Stable blue emission from a 2500 ppm thulium-doped ZBLAN fiber laser

Summary form only given. A great interest in blue thulium-doped ZBLAN fiber lasers has developed in recent years due to their potential for hundreds of milliwatts of output power and simple configuration compared to frequency-doubled solid-state lasers. However, blue fiber lasers have been reported to suffer from a degradation of their performance over minutes or hours of operation. This degradation has been associated with the formation of color centers in the fiber core leading to an increase in the background losses of the fiber. In this paper, we demonstrate a stable 70-mW blue thulium-doped ZBLAN fiber and report on two different methods to restore the full transparency of darkened fibers.