Raman amplification is added to a transmission system to provide an in
crease in power budget allowing for a four-fold upgrade in capacity ei
ther by TDM or WDM. Here, a TDM upgrade from 2.5 to 10 Gb/s and a WDM
upgrade from a single 10 Gb/s channel to four channels of 10 Gb/s each
were experimentally verified with an improvement in the power budget
of 7.4 dB, Raman gain is an attractive upgrade method for installed sy
stems requiring no changes to the fiber span.