Strong anisotropic perfect absorption in monolayer black phosphorous and its application as tunable polarizer

Black phosphorus exhibits extreme anisotropic properties due to its special lattice structure. In this paper, we numerically show that strong anisotropic perfect absorption can be realized in a nanostructured monolayer black phosphorus with the excitation of plasmonic resonances. Under normal incidences, the structure shows a 99.56% absorption for one polarization at the resonance wavelength while only 9.48% absorption for the other polarization at the same wavelength. The anisotropic responses are purely attributed to the intrinsic material anisotropy of black phosphorus which is different from conventional metallic or graphene plasmonic absorbers. The wavelength of peak absorption is tunable by changing the electron concentration in black phosphorus. As an example of application, we proposed a new design of tunable reflective polarizer based on black phosphorus and a polarization extinction ratio around 23 dB can be achieved.