Femtosecond soliton transmission in 18 km-long dispersion-shifted, distributed erbium-doped fibre amplifier

Femtosecond optical soliton transmission characteristics in a dispersion-shifted, distributed erbium-doped fibre amplifier as long as 18.2 km have been investigated. The erbium fibre has a dual shape core structure with a doping concentration of 0.5 ppm. Solitons (A=0.7-1.2) with a pulse width of about 450 fs have been successfully transmitted, and even a slight narrowing was observed. When the soliton width was reduced to 260 fs, the output pulse width always broadened up to around 470 fs.