Insert surface #7 and place a -1 pick-up solve on surface on the thickness.





In sequential mode, rays can only refract or reflect once from each surface sequentially, as listed in the Lens Data Editor. After the rays have reflected from the bottom mirror (surface #7), we need to re-define the beam splitter cube in the Lens Data Editor, since surfaces 2 to 6 are no longer visible to the rays. 
 
Insert following surfaces, after surface #7, in the Lens Data Editor. Using the tilt/decenter tool, tilt the diagonal surface of the cube by 45 degrees. Note that the material type for surface #10(diagonal) is N-BK7 and not Mirror, since after reflecting from the bottom mirror (surface 7) we need to trace the transmitted/refracted rays that reaches the top image surface.
 




Set the 3D layout to display the current configuration. The current selected configuration should be 2, indicated in the Lens Data Editor title bar (above).

Update the 3D layout