The noise in fiber could be used to increase data capacity

One normally wants to get rid of noise in data links, but scientists at ETH Zurich say you can harness it to increase the capacity of fiber-optic cables.

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Increasing the capacity of fiber-optic cables might one day be possible through the exploitation of a part of the signal commonly thought of as substandard. That imperfect element in a carrier, called “noise” is usually something one tries to avoid—it can muddy the accurate reading of the data.

However, scientists now suggest that one could, in fact, embrace the rubbishy, and thus far unusable, part of the signal to hold data and allow it to be decoded. The ordinarily data-obscuring hubbub could potentially be harnessed and used to increase data capacity in light waves.

“Information is encoded in the correlated noise between spatially separated light waves,” writes Oliver Morsch in an article on the website of ETH Zurich, a technical and scientific university. “The new coding technology, developed by ETH researchers, makes it possible to make better use of the transmission capacity of optical fibers.”

Noise occurs when signals are sent. It’s a kind of unwanted fluctuation adjacent to the signal. It’s not actually part of the signal, but it’s present in varying degrees nonetheless. In this case, the developers argue that noise should be capitalized on and considered just another multiplex. Multiplexing is where more signals are cleverly sent than the number of transmission channels available. In other words, they say one should look at noise simply as a channel—just like frequencies in a radio broadcast. All you have to do, then, is figure out how to encode and decode data in that noise. The key to it is figuring interference.

Shawn Divitt, an American Ph.D. student, came up with the school’s direction in the work. He used a traditional double-split experiment concept. That’s where splitting waves creates phase shifts, revealing an interference pattern (Wikipdia). Divitt experimented with identifying the extent that predictions can be made about those phase shifts, based on the correlations between the light waves in the two splits.

“Correlations indicate how well one can predict, for instance, the oscillatory phase of one light wave if one knows the phase of the other wave,” Morsch writes. “Even if both phases are ‘noisy,’ meaning their values fluctuate, they can still do so in a more or less synchronized fashion.”

The academics exploited the fact that strong correlations create visibly apparent interference and that weak ones cause the patterns to wash out. “The idea was to generalize that principle and to use it to encode information,” Divitt says in the ETH Zurich article.

Security and cost benefits

Interestingly, security ended up being a bi-product. The researchers explain that not only do they potentially increase the capacity of fiber through the use of the noise channels building on the data-encoded interference patterns, but that intrusions, where if someone tried to record the interference pattern, would be highly obvious. The subterfuge would obviously grab too much diverted optical power attempting it, and the hacker would be fingered.

Cost is also an advantage, they say. The channel doesn’t actually require extra resources, like light, to be produced, unlike a traditional capacity-increasing methods. “Their method does not require coherent laser light. It should be cheaper than conventional technologies,” Morsch says.

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