Tunable mid-infrared perfect absorber based on the critical coupling of graphene and black phosphorus nanoribbons

Abstract

We demonstrate theoretically a wide-angle and tunable mid-infrared perfect absorber by coupling the graphene and black phosphorus plasmonics and utilizing the concept of critical coupling. With the black phosphorus nanoribbons alone, the localized surface plasmon resonances (LSPR) can be excited, while the absorption is small due to its single-layer thickness. A Fabry-Perot cavity is formed by adding an Au mirror as the substrate, which is separated from the black phosphorus by a dielectric spacer, hence the absorption is enhanced markedly due to critical coupling. In order to further enhance the absorption, a graphene grating is introduced on the top of black phosphorus and is separated by a dielectric slab. It is shown that the perfect absorption can be obtained due to the critical coupling of LSPR of black phosphorus and graphene. Based on these result, it is further demonstrated that the perfect absorption can work in large incident angle range, and the working wavelengths can be adjusted by the Fermi level of graphene. Our results provide a new avenue to achieve wide-angle and adjustable perfect absorption, and it may be beneficial for a variety of mid-infrared plasmonic applications.