Gamma-Ray Irradiation Effects on the Femtosecond Laser-Written Fiber Bragg Gratings

This work presents the radiation response of fiber Bragg gratings (FBGs) inscribed by femtosecond (fs) laser point-by-point (PbP) technology with different fs-laser pulse energies in two different types of doped single-mode fibers: germanium-doped (Ge-doped) fibers and pure silica core (PSC) fibers. The inscribed FBGs were exposed to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula>-irradiation at room temperature with a dose rate of 3.835 kGy/h up to a total dose of about 100 kGy. The influence of fiber composition and laser energy used for FBG inscription by the fs-laser on the radiation-induced Bragg wavelength shifts (BWSs) of the FBGs was compared. Additionally, the radiation effects of FBGs inscribed using fs-PbP technology were compared with those inscribed using commercial ultraviolet (UV) laser phase mask technology. The irradiation results indicate that the FBGs inscribed in the PSC fibers by the fs-PbP method exhibit a lower BWS than those inscribed in the Ge-doped fibers. The FBG inscribed in the PSC fiber with the higher fs-laser energy is radiation-resistant and exhibits a lower BWS of only about 8.964 pm (equivalent to a temperature error of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 0.906~^{\circ }$ </tex-math></inline-formula>C), while the FBGs inscribed in the PSC fiber with the lower fs-laser energy and inscribed in the Ge-doped fiber with a commercial UV laser exhibit the BWS of about 13.94 and 68 pm, respectively. These findings provide experimental evidence that the FBGs inscribed on PCS fiber with relatively high laser energy offer a unique setting for strain and temperature sensing in harsh radiation environments.