Research On The Key Technology Of Metalens

Metalens is a kind of metasurface device,to a certain extent,which is expected to replace the optical system.With the continuous maturity of micro nano manufacturing technology,the great advantages of metasurface in phase modulation make it a hot spot to explore the related technologies of metalens to break through the limitations of traditional optical imaging technology.Similar to traditional optical elements,many problems still exist in the actual design of metalens,such as wide field of view,continuous zoom,polarization control,dispersion and so on,which will affect the imaging quality.This paper will focus on achromatic imaging and polarization control imaging in the above problems,in order to explore the solutions of metalens in related problems.The main contents include the following parts:1.At a wavelength of 660 nm,we first explored the difference between the response of polarized light and the design of different metalenses for nano units with circular,triangular and square cross sections.Secondly,the rotation invariance of the shape of nano units is destroyed,and we propose a new scheme of designing polarization independent metalens.Using the symmetrical way of nano unit array,a metalens which can focus circular polarized light with a wavelength of 660 nm and linear polarized light is designed.The focusing effect is similar and there is no obvious difference.The polarization independent focusing characteristic is verified.Finally,taking the incident light of different wavelengths in the visible band as the light field condition,it is further verified that the metalens has the ability of wide-band focusing and can realize polarization independent focusing at600nm～680nm.2.According to the construction formula of the metalens,the root cause of the chromatic of the metalens is analyzed,and the construction formula of the metalens is modified by adding the phase shift factor.Firstly,a metalens based on the transmission phase principle is designed to realize the basic lens phase and phase shift factor at the same time,and achromatic focusing is realized in the near-infrared band of 1000nm～1250nm.Secondly,in order to further increase the flexibility of phase modulation,a metalens based on the joint modulation of berry phase and transmission phase is designed.The phase distribution and phase shift compensation of the basic lens are realized respectively by changing the rotation angle of the nano unit and modifying the shape and size of the nano unit,and achromatic focusing is realized in the visible band of 400nm～600nm.3.According to the difference of specific conditions of different polarization imaging methods,it is decided to choose the polarization imaging method of real-time defocus plane.Based on the principle of joint modulation of transmission phase and berry phase,a database of nano units,which can respond to linearly polarized light and circularly polarized light at the same time,is designed and constructed.By constantly modifying the rotation angle and shape and size of nano units to meet the phase distribution required for different polarized light focusing,a metalens that can respond to incident light in different polarization states is realized at 950 nm in the near-infrared band.The eccentric focusing phase is adopted,The focusing spots formed by incident light with different polarization states are located in different coordinates in the four quadrants of the focal plane.