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| 1 May 2008 |
| Photonics |
Rob Morrison: Photonics and fibre optics are already an important part of telecommunications and now they're set to revolutionise many other areas of science and technology. Glass is a strange material. Solid but transparent, it's really a supercooled liquid. Because light passes through glass, it makes excellent windows and beautiful sculptures. But glass can also make light do tricks. And that's the science of photonics. Photonics is the science of the photon, which is the fundamental particle of light. And photonics is really the study of how we can generate light, like in a laser, how we can manipulate and control light. Professor Tanya Monro heads the Centre of Expertise in Photonics, based in the University of Adelaide in South Australia. Professor Tanya Monro: The Centre of Expertise is a fairly new research centre which has been formed to develop new kinds of optical fibres for applications beyond telecommunications. Left to itself, light likes to travel in straight lines. However, we can bend it round a corner using something like an optical fibre, that allows a ray of light to bounce around a corner within the material, and then you can see it at the end. So it's a way of confining light within a material. And because you can turn light on and off, you can create light signals and send them along optical fibres. Photonics already plays an important role in telecommunications, but the centre is developing novel glass fibres to make light do completely new things. We're interested in making fibres from new materials. And to do that, we start in our labs, by batching together different chemicals to make new compositions of glass that will have new properties when they're turned into fibres. The next step is to heat it up to a very high temperature - usually around 1,000 degrees - and to get it into a molten form so you can then pour the molten glass into a mould. It's very important to keep it pure. And so we mix them in gold or platinum crucibles in order to make sure that none of the material from the crucible becomes embedded in the glass. We need to pour it into a mould to define its shape. And that can be a rectangular mould or a cylindrical mould. We use cylindrical moulds generally when we want to make the precursors for fibre drawing. Different glass compositions transmit light at different wavelengths. It's important to polish these billets before you extrude them, in order to get a very good quality glass out at the end of the preform. Once you have a nice cylindrical billet of uniform glass, the next step is to introduce structure to that. Because, ultimately, we're looking to make fibres with tiny little airholes that are used to confine the light. Traditionally, fibres have just been made of a solid material. What we're doing is introducing airholes to these fibres to change the way light travels down the fibre. So what we do is we take this billet of uniform glass and we heat it up to the point where the glass just starts to become soft. And at high pressure, we squeeze that glass through a die. These dies give the otherwise uniform glass its internal structure. You can control the shape that you extrude by changing the internal structure of the die. And you do that by introducing little elements within the die that block the flow of glass and thus form holes within the preform. What comes out of the die is called the preform. And that preform's typically a few centimetres across and contains holes within it that are of order millimetres in size. In essence, we want to take something that's a few centimetres in diameter and pull it down to something that's the thickness of a human hair. We need to scale it down, we need to stretch it down so that those features become tiny. Fibre drawing works by heating up the preform and stretching it down to form the fibre. And by controlling the temperature and the speed at which this is done, you can control how small it becomes. The bottom of the preform falls under its own weight. Once the drop has come down the bottom of the fibre is attached to a rotating drum and that winds the fibre onto it. Once we've made optical fibres, it's important that we understand exactly how light travels down them. What we're doing with this experiment is measuring the dispersion within the fibre at different wavelengths. Introducing airholes means that for the first time you can interact light with materials that you put inside the holes, such as liquids or gases. We fill the holes of our fibres with solutions containing proteins. And by putting light into our fibre we can then excite these proteins which then glow or fluoresce at a different wavelength and we capture that glow as a way of telling us how many proteins are within our fibre. Photonics is already starting to change the way we do things. For example, more and more things are now being done with light, rather than with electronics. Some of the future advances we can expect include, for example, using light to monitor the health of bridges or to give us an early warning of corrosion within aircraft. This field is very exciting because we get to bring together a lot of different areas - we bring together physics, chemistry, engineering, material science. We bring these fields together to tackle new problems, to take crazy ideas, translate them into new realities. |
