Enhanced Mie Resonance Metalenses Investigation Based On High-index And Low-index Medium Structure

Metalenses is a kind of phase type metasurface to realize the arbitrary control of the electromagnetic wave's phase,amplitude and polarization state,which can be through the ordered arrangement of a certain number of sub-wavelength unit structures.Compared with the metal metalenses,the all-medium metalenses has become a hot spot in the current direction of electromagnetic wave imaging due to its low loss and high efficiency.For the high thickness and the technological process of the dielectric metalenses constituent elements are difficult problems in fact,westudy and design the enhanced Mie resonance metalenses based on a high&lowrefractive index medium.The elements structure thickness can be highly reduced,and the manufacturing difficulty and costwill be alsoreduced.What's more,under the trend of super lens research from metal type to dielectric type,it is a great significance to propose an enhanced Mie resonance metalenses investigation and the correlation applications.The research contents of this article are as follows:1.The basic principles and calculation methods of phase-type metasurface are described in detail.The physical mechanism of the Mie resonance of the dielectric super lens is discussed strictly,and a single structure unit and the whole lens structure are separately calculated and simulated.Through the calculation of the,The electromagnetic field distributions are calculated through the finite-time-difference principle and method.2.The characteristics of the enhanced Mie resonance metalenses structure based on the high&low refractive index dielectric media are studied and analyzed.The results show that,it can be achieved an arbitrary adjustment of the super lens phase from 0 to 2? with the less structure thickness,that is,the stronger phase modulation ability are obtained in the enhanced Mie resonance-adjusted metalenses than that in the ordinary lenses.The work wavelength is set as the near infrared band from 1300nm to 1600nm.The phase modulation curve also presents more flat and smooth,which is beneficial to the experimental preparation.3.The whole metalenses optical properties,such as the depth of focus(DOF),the focal spot size(WOF),and the intensity distribution,are studied.Different dimensions of the metalenses are designed and analyzed for the comparative study of the optical properties.The number of units are separated as 31 × 31(with the lens diameter 31 ?m),41 × 41(with the lens diameter 41 ?m),and 51 × 51(with the lens diameter 51 ?m);the center wavelength is set at 1450 nm and the designed focal lengths are 6 ?m,10 ?m,15?m and 20 ?m respectively.The results show that,the focusing spot almost be equal to the diffraction limit.The focal depth and its range increase as the focal length increases.The scattered light distribution of the whole focal plane decreases as the element numbers increase,and the mismatch error between the actual focal length and the designed focal length also decreases.For the lens diameter with 51?m,the focusing efficiency remains more that 51%,and maximum value is 65.8%as the focus length is 6 ?m;the minimum focal length mismatch error is 0.4%and the maximum value is 3.0%.We also give a further study on the abnormal deflection and achromatic properties.Through the wavefront coding method,it corrects the inclined light with an angle of 10° to the inclined about 2°and the focal depth range of the focus spot is also increased.The structure also realizes the achromatic function in the range with a bandwidth of more than 100 nm.