Study On Imaging Devices With A Nanoblock Array Based Metasurfaces

Metasurfaces are artificial two-dimensional material designed to solve some optical problems that are difficult to solve with traditional optical devices,it is composed of a series of sub-wavelength unit structure.By changing the material,shape,size,and other parameters of the unit structure,it can show extraordinary physical characteristic.By using these extraordinary characteristics and rational arranging the unit structure,it is possible to design metasurfaces with various functions.The anisotropic metal or dielectric nanoblock can be designed as half-wave plates or polarizers.The phase modulation of the circularly polarized incident light or the amplitude modulation of the linearly polarized light can be achieved by changing the orientation angle of the long-axis direction of the nanoblocks.Different from the metasurfaces that need to change the geometric parameters of unit structure to obtain different phase gradients,the unit structure of orientation-control nanoblock array metasurfaces have uniform geometric parameters,which make it less difficult to process,have higher fault tolerance,and can provide more phase gradients,which are beneficial to design more precise metasurfaces.This paper research and design the imaging devices with a nanoblock array based metasurfaces by using electromagnetic simulation software CST,FDTD combined with MATLAB.The main research is as follows:(1)By adjusting the structural parameters of the silver nanoblock,it can be designed as a reflective nano-polarizer.At the design wavelength of 650 nm,the reflectance of incident linearly polarized light whose polarization direction along the long-axis of the nano-polarizer is as high as 93.9%,while the reflectance of incident linearly polarized light along the shortaxis is only 3.6%.Governed by Malus law and orientation degeneracy of Malus law,an image display and encryption metasurface with broadband response in the wavelength range of 550nm-750 nm is proposed.This metasurface displays high-resolution images only when linearly polarized light in two particular polarization directions is incident,and when illuminated by other polarized light,the image will be encrypted.(2)By studying the relationship between the frequency response characteristics of silver nano-polarizer and its geometric parameters,two kind of narrow-band response nanopolarizers that can respond to two wavelengths of red(650nm)and green(585nm)respectively are designed,and these two kinds of nano-polarizers do not interfere with each other.In this paper,combined with Malus law,by decoding the original image into the orientation angle distribution of two kinds of nanoblocks,an image display metasurface that can display both red and green colors at the same time is designed.When linearly polarized white light is incident,the stored color image can be reproduced on the surface of the metasurface.(3)By designing the geometric parameters of the amorphous silicon nanoblock,there is a phase difference ? between the incident light whose polarization directions are along the long axis and the short axis at the design wavelength of 1.6?m,by this moment,the nanoblock can act as a half wave plate,moreover,in the wavelength range of 1.55?m-1.7?m,the cross-polarization transmission coefficient of circularly polarized incident light is above80%.In this paper,governed by the principle of geometric phase,a long depth of focus focusing lens by metasurface that works in the near-infrared band is designed.When the incident wavelength ? is 1.6?m,the depth of focus can high as 17.5?,while the full width at half height only 2?.And the simulation shows that the design method is equally effective for off-axis focusing.