Self-Healing Flexible Fiber Optic Sensors for Safe Underwater Monitoring

Abstract

The advancement of underwater monitoring technologies has been significantly hampered by the limitations of traditional electrical sensors, particularly in the presence of electromagnetic interference and safety concerns in aquatic environments. Fiber optic sensors are therefore nowadays widely applied to underwater monitoring devices. However, silicon- and polymer-based optical fibers often face challenges, such as rigidity, susceptibility to environmental stress, and limited operational flexibility. Here, we propose an ingenious flexible step-index fiber construction strategy for the preparation of core-cladding poly(polymerizable deep eutectic solvent (PDES)) optical fiber (CPOF) by in situ light curing of the functional PDES monomer in a commercial silicone tube. The liquid-free poly(PDES) fiber core not only possesses high transparency (>90%), excellent flexibility, and wide temperature range tolerance (from -27 to 156 °C), but the supramolecular network of it also provides self-adhesion and optical self-healing, which ensures the bonding stability of the core-cladding interface as well as the lifetime of the optical device. On the other hand, the hydrophobic fiber cladding allows CPOF to stably transmit optical signals under water, and the application potential of CPOF for underwater sensing devices was verified by underwater motion monitoring.