Irradiation effect on strain sensitivity coefficient of strain sensing fiber Bragg gratings

The effect of irradiation on the strain sensitivity coefficient of strain sensing fiber Bragg gratings (FBGs) has been investigated through experiments. FBGs were fabricated in single mode fibers with 3 mol% Ge-concentration in the core and with a H₂-loading treatment. In experiments, the FBGs were subjected to γ-radiation exposures using a Co⁶⁰ source at a dose-rate of 25 Gy/min up to a total dose of 10.5 kGy. The GeO defect in fiber absorbs photons to form a GeE’ defect; the interaction with H₂ is a probable reason for the γ-radiation sensitivity of gratings written in hydrogen loaded fibres. The effect mechanism of radiation on the strain sensitivity coefficient is similar to that of radiation on the temperature sensitivity coefficient. Radiation affects the effective index n_eff, which results in the change of the thermo-optic coefficient and the strain-optic coefficient. Irradiation can change the strain sensitivity coefficient of FBGs by 1.48%–2.71%, as well as changing the Bragg wavelength shift (BWS) by 22 pm–25 pm under a total dose of 10.5 kGy. Our research demonstrates that the effect of irradiation on the strain sensitivity coefficient of FBG is small and that strain sensing FBGs can work well in the radiation environment.