Strong coupling of topological edge states enabling group-dispersionless slow light in magneto-optical photonic crystals

Abstract

We investigate a two-way waveguide constructed by bringing close two identical magneto-optical photonic crystals which each supports a counterpropagating topological one-way edge state. We find a unique slow-light state that exhibits a very small group velocity $({n}_{g}=529.2)$, a zero group-velocity dispersion, distortionless pulse transport, and ease to be magnetically tuned within a broad frequency range, simultaneously. We show that this unique group-dispersionless slow-light state originates from the strong coupling of the two counterpropagating topological states, which causes complete exchange and transfer of energy flow between them, induces a vortexlike close loop of energy transport channel around the source, leads to complete destructive interference in the far field, and finally results in a very slow propagation velocity of electromagnetic waves. These results indicate that deeply digging into the interaction between photonic topological states can help to open up an arena in topological physics and find great potential of applications such as optical buffer memories and enhanced light-matter interaction.