title: Index-profiling method for preforms and multimode fibers.
abstract: A technique for refractive-index profiling is proposed and experimentally verified. The technique is an improved version of the bound near-field method in that it uses a butterfly-shaped spatial filter that eliminates leaky modes. The refractive-index distribution of an optical-fiber preform is measured by using this technique. The result agrees with values obtained by thin-slice interferometry. The technique is also applied to a multimode fiber, and its validity is confirmed. It could also be applied to necked-down preforms.
authors.forename: S
authors.initials: S
authors.lastname: Kawakami
authors.forename: K
authors.initials: K
authors.lastname: Shiraishi
authors.forename: K
authors.initials: K
authors.lastname: Yasuda