Research On Polarization Optical Devices Based On Metal Slit

As a new type of artificial two-dimensional material,the metasurface is composed of subwavelength structural units.Because it can realize on-demand adjustment of the polarization state,amplitude and phase of incident light waves,it has been extensively studied by the academic community.Based on different metasurface structures,metasurface optical devices with multiple functions have been designed and implemented,such as flat lenses,vortex phase plates,holographic dry plates,and polarization deflectors.Among them,the metasurface lens,as an important optical imaging element,has the advantages of high integration,small size and thin thickness,and is currently a research hotspot in the field of micro-nano photonics.Surface plasmon polaritons(SPPs)are electromagnetic waves that are generated by the coupling of free electrons on the metal surface and incident light waves that propagate along the metal/medium interface.Because of its unique optical properties that can break through the optical diffraction limit,surface localization,and near-field enhancement,it has become an excellent carrier for photon manipulation and integration at the nanometer scale,and is widely used in integrated photonics,biosensing,and holographic imaging.And Raman enhancement.The realization of surface plasmon light field control based on the metal slit structure is an important research content of sub-wavelength light field control.The design of the slit structure and its polarization-dependent characteristics are the key factors for the realization of light field control.Based on the nano-metal slit structure,this dissertation has carried out research work in two aspects: metasurface lens design and surface plasmon polaritons light field manipulation.In the first part,we designed a polarization-independent metal slit metasurface lens based on the principle of the binary phase Fresnel zone plate(FZP).This lens can overcome the polarization dependence of the incident light and is different from the traditional amplitude Compared with the type metasurface lens,its focusing efficiency has been improved;on this basis,we designed a multifocus FZP metasurface lens that can achieve multiple focusing.In the second part,we designed and experimentally prepared a square nano metal slit structure.By changing the width of the metal slit,the photonic mode and plasmonic mode light waves excited by it were adjusted to obtain a variety of two-dimensional interference light.Field pattern;at the same time,we use linearly polarized incident light in different directions to illuminate,and analyze the evolution of the lattice array with the polarization direction.The specific content of this paper is as follows:The first chapter is the introduction part of this thesis.First,it introduces the research background and characteristics of Surface plasmon polaritons briefly explains the dispersion threshold,energy limit and effective mode wavelength of surface plasmons,and analyzes the excitation and detection methods of Surface plasmon polaritons one by one,and introduces them in detail.The various applications of metal nano-slits to control Surface plasmon polaritons are introduced;the research background of metasurface and the classification of metasurface are introduced,including resonance phase metasurfaces,geometric phase metasurface,dynamic phase metasurface,and dynamic-geometric hybrid phases.Metasurface,and the application prospects of metasurface are reviewed;again,we briefly introduce the polarization of light and Jones matrix;finally,we describe the innovations of this paper.In the second chapter,based on the principle of the binary phase Fresnel zone plate,we design a polarization-independent nano-slit metasurface lens.This lens can achieve the focusing of incident light in any polarization state.At the same time,the dispersion characteristics of the metasurface lens are studied to prove that it can work in a wider wavelength band;the focusing efficiency of our designed lens is compared with the amplitude type supersurface lens in the previous literature.Comparing the surface lenses,it is found that the focusing efficiency of the metasurface lens is four times that of the latter;finally,based on the above research,we designed a multi-focus FZP metasurface lens,which has the advantages of overcoming polarization dependence and a wider band.Advantages of work.The metasurface lens we designed has potential application value in polarization-independent optical devices.Chapter 3 first analyzes the relationship between the amplitude and phase of the light wave of the photonic mode and plasmonic mode excited by a single slit with the width of the slit under the irradiation of vertically polarized light;on this basis,we design a square slit structure,by changing the width of the slit and the polarization state of the incident light,a variety of interference light field patterns including fringe,square grid array and diamond grid array are obtained;at the same time,samples of square slit structure are prepared experimentally,The interference pattern was collected by the far-field scattering imaging method;combined with the excitation efficiency of the two modes of light waves,we analyzed the evolution of the interference pattern with the slit width and the incident polarization state.Finally,the finite-difference timedomain simulation software is used for simulation verification,and the simulation results are consistent with the theoretical and experimental results.The fourth chapter explains the innovations of this paper,summarizes the research work,and introduces the next work plan.