The complex-amplitude reflection coefficients of p- and s-polarized light by a transparent freestanding, embedded, or deposited quarter-wave layer (QWL) are derived as explicit functions of the angle of incidence and layer refractive index. This provides the basis for the design of 50%-50% beam splitters for incident s-polarized or unpolarized light that use a high-index (e.g., TiO2 or Ge) QWL embedded in a glass cube in the visible and near infrared spectral range. These simple devices have good angular and spectral response and are insensitive to small film thickness errors to the first order.
R. M. A. Azzam and F. F. Sudradjat, "Reflection coefficients of p- and s-polarized light by a quarter-wave layer: explicit expressions and application to beam splitters," Appl. Opt. 47, 1103-1108 (2008).