  Black phosphorus (BP) as a promising two-dimensional material with
extraordinary optical properties constitutes an excellent building block in
multilayer hyperbolic metamaterials. In this work, we design a multilayer
structure composed of BP/dielectric layer stacking unit cells patterned on a
gold mirror and theoretically demonstrate the tunable anisotropic absorption in
the infrared regime. The electric dipole resonance between the adjacent unit
cells drives the structure in the critical coupling state, and impedance of the
structure matches to that of free space, showing the perfect absorption for one
polarization direction, while the impedance mismatch for the other polarization
direction leads to only 8.2$\%$ absorption at the same wavelength. The
anisotropic absorption response of the proposed structure can be attributed to
the intrinsic anisotropy of BP, which exhibits few dependence on the incident
angle. Furthermore, we investigate the tunable optical absorption of the
proposed structure with the electron doping of BP and the geometric parameters.
These results demonstrate great potentials of BP in constituting multilayer
hyperbolic metamaterials, and open up avenues in designing anisotropic
metadevices with tunable spectral and polarization selectivity in the infrared
regime.

Optics