Birefringent thin-film polarizers for use at normal incidence and with planar technologies

Abstract

We discuss the design and fabrication of an all-dielectric thin-film polarizer that is compatible with existing planar technologies. This polarizer consists of a stack of quarter-wave biaxial layers. Each quarter-wave layer is formed by reactive electron-beam evaporation, using a bideposition technique that causes a columnar structure to grow perpendicular to the substrate, produces large normal-incidence linear birefringence, and avoids thickness wedging that is inherent in tilted-columnar biaxial layers. p-polarized light that is incident on the polarizer encounters an index-matched stack and is transmitted, whereas s-polarized light is rejected by a coexisting high-reflectance stack. A fabrication figure-of-merit of ten film periods per decade in the extinction ratio has been achieved in practice for a titanium oxide/tantalum oxide polarizer.