Contents 1. Introduction
As we begin to see recovery in carrier spending, reconfigurable optical add/drop multiplexers (ROADMs) have emerged as key building blocks for the next-generation systems which are now starting to be deployed [1]. ROADM solutions are available based on liquid crystal or MEMS wavelength blockers, monolithic or hybrid PLCs, tunable filters, or multiport wavelength selective switches. As carriers and system vendors continue to strive for competitive advantage, it is unlikely that a single solution will be universally adopted. The drive towards common platforms could however influence the choice of a particular system vendor.
