Manufacturers of optical coatings and components

Reflectance curves for various 45^° plate beamsplitters for random polarization (second surface anti-reflection coated)

Plate beamsplitters (PBS) are constructed of flat glass with a dielectric multilayer beamsplitter coating on one surface and an anti-reflection coating on the second surface.   Beamsplitters can be designed for a wide range of angles, but are typically used at 45^°.  The dielectric coating used to construct plate beamsplitters have low absorption coefficients, so to a very good approximation, R + T = 1.  The result is that the transmittance equals the difference between 100% and the percent reflectance.