A femtosecond laser inscribed fiber Bragg grating as a refractive index and temperature sensor based on side-polished method

A fiber Bragg grating (FBG), inscribed directly by a femtosecond laser and based on the side-polished technique, was proposed and experimentally demonstrated for refractive and temperature sensing. The first-order FBG was inscribed by a 800 nm femtosecond pulsed laser, using the point-by-point method, in a fiber core with a length of 3 mm; the grating period was 537 nm. The fiber grating region was subsequently polished for 5 h and a light leak window was polished through the fiber cladding, with a length and depth of 20 mm and 37.5 mu m, respectively. This changed the evanescent field around the grating area to realize refractive index (RI) sensing. In the experiment, the NaCl solution RI sensitivity of the proposed fiber sensor was 854.2 nm/RIU and the linearities were 0.9989. For the temperature measurement, the sensitivity was 11.66 pm/degrees C and the linearities were 0.9854, between 50-450 degrees C.