Modeling interferometer

I have a need for modeling an interferometer. I am presently using
Zemax. However, Zemax cannot properly handle plane waves with decent
size apertures (each beam having about 200 wavelengths OPD).
However, this can be fixed by fooling the program by increasing the
wavelength to reduce the wavefront deviation.

Unfortunately I have discovered other computational errors in Zemax
and have no confidence in its accuracy.

Has anyone used any software, preferably easy to learn and
inexpensive, that does a good job of modeling interferometers?
.