Graphene-based Tunable Phase Gradient Metasurface And Electromagnetic Coupling-based Huygens' Metasurface

Phase gradient metasurface can be regarded as a two-dimensional metamaterial composed of subwavelength antenna elements,and its thickness is much smaller than the operation wavelength.The electromagnetic responses(including phase,amplitude,and polarization characteristics)of the antenna elements and the phase discontinuity along the interface provide perfect control over the propagating wavefront,dispersion,polarization and even frequency.However,in order to achieve full control of the wavefront,2? phase coverage is needed.So in the past few years,many researchers have struggled to find the appropriate plasmonic or dielectric nanostructures providing full phase coverage response while maintaining high scattering efficiency.In recent years,more and more people are devoted to the study of metasurface with tunable performance because they can be used to prepare some dynamically reconfigurable optical devices such as optical switches and spatial light modulators.In this thesis,graphene-based tunable and coupling-based gradient metasurfaces are mainly studied.The optical properties of graphene and its optical simulation model are introduced firstly.Then,the dipole array model is introduced,which provides guidance for us to understand and design metasurface.Furthermore,the Metal-Insulator-Graphene antenna unit structure is introduced and the FDTD Solutions software is used to study its electromagnetic response characteristics.Simulation results show that changing the Fermi level can control the 0-2? phase response of the graphene antenna.The distribution change of voltage applied on the graphene strip antenna enables multiple functions such as beam scanning and Surface Plasmon Polariton coupler.We have also designed a variable-focus cylindrical lens that can be switched from 20 to 100?m by changing the bias-voltage distribution of the lens.We also propose a Huygens' metasurface using bilayer complementary structure via the inherent electromagnetic coupling in it.The optical nanocircuit model was used to analyze the vertical and horizontal coupling effects and resonance characteristics of the structure.The calculation results show that the electromagnetic coupling effect caused by the dislocation between the two nanostructures is enough to realize the manipulation of the wavefront without changing the size or the orientation angle of the antenna.With this structure we designed a reflective gradient metasurface working in low-frequency coupling mode and a high-efficiency transmissive gradient metasurface working in the spectral overlap of electric and magnetic resonances.The proposed electromagnetic coupling metasurface is a new type of plasmonic metasurface,which has the characteristics of enhancing the interaction between light and matter.