Investigation of the phase-contrast technique using two-dimensional amplitude transmittance filters.

Phase contrast is an optical imaging technique used to visualize phase objects through spatial filtering that combines amplitude and phase modulation. Comparable results, however, can also be achieved using purely amplitude-based filters. In this work, we present a numerical study on the influence of the transmittance shape and size of two-dimensional amplitude filters on the visualization of specific binary and quadratic phase distributions in a coherent 4f Fourier optical system. Five types of amplitude transmittance filters are analyzed: opaque disk, conical five-stepped conical, conical, Gaussian, and angularly variable. An experimental implementation of the technique using opaque disks and a simplified version of an angular variable transmittance filter is used to demonstrate the impact on the resulting images of the binary and quadratic phase objects.