Abstract

Optics has become the unique transmission technology in backbone networks, providing capacities absolutely unknown before, a very high transmission quality and a reduction of operational costs per transmitted bit. This is due to the development of wavelength division multiplexing (WDM) introduced in 1995 and allowing to transmit around 800 Gbit/s (80 and 10 Gbit/s channels) over one single mode fiber in 2005. This chapter describes this history, puts in evidence the basics of optical transmission and the development of WDM technology, and shows how the capacity of WDM systems can be increased by extending the used bandwidth, increasing the channel number or the bit rate per channel.