Angle-independent topological interface states in one-dimensional photonic crystal heterostructures containing hyperbolic metamaterials

Topological interface states (TISs), known for their distinctive capabilities in manipulating electromagnetic waves, have attracted significant interest. However, in conventional all-dielectric one-dimensional photonic crystal (1DPC) heterostructures, these TISs strongly shift towards higher frequencies with the increasing angle, which limits their practical applications. Here, we realize an angle-independent TIS for transverse magnetic polarized wave in 1DPC heterostructures containing hyperbolic metamaterials (HMMs). We begin with the design of two kinds of angle-independent photonic bandgaps (PBGs) in two 1DPCs with symmetric unit cells based on the phase variation compensation effect. From the Zak phases of the upper and lower bands, the topological properties of PBGs in two 1DPCs are different. By harnessing these different topological properties, we can realize an angle-independent TIS in the heterostructure composed of these two 1DPCs. Moreover, we further discover that the angle-independent property of the TIS is robust against the layer thickness variation due to the topological protection, making the experimental realization of the angle-independent TISs more feasible. It is noted that the TISs under transverse electric polarized waves strongly shifts towards higher frequencies as the incident angle increases because the iso-frequency curve of the HMM is a circle. Empowered by the polarization-dependent property of the TIS, we design a wide-angle polarization selector with an operating angle range up to 45.9°. Our work provides a viable route to realizing angle-independent TISs with substantial angular tolerances under current experimental conditions, which facilitates the design of optical devices including polarizers, filters, and sensors with robustness against disorder.