Topological supermodes in photonic crystal fibre

Topological states enable robust signal propagation within disorder-rich media. These states are defined by integer invariants inextricably tied to the transmission of light, sound, or electrons. However, a challenge remains to exploit topological protection inside a scalable communications platform. Here we use both modelling and experiments to realise photonic crystal fibre that supports topologically protected supermodes. Our fibre exhibits topological guidance for visible light over metre scales, millions of times longer than the wavelength, in contrast to size-limited planar devices and resonance-based metamaterials. We directly measure the photonic winding-number invariant in the bulk and observe the associated boundary modes predicted to exist by bulk-boundary correspondence. By bending this fibre, we reversibly reconfigure its topological states using transverse strain. Future technologies could exploit our scalable fibre platform for topological robustness inherited by lasing modes and entangled quantum states.