Complex Amptitude Modulation Of Light Waves And Surface Waves Based On Metasurface

As a special kind of metamaterial,Metasurfaces can realize special physical properties that natural materials do not have by artificially designed two-dimensional structures.With the continuously proposed design and modulation methods,the application fields of metasurfaces are expanding,showing powerful wavefront control ability in many fields such as wavefront shaping,holographic display and orbital angular momentum manipulation.In the wavebands of near infrared and visible light,the realization of optical response is usually based on structures with smaller size.Therefore,more concise structures need to be designed for physical processing.Besides,for a wider range of applications in color holographic display,plasmonic integrated circuit and the generation of complex light field,it is necessary to realize tunable and broadband nondispersion design,as well as the combination of modulation methods for different optical parameters.The basic concepts of metamaterials and metasurface are described in this thesis,and the modulation existing modulation methods and application of metasurfaces are introduced.Through the analysis and extension of the basic theory of wavefront control by phase and ampltitude with metasufaces,a variety of design methods are proposed applied in the modulation of propagation light field in free space and surface plasmon polaritons in the near field regime.Simulation analysis,sample processing and experimental verification are carried out for the applications of three dimensional vortex array,selectable diffraction order excitation,tunable multiport surface plasmon excitation and focusing,and Airy plasmon.The main work and achievement include following aspects:1.The phase distributions of Dammam vortex grating,spiral Dammann zone plate and lens factor are realized in the design of metasurface with dielectric nanorods.Through the combination of the three distributions,according to phase modulation in the subwavelength pixel size Based on Berry phase principle,three-dimensional vortex arrays are generated with a single device.According to the principle of Berry phase,different phase changes are produced when the propagation beam passes through different polarization states to the same final polarization state.With the circular polarized incident light,different linear polarization responses are generated based on the azimuthal angle of metal or dielectric nanorod cells on metasurface.The design of silicon dielectric metasurface is verificated by sample processing and experimental measurement.In the three dimensional vortex array,the number of topological charges in each focus node can be controlled independently by the phase design and orbital angular momentum of incident light.2.The modulation method based on Berry phase is extended to complex amplitude modulation of amplitude and phase.Besides the phases modulated by azimuth angles of nano-units on metasurface,the amplitude values are modulated by the change of the geometry size,and the caused phase change in such procedure is compensated by additional azimuth angle.For the propagation field in free space,a design of selective excitation of two-dimensional diffraction order based on the method of complex amplitude control is proposed,which can stimulate the selected diffraction orders while completely restrain the unselected ones.Samples were processed through the dielectric metasurfaces.The results of the generation diffraction orders are measured,and diffraction angles of different orders in the experimental results are compared with theoretical values.As a comparision,the sample designed by phase-only modulation is also processed and measured in the experiment.3.According to the momentum matching condition and polarization selectivity of surface plasmon excitation,as well as the holographic control method for surface wave,two kinds of design are proposed for realizing the tunable multiport surface plasmon excitation and focusing respectively.With the change of the wavelengths and polarization states of the incident light,the control of the propagation and focusing directions of the surface plasmon can be realized.The focusing efficiency of two structures under different incident conditions is compared by a quantitative analysis method,including the special cases of radial polarized light incident.4.The complex amplitude modulation method based on Berry phase is applied in the field control of Surface Plasmon Polaritons in near field regime.Based on the metasurface structure of rectangular nanoapertures,a wavefront control design for near-field regime is proposed,which achieves the excitation of surface plasmon and the distribution of surface wave by complex amplitude modulation.In order to verify such method of complex amplitude regulation for surface waves,metasurface structures for Airy plasmon and axisymmetric Airy beam are designed,with the physical processing and near field measurement.In addition,in order to reduce the computation time,the method of two dimensional equivalent dipoles is also used in numerical simulations.The theory is in good agreement with the experimental results.