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The problem was to measure the diameter of the transparent protective coatings on an optical fibre. The novel wedge-shaped prism, shown below, was designed to provide dark-field illumination across the fibre. The coating boundaries, acting like negative cylindrical lenses, cause light to enter the collection optics and form an image on the camera consisting of a series of bright lines on a dark background. |
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Requirement: Measurement of fibre coating geometry |
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For more details on the technology see: 'Measurement and Calibration of Fiber Coating Geometry by Grey-Scale Analysis', Journal of Lightwave Technology, vol 13, no. 8, Aug 1995. |
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The figure, shown right, shows an intensity plot across the fibre diameter. The diameter and concentricity of the cladding and the two coating layers can be readily computed from measurements made at different angular positions of the fibre. |
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Radial position |
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camera |
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objective |
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prism |
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fibre |
