Compact read-only memory with lensless phase-conjugate holograms

Abstract

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.

Holographic data storage technology

“…Several authors have proposed bypassing these requirements by using phase-conjugate readout of the volume holograms [12][13][14][15]. After the object beam is recorded from the SLM with a reference beam, the hologram is reconstructed with a phase-conjugate (timereversed copy) of the original reference beam.…”

“…The diffracted wavefront then retraces the path of the incoming object beam in reverse, canceling out any accumulated phase errors. This should allow data pages to be retrieved with high fidelity with a low-performance lens, from storage materials fabricated as multimode fibers [12,13], or even without imaging lenses [14,15] for an extremely compact system.…”

Holography for information storage and processing

“…This allows data pages to be retrieved with high fidelity using an inexpensive lens [30,31], or even without imaging lenses for an extremely compact system [32,33].…”

Noise-free readout in holographic storage by concave mirror

“…So noise is added onto the reproduced message. The noise caused by the superimposition can be suppressed by using the conjugated beam from phase conjugate mirrors (PCMs) [3][4][5] . But the low reflectivity and the long responding time of normal PCMs limit the application of the method by using PCMs.…”