COMPENSATION OF RAMAN-SCATTERING AND EDFAS NONUNIFORM GAIN IN ULTRA-LONG-DISTANCE WDM LINKS

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.