Fiber optic temperature sensor based on Vernier effect generated by a linear sagnac interferometer in parallel with a Fabry-Perot interferometer

A novel fiber-optic temperature sensor based on a Linear Sagnac Interferometer (LSI) in parallel with a Fabry-Pérot Interferometer (FPI) has been developed. This sensor leverages the superposition of the FPI and LSI to generate a Vernier effect. Theoretical and experimental results demonstrate that within the temperature range of 40 °C–50 °C, the temperature sensitivity of the parallel structure reaches 13.27 nm/°C, aligning well with theoretical predictions. Notably, when the LSI and Circular Sagnac Interferometer (CSI) exhibit identical temperature sensitivities and free spectral ranges (FSR), the length of the LSI is only half that of the CSI. The LSI is constructed from a single segment of Panda fiber and does not form a loop. Consequently, this sensor is simpler and easier to manufacture compared to conventional CSI sensors, offering significant advantages in structural simplicity and fabrication efficiency. This makes the proposed sensor a valuable reference for sensing applications in diverse environments.