A method for measuring non-circularity of a core portion of an optical fiber base material includes a distribution measuring step of (i) moving the optical fiber base material in a direction parallel to a central axis of the core portion while light is irradiated, in a direction perpendicular to the central axis, to the optical fiber base material which is immersed in the matching oil, and (ii) recording a variation in a width of a portion of the irradiated light which transmits through the core portion in association with a moved distance of the optical fiber base material, thereby measuring a distribution of relative values of an outer diameter of the core portion in terms of a longitudinal direction of the optical fiber base material, a distribution storing step of performing the distribution measuring step each time the optical fiber base material is rotated about the central axis by a predetermined angle, thereby recording a plurality of distributions of the relative values of the outer diameter of the core portion each of which is associated with the predetermined angle, and a non-circularity calculating step of calculating a plurality of values, in terms of the longitudinal direction of the optical fiber base material, each indicating non-circularity of the core portion, based on the plurality of distributions of the relative values of the outer diameter stored in the distribution storing step.

Method for measuring non-circularity at core portion of optical fiber parent material

PROBLEM TO BE SOLVED: To provide an improved technique for detecting the core/clad interface position of a blank used for manufacturing a light guide path fiber. SOLUTION: A method and a device for detecting the air/clad and core/clad interface of a blank 13 used for manufacturing a light guide path fiber are provided. A coherent light beam is scanned across the blank 13, and a space light intensity pattern generated by it is detected and analyzed. When the beam is moved in the center direction of the blank 13, the air/clad interface corresponds to the decrease of the width of a single-mode space light intensity pattern. When the beam is moved in the center direction of the blank 13, the air/clad interface corresponds to at least the start point of a two-mode space light intensity pattern. When the blank 13 is rotated and the measuring process at two or more angle positions is repeated, the concentricity and ellipticity of the blank 13 can be determined.

Detecting method and device for core/clad interface of light guide path blank

PURPOSE: To measure the external diameter of a core, etc., with high accuracy even when an optical fiber base material and refractive index matching liquid has a difference in refractive index by multiplying the apparent core diameter of the optical fiber base material by a correction coefficient and determining the real core diameter. CONSTITUTION: The optical fiber base material 11 is dipped in the refractive index matching liquid 18 with a refractive index (n), laser luminous flux 15 is scanned at right angles to the center axis of the base material 11, and the time when the luminous flux 15 is cut off by the base material 11 is measured electrically. Then the center position of the base material 11 and the center position of the core are determined according to the obtained data and the observed distance between the center of the base material 11 and the center of the core is found from those data. Then, the external diameter and apparent core diameter are determined according to those data and the apparent core diameter is multiplied by the correction coefficient K=n/n 1 (n 1 : refractive index of the clad of the base material 11) to determine the real core diameter. Thus, simple calculation or correction like this is added to accurately evaluate the shape of the base material with high accuracy. COPYRIGHT: (C)1988,JPO&Japio

Hiroki Ito

Papers

Measuring method for shape of optical fiber base material