This paper describes a new method (the scattering-pattern method) for determining the refractive-index profile in an optical fiber from its scattering pattern for a normally incident laser beam. The proposed method is applicable to an arbitrary profile and is nondestructive. The spatial resolution is high, and the accuracy is good when the fiber diameter and the refractive-index variation are relatively small. The drawback is that a large number of data are required; however, this difficulty has been overcome by using the automated measuring system described in this paper. The profile obtained shows good agreement with design data.
T. Okoshi and K. Hotate, "Refractive-index profile of an optical fiber: its measurement by the scattering-pattern method," Appl. Opt. 15, 2756-2764 (1976)