Research In Imaging Based On Titanium Dioxide All-dielectric Metalens Doublet

The all-material metamaterial based on the Mie scattering mechanism has no ohmic loss,and its efficiency in the visible light band can reach more than 90%.In the visible light band,titanium dioxide has a large n part of the refractive index,and the imaginary part k is small and almost zero.It has strong interaction with light,and can easily reach the 2? phase coverage,achieving complete regulation of the optical wavefront and maintaining ultra-high efficiency.,theoretically up to 100%.Therefore,the super-surface of titanium dioxide has a very broad development prospect.The metalens is an application form of the metasurface,whose phase is transient,is different from that of the conventional lens,and the antenna is arranged to meet the required phase requirement.The lens is an important part of the mobile phone limited by the thickness of the traditional lens,In order to meet multiple functions,an additional lens group is required,and the thickness of the mobile phone cannot be made thin.In this paper,two different metalenses whose working wavelength is 520 nm,are prepared by using titanium dioxide all-dielectric material,combinning into a metalens group.By adjusting the distance between the lenses and the nature of the incident light,three functions of the mobile phone lens,the microscope and the Galileo telescope can be realized.In order to achieve complete control of the wavefront of light,it is necessary to satisfy the complete coverage of phase 0-2?.In order to eliminate the influence of the first metalens(objective)imaging on the imaging of the second metalens(eyepiece),two methods are used in this paper: nano-cylindrical and nano-squares.Through the understanding and research of the basic theory,the silica substrate + Ti O2 antenna is used as the basic unit,and the Max equation solving software is used for simulation to set appropriate optical parameters and geometric parameters,such as refractive index,period,thickness,and nanocylinder.The thickness,the length of the nano-squares,etc.,give a basic structure in which the transmittance is 90% higher and the phase covers 2?.According to the metalens phase distribution formula,the coordinates corresponding to the basic unit are determined,and the irregular arrangement is performed.Metalenses are prepared using micro-nano processing techniques.Since the size of the antenna is at the sub-wavelength level,its accuracy is very high.In this paper,micro-nano preparation techniques,such as electron beam sputtering coating,electron beam exposure(EBL),reactive ion etching,etc.,are strictly controlled to control the size of the basic unit,and the design size error is within 10 nm.The metalens is optically characterized by the built measuring optical path.The objective lens is at the design wavelength ?=520 nm and its focusing efficiency is 70%,NA = 0.258,half width = 1400 nm,and the strell ratio is 0.91 and 0.89 in the x and y directions,respectively.The eyepiece has a focusing efficiency of 60% at the design wavelength,NA = 0.66,half width = 390 nm,and the strell ratio is 0.827 and 0.829 in the x and y directions,respectively.In this paper,the objective lens and the eyepiece are combined.By a djusting the distance of the lens and the nature of the incident light,the three functions of the mobile phone lens,the microscope and the Galileo telescope are realized.Using the micro-nano preparation technology,the micro-nano-resonance board of HIT,the abbreviation of HIT of Harbin Institute of Technology,was prepared.The HIT board was magnified,reduced or long-distance observed by the super lens group.When the objective lens and the eyepiece are combined into a lens group as a mobile phone lens,the HIT board can be reduced by 11.74 times.As a microscope,it can achieve 20.58 times magnification of the HIT board,and the resolution is 1.07 ?m.As a Galileo telescope,it can image LED light with a distance of 11 m.The lens group is also operable in blue light having a wavelength of ? = 445 nm and red light of ? = 632 nm.When ? = 445 nm,14 times magnification can be achieved,and when ? = 632 nm,19 times magnification can be achieved.