Static information storage and retrieval – Information masking – Diffraction
Reexamination Certificate
2000-03-08
2001-04-24
Mai, Son (Department: 2818)
Static information storage and retrieval
Information masking
Diffraction
C365S126000, C359S028000, C359S032000
Reexamination Certificate
active
06222755
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a holographic read-only memory, and more particularly to a compact holographic read-only memory that does not need to have any movable parts.
Optical storage systems have a number of distinct advantages over magnetic storage systems. For example, they have higher storage capacity than magnetic storage systems. Also, data access is done optically, without the need for contact.
One approach to access data optically is based on CD-ROMs and DVDs. Even movies are now available in these formats. Unfortunately, they have a number of weaknesses. For example, to access data, disks are typically spun around. The need for moving the disks before data can be accessed reduces data-access speed, and increases power consumption.
Another approach is based on holographic optical disks. They offer much higher storage capacity than the compact discs. However, again they have to rely on moving or spinning the disks, reducing data-access speed and increasing power consumption.
A third option is based on optical RAMs, as discussed in U.S. Pat. No. 5,696,714. An optical RAM is a non-holographic optical memory, with an array of imaging optics integrated on top of a storage medium. Fabricating such integrated optical devices, with imaging optics on top of a storage medium, can be both difficult and expensive.
It should be apparent from the foregoing that there is still a need for an apparatus and method to access information optically, with higher storage capacity than compact disks, lower power consumption than existing optical disks, and simpler manufacturing processes than optical RAMs.
SUMMARY
The holographic memory systems and methods provided by the present invention can be very compact, with high storage capacity and low power consumption. It can be also relatively easy to manufacture, without even the need for any lenses in the system.
In one embodiment, the holographic memory system for reading holograms includes a holographic storage medium with a number of shift-multiplexed holograms, a detector array to read the holograms, and an array of light sources, each generating a diverging reference beam for illuminating one of the holograms. In this embodiment, each hologram can be read as an image on the detector array by illuminating the hologram with one of the diverging reference beams. Thus, to read different holograms, this embodiment does not need any lenses, and the storage medium does not have to be moved.
In another embodiment, the holographic memory system for recording shift-multiplexed holograms includes a holographic storage medium for recording the holograms, a data mask, an array light sources, and a converging signal beam. Each light source generates a converging reference beams for illuminating an area of the storage medium. The converging signal beam can be tilted to cover different areas on the storage medium. In this embodiment, each hologram is created through illuminating an area of the storage medium by both the converging signal beam and one of the converging reference beams. Before the signal beam converges to that area, it propagates through the data mask, which stores data of the corresponding hologram electronically.
In the above embodiments, holograms are read through diverging reference beams, and recorded through converging beams. Another embodiments can be with converging reference beams for reading holograms, and diverging reference beams for recording holograms. The reference beams are non-plane waves, and can be spherical waves or cylindrical waves.
Since different holograms can be accessed by activating different reference beams, the information access speed of the present invention can be very high. Also, since there is no need for mechanically moving the holographic medium to gain access to information in different holograms, the power consumption can be very low. Thus, the present invention can have very fast access speed, very low power consumption, and can also be relatively easy to manufacture.
Note that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter. Also, the features and advantages described in the specification are not all-inclusive. Other aspects and advantages of the present invention will become apparent to one of ordinary skill in the art, in view of the specification, which illustrates by way of example the principles of the invention.
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Feng Zhao and Koichi Sayano, “Compact read-only memory with lenses phase-conjugate holograms,” Optics Letters, vol. 21, No. 16, pp. 1295-1297, Aug. 15, 1996.
An Xin
Mok Fai Ho
Psaltis Demetri
Zhou Gan
Fliesler Dubb Meyer & Lovejoy LLP
Holoplex Inc.
Mai Son
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