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US 6,686,097 B2Granted
Reversible hologram fixation in photorefractive materials using incoherent ultraviolet light
AssigneeNone recorded
InventorAdil Lahrichi
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AssigneeNone recorded
InventorAdil Lahrichi
Estimating the term…
A holographic information storage and retrieval system provides an all-optical reversible method to fix information in doped or undoped photorefractive materials. The fixed information is sufficiently stable to provide long term archival storage over a period of decades or more and can be read out non-destructively by a coherent reference beam. Holograms recorded in a photorefractive material are fixed when the material is irradiated with incoherent ultraviolet light. Hence, the holograms are preserved indefinitely against erasure by a coherent beam and against dissipation in dark storage. Holograms, which are fixed in the photorefractive material with incoherent ultraviolet light, are also erased with incoherent ultraviolet light, thus making the process reversible.
A method of recording information in a nonlinear optical material, comprising the steps of:
A method of fixing a refractive index pattern in a nonlinear optical material, comprising the step of inducing a replica of the refractive index pattern by illuminating the nonlinear optical material with light from a plurality of ultraviolet light sources, the light having a cumulative intensity, the cumulative intensity being adequately high to produce the replica, the cumulative intensity further being below a level that would erase the replica and wherein the fixing and recording of the refractive index pattern are not overlapping.
Dependencies are inferred from the claim text.
From the US filing history. Foreign family members aren’t listed.
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Disturbance prevention or evaluation; Refreshing of disturbed memory data: circuits or methods to detect disturbed nonvolatile memory cells, e.g.…
Processes or apparatus for producing holograms: particular processing of hologram record carriers, e.g. for obtaining blazed holograms
Auxiliary circuits: disturbance prevention or evaluation; Refreshing of disturbed memory data
Using optical elements ; using other beam accessed elements, e.g. electron or ion beam: using information stored in the form of interference pattern
Term ended 1 Jun 2019 (estimated)
1. Field of the Invention
The present invention pertains to photorefractive materials that are used as holographic storage materials and, particularly, to methods and materials for optical fixation of information in the photorefractive materials for long term storage where the information can be read out non-destructively with a uniform beam, archived for long term storage, and erased if desired.
2. Description of Prior-Art
FIG. 1 shows a photosensitive electric charge, which moves from a trap by drift and diffusion under the influence of light and is captured at a different site within a storage material;
FIG. 2 shows a light interference pattern in a photorefractive storage material;
FIG. 3 shows an electronic charge distribution, a periodic space charge electric field, and a modulation of the index of refraction when two beams interact within a storage material;
Schematic System Diagram
FIG. 4 shows a holographic image recording and reading system 400 according to the present invention. System 400 is used to record and fix holograms in a storage material 402, as well as for reading the stored holograms, erasing the stored holograms, and for altering the optical recording and erasure characteristics of the storage material 402.
A laser source 404 emits a laser beam 406, which passes through a polarizer 408. The polarization of the laser beam 406 is usually set horizontal, but may include any combination of s-polarized and p-polarized components to provide linear, circular, or elliptically polarized light. The laser beam 406 passes through an optics assembly 410 comprising lenses, a spatial filter, and beam expander to provide an expanded laser beam 412. An iris 414 positioned behind the optics assembly 410 limits the diameter of the expanded laser beam 412 to a laser beam 416 of the desired size. The laser beam 416 impinges on a beam splitter 418 where it is divided into an object beam 420 and a reference beam 422. The reference beam 422 passes through an optional light attenuator 424, which is selectively used to control light intensity, as desired.