| Using a sol-gel process for rare earth doping, a minimum background loss of less than 2 dB/km at 1.1 {dollar}mu{dollar}m has been achieved in erbium doped Al:SiO{dollar}sb2{dollar} single-mode fibers. The long lifetime for fluorescence of 520 {dollar}mu{dollar}sec for neodymium in an Al:SiO{dollar}sb2{dollar} glass host prepared by the sol-gel method suggested that this approach provides a very uniform doping of rare earths in silica based glass. In the sol-gel dipcoating to deposit a thick film, the key to achievement of low loss fiber was found to depend critically on a process capable of providing a crack-free film.; A wide range of rare earth doping concentrations and a variety of rare earth ions, including Er{dollar}sp{lcub}3+{rcub}{dollar}, Nd{dollar}sp{lcub}3+{rcub}{dollar} and Tm{dollar}sp{lcub}3+{rcub}{dollar}, were introduced into silica based Al:SiO{dollar}sb2{dollar} single-mode fibers using this technique. The numerical aperture of the doped fiber ranged up to 0.4. The rare earth doping concentration could be adjusted from several parts per million to a few mole percent.; The optical properties of rare earths in the sol-gel prepared silica based glasses and fibers were also studied. A fiber laser was made with the sol-gel prepared Nd-doped single-mode fiber. A conversion slope efficiency of the laser output to the absorbed pump power of 42% was measured in a fiber laser oscillator. The pump wavelength dependence of fluorescence and lasing spectra was also measured for Nd-doped Al:SiO{dollar}sb2{dollar} single-mode fibers. Superfluorescence near 2 {dollar}mu{dollar}m was observed in a 2.5 wt% Tm-doped single-mode fiber. |
