Study On Light Field Control And Imaging Of All-dielectric Metasurfaces

The rapid development of micro and nano processing technology in recent years and the increasing demand for device integration in the development of science and technology have led researchers to pay attention to the research of micro-nano devices.Micro-nano devices have lightweight quality and high integration,which is very beneficial to the integration of devices.Metasurface is an artificially designed micro-nano optical device with a highly integrated planar structure.Compared with traditional optical devices,metasurfaces possess unique optical properties.By designing the metasurface,it can arbitrarily control the phase,amplitude and polarization of the light wave front.Therefore,metasurfaces can generate more interesting optical phenomena on the basis of realizing the functions of traditional optical lenses,which makes them have the potential to replace traditional lenses.The research on the ability and application of metasurface light field regulation is of great significance for promoting the process of metasurface replacing traditional lenses and realizing the high integration of optical instruments.However,the current unit structures of metasurfaces mostly adopt simple structures such as rectangular antennas,which makes the designable structural parameters relatively simple and limits the flexibility of metasurface unit structure design.And most of the metasurfaces that have been proposed are only able to work at the designed wavelength,which limits the application of metasurfaces.In this paper,two all-dielectric metasurfaces are designed to solve the above problems,and the light field control ability of the designed metasurfaces and their applications are studied.The performance of the proposed metasurfaces are verified by theoretical simulation.The main contents and innovations of this paper are as follows:A silicon-based tetragonal pyramid-structured metasurface is designed for multifocal focusing.The metasurface we designed adopts a novel quadrangular pyramid structure as the unit of the metasurface.Compared with simple rectangular or cylindrical nanoantennas units,the quadrangular pyramid structure has more structural parameters that can designed.Under the premise that the incident wavelength is fixed,we can adjust the transmission phase and geometric phase of the unit by designing the base side length of the quadrangular prism unit and the rotation angle of the unit,respectively.We used the finite element method to scan the structural parameters of the above unit,and screened out twelve units for designing metasurfaces.There is a phase difference of π/6 between each screened unit in turn.Therefore,the screened unit group can realize a period of phase regulation.In addition,we also optimized other invariant structural parameters,enabling each unit to achieve phase control under the premise of higher transmittance.Based on the selected unit groups,combined with the phase distribution principle of lens focusing,we designed one-dimensional and two-dimensional single-focal focusing metalens and one-dimensional multi-focal focusing metalens.The focusing effects of the designed metalens are verified by the electromagnetic field simulation software based on the finite element method.We design transmissive metasurfaces based on halide perovskite rectangular nanoantennas.Since the long and short axes of the rectangular nanoantennas have different effective refractive indices,each nanoantenna can be regarded as a wave plate,which enables the metasurfaces we designed can control the phase and the polarization of the incident light at the same time.We design focused metasurfaces with polarization conversion function by adjusting the geometric phase of the units by changing the rotation angle of the nanoantennas.When left-handed circularly polarized light is incident on the metasurface,a right-handed circularly polarized focal point can be generated at the designed focal length.In addition,the halogen atoms in halogen perovskite materials can be replaced by chemical methods,and the replacement of halogen atoms will affect the band gap of the material and then affect the optical properties of the material.Based on the above properties,we designed halide perovskite tunable holographic metasurfaces.We can control the optical function of metasurfaces by tuning the band gap of halide perovskites.The tunable metasurface we designed can control the display and disappearance of images and change the imaging pattern.In addition,we selected three halide perovskites to design a composite metasurface for color holographic imaging.Due to the monochromatic transmittance of the three halide perovskites,when we design the three halide perovskites in the same metasurface,the three halide perovskites only image their corresponding sensitive wavelengths of incident light.We combine the Gerchberg-Saxton(G-S)algorithm to design the phase information corresponding to the RGB color channels of color images in three monochromatic imaging channels,thereby realizing a color holographic metasurface with low color crosstalk.