I. Introduction
Wavelength-division multiplexing (WDM) is a key optical networking technology for realizing low-cost, high-bandwidth, and scalable data services. Each fiber optical physical link in a WDM network is partitioned into multiple data channels each of which operates on a separate wavelength. Thus, WDM permits use of enormous fiber bandwidth by providing data channels whose individual bandwidths more closely match those of the electronic devices at their endpoints [20]. As WDM technology matures, it is likely to be widely used in systems ranging from local and metropolitan area networks to the backbone of the next-generation Internet.