Non-diffracting meronic spin defects of light

TL;DR

This paper reveals complex, localized topological structures of transverse spin in optical vortices, including non-spreading, subwavelength features with unique defects and textures.

Contribution

It introduces the concept of meronic spin defects in light, unifying topological textures and defects in a novel way not previously described.

Findings

Identifies non-spreading, localized spin topologies below wavelength scale.

Describes a point defect of undefined spin surrounded by a meronic texture.

Highlights the diversity of topological structures in spin and Poincaré spheres.

Abstract

Optical vortices are singularity lines where the light field intensity vanishes and its phase is undefined. These threads of darkness are adorned by Gauss's law as lines of pure longitudinal polarization where the polarization plane tilts and winds around. We unveil the resulting spin field as a unique structure which unifies both topological textures and defects, as it includes a point defect of undefined spin surrounded by a meronic texture which spans half the spin unit sphere. Moreover, this intricate topological structure of transverse spin does not spread in propagation, is localized arbitrarily below the wavelength of light and presents highly anisotropic features. Here we describe these hidden topologies of transverse spin embedded in simple scalar vortex beams, highlighting the diversity of topological structures that arise in two different spaces -- the spin unit sphere and the transverse-axial Poincar\'e sphere -- and discuss the underlying aspects behind their subwavelength localization.