Fabrication of low-loss microfiber bragg gratings for highly sensitive sensor applications

We report on the fabrication of a low-loss microfiber Bragg grating (MFBG) through hydrofluoric acid (HF) etching process for highly sensitive sensor applications. In order to minimize the optical transmission loss at the tapering region of the microfiber, the fiber grating etching process has been motorized with computer control together with real-time monitoring of the reflection spectrum and power. The shape of the fiber taper is optimized through a control of the fiber lifting speed from the etchant solution. The difference of etching rates between the doped core and undoped cladding has been reduced to diminish the abrupt diameter change induced optical losses. A microfiber with smooth surface was obtained and a decrease of 6.29 dB in optical loss was achieved. Moreover, an MFBG with diameter of 4 μm was demonstrated as a high-sensitivity refractive index (RI) sensor whose sensitivity is measured to be 82.4 nm/RIU in the RI range from 1.418 to 1.431.