Enhanced stability of higher UV-densified Fiber Bragg Gratings after thermal regeneration

Abstract The stability of the Bragg peak strength during isothermal regeneration of Fiber Bragg Gratings (FBGs) depends on their UV photosensitivity. In low Ge-doped fused silica fibers, lower photosensitivity results in improved thermal stability over time, due to enhanced densification effects occurring during UV-exposure. The contributions of UV-inscription parameters and fiber composition to the power, the spectral width and the wavelength shifts of the transmitted signal through FBGs are examined in detail, indicating how the photosensitivity affects the refractive index, the grating period and the optical coupling inside the fiber core. The changes reported for low- and high-Ge doped fibers are mainly attributed to densification effects induced by UV-imprinting, where stronger compaction is found to significantly improve the long-term stability of FBG sensors after thermal regeneration.