For the first time to our knowledge, digital holography is used to determine the distribution of parabolic or nonparabolic refractive index fields in graded index optical fibers. The fiber is embedded in an index matching fluid whose refractive index can be varied to a matching and mismatching index with respect to that of the cladding. In experiments for both cases high precision phase-shifting digital holographic interferometry is applied with numerical evaluation employing the multilayer model for recognition of the refraction. Due to the higher redundancy in the multiple phase-shifted holograms better accuracy can be obtained compared to classical two-beam interferometry. Therefore the holographic method is recommended as a nondestructive and noncontacting method for characterizing graded index optical fibers.
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