Map: The world's new ocean-spanning fibre-optic cables

As bandwidth demands increase, more fibre-optic cables are crossing the sea. Here's where they're being built.

A millisecond isn’t a long time, but for day traders working the stock market, it can be a $100,000 difference. For large institutional traders, transactions a few milliseconds faster can mean millions of extra dollars in profit each year. Fibre-optic cables carry more data, faster and with less interference than satellites. As the world’s bandwidth demands continue to grow, billions are spent to put more cable in the water. From a $300-million cable sprouting from Canada’s east coast, to a $700-million link between Europe and Africa, here’s a look at the growth of the world’s submarine information superhighway.




Laying a cable often begins with a survey of the ocean floor. This maps out a path that will minimize environmental impact, avoid areas prone to earthquakes or volcanic activity and navigate oceanic mountain ranges and deep-sea trenches. To avoid the nearly 10-kilometre-deep Marianas Trench, for instance, oceanographers found a natural bridge for the cable six kilometres down.


The fiber-optic cable is made in a factory near the water. The finished product—which looks like a long, thick garden hose— is then fed right onto a specially designed ship where workers begin to wind it into massive coils in the hull. These spools can be seven metres deep and 19 metres in diameter. It can take the crew weeks to coil the cable for the voyage.


Once the boat is ready to depart, the cable is fed from inside the hull through a gap in the floor onto the ship’s back deck. Large steel support beams feed the cables up over the stern of the boat, where it slips into the water at a rate of one kilometre an hour. At that speed, it can take seven months to complete a transatlantic journey.


Over such large distances, the signal travelling through the cable is weakened. Large metal cylinders called repeaters are added to amplify the signal using lasers. Repeaters are loaded onboard at the start of the voyage, and the crew adds one to the cable approximately every 50 to 100 kilometres.


Sometimes the cable is left to sink to the ocean floor and rest on the sandy bottom, but for the best protection from ship anchors, fishing nets and shark attacks, a sea plow or remotely operated vehicle may be used to bury cable between 1.5 and 3 metres below the bottom. These assisting devices launch from the back of the ship and will follow behind the boat digging a trench and feeding the cable into the seabed.


Cables often get damaged, and transmission traffic must temporarily be rerouted. A ship will send down a device called a “grapnel,” essentially a big hook, to catch and cut the damaged cable. Another hook on a chain drags the ends up to the ship deck one at a time and splices new cable in the middle. This adds length, and the excess cable forms a “U” shape on the ocean floor. If the cable is close to the surface, a small submersible may be sent down instead of the grappling hooks.

Illustrations by Remie Geoffroi