Google looks likely to be first to commercial implementation of technology called space-division multiplexing (SDM) for significant bandwidth improvements.

Mitch Wagner, Executive Editor, Light Reading

April 8, 2019

3 Min Read
Google Sets Sail for Bandwidth Breakthrough

Google is on course to deliver a bandwidth breakthrough for its Dunant subsea cable and, in doing so, believes it will be first to implement space-division multiplexing (SDM) technology in a submarine cable network.

The private, 6,400km Dunant cable, connecting the US and France, will transmit at a rate of up to 250 Tbit/s when it goes live in the third quarter of 2020. SDM uses additional fiber pairs -- 12, rather than six or eight in traditional subsea cables -- and power-optimized repeater designs, Google stated in its Google Cloud Blog.

Google is implementing the technology in partnership with subsea cable network builder and technology developer SubCom.

Figure 1: The Dunant cable will run between Virginia and northern Spain. The Dunant cable will run between Virginia and northern Spain.

Dunant's transmission potential of 250 Tbit/s is noteworthy -- Google says that's "enough to transmit the entire digitized Library of Congress three times every second." That compares with 160 Tbit/s for the Marea cable built by Facebook and Microsoft that connects the US (Virginia Beach, Virginia) with Bilbao, Spain.

Traditional subsea cables rely on dedicated lasers for each fiber pair to amplify the optical signal along the length of the cable; SDM allows pump lasers and associated optical components to be shared among multiple fiber pairs.

Even though it'll be more than a year before the network is operational, Google will likely be first to market with an SDM-enabled network, notes Heavy Reading principal analyst and optical technology specialist Sterling Perrin.

Why this matters
SDM has been in the theoretical and academic realms for years; commercial deployment would be a breakthrough, Perrin says. The transition shows the industry is running out of fiber-optic capacity using conventional techniques. "Optical networking is approaching the Shannon Limit, which is forcing companies to seek capacity gains in new areas that will be more economical. SDM is an example of this," Perrin says.

The Shannon Limit is a theoretical maximum information transfer rate for a channel.

"SDM has been a big area of research for many years," Perrin says. "Recent research has focused on subsea networks because the need is greatest, due to the high cost of laying new fibers cross oceans and also limitations to the number of fibers that can be packed into a subsea cable."

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In addition to Google, other web-scale giants such as Facebook and Microsoft have been very active in similar research, and Nokia is "strongly promoting SDM as the inevitable future of optical transmission," Perrin says.

Infrastructure improvements such as those to be deployed on the Dunant cable are required as Internet users demand more bandwidth for video and other cloud applications, and that demand is set to increase further with the advent of 5G, edge computing and the Internet of Things.

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About the Author(s)

Mitch Wagner

Executive Editor, Light Reading

San Diego-based Mitch Wagner is many things. As well as being "our guy" on the West Coast (of the US, not Scotland, or anywhere else with indifferent meteorological conditions), he's a husband (to his wife), dissatisfied Democrat, American (so he could be President some day), nonobservant Jew, and science fiction fan. Not necessarily in that order.

He's also one half of a special duo, along with Minnie, who is the co-habitor of the West Coast Bureau and Light Reading's primary chewer of sticks, though she is not the only one on the team who regularly munches on bark.

Wagner, whose previous positions include Editor-in-Chief at Internet Evolution and Executive Editor at InformationWeek, will be responsible for tracking and reporting on developments in Silicon Valley and other US West Coast hotspots of communications technology innovation.

Beats: Software-defined networking (SDN), network functions virtualization (NFV), IP networking, and colored foods (such as 'green rice').

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