Hi Yang,

Yes, you found the solution I was going to recommend.  Basically, using a Birefringent Surface is the same as using a multi-Config system and there are only a handful of analysis that support multi-config systems.  Any ray based analysis can simply be superimposed in a multi-config system to provide the output, but if you need a diffraction based multi-config analysis, the Huygens PSF with Config=All is one of the most powerful tools that OpticStudio has.  I would avoid any pupil-based calculations including FFT analysis because there is no “common” image-space reference point to superimpose the results onto a common plane.