Dual‐Polarization Topological Fano Resonances Enabled by a Polarization‐Independent Topological Corner State

ABSTRACT A second‐order topological photonic crystal design based on an all‐dielectric silicon platform is proposed, featuring truncated rectangular air holes to realize a wide common photonic bandgap. A polarization‐independent topological corner state (TCS) cavity is constructed, realizing degenerate resonant frequencies for both transverse electric and transverse magnetic polarizations via geometric optimization. By integrating this TCS cavity with a dual‐polarization topological edge state waveguide, a compact topological cavity‐waveguide coupled system is formed, demonstrating asymmetric Fano resonances for both polarizations, which arise from the interference between localized corner states and propagating edge states. This system achieves ultrahigh quality factors, high refractive index sensing sensitivities along with exceptional figures of merit, and excellent robustness against structural imperfections. It offers promising prospects for practical applications in polarization‐division multiplexing, integrated photonic circuits, refractive index sensors, and quantum information technologies.