In an amazing feat of electrical engineering, scientists have managed to set a new landmark in optical communications by transmitting data at the remarkable speed of 26 terabits per second, or about 700 DVDs downloaded in an instant, all using a single transmitting laser.

uses very brief but broad-spectrum laser pulses to send data. Wavelength division multiplexing [WDM, center] packs in bits by using several frequencies of light at once. Orthogonal frequency division multiplexing [OFDM, right] y. does the same, but uses overlapping frequencies to make better use of the available spectrum. (c) Nature Photonics.”] Time division multiplexing [TDM, left] uses very brief but broad-spectrum laser pulses to send data.  Wavelength division multiplexing [WDM, center] packs in bits by using several frequencies of light at once. Orthognonal frequency division multiplexing [OFDM, right] does the same, but uses overlapping frequencies to make better use of the available spectrum. (c) Nature Photonics. The research was lead by scientists from the Karlsruhe Institute of Technology, in Germany, who published the research paper in Nature Photonics.

 

 

For the device, German scientists worked upon an existing and fairly common technique used in wireless communications called orthogonal frequency-division multiplexing. The technique starts by encoding data onto carrier waves whose frequencies overlap quite a bit, then combining those waves to create a new waveform. “Now, instead of having four transmitters, you have one transmitter,” Juerg Leuthold, a professor at Karlsruhe Institute of Technology, explains. What makes the OFDM transmission technique so popular, mostly, is that it uses a much broader data transmission spectrum, meaning it have a much better efficiency when real data transmission speeds are concerned. The adding and extracting of the waves is done through a mathematical process called the Fast Fourier Transform (FFT) and its inverse.

“This is so awfully fast that there is no electronic receiver that could detect it,” Leuthold said, explaining a major problem the team had to overcome. The issue was solved by the German scientists who used optical FFT device instead of an electronic one.

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While the transfer speed achieved is indeed remarkable, other much larger transmission speeds have achieved albeit with multiple lasers. NEC Laboratories, of Princeton, N.J., for instance, presented a paper at the annual Optical Fiber Communication Conference in March showing a rate of 101.7 terabits per second, also using OFDM, but with 370 lasers, each transmitting at 294 gigabits per second.

One of the NEC researchers, Tim Wong, has learned about Leuthold’s work and believes it is very well done and quite significant, however, he states that the multiple laser arrangement from NEC has a better spectral efficiency, meaning a much bigger useful bits capacity.

NEC researchers performed a trial with telecom carrier Verizon last year in which they were able to reach rates of 1 Tb/s over 3560 km of fiber. The Karlsruhe researchers have so far only managed to test the single laser across 50 km of fiber, but Leuthold hopes he’ll be able to test it across a much broader distance in the future.

Much of today’s equipment works at 10 or 40 Gb/s, and analysts believe that by the middle of the decade we’ll be well into the terabit Ethernet.

via IEEE Spectrum

 

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