Exploitable results
The project demonstrates the feasibility of very high bitrate (20 Gbit/s up to 40 Gbit/s) optical transmission systems in the transit network, using the electrical time division multiplexing (ETDM) approach. Transmission on both dispersion-shifted and standard single-mode fibre are studied with special emphasis on the reuse of existing fibre infrastructure. Thus, taking into account a typical repeater spacing of about 40 km used today, the goal of the project is to transmit up to 40 Gbit/s over at least 40 km (or multiples) of standard single-mode fibre. It is expected, that fibre dispersion will be the most severe limiting effect. To cope with the fibre dispersion, advanced modulation formats, especially an upgrade of dispersion supported transmission (DST) technology and the use of different multi-level modulation and detection formats are studied in detail. The achievements so far are:
semiconductor circuit technologies suitable for 40 Gbit/s operation have been identified;
simulations for 40 Gbit/s circuits have been carried out using different technologies;
numerical system simulations demonstrate the feasibility of four-level DST at 20 Gbit/s over 140 km and at 40 Gbit/s over more than 40 km of standard single-mode fibre;
system simulations on duobinary-DST and modified duobinary-DST have been carried out;
experimental characterization of high speed laser diodes shows their suitability for 40 Gbit/s 4-level modulation;
a 20 Gbit/s photo-receiver has been realised;
a 20 Gbit/s field experiment over a 46.2 km installed standard single-mode fibre loop between Stuttgart and Ludwigsburg in Germany (using fibre cable rented from Deutsche Telekom) has been carried out successfully using four-level DST;
a 40 Gbit/s 4-level DST feasibility field experiment yields an open eye-diagram.
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