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Low-coherence spectral interferometry with channelled spectrum detection, extensively used for dispersion characterizing optical fibers, utilizes the fact that the spectral interference between two modes of an optical fiber shows up at its output as a periodic modulation of the source spectrum with the period dependent on the group optical path difference (OPD) between modes. However, this measurement technique cannot be used to measure intermodal dispersion in the optical fiber for which the period of modulation is too small to be resolved by a spectrometer. We proposed and realized a new measurement technique utilizing a tandem configuration of a dispersive Michelson interferometer and the two-mode optical fiber in which the intermodal spectral interference can be resolved even if a low-resolution spectrometer is used. In the tandem configuration of the dispersive Michelson interferometer and the two-mode optical fiber, the OPD in the Michelson interferometer is adjusted close to the group OPD between modes of the optical fiber so that the low-frequency spectral modulation that can be processed is produced. Using the Fourier transform method in processing the measured spectral modulations and subtracting the effect of the dispersive Michelson interferometer, the intermodal dispersion of the two-mode optical fiber over a limited spectral region has been obtained.
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