High-temperature measurement with Brillouin optical time domain analysis of an annealed fused-silica single-mode fiber.

The effect of annealing is experimentally studied for a fused silica, fully distributed fiber optic sensor based on the pulse pre-pump Brillouin optical time domain analysis (PPP-BOTDA). Within a heating rate of 4.3°C/min and 30.6°C/min, and a sustained peak temperature for 120 and 240 min, annealing extended the sensor's upper operation temperature from 800°C to 1000°C and reduced the sensor's measurement variability over a temperature range of 22°C to 1000°C with a maximum Brillouin frequency variation of 1%. The annealed sensor had a linearly decreasing Brillouin frequency sensitivity from 1.349×10^-3  GHz/°C at 22°C to 0.419×10^-3  GHz/°C at 1000°C. The time required to achieve a stable annealing effect decayed exponentially with annealing temperature.