Coaxial Hydrogel Optical Fibre Skin for Interference-Free Multimodal Tactile Perception.

Flexible photonic fibers enable precise, interference-free multimodal tactile sensing in wearable interfaces, owing to their intrinsic immunity to electromagnetic interference and cross-modal coupling, together with rapid response. Until now, optical fibers that simultaneously exhibit mechanical robustness, signal decoupling, and environmental stability remain scarce, and system-level integration is even rarer. Inspired by the distributed sensory arrangement of jellyfish tentacles, we propose a photonic skin composed of coaxially structured hydrogel optical fibers, in which pressure and temperature signals are routed through independent photonic and ionic channels for interference-free multimodal sensing. The stretchable, highly reproducible, refractive-index-matched core-cladding photonic fiber was constructed by continuous coaxial spinning with in situ photopolymerization. It resolves the long-standing trade-off between mechanical stretchability, low-loss optical guiding, and temperature/humidity robustness in hydrogel fibers. The assembled sensing skin achieves high pressure and temperature sensitivity with a sub-10-ms response, surpassing existing benchmarks. It integrates with a lightweight, flexible printed circuit and multimodal tactile fusion machine-learning architecture to form a wearable system, enabling wireless control, adaptive gesture recognition (99.21% accuracy), and multimodal object classification (99.22% accuracy). This work presents a fully integrated photonic skin platform bridging material-level signal decoupling and system-level multimodal perception for intelligent tactile interfaces in complex environments.