Sub-nanosecond all-optically reconfigurable photonics in optical fibres

Reconfigurable photonic systems provide a versatile platform for dynamic, on-demand control and switching. Here we introduce an all-optical platform in multimode and multicore fibres. By using a low-power probe beam and a counter-propagating control beam, we achieve dynamic control over light propagation within the fibres. This setup ensures simultaneous phase-matching of all probe-control beam four-wave mixing interactions, enabling all-optical reconfiguration of the probe modal state by tuning the control beam power. Key operations such as fully tuneable power splitting and mode conversion, core-to-core switching and combination, along with remote probe characterization, are demonstrated at the sub-nanosecond time scale. Our experimental results are supported by a theoretical model that extends to fibres with an arbitrary number of modes and cores. The implementation of these operations in a single platform underlines its versatility, a critical feature of next-generation energy-efficient photonic systems. Scaling this approach to highly nonlinear materials could underpin photonic programmable hardware for optical computing and machine learning.