Stability of grating-based optical fiber sensors at high temperature

Abstract

We present a comparison of four different grating-based optical fiber high temperature sensors. Three of the sensors are commercially available and include a heat treated, twisted (chiral) pure-silica microstructured optical fiber, a femtosecond laser written Bragg grating in a depressed cladding single mode fiber and a regenerated fiber Bragg grating. We compare these to an in-house fabricated femtosecond laser ablation grating in a pure-silica microstructured optical fiber. We have tested the sensors in increments of 100°C up to 1100°C for durations of at least 24 hours each. All four sensors were shown to be operational up to 900°C, however the two sensors based on pure-silica microstructured fiber displayed higher stability in the reflected sensor wavelength compared to the other sensors at temperatures of 700°C and higher. We further investigated high temperature stability of silica suspended-core fibers with femtosecond laser inscribed ablation gratings, which show improved stability up to 1050°C following thermal annealing. This investigation can be used as a guide for selecting fiber types, packaging, and grating types for high temperature sensing applications.