Abstract

The ever-growing demand for increased capacity over the already-embedded cable plants is wearing out the availability of the fiber. The ability of the network facilities to carry ever-increasing traffic loads is critical for operators since the system speeds have been doubling every two and a half years [1]. Therefore, the line rate, supported by a single optical fiber, is likely to be extended in the near future beyond 2.5 Gbit/s (corresponding to present STM-16/OC-48 line systems). Although the development and deployment of 10-Gbit/s TDM systems are currently in progress, considerable attention is simultaneously paid to wavelength division multiplexed (WDM) approach. This is due to the fact that the terrestrial optical backbones predominantly contain standard 1310-nm optimized fibers, while signal wavelength near 1550 nm is preferentially used in order to take advantage of both the lowest fiber attenuation and the only one mature optical amplification technology (erbium-doped fiber amplification). Because of the large chromatic dispersion encountered at 1550 nm (≈+18 ps/nm.km), the maximum distance that can be spanned without regenerator using a single 10-Gbit/s NRZ channel is practically limited to about 100 km, unless some specific dispersion compensation techniques or more dispersion-tolerant modulation formats are implemented [1]. Conversely, N×2.5-Gbit/s transmission systems offer a 16-fold increase in the nonregenerated spans over standard fiber, as far as chromatic and polarization mode dispersions (PMD) are concerned [2], Therefore, the first WDM application is the development of new N×2.5-Gbit/s long-haul line systems with enhanced capacity per fiber, where the existing cable plants are reused and regenerators are replaced by in-line optical amplifiers for system and maintenance cost reductions. In addition, the deployment of WDM line systems will pave the way to wavelength-routing networks.

© 1996 Optical Society of America