GUIDELINES FOR OPTIMIZING SYSTEM PERFORMANCE FOR 20 WDM CHANNELS PROPAGATING THROUGH A CASCADE OF EDFAS

We analyze 20 wavelength-division-multiplexed (WDM) channels propagati ng through a cascade of erbium-doped fiber amplifiers (EDFA's) coverin g megameter distances. Optimal operating conditions are found for achi eving a high signal-to-noise ratio (SNR), with as small an SNR differe ntial between channels as possible without resorting to external equal ization methods. Issues considered are the link loss between amplifier s, the small-signal gain per amplifier, the wavelength and power of th e pump, and the input signal power. We find that the link loss is the most critical parameter for narrowing the SNR differential among the 2 0 channels. Furthermore, 20-dB small-signal gain for each amplifier pr ovides the highest overall SNR for the 20 channels transmitted across 4500 km. Additionally, either 0.98 or 1.48 mum pump wavelength can be equivalently used, and the cascade performs well with moderate pump an d signal powers.