Subwavelength-scale non-diffracting optical polarization skyrmions

Optical skyrmions, as photonic topological quasiparticles, have been extensively studied in various optical fields ranging from the electric field of evanescent waves to the Stokes field in parameter space. Recent demonstrations on the subwavelength-scale optical skyrmions hint at novel applications, yet they face a fundamental limitation: strong diffraction and limited propagation range. Here, we theoretically propose and experimentally verify a distinct technique for generating subwavelength-scale non-diffracting polarization skyrmions. Our technique uniquely exploits a sharp-edge circular obstacle to binarily modulate an incident skyrmion, which induces propagating high-spatial-frequency vector waves in the far field. The coherent superposition of these vector waves allows us to recover the skyrmionic field at the subwavelength scale. Importantly, the generated subwavelength polarization skyrmion propagates along the distance up to many times of the Rayleigh range, with negligible diffraction, manifesting its non-diffracting property. Our demonstration opens opportunities to generate and manipulate optical polarization skyrmions at the deep subwavelength scale, benefiting potential research fields such as precision measurement and nano-scale structured light–matter interaction.