  Metamaterials based on effective media have achieved a lot of unusual physics
(e.g. negative refraction and invisibility cloaking) owing to their abilities
to tailor the effective medium parameters that do not exist in nature.
Recently, coding metamaterials have been suggested to control electromagnetic
waves by designing the coding sequences of digital elements '0' and '1', which
possess opposite phase responses. Here, we propose the concept of anisotropic
coding metamaterial at terahertz frequencies, in which coding behaviors in
different directions are dependent on the polarization status of terahertz
waves. We experimentally demonstrate an ultrathin and flexible
polarization-controlled anisotropic coding metasurface functioning in the
terahertz regime using specially- designed coding elements. By encoding the
elements with elaborately-designed digital sequences (in both 1 bit and 2
bits), the x- and y-polarized reflected waves can be deflected or diffused
independently in three dimensions. The simulated far-field scattering patterns
as well as near-electric-field distributions are given to illustrate the
bifunctional performance of the encoded metasurface, which show good agreement
to the measurement results. We further demonstrate the abilities of anisotropic
coding metasurface to generate beam splitter and realize anomalous reflection
and polarization conversion simultaneously, providing powerful controls of
differently-polarized terahertz waves. The proposed method enables versatile
beam behaviors under orthogonal polarizations using a single metasurface, and
hence will promise interesting terahertz devices.
