Subdiffraction confinement and non-diffractive propagation of optical Stokes skyrmions enabled by a super-oscillatory metalens

Abstract

Optical Stokes skyrmions have garnered extensive interest due to their intrinsic topological robustness and potential in informatics.However, most research remains confined to paraxial, low-numerical-aperture (low-NA) regimes, where their large transverse dimensions restrict broader applications.Under high-NA focusing, the polarization texture typically degrades or transforms abruptly as the beam traverses the focal region, hindering topology-preserving transport.In this work, we propose a strategy to generate a skyrmion needle field that maintains both subdiffraction confinement and non-diffractive propagation under high-NA conditions, thus preserving their topological characteristsics. Leveraging the polarization invariance of conventional optical needles, we realize the Stokes skyrmion needle using a single plasmonic metalens,designed to function as both a polarization filter and a super-resolving focusing element.Experimental and simulation results verify non-diffractive propagation over an extended depth of focus (up to 5 lambda), while the Stokes-vector texture retained at subdiffraction scales throughout propagation. This skyrmion needle not only addresses previous propagation constraints but also opens new avenues for diffraction-unlimited information transport. Such skyrmion needles exhibit substantial potential in fields including light-matter interaction, optical metrology, and informatics.