Solitons Work in Real Network
Dr. Flavio Fontana
The increasing demand for bandwidth in optical links has found an answer in nonlinear propagation, which recently was put into play by Pirelli Cables and Systems and MCI Telecommunications Corp. This method increased the system's capacity, representing a breakthrough in high-speed telecommunications.
It has been known since the 1980s that soliton pulses may provide a way to reach very high bit-rate transmission in single-mode fibers because of their resistance to temporal spreading. Despite its promising characteristics, soliton transmission has been limited -- its use is being considered for submarine links -- because developments in high-capacity transmission have favored the straightforward but bulky and costly approach of dense wavelength division multiplexing (WDM) of 2.5-Gb/s channels.
MCI decided to evaluate the use of 10-Gb/s channels as building blocks for a WDM system based on step-index fiber, and successfully used a soliton transmission system that permits very long distance unregenerated connections. Unveiled by Pirelli's Pierluigi Franco, the core component of the link is a soliton transmitter that allows the generation of chirp-free pulses, a crucial requirement in the highly dispersive step-index fiber. Customized amplifiers and partial compensation of chromatic dispersion further enhance high-bit-rate soliton transmission.
In the first field trial, carried out in February, the system succeeded in operating at 10 Gb/s over a distance of more than 900 km, maintaining a repeater spacing of at least 90 km. The trial also demonstrated the upgradability of the system to a WDM configuration in which 16 or 32 channels will be transmitted simultaneously.
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