Scientists find a way to greatly improve the performance of fiber optic cables
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February 5, 2015
Scientists at the University College in London say they have found a method to dramatically
increase the distance that data can be sent intact over ordinary fiber optic cables by partially
working around the so-called 'Kerr Effect'.
To be sure, a phenomenon discovered by Scottish physicist John Kerr in 1875 limits the distance coherent data
Back then, the effect that Kerr noticed was that the refractive index of materials changes in
direct response to an electric field, which distorts the transmitted information, and places a cap on
how far data can travel along a glass fiber without the use of several repeater stations.
Those repeater stations are a major inconvenience and points of failure when you're laying undersea
data cables. And add to that the extra cost of the repeaters and you have some major reasons to try and find a better
way of doing things.
By using a new type of receiver and refined signal-processing algorithms, the team claims
they can sustain vastly better performance along unmodified cables.
This simply means that communications around the internet can be vastly improved, in theory, without
having to lay down super-expensive new undersea cables which connect networks across the globe.
Instead, the end points can be upgraded to greatly reduce errors and improve signal quality, possibly
allowing the reliable transfer of more information per second around the web.
Future cables can be even longer than today's without having to install lots of annoying repeaters.
"By eliminating the interactions between the optical channels, we are able to double the distance
signals can be transmitted error-free, from 3190 km to 5890 km, which is the largest increase ever reported
for this system architecture," said Dr Robert Maher, from UCL's electronic and electrical engineering department.
"The real challenge is to devise a technique to simultaneously capture a group of optical channels,
known as a super-channel, with a single fiber-optic receiver. This allows us to undo the distortion by sending
the data channels back on a virtual digital journey at the same time," he added.
For example, that 5890 km distance (3659 miles) is enough to stretch from London, England, to New York City without a
The university research, to be published in the journal Scientific Reports, used a "DP-16QAM super-channel,
consisting of seven spectrally shaped 10 GBd sub-carriers spaced at the Nyquist frequency" within a single cable.
To be sure, a so-called 'super-receiver' allowed the scientists to pick up the signal clearly over
the great distances shown above. The team used 81.8 km of Corning SMF-28H ultra low-loss fiber optic cable to test
their overall design.
Source: University College in London.
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