Broadband coloured skyrmions generated by on-chip ferroelectric spherulites

Abstract Optical skyrmions, particle-like topological textures of light with resilience to perturbation, hold great promise for next-generation robust information carriers. Recent advances have enabled their efficient generation and modulation in both classical and quantum regimes via artificial nanostructures with certain topological landscapes. However, existing studies are largely confined to (quasi)monochromatic domain, because the resonance-based linear and nonlinear light-matter interactions are constrained by narrowband response and strong spectral dispersion. Therefore, the exploration of coloured and white light skyrmions is virtually zero, blocking their extension to broadband information technologies. Here, we present an ultra-compact micro-generator that generates ultra-broadband coloured skyrmions from a natural ferroelectric spherulite crystal through the combined action of the photonic spin-orbital coupling and optical focusing. This approach circumvents the resonance effects intrinsic to artificially nanostructured optical systems. The resulting polychromatic skyrmions cover the entire visible spectral range and can propagate over an appreciable distance in free space. Their topological textures can be continually modulated by tuning the polarization of the incident beam, enabling switching among multiple topologies, such as skyrmions, biskyrmions, and quadrumerons. Furthermore, we reported the experimental evidence of spontaneous parametric down conversion process occurring within the ferroelectric spherulite, which implies the possibility to generate the correlated topological quantum states in further research. These distinctive features will revolutionize modern informatic applications spanning optical communication, data storage, and topological photonic devices.