Error-free solition transmission at a bit rate of 5 Gbit/s over 250 km has been accomplished. The transform-limited soliton pulse source is a gain-switched DFB laser diode with a narrow-band spectral filter and Er amplifiers. A LiNbO3 light intensity modulator is used for pulse switching. A new 'pre-emphasis technique' for sending solitons over a longdistance is used, in which an Er3+-doped fibre amplifier is installed every 25 km as a lumped amplifier.
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