Diffraction-free natural optical skyrmions and their subwavelength confinement around vortices
Diffraction causes waves to spread out as they propagate freely. The tighter the lateral confinement, the faster the spreading. Past research on how to suppress diffraction has been based on wave engineering and has led so far to idealized waves that, in real settings, eventually diffract. Here, we find a propagating light wave structure naturally present in optical vortices, a natural skyrmion, that is exempt from diffraction. Moreover, diffraction-free propagation occurs with lateral confinement at any scale below the wavelength of light. In our experiments, we observe non-diffraction over a propagation distance above three orders of magnitude greater than expected from the skyrmion subwavelength size. We thus provide a factual, real-world form of ideal non-diffracting propagation. This form substantially differs from previous forms of light propagation, including propagating optical skyrmions known to date, and could open up new perspectives in its various applications.