Efficient thulium-doped 2-/spl mu/m germanate fiber laser

We report an efficient fiber laser operating near 2 μm. The glass for the fiber is germanate that is highly doped with thulium. The effect of cross relaxation energy transfer between thulium ions as observed from emission spectrum of the glass samples results in the laser having a very high slope efficiency of 58% with respect to launched power. This corresponds to a quantum efficiency of 1.79, indicating that each pump photon leads to near 1.8 excited Tm/sup 3+/ ions.