Investigation On Multi-wavelength Focusing Lens Based On Metasurface

As an artificial two-dimensional sub-wavelength electromagnetic material,metasurface has the characteristics of ultra-light and ultra-thin.By optimizing the geometry,parameters and arrangement of these sub-wavelength structures,it can control the amplitude,phase and polarization of electromagnetic wave flexibly.Because of the flexible regulation ability of metasurface to electromagnetic wave,it can realize various optical functions.As a common component in optical systems,traditional lens has a single function and is hard to integrate,therefore,multifunctional metalens has become a hot spot.However,in multi-wavelength design of metasurface,polarization independent structures are often used or only response to a single polarization state.There is a lack of research on polarization multiplexing metasurface,and the phase response to multiple wavelengths is similar,so the function is single.In order to solve the problems,the circular polarization multiplexing metasurface focusing lens and wavelength multiplexing metalens are studied in this paper.The main research of this paper includes:1.A geometric phase polarization multiplexing metasurface is designed.The amplitude and phase are modulated by changing the geometric size and direction angle of nano-cylinder in sub-wavelength structure.According to the principle of geometric phase modulation for circularly polarized light,the modulation phase obtained by cross-polarized light has a linear relationship with the structure direction angle,can be designed as a focusing lens for 473 nm,532nm and 632 nm.The obtained modulation phase of co-polarized light is independent of the direction angle,can be designed as a transmission glass for 400nm-700 nm in visible light.Using this method,a polarization multiplexing metasurface with three right circular polarized light and broadband left circular polarized light is designed.Through further research and optimization,this kind of metalens is expected to be used as transparent display eyepiece.2.Focused on the focusing difference of multi-wavelength focusing lens under off-axis incident condition,a wavelength multiplexing transmission phase metalens is designed.The phase and amplitude of three wavelengths are controlled by different width of dielectric nano-pillar.Due to the sensitivity of wavelength to the structure,the phase response with different wavelength can be obtained,a database corresponding to the structure and phase is established.By constructing a mathematical model of metasurface phase distribution and using particle swarm optimization algorithm,the full-mode design is carried out,and the function of multi-wavelength chromatic aberration adjustment is realized.According to the off-axis incidence,a metalens which can multiplex the multi-wavelength is designed,it can realize the function of three wavelengths incident at three different angles,and finally focus on the axis with the same focal length.