Diameter determination of graded-index optical fibers from backward-scattered pattern

Abstract

The backscattered pattern of an optical fiber with arbitrary refractive-index profile is used to determine the fiber diameter. Two methods are presented: the fiber diameter can be determined either by noting the position of a particular fringe maximum or by counting the total number of fringes in the pattern. This method is fast in that it does not require any mechanical moving part, and the measurement error is 1%. This method is based on the prior knowledge of the refractive-index profile of the fiber, but it is shown that the error incurred by assuming the wrong profile is less than 1%. It is also shown in this paper that the method can be used to monitor the diameter variation while the fiber is being pulled. This is done by tracking the displacement of a particular fringe. It is shown that this method is also applicable to fibers with elliptical cross section.

A Simple Method for Calculating Scattering Patterns of Light from Optical Fibres

“…Many techniques have been developed to determine the refractive index and diameter of optical fibres [1][2][3][4][5][6][7][8][9][10] . The refracted near-field (RNF) method [3,4] has been commonly used .…”

“…The refracted near-field (RNF) method [3,4] has been commonly used . Another extensively employed method is the light scattering technique [5][6][7][8][9][10] . One of the advantages of this technique is its potential for conducting an on-line inspection .…”

“…In order to recover the refractive index and diameter of fibres from the measured scattering patterns, one has to not only measure but also calculate the scattering patterns . Theoretical approaches based on geometric ray optics [5][6][7][8] and wave optics [9,10] are developed .…”