Facebook and Nokia have found a way to push a lot more data through a submarine cable across the Atlantic, which could help the social network keep up with the growth of video and virtual reality.

On a 5,500-kilometer (3,400-mile) cable between Ireland and New York, the companies tested a new technique developed at Nokia Bell Labs for increasing the efficiency of fiber-optic cables. They say it comes close to the absolute limit for sending bits over a fiber.

Facebook CEO Mark Zuckerberg has said VR is the future of social media. If it is, then the networks that link consumers and data centers will have more data than ever to carry. Higher resolution video also is increasing the burden on networks. For example, Netflix recommends subscribers have at least a 5Mbps broadband connection to stream HD video and 25Mbps for Ultra HD (4K) streams.

The good thing about fiber-optic networks is that new equipment on each end of a link can boost its capacity far beyond what was available when the cable was laid. Nokia recently tested new technology on a pair of fibers Facebook uses on the AEConnect cable across the Atlantic. It increased the capacity of that fiber pair by about 2.5 times.

Facebook's fibers can carry about 13Tbps (bits per second) now. With the experimental technology they recently tested, the fibers could carry 32Tbps, said Kyle Hollasch, Nokia's director of marketing for optical networking. The companies say this is a record.

The new technique, called PCS (probabilistic constellation shaping), gives the network more flexibility to get the most performance out of a particular fiber.

"Every fiber in the ground, everywhere in the world, is different," he said. Its ability to carry data depends on how long it is, the characteristics of the glass it's made of, and other factors.

To send data over that fiber most efficiently, the network needs different settings, like gears, to adjust for those differences. Current equipment has just a few of these "gears" at most. PCS changes that equation because it's like a continuously variable transmission, so it can adjust the network precisely to best use any fiber, Hollasch said.

PCS should be available for installation in fiber networks in three years, according to Nokia. But the company is already making its equipment more efficient, with commercially available gear today that could increase the current connection by about one-third to 17Tbps.

For Facebook, which has invested in several submarine cables and bought fibers on others, higher efficiency is just good business.

"Facebook pays the same for this cable regardless of how much data they put on it. So they might as well put as much as they can," Hollasch said.