The authors experimentally demonstrate passive equalisation of the non
-uniform gain of cascaded EDFAs over a 7.4nm wavelength range by perio
dically using notch filters along a 1000 km transmission link. The 100
0km equalised transmission was accomplished using a recirculating loop
and a single intra-loop notch filter. The signal power differential a
mong the four WDM channels is reduced from 19 to 4dB.