Science in Mind

Developing new technology to alleviate the coming bandwidth bottleneck

Fiber cables run along the yellow cable trays near the ceiling at one of Google’s data centers in Council Bluffs, Iowa.
Fiber cables run along the yellow cable trays near the ceiling at one of Google’s data centers in Council Bluffs, Iowa. Credit: AP Photo/Google, Connie Zhou

It’s only a matter of time before the data pipes that connect us to our social networks, work e-mail, and the Internet's vast repository of useful and useless information fill up. It could be five years, it could be 15, but our boundless appetite for bandwidth-consuming apps, streaming video, and other data will soon clog up current fiber optic cables.

Since the 1990s, scientists have been trying to develop ways to increase capacity. Since data is encoded in pulses of light that travel through fiber optic cables, the first obvious approach was to use different kinds of light. For years, scientists have used different colors of light to transmit information, essentially creating new channels by using different colors. But as they have crammed more and more colors of light into fiber optic cables, they’ve found they are rubbing up against a physical threshold—either running out of colors or foiled by the way that different streams of light interact with each other, providing a scrambled output at the end.

“The road map, when we look at all the demand for bandwidth, essentially says at some point we have to get to 1 million terabits per second—in the next 10 to 20 years,” said Siddharth Ramachandran, an engineering professor at Boston University.

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As they had found themselves running out of new colors of light, many scientists had turned to computational methods that Ramachandran calls “math games.” Essentially, they have been searching for mathematical methods that would enable them to take the jumbled signal that comes out at the end of a fiber optic cable and comb that apart to figure out what the original messages were. Ramachandran, in collaboration with a Danish fiber optic company called OFS-Fitel, took an alternate approach, working to build a whole new type of fiber that could carry light in separate modes, each of which would travel a separate path that would mean they could not get jumbled up.

In a study published in the journal Science on Thursday, the scientists demonstrated that they could create four channels carrying separate modes of light in a specially-designed fiber. They showed that at least two of those channels could carry 10 colors of light, creating data transmission rates of 1.6 terabits per second.

In each channel, the light travels in a distinctive corkscrew pattern, rotating around a center like a donut as it travels through the cable. The researchers showed in a stretch of cable that was about two-thirds of a mile long that they could transmit large amounts of data, without channels getting crossed. The study is an early proof of concept, but Ramachandran eventually hopes to create more channels and to show that it’s possible to route more colors of light into each one. He said it is also crucial to test whether the same principle will work over much longer lengths of cable, since many cables extend for hundreds of miles, not just one.

The research was supported by the Defense Advanced Research Projects Agency, with the hope that higher-capacity fiber optic cables would allow new forms of more secure cryptography. But Ramachandran thinks the technology might, if scaled up, be capable of addressing the looming bandwidth bottleneck facing the telecommunications industry and newer companies, such as Facebook and Google.