A nondestructive technique, based on Fresnel diffraction from phase objects, is proposed for specifying the refractive indices of optical fibers without requiring index matching liquid. The method involves measurement of normalized intensity distribution on the Fresnel diffraction pattern of a monochromatic plane wave diffracted from a fiber, and evaluation of the fiber core refractive index from the intensity distribution by the least-square method. It is also shown that for the case of an unknown fiber core radius, by fitting a suitable theoretical intensity distribution on the corresponding experimental intensity distribution, the core radius and refractive index can be obtained with reasonable accuracy. Simulation and experimental studies show that the technique is reliable and quite sensitive to refractive index change.
A nondestructive technique for determining the refractive indices of the core and the cladding of step index
optical fibers is presented. This method involves diffraction of plane wave from an optical fiber and application
the iterative method on Fresnel-Kirchhoff integral, the refractive indices of the core and the clad obtained by
this method are in good agreement with the results of other techniques.
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