High-Temperature Fiber Laser Sensing Based on Low-Reflectivity Regenerated Fiber Bragg Grating and Saturable Absorber

Regenerated fiber Bragg grating (RFBG) cannot be directly used in practical engineering for temperature measurement due to its low reflectivity, so a high-temperature fiber laser sensing method based on low-reflectivity RFBG is proposed. RFBG is used as one mirror of the resonant cavity, and a length of unpumped Er-doped fiber (EDF) as saturated absorber is adopted to compress line width and suppress multi-longitudinal mode of laser. The current threshold of fiber laser is 68.9 mA. At 150 mA, the output laser is stable and has a good linear relationship with temperature when temperature varies in the range of 300 to 800 degrees C. In the temperature rising and falling test, the correlation coefficient is up to 0.99974, and the average temperature sensitivity is 15.11 pm/degrees C. During 3 h of laser stability test at 700 degrees C, the maximum variation of the laser wavelength and intensity is 0.032 nm and 0.109 dB, respectively. The results show that the signal-to-noise ratio is higher than 50 dB, the output laser is stable, and there is no mode hopping phenomenon in the temperature-rising and temperature-falling process.