The difference between a cube beam splitter and a plate beam splitter

Firstly, a beam splitter is an optical component used to split an incident light into two separate beams with a specified ratio. Additionally, a beam splitter can be used in reverse to combine two different beams into a single beam. Based on their structure, beam splitters are typically classified as cube beam splitters or plate beam splitters.

A cube beam splitter is constructed using two typical right-angle prisms. One of the prisms has a coated hypotenuse surface, and the two prisms are cemented together to form a cube. To avoid damaging the cemented layer, it is recommended to transmit the light into the prism with the coated surface, which usually has a reference mark on its base.

A plate beam splitter consists of a thin, flat glass plate with a coated surface on its outer face. Most plate beam splitters have an antireflection coating on their inner surface to minimize unwanted Fresnel reflections. Plate beam splitters are typically designed to have an incident angle of 45 degrees. For a substrate with a refractive index of 1.5 and an incident angle of 45 degrees, the optical path difference (d) can be approximated by the equation.