Polarization-independent topological corner states based on all-dielectric valley photonic crystals

Recently, topological edge states and corner states have provided new ways to manipulate light transmission and localization. Up to now, most works have focused on either transverse magnetic or transverse electric polarization. In contrast, dual-polarization photonic topological states have attracted extensive attention because of their potential applications in polarization-independent photonic devices. Previous study realizes the polarization-independent topological corner states by independently tuning the out-of-plane permittivity and the in-plane permittivity of the anisotropic elliptic metamaterial, which is difficult to realize in the optical regime. In this work, we achieve polarization-independent topological edge states and corner states based on all-dielectric fishnet photonic crystals made of isotropic material. Note that the frequencies of the topological edge states and corner states depend on the structure’s effective refractive index, which is related to the filling ratio of the dielectric material. By selecting a suitable filling ratio of the dielectric material, polarization-independent edge states and corner states are realized. In addition, we further construct a topological waveguide-cavity coupling system and demonstrate the function of a polarization-independent optical notch filter. Our work paves the way for the implementation of polarization-independent topological photonic devices.