Measurement of local polarization for multi-mode photonic crystal fibers

Photonic crystal fibers allow the guidance of an advisedly chosen number of modes and a simultaneous realization of large mode areas that are essential for high power fiber lasers. The occurring multi-mode beams have spatially inhomogeneous polarization (e. g. radially polarized light), which is significant for several fiber laser applications. We report on a measurement technique to determine this local property using a modal polarization analysis based on a rapid Stokes parameter measurement combined with a computer-generated hologram. We use this method to obtain and visualize spatially varying polarization ellipses as well as modal polarization states depending on the input polarization.