High temperature-sensitivity sensor based on long period fiber grating inscribed with femtosecond laser transversal-scanning method

We propose a high temperature-sensitive long period fiber grating (LPFG) sensor fabricated by using the femtosecond laser transversal-scanning method. The femtosecond pulses scan over the whole fiber core and some part of the cladding region; the modified regions are more extended. It is found that the LPFG-I fabricated by the transversal-scanning method shows higher temperature sensitivity and better temperature uniformity than that of LPFG-II written by the femtosecond laser point-by-point method. The LPFG-I with a temperature sensitivity of 75.96 pm/degrees C in the range of 25 degrees C-400 degrees C is measured. Moreover, in the range from 400 degrees C to 800 degrees C, a higher temperature sensitivity of 148.64 pm/degrees C and good linearity of 0.99 are achieved, while the temperature sensitivity of LPFG-II is only 95.55 pm/degrees C. LPFG-I exhibits better temperature characteristics, which, to the best of our knowledge, has the highest sensitivity in silica fiber temperature sensors.