Investigation Of Calculation Method Of Geometric Phase Metasurfaces Diffraction Light Field Based On Vector Diffraction Theory

Metasurfaces are ultrathin planar artificial devices composed of subwavelength structure.Own to the flexible electromagnetic control capability,metasurfaces can perform many novel functions,such as electromagnetic stealth and anomalous refraction.As a kind of metasurfaces,geometric phase metasurfaces has the advantages of large phase tolerance,wide band response and simple design.In the design of geometrical phase metasurfaces,numerical simulation is often needed to verify its function.The methods of accurately calculating the diffraction field include Finite Difference Method,Finite Integral Method and Finite Element Method.The basic idea of these methods is to divide the solution region into several grids,and then calculate the distribution of diffraction light field in the simulation region based on Maxwell's equations.However,when the solution area is too large or the diffraction distance is too far,such numerical calculation method will be time-consuming.Therefore,it is necessary to propose a fast and accurate simulation method to caculate the diffraction field distribution of geometric phase hypersurface.Without considering the interaction between the incident light and the material,the vector diffraction theory can quickly calculate the diffraction field distribution of the structure.The phase control of geometric phase metasurfaces is only related to the rotation angle of the structural elements.Therefore,we can use vector diffraction theory to calculate the diffraction optical field characteristics of geometrical phase metasurfaces.Based on this method,the following works have been carried out in this article:1.K-type and S-type subwavelength structures are designed,and the intensity distribution of the structure is calculated by using vector diffraction theory combined with geometric phase method.At the same time,the intensity distributions of the two structures are calculated by using the electromagnetic simulation software Computer Simulation Technology(CST)based on the Finite Integral Method.By comparison,it can be found that the vector diffraction theory combined with the geometric phase method can obtain basically the same results as CST,which proves that the method can be used to solve the intensity distribution of geometric phase metasurfaces diffraction.Both CST and vector diffraction theory combined with geometric phase method can be used to obtain the diffraction field distribution of the two structures,but the calculation time of the latter is 50 to 100 times less than that of the former.2.Two kinds of catenary geometric phase metasurfaces,a planar focusing lens and a Bessel beam generator are designed.The optical field distribution is calculated by vector diffraction theory combined with geometric phase method.By this method,the focal length of the focusing lens can be obtained at about 13.5 ?m from the device,and the focal length obtained by CST is about 13.2 ?m;the equal intensity region of Bessel beam generator is in the range of 100-125 ?m from the device,and the region obtained by CST is in the range of 95 to 130 ?m.As can be seen from the results,the error range of the two methods is less than 10%.