JOHN WILLIAMSON ROADMS
support the greater number of ROADM degrees without the complexity and cost of passive splitting and parallelised modules.” Heeks reports that a new generation of high-capacity WSS devices in development at HUBER+SUHNER makes use of ultra-high definition 4k LCoS panels and 2D holographic beam- steering. “The expectation is that this disruptive WSS platform will allow the reimagining of ROADM architectures across all levels of the network and pave the way for a new class of ROADM that enables contentionless routing of both WDM and SDM traffic in an integrated network node,” he states. As future prospects Xenos instances: multi-degree integration in a single module; higher integration of modules supporting multi-rail architectures; and more and more embedded instrumentation. “There’ll also be more ‘design-from-the-ground-up with modern container-based software architecture,” she anticipates. But it’s likely that there will be bumps in the ROADM ahead. “There are going to be many challenges to overcome,” concludes Xenos. “For example, how to manage software upgrades? How are we going to connect systems with different WSS technology? Who is going to do the integration testing? And trouble-shooting will be difficult.”
There’s also demand for ROADMs in long haul Data Centre Interconnect (DCI) networks at >100 km, while Lumentum sees a new ROADM application space opening up at the edge of the network to support the increased traffic growth driven by 5G, edge computing and content caching. THE ROADM AHEAD So, what’s coming down the ROADM turnpike? “Going forward”, predicts Nagarajan, “ROADM will continue to evolve to improve the cost per unit bandwidth as network capacity grows, taking advantage of higher levels of WSS integration such as collapsing the functions of separate C- and L-band WSSs, allowing continuous C+L operation in a single device.” Heeks agrees that upcoming ROADMs must not only deliver increased capacity and versatility, but must do so at increasingly lower cost-per-bit. This will require a new generation of WSS, with higher port counts and flexible configurations. “Line-side WSSs will require future-proofing against both degree and bandwidth increases, to allow pay-as-you-grow expansion of the nodal capacity. Spectral coverage is less critical for client-side switches, where the bandwidth can be split across multiple modules,” he maintains. “The key challenge here is, instead, to
“The core network requires high- degree ROADMs - for example an 8-degree node may require a 16-, 24- or 32-degree ROADM for fully CDC operation,” continues Heeks. “Simultaneously the number of client- side ports as a proportion of the ROADM degree is reducing, with fewer but higher-capacity channels to add and drop from each degree.” Other innovations are: the MxN connectionless Wavelength Selective Switch (WSS), in which ‘N’ denotes the number of add-drop ports and M is the number of directions the ROADM supports; and inherent filtering. “The recent introduction of contentionless MxN WSS allows seamless evolution of coherent transmission to higher data rates, enabling lower cost per bit in CDC ROADM nodes, while inherent filtering enhances performance, optimising spectral efficiency x reach,” explains Nagarajan. FORKS IN THE ROADM Nagarajan remarks that today ROADMs are widely used in long-haul and metro networks, with the bulk of the volume deployment being in the latter. “It is worth pointing out that metro volumes are larger simply due to metro networks having a larger volume of network nodes relative to long-haul networks,” he qualifies.
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ISSUE 25 | Q3 2021
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