May 23, 2011

Researchers Set New Data Speed Record With Laser

Researchers report in Nature Photonics that they have set a new record of 26 terabits of data per second for the rate of data transfer using a single laser.

The entire Library of Congress collections could be sent down an optical fiber in just 10 seconds at this new record rate.

The researchers used a "fast Fourier transform" to unpick over 300 separate colors of light in a laser beam, each encoded with its own string of information.

"With 26 terabits per second, you can simultaneously transmit up to 400 million telephone calls per second," said Professor Juerg Leuthold of the Karlsruhe Institute of Technology (KIT) in a statement to the AFP news agency.

The earliest fiber optic technologies encoded a string of data known as "wiggles" within a single color of light sent down a fiber.  The newer approaches have used a number of tricks to increase data rates.

One of the newer techniques is known as "orthogonal frequency division multiplexing," which uses a number of lasers to encode different strings of data on different colors of light, all sent through the fiber together.

Another set of laser oscillators can be used to pick up these light signals at the receiving end, which reverses the process.

Wolfgang Freude, a co-author of the study, said the total data rate possible using such schemes is limited only by the number of lasers available.

"Already a 100 terabits per second experiment has been demonstrated," Freude told BBC News.

"The problem was they didn't have just one laser, they had something like 370 lasers, which is an incredibly expensive thing. If you can imagine 370 lasers, they fill racks and consume several kilowatts of power."

The researchers have worked out how to create comparable data rates using just one laser with exceedingly short pulses.

There are a number of discrete colors of light in these pulses known as a "frequency comb."

These pulses are sent into an optical fiber, the different colors can add or subtract, mixing together and creating about 325 different colors in total, each of which can be encoded with its own data stream.

Professor Freude and his collaborators first demonstrated how to use a smaller number of these colors last year to transmit over 10 terabits per second.

The team sent their signals down 31 miles of optical fiber and then implemented fast Fourier transform to unpick the data streams.

The Fourier transform is a well-known mathematical trick that can extract the different colors from an input beam, based solely on the times that the different parts of the beam arrive.

The team does this optically by splitting the incoming beam into different paths that arrive at different times.

This enabled the researchers to string together all the data in the different colors into the simpler problem of organizing data that essentially arrive at different times.

Freude said the current design outperforms earlier approaches by moving all the time delays further apart.  He said this technology could be integrated into a silicon chip, making it a better candidate for scaling up to commercial use.

"Think of all the tremendous progress in silicon photonics," he said. "Nobody could have imagined 10 years ago that nowadays it would be so common to integrate relatively complicated optical circuits on to a silicon chip."


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