Fiber Bragg grating fabricated in micro-single-crystal sapphire fiber

This Letter introduces a fiber Bragg grating (FBG) in a micro-single-crystal sapphire fiber (micro-SFBG) for sensing applications in high-temperature and harsh environments. The FBG was fabricated by a point-by-point method via an IR-femtosecond laser in a large-diameter sapphire fiber that was then wet-hot acid etched to achieve microfiber size, which culminated in fabricating and characterizing a 9.6 μm diameter micro-SFBG. The refractive index measurement ranging from 1 to 1.75 and temperature measurement from room temperature to 1400°C are also reported.