Optical Spectral Singularities and Coherent Perfect Absorption in a Two-Layer Spherical Medium

TL;DR

This paper investigates optical spectral singularities and coherent perfect absorption in a two-layer spherical medium, revealing how coatings influence the spectral singularity conditions and their spectral distribution.

Contribution

It analyzes the effects of coating layers on spectral singularities in spherical media, showing reduced radius thresholds and increased spectral singularity clusters or counts.

Findings

Coating reduces the minimum radius for spectral singularities.

Coating creates clusters of spectral singularities with spectral gaps.

Coating doubles the number of spectral singularities.

Abstract

An optical spectral singularity is a zero-width resonance that corresponds to lasing at threshold gain. Its time-reversal causes coherent perfect absorption of light and forms the theoretical basis of antilasing. In this article we explore optical spectral singularities of a two-layer spherical medium. In particular, we examine the cases that a gain medium is coated by a thin layer of high-refractive index glass and a spherical glass covered by a layer of gain material. In the former case, the coating reduces the minimum radius required for exciting spectral singularities and gives rise to the formation of clusters of spectral singularities separated by wide spectral gaps. In the latter case, the coating leads to a doubling of the number of spectral singularities.