Sub-diffraction metalens for generating longitudinal bifoci and optical needles

Abstract

Lenses are a fundamental component of optical systems. Bifoci and optical needle devices have excellent application potential in many optical systems. Conventional lenses are limited by their diffraction limits, and the spot size has a considerable influence on the resolution of optical and microscopic images. Optical super-oscillation is a novel technique, to the best of our knowledge, for far-field sub-diffraction focusing. In this study, we proposed a binary-amplitude super-oscillatory lens (SOL) approach for generating bifoci and optical needles (ON), and it was based on the angular spectrum method (ASM) and a binary-particle-swarm optimization (BPSO) algorithm. We reported a class of binary-amplitude-based Bifoci- and ON-SOLs that generated sub-diffraction bifoci and optical needles. Sub-diffraction bifoci with a transverse range of 0.401λ−0.522λ were recorded for a work wavelength of λ=632.8nm. The generated optical needle had a sub-diffraction length of 4.122λ, and the super-oscillation region was 2.083λ long. This provides potential applications for further super-resolution imaging, optical communication, and precision manufacturing.