Nondestructive determination of refractive index profile of an optical fiber: fast Fourier transform method.

A nondestructive technique of determining the refractive index profile of an optical fiber is presented. This method involves collecting the pathlength data of rays passing through the fiber due to side-illumination and taking the fast Fourier transform of these data followed by a numerical integration. It is found that this technique yields results in good agreement with measurements from the near-field scanning technique. The advantage of the present method is that it can readily be extended to fibers of noncircular cross section.