The puzzles come from when I try to use POP to simulate the diffraction effect of my Grid phase which is written in Matlab.

I set a system with object at infinity, surface one is a dummy surface. Surface two is my Grid phase with distance 0 behind the surface one.

First I check the Grid phase in the phase map. Intepolation is pixelated. The phase ranges from -0.49~0.49 (unit 2pi) and center point has phase 0. Operade RAED at surface two for the chief ray of on axis is 7e-4. Total pixel is an odd number to ensure no offset.

The propagation in POP starts from surface one and ends at surface two. The pixel size is set the same as in the phase map. The phase after surface two ranges from -3.09~3.14 (radians), which is non-symmetric and different from what I see in phase map. The center phase is non-zero, phase refers to a plane. Since the propagation distance is 0, I don’t understand why.

An additional general question is (not related to the above), if the chief ray is slightly tilted and select the pilot radius as ‘plane’, is the plane also tilted or not?

I thanks for your attention!