The beam from the MMF passed through the field stop, aperture stop, and achromatic doublet lens, designed for the Köhler illumination. After that, the beam was split by a beam splitter (BS) into reference and sample arms. Both arms were equipped with identical water immersion microscope objectives and the AQWPs. Also, a neutral density filter for attenuation of light intensity and a glass plate to match the dispersion with the reference arm were positioned in reference and sample arms, respectively. For the sample arm, the AQWP was set to be oriented at 45 deg so that the linearly polarized input beam changes into a circularly polarized one. For the reference arm, the AQWP was set to be oriented at 22.5 deg; the polarization direction of the round trip beam was oriented at 45 deg, and vertical and horizontal polarization components of the round trip beam thus had identical amounts. The beams reflected and backscattered from the reference and the sample arms recombined at the BS. The combined beams passed through the BSPS device and then were detected by the single CCD camera (CCD1020, 10-bits, , , VDS).