The forward scattering of light by an optical fiber produces an interference fringe pattern, and the fringe period is inversely proportional to the fiber diameter. An electrooptic system has been developed to produce and detect this scattering pattern to provide an instrument which will measure fiber diameter during the drawing operation. The system measures the fiber diameter at a 1-kHz rate with a precision of 0.25 microm and an accuracy of +/-0.25 microm over a range of 50-150-microm diams. The instrument allows the fiber to move laterally in a 1-cm diam window maintaining the above accuracy. The system can be calibrated optically and does not need a standard fiber for this procedure. The instrument has been used for months without the need for recalibration. In addition to the digital diameter output, the system employs a microprocessor to compute mean and standard deviation values for various sample lengths and provides suitable signals for feedback control of fiber diameter.

A technique has been implemented to measure and control the eccentricity of lightguide fiber in transparent polymer coating materials. It is based upon a model which describes the characteristics of a forward‐scattered light pattern generated by transversely illuminating coated fiber with a laser beam. The model predicts the behavior of the principal characteristics of the pattern as a function of fiber eccentricity within the coating. The implementation automatically detects and controls the position of the dominant pattern feature to maintain an average fiber‐coating concentricity within 2 μm over multikilometer lengths of 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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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.