Graphene-functionalized Terahertz Metasurfaces For Dynamic Wavefront Control

Terahertz waves have the advantages of low radiation,high penetration,and transient properties,and have important research significance in the fields of lidar,medical inspection,intelligent communication,and security imaging.Metamaterials are artificially synthesized periodic array materials that can achieve arbitrary permittivity and permeability,making up for the lack of terahertz-responsive materials.As a two-dimensional planar structure of metamaterials,a large number of studies tend to be directed towards wavefront regulation,but the structure is fixed and lacks flexible and efficient tuning methods.Graphene is a two-dimensional honeycomb structure of carbon atom layers,which has the characteristics of strong stability,fast response and easy fabrication,and its electrical conductivity can be dynamically controlled by electrical or chemical doping.Based on the advantages of terahertz metasurfaces and graphene,this paper proposes a terahertz metasurface based on integrated graphene to achieve tunable planarization control of the wavefront.The main research contents are as follows:1.A graphene-based tunable terahertz beam steering metasurface is designed.The device consists of a periodic arrangement of graphene bulk resonators whose cells excite terahertz surface plasmons.Controlling the Fermi level of the graphene bulk by applying an external bias voltage can enhance the electromagnetic response between graphene units and obtain uniform reflection amplitude and phase values at the resonance point.According to the generalized Snell's law,surface wave and plane camouflage principles,the full-angle anomalous reflection of terahertz waves,the equivalent camouflage of structural plane surface waves and bump planes can be realized by using graphene bulk resonator units.2.A graphene-silicon-based double-tuned terahertz metalens is proposed.The superlens consists of a periodic arrangement of graphene ribbon top layer,Si O2 dielectric layer,silicon regulation layer,Si O2 dielectric layer and gold floor bottom layer to form a five-layer structure.A Fabry-Perot resonator is formed between them,and a uniform amplitude value and 1.72 p phase coverage are obtained at the resonance point.When the x-polarized terahertz wave is incident,according to the structural invariance of the graphene metasurface,the focal length transformation,focal horizontal shift and single and double focus switching of the cylindrical focusing lens can be realized by adjusting the Fermi energy of the graphene ribbon,respectively.Three functions.By pumping the silicon layer with a laser to generate photogenerated carriers,the focus intensity can be further dynamically tuned.3.A metal-graphene based tunable vortex beam metasurface is established,which consists of a high-efficiency double-slit-ring metal array structure with graphene integrated at the opening.Linear phase shift and uniform reflection amplitude can be obtained by rotating the structural unit according to the P-B phase theory.According to the principle of vortex phase plate,Bessel beam generation and the superposition principle of vortex and divergence,high-order vortex,vortex divergent beam and Bessel beam can be realized respectively by using graphene-metal crossed structural units;On this basis,controlling the electrical conductivity of graphene by loading a bias voltage can suppress the electromagnetic response in the unit structure,thereby realizing flexible regulation of the beam intensity.