Soliton propagation in long fibers with periodically compensated loss

With computer simulation, we study soliton propagation in an all-optical, long-distance communications system where fiber loss is periodically compensated by Raman gain. We find that distortion of the transmitted pulses from true solitons shows a peak near
z_{0} = L/8
where
L
and z
0
are the amplification and soliton periods, respectively. We also describe optimal system design based on the exceptional pulse stability and low soliton powers obtained in the region
z_{0} \gg L/8
. Typical amplification periods are in the range 30-50 km, pump powers are less than 100 mW, and for bit rates in the 10 GHz range, time average signal powers are at most a few milliwatts. The single-channel rate-length product for error rate less than 10
^-9
is
\sim29 000
GHz Km. Finally, we show that in the gain-compensated system with wavelength multiplexing, soliton-soliton collisions produce random modulation of individual pulse velocities. Nevertheless, multiplexing can yield rate-length products greater than 300 000 GHz km.