Echoless light


The fact that light does ‘echo’ is in itself is quite a strange idea to wrap your head around, but a team at the University of Queensland have discovered how to eliminate these echoes, and doing so could be the key to solving a vast array of technological problems. Also, although ensuring that your Netflix streams House of Cards in full HD without buffering wasn’t the main aim of their experiment, their findings will probably make your Wi-Fi quicker, so everyone’s a winner.


(V838 Monocerotis, a red variable star about 20,000 light years from the Sun, and its light echo)

Optical fibres are transparent cables made of flexible glass and plastic that are commonly used to supply internet connections; beams of light can reflect their way through them, bouncing off the walls of the fibre in a zig-zag fashion from one end to the other. As a wave of light travels along an optical fibre, the wave itself can scatter or ‘echo’, which causes dispersion of the light rays. This means that the light pulses may spread out before they reach the other end of the fibre, which isn’t very useful considering that the light pulses carry information and if these pulses are stretched out when they exit, we won’t receive the same information that the light was carrying when it entered the optical fibre. However, the team from Queensland seem to have found a way around this issue.

Firstly, they shone light through a long optical fibre and monitored how the light was scattered and distorted as it travelled through the fibre, mapping how the pulse behaved throughout its journey. Specifically, the behaviour of the tiny particles that make up beams of light called photons were closely analysed, as how these particles interfere and interact as they move down the fibre is what determines the path the pulse takes. From this, it was possible for them to create a new light pulse with a specific shape, specially designed to exactly cancel out the effects of the ‘echoes’ that the pulse would experience as it travelled along the optical fibre. The upshot of this is that the pulse that leaves the fibre is identical to the one which entered it originally. The light may still get scattered in the middle, during its route through the fibre, but overall no distortion has occurred at all. None.

This might not sound like a terribly exciting outcome. What came in coming out looking exactly the same as it did before; you don’t get all excited if someone walks through a door and comes out the other side looking the same as they did before do you? But the fact is this discovery could have far-reaching implications on various different industries, technologies and every-day life. For starters, as well as making your internet faster, this discovery could also save thousands of lives. Endoscopes are used in medicine to view the internal organs of a patient and they rely on optical fibres in order to produce an image; if the pulses of light travelling through said optical fibres can pass through completely undistorted, then the image we see from the endoscope would be of a much higher resolution, allowing doctors to examine internal organs far more easily, and make much more accurate diagnoses whilst avoiding surgery.

Stepping away from our own planet for just a second, this process for creating echoless light could be extremely useful in terms of using lasers to communicate over extreme distances, like across the solar system. In 2013, NASA beamed an image of the Mona Lisa from Earth, all the way to a probe orbiting the moon 240,000 miles away, and all that before the introduction of this new technology, so who knows what could be accomplished next. There was already hope that in the future we would be able to bridge interplanetary distances using laser beams and with this recent discovery, that seems more and more likely to become a reality. A system such as that would be invaluable should mankind ever choose to colonise another planet, as the laser communication beams would allow us to transmit huge amounts of data extremely quickly, to a human colony on Mars for example. It seems trivial, but transferring data and information to and from Earth and communicating with the colony would be major considerations in any sort of proposed mission to inhabit another planet in our solar system.

It might not be rocket science, but it’s laser science, and that’s just about as cool, right?

#Physics #LightEcho #TomMcDonald

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