Phase-stepping an all-fiber Sagnac loop for full characterization of femtosecond PMD

A novel phase-stepping technique is demonstrated in a Sagnac loop for measuring femtosecond first-order polarization-mode dispersion (PMD) spectra and wavelength-dependent principal states of polarization without the polarization-dependent loss impairing the measurement. The technique allows full characterization of the secondorder PMD. The measurements agree well with the ones obtained using the (pi)-shifted Sagnac loop previously proposed by the authors.