Femtosecond-laser-inscribed Fiber Bragg grating array for quasi-distributed high-temperature sensing

We propose and demonstrate a fiber Bragg grating (FBG) array inscribed with femtosecond laser point-by-point (PbP) method for quasi-distributed high-temperature sensing. Via optimization of grating length, femtosecond laser energy and grating pitch, a wavelength-division-multiplexed (WDM) FBG array including nine FBGs with various Bragg wavelengths ranging from 1510 nm to 1590 nm and an identical ultra-weak FBG array including 60 FBGs with a peak reflectivity of ~0.1‰ were fabricated. After annealing at 700°C for nearly 200 hours, the FBG exhibited a an extremely low Bragg wavelength shift (i.e., -2 pm/h). In addition, the modulation of WDM FBG array was studied. A generalized calibration curve was applied to the FBG array and the maximum fitting error of 27 pm and the temperature measurement accuracy of ± 1.8°C were achieved. And then, the fabricated WDM FBG array was used to realize the quasi-distributed high-temperature sensing up to 700°C in the static and dynamic environment. Such WDM FBG array could be developed for quasi-distributed high-temperature sensing in metallurgical, chemical, and aviation industries.