What is- and what is not- Electromagnetically-Induced-Transparency in Whispering-Gallery-Microcavities

TL;DR

This paper systematically distinguishes between electromagnetically-induced transparency (EIT) and Autler-Townes splitting (ATS) in whispering-gallery microcavities, using the Akaike Information Criterion to clarify their physical origins and transitions.

Contribution

It introduces a method to objectively differentiate EIT and ATS in microcavity systems using the Akaike Information Criterion, clarifying their physical mechanisms and transition.

Findings

A systematic analysis of EIT, Fano, and ATS pathways in coupled microresonators.

First application of Akaike Information Criterion to distinguish EIT and ATS.

Clarification of the transition between EIT and ATS in optical microcavities.

Abstract

Electromagnetically-induced-transparency (EIT) and Autler-Townes splitting (ATS) are two prominent examples of coherent interactions between optical fields and multilevel atoms. They have been observed in various physical systems involving atoms, molecules, meta-structures and plasmons. In recent years, there has been an increasing interest in the implementations of all-optical analogues of EIT and ATS via the interacting resonant modes of one or more optical microcavities. Despite the differences in their underlying physics, both EIT and ATS are quantified by the appearance of a transparency window in the absorption or transmission spectrum, which often leads to a confusion about its origin. While in EIT the transparency window is a result of Fano interference among different transition pathways, in ATS it is the result of strong field-driven interactions leading to the splitting of energy levels. Being able to tell objectively whether a transparency window observed in the spectrum is due to EIT or ATS is crucial for clarifying the physics involved and for practical applications. Here we report a systematic study of the pathways leading to EIT, Fano, and ATS, in systems of two coupled whispering-gallery-mode (WGM) microtoroidal resonators. Moreover, we report for the first time the application of the Akaike Information Criterion discerning between all-optical analogues of EIT and ATS, and clarifying the transition between them.