Banding in optical add-drop multiplexers in WDM networks: preserving agility while minimizing cost

In this paper, we examine the use of limited tunability in reconfigurable optical add-drop multiplexers (L-ROADM). L-ROADMs can add or drop from only a subset of adjacent wavelengths on the network and are less costly than fully-reconfigurable optical add-drop multiplexers (F-ROADMs). We quantify the trade-off between tuning range and the number of F-ROADMs that can be replaced by L-ROADMs without sacrificing the set of connections that can be established. For the limited-add and drop case, an analytical solution for the band size is found. For the limited-add or limited-drop case, a nearly linear relationship was found between the size of the band and the number of L-ROADMs required, and the number of additional wavelengths required never exceeded 20%. For example, if half of the nodes in the ring were equipped with L-ROADMs that operated on 50% of the total spectrum, full connectivity could still be achieved by employing as few as 7% extra wavelengths.