Design of a nonpolarizing beam splitter inside a glass cube

The reflectance and transmittance of dielectric thin films at oblique angles of incidence have strong polarization effects. For some applications these effects are undesirable. A nonpolarizing beam splitter design concept is shown, which is based on the fact that in a quarter-wave stack at lambda(o) two effective indices that obey the Brewster condition affect only the spectral performance of the s state at lambda(o). This property is used as a design tool. The concept can be applied to a wide range of angles and transmittance values, with the use of effective quarter-wave layers of at least three different materials. A few examples are elaborated where these values are designed and optimized to give either T(p) = T(s) or T(p) + T(s) = constant, in the vicinity of lambda(o).