Improved robustness in long-haul lightwave all-amplifier systems

The issue of system robustness of a long-haul lightwave communication system that uses erbium-doped fiber amplifiers to periodically boost 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 level is the same throughout the system, and that it depends only on the amplifiers´ gain characteristic and the span loss and is independent of the launched power at the input to the chain, provided it is close to the design value. As such, the systemwide signal power level is sensitive to systematic design and/or manufacturing errors. The sensitivity of the signal power level to errors in amplifier design and span loss is studied, and a simple technique is proposed that reduces this sensitivity, thus making the system more robust