Summer 2021 - Optical Connections Magazine



It’s difficult to overstate the criticality of subsea optical systems to the functioning of the planet’s global telecommunications ecosystem, writes John Williamson. One estimate by Pioneer Consulting is that submarine cable fibre systems support 99% of international telecommunications traffic. Market research and consultancy TeleGeography calculates in early 2021 there were approximately 426 submarine cables in service around the world, extending over 1.3 million km. Subsea communications is also a giant business in and of itself. According to a report available from research publishing house StrategyR, the 2020 global market for submarine optical fibre systems was valued at US$14.1 billion, and this could reach US$32.7 billion by 2027.

N otwithstanding the scale of present activity, there’s intense and intensifying pressure to greatly expand the operations and performance windows of subsea optical systems, both by upgrading extant cables and planning and installing new, better-efficient plant. Several factors are at work.

managing director for Western Europe and Middle East at Ciena, also lists PCS, along with soft-decision Forward Error Correction (FEC), nonlinear mitigation techniques, selectable baud, and machine learning–based link monitor metrics that are accessible via open APIs, as some of the technologies that allow operators to massively increase the total information- carrying capacity of existing (and new) submarine cable networks. At the same time, she observes, with some of these technologies, costs are reduced by requiring fewer modems. Meantime, according to Luca Luchesini, Nokia senior director, subsea business development, there’s advances in component technology. He describes the continuous improvement of optical hardware via more sophisticated DSPs and integrated silicon photonics that have almost reached Shannon limit capabilities, and says that most vendors are moving to 7nm technology from previous 16nm and 28nm chipsets. “We can say that these systems allowed on average an additional 10 to 20% gain in terms of overall performance, that is, capacity for the same reach or reach for the same capacity.” He adds that there’s a race on to reach 5nm solutions but that gains here may be not so much in total capacity made available, but in performance and operability such as

practical way of increasing the capacity of an existing cable system is to deploy new terminal equipment - the Submarine Line Terminal Equipment (SLTE) that handles optical-to-electrical-to-optical conversion - at each end. And here, explains Bertrand Clesca, director of client solutions at Pioneer Consulting, coherent transmission has come to the fore. “Developed by Nortel about 12 years ago, optical coherent technology has offered a ten-fold increase in the capacity per fibre pair in the last decade,” he reports. Second generation coherent systems are further expanding subsea fibre capabilities. “We have a whole presentation on the toolkit of features that a modern transponder can use to maximise either the fibre capacity or the wavelength data rate,” states Bennett. “But two of the biggest contributors are Nyquist subcarriers and Probabilistic Constellation Shaping (PCS).” Olivier Courtois, director, submarine product management, strategy and marketing, Alcatel Submarine Networks, reflects that all major vendors have today some kind of PCS-based solution in their catalogues, and PCS has been adopted in virtually all new cable deployments and upgrades over the last couple of years. “Classic modulation schemes like, for example, BPSK/QPSK are by now confined to legacy systems.”

A major one, says Geoff Bennett, Infinera’s director of solutions &

technology, is the circumstance that hyperscale Internet Content Providers (ICPs) are continuing to massively grow their share of international capacity. This is at a time when conventional Communication Service Providers (CSPs) are also exhibiting healthy subsea growth. In addition, he cites the major trend towards direct routes, and instances Ellalink linking Portugal and Brazil, with onward connections at both ends to Spain and the rest of Latin America. “Previously traffic would follow twice the distance – Europe to USA to Brazil,” he observes. “EllaLink’s route will halve the latency for applications like financial trading and gaming.


Since it’s not realistic or economically viable to recover and replace wet plant, the

Virginie Hollebecque, vice president and


| ISSUE 24 | Q2 2021

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