I am agree with Alessandro about the use of EDFa in the system.System on which gurinder woeking on is realized by incorporating symmetri arrangements by using two smf28.it is better to use a small distance fiber followed by the amplifier to get good results.however the dispersion compensation is used to get longer transmission distance.in one of my ofdm wdm system i got good results for even 6600 km using non linear compensation by opc.