JOHN WILLIAMSON ROADMS
KEEPING THE SHOW ON THE ROADM
Reconfigurable Optical Add Drop Multiplexers (ROADMs) have numerous attractions for optical network operators and service providers. So much so, in fact, that an analysis available from the TECHNAVIO market research house is forecasting the value of the global ROADM market could reach US$5 billion by 2024, up from US$2 billion in 2019, writes JohnWilliamson .
E xpert opinion differs somewhat as to which of the various ROADM improvements over OADMs is of most consequence. Helen Xenos, Ciena’s senior director, Portfolio Marketing, opts for the flexibility they deliver, in what is an unpredictable environment, to evolve the network in terms of scale and more easily support new coherent technologies. She also cites re-configurability that enables rerouting of wavelengths as needed and the management of power profiles when moving from one fibre to another. As well as network flexibility, re- configurability and boosting network expansion, Raj Nagarajan, Lumentum’s senior product line manager, mentions optical by-pass of express traffic which helps eliminate optical-electrical-optical regeneration to lower the overall network ownership cost. Elsewhere in the ROADM industry playbook claims are made for improved network utilisation; accelerated service provision; simplified network management; higher network resilience and automated network and node reconfiguration. ROADMWORKS From their initial use to remotely switch traffic in long haul Wavelength Division Multiplex (WDM) networks in the early 2000s, ROADM repertoire, technology
hardware innovation. Given average traffic growth rates of 30% to 50%, she also reckons the addition of L-band is a big deal. “With respect to ROADM technology, the biggest change we have seen is the move to C- and L-band systems,” she says. Migration to L-band has had teething problems with regard to it sometimes requiring a non-trivial manual engineering effort, and there’s the prospect of possible traffic loss through adverse impact on the in-service C-band channels. Xenos says one solution is Amplified Spontaneous Emission (ASE) loading. According to a Ciena account, filling the unused spectrum with ASE maintains full loading conditions on the system, so that system performance can be known and optimised at the time of deployment. As a result no additional margin needs to be budgeted for an L-band upgrade, and system performance will remain consistent across its lifetime, regardless of channel loading conditions. Whether the L-band is carrying live traffic or not, the system behaves as if it is fully loaded from day one. Karl Heeks, senior programme director, ROADM Systems Group, HUBER+SUHNER, describes how increased capacity is being provided by increased bandwidth within the super C and C-& L-bands, broader spectral channels to support higher baud rates, together with spatial parallelism with multiple fibres per degree, and perhaps ultimately, multi-core or multi-mode fibres in some applications.
and areas of application have evolved considerably. On the extended repertoire front, modern ROADMs can offer ‘Colorless’ (C), ‘Directionless’ (D) and ‘Contentionless’ (C) capabilities, collectively styled ‘CDC’. The first enhances the basic ROADM with the ability to connect any channel to any mux port, the second enables the sharing of muxes between directions, and the third enables multiples of the same wavelength to be added/ dropped to the same mux. In their most ambitious iterations, ROADMs add ‘Flexible-grid’ (F) to CDC to provide a degree of future-proofing with the ability to dynamically accommodate elevated traffic demands. Not everyone is in the market for the full-blown CDC/F treatment. Requirements vary from operator to operator, and from network to network. Cost may be an issue. As Nagarajan observes, Colorless is cheaper than Colorless combined with Directionless, which in turn is cheaper than CDC. “We really do not see that a ‘one size fits all’ approach is what our customers are asking for,” adds Xenos. NUTS AND BOLTS CHANGING Meantime, the nuts and bolts of ROADM technology is changing. Here Xenos includes an increased adoption of compact modular disaggregated line systems, and the circumstance that software has become as important as
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| ISSUE 25 | Q3 2021
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