I was working in simulating Huygens PSFs of a optically fabricated hologram surface. My PSFs look like suffering from aliasing effects as shown in a below picture. I was thinking a correct PSF should look similar to one in the spot diagram; however, in case of 128x128 pupil sampling, some parts of the main spot are duplicated and appear in the side or bottom part of a simulated window. Moreover, in case of 256x256 sampling, a whole psf looked like split up by two parts and appeared at upper and lower, respectively. I was trying to improve the sampling numbers of a pupil and an image space until 1024x1024, but the problem was still occured. Is there any way ro solve this problem?