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Abstract

In the determination of deviation from a concentric position for a protective polyimide coating disposed on an optical fiber, the absorption of light in the coating is used. A light source such as a laser provides a light ray which is split by a beamsplitter in two light rays. By suitably placed mirrors, the light rays are guided to hit two opposite sides of the fiber at oblique and equal incidence angles to the longitudinal direction of the fiber. The light rays hit the fibers at positions which are a little displaced in the longitudinal direction of the fiber in order to prevent wrong light rays from hitting the detectors which receive the reflected light. The detectors provide signals representing the intensity of the reflected light to a subtraction circuit which forms the difference of the signals from the detectors. The different signal is then a measure of the concentricity error of the coating. A simple method and device are obtained in this way which can also be used on-line in the determination of concentricity in the case where the coating is extruded in a drawing tower where the fiber is produced. Absolute determinations of the thickness of a coating can also be made by making a measurement on a fiber having a calibrated coating.

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First Claim