Femtosecond laser inscribed Bragg grating in hollow suspended-core fiber for refractive index sensing

Abstract

The fiber Bragg grating (FBG) was written in hollow suspended-core fiber (HSCF) using femtosecond laser point-bypoint technology. The HSCF based-FBG has a higher refractive index (RI) sensitivity to liquid in the air hole because the core of HSCF is completely exposed to air. In the RI range of 1.35~1.45, the reflection peak of the FBG moves toward the longer wavelength with the increase of the external RI. The wavelength shift of FBG is greater for the higher RI, which means that the HSCF-FBG has a higher sensitivity for the high RI environment. The RI sensitivity of the HSCF-FBG is 14.24 nm /RIU in the range of 1.42~1.44. The axial strain sensitivity of the sensor is 1.02 pm /με in the range of 0~900 με, and the temperature sensitivity is 10.22 pm /℃ in the range of 30~150 ℃. The HSCF-FBG RI sensor has higher sensitivity and lower temperature and strain crosstalk, therefore, proposed HSCF-FBG has prospective applications in biological detection, medical and health fields.