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, are independent of angle of incidence, or increase
with angle of incidence away from the normal. As a result, multilayer
films having high reflectivity (for both planes of polarization for any
incident direction in the case of mirrors, and for the selected direction
in the case of polarizers) over a wide bandwidth, can be achieved.