Ultra-thin 2-bit anisotropic Huygens coding metasurface for terahertz wave manipulation.

In this work, we design an ultrathin 2-bit anisotropic Huygens coding metasurface (AHCM) composed by bilayer metallic square-ring structures for flexible manipulation of the terahertz wave. Based on the polarized-dependent components of electric surface admittance and magnetic surface impedance, we confirm that both the electric and magnetic resonances on coding meta-atoms are excited, so as to provide a full phase coverage and significantly low reflection. By encoding the elements with distinct coding sequences, the x- and y-polarized incident waves are anomalously refracted into opposite directions. More uniquely, we also demonstrate that the designed AHCM can be utilized as a transmission-type quarter-wave plate. The proposed metasurface paves a new way toward multifunctional terahertz wavefront manipulation.