Auxiliary film modulated SPR sensor for simultaneous refractive index and temperature sensing

Abstract

A dual-channel surface plasmon resonance (SPR) optical fiber sensor for simultaneous refractive index (RI) and temperature sensing is proposed on the modulation effect of auxiliary films. Magnesium fluoride (MgF2) and titanium dioxide (TiO2) films sputtered onto the silver film induce a thickness-dependent redshift of the resonance wavelength. With different films assigned to the two channels, each channel responds differently to RI and temperature. Consequently, the combined readings of the two channels allow independent detection of both parameters. Experimental validation confirms that the auxiliary films effectively alter the SPR resonance conditions, enabling clear spectral separation between two sensing channels. The RI channel operates within 500–700 nm, while the temperature channel operates within 750–1000 nm. The sensor achieves maximum sensitivities of 5000 nm RIU−1 and 4.3 nm °C−1 over RI and temperature ranges of 1.33–1.40 and 10 °C–100 °C, respectively. These results not only demonstrate the feasibility of the proposed design but also offer practical guidelines for developing high-performance dual-channel SPR optical fiber sensors.