Polarized bound state in the continuum and resonances with tunable Q-factor in an anisotropic photonic crystal

TL;DR

This paper demonstrates the existence of tunable high-Q resonances in an anisotropic photonic crystal with a defect layer, supported by analytical and numerical analysis, and proposes an experimental setup using liquid crystals for tuning.

Contribution

It introduces a novel anisotropic defect layer in a photonic crystal to support bound states in the continuum with tunable Q-factors, supported by analytical and numerical methods.

Findings

Bound states in the continuum can be supported in anisotropic photonic crystals.

Tilting the defect layer's axes tunes the resonance Q-factor.

Analytical decay rate matches numerical simulations.

Abstract

We consider a one-dimensional photonic crystal composed of alternating layers of isotropic and anisotropic dielectric materials. Such a system has different band structures for different polarizations of light. We demonstrate that if an anisotropic defect layer is inserted into the structure, the crystal can support an optical bound state in the continuum. By tilting the principle dielectric axes of the defect layer relative to those of the photonic crystal we observe a long-lived resonance in the transmission spectrum. We derive an analytical expression for the decay rate of the resonance that agrees well with the numerical data by the Berreman anisotropic transfer matrix approach. An experimental set-up with a liquid crystal defect layer is proposed to tune the Q-factor of the resonance through applying an external electric field. We speculate that the set-up provides a simple and robust platform for observing optical bound states in the continuum in the form of resonances with tunable Q-factor.