Research On Special Beam Generation And Absorber Based On Dielectric Metasurface

Metasurface is an artificially designed ultra-thin and easily integrated micro-nano two-dimensional material.It is widely used in the transmission and reflection control of electromagnetic waves because it can freely shape the wavefront.In this thesis,two kinds of metasurface devices with special functions are proposed,which are switchable Airy beam generator and elliptical Airy vortex beam generator,both of which can realize beam control of transmitted and reflected light fields.At the same time,metasurfaces can also be carefully designed to perfectly absorb electromagnetic waves.In order to explore the absorption function of metasurface to electromagnetic wave,a tunable ultra-wideband terahertz metasurface absorber is designed by using phase change materials.The specific content is mainly summarized as the following three parts:1.In the visible region（λ～532?nm）,this thesis proposes a switchable all-dielectric metasurface that can be switched to generate a two-dimensional（2D）Airy beam with transmission and reflection.In this work,the metasurface is mainly composed of a titanium dioxide nanopillar and a vanadium dioxide substrate.The switchable Airy beam is generated by using the transformable state properties of vanadium dioxide and a regular array of nanopillars to vary the wavefront phase.The results show that the transmission metasurface converts 97%of the incident light,while the reflection mode achieves a polarization conversion rate of 70%.Based on its significant advantages,the switchable Airy beam generator will be of interest to researchers in biomedical and applied physics,and has promising applications in this field.2.Elliptical Airy vortex beams（EAVBs）carry vortex angular momentum.In this thesis,the complex amplitude and pure phase metasurfaces are designed to generate and modulate EAVBs at an operating wavelength of 1500 nm by adopting the principles of transmission phase and Pancharatnam-Berry phase,respectively.The results show that the focusing pattern of the elliptical Airy vortex beam in the self-focusing plane splits into|m|+1 tilted bright spots,and the tilting direction is related to the topological charge number m.This metasurface device has potential applications in improving channel capacity,information encoding and particle detection and capture for orbital angular momentum-based communication.3.The tunable ultra-wideband terahertz metasurface absorber based on vanadium dioxide（VO₂）consists of four identical VO₂ synthetic patterns,dielectric layers and metal reflective layers from top to bottom.Compared with the previously reported terahertz absorber,the absorber significantly improves the absorption bandwidth,and has many advantages such as simple structure,polarization insensitivity and wide-angle absorption.