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The requirement was to form an image of a 1mm plastic optical fibre with a magnification of x4 onto a CCD camera. Sounds quite easy, but there were constraints. Firstly, for mechanical reasons, the image plane had to be 155 mm from the fibre end and, secondly, near diffraction-limited performance was required for a minimum fibre NA of 0.2. Thirdly, for reasons of time and cost, the components had to be off-the-shelf. As the application was for modal-profiling it was not possible to use stops as all the light from the fibre had to reach the camera. Fortunately, chromatic aberrations were not an issue as the light source was virtually monochromatic. |
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The final system consisted of a first achromat with the fibre at its front focus, and a second group consisting of an achromat, a negative field-flattener lens and a plano convex lens. The through-focus spot diagrams show that the aberrations are well balanced. The small residual field curvature is within the depth of focus of the system. |
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Requirement: Plastic Optical Fibre (POF) imaging System |
