D-shaped optic fiber temperature and refractive index sensor assisted by tilted fiber bragg grating and PDMS film

A sensor combining a polydimethylsiloxane-coated Mach-Zehnder interferometer with a tilted fiber Bragg grating is proposed for dual-parameter sensing of liquid temperature and refractive index. Mach Zehnder interference is used for high sensitivity temperature sensing while the core mode of tilted fiber Bragg grating is used to distinguish the temperature range and avoid spectral overlap. Meanwhile, the cut-off mode of tilted fiber Bragg grating is used for refractive index sensing, which can effectively eliminate crosstalk between temperature and refractive index. The average temperature sensitivity of the sensor can reach 4.88, 5.15, 4.53 and 4.38 nm/°C over the range of 20, 30, 40 and 50 °C, respectively. The refractive index is in the range of 1.3330–1.3614, and the sensing sensitivity can reach 521.92 nm/RIU. Compared with other optical fiber sensors, the sensor proposed in this paper has the advantages of simple fabrication, compact structure, stable mechanical structure and high sensitivity, which is expected to be applied in the sensing field where refractive index and temperature need to be detected simultaneously.