Study About Light Beams With Controllable Propagation Trajectories And Their Wavefront Modulation Based On Metasurfaces

Beams with controllable propagation trajectory and customized wavefront have important application prospects.Accelerating beams exhibit self-bending phenomena during the propagation,and they have been widely used in optical manipulation,material processing,optical soliton generation and transmission,and the formation of plasma channels because of their unique diffraction-free,self-accelerating and self-healing properties.Optical vortices with spiral wavefront have also received much attention both domestically and internationally for the generation of vortex beams and their applications in optical communications,optical manipulation and optical processing because they carry orbital angular momentum to provide powerful conditions for light-matter interaction.The organic combination of controllable propagation trajectory and customized wavefront to generate new beams must bring broader application prospects for accelerating beams and vortex beams.Conventional optical field modulation is often accomplished with the help of cumbersome optical system,electrically controlled spatial light modulator,or specially designed optical component.This not only requires precise fabrication and complex operation,but also the large size and low spatial resolution hinder the miniaturization and integration of device,and it is more difficult to realize the optical field modulation in nanometer scale.Optical metasurface points to ultra-thin structure composed of nanounit array,and optical metasurface shows powerful optical field modulation capability only with the help of structure setting.Because of the ability to achieve optical field modulation at the nanoscale,the design of diverse functional devices and optical field modulation based on metasurface have become the hot research topic in the field of nanophotonics.Currently,metalens,conical mirror,perfect absorber,miniature differentiator and multiplexed functional devices have been designed with the help of metasurfaces,which lay a sound foundation for further advancement of ultra-thin and compact microphotonic devices.In this thesis,the optical field modulation is realized based on the metasurface and the metasurface devices are designed to effectively control the propagation trajectory and optical wavefront of light beams.The optical fields with customized propagation trajectory and optical wavefront are obtained through analyzing the optical field modulation mechanism of metasurface,selecting suitable theoretical model and constructing effective metasurface structure.Therefore,the content of this paper includes the comparison of three phase modulation ways of metalens,the exploration of different spiral wavefront generation and their characterization,the formation of accelerating beams with steerable and reversible trajectories based on the phase modulation of metalens,and the combination of optical vortex with accelerating beam to generate accelerating vortex beam.The innovative works of this thesis are as follow,First,the optical properties of the metalenses and vortex metalenses formed by three phase modulation methods are systematically studied,and the advantages of three phase modulation methods are compared to provide a basis for the future design of metasurface devices through choosing one of phase modulation methods.Second,uniform vortex and non-uniform vortex are characterized,and the method to generate different vortices based on the metasurface is proposed.Third,one concise analytical expression for the input phase of accelerating beam is proposed and the accelerating beam with reversible trajectory is generated based on the designed metasurface,which breaks the limitation of the existing unidirectional bending trajectory among the generation of accelerating beams.Fourth,the multi-point focusing method is proposed to generate the accelerating beam with arbitrary propagation trajectory,and the accelerating vortex beam is achieved through organically combining vortex and accelerating beam.The details of this thesis are divided into six chapters.The first chapter is the introduction of this thesis.This chapter describes the accelerating beam,vortex beam,metasurface and their related contents.Chapter 2 is the generation and characterization of optical vortices.The mathematical descriptions of uniform and non-uniform vortices are presented,the distortion characteristics of non-uniform vortex fields are investigated,and uniform and non-uniform vortex fields are generated with the help of metasurface.Chapter 3 is the phase modulation of the metasurface and optical metalens.The focusing metalens and vortex metalens are designed based on three phase compensation methods and their optical performances are compared.Chapter 4 is the study of the generation of steerable accelerating beams based on the metasurface.The analytical formula of the input phase of the steerable accelerating beam is constructed through cleverly introduced one parameter considering the translation symmetry of the propagation trajectory.The accelerating beam with the reversible propagation trajectory or with an inflection point is generated theoretically,and the simulation and experimental results give the sound confirmation.Chapter 5 is the study of the generation of accelerating beam and accelerating vortex beam with arbitrary trajectory.The multi-point focusing method is used to generate the accelerating beam and the accelerating vortex beam is achieved through introducing the vortex into the accelerating light field.Chapter 6 gives the summary and outlook of this thesis.