A New Method of transporting Optical Images without Aberrations

• DOI: 10.1038/173039a0
• Publication Date: 2006-05-30T11:11:14Z
• Authors: A. C. S. VAN HEEL

THE transportation of optical images has been carried out hitherto with the aid of lenses or mirrors or both. As with all optical systems, aberrations are introduced and the parts have to be aligned carefully ; it seemed worth while, therefore, to search for a method by which no aberrations are introduced and which allows (strong) deviations from alignment without deterioration of the image. Consideration of the construction of the eye of some insects suggested another approach. If a bundle or sheaf of thin transparent fibres is cut off perpendicularly at both ends and an optical image is formed on one end, it will be seen at the other end, as the light entering one fibre can only leave this at the other end, provided leakage of light from one fibre to another of the bundle is prevented. Moreover, the cylindrical wall of each fibre must reflect the light as nearly completely as possible, because of the very numerous reflexions occurring when the fibres are thin compared to their length. Preliminary experiments, started in January 1950, have shown that coating the fibres with silver or any other metal yields an unsatisfactory transmission. A much better result was obtained when the fibres were coated with a layer of lower refractive index, which ensured total reflexion. This coating was isolated from the neighbouring fibres by a thin coat of black paint. In this way, flexible ‘image rods’ have been obtained with satisfactory transmission, a very good contrast in the end image, and with the possibility of using forms bent in any direction (up to at least 360°).