Multiparameter Sensing of the Vernier Effect Based on Cascaded Sagnac and Fabry–Perot Interferometers

In this paper, a multiparameter optical fiber sensor based on the vernier effect of the parallel cascaded Sagnac interferometer (SI) and Fabry-Perot interferometer (FPI) is designed and experimentally demonstrated for the temperature, strain, and humidity measurements. The proposed sensor comprised of a single-mode fiber (SMF) fusion spliced to a polarization-maintaining fiber (PMF) for SI and an SMF fusion spliced to a hollow capillary fiber (HCF) for FPI. Combining the sensing characteristics of the two hybrid interferometers can realize complementary sensing advantages in three-parameter measurements based on the vernier effect. Experimental results show that the maximum temperature sensitivity of -9.689 nm/°C and the maximum strain sensitivity of 0.0505 nm/με, respectively, with the SI used as the sensing arm. There values are approximately 200 times higher than those obtained with the FPI used as the sensing arm. In humidity measurement, the highest humidity sensitivity of the sensor can reach the 0.16 nm/%RH, with the FPI used as the sensing arm. Experimental results reveal that the sensor is based on the vernier effect. Its humidity sensitivity is 17.13 times higher than that obtained using the single FPI under the same humidity conditions. Our proposed sensor has the advantages of easy preparation, low loss, and high sensitivity. Which make it a suitable candidate for multi- parametric monitoring sensors.