High-Sensitivity MMF–TCF–MMF Sensor Based on the Synergistic Effect of Au Film and AgNPs

In this work, a high-performance sensor based on a multimode fiber-thin core fiber-multimode fiber (MMF–TCF–MMF) structure is demonstrated. By using a continuous Au film and covalently anchored AgNPs on the TCF surface, the synergistic coupling between exciting surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR) is realized. Following a systematic optimization guided by COMSOL simulations and experimental validation, the refractive index (RI) sensitivity reached 2525.06 nm/RIU with a figure of merit (FOM) of 9.494 RIU−1, and the temperature sensitivity reached −1.07 nm/°C. The system demonstrated excellent linearity, repeatability, and stability. The proposed sensor effectively merges cost-efficiency with robust precision, showing significant potential for biochemical, environmental, and industrial sensing applications.