Material and radiation losses in structures with bound states in the continuum: Ge2Sb2Te5 as an example

TL;DR

This paper introduces a spectroscopic method to measure material and radiation losses in resonators with bound states in the continuum, exemplified by Ge2Sb2Te5, and demonstrates phase-change switching effects.

Contribution

The study develops a novel spectroscopic approach to quantify losses in BIC-supporting structures using Ge2Sb2Te5, including experimental refractive index measurement and loss characterization.

Findings

Material quality factor Qmat = 46 for amorphous Ge2Sb2Te5

Radiation quality factor Qrad = 608 for cylinder resonator

Radiation quality factor Qrad = 332 for ring resonator

Abstract

The problem of losses in resonators is a key issue in the design and use of modern plasmonic and photonic meta-devices. We propose a spectroscopic method for determining material and radiation losses in structures with bound states in the continuum using as example the phase-change chalcogenide Ge2Sb2Te5. The complex refractive index for the amorphous and crystalline Ge2Sb2Te5 phases was measured experimentally, and the resonance optical properties were calculated for a telecommunication wavelength of 1500 nm. To demonstrate the validity of the method, two types of resonators were considered - a cylinder and a ring which support bound states in the continuum according to the Friedrich - Wintgen mechanism. We have determined the value of the material quality-factor for the amorphous Ge2Sb2Te5 as Qmat = 46 and the values of the radiation quality-factors Qrad = 608 for the cylinder and Qrad = 332 for the ring of a pair of TE0,1,2 and TE0,2,0 modes in the regime of bound states in the continuum. We also demonstrated two mechanisms for efficient switching of the scattering spectra between the amorphous and crystalline phases of Ge2Sb2Te5.