Exotic light transition between superluminal and subluminal group velocity in a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si0011.svg"><mml:mi mathvariant="script">PT</mml:mi></mml:math> coupled slab waveguide

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