Optical EngineeringMeasuring a two-mode optical fiber using modulation of the spectrum of a low-coherence source at its output
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It is demonstrated experimentally at the output of an optical fiber excited by a low-coherence source that the mutual interference of two linearly polarized (LP) modes can be resolved in the spectral domain when the optical path difference between both LP modes exceeds the source coherence length. The spectral interference between two LP modes, which shows up as a periodic modulation of the source spectrum, serves as an illustration of the feasibility of a novel measuring technique utilizing a high-resolution spectrometer in the evaluation of the group delay time difference between both LP modes. Moreover, it is shown that the spectral analysis performed across the output modal pattern of the two-mode optical fiber leads to spectral modulations in which the effects of both polarization properties and overlaps of modes are inscribed.