Beam splitters can be modeled either in sequential or non-sequential raytracing modes of ZEMAX.

In non-sequential mode, rays can split into refracted and reflected rays at a refractive surface. This is the core benefit of non-sequential mode: rays can split at the surface of an object into reflected and transmitted components.

Sequential rays either refract at refractive surfaces or reflect at mirror surfaces, The multi-configuration capability of ZEMAX can be used to model both refracted and reflected ray paths in sequential mode. We will construct the system shown in the following layout to demonstrate how to model a beam splitter in sequential mode.

The system above has a polarization-independent 50/50 beam splitter cube. The cube is made out of MgF₂ coated N-BK7 glass. The 50/50 coating is ideal, being independent of polarization, incident angle and wavelength. The reflected rays, shown in green, reflect from the bottom mirror before reaching the top image surface. We will calculate the correct intensities at both image surfaces, accounting for N-BK7 bulk absorption, Fresnel losses from thin-film coated surfaces,  and 50/50 splitting from ideal coatings.

Before getting started with the example, you should know how to specify system and surface properties in ZEMAX. If not, please refer to the following articles, Designing A Singlet in ZEMAX and How to Tilt and Decenter a Sequential Optical Component.

Note that ZEMAX-EE can model coated surfaces in detail, including metallic and multi-layer dielectric coatings. In this example, we will concentrate on setting up the geometry, and we will restrict ourselves to simple coatings.