Research On Electromagnetic Field Control Via Dielectric Metasurface

Light is part of electromagnetic waves and is an important carrier for human beings to obtain information.The manipulation of light fields to transmit information has greatly contributed to the development of the society.Traditional optics rely on thickness changes to manipulate light.However,due to the limited choice of refractive index of natural materials,traditional optical elements are usually bulky and single functional can not meet the needs of modern optical system miniaturization and integration.Metasurfaces are two dimensional array of artificial electromagnetic nanostructures that rely on the strong interaction of light with the scatters to manipulate the light field.The subwavelength properties endow the metasurface with powerful wavefront modulation capabilities.With the development of nano processing technology and nano-photonics theory in recent years,the research on metasurfaces has embraced a rigorous development,and a series of novel optics based on metasurfaces have been proposed one after another,which has greatly promoted the development of integrated optics.However,although the current metasurface research has made remarkable achievements,it still faces the problems of narrow working bandwidth,small working incident angle,functional limited and working band limited,which make it difficult for metasurface to meet the requirement of practical applications.In this thesis,a novel theory of electromatic wave manipulation based on all dielectric metasurfaces is established,and a design method to expand the working bandwidth,widen the working angle and integrate multi-function is proposed.The details of this thesis are as follow:1 Study on the theory and design method of broadband achromatic metasurface was conducted.Based on ray tracing method and generalized Snell`s law,the dispersion properties of metasurface and the theoretical evaluation formula of the chromatic aberration of metalens are derived.A universal broadband achromatic metasurface design method is proposed,based on which an achromatic metalens working from9.6μm to 11.6μm is realized.Simulation results show that the Strehl ratio of the metalens is above the diffraction limit in the whole band,indicating broadband achromatic diffraction limited focusing is achieved.To demonstrate the generality of the method,we also presented a anomalous deflection metasurface whose deflection angle does not vary with wavelength,while the deflection angle of a conventional beam deflection metasurface varies from 25°to 34°.2 Research on wide field of view/ high resolution bifunctional metalens has been conducted.Based on ray tracing method ang aberration theory,we analyzed the reasons for the limited field of view of the metalens,and summarized the current methods of expanding the field of view of metalens and their intrinsic physical mechanism,and theoretically point out the essential reasons why it is difficult of realize a single layered wide field of view metalens.Then,we presented a design scheme of wide field of view metalens based on quadratic phase profile,and it is confirmed that it can achieve stable focusing property over a wide field of view but resolution is limited due to spherical aberration.Finally,a polarization dependent bifunctional metasurface with wide field of view or high resolution is proposed.We independently manipulates the phase of orthogonal polarization by exploiting the form birefringence of anisotropic meta-atoms.By applying hyperbolic and quadratic phase profile in the orthogonal polarization respectively,a metalens with both wide field of view and high resolution dual functions is realized,which is of great significance for the integration and miniaturization of search/ reconnaissance dual functional optical system.3 Research on the theory and design method of optical vortex generator metasurfaces has been conducted.Firstly,the principle of geometric phase based vortex generator metausrface has been investigated,and scalar vortex beams,radial vector beams and angular vector beams have been generated based on it.Based on the higherorder Poincaré sphere to explain the generation mechanism of optical vortex of arbitrary vector polarization state,the decoupling regulation of SAM and OAM is realized based on the hybrid phase mechanism to realize the generation of complex vector vortex beam.After that,we propose a metasurface design method for generating focused vector vortex beams of arbitrary polarization state,and verify its ability to generate broadband achromatic high-purity optical vortex with high efficiency through simulation.Finally,to verify the feasibility of the method,we also extend the above design method to the design of metalens,and realize a polarization-insensitive broadband achromatic metalens based on anisotropic meta atoms.