PHOTOBLEACHING OF THULIUM-DOPED ZBLAN FIBERS WITH VISIBLE-LIGHT

Photobleaching of darkened thulium-doped ZBLAN fibers is observed afte r short exposure to visible light. The bleaching process is characteri zed by a stretched-exponential function of time with an exponent beta independent of both the bleaching intensity and the thulium concentrat ion. The bleaching rate 1/tau is also shown to scale linearly with the bleaching intensity and to have a 1/3-power dependence on the thulium concentration. Incomplete and slow recovery of the color centers is o bserved in previously bleached fibers, suggesting the presence of at l east two types of defect. (C) 1997 Optical Society of America