1200°C high-temperature distributed optical fiber sensing using Brillouin optical time domain analysis

Area of Science:

• Optical Fiber Sensing
• High-Temperature Measurements
• Materials Science

Background:

• Distributed Brillouin sensing is crucial for high-temperature environments.
• Standard linear models for Brillouin frequency shift (BFS) are insufficient at extreme temperatures.
• Fiber optic sensors require characterization for advanced applications.

Purpose of the Study:

• To demonstrate high-temperature distributed Brillouin sensing up to 1100°C and 1200°C.
• To investigate the temperature dependence of BFS in germanium dioxide-doped single-mode fiber (SMF) and pure silica photonic crystal fiber (PCF).
• To assess the stability and repeatability of BFS measurements after high-temperature exposure and annealing.

Main Methods:

• Utilized distributed Brillouin sensing with SMF (up to 1100°C) and PCF (up to 1200°C).
• Analyzed the nonlinear relationship between Brillouin frequency shift (BFS) and temperature.
• Observed and characterized BFS hopping phenomenon during initial annealing processes (800°C-900°C).

Main Results:

• Demonstrated high-temperature sensing capabilities for both SMF and PCF.
• Observed nonlinear BFS-temperature dependence attributed to acoustic velocity changes.
• Achieved stable and repeatable BFS measurements post-annealing with accuracies of ±2.4°C (SMF) and ±3.6°C (PCF).
• Identified BFS hopping as a temperature-dependent process accelerated by temperatures >800°C.
• Noted coating burning effects (∼300°C-500°C) causing micro-bending loss and compressive stress, impacting BFS.

Conclusions:

• High-temperature distributed Brillouin sensing is feasible using specialized fibers.
• Nonlinear BFS-temperature behavior and BFS hopping are critical considerations for accurate measurements.
• Post-annealing, both SMF and PCF offer reliable performance at elevated temperatures.