Abstract: A polarizing beam splitter has a pair of opposed transparent prism substrates with a refractive index n0, and providing at least one input port and at least one output port. The input port accepts light incident over a range of operational angles including a central operational angle. A multilayer thin film structure is sandwiched between the pair of opposed transparent substrates and consists essentially of a plurality of layers l1 . . . lm having respective refractive indices n1 . . . nm, wherein at least three of said refractive indices n1 . . . nm are different, and wherein the refractive index of the substrates n0 lies between the highest refractive index nH and lowest refractive index nL, and wherein nH, nL and n0 define a Brewster angle ?0B: ? 0 ? B = arcsin ( n L ? n H n 0 ? n L 2 + n H 2 ) , and a critical angle ?c: ? C = arcsin ? ( n L n 0 ) . The refractive indices n0 and n1 . . .