Drastically Improving Submarine Cable Capacity Using Space-Division Multiplexing

A field trial improves transmission capacity by nearly 40 percent by introducing additional fiber pairs.

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The Optical Fiber Communication Conference and Exhibition (OFC)

Mar 03, 2022, 10:00 ET

WASHINGTON, March 3, 2022 /PRNewswire/ -- As our world becomes increasingly connected, communication infrastructure must scale to meet the growing demand. Critical parts of that infrastructure are submarine cables connecting networks between continents.

These submarine cables operate in an environment where space is a luxury. One of the biggest challenges in designing next-generation submarine cables is how to increase data capacity without increasing the cable's size. Even a simple change, like adding more fiber pairs, comes with additional power requirements that complicate the design.

Schematic of the Dunant cable, showing its route across the Atlantic Ocean as well as its internal structure.
Image Credit: Varughese et al. — Schematic of the Dunant cable, showing its route across the Atlantic Ocean as well as its internal structure. Image Credit: Varughese et al.

Pierre Mertz and Siddharth Varughese are part of a team behind a submarine cable field trial that succeeded in transmitting data at a record 307.2 terabits per second without any required size increase. They will present their results next week at the Optical Fiber Communication Conference and Exhibition (OFC), San Diego, California.

The team achieved this record on the transatlantic cable Dunant and employed a nascent technology called space-division multiplexing (SDM). With SDM technology, each fiber pair operates at a lower optical power and signal-to-noise ratio.

"At first thought, it would seem counterintuitive to reduce the optical power as this would reduce the capacity of the individual optical fiber," said Varughese. "However, reducing the power on individual fiber allows one to introduce additional fiber in the submarine cable, which can thereby increase the total capacity of the cable."

The researchers compared the Dunant cable to a previous cable, Marea, that they worked on in the past. Marea has eight fiber pairs, which support 27.8 Tbps each. Dunant, in contrast, has 12 fiber pairs that can support 25.6 Tbps each. Each fiber pair in Dunant is less efficient than the fiber pairs in Marea, but the cable, as a whole, supports nearly 40 percent more capacity.

"Through our field trial, we demonstrated how the simplest SDM cable consisting of 12 fiber pairs can improve capacities by as much as 38%," continued Varughese. "SDM cables are the way forward if we are to meet the exponentially scaling global data rate requirements."

Implementing SDM architecture in Dunant was no easy feat due to the lower signal-to-noise ratio involved. The researchers paid close attention to their modulation formats, operating baud rates, and digital signal processing algorithms to make the most of their limited optical power.

The result is a successful proof of concept for SDM technology. The Dunant cable achieved a capacity of over 300 Tbps, which approaches or exceeds the limits of traditional cables. The team expects future SDM cables should have an even greater capacity and hopes their demonstration will provide a motivation to build these future cables.

"We believe our field trial experimentally answered the first question everyone had about SDM cables: how much more capacity we can obtain from an SDM cable when compared to a traditional cable," said Varughese. "We hope that these results will encourage submarine cable vendors as well as internet service providers and internet content providers to continue to investigate SDM cables and deploy more of such cables in the future."

About OFC

The 2022 Optical Fiber Communication Conference and Exhibition (OFC) is the premier conference and exhibition for optical communications and networking professionals. For more than 45 years, OFC has drawn attendees from all corners of the globe to meet and greet, teach and learn, make connections and move business forward.

OFC includes dynamic business programming, an exhibition of global companies and high impact peer-reviewed research that, combined, showcase the trends that are shaping the entire optical networking and communications industry. OFC is co-sponsored by the IEEE Communications Society (IEEE/ComSoc) and the IEEE Photonics Society and co-sponsored and managed by Optica. OFC in 2022 will be presented in a hybrid format with in-person and virtual components and will take place 06-10 March 2022 at the San Diego Convention Center in San Diego, California, USA. Follow Twitter @OFCConference, learn more at OFC Community LinkedIn, and watch highlights on OFC YouTube.

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