Differential phase-contrast microscope with a split detector for the readout system of a multilayered optical memory

A transmission differential phase-contrast microscope with a split detector is used as a readout system for a multilayered three-dimensional optical memory. The system is applicable to data recorded as refractive-index changes. The system is compact and easy to use. The three-dimensional optical transfer function for the system is derived. This shows that the spatial bandwidth of the system is the same as that of a conventional microscope with incoherent illumination but with much improved contrast. Six layers of information are recorded in a photopolymer and are read out with little cross talk and high contrast.