Automatic refractive-index profiling of optical fibers.

A video-based system, which analyzes the output field of an interference microscope directly, has been developed to measure automatically the refractive-index distribution of optical fibers. Selected regions of the fringe field, detected with a silicon-vidicon, are digitized to 8-bit accuracy by an addressable video digitzer controlled with a programmable calculator. The calculator also makes fringe displacement measurements, corrects for certain misalignments, computes and plots the profile, and determines a best-fit power-law (alpha) curve. Profiles, with relative Deltan measured accurate to a few parts in 10(5), obtained at different wavelengths and for different fiber orientations are presented.