A research group at KDD R&D Laboratories (Saitama, Japan) has demonstrated 40-Gbit/s single-channel soliton transmission across 10,200 km without any active inline transmission control. In the transmission-control scheme developed by the researchers, the cumulative chromatic dispersion is offset periodically along the system by dispersion-compensation fiber with negative (normal) dispersion. Total system dispersion is close to zero.
Good transmission performance depends on use of a dispersion map where both the Gordon-Haus timing jitter and soliton-soliton interaction are effectively suppressed. Polarization-division multiplexing is used only in the transmitter to further reduce soliton-soliton interactions. According to the researchers, the technique requires only dispersion-compensation fibers and wideband optical bandpass filters in the transmission line and not the ultrahigh-speed optical modulators and electronics required in earlier long-haul transmission experiments exceeding 10,000 km. For more information, see www.Lab.kdd.c.jp.—Paula Noaker Powell