Entrance pupil masks for enhancing moiré-based distance/motion sensing

Detection of higher-order diffraction patterns when range-finding using moiré images of fork gratings, as previously developed, is key for increased sensitivity. However, higher-order frequencies are inherently lower contrast than the fundamental frequency. Here we explore means of optically increasing contrast of moiré patterns via pupil function design. Two candidate pupil forms that increase performance above diffraction limited capabilities at specific spatial frequencies are considered, and one is chosen to proceed to experimentation. Contrast of the moiré image when using the specially designed pupil is compared to a clear aperture. Both simulation and experimental data are analyzed to show the increased contrast and sensing capabilities of the candidate entrance pupil mask.