Tiny holes just thousandths of a millimeter in size look set to revolutionize the world of telecommunications within the next few years. As internet use grows and activities such as electronic shopping become increasingly international, our need to be able to send vast quantities of data almost instantaneously around the globe is rising steeply.
Holey fibers, a new kind of optical fiber created and being researched at Southampton University in England, could provide the solution. Holey fibers look just like the optical fibers already widely used, for example, to send cable TV signals or to make fiber-optic table lamps.
The difference is that they have tiny holes running along the length of them which give them special advantages when it comes to transmitting data.
These special properties and how holey fibers might be used not just in telecommunications applications but also for pollution sensing and even for ultra-sensitive gravity detection, was explained by Dr. Tanya Monro of the University of Southampton Optoelectronics Research Centre on Wednesday at the Institute of Physics Congress 2001, taking place in Brighton.
Holey fibers are created by stacking tiny hollow glass tubes around a small solid glass rod to form a cylinder perhaps 3cm across and a meter long. This is then heated up and stretched out using a fiber drawing tower (a standard piece of equipment in optical fiber creation) to produce a fiber several kilometers long and perhaps 125 microns across (one micron, or micrometer, is a millionth of a meter or a thousandth of a millimeter).
Cutting the cable at any point and looking at its cross-section shows a solid core encircled by holes in the surrounding area (the cladding).
Each hole can be less than a micron in diameter. The positioning and size of the holes affect the way that light is transmitted by the fiber. By introducing holes which are of a similar size to the wavelength of light -- a few hundred nanometers (a few hundred millionths of a millimeter) -- light of different wavelengths (i.e., different colors) can be made to "see" different structures in the fiber.
Different wavelengths see different amounts of glass, with shorter wavelengths being more tightly confined to the core. In telecommunications terms, this means that holey fibers can guide a single mode over all wavelengths. An undersea telecommunications link needs a single mode so that it can transmit a high data rate.
Because the size and positioning of the holes can be specified, the fiber can be designed to confine the light it is sending to a small central region of, say, a micron square, or a "big" region of several thousand square microns.
If this central region is small, it is possible to operate an optical switch using very low light intensities, which is important for the future development of optical computers. (Indeed, optical switching has recently been demonstrated in a holey fiber by researchers at Southampton University.)
In a "large mode" holey fiber, the cable can send lots of power, which makes these fibers useful for applications such as laser welding and machining, as well as the development of high-power fiber lasers.
Being able to tailor the way light is guided by a holey fiber could revolutionise the way data is transmitted and there are likely to be many other exciting applications which have yet to be discovered.
Holey fibers could also provide a way of measuring pollutants in gases or liquids. Putting the fiber into a liquid or driving gas through it and then seeing how light shone through the fiber is affected could give fast and accurate information about pollutant concentrations.
Experiments also indicate that microstructured fibers like holey fibers could be used to guide atoms. A fiber is made with four holes in a square and a central hole. A wire is inserted in each of the four outer holes and a current passed through it. This creates a magnetic field that can guide atoms through the central channel.
Proof of principle experiments have shown that this is possible, but research here is only just beginning. Ultimately, the technique could provide a way of measuring gravitational fields with unprecedented accuracy.
Although holey fibers are not yet readily available, the demand from industry is clear. It looks likely that within the next few years they will be making a hole world of difference.
Related website:
Institute of Physics Congress 2001
[Contact: Dr. Tanya Monro, Dr. Alice Larkin]
22-Mar-2001