Abstract: An apparatus for polarizing natural light incident on a polarizer with an intermediate layer of one birefringent or biaxial material mounted between a pair of prism substrates of a second birefringent or biaxial material with a liquid or other index matching medium between the prism substrates and the intermediate layer to provide optical coupling between the three above-mentioned constituent parts of the prism. The materials of the prism substrates and of the intermediate layer being selected to be substantially transparent and to have orthogonal indices of refraction (n.sub.o and n.sub.e for birefringent materials and any two of n.sub.a, n.sub.b and n.sub.c for biaxial materials) which are considerably different for each individual material over the spectral region of the desired polarization.