Fabrication and characterisation of rare earth doped optical fibres

The authors compare the properties of fibers with P co-doped cores to those with Ge and Al co-doped cores. Rare-earth doped fibers with various compositions have been fabricated and characterized. P co-doped fibers have significant advantages as amplifiers compared with other co-dopants. The excited state absorption is greatly reduced at the 1300-nm window in a P co-doped Nd³⁺ fiber. Furthermore, the excited state absorption in Er³⁺ doped fibers for 514.5-nm pumping is also significantly reduced. As a result, the largest gain yet reported (1.6 dB/mW) in such fiber using this pump wavelength was measured. The absorption, fluorescence and gain spectrum indicates that P co-doping offers improvements over conventional co-dopants such as Ge and Al