A fiber optic temperature sensor based on parallel dual Fabry-Pérot interferometers with Vernier-effect

A PDMS-optical fiber Fabry-Pérot interferometric (FPI) temperature sensor based on the Vernier effect is proposed. The sensing probe is formed by cascading two single-mode fibers (SMFs) with a PDMS cavity, while the reference probe consists of two SMFs spliced to a hollow-core fiber (HCF). The two cavities have lengths of 146.8 and 218.4 µm, respectively. The structure is compact and easy to fabricate. The air-filled cavity provides a highly stable reference interference signal, while the PDMS cavity, which is sensitive to temperature, undergoes significant cavity-length variation under temperature changes. Due to the slight mismatch between the free spectral ranges (FSRs) of the two cavities, a distinct Vernier envelope is generated in the reflection spectrum, effectively amplifying the temperature-induced spectral shift and thus greatly improving the sensing sensitivity. Experimental results show that the parallel FPI structure achieves a temperature sensitivity of approximately 21.54 nm/℃ in the range of 25-30 ℃, with a linearity better than 99.975%, which is significantly higher than that of conventional PDMS-based FPI sensors. The sensor also exhibits good temperature reversibility, demonstrating great potential for applications in industrial, medical, environmental, and aerospace fields.