Wavelength tunable fiber Bragg gratings fabricated by stress annealing assisted femtosecond laser direct writing.

• The resonant wavelength of FBG was fine-tuned by stress annealing. • The fine-tuning of resonance wavelength depends on the applied stress. • FBG fine-tuned by stress annealing is suitable for high-temperature conditions. • Elastic-plastic transition of silica fiber is analyzed by nonlinear shift of resonant wavelength. The resonant wavelength is an important parameter of fiber Bragg grating (FBG). When FBGs are fabricated by femtosecond (fs) laser direct writing, it can be fine-tuned through the process of stress annealing. By changing applied stress, it can be permanently fine-tuned in the range of 20.76 nm relative to the original one, and the tunable sensitivity is 1.48 nm/MPa. Besides, the elastic limit strength of silica can be measured at high temperature by analyzing nonlinear shift of FBG resonance wavelength during the stress annealing process. The temperature sensing properties of FBG are measured from 20 °C to 1150 °C. The sensitivity and high-temperature stability of FBG are improved after stress annealing, which means that the fine-tuned FBG is still suitable for high-temperature sensing, high-power fiber lasers and other high-temperature conditions. [ABSTRACT FROM AUTHOR]