Design And Research Of Wavefront Control Device Based On Terahertz Metasurface

With the popularization of 5G technology,expanding the communication band and increasing the channel capacity have become the growing tendency of communication technology.Exploiting terahertz frequency band is an effective means to expand the communication frequency band.As an artificial composite structure composed of subwavelength resonant units,metasurface has great advantages in terahertz wave control.In this paper,two kinds of metasurfaces are proposed and studied at terahertz band based on the transmission phase theory and geometric phase theory,and a variety of planar terahertz wavefront control devices are designed.The main research contents and innovations are as follows:(1)Based on the transmission phase theory,a transmission-type metasurface with high efficiency and broadband is designed.The Fabry-Perot interference model is established to verify the physical mechanism theoretically.By constructing appropriate gradient phase,anomalous refraction and generation of vortex beam are realized at0.4-1.0THz.Then,two focusing lenses are designed at 0.8THz.The simulation results(anomalous refraction/reflection angle,focal length,etc.)are in good agreement with the theoretical values.(2)Based on geometric phase theory,an efficient full-space metasurface is designed.The incident circularly polarized wave can be converted into the cross-polarized wave by metasurface and transmitted at 0.6THz,reflected at 1.67 THz.In both modes,the gradient phase can be manipulated independently.The surface current distributions are introduced to study the physical mechanism of independent operation.Anomalous refraction/reflection and full-space lenses are realized by arranging the elements properly in one-dimensional direction.Finally,full-space vortex beam generators are designed.The purity of the +1-order orbital angular momentum of two operation modes reaches 0.692 and 0.659,which is much higher than the weight of the submodule.The above work provides an effective method for the design of high efficiency and broadband terahertz wavefront control devices,and promotes the miniaturization and integration of multifunctional terahertz devices.Our designed devices have huge potential applications in terahertz imaging,communications,radar,etc.