Research On Anomalous Refraction Effect Of All-dielectric Metasurface

In recent years,metasurfaces have gained more and more attention because of their ultra-thin structure and ability to accurately control electromagnetic field.Metasurface is a kind of special ultra-thin artificial electromagnetic metamaterials,which can flexibly and effectively control the phase,polarization mode,propagation mode and other characteristics of incident light at the sub-wavelength scale.It can realize focusing imaging,anomalous refr-action,anomalous reflection,perfect absorption,polarization rotation and other physical functions.Compared with traditional bulk metamaterials,the metasurface has significant advantages such as small size,thin thickness,easy preparation and integration.At the same time,the flexible and accurate control of light on the metasurface is also superior.Anomalous snell's law shows that linear phase gradient in the horizontal direction will result in anomalous deflection of incident light,resulting in additional deflection angles.According to this theory,the phase gradient metasurface composed of the classical discrete antenna array has been widely studied and realized.The metasurface of this kind of structure is easy to design and the research results are abundant.It has been widely used in many fields such as flat lenses,meta-holograms,optical vortex,polarization converter and so on.However,the structure of discrete antenna array has some defects,such as difficulty in preparation and low fault tolerance.The quasi-continuous phase gradient metasurface proposed in recent years is composed of trapezoidal dielectric plates arranged periodically,which effectively reduces the difficulty of preparation.The all-dielectric quasi-continuous phase gradient metasurface has significant advantages such as low loss,high efficiency,easy preparation and low preparation cost.Based on the design and analysis of a kind of classical discrete antenna array supersurface,we further designs a new type of quasi-continuous phase gradient metasurface that works in the visible light and transmission mode,and deeply analyzes the anomalous transmission performance,physical mechanism and preparation feasibility of the designed metasurface.The main works are as follows:1.Simulation design an all-dielectric phase gradient metasurface based oin discrete rectangular cylindrical antenna array and obtain a full 2n phase shift and high transmission efficiency.It lays a foundation for designing quasi-continuous phase gradient metasurface.In addition,the magnetic field distribution of the rectangular cylindrical antenna at the concave point of the transmission curve during the change of the side length is analyzed,and the physical mechanism of phase gradient generation is analyzed by using fabry-perot resonance cavity.2.The transformation fr-om discrete nano-antenna array to quasi-continuous trapezoidal antenna array is realized by two splicing methods.A kind of quasi-continuous all-dielectric phase gradient metasurface working in transmission mode is proposed for the first time,and the anomalous snell's law is verified.Under the vertical incident of linearly polarized plane light at the wavelength of 751nm,and when the polarization direction of linearly polarized light is perpendicular to the phase gradient direction of the supersurface,the anomalous transmission angle is 29.62°,and the total transmission rate is as high as 88%.The anomalous part of the transmission efficiency is as high as 80.4%,which shows that the structure has high anomalous transmission efficiency.The reasons for the loss of the metasurface,the performance change in the near-infrared band,the efficiency change in the case of larger abnormal transmission angle and the influence of the thickness of the dielectric plate on the transmission efficiency of the supersurface are further analyzed.This structure is much simpler than the metasurface based on discrete nano-antenna array structure,which lays a foundation for the design and application of highly integrated wave-front control optical devices with highly efficient all-dielectric phase gradient metasurface.To summary,based on the design and analysis of a kind of classical discrete nano-antenna array metasurface,we design a new type of all media quasi-continuous phase gradient metasurface,and further study its characteristics and physical mechanism.