Focusing Property And Angle Control Of Metal-dielectric Multilayer Structure

The improvement of modern information technology has given rise to crying needs for high resolution in the field of nano-optical imaging and focusing.For conventional optical systems,however,the image resolution is only about half of the incident wavelength due to the restriction of the diffraction limit.Diffraction limit derives from the reason that the evanescent waves carrying the detailed information cannot propagate in a conventional material.Therefore,they have no contribution to the formation of the final imaging or focusing.In recent years,studies have shown that surface plasmon polariton can be coupled with the evanescent waves,and led to the amplification of the evanescent waves,which could pave the way for the detailed study of super-resolution focusing.Metal-dielectric multilayered structures are artificial anisotropic materials,whose dispersion can be tuned by structural and material parameters,thus result in their ability to regulate and control the light transmission effectively.This paper studies the focusing property and angle control of metal-dielectric multilayered structure systematically.The research content and results are as follows:1.Based on effective medium theory(EMT),the optical properties of multilayers have been investigated.And the results show that,multilayers with hyperbolic dispersion support the directional propagation of evanescent wave,which provides the possibility for realizing super-resolution focusing.Combined the multilayers and diffraction grating,two types of focusing devices(Type I and II multilayers)have been proposed and used to study the focusing effect while the light incident on multilayers in the direction of perpendicular or parallel to the films.The focusing performances of structures have been verified by finite difference time domain(FDTD)method,the focus size of Type I and II multilayers are 125nm and 63nm,respectively.So it will get a better focus when the light is perpendicular to the layers.In addition,the focusing of each component of the electric field is analyzed in detail.It can be found that the component E:has two symmetrical peaks in the vicinity of x=0,thus reducing the focusing resolution of electric field intensity.The impacts of the slit width,the dielectric permittivity,filling ratio of metal and gain medium have been explored,which will provide a valuable reference for further optimizing the focusing device.2.Refraction phenomena of energy flow and wave vector in different types of metal-dielectric multilayered structures have been studied from the perspective of equal-frequency contours(EFCs).The results show that negative refraction phenomenon occurs in the Type I multilayers except normal incidence.And oblique incident or output surface has an influence on the refraction phenomenon.The high and low pass angle spectrum filtering characteristics of Type ? and ordinary multilayers have been given a preliminary validation,which establish the foundation for investigation of complex space angle spectrum filter in future.