Abstract: Successful applications of low-coherence interferometry both in the time and spectral domains are demonstrated in the evaluation of the group optical path differences (OPDs) between two linearly polarized (LP) modes of weakly guiding optical fibers excited by a multimode laser diode TOLD 9201. Using the first measuring technique, the visibility of spatial interference fringes is measured as a function of the OPD in the experimental setup comprising a bulk-optic Michelson interferometer and a two-mode optical fiber under test. From the visibility dependences, the group OPDs between two LP modes of the optical fibers are obtained. Using the second measuring technique with the same exciting source TOLD 9201, the wavelength-dependent modulations of the source spectrum are obtained at the outputs of the two- mode optical fibers. By processing three spectral modulations using the Fourier-transform method, the wavelength dependences of the group OPDs between two LP modes are obtained and good agreements with the time-domain measurements are confirmed. When a halogen lamp is used as an exciting source, the wavelength-dependent modulation is resolved only in the vicinity of the equalization wavelength, where the period of modulation is sufficiently large to be resolved by the spectrometer. From the corresponding dependence, a value of the equalization wavelength of two LP modes of a single optical fiber is obtained.!24
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