Optical fiber sensor based on Vernier effect of Fabry–Perot and Sagnac interferometers for simultaneous temperature and salinity measurement

Abstract This paper proposes a structure cascading Fabry–Perot interferometer (FPI) and Sagnac interferometer (SI). This sensing structure achieves dual-parameter simultaneous detection through the Vernier effect, further stability testing is conducted. The FPI is formed by filling PI material, which is sensitive to both temperature and salinity, between the facets of paired single-mode fiber (SMF) segments, with the assembly encapsulated by a hollowed-out stainless steel tube, while the SI is composed of SMFs spliced with a polarization-maintaining fiber (PMF), which is only sensitive to temperature. By constructing a sensitivity coefficient matrix and incorporating the Vernier effect, simultaneous measurements are accomplished, presenting sensitivities of 1.76 nm/% and −6.09 nm/°C. Data from the stability test indicate that the maximum fluctuations in salinity and temperature are 0.18% and 0.14 °C respectively. While repeating measurement experiments, the maximum deviation in salinity sensitivity is 0.02 nm/%, which shows that this structure exhibits ideal measurement stability and repeatability. The sensor is distinguished by its robust stability, repeatability, and ease of preparation, making it have promising prospects in the field of marine parameter detecting.