German investigators achieved a transfer rate of 26 Tbits/s over 50 km of single-mode fiber by using a multiplexing technique borrowed from wireless communications.
Conceptual image of OFDM data stream down a single-mode fiber..
Researchers led by Wolfgang Freude, David Hillenkuss and Juerg Leuthold of the Karlsruhe Institute of Technology (Germany) achieved a transfer rate of 26 Tbits/s over 50 km of single-mode fiber by using a multiplexing technique borrowed from wireless communications (Nature Photon. 5, 364).
In the technique, known as orthogonal frequency-division multiplexing, or OFDM, the data sidebands overlap each other, according to Freude. Single-bandpass filters cannot decode these mixed streams, but optical Fourier transform processing can.
One way of sending hundreds of data streams down a fiber would require hundreds of separate lasers, which would draw several kilowatts of electrical power and several more kilowatts just for cooling. One recent data-transfer “hero experiment” used 370 lasers, but Freude said that type of transmission is hardly affordable for practical use, especially as global telecommunications providers become more concerned about their energy consumption.
Instead, the European researchers used the beam from a single mode-locked laser to generate a 320-line frequency comb, then processed the separated frequencies into OFDM subchannels. At the other end, a fast Fourier transform setup separated the signals. Freude estimated that the experiment consumed less than half a kilowatt.
The team performed the experiment at 10.1 Tbits/s before tweaking the frequency comb and other components for the 26-Tbits/s run. Several of the Karlsruhe researchers published the theoretical background for their experiments in Optics Express last year.
Although the researchers aimed their work primarily at the long-haul communications regime, Freude said the technique could be reimagined for rack-to-rack or even chip-to-chip data transfer. A potential next step would be to integrate an optical fast Fourier transform processor onto a silicon-photonics chip that could be mass-produced. Of course, the research group will also try to increase the number of data subchannels that can travel down a fiber. “Spectral space is a very precious resource,” Freude said.
Patricia Daukantas is a freelance science writers who specialize in optics and photonics.