Exotic light transition between superluminal and subliminal group velocity in a $\mathcal{PT}$ coupled slab waveguide

TL;DR

This paper presents a full-wave modal analysis of a $ ext{PT}$-symmetric slab waveguide, revealing a transition of the fundamental supermode's group velocity from superluminal to subluminal near a critical point close to the exceptional point.

Contribution

It introduces a rigorous eigenmodes approach to analyze group velocity transitions in $ ext{PT}$-symmetric waveguides, highlighting novel light propagation phenomena near exceptional points.

Findings

Fundamental supermode's group velocity transitions from superluminal to subluminal.

First higher-order supermode exhibits slow light near the exceptional point.

Analysis provides insights into light dynamics in $ ext{PT}$-symmetric structures.

Abstract

We propose a rigorous full-wave modal analysis based on the eigenmodes approach (\textquotedblleft supermodes\textquotedblright), that allows the calculation of the transverse electric ($TE$) and transverse magnetic ($TM$) stationary propagation eigenmodes in a coupled $\mathcal{PT}$-symmetric slab waveguide. Our findings show that the group velocity, for the fundamental $TE_{0}$ supermode, passes from superluminal to subluminal speed over both sides of a critical point (CP), located near to the exceptional point (EP). We also demonstrate that the first higher-order supermode, $TE_{1}$, exhibits a slow light phenomenon around the EP.