Study About Light Focusing And Color Display Based On Metasurface

Conventional optical components possess some specific functions that can control the polarization,phase,amplitude,and frequency spectrum of the light field through the accumulation effect of absorption or dispersion along the propagation path.This makes the traditional optical devices bulky,and it is difficult to meet the needs of integrated optical components in modern optical technology.Metasurfaces point to two dimensional metamaterials possessing ultrathin structure,easy integration and flexible manipulation of optical field.The nanostructures to construct metasurfaces can be holes,slits or bulges.The metasurface can precisely manipulate the light field through the interaction of nanostructures and the illuminating light,thus it is widely used in the abnormal transmission and reflection,wavefront regulation,polarization conversion and color filtering.The wide application prospect of metasurfaces makes the relevant basic and applied research become a research hotspot in the field of nanophotonics.In this paper,the metasurface is formed the nanostructure etched on the silver film,and the parameters of the nanostructure units and their spatial arrangement are adjusted to achieve effective control for the optical amplitude,phase,polarization state and light spectrum.The innovative work of this thesis mainly includes three aspects.Firstly,the additional phase shift is obtained by adjusting the size of the rectangular nanoholes,and the polarization insensitive metalens is realized based on the principle of in-phase constructive interference.Secondly,the cross hole structure unit is optimized to be equivalent to the half-wave plate,and the color polarization multiplexed metalens generates based on the geometric phase introduced by the rotation of the nanostructure units.Finally,the transmission spectrum of different wavelengths is obtained by adjusting the sizes of the rectangular nanoholes in the visible light band to realize color filtering and color display.Chapter 1 is the introduction part of this paper.This chapter introduces the study process of metasurfaces.The precise adjustment to the light field enables metasurface widely used in the design and development of new optical devices.The metasurface can be used to adjust the phase and polarization of the light to achieve a multi-functional metalens.The dependence ofspectral transmission on the nanostructure can be used to tune its spectrum,and the color filtering and color display can be achieved by using the metasurface.Since the main work of this thesis involves metal metasurfaces,this chapter also introduces the interaction of light and metal,including the basic characteristics of surface plasmon polaritons.Since the metasurface consists of nanostructure and the unit arrays,several fabrication methods for micro-nano structures are introduced at the end of this chapter.Chapter 2 proposes the metalens that is composed of rectangular nanoholes etched on the silver film,and it can achieve the focusing effect in the visible region.These rectangular holes are arranged on concentric circles,and the transmission phase is obtained by optimizing the size of the rectangular holes and the radius of ring.The light fields excited by rectangular holes at different positions have the same transmission phase with respect to the focus spot and they constructively interfere.The proposed metalens can realize the beam focusing under linear or circularly polarized light illumination.The focusing performance of the metalens is confirmed by numerical simulations and experimental measurement.The proposed metalens has the advantages of compact structure,insensitive polarization,ease to make and simple experimental operation.This is helpful for the applications of metalenses in optical integration and visible light imaging.Chapter 3 proposes a kind of color polarization multiplexing metalenses composed by two sets of cross nanoholes etched on the silver film.The cross nanoholes are arranged on the concentric rings and the spherical wave phase delay is introduced through the rotation of the cross nanoholes.We optimize the cross nanoholes equivalent to half wave plates for two different wavelengths.For ensuring the beam focusing for different wavelengths of the metalens under right-handed and left-handed circularly polarized illumination,one set of cross holes rotates counterclockwise,while the other set of cross holes rotates clockwise.The use of equivalent to half wave plates can achieve the effective conversion for circular polarization and obtain the focusing field with high signal-to-noise ratio.Theoretical analysis shows the working principle of color polarization multiplexing metalens.Numerical calculations and experimental measurements confirm the focusing effect of color polarization multiplexing metalenses.Our designed color polarization multiplexing metalenses possess the advantages of color control,polarization multiplex and high quality focusing,and they arehelpful for the applications of metalenses in color information processing and optical imaging.Chapter 4 shows the metasurface color displays based on the rectangular hole arrays and their combination.According to the dependence of the transmission spectrum on the nanostructure and the incident polarization state,we can adjust the length and width of rectangular holes,the period of hole array etched on the silver film and the polarization direction of illuminating light to obtain three primary colors with high purity.The color displaying is realized according to the polarization dependence of the transmission spectrum.Our proposed color displays consisting of three suits of hole arrays and each set of rectangular holes array corresponds to the corresponding transmission spectrum.Different combinations of three sets of rectangular holes realize a variety of color display patterns,and the simulated results give corresponding verification.The proposed metasurface color displays can be used to separate colors with high fidelity,analyze the incident polarization according to different colors display patterns,and their ultrathin and compact structures are benefit to expanding its applications in color information processing.Chapter 5 is the summary of this paper and the prospects for following work.This chapter summarizes the main work of the paper and the following plan in the next work.