Modeling of ion pairs in erbium-doped fiber amplifiers

The effects of Er-Er pairs on the characteristics of Er-doped fiber amplifiers are analyzed theoretically. Pairs are found to have little effect on the amplifier optimum length, signal saturation power, and noise figure (at constant gain) but to cause significant reduction in the gain, even at residual levels, quantitatively consistent with fiber laser measurements. A maximum tolerable fraction of paired ions near 8%, corresponding to approximately 400 mole parts in 10(6) Er(2)O(3), is predicted for near-optimum gain efficiency in Al-Ge silica fibers.