Western Electric Company, Inc.

Bell Telephone Laboratories

Luther M Boggs

William B Gardner

James A Hudson, Jr

A method is disclosed for determining the index of refraction profile of a stepped or graded index type optical fiber having a core encased within a surrounding cladding. An interferogram is formed with a beam of radiant energy passed transversely through the optical fiber. Fringe line shift is measured at a series of points corresponding to a series of mutually parallel ray chord paths extending through the core at mutually diverse minimum radial distances from the core axis. That portion of the measured fringe line shift attributable to discrete differences in indices of refraction of cylindrical core ring portions of thicknesses defined by successive minimum radial distances in the series of ray paths and that of the cladding is sequentially calculated from the outermost core ring portion inwardly towards the core center.

Method of determining an index of refraction profile of an optical fiber

An opening in a jacket (15) of a cable (16) is detected as the jacketed cable is moved from an extruder (14) through a probe (21) which is positioned in a cooling trough (17) and which comprises first and second aligned, spaced sensors (24, 26) with each of the sensors being connected to an arm of a bridge transformer (37). Electrical circuitry is designed to cause an unbalance voltage in a secondary (43) of the transformer (37) in response to conductance unbalance as the opening in the jacket (15) is advanced through the first sensor (24) and to cause an unbalance voltage of opposite polarity in the secondary (43) in response to conductance unbalance as the opening in thejacket (15) is advanced through the second sensor (26). Logic circuitry (66) tests the unbalance voltages for threshold and peak values to discern jacket holes despite the presence of extraneous signals such as those which are caused by noise.

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Dunwoody, GA, United States of America

Luther M Boggs