1. An apparatus, comprising: a Sagnac interferometer that includes a pair of diffraction gratings so as to produce a dispersion compensated shear between first and second portions of an input light flux, the Sagnac interferometer comprising a polarizing beam splitter that directs the first and second portions of the input light flux along respective interferometer optical paths to the pair of diffraction gratings; a polarization analyzer situated to receive a combination of the sheared first and second portions of the input light flux and produce an associated output light flux; a detector situated to receive the output light flux and produce an image signal; and an image processor that produces a polarization image based on the image signal.