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

Abstract

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 [Formula: see text]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/[Formula: see text]C and the linearities were 0.9854, between 50–450[Formula: see text]C.

Femtosecond laser direct written fiber Bragg gratings with narrow bandwidth and high sideband suppression

“…Similar to the LbL method, the Pl-b-Pl method is still time-consuming, and not conducive to FBG arrays and mass production. For the previously reported PbP method, a relatively low overlap factor between the refractive index modification (RIM) region and the fiber core leads to a localized effect and therefore causes strong cladding mode loss [16] . Several methods have been proposed to suppress the cladding mode loss, including PbP parallel-integrated inscription and beam-shaping technologies.…”

Process improvement of high aspect ratio nano-gratings based on synchrotron x-ray

“…Femtosecond laser technology is commonly used to fabricate refractive index sensors due to its short pulses and extremely high peak power. He et al [27] used an 800 nm femtosecond pulsed laser to inscribe a fiber Bragg grating with a period of 537 nm directly onto a 3 mm single-mode fiber using a point-by-point method in 2020. In addition, femtosecond laser technology is simple to operate for fabricating complex 3D nanostructures, but the size of the structures is limited and requires an excessive amount of time for fabricating large size devices [28,29].…”