Research on the characteristics of distributed optical fiber temperature sensing based on spectrum

Distributed fiber optic sensing technology is widely used in fields such as civil engineering, pipeline monitoring, power systems, and environmental monitoring due to its advantages of large-scale monitoring, high precision, electromagnetic interference resistance, and long service life. Distributed fiber optic temperature sensing based on spectral analysis achieves precise temperature distribution measurement by monitoring the spectral changes of Fiber Bragg Gratings (FBG). This study proposes a new spectral method, utilizing changes in the spectral center wavelength and power for temperature sensing, and establishes an experimental platform to verify its feasibility and sensitivity. The experimental setup includes an ASE light source, an optical circulator, five 3-meter fiber optic segments, a 2-kilometer fiber optic segment, and an FBG. By heating the fiber at different positions, the effect of temperature changes on the center wavelength and power is analyzed. The experimental results show that as the heating position increases, the center wavelength gradually increases, while the power decreases, with more significant changes observed at heating positions of 9 meters and beyond. When unheated, the center wavelength is 1536.489654nm. At heating positions of 3 meters, 6 meters, and 9 meters, the wavelength increases to 1536.490434nm, 1536.492128nm, and 1536.498743nm, respectively. When unheated, the power is 1.1554 × 10^⁻4 mW. After heating at 3 meters and 6 meters, the power slightly decreases to 1.1471 × 10^⁻4 mW and 1.1429 × 10^⁻4 mW, with minimal attenuation. However, after heating at 9 meters, the power decreases significantly to 1.0883 × 10^⁻4 mW and further decreases to 1.0837 × 10^⁻4 mW and 1.0667 × 10^⁻4 mW at 12 meters and 15 meters, respectively. The changes in fiber refractive index and physical length caused by heating lead to alterations in the phase and amplitude of the optical signal, thereby affecting the spectral characteristics. The study demonstrates that by monitoring changes in the center wavelength and power of the spectrum, temperature variations at different locations can be detected, validating the feasibility of distributed fiber optic temperature sensing technology and providing theoretical and experimental support for its engineering applications.