Resonant wavelength thermal stability of femtosecond FBGs

We report on a thermal stability study of the resonant wavelength of fiber Bragg gratings fabricated by femtosecond laser. We propose a new method to analyze the decay of the central wavelength shift of Bragg gratings based on isothermal and isochronal processes up-to a maximum temperature of 800 °C. The obtained thermal decay follows a typical power-law function, which allowed us to fit theoretical equations to our experimental data and simulate the refractive index decay. A method to mitigate this decay is proposed and the results demonstrate the potential of using femtosecond fiber Bragg gratings as high temperature sensors.