Manufacturers of optical coatings and components

Transmittance for a right angle cube beamsplitter.  The blue curve is for p-polarized light, the red curve is for s-polarized light and the purple curve is for randomly polarized light.

Cube beamsplitters (CBS) are typically constructed from two right angle prisms that are cemented together with an index-matched adhesive hypotenuse-to-hypotenuse with a multilayer dielectric coating in between.  For most applications, the prism legs are anti-reflection coated.  Cube beamsplitters operate by passing one polarization and reflecting the other over a relatively narrow wavelength region.  So for randomly polarized light (50% p-polarized and 50% s-polarized), the cube beamsplitter passes one polarization and reflects the other, resulting in a polarizing 50/50 beamsplitter.   For this reason, cube beamsplitters are also employed as polarizers.

Unpolarized light incident upon the entrance face of the cube at normal incidence is internally incident at 45^° upon the multilayer coating.  The coating serves to separate energy into two polarized beams.  The beam transmitted through the cube is linearly polarized to a purity of 98% or better, with the plane of the electric field vector parallel to the plane of incidence (p-polarized).  The beam which exits the cube at a right angle to the incident beam (reflected by the coating) is linearly polarized to a purity of 98% or better with the electric field vector orthogonal to the plane of incidence (s-polarized).   Beamsplitting cubes can be designed for any wavelength region.