Photoinduced absorption and photobleaching in thulium-doped fluorozirconate fibers

Over the past few years, thulium-doped fluorozirconate fibers have been studied for application as blue fiber lasers. Blue upconversion fiber lasers at 480 nm [1] and 455 nm [2] in a thulium-doped fluorozirconate fiber have been demonstrated at room temperature. Recently, a potentially important application of these fibers for amplification near 800 nm in the first telecommunication window has been reviewed [3]. In our work, we have observed a strong photodarkening of thulium-doped fluorozirconate fibers when pumped at 1.12 μm [4]. A similar behavior was reported in thulium-doped aluminosilicate fibers exposed to 1064 nm light [5]. We have also observed that it is possible to bleach a fluorozirconate fiber by exposing it to 488 nm radiation. These results have stimulated the present study on the formation of photoinduced absorption which may limit the efficiency of blue fiber lasers and other devices using thulium-doped fluorozirconate fibers.