Wide-angle, high-extinction-ratio, infrared polarizing beam splitters using frustrated total internal reflection by an embedded centrosymmetric multilayer.

A centrosymmetric multilayer stack of two transparent thin-film materials, which is embedded in a high-index prism, is designed to function as an efficient polarizer or polarizing beam splitter (PBS) under conditions of frustrated total internal reflection over an extended range of incidence angles. The S(LH)(k)LHL(HL)(k)S multilayer structure consists of a high-index center layer H sandwiched between two identical low-index films L and high-index-low-index bilayers repeated (k times) on both sides of the central trilayer maintaining the symmetry of the entire stack. For a given set of refractive indices, all possible solutions for the thicknesses of the layers that suppress the reflection of p-polarized light at a specified angle, and the associated reflectance of the system for the orthogonal s polarization, are determined. The angular and spectral sensitivities of polarizing multilayer stacks employing 3, 7, 11, 15, and 19 layers of BaF(2) and PbTe thin films embedded in a ZnS prism, operating at lambda=10.6 microm, are presented. The 15- and 19-layer stack designs achieve extinction ratios (ER) >30 dB in both reflection and transmission over a 46 degrees -56 degrees field of view inside the prism. Spectral analysis reveals additional discrete polarizing wavelengths other than the design wavelength (lambda=10.6 microm). The 11-, 15-, and 19-layer designs function as effective s-reflection polarizers (|R(s)|(2)>99%) over a 2-3 microm bandwidth. The effect of decreasing the refractive index contrast between the H and L layers on the resulting ER is also considered.