The Design Of Chromatic Dispersion Manipulation Devices Based On Metasurfaces

In recent years,due to their powerful light field control abilities,dielectric metasurfaces exhibit broad application prospects in imaging,display and detection,etc.Compared with traditional materials,the dielectric metasurfaces can control electromagnetic wavefront effectively,with advantages of thin structure,low loss and convenience for integration.However,due to the electromagnetic resonance of the metasurface units and the dispersion of optical materials,the metasurface devices present obvious chromatic aberration,which greatly limits their applications in frequency of wide band.How to eliminate or effectively utilize the chromatic aberration of metasurface devices has become a hot topic of extensive attention.This thesis will start from the electromagnetic wave manipulation theory of metasurfaces,revolving around the focusing and dispersive properties of metasurface in all dielectric optical devices,and mainly demonstrates the application of the metasurfaces focusing effect(called metalens)and the transmission diffraction plate.By designing the shape,size,rotation angle and spatial arrangement of metasurface units,the chromatic dispersion manipulation in wide band is realized.The main content of this thesis is as follows:1.Because of the wide range of applications of mid-infrared region in material detection and remote sensing detection,we study the achromatic metalenses with working band of 8～12 μm.According to the phase division method,the focusing phase required by the metalens is divided into basic phase and chromatic aberration phase,which are realized by geometric phase and resonance phase respectively.We use Si structures to design achromatic metalenses with different numerical apertures.The numerical simulation results show that the metalenses all achieve excellent achromatic effect in mid-infrared region.2.According to the multi-wavelength spectroscopic ability of optical metasurfaces,a wide-band dispersion enhancement metalens is designed in this paper.And numerical simulation results show that the metalens realizes excellent spectroscopic effect in midinfrared region.Because of certain universality and practicability of the phase division method,the design still follows this method.The simulation results show that the multiwavelength spectroscopic ability in metalens designed by the method is greatly improved,compared with the metalens designed by geometric phase with the normal chromatic metalens.In our design,the relative chromaticity rate,defined by the ratio of the focal length deference in dispersion enhancement metalens and in normal dispersion metalens in the range of working band,is 3.48.3.The wide-band achromatic transmission diffraction plate of metasurface is also studied by using the unit structures designed previously.The numerical simulation results show that in working band of 8～12 μm,the transmission angle of light in any wavelength after passing through the diffractive plate is kept around 26.5°,and the error is within the range of ±1°.The results verify that the design possesses good wide-band achromatic capability in mid-infrared region.4.According to the application needed for optical information processing and spectral analysis,the thesis further exploits the dielectric cylinder and dielectric hole structure to obtain a larger phase compensation,and designs the chromatic aberration enhanced diffraction plate in mid-infrared region and visible light.The numerical simulation results show that the spectral angle of diffraction plate is 25°～ 47.6° in the range of 8～12 μm,and the spectral angle of diffraction plate is 27.5°～ 44.0° in the range of 450～ 630 nm.It provides a new scheme to realize the flexible chromatic dispersion manipulation with simplicity and efficiency.