Fibre optics rev up

Optics develop to send 400Gbits per second down an optical fibre 12800km long and could reduce the price and increase the reliability.
30 May 2013


A fibre-optic cable


Whether you know it or not you are probably using fibre optics every day...

They are the very  thin glass fibres which carry most of the information around the internet and telephone systems.

The information travels in the form of incredibly short pulses of infrared laser light, this is picked because the glass is very transparent in this colour, and can travel tens of kilometers and still be detected, it can then be amplified and continue travelling.

The problem is that the further the pulses travel the more they tend to spread out due to imperfections in the glass's properties, this means that you have to make them longer, so you can get fewer though per second and so you can't transmit as much data, or you need to regenerate the signal every few hundred kilometres in a very expensive process.

But Xiang Lui and collegues from Bell labs in New Jersey, have come up with a system that might help. A pulse of light will disperse and spread out along an optical fibre, but there is a pattern of light that the imperfections of the fibre will cause to have exactly the opposite effect, which is called it's phase conjugate. The group sent these two signals down the fibre optic one with a horizontal polarisations and one with a vertical one, and then recombined them at the end and reduced the distortions by a factor of nearly 30.

This has allowed them to send 400 gigabits per second down an optical fibre which is 12800km long, which is very impressive and could reduce the price and increase the capacity and reliability of long data cables...


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