Depletion of soliton energy by four-wave mixing between a soliton and
amplifier noise in a system with 100-km amplifier spacing is studied.
Dispersion exponentially decreasing fiber is used as transmission fibe
r. Improvement of the system by the use of a sliding-frequency filter
to reduce noise power and the depletion of soliton energy is shown. Th
e system can be further improved by compensation for depleted soliton
energy. (C) 1997 Optical Society of America.