Recovering a rare-earth-doped optical fiber under irradiation

An optical fiber apparatus and a method of recovering radiation-induced-attenuation (RIA) onto a rare-earth-doped optical fiber under irradiation are provided in this disclosure. A light source is coupled to a rare-earth doped optical fiber. The light source emits a combination of mode locked pulsed light and non-mode locked quasi-continuous-wave light. The mode locked pulsed light are used to recover RIA onto the rare-earth doped optical fiber in real time, and the non-mode locked light are used to pump the rare-earth doped optical fiber as a gain medium. Each pulsed duration of the mode locked pulsed light is much shorter than operation duration of the non-mode locked light, such that an instantaneous power of the mode locked pulsed light exceeds a saturated pumping power required for the rare-earth doped optical fiber, so as to effectively elevate the core temperature of rare-earth doped fiber to achieve a confined photo-annealed recovery of RIA onto rare-earth doped fibers.