Compact read-only memory with lensless phase-conjugate holograms.

A new approach to holographic storage that uses lensless phase-conjugate holograms is proposed and demonstrated. Near-field holography is used for data recording, and a phase-conjugate reference beam is used for data retrieval. The data array can be directly transferred from the storage medium to the sensor without the need for imaging optics. It is shown that large space -bandwidth product holographic images (N x N x 10(6)) with pixel sizes of a few micrometers are feasible with a reasonable-sized recording material.