Multiband topological states from band fold of photonic crystals

To find more simple and universal method to realize the topological photonic crystals (PCs), we use the fold effect of bands of PCs and the Su–Schrieffer–Heeger model. Through the change of structure parameters, a lattice can undergo the transformation from topologically trivial to nontrivial states. The fold effect of bands leads to the multiple topological edge bands, which increase the band width of topological states. Furthermore, the topological corner states can be formed in the designed structure.