Research On The Characteristics Of Bifunctional Metasurface At Visible Wavelength

In recent years,optical technology has been widely used in the nano field,the complete control of electromagnetic waves has always been an emerging field of research.Traditional metamaterials have many drawbacks,such as high inherent losses and manufacturing difficulties,which limit the miniaturization of the device in practice.Metasurface,which is regarded as a two-dimensional metamaterial,is an artificially arranged sub-wavelength micro-structure array,where each structure can be regarded as a unit cell that is controlled by electromagnetic waves.Due to its ultrathin sub-wavelength structure,relatively easy to manufacture and conformal integration with systems,in the sub-wavelength range,it can achieve flexible and effective control of electromagnetic wave propagation mode,polarization,phase and other characteristics,and realize functions such as anomalous refraction,anomalous reflection,polarization conversion and holographic imaging.Meanwhile,the accuracy of the metasurface for electromagnetic wave regulation is also greatly improved compared to traditional matamaterials.However,the metasurfaces invented bt people have a single function.With the increasing demand for data storage and information management,it is desirable to fabricate a device that has multiple functions.Based on the classical antenna array metasurface,in this study,we propose a highly efficient bifunctional metasurface,enabling beam anomalous refraction and focusing under different normal incident polarized light,and deeply analyzes the anomalous refraction and focusing characteristics of the metasurface.Based on the proposed metasurface above,we further design the other two metasurfaces demonstrating high-order beam anomalous refraction and focusing by increasing the phase gradient between neighboring unit cell in the horizontal direction.For the designed bifunctional metasurface,we simulate with the finite difference time domain(Finite Difference Time Domain,FDTD Solutions,Lumerical,Canada)to carry out a series of research,the main contents are illustrated as follows: 1.Construct a geometric model,and design a unit cell with 0-2? phase shift and higher transmission efficiency(more than 86%)according to the material properties of silicon and silicon dioxide.2.Based on the generalized Snell's and focusing law,design the bifunctional metasurface,demonstrating beam anomalous refraction and focusing at660 nm and realizing the refraction angle of 14.02° and a focal length of 10.9?m,which closely agree with the theoretically calculated value of 14.48° and 11?m.In addition,we also analyze the relationship between the period of the unit cell and the anomalous refraction angle and focal length.3.Based on the designed metasurface above,by increasing the phase gradient between neighboring unit cell in the horizontal direction,the metasurfaces working in 2nd and 3rd order anomalous refraction modes while maintaining the focusing characteristics are designed successfully,we verify the accuracy of design by comparing the simulated and theoretical calculation value.In conclusion,we design a bifunctional metasurface based on the classic dielectric phase gradient metasurface,and on this basis,we design the other two metasurfaces that work in high-order modes with the grating diffraction theory.Our work can be extended to the design of other optical transmitting facilities with high-efficiency,which will be useful in the fabrication of miniaturized and multifunctional metadevices and open the way for wavefront regulation that can achieve different functions on a same device.