title: Efficient subwavelength focusing of light with a long focal depth.
abstract: We demonstrate an efficient method for far-field subwavelength focusing by a novel two-component axicon structure. Annular beams generated by a fiber axicon are focused using a micro-cone reflector, creating a quasi-Bessel beam with a high convergence angle of up to 40°. A center focal spot diameter of 0.41λ was achieved at a power efficiency of over 40%, with a focal depth of 9λ and a working distance as long as 35 μm. We further demonstrate that experimental knife-edge measurements mapping the beam focal intensity agree with numerical simulations of the structure. This method shows demonstrable promise in overcoming the optical focusing limit of single-element axicons and great potential for use in high tolerance, high-resolution applications in optical systems.
authors.affiliation: College of Optical Science and Engineering, Zhejiang University, Hangzhou, 310027, China. xingkunwu@zju.edu.cn.
authors.forename: He
authors.initials: H
authors.lastname: Huang
authors.forename: Qing
authors.initials: Q
authors.lastname: Li
authors.forename: Jian
authors.initials: J
authors.lastname: Fu
authors.forename: James
authors.initials: J
authors.lastname: Wu
authors.forename: Feng
authors.initials: F
authors.lastname: Lin
authors.forename: Xingkun
authors.initials: X
authors.lastname: Wu