Polarization-Independent and Broadband THz Coherent Perfect Absorber based on Black Phosphorus Bifacial Metasurfaces

This work reports a novel black phosphorus (BP)-based metasurface exhibiting broadband and polarization-insensitive coherent perfect absorption (CPA) at THz frequencies. The proposed design is composed of a thin dielectric layer sandwiched between two BP monolayers patterned in patches. An equivalent microwave circuit model is developed to accurately model and analyze this design. It is shown that CPA can be achieved over a broad bandwidth of 1.5 THz for both TM and TE waves. The broadband and polarization-independent CPA response is achieved due to the ultrathin thickness of the proposed design and the anisotropic dispersive properties of BP. The presented ultrathin and broadband CPA devices can be used as tunable planar THz modulators, detectors, and signal processors.