Lasers make fibre optic tubes out of thin air

[Nipuna]

Optical fibres made from thin air could transmit data to and from hard-to-reach places.

Regular optical fibres are made from two transparent materials that slow light down by different amounts. The difference in materials lets light reflect along the length of the cable without leaking out – perfect for sending a signal over long distances.

But it's hard to put fibres in some places, like the upper atmosphere or inside nuclear reactors. And signals sent through open air often degrade because the light spreads out.

Now, Howard Milchberg of the University of Maryland, College Park, and his colleagues have come up with a way to mimic a fibre in the air itself.

Sending lasers with lasers
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The team shone four lasers in a square arrangement, heating air molecules and creating a low-density ring around a denser core of air. Light bounces around the dense core just like in a fibre.

The air fibre lasts for a few milliseconds – more than enough to send a signal. "This is an extremely long time from the vantage point of a laser," says Milchberg. The results are published in the journal Optica.

So far the team has tested air fibres over a range of 1 metre. These delivered a signal 50 per cent stronger than through air alone over the same distance. Sending signals further gives light more chance to spread, so in theory, a 100-metre air-fibre could deliver a signal 1000 times stronger than sending it through air alone.

The team also transmitted a laser with 100 times more energy than those used to make the fibre. And they were able to receive signals: small flashes of light from the other end were detected. This suggests the fibre could be used for remote sensing, which could include detecting explosives at a distance.