  Programmable metasurfaces incorporated with tunable materials controlled by
external stimuli can provide an unprecedented degree of freedom in dynamical
wave manipulation in real-time. Beyond the scope of isotropic reconfigurable
metasurfaces that only support unique tunable responses for excitation with a
certain single-polarization, here, for the first time a new generation of
ultrafast reprogrammable multi-functional anisotropic metasurface is reported
to enable interchangeable missions independently for two orthogonal linearly
polarized THz wavefront excitations. The reconfigurability of the proposed
anisotropic meta-device was guaranteed by elaborately designed meta-particle
composed of two perpendicular VO2 microwires whose operational statuses can be
arbitrarily and dynamically tuned among two digital states of 0 and 1
independent for dual-polarization channels by mere changing the biasing voltage
via two independent computer-programmed multichannel DC network. Capitalizing
on such meta-particle design, single/multiple focused THz beam into a
pre-determined focal spot and single/multiple focused vortex beams with
interchangeable OAM modes satisfactorily generated by encoding a metasurface
with different parabola and spiral-parabola-like coding sequences respectively.
Besides controlling the near field behaviors, the versatility and flexibility
of the proposed anisotropic metasurface also can furnish an inspiring platform
to manipulate the far-field scattering patterns in each desired polarization
channel. Anisotropic meta-device bringing new degrees of freedom in achieving
versatile tunable control of differently polarized electromagnetic waves which
will significantly enhance storage density and data capacities and has the
potential for complicated wave manipulation such as ultrafast THz communication
and dynamic holography.
