Birefringent optical films have a Brewster angle (the angle at which reflectance of p-polarized light goes to zero) which is very large or is nonexistent. This allows for the construction of multilayer mirrors and polarizers whose reflectivity for p-polarized light decreases slowly with angle of incidence,...http://www.google.ca/patents/US7297393?utm_source=gb-gplus-sharePatent US7297393 - Optical film
