Combining optical topologies for ultrarobust high dimensional states of light in optical fibre

Abstract

Optical topologies have recently garnered much attention due to their robustness to a variety of noise sources. However, different topologies are robust to different forms of noise, and no single topology offers universal resilience through general channels. Here, we combine two well-known optical topologies, namely phase singularities and optical Skyrmions, to form ultra robust states of light that inherit the robust properties of both. We first demonstrate that optical Skyrmions can be formed using the newly discovered set of topologically confined modes (TCMs), eigenmodes of the fibre that are guided beyond cutoff due to their orbital angular momentum (OAM) and are highly resilient to the effects of inter-modal coupling. By creating vectorial combinations of TCMs, we can couple the space and polarisation degrees of freedom, creating exotic, spatially varying polarisation structures which map an integer number of times to the Poincar´e sphere and define a skyrmionic mapping. TCMs allow us to transport a variety of optical Skyrmions through a 450m long fibre with high fidelity, which would be near impossible if using Skyrmions alone. Additionally, we show that such states are immune to the effects of depolarisation and decoherence, inherited from the skyrmionic topology and which would otherwise degrade the purity and non-separability of the state if one only leveraged the properties of TCMs. This combined robustness is crucial for the future of optical communication, both quantum and classical, allowing for a high dimensional topological alphabet that is unaffected by the effects of noise and paves the way for fast, efficient and secure optical information transfer.