Effects of aberrations on 3D optical topologies

Optical knots and links are nontrivial three-dimensional topologies consisting of trajectories of phase or polarisation singularities. They are theoretically predicted and experimentally observed in paraxial and nonparaxial regimes and in random and speckle fields. The topological nature of optical knots suggests that environmental disturbances should not alter their topology, hence becoming a resilient vector of information. However, the robustness of optical knots under typical disturbances encountered in optical experiments has not been investigated. Here, we provide the experimental analysis of the effects of optical phase aberrations on optical knots and links. We demonstrate that Hopf links, trefoil and cinquefoil knots are robust to misalignment and phase aberrations. The observed knots are obliterated for high aberration strengths and defining apertures close to the characteristic optical beam size. Our observations indicate these photonic topological structures as viable alternatives for both classical and quantum information processing noisy channels, where optical modes are not applicable.