Polarization mode dispersion measurement using a Sagnac interferometer and a comparison with the fixed analyzer method

Polarization mode dispersion measurement using a Sagnac interferometer is compared with the well-known fixed analyzer technique both theoretically and experimentally. It is shown that in the case of weak mode coupling in the fiber the Sagnac interferometer method is equivalent to the fixed analyzer method but gives better readability of the measured optical spectrum. For strong mode coupling, we develop a theory that relates the differential group delay to the number of mean-level crossings in the measured spectrum