Reconfigurable optical add/drop multiplexers (ROADMs) are the wavelength division multiplexing (WDM) equivalent of the add/drop multiplexing that has been used in the Synchronous Digital Hierarchy (SDH) and Synchronous Optical Network (SONET) markets for more than a decade. ROADMs enable communications service providers (CSPs) to automate the way individual wavelengths of WDM systems are routed through their networks, mainly in ring configurations, with protection switching and easy provisioning being the major benefits.