The system aperture in sequential ZEMAX is circular and all surfaces have circular apertures by default. To make the beam splitter shape cubic, place a 10 X 10 rectangular apertures on surfaces 2 and 6 and 10 X {root (2)*10} aperture on surface 4.

Set the following apertures on surfaces 2 and 6 in the surface properties window.

Set the following aperture on surface 4



Update the 3D layout

To remove the vignetted marginal rays from the layout, check “Delete Vignetted” box in the 3D layout settings

Update the Layout

Place the ideal 50/50 coating “I.50” on surface 4, and "AR" coating on surfaces 2 and 6. The I.50 is an ideal 50% transmission coating and the AR is a quarter-wave thick MgF₂ anti-reflection coating.