On scaling transport networks for very high nodal degree ROADM nodes using state-of-the-art optical switch technology

ROADM nodes of both legacy and modern DWDM transport networks have fairly small nodal degrees, since in the majority of cases each node has only a fibre pair interconnecting it to a small set of neighbour nodes and only seldom there are two or more fibre pairs involved in the interconnection or the set of neighbour nodes is large (e.g., above 6). State-of-art optical switch technology is suitable to design ROADMs with the most demanding nodal degrees deployed today and support at least a two-fold increase of these values. However, despite the transmission capacity improvements over a single fibre provided by recent technologies such as advanced modulation formats and superchannels, capacity augmentation in future DWDM networks will likely rely on either simply using more fibres, increasing the nodal degree, or using fibres with multiples cores and/or exploiting multiple modes. This paper provides an outlook on how DWDM networks can scale to very high nodal degrees based on current optical switch technology, highlighting potential ROADM designs and their impact on upgrading network capacity.