Dual-Polarization Topological Interface States in Ridge Photonic Crystals

Lifting the nodal ring degeneracy can result in topologically nontrivial ridge bulk states and associated interface states, which have been realized by 1D photonic crystals. However, the ridge interface states exist only for p polarization, which limits their potential applications in polarization-independent optical devices. Here, a scheme to design the polarization-independent nodal ring using a 1D photonic crystal is proposed. It is revealed that the fourfold degeneracy exactly lies at the position where the absentee layer condition is satisfied for each layer. Once the absentee layer condition cannot be satisfied for each layer, the nodal ring will be gapped, accompanied by ridge interface states traversing the gap. Interestingly, these p-polarized and s-polarized ridge interface states are degenerate almost in the whole band gap, which facilitates polarization-independent optical filtering. This work proposes a novel way for polarization-independent optical filtering and associated applications, such as high-efficiency solar energy conversion and privacy screen.