pi-shifted Sagnac interferometer for characterization of femtosecond first- and second-order polarization mode dispersion.

A novel configuration for measuring femtosecond polarization mode dispersion (PMD) with a pi-shifted Sagnac interferometer is studied. The advantages of this configuration include a response that is independent of the orientation of the device under test. This independence allows characterization of the first-and second-order PMD by measurement of the wavelength dependence of the differential group delay and of the orientation of the device's principal states of polarization. The method provides an extension of the dynamic range of the Sagnac interferometer technique to few-femtosecond PMD measurement.