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.© 1979 Optical Society of America.