Research And Applications Of Dielectric Phase Gradient Metasurfaces

Phase gradient metasurfaces are a kind of two-dimensional artificial metamaterials composed of periodic sub-wavelength structure arrays,which equipped with highly flexible electromagnetic response properties,and can flexibly manipulate the amplitude,phase and polarization of electromagnetic waves within the sub-wavelength scale.Due to the inherent absorption loss of metallic materials in the optical band,dielectric phase gradient metasurfaces with high refractive index and low loss are developed.Compared with traditional optical devices,dielectric phase gradient metasurfaces have the advantages of flat and ultra-thin,flexible design,compact and easy integration,which can meet the needs of modern optical devices and systems for miniaturization,integration and multi-functionality,and have broad application prospects and great potential in the fields of optical imaging,detection and sensing,intelligent display,etc.In this dissertation,based on the principles of geometric phase and transmission phase,the applications of dielectric phase gradient metasurfaces for metalens and meta-holography are focused.A metalens array for optical multi-parameter detection,a rotating zoom metalens with large magnification,a multi-foci metalens for spectra and polarization reconstruction,and a dynamic meta-holography are demonstrated,respectively.The details are as follows:(1)An optical multi-parameter detection device based on silicon-based metalens array is proposed and experimentally verified.The device is composed of a pixelated and polarization-dependent metalens array.By measuring the intensity and position shift of the focal point,the amplitude,polarization and phase of the beam at 1550 nm can be detected simultaneously.The performances of the device are verified by experimentally testing 22scalar polarized beams,two vector beams with spatial polarization distribution(a radially polarized beam and an angularly polarized beam)and a 20th-order vortex beam with spatial phase distribution.The experimental errors are 4.24%,6.28%,2.49%and 6.4%,respectively.And the average focusing efficiency of the metalens is 48%.(2)A rotating zoom metalens is proposed and experimentally verified,which composed of two polarization-independent silicon-based metasurface elements.By changing the relative rotation angle between the two metasurface elements,the optical zoom and zoom imaging at 1550 nm with large magnification are realized.In the experiments,the zoom test of±1×?±18×and the zoom imaging of(10)1×?(10)18×are achieved,respectively.The average error between the experimental focal length and the theoretical value is only 1.7%.The zoom range is demonstrated from±3 mm to±54 mm,and the average focusing efficiency is 54%.(3)A silicon nitride based multi-foci metalens that enables spectra and polarization reconstruction is proposed and experimentally demonstrated.The multi-foci metalens with wavelength and circular polarization dependence is capable of generating 12 focal points or images at different positions in the same focal plane or image plane.The focal point or image at each position corresponds to a specific wavelength and circular polarization state of the incident beam.By analyzing the intensity and position information of the focal points or images,the identification and reconstruction of the spectra and polarization are verified under the incidence of coherent and incoherent light,respectively.(4)A dynamic holographic display method based on spatial channel-type metasurface is proposed and experimentally verified.The design is mainly composed of a silicon nitride based metasurface and a high-speed dynamic laser beam modulation module.By modulating and encoding the incident beam in time sequence and selectively opening specific spatial channels on the metasurface,the dynamic meta-holographic with large frame numbers(2²⁸),high frame rates(9523 fps)and high efficiency(70.2%)at 633 nm are realized.