  In this paper, for the first time, a new generation of ultrafast
reprogrammable multi-mission bias encoded metasurface is proposed for dynamic
THz wavefront engineering by employing VO2 reversible and fast monoclinic to
tetragonal phase transition. The multi-functionality of our designed VO2 based
coding metasurface (VBCM) was guaranteed by elaborately designed meta-atom
comprising three-patterned VO2 thin films whose operational statuses can be
dynamically tuned among four states of "00"- "11" by merely changing the
biasing voltage controlled by an external FPGA platform. Capitalizing on such
meta-atom design and by driving VBCM with different spiral-like and
spiral-parabola-like coding sequences, single vortex beam and focused vortex
beam with interchangeable OAM modes were satisfactorily generated respectively.
Additionally, by adopting superposition theorem and convolution operation,
symmetric/asymmetric multiple beams and arbitrarily-oriented multiple vortex
beams in pre-demined directions with different topological charges are
realized. The versatility of our designed VBCM also has equipped a platform to
focus the incident THz wavefront into a pre-determined point which can be
dynamically altered. Several illustrative examples successfully have clarified
that proposed VBCM is a promising candidate for solving crucial THz challenges
such as high data rate wireless communication where ultrafast switching between
several missions is required.
