IMPROVED ROBUSTNESS IN LONG-HAUL LIGHTWAVE ALL-AMPLIFIER SYSTEMS

The issue of ''system robustness'' of a long-haul lightwave communicat ion system that uses erbium-doped fiber amplifiers to periodically boo st the signal power level is addressed. The signal power level at the output of each amplifier is the focus. It is found that this power lev el is the same throughout the system, and that it depends only on the amplifiers' gain characteristic and the span loss and is independent o f the launched power at the input to the chain, provided it is close t o the design value. As such, the system-wide signal power level is sen sitive to systematic design and/or manufacturing errors. The sensitivi ty of the signal power level to errors in amplifier design and span lo ss is studied, and a simple technique is proposed that reduces this se nsitivity, thus making the system more robust.