Spin-dependent metalens with intensity-adjustable dual-focused vortex beams

TL;DR

This paper presents a novel spin-dependent metalens capable of generating dual-focused vortex beams with adjustable intensity and separation, advancing optical manipulation technologies.

Contribution

It introduces a new design method combining geometric and propagation phases to create spin-dependent dual-focused vortex beams with tunable properties.

Findings

Dual-focused vortex beams observed under elliptical polarization

Relative focal intensity adjustable via incident beam ellipticity

Separation and topological charge of beams can be independently tailored

Abstract

Vortex beams with orbital angular momentum has been attracting tremendous attention due to their considerable applications ranging from optical tweezers to quantum information processing. Metalens, an ultra-compact and multifunctional device, provide a desired platform for designing vortex beams. A spin-dependent metalens can boost the freedom to further satisfy practical applications. By combining geometric phase and propagation phase, we propose and demonstrate an approach to design a spin-dependent metalens generating dual-focused vortex beams along longitudinal or transverse direction, i.e., metalenses with predesigned spin-dependent phase profiles. Under the illumination of an elliptical polarization incident beam, two spin-dependent focused vortex beams can be observed, and the relative focal intensity of them can be easily adjusted by modulating the ellipticity of the incident beam. Moreover, we also demonstrated that the separate distance between these dual-focused beams and their topological charges could be simultaneously tailored at will, which may have a profound impact on optical trapping and manipulation in photonics.