Q J Med 2003; 96: 783
© 2003 Association of Physicians
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Scanning near-field image of the wave front at the end of a holey fibre
Department of Chemistry University of Southampton
Photograph by Jeremy Frey
Glass fibres as thin as a human hair now carry most of our long-distance telephone calls. To squeeze even more information down a fibre, new types have been developed that have holes with nothing but air inside them. The holes act to improve the confinement of the radiation in the fibre, and can also be designed to modify the light wave in a variety of ways. These holey fibres are an example of a photonic crystal, an assembly of varying refractive index designed to manipulate light. Natural versions of such crystals are found in opals, and (it is thought) in the intense blue of an Amazonian butterfly.
Electron microscopy can be used to look at the structure of the fibres, but to understand how the holes modify the fibre properties, the intensity of the light across the fibre needs to be measured. This measurement can not be achieved with conventional microscopy, as we need to look at the way the light behaves within objects smaller than the wavelength of the light. To record the light wave-front across the holey fibre, another very thin fibre tip, which captures some of the light wave, is scanned across the holey fibre in a technique known as Scanning Near Field Optical Microscopy (SNOM). SNOM has been used on biological samples, and provides much higher spatial resolution than, for example, confocal fluorescence techniques. Working in the near field (i.e. closer than the wavelength of visible light) allows much higher spatial resolutions to be achieved. The greatest intensity is in the central core; the contours reflect the underlying structure of the holes in the fibre.
The image shown is one from an exhibition shown at the Christchurch Picture Gallery (Oxford) in 2002 from a collection made by Jeremy Frey (School of Chemistry, Southampton) funded by an EPSRC Partnership in Public Appreciation Grant. For this image, the SNOM experiments were conducted in the group of W.S. Brocklesby (School of Physics & Astronomy and Optoelectronics Research Centre, Southampton) on a holey fibre produced by the group of Tanya Monro (Optoelectronics Research Group, Southampton). The images project was inspired by the work of Felice Frankel at MIT, whose photography has produced superb images of scientific results. In my work I have frequently taken a little more licence with the images, to enhance the attraction of the image and draw the general public's attention. However, for this particular image, little manipulation was needed beyond that required for the actual experiment.
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