A design procedure is developed which yields layer combinations having a polarization independent effective index of refraction. A method of transforming massive media to nonpolarizing effective massive media is shown. These two design techniques are then applied to the problem of making polarization independent metal-dielectric-metal interference filters and polarization independent beam splitters.
V. R. Costich, "Reduction of Polarization Effects in Interference Coatings," Appl. Opt. 9, 866-870 (1970)