Femtosecond Laser-Inscribed Ultra-Weak Fiber Bragg Grating Array for Distributed High-Temperature Measurements

We propose and demonstrate an identical ultra-weak fiber Bragg grating (uwFBG) array inscribed with femtosecond laser point-by-point (PbP) method for distributed high-temperature sensing. An identical uwFBG array including 200 uwFBGs was fabricated along a 2 m conventional single-mode fiber (SMF) with an interval of 10 mm, and interrogated with an optical frequency domain reflectometer (OFDR). In addition, the high-temperature response of uwFBG was studied. The experiment result showed that uwFBG can withstand a high-temperature of 1000°C for long time. After annealing at 1000°C for 20 hours, the heating and cooling responses of uwFBG were basically the same and the uwFBG exhibited a sensitivity of 18.2 pm/¼C at 1000°C. And then, the fabricated identical uwFBG array with OFDR demodulation was used to realize the distributed high-temperature sensing up to 1000°C. Such identical uwFBG array are promising in many distributed high-temperature sensing areas, such as aerospace vehicles, oil and gas explorations, and nuclear plants.