High speed measurement of the core diameter of a step-index optical fiber.
The forward scattering light pattern from a clad optical fiber illuminated perpendicular to its axis is characteristic of the outer diameter, the core diameter, and their respective refractive indices. This pattern is detected by a diode array detector to produce a video signal representation of the scattering pattern. Electronic circuits have been developed to analyze the scattering pattern and detect the angular position of the modulation characteristics of the pattern. This provides a determination of the core to outer diameter ratio of the fiber. Using linearization circuits and the outer diameter measurement signal, linear measurement signal voltages of both core ratio and core diameter are derived. The measurement of core ratio refers to a particular radius vector and means that determinations of circularity and concentricity can also be made.
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Watkins
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Frazee