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Twisted light transmits more data

Spiral beams allow multiple information streams in one cable

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A new fiber-optic cable that seamlessly shuttles multiple beams of light simultaneously could drastically speed data transfer over the Internet.

“It’s like having more fibers without actually laying more fibers,” says Andrew Weiner, a physicist at Purdue University in West Lafayette, Indiana.

Telecommunications companies use light to encode and send data through fiber-optic cables. Over the last few decades, scientists have increased bandwidth by enabling a single beam to carry more information, but their progress soon will be outpaced by the vast amounts of data people exchange. Laying more fibers would be expensive. “We’ve gotten to the point where the [telecom] community has been asking what else we can do,” says Siddharth Ramachandran, a physicist at Boston University.

The solution he and his team came up with was to dispatch multiple beams of light through a single fiber. The idea goes back nearly four decades, but it’s not an easy thing to do because traditional fibers allow light beams moving in parallel to interfere with each other, jumbling the 1s and 0s encoded in each beam.

Recently, scientists have tried imparting twists into some of the beams so that they spiral along the fiber while others travel in a straight line, but that hasn’t worked either. Resigned to this light mixing, some researchers have created complex algorithms that decipher the amalgamated beams at the end of the cable, but the algorithms are slow and not 100 percent effective.

In the June 28 Science, Ramachandran and his team report building a 1.1-kilometer-long fiber that, for the first time, allows multiple beams to reach their destination intact. Their silica fiber is doped in places with other materials, which cause the beams to move at slightly different speeds and prevent them from mixing with each other.

Using an instrument called a spatial light modulator to twist the beams, the researchers sent as many as four concurrent beams, transmitting data at speeds up to 1.6 trillion bits per second, through their custom fiber. They hope to squeeze more data into each of those beams using methods already exploited by the telecom industry. Ramachandran notes that the team manufactured its fiber at a commercial facility using standard methods, so if it were mass produced, the fiber should not cost much more than those now in use.

Ramachandran says he is unsure whether the new fiber will work for communicating data over long distances, but hopes that it will improve transmission in dense metropolitan areas. It could also help in vast data server farms, where thousands of computers that store data for companies like Google and Facebook require tight, fast networks to exchange information.

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