Random walk of coherently amplified solitons in optical fiber transmission

In an optical-communications system using soliton pulse transmission, periodic amplification is needed to maintain the energy of the solitons. We show that amplifier noise causes a soliton's group velocity to undergo a random-walk process. The resultant timing errors at the receiver limit the system's product of length times bit rate, in one example, to about 24 000 GHz-km.