Guidelines for optimizing system performance for 20 WDM channels propagating through a cascade of EDFA's

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Abstract
We analyze 20 wavelength-division-multiplexed (WDM) channels propagating through a cascade of erbium-doped fiber amplifiers (EDFA's) covering megameter distances. Optimal operating conditions are found for achieving a high signal-to-noise ratio (SNR), with as small an SNR differential between channels as possible without resorting to external equalization methods. Issues considered are the link loss between amplifiers, the small-signal gain per amplifier, the wavelength and power of the pump, and the input signal power. We find that the link loss is the most critical parameter for narrowing the SNR differential among the 20 channels. Furthermore, 20-dB small-signal gain for each amplifier provides the highest overall SNR for the 20 channels transmitted across 4500 km. Additionally, either 0.98 or 1.48 mu m pump wavelength can be equivalently used, and the cascade performs well with moderate pump and signal powers.