Photodarkening and photobleaching of an ytterbium-doped silica double-clad LMA fiber.

We studied the temporal evolution of the photodarkening effect in an Yb-doped silica LMA fiber. The absorption spectra exhibit an increase in absorption in the visible and in the near infrared spectral range when the fiber is exposed to pump light around 980 nm. We show the influence of the photodarkening on the cw lasing properties of the fiber, and demonstrate photobleaching of the same fiber by exposure to UV light at 355 nm. The corresponding absorption spectra and lasing performances are shown and are entirely comparable to those of a new fiber.