Study On The Principle And Technology Of Geometric Phase Based On Metallic Metasurfaces

As a kind of two dimensional artificial electromagnetic materials,metasurfaces can freely modulate the phase,amplitude,and polarization of electromagnetic waves at the subwavelength scale.Compared with traditional devices,metasurfaces have the advantages of light weight,flatness,flexible control,etc.,which provide a new technical approach for achieving compact and integrated electromagnetic wave control systems.Phase is one of the basic physical parameters of electromagnetic waves.In recent years,the use of metasurfaces to regulate the phase of electromagnetic waves has achieved a series of novel functions and phenomena,such as optical spin Hall effect,the generation and modulation of vortex beams,holographic display,and virtual shaping etc.Among various types of phase-type metasurface devices,geometric metasurfaces have received wide interests for their advantages such as wide operating bands,simple design,and large tolerances.At present,there are still some problems with metasurfaces based on geometric phase,such as inadequate theoretical system,low operating efficiency,single working spectrum and function,and so on.Aiming at these problems,this paper conducts research on the principle and technology of geometric phase modulation based on metasurfaces,with emphasis on metallic metasurfaces.The main contents include:1.Subwavelength structures with high-order rotational symmetry such as regular triangles and regular pentagons are introduced into linear optical metasurfaces,and their interaction with electromagnetic waves is studied.It is found that these structures can also generate frequency-independent geometric phase,and the phase gradient is related to the rotational symmetry of the meta-atoms.The relationship between the geometric phase and symmetry of the meta-atoms in linear optical metasurfaces is summarized,and then a generalized geometric phase is proposed.2.All-metallic metasurfaces are proposed,which have smaller ohmic loss than the classic metal-insulator-metal configurations,thereby enabling higher energy efficiency.Based on this idea,a metasurface composed of discrete elements is first designed,and the measured energy efficiency reaches 84%.Next,to further improve the efficiency,a metasurface beam splitter is designed based on quasi-continuous catenary structure.The measured efficiency reaches 92%.On this basis,the working frequency is adjusted by injecting alcohol into the metal groove and controlling the height of the liquid surface.In addition,a mathematical model based on the catenary optical fields and dispersion is established to clarify the electromagnetic coupling mechanism in subwavelength metal pillars and gratings.3.All-metallic metasurfaces are applied to virtual shaping technology to achieve multi-band target characteristic signal control.First,a metallic metasurface with low infrared emissivity is used to reflect laser abnormally to implement the compatibility of laser and infrared.Subsequently,the all-metallic structure is extended to the microwave regime for realizing the compatibility of radar and infrared,and a catenary dispersion model is established to optimize the operation bandwidth.Compared with the conventional metal-dielectric composite structures,all-metallic metasurfaces have better properties such as high temperature resistance and corrosion resistance.Finally,the all-metallic metasurface is integrated with a metamaterial microwave absorber to achieve laser-infrared-microwave compatibility.It is worth mentioning that a single-layer dielectric metasurface is also designed to realize dual-band and ultra-broadband virtual shaping in the infrared regime.