Multifunctional terahertz metasurface for broadband absorption and wavefront manipulation based on graphene and vanadium dioxide

A multifunctional terahertz (THz) metasurface for broadband absorption and wavefront manipulation based on graphene and vanadium dioxide (VO2) is proposed in this paper. While VO2 is in the metallic state, a broadband absorber is obtained. The bandwidth of over 90% absorption rate is 1.11 THz. By adjusting graphene Fermi level, absorption bandwidth dynamical tunning is realized. The modulation depth for bandwidth tuning is 64 %, and the drift of center frequency is slight. Also, an equivalent circuit model is explored to explain the absorption mechanism. While VO2 is in the insulating state, the metasurface acts as a deflected vortex beam generator. Based on the convolutional operations, the functionalities of deflector and spiral phase plate are integrated into the proposed metasurface. Through precise phase arrangement based on the rotation angle of the metal resonator, arbitrary manipulation of transmitted vortex beams can be performed in the range of 0.75-0.85 THz. We also develop a 1D focusing metalen operating at different frequencies, which exhibits remarkable subwavelength focusing capabilities. Thus, multifuncitons including broadband absorption, beam deflection, vortex beam generation, and focusing metalen are integrated into one single metasurface successfully. It holds the great potential in diverse applications, such as optical stealth, beam generation, and holographic technique in the future.