Topological insulators are materials that conduct on the surface and insulate in their interior due to non-trivial topology of the band structure. The edge states on the interface between topological (non-trivial) and conventional (trivial) insulators are topologically protected from scattering due to structural defects and disorders. Recently. it was shown that photonic crystals (PCs... https://bellfordtoysandhobbiers.shop/product-category/book/