Xy. Zou et al., COMPENSATION OF RAMAN-SCATTERING AND EDFAS NONUNIFORM GAIN IN ULTRA-LONG-DISTANCE WDM LINKS, IEEE photonics technology letters, 8(1), 1996, pp. 139-141
Two physical mechanism effects which cause nonuniform spectral gain in
a long-distance WDM system are Raman scattering and EDFA's, with the
Raman gain increasing with wavelength and the EDFA gain profile in a c
ascaded-amplifier system having a peak at 1560 mm. Both effects limit
system capacity by causing a wide variation in signal powers and SNR a
mong several WDM channels. We analyze the scenario in which these two
deleterious effects partially compensate each other so that a more uni
form overall spectral gain can be achieved. By adjusting the link-loss
between amplifiers and by strategically placing six WDM channels betw
een 1560 and 1563 mm, the SNR differential among these channels is red
uced from 10 dB to 0.5 dB for a 10000 km link, thereby significantly e
nhancing the system performance.