Ho3+: (5S2,5F4)→5I5 transition in fluoride glasses

We propose that Ho3+ and Ho3+/Yb3+-doped fluoride glasses are a good candidate material for fiber amplifiers operating at 1340–1400 nm band. Upconversion excitation in the wavelengths of 880–920 and 970–990 nm is achieved for Ho3+-single-doped glasses, while wavelength region of 910–1000 nm for Ho3+/Yb3+-codoped glasses. Ho3+ concentration is preferably less than 0.5 mol% to avoid lifetime decrease of (5S2,5F4) manifold. Yb3+ codoping enhances the upconversion excitation efficiency, however as Yb3+ concentration increases, back energy transfer from holmium to ytterbium slightly diminishes the fluorescing level lifetime. Some transition-metal ions and rare-earths ions doped in the clad part of a fluoride fiber waveguide, for example, may quench unwanted amplified spontaneous emissions at ∼540 nm and ∼750 nm.