The wavelength add/drop multiplexer for lightwave communication networks

Lightwave systems are progressing toward optical networks capable of manipulating data paths by optical means rather than by traditional electronic switching. This is facilitated by wavelength multiplexed transmission, in which narrow bandwidth optical filters can be used to remove specific channels and reinsert new ones anywhere in the optical link. Wavelength add/drop multiplexers performing this optical channel processing can range in capability from providing dedicated add/drop of a single channel to having fully reconfigurable add/drop of many, if not all, of the wavelength division multiplexed (WDM) channels. Careful placement of wavelength add/drop multiplexers can dramatically improve a network's flexibility and robustness while providing significant cost advantages. This paper summarizes the rationale for incorporating wavelength add/drop multiplexers in modern optical networks, outlines their logical and optical characteristics, and introduces the predominant technology choices.