Switchable optical trapping based on vortex-pair beams generated by a polarization-multiplexed dielectric metasurface.

Abstract

Optical trapping is a state-of-the-art methodology that plays an integral role in manipulating and investigating microscopic objects but faces formidable challenges in multiparticle trapping, flexible manipulation, and high-integration applications. In this study, we propose and demonstrate a switchable optical scheme for trapping microparticles incorporating disparate vortex-pair beams generated by a polarization-multiplexed metasurface. The miniaturized all-dielectric metasurface, which comprises an array of titanium dioxide nanoposts, was manufactured and characterized to provide polarization-tuned two-fold vortex-pair beams. The profiles of the created vortices can be flexibly tailored by adjusting the combination of topological charges and the separation among phase singularities. Under transverse electric polarized light conditions, a vortex-pair beam with opposite topological charge combinations traps a single microparticle within one beam spot, while under transverse magnetic polarization conditions, two microparticles are captured simultaneously by a vortex-pair beam with the same topological charge signs. The proposed switchable trapping scheme (incorporating a vortex-pair light beam) is expected to feature enhanced integration and flexible manipulation of multiple particles with potential applications in biophysics, nanotechnology, and photonics.