Photosensitivity and thermal stability of UV-induced fiber Bragg gratings in phosphate glass fibers

The photosensitivity of highly Er/Yb doped and undoped phosphate glass fibers is characterized under irradiation with intense pulsed 193 nm light from an ArF excimer laser through a phase mask. The ultraviolet photosensitivity of the active fibers is shown to be roughly half that of the passive fibers. We also demonstrate that the strong growth of the fiber Bragg grating reflectivity observed upon heating at temperatures between 100-250 °C is directly related to the UV irradiation time, but not to the size of the index modulation of the seed grating or even to the fiber type (Er/Yb doped or undoped). The conditions to reliably obtain final index modulations amplitudes between 5 and 10 × 10^-5 are given.