KAZUICHI ICHIKAWA FLEXIBLE ROADM TECHNOLOGY
LOWERING COSTS WITH AN OPEN SPECIFICATION FLEXIBLE ROADM TECHNOLOGY:
EVOLUTION OF OPTICAL NETWORKS The rapid increase in data traffic is driving the global construction of additional data centres, as well as the expansion of existing networks. As a result, the demand for high-performance, scalable, and flexible network solutions has risen, leading to growth in the reconfigurable optical add/drop multiplexer (ROADM) market. ROADMs can switch the destinations of optical signals with different optical wavelengths, with many ROADMs being deployed in optical communication networks, where they serve as key devices. ROADM TECHNOLOGIES AND ADVANTAGES ROADM simplifies network design, supports bandwidth change requests, and improves operational efficiency through remote reconfiguration. A typical ROADM consists of multiple Wavelength Selective Switches (WSS), which in turn consist of a combination of MUX/DEMUX, optical switches, variable optical attenuators (VOAs), and control modules. The functionality of ROADMs, which switch the destination of optical signals without electrical conversion, provides operators with the capability to streamline route design.
configurations, ensuring efficient communication conditions. This approach minimises the risk of network disruptions caused by human error and significantly reduces the operational workload incurred by network management. ROADMs enable network operators to add, drop or pass-through the required wavelengths at any site to ensure optimal network efficiency, as traffic routing and services can be altered with no physical changes. They are easily scaled, enabling the quick addition of new wavelengths, services or network nodes as bandwidth demand increases. Multi-degree ROADMs, which will allow connections between multiple fibre paths, can also be used to reroute traffic in the case of fibre cuts or hardware failures, providing enhanced network resilience and redundancy. The ROADM has become a key technology in developing high-capacity, flexible, agile optical networks such as 400G Wavelength Division Multiplexing (WDM) for demanding cloud, 5G and data centre use cases. LOW LATENCY EDGE COMPUTING There are various architectures that network designers can deploy. One example is CDC (Colourless, Directionless and Contentionless), which enables non- blocking mesh configurations. Colourless adds or drops any wavelength or colour at any port, directionless adds or drops wavelengths in any direction, while contentionless adds or drops wavelengths without interference. Multi-degree and CDC ROADMs are essential to enabling detours and fast switching that ensure low latency. This type of remote dynamic rerouting enables edge services such as AI workloads, real-time analytics, and 5G use cases to maintain optimal direct low- latency routes even under high congestion or when a link fails.
ROADMs not only provide automation and maximise spectral efficiency, but can also keep data in the optical domain for longer by passing wavelengths through optically without optical-electrical-optical (OEO) regeneration. Such ROADMs cut equipment costs and lower latency across edge nodes and data centre interconnections. PROMOTING OPEN NETWORKING Since the 2010s, the adoption of ROADM technology has gained significant momentum, leading to the emergence of new technical challenges. Historically, the design and production of ROADM equipment were undertaken only by a small number of specialised hardware vendors. This lack of diversity resulted in minimal interoperability across devices from different manufacturers. Consequently, ROADM-related systems were constrained in their ability to be flexibly integrated based on specific functional requirements or cost considerations. The increasing demand for optical networks to be flexible, scalable, and autonomously operable has necessitated significant efforts to ’open up optical networks.’ These efforts encompass the establishment of standardised technical specifications and the enhancement of interoperability among devices from multiple vendors. Such initiatives are being actively pursued under the ‘OpenROADM’ project, which was initiated in 2015, with AT&T and other industry leaders as founding members. The project currently has over 30 member organisations. OpenROADM focuses on standardising optical interfaces and their specifications to ensure seamless interoperability among ROADM systems supplied by diverse manufacturers. This initiative further emphasises the development of integrated
Figure 1: Typical WSS configuration with four ports.
ROADMs enable the dynamic adjustment of wavelength bandwidth based on data transmission requirements. They facilitate the remote management of optical signal routing for individual wavelengths, effectively eliminating the need for manual on-site interventions by network technicians. In networks utilising ROADM technology, software- driven automation optimises connection
Figure 2: Optical network systems become open.
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| ISSUE 42 | Q3 2025
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