Long span optical transmission experiments at 34 and 140 Mbit/s

Long-haul optical fiber transmission system experiments have been carried out over unrepeatered spans up to 250 km. In this paper the design options for such systems will be discussed, followed by a description of five laboratory trials: a dispersion-limited 176-km 34- Mbit/s experiment, employing commercial components throughout; two loss-limited system trials over 220 km at 140 Mbit/s and 233 km at 34 Mbit/s, based on multimode lasers and dispersion-shifted fiber; and a further two experiments over 223 and 251 km at the same line rates, featuring single-line DFB lasers and step-index monomode fiber.