Full-Field Mode Sorter for Optical Knots

Abstract

Optical knots are topologically structured light fields whose phase or polarization singularities trace linked or knotted trajectories during propagation, making them promising candidates for high-dimensional optical information carriers. Their use in communication or quantum-information protocols, however, requires a practical readout method that can distinguish a chosen knot alphabet with low crosstalk. Here, we demonstrate a proof-of-principle full-field sorter for optical knots using one or two optimized phase-only elements. The sorter maps each input knot to a predefined output region and is optimized directly from the output intensity distributions to enhance correct assignment, suppress crosstalk, and avoid degenerate mappings between distinct knots. We apply the method to an alphabet composed of the Hopf link, trefoil, and cinquefoil optical knots. Two optimized phase planes improve the sorting performance relative to a single plane and enable high distinguishability for the three-knot alphabet. We further benchmark the sorter under common experimental imperfections. These results extend full-field optical mode sorting to topologically structured light and provide a readout route for knot-based high-dimensional optical communication.