Polarizing beam splitters

Abstract

A polarizing beam splitter has a pair of opposed transparent prism substrates with a refractive index n, 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 l. . . lhaving respective refractive indices n. . . n, wherein at least three of said refractive indices n. . . nare different, and wherein the refractive index of the substrates nlies between the highest refractive index nand lowest refractive index n, and wherein n, nand ndefine a Brewster angle θ: a critical angle θ: The refractive indices nand n. . . nare selected such that the central operational angle for a beam incident on the multiple thin film structure lies above the Brewster angle θand such that most or all the operational angles defined by said input port lie above the Brewster angle θ. For p-polarized light at least one optical admittance of the layers with refractive indices n. . . nis lower or very close to that of the optical admittance of the substrate for the operational angles such that the thin film polarizing beam-splitter favors the transmittance for p-polarized light incident at that input port such that most of the p-polarized light is transmitted through the multiple thin film structure. For s-polarized light the polarizing beam-splitter acts as a high reflective coating to favor the reflectance for s-polarized light incident at the input port such that most of the s-polarized light is reflected from said multiple thin film structure. The polarizing beam splitter is compact and yet remains functional over a wide range of operational angles.