Optimization of Equalizer Spacing Period in Multispan Fiber-Optic Lines

We study statistics of signal power spectrum ripple in a chain of erbium-doped fiber amplifiers (EDFAs). It is found that allowance for the statistical properties of EDFA gain ripple can markedly increase the accuracy of estimating the magnitude of spectrum ripple of a multichannel signal (by 4 dB in a chain of five EDFAs). By analyzing the simulation results for various configurations of fiber-optic communication lines (FOCLs), an optimal equalizer spacing period is estimated. It is shown that the signal quality deterioration in a FOCL caused by the EDFA gain ripple depends on the number of spans between devices flattening the signal spectrum, and on statistical characteristics of gain spectrum ripple of the used EDFAs; however it is practically independent of the number of spectrum equalizing sections, signal parameters, and span length. The simulation results are used to construct a model for calculating the penalty from accumulated EDFA ripple. An algorithm is proposed for estimating the penalty, applicable for an arbitrary FOCL configuration with known statistics of EDFA accumulation ripple.