Unveiling Spin and Poynting Dual Textures of an Optical Skyrmionic Tube in Free Space

Optical skyrmions are topological textures of electromagnetic fields with promising applications in information processing, transport, and storage. Exquisitely tailoring the optical fields of diverse physical quantities has expanded the family of skyrmions, yet such skyrmions only exhibit a single-quantity texture in free space. Herein, dual skyrmionic textures concurrently portraying spin and Poynting vectors are unveiled in the tight focus of an annular second-order circularly polarized vortex beam. The focal electric and magnetic fields exhibit an elongated and identical spatial distribution but a phase difference of π/2, leading to dual skyrmionic textures with vector orientations that are either opposite or identical, depending on the handedness of the incident beam. Unlike conventional optical skyrmions that are exclusively regarded as quasiparticles distributed in a two-dimensional plane, a skyrmionic tube structure that extends over a longitudinal depth approaching 10λ while preserving its topology is demonstrated. Our Letter enhances the comprehensiveness of optical skyrmions and paves the way toward their practical applications by bolstering skyrmion-matter interactions.