Measuring dispersion characteristics of elliptical-core optical fiber using white-light spectral interferometry

A spectral-domain white-light interferometric technique employing a low-resolution spectrometer is used for measuring dispersion characteristics of a two-mode elliptical-core optical fiber. The technique utilizes the fact that the spectral interference fringes axe resolved at the output of a tandem configuration of a Michelson interferometer and a two-mode optical fiber under test only in the vicinities of so-called equalization wavelengths at which the optical path difference (OPD) in the interferometer is the same as the intermodal or differential group OPD. Measuring the OPD adjusted in the interferometer as a function of the equalization wavelength serves for dispersion characterization of the optical fiber guiding two spatial modes in two polarizations. We measured the dispersion of the intermodal group OPD between the LP01 and LP11 spatial modes, which were X-polarized or Y-polarized, and the dispersion of the group modal birefringence for the LP01 and LP11 spatial modes. The measured data were fitted to polynomials to obtain the dispersions of both the differences between propagation constants of the LP modes and the phase modal birefringences.