Patent ID: 8817371

Claim:
A polarizing beam splitter comprising: a pair of opposed transparent prism substrates having substantially the same refractive index n 0 , said pair of opposed transparent substrates providing at least one input port and at least one output port, wherein said input port accepts light incident over a range of operational angles including a central operational angle; a multilayer thin film structure sandwiched between said pair of opposed transparent substrates and consisting essentially of a plurality of layers l 1 . . . l m having respective refractive indices n 1 . . . n m , wherein at least three of said refractive indices n 1 . . . n m are different, and wherein each pair of adjacent layers form a layer interface with different refractive indices, and wherein the refractive index of the substrates n 0 lies between a highest refractive index n H and a lowest refractive index n L , and wherein n H , n L and n 0 define a Brewster angle θ 0B : θ 0 ⁢ ⁢ B = arcsin ( n L ⁢ n H n 0 ⁢ n L 2 + n H 2 ) , and a critical angle θ C : θ C = arcsin ⁡ ( n L n 0 ) , and wherein said refractive indices n 0 , and n 1 . . . n m are selected such that the central operational angle for a beam incident on said multilayer thin film structure lies at least 4° above the Brewster angle θ 0B and such that most or all the operational angles defined by said input port lie above the Brewster angle θ 0B ; wherein said multilayer thin film structure is a non-quarterwave stack, at least three different layer interfaces that each occur more than once are present within said multilayer thin film structure; and wherein for p-polarized light at least one optical admittance of said layers with refractive indices n 1 . . . n m is lower or very close to that of the optical admittance of said substrate for said operational angles such that said polarizing beam-splitter favors transmittance for p-polarized light incident at said input port such that most of the p-polarized light is transmitted through said multilayer thin film structure; and thr s-polarized light said polarizing beam-splitter acts as a high reflective coating to favor reflectance for s-polarized light incident at said input port such that most of the s-polarized light is reflected from said multilayer thin film structure.