WDM technologies in telecommunications

The drive towards WDM applications is motivated by a number of commercial and economic factors. These range from cost of installed fiber, issues regarding fiber right of way, to the increasing demand for bandwidth as the emerging broadband technologies of ATM, frame relay and video on demand, consume the currently available bandwidth. In this environment WDM is seen as a viable technique to increase the available bandwidth of the currently installed fiber base. The advent of the optical amplifier technologies is closely coupled with the viability of WDM in the market place. With launch powers of exceeding 10 dBm the initial drawback of insertion loss are largely overcome. NT has been active in developing WDM technology. Products like the telecommunications network16X, a 2.4 Gbit/s SDH ring system currently offer WDM. In WDM applications the capacity of a link may be doubled from 2.4 Gbit/s to 4.8 Gbit/s. With high power transmitters a commercially viable 4.8 Gbit/s link with spans exceeding 100 km is possible. Another leading edge product offers 10 Gbit/s capacity at a single wavelength. This paper discusses the main market drivers for WDM. It also examines the advances of technology and materials, both of WDM and optical amplifiers that make the commercial application of this technology viable. Noise levels, ASE limitations, and laser material technologies are all considered. The paper deals with the practicalities of the technology, how technical problems are overcome and presents proven performance of WDM technology in Northern Telecom products