Band structure of plasmons and optical absorption enhancement in graphene on subwavelength dielectric gratings at infrared frequencies

We study theoretically optical properties of a graphene monolayer supported on subwavelength dielectric gratings (SWDGs) using a scattering-matrix method. It is found that due to the formation of band structure of graphene plasmons (GPs) on the SWDG, optical excitations of GPs can be controlled by GP bands above the light line, resulting in optical absorption enhancement in graphene. In particular, very flat GP bands can exist above the light line at midinfrared frequencies. As a result, high optical absorption in graphene can be realized over a wide angular range at these flat bands when using a metallic substrate. Our results could find applications in graphene-based optoelectronics.