Polarization‐independent absorption enhancement in a graphene square array with a cascaded grating structure

The polarization‐independent enhanced absorption effect of graphene in the near‐infrared range is investigated. This is achieved by placing a graphene square array on top of a dielectric square array backed by a two‐dimensional multilayer grating. Total optical absorption in graphene can be attributed to critical coupling, which is achieved through the combined effect of guided‐mode resonance with the dielectric square array and the photonic band gap with the two‐dimensional multilayer grating. To reveal the physical origin of such a phenomenon, the electromagnetic field distributions for both polarizations are illustrated. The designed graphene absorber exhibits near‐unity polarization‐independent absorption at resonance with an ultra‐narrow spectrum. Moreover, the polarization‐independent absorption can be tuned simply by changing the geometric parameters. The results may have promising potential for the design of graphene‐based optoelectronic devices.