Stability of Grating-Based Optical Fiber Sensors at High Temperature

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 the duration 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 the temperatures of 700 °C and higher. We further investigated the 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.