Optical hopfions with arbitrary two winding numbers

TL;DR

This paper demonstrates how to generate tunable optical hopfions with arbitrary winding numbers using superpositions of Laguerre-Gaussian modes, enabling new topological structures in free-space optics.

Contribution

It introduces a systematic method to create optical hopfions of any order with controllable winding numbers using tailored mode superpositions.

Findings

Achieved control of hopfions up to orders 5 and 3 for poloidal and toroidal winding numbers.

Visualized topological structures via polarization filaments in experiments.

Provided a new platform for topological photonics and optical communications.

Abstract

Hopfions, as three-dimensional topologically nontrivial structures described by poloidal and toroidal winding numbers, hold promise as robust information carriers in spintronics, functional materials, and optical communications. Although they have been experimentally realized in various physical systems, such realizations have been restricted to low orders, with the winding numbers lacking tunability. Here, using optical fields as our platform, we outline how to make tunable hopfions in any order with any winding number. We use tailored superpositions of Laguerre-Gaussian modes in free-space as our construction, achieving effective control for arbitrary-order poloidal and toroidal winding numbers, which we demonstrate up to orders 5 and 3, respectively, for a new state-of-the-art. The resulting torus-knot structures are visualized experimentally via polarization filaments, confirming the designed topological textures. Our work reports an exotic optical topologies observed in free space, provides a systematic route hopfions of any order, with implications for topological photonics, optical communications, and analogies in magnetic and condensed-matter systems.