Magnetically tunable angle-insensitive multimode absorption in graphene embedded topological photonic heterostrucures

This work examines the angle-insensitive multimode absorption characteristics of topological interface states (TISs) in a graphene-embedded hybrid one-dimensional (1D) topological photonic crystal (TPC) heterostructure composed of cascaded TPC. Angle-insensitive photonic bandgap (PBG), aroused in TPC, is achieved using the all-dielectric elliptical metamaterial defined by its filling factor, $\rho$. Combining two different types of TPC i.e. TPC₁ and TPC₂, enables angle-insensitive excitation of TISs, leading to angle-insensitive absorption with the presence of graphene at the interface. To achieve multimode absorption, the structures are further cascaded, forming configurations such as TPC₁-graphene-TPC₂-graphene-TPC₁ and TPC₁-graphene-TPC₂-graphene-TPC₁-graphene-TPC₂, which exhibit dual-mode, $M_2$ and triple-mode, $M_3$ absorption, respectively. The application of an external magnetic field and variation of Fermi level significantly enhances the maximum absorption, $A_{max}$ irrespective of the modes.