AgNP-based localized surface plasmon resonance U-shaped fiber dual-channel sensor for simultaneous refractive index and temperature detection.

A dual-channel fiber sensor based on surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR) is proposed for simultaneous detection of the surrounding refractive index (SRI) and temperature (T). The sensor consists of an Ag-coated multimode fiber-thin core fiber-multimode fiber (MMF-TCF-MMF) structure for SRI detection and a U-shaped MMF coated with Ag-polydopamine (PDA)-Ag nanoparticle (AgNP)-polydimethylsiloxane (PDMS) film for temperature detection. The U-shaped fiber and AgNP-induced LSPR shift the resonance wavelength and enhance the sensing response, enabling two separated sensing channels in a single spliced fiber sensor. The AgNP size was optimized through simulation and experimentally verified. The proposed sensor achieved sensitivities of 2116.27 nm/RIU and -4.89 nm/°C over the ranges of SRI = 1.333-1.376 and T = 0-30 °C, respectively. The two channels also showed good stability, fabrication reproducibility, and simultaneous detection capability.