Optimization of the period of equalizer arrangement in multi-span fiber-optic lines

The statistics of the unevenness of the signal power spectrum in a chain of erbium amplifiers EDFA (Erbium Doped Fiber Amplifier) was studied. It was established that, the statistical properties of EDFA gain unevenness taken into account can significantly increase the accuracy of estimating the magnitude of spectrum unevenness of multichannel signal (by 4 dB in the chain of five EDFAs). Basing on the analysis of the results of numerical modeling of various configurations of fiber-optic communication lines (FOCL), we estimated the optimal period for placing equalizers. It is shown that the deterioration of the signal quality in a fiber-optic link caused by the unevenness of the EDFA amplification depends on the number of flights between the devices leveling the signal spectrum and the statistical characteristics of the unevenness of the amplification spectrum of the used EDFAs, but practically does not depend on the number of spectrum equalization sections, signal parameters and flight length. Basing on the simulation results, we made a model aimed at the calculation of the penalty due to the accumulated unevenness of the EDFA. An algorithm is proposed for estimating the penalty, applicable for the arbitrary configuration of fiber-optic lines with the known statistics of the accumulation of irregularities in EDFA.