Abstract

The performance of fiber amplifiers is extremely sensitive to the material-dependent properties of the pump band. High-power, reliable, low-cost diode lasers are currently only available at 800 nm, a poor pump band for Er³+ due to the low strength of the ground state absorption (GSA) transition and an intense, overlapping excited state absorption (ESA) band. High gains have been achieved with silica fibers by pumping the long-wavelength wing of the GSA band at ≈820 nm [1,2], thereby avoiding the ESA at shorter wavelengths but introducing another problem by reducing the already low GSA cross section at the pump wavelength. Alternatively, the use of other glass host compositions with reduced ESA has been proposed [3]. We have examined both approaches using experimentally determined parameters in a highly quantitative numerical model to compare the performance of Al/P-silica, Ge/P-silica, and fluorophosphate fiber amplifiers. The analysis was performed for co- and bi-directional pumping and included treatments of waveguide design, Er³⁺ confinement, pump-wavelength dependence of gain and noise figure, and quantum conversion efficiency for power amplifiers.

© 1991 Optical Society of America