Applications of low-coherence interferometry in fiber optics

摘要

The aim of this paper is to review some important experimental results we have obtained in the application of time-domain and spectral-domain low-coherence interferometry for dispersion characterizing optical fibers whose intermodal optical path differences (OPDs) exceed the source coherence length. In time-domain measurements, a tandem configuration of a Michelson interferometer and a few-mode optical fiber is used and the spatial interference fringes are obtained at its output when the OPDs between beams and modes are matched within the source coherence length. In spectral-domain measurements, the intermodal interference at the output of an optical fiber alone shows up as a periodic modulation of the source spectrum when a high-resolution spectrometer is used. By processing the measured spectral modulation, the wavelength dependence of the overall phase can be obtained and then, e. g., the intermodal group OPD can be evaluated. When the spectral modulation is not resolved by the spectrometer, a tandem configuration of a Michelson interferometer and the optical fiber is used to obtain the low-frequency spectral modulation and to evaluate the intermodal dispersion in the optical fiber. In this paper, two different low-coherence sources with different temporal and spectral characteristics are used to obtain the intermodal group OPD and its wavelength dependence for two different optical fibers.