SPR fiber optic sensor based on MMF-NCF doped with MgF₂ for dual-parameter measurement of temperature and humidity

Dual-parameter temperature and humidity sensors based on optical fiber sensing have wide applications. Among various optical fiber sensors, surface plasmon resonance (SPR) sensors exhibit excellent sensing sensitivity. To address the bandwidth issue and expand the sensitivity, this paper proposes a multimode fiber-no core fiber (MMF-NCF) SPR sensor. The humidity channel covers an Ag/PVA composite film, while the temperature channel covers an Ag/MgF₂/PDMS composite film. The MgF₂ modulates the shape of the resonance curve, shifts the resonance curve towards the infrared direction and enhancing the sensitivity by 0.245 nm/^oC. Compared with previous temperature and humidity detection ranges up to 20°C ∼ 100°C and 40% ∼ 100%, this has obvious improvement. The maximum sensitivities are -0.5683 nm/%RH and -3.259 nm/^oC. The mean temperature sensitivity is -1.88877 nm/^oC and the mean humidity sensitivity is -0.51249 nm/%RH. The polynomial fitting degrees reach 0.99914 and 0.99875, and FOM values are 2.715 × 10^-2/^oC and 4.735 × 10^-3/%RH, which is expected to be in agriculture, food industry, such as biological implementation is widely used in production activities.