Research On All-Dielectric Metasurface For Near-Filed Imaging

Metasurfaces can manipulate the amplitude,phase and polarization of light with high spatial resolution,which is different from traditional optical components that use phase accumulation on the light propagation path to control light waves,breaking the limitations of traditional components that are bulky and costly.However,most of the current research on metasurfaces focuses on metal structures.The ohmic loss in metals makes them inefficient,and multilayer cascades are needed to obtain high transmission coefficients and full phase coverage.The all-dielectric metasurfaces can effectively avoid the defects of the metal metasurfaces.Only a single layer is needed to achieve extremely high transmittance,and the phase of the transmitted wave can be adjusted within the range of 0-2?,it can achieve complete control of the electromagnetic wave.The all-dielectric metasurfaces can replace the traditional optical lens to provide support in imaging,so it is of great significance to study the working mechanism and characteristics of the all-dielectric metasurfaces.Based on the above background,this paper mainly studies the all-dielectric metasurfaces used for near-field imaging.The designed metasurfaces all work in transmission mode,showing excellent near-field focused imaging capabilities.Firstly,a metasurface of disk unit based on transmission phase is designed.Starting from the working mechanism of the unit,combined with the Mie scattering theory and Kerker conditions,the working characteristics of the dielectric unit excited electromagnetic dipole resonance and the general design method of the unit are studied.A polarization-insensitive beam focusing metasurface is designed.The metasurface has the beam focusing capability in 33-37 GHz,and the focusing performance of the metasurface is analyzed.The effects of the metasurface numerical aperture and partial feed angle are also analyzed.Next,a metasurface of elliptical volume element based on geometric phase is designed.With an in-depth understanding of the working mode of the high aspect ratio unit,combined with the geometric phase theory,a dielectric unit with broadband characteristics working in the circular polarization mode is designed.Based on the feasibility of actual operation,the working performance of the beam focusing metasurface under two conditions is compared and analyzed.The focusing efficiency of the metasurface is greater than 40% in the 32-39 GHz range,and the broadband high-efficiency and high-resolution focusing effect is achieved.The effects of numerical aperture and partial feed angle on focusing effect are analyzed.Subsequently,a holographic imaging metasurface is designed,and the imaging effect showed that the metasurface has an excellent ability to regulate and control electromagnetic waves.Finally,a polarization multiplexing metasurface combining transmission phase and geometric phase is designed.Based on the theory of phase control of orthogonal polarizations,the characteristics of geometric phases of orthogonal polarizations are analyzed,and then an elliptical volume element structure is designed for independent phase control of orthogonal circular polarization states.The design of the metasurface realizes the independent imaging field distribution of left and right circular polarization incidence in the 33-38 GHz range,that is,the polarization multiplexing of the metasurface is realized,and the design method of the orthogonal polarization state holographic metasurface is explained in detail.