The Research On Terahertz Wavefront Control Based On Metasurface

Terahertz(THz)radiation is located in the region between microwave and infrared in the electromagnetic spectrum.With the development of THz wave detection technology,THz technology has attracted attention from researchers.Because of the advantages of low photon energy,high penetration,and high resolution,THz wave has been widely applied in fields such as wireless communications,medical biology,and security monitoring.THz wavefront control plays an important role in the application of THz wave.Unfortunately,conventional THz devices are usually of bulky sizes and low efficiencies due to weak interactions between natural materials and THz waves,the applications of traditional THz wavefront control devices are very limited.The emergence of electromagnetic metamaterials makes up for some of the shortcomings of natural materials.Furthermore,the proposal of a two-dimensional metamaterial electromagnetic metasurface opens up a new degree of freedom for controlling THz wave.This paper focuses on metasurfaces to study the manipulation of THz wavefront.The main research contents and results are as follows:1.We propose the new global degree of freedom of reconfigurable spatial configuration to achieve free and dynamic control of the propagation direction and polarization of electromagnetic waves.Different from the metasurfaces that combine active elements to control local meta-atoms,we have constructed a multi-layer cascaded transmissive metasurface system.Each layer metasurface has a pre-designed phase distribution.By giving each layer metasurface a specific rotation speed,we can dynamically control the Jones matrix property of the entire system,so as to achieve dynamic control of the wavefront and polarization of the THz wave.As a proof of concept,we design and fabricate two meta-devices which working frequency is 0.7 THz and performed terahertz experiments,the experimental results show good consistency with the theoretical and simulation results.2.We propose a metasurface that uses Pancharatnam-Berry(PB)phase to integrate focusing and vortex generation functions in THz,which greatly simplifies the design complexity of high-frequency transmission integrated optical devices.The metasurface is composed of sub-wavelength microstructure of all dielectric materials,which has high transmittance and is simple to fabrication.We designed three kinds of focused vortex metasurfaces with topological charges of 0,1,and 2 which working frequency is 0.59 THz to verify the concept.We fabricated a THz sample with a topological charge of 1 and characterized the performance of the sample through experiments.The experimental results are in excellent agreement with the full-wave simulation results,and verify the theoretical prediction.