A trilayer pellicle that consists of a high-index center layer that is symmetrically coated on both sides by a low-index film can be designed to produce differential reflection and transmission phase shifts of ∓90° at oblique incidence and equal throughput for the p and the s polarizations. Such a device splits a beam of incident linearly polarized light into two orthogonal circularly polarized components that travel in well-separated angular directions. Examples of infrared dual quarter-wave retarders that use a symmetrically coated Ge pellicle at 77° angle of incidence are presented. A 50–50% splitter requires a symmetric pellicle with at least five layers. Error analysis shows that the thicknesses of the high-index layers must be tightly controlled. These circular polarization beam splitters are intended for operation with a well-collimated light source and can be used as the basis of a novel circular polarization Michelson interferometer.
Rasheed M. A. Azzam and Fadi A. Mahmoud, "Symmetrically Coated Pellicle Beam Splitters for Dual Quarter-Wave Retardation in Reflection and Transmission," Appl. Opt. 41, 235-238 (2002)