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Ultra-high-temperature monitoring is of great significance in many extreme environments, such as aerospace and power industries. Since the melting temperature of single-crystal sapphire fibers is up to 2045 ℃, sapphire fiber Bragg gratings (SFBGs) can serve as an ideal ultra-high-temperature sensors. However, SFBGs suffer from lossy spots due to high temperature oxidation, resulting in a significant deterioration of spectral signal-to-noise ratio (SNR) and a decrease in demodulation accuracy. Here, an ultra-high-temperature sensor based on an SFBG, which was inscribed by a femtosecond laser line-by-line scanning technique and sealed in a sapphire tube infiltrated with argon gas, is proposed and demonstrated. Moreover, since the spectrum of SFBG exhibits multiple peaks and large bandwidth, the conventional peak detection algorithm of single-mode FBG is not desirable for realizing the high-precision demodulation of SFBG. We proposed an high-precision temperature demodulation for SFBG sensors, including spectral data de-noising, a Gaussian-like profile fitting and peak search. Furthermore, the ultra-high-temperature response of the sensor in the range of 800 ℃ to 1900 ℃ was studied by utilizing a high-temperature blackbody radiation source. Additionally, the results showed that the temperature sensitivity of SFBG sensor was 44.3 pm/℃ at 1900 ℃ and the temperature uncertainty with one σerror bar was less than ±1.5 ℃. As such, the proposed SFBG sensor is desirable for harsh environments in aviation, nuclear power and smelting industries.
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