  We outline polarization fringe predictions derived from a new application of
the Berreman calculus for the Daniel K. Inouye Solar Telescope (DKIST) retarder
optics. The DKIST retarder baseline design used 6 crystals, single-layer
anti-reflection coatings, thick cover windows and oil between all optical
interfaces. This new tool estimates polarization fringes and optic Mueller
matrices as functions of all optical design choices. The amplitude and period
of polarized fringes under design changes, manufacturing errors, tolerances and
several physical factors can now be estimated. This tool compares well with
observations of fringes for data collected with the SPINOR spectropolarimeter
at the Dunn Solar Telescope using bi-crystalline achromatic retarders as well
as laboratory tests. With this new tool, we show impacts of design decisions on
polarization fringes as impacted by anti-reflection coatings, oil refractive
indices, cover window presence and part thicknesses. This tool helped DKIST
decide to remove retarder cover windows and also recommends reconsideration of
coating strategies for DKIST. We anticipate this tool to be essential in
designing future retarders for mitigation of polarization and intensity fringe
errors in other high spectral resolution astronomical systems.
