Research On Holographic Imaging Technology Based On Metasurfaces

Metasurface is a new artificial composite composed of sub-wavelength structural unit arrangement,and its structure can be designed to achieve flexible regulation of electromagnetic waves,which makes it an ideal coding material for calculating holograms.At present,metasurface has made great progress in the field of holographic imaging,and has certain research results in polarization channel multiplexing imaging,multi-wavelength multiplexing imaging,broadband imaging,spiral multiplexing imaging,etc.Among them,most of the application results of multi-wavelength multiplexed metasurface are color holographic imaging,and there are relatively few studies on the use of the difference in the frequency of incident electromagnetic waves at the same imaging location to construct different imaging results.From the perspective of improved metasurface information storage capabilities,this paper studies the dual-wavelength multiplexed metasurface and multiwavelength multiplexed metasurface.The main research work is as follows:(1)Using the time-domain finite difference method,the electromagnetic simulation results of the two cell structures were compared and analyzed,the elliptical nanopore element structure was designed,and the influence of the element structure parameters and incident electromagnetic wave characteristics on the electromagnetic radiation characteristics of the unit was studied.The results show that the response bandwidth of the cell is proportional to the center width of the nanopores,and inversely proportional to the cell cycle size and the thickness of the metal layer.The response wavelength of the unit is proportional to the center length of the nanopore;When the incident electromagnetic wave is circularly polarized,there is an electromagnetic component orthogonal to the incident wave in the transmitted electromagnetic wave,and its phase change is twice the change in the azimuth of the unit,which lays the foundation for the subsequent design of metasurface element structure for wavelength multiplexing.(2)Through the composite treatment of elliptical nanopore cells,the unit structure of dual-wavelength multiplexing was designed,and the influence of unit structure parameters on the electromagnetic radiation characteristics of the unit was studied,and the unit structure was optimized by genetic algorithm.The optimized unit has a transmittance of more than 20%to orthogonally polarized electromagnetic waves at operating wavelengths of 530 nm and710 nm,and the phase change is twice the azimuth change of the two nanopores,respectively.The cells were encoded and arranged to obtain a metasurface hologram of dual-wavelength multiplexing.By changing the wavelength of electromagnetic waves,different images can be presented separately at the same location.The peak signal-to-noise ratio of the imaging map at the two working wavelengths was about 10.81 d B and 12.37 d B,and the structural similarity was about 0.603 and 0.792,respectively.(3)The three-wavelength and four-wavelength multiplexed unit structures are designed,and the transmittance of the orthogonal polarized electromagnetic waves of the two composite units at the working wavelength is more than 20%,and the phase change is twice the azimuth change of the nanopores,respectively.The two units are coded and arranged according to the phase hologram to form a metasurface hologram.At the working wavelength of the three-wavelength multiplexed metasurface hologram,the peak signal-to-noise ratio of the imaging map was about 10.97 d B,13.98 d B,9.21 d B,and the structural similarity was about 0.523,0.807,and 0.513,respectively.At the working wavelength of the fourwavelength multiplexed metasurface hologram,the peak signal-to-noise ratio of the imaging map is about 13.98 d B,15.85 d B,12.44 d B,11.94 d B,and the structural similarity is about0.928,0.902,0.662,and 0.620,Both metasurface holograms reproduce different preset images at the same location by changing the wavelength of the incident electromagnetic wave,and the imaging results obtained are clear.