The wavelength add drop multiplexer for lightwave communication networks

Lightwave systems are progressing toward optical networks capable of manipu lating data paths by optical means rather than by traditional electronic sw itching. This is facilitated by wavelength multiplexed transmission, in whi ch narrow bandwidth optical filters can be used to remove specific channels and reinsert new ones anywhere in the optical link. Wavelength add/drop mu ltiplexers performing this optical channel processing can range in capabili ty from providing dedicated add/drop of a single channel to having fully re configurable add/drop of many, if not all, of the wavelength division multi plexed (WDM) channels. Careful placement of wavelength add/drop multiplexer s can dramatically improve a network's flexibility and robustness while pro viding 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 pre dominant technology choices.