Excitation of a bound state in the continuum via spontaneous symmetry breaking

TL;DR

This paper presents a theory for exciting bound states in the continuum (BICs) in nonlinear systems through spontaneous symmetry breaking, enabling their coupling with bright modes and potential applications in photonics.

Contribution

It introduces a general theory for parametric excitation of BICs via nonlinear symmetry breaking, including threshold analysis and stability considerations.

Findings

Identified the threshold intensity for BIC excitation.

Analyzed stable and unstable solutions depending on pump parameters.

Suggested BICs can be used for frequency comb generation.

Abstract

Bound states in the continuum (BICs) are non-radiating solutions of the wave equation with a spectrum embedded in the continuum of propagating waves of the surrounding space. The complete decoupling of BICs from the radiation continuum makes their excitation impossible from the far-field. Here, we develop a general theory of parametric excitation of BICs in nonlinear systems with Kerr-type nonlinearity via spontaneous symmetry breaking, which results in a coupling of a BIC and a bright mode of the system. Using the temporal coupled-mode theory and perturbation analysis, we found the threshold intensity for excitation of a BIC and study the possible stable and unstable solutions depending on the pump intensity and frequency detuning between the pump and BIC. We revealed that at some parameters of the pump beam, there are no stable solutions and the BIC can be used for frequency comb generation. Our findings can be very promising for use in nonlinear photonic devices and all-optical networks.