Nondestructive determination of refractive index profile of an optical fiber: backward light scattering method

Abstract

A new nondestructive technique is presented for determining the refractive index profile of an optical fiber from its backscattered pattern arising from a normally incident laser beam to the fiber axis. The proposed method requires no sample preparation or index matching liquid. The principle of the method is to construct a deflection function from the measured pattern. The index profile can then be determined by the inversion of an Abel integral equation. Good agreement is obtained between the index profile determined by this technique and that measured by the near-field scanning technique.

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 .…”

Zero-order bows in radially inhomogeneous spheres: direct and inverse problems

“…This involves inverting an Abel integral equation [3][4][5], a topic that has received attention in a wide range of fields, especially in recent years. Abel inversion techniques have been used in fields such as x-ray radiography [6][7][8], galactic astronomy [9,10], optical fiber evaluation (extensively so, see [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]), satellite photometry using radio occultation techniques [26][27][28][29][30][31][32][33], microscopy, plasma electron diagnostics [34][35][36][37], and seismology [38][39][40]. In particular, radio occultation experiments using radio links between the Earth spacecraft that pass behind planets as seen from Earth have provided valuable information about planetary atmospheres.…”

Refracted-ray scanning (refracted near-field scanning) for measuring index profiles of optical fibers

“…Transverse-scattering methods, including backscatter, have been implemented by several groups [12][13][14]. With these techniques, a fiber (also immersed in oil) is illuminated transversely by a laser, and the far-field diffraction pattern is observed.…”