Non-geodesic propagation of light in integrated curved nanophotonic structures

In fundamental physics, it is established that trajectories of light (geodesics) in general curved space can be mapped to those in inhomogeneous material media. This mapping has motivated an increasing interest in emulating gravitational phenomena in table-top optical experiments, which was accelerated by the development of new optical materials and devices in the field of metamaterials and nanophotonics. To access a so-far uncharted regime for table-top experiments, with the curvature being comparable to the light effective wavenumber, we fabricated a nanophotonics grating integrated to a curved surface waveguide. This grating shapes non-paraxial light waveforms within the confined structure. This enables the exploration of polarization-dependent trajectories that exist only in this highly curved space. The specific design enables observation of wavepackets with pre-designed trajectories that do not necessarily coincide with geodesics, manifesting interference effects in a curved background. Our work presents arbitrary miniature three-dimensional integrated structures useful for full light control applications and therefore marks a step toward integrated curved-space nanophotonic.