Temperature sensing system based on OFDR demodulation principle for identical weakly reflecting FBGs

Fiber grating sensing technology is a widely used fiber optic sensing technology due to its ability to form a distributed sensing system for measuring multiple parameters. The number of multiplexed gratings and spatial resolution are important performance indicators of fiber Bragg grating (FBG) sensing systems. This paper proposes a fast distributed temperature measurement system based on the Optical Frequency Domain Reflectometry (OFDR) principle, using a single-mode fiber engraved with five identical weak gratings spaced 30cm apart with a reflectivity of 1% as the sensing fiber. To minimize the impact of light source nonlinearity on demodulation, we use the SiO₂ process Mach-Zehnder interferometer (MZI) module with a refractive index difference of 1.5 as an auxiliary interferometer and employ cubic spline interpolation FFT transformation for signal processing. This approach simplifies the design of the laser drive circuit and achieves a temperature resolution of 0.5°C.