Sapphire fiber Bragg gratings array demodulated with the multi-peak auto-tracking algorithm for quasi-distributed...

Sapphire fiber Bragg gratings (SFBGs) are promising high-temperature sensors in many harsh environments, such as aviation, nuclear power, and furnaces. Here, we proposed and experimentally demonstrated a quasi-distributed high-temperature sensor based on an SFBG array sealed in an argon gas-infiltrated sapphire tube interrogated by using an InGaAs-based interrogator. An SFBG array including five SFBGs was inscribed using the femtosecond laser line-by-line method and sealed in an argon gas-infiltrated sapphire tube. A multi-peak auto-tracking algorithm, including the Hilbert transform and cross correlation algorithm (CCA), was employed to demodulate the array. The Hilbert transform method is introduced for the segmentation of the peak region in the reflection spectrum. The CCA was used to obtain the Bragg wavelength shift of each SFBG reflection peak. Then, we investigated the stability in demodulation of the SFBG array, and the result shows that Bragg wavelength dispersion is less than ±12 pm, which indicates that the interrogator and the proposed algorithm exhibit high accuracy and stability. Moreover, the SFBG array was calculated at high temperatures up to 1676 °C, and the thermal response curves of the SFBG array were obtained. Furthermore, the temperature distribution measurement of the blackbody radiation source was successfully carried out using the calibrated SFBGs array sensor, with a maximum test temperature of 1900 °C. Therefore, such a quasi-distributed high-temperature sensing system, including an SFBG array, interrogator, and multi-peak detection algorithm, is promising in applications with thermal gradients, such as metallurgical, aviation, and nuclear power industries.