Reconfigurable Optical Add/Drop Multiplexers (ROADM) are reconfigurable optical add/drop multiplexers that can be reconfigured remotely.
ROADM multiplexers differ from static optical add/drop multiplexers(OADM) in that they have configurable switches and tunable filters with which individual wavelengths can be filtered out of the light stream. With such ROADMs, the network administrator can, for example, dynamically reconfigure the wavelength routing. He can add or remove individual wavelengths. This capability eliminates the need for packaging during installation, as it can be done at a later time during ongoing operation.
ROADMs are divided into those with Planar Lightwave Circuits( PLC), which work with many wavelengths, others that use Wavelength Selective Switches(WSS) and support a limited number of wavelengths, and others that have Wavelength Crossconnects( WXC). The optical multiplexers are used in optical transport networks and also in IP over DWDM( IPoDWDM).