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Look out, Google Fiber - scientists build 400G connection


A research team led by Bell Labs' Xiang Liu has published an article in Nature Photonics describing a way to send and receive information at 400Gbps across 12,800km of optical fiber - an enormous potential gain of both speed and effective distance compared to current technology.


The idea was likened, by the BBC, to the wave-canceling technology used in headphones that block outside noise: Ambient soundwaves are detected by the headphones, which then play back an inverse waveform to cancel them out.

However, Liu tells Network World that the fiber-optic technique his team used is – at least in principle – actually simpler than noise-canceling headphones.

"In noise-cancelling headphones, one needs to detect the noise and then remove it from the signal, while in the twin-wave case, we do not need to detect the nonlinear ‘noise' at all (as it is signal-dependent and hard to detect), but instead rely on physics itself to do the cancellation for us," he says.

The researchers used two streams of light instead of the usual one – when both signals are combined at the endpoint of a transmission, any "noise" created by interference within the optical fiber itself can be identified and canceled out, dramatically reducing signal loss and improving efficiency.

This works, according to the article, because these twin signals create distortions that are "essentially anti-correlated," meaning that, when combined, they should nullify each other.

"The idea came up during our study on the benefit of coherent superposition for improving the fiber transmission performance of an optical signal," says Liu, "particularly when the time-reversal picture of phase conjugation went into my mind: why don't we superimpose two phase-conjugated (twin) waves to see if their nonlinear distortions cancel each other automatically by nature? And it worked, especially when a symmetry condition is satisfied. The rest is now known."

Citing colleagues Peter Winzer and Andrew Chraplyvy, Liu said technology that takes advantage of this technique could become available within as little as three years' time.

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