Distributed, dispersion-shifted erbium-doped fiber amplifiers with doping concentrations as low as 0.1-0.5 ppm (0.1-0.5 x 10-4 wt%) have been fabricated and their gain characteristics studied for the purpose of soliton amplification for the first time. A 9.4 km dual-shape-core type amplifier with a 0.5 ppm concentration has a gain of more than 20 dB at 1.535 μm and 10 dB at 1.552 μ m with a forward pumping configuration, and can successfully amplify and transmit a 20 ps soliton pulse train at 2.5 GHz repetition rate. Soliton transmission characteristics of an 18.2 km long fiber amplifier are studied using backward and forward pumping. It is found that A = 1.5 soliton pulses with a pulsewidth of 20 ps can be amplified over 18.2 km at a repetition rate of 5 GHz, where soliton narrowing to 16 ps is observed.
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