Index-profiling method for preforms and multimode fibers.
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.
Kawakami
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Shiraishi
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Yasuda
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