Fabrication and characterization of low-loss optical fibers containing rare-earth ions

Low-loss fibers containing rare-earths have been produced with high absorption levels in the visible and near infrared regions. Although containing relatively large quantities of rare-earth impurity dopants, the fibers possess low-loss windows where the attenuation is similar to that observed in undoped fibers. This attribute makes the fibers attractive for use in long distributed sensors, as well as low-threshold fiber lasers. Fiber characteristics relevant to these two applications are uniformity of dopant incorporation, absorption and fluorescence spectra, and fluorescence lifetime. These measurements are presented, together with their respective temperature dependences. The fiber fabrication method is described and results given for Nd³⁺-, Er³⁺-, and Tb³⁺-doped fibers.