Study on binary-amplitude far-field super-resolution achromatic focusing devices

Abstract

The far-field super-resolution focusing devices possess characteristics such as super-resolution focusing, achromatic, small size and easy machining, making them highly promising in optical imaging, optical microscopy and lithography. In this study, we propose a binary-amplitude modulation-based method for generating far-field super-resolution achromatic focusing. By leveraging the principles of optical super-oscillation along with angular spectral diffraction theory and binary particle swarm optimization (BPSO), we optimize the binary amplitude-type far-field super-resolution focusing devices with radii of 100λ and the focal length of 25λ (λ=632.8nm) for λ<sub>1</sub>=405nm, λ<sub>2</sub>=532nm and λ<sub>3</sub>=632.8nm, respectively. Additionally, an achromatic metalens is integrated using Boolean AND operation. To assess the feasibility of our proposed approach, numerical simulations are conducted via COMSOL Multiphysics employing FEM analysis. The simulation results demonstrated that the generated spot located at 25.105λ、25.106λ, and 25.105λ, respectively. The corresponding full width at half maximum (FWHMs) are 0.441λ<sub>1</sub>(0.179μm), 0.469λ<sub>2</sub>(0.249μm) and 0.427λ<sub>3</sub>(0.270μm), which are smaller than the Abbe diffraction limit, and the far-field super-resolution achromatic focusing is realized. The sidelobe ratios are at low levels:12.5%, 12.6%, and 14.2%. The binary amplitude-type far-field super-resolution achromatic devices have the advantages of easy machining, achromatic and super-resolution, and are suitable for miniaturization and integration of optical systems.