Reflective Optical Fiber Refractometer Based on Long-Period Grating Tailored Active Bragg Grating

A reflective optical fiber refractometer based on a long-period grating (LPG) followed by an active fiber Bragg grating (AFBG) is proposed. The AFBG is inscribed in a short section of cobalt-doped optical fiber, which can be heated by pump laser and acts as a sensing signal indicator. The LPG functions as a bridge between the surrounding refractive index (RI) and the AFBG reflection, tailoring the power of pump laser for heating. Experimental results demonstrate that the wavelength response of this fiber grating-based reflective refractometer can be easily adjusted, and a significantly improved sensitivity within the RI range from 1.3403 to 1.4654 has been achieved.