Investigations Of Light Manipulation Of Planar Lenses Based On The Optical Metasurface

Metasurfaces are ultrathin two-dimensional flat structures composed of nano-scatterer arrangements,which can manipulate the phase,polarization and amplitude of light,and is the one of research hotspots of metamaterial in recent years.Metasurfaces can generate local abrupt phase shift,and they can achieve anomalous refraction and reflection based on the Generalized Snell's law,so they have stronger light control ability compared with conventional optical elements.Metasurfaces indicate large potential application value in many fields owing to its ultrathin volume and strong light control ability,including photonics integrated chip,optical imaging,sensing technology,wearable display and invisibility cloak.Therefore,it is very important to deeply study the optical properties and practical application.In this thesis,based on the Pancharatnam–Berry?PB?phase theory,using the using finite difference time domain?FDTD?method,we have proposed the near infrared metasurface zoom lens and the flat lens based on the reflective hybrid metasurface at the visible wavelengths.The major researching contents of this thesis can be concluded as follows:1.A near infrared zoom lens based on dielectric metasurface is proposed.Based on the sensitive of PB phase to the polarization of circular light,the zoom lens was formed by cascading two metasurfaces with the same polarity.The zoom lens can operate with long and short focal length modes by easily converting the handedness of the incident circular polarized light,meanwhile the focal plane remained unchanged.The zoom lens exhibit excellent focusing and zoom performance.When the incident wavelength?=1550nm,two tight focal spots 0.57?and 0.79?for NA=0.95 and 0.66were obtained with corresponding high efficiencies 58.2%and 80.7%,respectively.The long and short focal lengths are 7.5?m and 1.5?m,and the zoom ratio is 5.Additionally,the two focal spots are very symmetric,which leaded to high-quality imaging.2.We proposed a reflective dielectric-metal hybrid metasurface at visible wavelength.Titanium dioxide?TiO₂?elliptical nanoposts are placed on a silicon dioxide?SiO₂?spacer layer above an aluminum?Al?mirror.The reflective metasurface provides a broadband optical response of 550⁷00nm and high polarization conversion efficiency more than 87%.The planar lens based on the metasurface obtained a focal spot?434nm?which was much closed to the diffraction limit,when the work wavelength is 600nm,and focal length is 5?m.3.Based on the fundamental reflective flat lens,the double-focal and double-wavelength lenses are also designed by utilizing the superimposed phase distribution idea.The double-focal lens obtained two focal spots which show good consistence with the designed focus positions at 600nm wavelength.The double-wavelength lens obtained two focal spots which both were near the designed position z=5?m at 550nm and 680nm wavelengths.Besides,the focal spots of the two planar lenses are both closed to the diffraction limit.