Near-End Crosstalk Suppression in Coupled Contra-Directional Chern Topological Edge Modes

Line modes emerging at the edge of 2D Chern photonic topological insulators (PToIs) exhibit robust unidirectionality and immunity to disorder and perturbations. When identical line modes are placed in close proximity, far-end crosstalk is inherently suppressed because backscattering is topologically forbidden. However, near-end crosstalk (NEXT) becomes a severe problem. The underlying cause for NEXT is the dispersion crossing of the neighboring line modes within the topological bandgap. Here, we demonstrate that dispersion engineering of coupled line modes provides an effective route to suppress NEXT. We introduce a simple fabrication approach for realizing Chern topological lines by employing permanent magnets to bias YIG-based PToIs. The magnets are modeled to ensure the required magnetic bias profile. Both simulations and experiments confirm ≥ 20dB NEXT suppression between two topological line modes separated by only a few unit cells.