High-temperature pressure sensor based on a highly birefringent fiber Bragg grating created in a dual side-hole fiber

We demonstrate a novel high-temperature pressure sensor based on a highly birefringent fiber Bragg grating (Hi-Bi FBG) inscribed in the cladding of a dual side-hole fiber (DSHF). This grating consisting of a sawtooth stressor perpendicular to the two air holes, are created by using a femtosecond laser direct writing technology. The unique sawtooth structure serves as in-fiber stressor and also generates Bragg resonance due to its periodicity. In order to increase the pressure sensitivity of grating, the air hole size of DSHF was enlarged to 49.6 μm by HF etching. Then a Hi-Bi FBG with a birefringence of 1.9 × 10–
³
was successfully fabricated in this etched DSHF and two polarization peaks could be obtained by using commercial FBG interrogator. Moreover, pressure measurement from 0 to 3 MPa at a high temperature of 700°C was realized by monitoring the wavelength separations and the grating exhibited a pressure sensitivity of -22.4 pm/MPa. And then a wavelength-division-multiplexed (WDM) Hi-Bi FBGs array was successfully constructed in DSHF and was used for quasi-distributed high-pressure sensing of up to 2.5 MPa. As such, the proposed femtosecond laser-inscribed Hi-Bi FBGs is promising for high-temperature pressure sensing in hash environments, such as aerospace vehicles, nuclear plants, and petrochemical industry.