Deep UV-induced near-infrared photodarkening of Er/Yb-doped and undoped phosphate fibers

Photodarkening (PD) of Er/Yb-doped and undoped phosphate fibers caused by pulsed 193 nm irradiation from an ArF excimer laser to form Bragg grating mirrors is investigated. Doped and undoped phosphate fibers exhibit the same level of significant UV-induced PD loss, which is associated with the formation of a color center band at 467 nm. The UV-induced absorption extends into the NIR and creates a loss on the order of 1 dB/cm across the C-band. Photo-bleaching by a high-power supercontinuum source, and thermal-bleaching processes are performed on photodarkened samples. Both bleaching processes are found effective to fully erase the UV-induced PD loss.