Design Of Metasurfaces Plasma Imaging System And Study Of The Optical Effect

Surface Plasmon Polaritons(SPPs)are electromagnetic evanescent waves propagating along the interface between metals and dielectrics that are excited by the photon-electron resonance coupling.In recent decades,SPPs have been paid a lot of attention because of their unique optical properties and have been made a remarkable breakthrough development.In the imaging system,a variety of plasma lenses have been designed,and have exceeded the limits of the traditional diffraction limit in beam focusing,beam deflection,exhibiting unique effects.With the development of science and technology and the increase of production and living requirements,the metasurface structure has become the main force in the current plasma imaging system design.Its role in modulating the phase and amplitude of the electromagnetic wave has made it bear very large application potential in many fields.At the same time,the extensive research of 2D materials such as graphene also makes the design of the metasurface imaging system towards the direction of high efficiency,low loss and easy modulation,which is more in line with the needs of human society today.In this paper,the following related work has been completed by combining theoretical design and simulation research methods:First,a flat lens composed of an array of slant metal slits is proposed.Under the irradiation of incident light,the excited SPPs are transmitted to the free space through the slits,and each slit provides a different transmission distance.Theoretical and simulation results show that the spatial phase of the wavefront can be controlled,so that the excited light from each slit is superimposed on the preset focus of the free space to obtain the focusing effect.In addition,by controlling the asymmetry of the array structure and controlling the slant angle of each slit,the spatial focus position can be adjusted,making its functionality be enhanced in practical applications.Then,based on the study of the metasurface,an anti-Babinet nanometer antenna structure based on non-parallel double slits is designed.The modulation effect and law of the unit structure on the spatial phase and amplitude are analyzed.The eight basic units with over2? phase and similar transmission amplitude are pick out,so that a certain wavefront phase can be achieved through reasonable arrangement.In this work,beam deflectors and focal lenses with different focal lengths were designed by phase analysis.Among them,several focal points were also included.The numerical simulation of the finite element method proved our design well and we can observe its numerical aperture is very large,and the focus size is very small,which is very conducive to the integration of high-precision optical devices.In addition,a multi-channel filter device based on Bragg grating and graphene waveguide is also designed.As a mid-infrared waveguide,graphene exhibits the characteristic that the local optical parameters can be adjusted by the electric field.By applying a voltage to this structure,the effective refractive index of the graphene waveguide can be periodically changed,and at this time the Bragg effect will occur when the graphene SPPs are transmitted.When a defect is introduced,a defect resonance mode is generated in the waveguide,and the structure can be regarded as a Fabry-Perot cavity,generating a filter channel.According tothis,by further introducing multiple defects,the effect of multi-channel filtering can be achieved.In this work,two design methods for multi-channel filter structures,a cascade multi-defect structure and a double-symmetric Fabry-Perot structure,are proposed,and the COMSOL numerical simulations well validated their precise tunable effects.