to interference between eigenmodes

Analyzed spectral properties using Weierstrass factorization

Abstract

We study a photonic analog of a modified Fano-Anderson model -- a waveguide array with two additional waveguides and by using the coupled mode theory we calculate its spectral and scattering properties. We classify eigenomodes according to vertical symmetry of the structure given by self-coupling coefficients of the additional waveguides and establish the conditions for BIC existence. We use the Weierstrass factorization theorem and interpret the scattering spectra of the systems with broken symmetry in terms of the eigenmodes. The Fano resonance related with excitation of quasi-BIC is explained as arising from the interference between this mode and another leaky mode.