Exotic light transition between superluminal and subluminal group velocity in a [formula omitted] coupled slab waveguide

Abstract

We propose a rigorous full-wave modal analysis based on the eigenmodes approach (“supermodes”), that allows the calculation of the transverse electric (TE) and transverse magnetic (TM) stationary propagation eigenmodes in a coupled PT-symmetric slab waveguide. Our findings show that the group velocity, for the fundamental TE0 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, TE1, exhibits a slow light phenomenon around the EP.