Abstract
Repeaterless transoceanic optical communication links are the subject of active research and development. Recently several groups1,2 have reported error free soliton transmission over more than the trans-Pacific distance (9,000 km) at GHz bit rates. Different techniques (passive filters2,3 and pulse retiming1) have been used to overcome the Gordon-Haus limit4 (accumulation of amplified spontaneous emission in the erbium-doped fibre amplifiers regularly spaced along the optical link). Soliton pulses have been generated from mode-locked diode lasers2 and from gain-switched diode lasers1. Mechanical instability and fixed repetition rates of mode-locked external cavity lasers seem to be a problem for practical applications. Unlike the mode-locking techniques, gain-switching does not require an extension of the laser cavity. However, its output is severly chirped and a narrow-band optical filter must be used to limit the bandwidth of the signal. Despite the fact that the τ Δ f product obtained with such a source is apparently satisfactory (0.4), gross excess pulse broadening is observed for distances greater than a few thousand kilometers5.
© 1993 Optical Society of America
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