Sapphire fiber Bragg gratings inscribed with a femtosecond laser line-by-line scanning technique

We propose and demonstrate the fabrication of single-crystal sapphire fiber Bragg gratings (SFBGs) using a femtosecond laser line-by-line scanning technique. This approach provides a robust method for producing SFBGs at various Bragg wavelengths with an acceptable reflectivity. The spectrum characteristics of the SFBGs with various fiber diameters, track lengths, and grating pitch quantities were investigated. An SFBG with a reflectivity of 6.3% was obtained via optimization of fabrication parameters. Additionally, a serial array consisting of five SFBGs at different wavelengths was successfully constructed. The high-temperature response of these SFBGs was tested and the experimental results showed the SFBGs could withstand a high temperature of 1612°C. Moreover, a temperature sensitivity of 36.5 pm/°C was achieved in the high-temperature region. Such SFBGs could be developed for promising high-temperature sensors in aero engines.