Effect of Er3+ pairs on the gain and noise figure of EDFAs

Simulations are used to examine the effects of Er3+ pairs on the characteristics of erbium-doped fiber amplifiers. As the percentage of pairs is increased, the most significant effect is that the small-signal gain steadily drops. On the other hand, the optimum fiber length (for maximum gain at a given pump power) and the saturation power (at optimum length and constant gain) vary minimally up to pair concentrations of 40%. The noise figure shows degradation with increasing pair concentrations that is due entirely to the reduction in gain, i.e., at constant gain a paired and unpaired amplifiers are predicted to have the same noise figure. The main effect of pairs is therefore to increase the amplifier pump power requirement.