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Bench Talk for Design Engineers

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Bench Talk for Design Engineers | The Official Blog of Mouser Electronics

Submarine Cables: Long-Distance Pathway for Internet Data Traci Browne

Next year, Google will commission three new submarine communications cables: Curie (named after physicist Marie Curie), connecting Chile to Los Angeles; Havfrue, connecting the U.S. to Denmark and Ireland; and the Hong Kong-Guam Cable system (HK-G), which will create paths to Australia. Of these three, Curie represents Google’s most significant investment.

Traditionally, tech companies have leased or purchased fiber-optic pairs in cables owned and installed by telecom companies, or they invested through a consortium of tech and telecom organizations. Back in 2008, when Google announced its first involvement in a cable consortium, Francois Sterin, Manager, Network Acquisitions posted on Google’s website, “If you're wondering whether we're going into the undersea cable business, the answer is no.”

What a difference a decade makes, Mr. Sterin. The Curie cable makes Google the first non-telecom company to build a private intercontinental cable.

Submarine Cable Then vs. Now

The first submarine cables were installed in the 1850s for the transmission of telegraph communications. In the ensuing 150 plus years, one could argue that while there have been tremendous technological leaps in submarine cables, the construction and installation of the cable has not fundamentally changed at all.

Early undersea cables were made by wrapping a core of copper wire with gutta-percha, a natural polymer similar to rubber. That layer was coated in India rubber and then the entire thing was wrapped in cable iron for protection.

Today, fiber optics have replaced the copper wiring, and plastic tubing, rather than gutta-percha, is used to protect the core. Steel wires are wrapped around the plastic, and then a copper tube is placed over that. Next, another plastic tube is placed around the copper to provide insulation. In very deep water that’s all you need. However, when you get closer to shore and have fishing boats to contend with, the cable gets additional layers of galvanized steel, a coating of nylon thread covers that layer, and then the whole package is coated in tar (Figure 1).

Figure 1: Today, fiber optics have replaced the copper wiring, and plastic tubing, rather than gutta-percha, is used to protect the core.

The cable is then hand spun onto giant spools loaded onto a cableship, and from there, it’s slowly dropped onto the sea floor. Today’s superior boats and accurate maps of the sea floor make this an easier task than it was with steamships in the 1800s. Once the cable is laid and hooked up to the terminal landing stations on shore, data can flow from continent to continent.

How fast does the data flow? The Marea cable, owned by Microsoft, Facebook, and Telxius, can achieve speeds up to 160Tbps—the equivalent of about 71 million people streaming HD cat videos at the same time. Who knows what speed Google is hoping to achieve with the Curie cable? They are keeping it a secret for now.

Control Over Technology

Tech companies look into building their own cables for control and flexibility. In Google’s case, because they have no partners to contend with, they will have complete control over the cable’s design and construction process, technical specifications, deployment, and routing decisions. While Google may be confident in developing the technology that goes inside the cable, the actual manufacturing of the cable will be in the hands of experts. These experts know how to manufacture cable for deep water versus shallow water and a smooth ocean bottom versus a mountainous one, and how to send light signals across great lengths.

Sending a light signal across short distances, such as the English Channel, is made easy using amplifiers at either end. Getting a signal from Los Angeles to Spain, or any range over about 240km, requires a boost in the form of a repeater placed every 80km or so, which regenerates the light wave across the ocean. This is where the copper layer of the cable comes into play, as the repeaters require a power source to operate. Power feed equipment is installed at each end of the cable and injects anywhere from 3,000 to 10,000 volts of power to the repeaters. As long as nothing interferes, you can sit in your office in New York and Skype your co-worker located in London.

Maintenance and Repair

Unfortunately, interference with the cables does happen from time to time. Despite what you may have read (or have seen in Jaws II), the industry reports that sharks have never actually caused serious damage to undersea cables, though they have given them a nip or two. Fishing boats or boats dragging anchors are to blame for two-thirds of the approximately 100 instances of cable damage per year. Other culprits include environmental factors like earthquakes or abrasion, which typically occur in mountainous areas of the seabed, or component failure, which is infrequent. 

Whatever the cause, technicians on land pinpoint the location of the damage and deploy a cableship to fix it. Cableships are stationed around the globe and are ready to go at a moment’s notice. Once they arrive at the site of the damage, a cutting grapnel is dragged across the seabed, where it catches the cable, lifts it, and cuts it. The ends of the cable are then brought aboard the cableship for repair and testing, then spliced back together and dropped back onto the seafloor. The entire repair operation (grossly simplified here) can take days to complete. The Internet user is none the wiser, of course, because traffic can be routed instantly from the broken cable to a working one.

It will be interesting to see what Google creates with the Curie cable. Will they exceed the speeds of the Microsoft et al. Marea cable, or do something completely revolutionary? Whatever they come up with, you can be fairly certain it will be covered in tar and dropped off the back of a ship.

Sidebar: An Ecological Twist

If you happen to be a design engineer with a passion for saving the world, there is a place in undersea fiber optics for you. An international Joint Task Force (JTF) of three United Nations agencies—the International Telecommunication Union, the World Meteorological Organization, and the Intergovernmental Oceanographic Commission of UNESCO—hopes to put the millions of miles of cable to additional use. The JTF’s objective is to use existing cables and new installations as a platform for collecting environmental data.

The JTF is developing a strategy to equip submarine repeaters with sensors for ocean and climate monitoring and disaster risk reduction (tsunami early warning systems). Another option they are considering is the renovation and relocation of out-of-service cables, which are commonly referred to as “dark fiber” infrastructure.


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