Design And Implementation Of Colorful Display And Metalens Based On Optical Metasurfaces

Nowadays,optical devices and optical systems are everywhere in modern industry and daily life.Laser,as invented in twentieth century,has greatly enriched studies of the interactions between light and matter.In the past decades,benefited from the development on nanotechnology,metamaterials have rejuvenated the design and application of optical systems,flourished the subject of optic s.Optical metamaterials are artificial structural materials composed of structures at a scale much smaller than their working wavelength.Although based on natural materials,metamaterials can achieve many anomalous optical phenomena that are “impossible” for natural materials and provide unprecedented degrees of freedom to design innovative optical components,ascribed to their subwavelength design.In recent years,two-dimensional metasurfaces emerged to overcome the obstacles encountered by three-dimensional metamaterials,such as lossy and difficult to fabricate.Metasurfaces are quasi-2D structured interface composed of subwavelength nanostructures which can be used to efficiently manipulate the amplitude,phase and polarization of light,therefore realize desired optical functionalities.The phase manipulation of conventional optical devices depends on the optical phase differences accumulated when the light passes through the bulk optical devices.Instead,by using the resonances of the subwavelength structure and principles such as the geometric Berry phase,metasurfaces can introduce abrupt phase change on the interface,making it possible to manipulate the phase of light and realize planar optical devices at ease.In this thesis,by combining theories such as surface plasmon polariton,dielectric resonance,geometric Berry phase and so on,we design and realize colorful display and metalens based on aluminum and silicon nitride metasurfaces,respectively.The optical performances of the two metasurface components are experimentally characterized.Compared with traditional dyes,one distinguished advantage of metasurface colorful display is its endurance.In this thesis,he metasurface colorful display is based on reflective metasurface,comprising a sandwiched structure of aluminum nanorods,silica spacer and aluminum mirror.The FDTD simulation software is used for optimizing three types of unit cell with narrow band characteristics at three wavelengths: red(630 nm),green(530 nm)and blue(450 nm).The influence of varying geometric parameters of the unit cell on the optical conversion efficiency is analyzed.The three channels of the target color image and the corresponding intensities are then mapping into the distributions of three optimized unit cell to forms the metasurface,according to the Malus’ s law and the geometric Berry phase.Finally,we fabricate the optical metasurface and experimentally demonstrated its capability for colorful display.Metalens can replace the bulky conventional lens by using planar design.Its design flexibility and easy-to-integrate nature hold great potential for practical applications.In this thesis,we design and fabricate a dielectric transmission metalens based on silicon nitride nanopillars.The diameter of the designed metalens is 500 m,the numerical aperture(N.A.)is 0.05,the focal length 5 mm,and the working wavelength 532 nm.We first optimize the unit cell with high conversion efficiency at wavelength of 532 nm by using the FDTD software,and the theory of dielectric resonance.The influence of varying geometric parameters of the unit cell on the optical conversion efficiency is numerically analyzed.Then,according to the Huygens principle,the Fermat principle and geometric Berry phase,the phase distributions of the metalens can be calculated and mapped into the design of metasurface.Finally,we fabricated the metalens and measured their optical focusing performances.This thesis also presents the detailed fabrication processes of the optical metasurfaces and analyses the influences of the process parameters on performances of the fabricated samples.Firstly,Electron Beam Evaporation is used to prepare the aluminum film and the silica spacer,the Plasma-Enhanced Chemical Vapor Deposition is used for depositing the silicon nitride films.The thicknesses and the refractive indices of the films are characterized by using the Spectroscopic Ellipsometry.Next,the pattern transformation is performed by Electron Beam Lithography.At last,the metal lift-off process is used for fabricating the aluminum metasurface,and the Induction Couple Plasma Reactive Ion Each for the sili con nitride metasurface.