Straightforward upgrading of transmission systems to 4/spl times/10 Gbit/s through 617 km and 8/spl times/10 Gbit/s through 412 km of SMF

The authors show, for the first time, the feasibility of upgrading existing transmission systems, by straight-forward means, to 40 Gbit/s through 617 km and 80 Gbit/s through 412 km of standard singlemode fibre, since 10 Gbit/s-based WDM transmission was achieved without gain-flattening the commercial optical amplifiers and without intermediate filtering. Dispersion management was performed by dispersion compensating fibre units.