Study: Light Beam "Twins" Hold Key to Better Signals
May 27, 2013 10:12 PM
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By mirroring beam in line, noise is cancelled
It is an elegant and simple solution, but one that is relatively new to the world of fiber optic signaling -- beam mirroring. The approach, already frequently used in the noise-cancelling headphones, is being touted as a promising new route to improving fiber optic routing in a new study by researchers at telecommunications company Alcatel-Lucent SA's (
) Bell Labs unit.
The idea involves making "twins" -- dual beams of light in a fiber that mirror each other. Each peak in one beam is a trough in its twin. Together they bounce along the line, much as a single beam would.
One major limiting factor in fiber optics is noise. In order to send signals farther, beams are transmitted at higher power. But the higher the power, the more beams tend to interact with the material in the fiber's walls, adding noise. Beams have a limiting maximum distance they can travel and maintain fidelity -- after that they need to be received and rerouted, hopping along the next link.
By adopting the "twin" approach, light can travel four times farther that a single beam could. In their study, the Bell Labs stream piped data at 400 Gigabits per second (Gbps) -- four times faster than the best commercially available speeds, down 12,800 kilometers (7953 miles) of fiber. That's a longer line than the longest
While note the first study to suggest the phase conjugate approach, Bell Labs claims its work offers the most straightforward implementation and is proven to travel farther without rerouting. That means
the need to reroute or boost signals
during long transoceanic links may no longer be needed.
[Image Source: Guardian UK]
Lead author Xiang Liu of Bell Laboratories in New Jersey
in an interview with
Sometimes you may send data from London to New York, sometimes you may send it from London to Paris. The links are changing and you cannot keep sending people to the middle of the link.
At the receiver, if you superimpose the two waves, then all the distortions will magically cancel each other out, so you obtain the original signal back. This concept, looking back, is quite easy to understand, but surprisingly, nobody did this before.
Nowadays everybody is consuming more and more bandwidth - demanding more and more communication. We need to solve some of the fundamental problems to sustain the capacity growth.
The approach may allow
faster data transfer speeds
too. As it reduces signal noise, it allows for less repetition of information in a given beam.
The study on the work
in the prestigious peer-reviewed journal
Alcatel-Lucent in currently
in the midst of constructing
a 100 Gbps undersea fiber link between Malaysia, India, and the Middle East.
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RE: 2 separate frequencies?
5/28/2013 5:43:06 AM
Integr8d's gave a nice written description, but sometimes a picture is worth a thousand words. Apple has a very nice description with pictures of how it works.
XLR cables and balanced phono cables use this trick, but its primary use is in UTP - unshielded twisted pair. Pretty much every phone and ethernet cable you've ever run across uses this trick to reject noise. That's the reason they're twisted - to ensure the pair of wires stay right next to each other no matter how you coil the cable, so they pick up the exact same noise.
Audio cables are usually shielded, but this trick works so well that if you're careful to match up the right signal pairs, you can solder an XLR cable to UTP cable (which is not shielded) and it'll work just fine. I've run balanced audio through >100 feet of cat5 network cable with no audible degradation. I've heard of people doing it to 500 feet without problems. The vast majority of the noise rejection is from the balanced signals, not the shielding.
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