ROADMs for reconfigurable metro networks

Abstract

Reconfigurable Optical Add-Drop Multiplexers (ROADMs) are the key nodal sub-systems that are used to implement modern DWDM networks. They provide network flexibility by switching wavelengths among fibers under software control without expensive conversion to the electronic domain. They speed up provisioning time, reduce operational costs and eliminate human errors. Two general types of ROADMs are used in Metro optical networks, two-degree and multi-degree, where the degree refers to the numbers of DWDM fibers entering and exiting the ROADM node. A twodegree ROADM is like a location on a highway with off and on ramps to drop off and accept local traffic while a multidegree ROADM is like an interchange where highways meet and is used for interconnecting DWDM rings or for mesh networking. The paper describes two-degree and multi-degree ROADM architectures and how these relate to the technology alternatives used to implement the ROADMs themselves. Focus is provided on the role and expected evolution of the wavelength selective switch (WSS) which is the primary engine used to power ROADMs.