A Dual-Parameter Optical Fiber Sensor Based on SPR and LMR for Measuring Liquid Refractive Index and Temperature

A compact dual-parameter optical fiber sensor combining surface plasmon resonance (SPR) and lossy mode resonance (LMR) technologies was proposed for the simultaneous measurement of liquid refractive index (RI) and temperature. The sensor uses an Au film deposited on one side of a D-shaped quartz no-core optical fiber to excite SPR for RI measurement, and a TiO2 film deposited on the other side, which is coated with PDMS to excite LMR for temperature sensing. Numerical simulation results show that the sensor achieves a maximum sensitivity of 16450 nm/RIU in the RI range of 1.33–1.42, and an average sensitivity of −4.36 nm/°C in the temperature range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20~^{\circ }$ </tex-math></inline-formula>C–<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$100~^{\circ }$ </tex-math></inline-formula>C. Furthermore, by further depositing a TiO2 film on the Au film surface to enhance the electric field, the maximum RI sensitivity of the sensor increases to 21650 nm/RIU. This sensor offers a wide measurement range and excellent sensitivity, making it promising for multiparameter measurement applications.