Colorless and directionless multi-degree reconfigurable optical add/drop multiplexers

The reconfigurable optical add/drop multiplexer (ROADM) has become one of the most important elements in the DWDM network. The next generation multi-degree ROADM requires two main features: colorless and directionless. Colorless means that add/drop ports are not wavelength specific, and directionless feature enables any transponder to be connected to any degree. In this paper we review and analyze different multi-degree ROADM node architectures that offer full colorless and directionless features. Their key characteristics and properties, including optical loss, size, cost, modularity and upgradability, are compared and discussed.