Efficient generation and tight focusing of radially polarized beam from linearly polarized beam with all-dielectric metasurface

Fei Zhang,Jian Wang,Sicheng Chen,Honglin Yu,Ming Zhang,Junyan Chen,Anguo He,Jiawen Fang

doi:10.1364/oe.24.006656

Abstract

We propose a single layer all-dielectric metasurface lens to simultaneously convert and focus an incident linear polarization into a radial beam with high efficiency and high numerical aperture (NA). It shows a better focusing property compared with the linearly polarized metasurface lens for high NA. A tight spot size (0.502λ) is achieved for the NA = 0.94. Additionally, the emergent polarization can in principle be switched flexibly between radially and azimuthally polarized beams by the adjustment of incident polarization direction. It is expected that our scheme may have potential value in microscopy, material processing, medicine, particles accelerating and trapping, and so on.

Highlights

During the past decades, the cylindrical vector beams have received particular attention for their notable high-numerical-aperture focusing properties [1,2,3]
The strong longitudinal electric field component is of existence at the focus of radially polarized (RP) beam [4], leading to a sharper focal spot than a homogeneously polarized beam [5,6], which results in many significant applications in high-resolution microscopy [7], surface plasmon excitation [8], particles accelerating [9], material processing [10,11], and so on
The applications of the focused azimuthally polarized (AP) beam based on conventional spherical lens and annular apertures are limited by their size, planarity and volume [18,19,20]

Summary

Introduction

The cylindrical vector beams have received particular attention for their notable high-numerical-aperture focusing properties [1,2,3]. The plasmonic meta-lens with arrayed metal nanoantennas has been reported and posses the capability of focusing RP or AP beam into a spot [29] It encounters the difficulty of keeping the centers of the cylindrical vector beam and meta-lens coaxial, and this type of single-layer plasmonic metasurfaces suffer from the low transmission or polarization conversion efficiency because of fundamental limits [27,28,29,30] and metal absorption loss [31,32]. There is no all-dielectric meta-lens that can simultaneously generate and focus RP beam into a tight spot from linearly polarized beam with high efficiency and high NA, it has been reported that a metasurface could provide complete control of polarization and phase [36]. The polarization conversion is achieved ingeniously by introducing one phase difference of π between two special orthogonal polarizations of linearly polarized incident light It could solve the problem of the harshly coaxial condition in practical applications. We believe that our scheme may have potential applications in microscopy, material processing, medicine, particles accelerating and trapping, etc

Structure model design

Findings

Conclusion