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The spectrum of light changes on its propagation through few-mode optical fibers due to the coherence-induced changes. They lead to the presence of modulated spectrum affected by intermodal dispersion when two completely spatially coherent modes of an optical fiber are included. This spectral modulation can be resolved even if the group optical path difference (OPD) between modes is greater than the source coherence length. In this contribution, the spectral changes of light occurring on its propagation through a two-mode optical fiber are analyzed both theoretically and experimentally. It has been confirmed experimentally, in accordance with theory, that the spectral modulations characterized by the wavelength-dependent periods of modulations can be resolved at the output of a two-mode optical fiber excited by low-coherence sources having different spectral widths. It has also been confirmed that the characteristics such as the unmodulated spectra and the wavelength dependences of both the visibilities of spectral fringes and the group OPDs between modes can be obtained. Moreover, it has been revealed theoretically that the configuration of a two-mode fiber, for which no spectral fringes are resoled, and a Michelson interferometer is suitable for the spectral analysis with a low-resolution spectrometer.
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