Characterization of High-Temperature Performance of a Sapphire Fiber Bragg Grating With a Single-Mode Demodulation System

The high-temperature performance of a sapphire fiber Bragg grating (FBG) has been characterized by a commercial single-mode interrogator. By using the mode field matching fusion splicing method, we proposed before, high-order modes in the reflection spectrum of the sapphire FBG could be suppressed and a quasi-single-mode reflection spectrum could be obtained from a single-mode fiber-based demodulation system. A 48-h isothermal annealing at 900 °C and two temperature calibration processes, one up to 800 °C and another up to 1200 °C, were carried out successively. There was no obvious reflectivity decay or wavelength drift during the 900 °C annealing process, and no hysteresis during the two temperature calibration processes. The precisions of the sapphire FBG were ±0.25 °C in the 800 °C calibration process, while increased to ±5 °C in the 1200 °C calibration process.