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WO2009051775A1 - Système optique et procédé pour une recherche adressable de contenu et une récupération d'informations dans un système de stockage de données holographiques - Google Patents

Système optique et procédé pour une recherche adressable de contenu et une récupération d'informations dans un système de stockage de données holographiques Download PDF

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Publication number
WO2009051775A1
WO2009051775A1 PCT/US2008/011844 US2008011844W WO2009051775A1 WO 2009051775 A1 WO2009051775 A1 WO 2009051775A1 US 2008011844 W US2008011844 W US 2008011844W WO 2009051775 A1 WO2009051775 A1 WO 2009051775A1
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WO
WIPO (PCT)
Prior art keywords
detector
correlation signal
correlation
reflector
storage location
Prior art date
Application number
PCT/US2008/011844
Other languages
English (en)
Inventor
David A. Waldman
Joby Joseph
Christopher J. Butler
Original Assignee
Stx Aprilis, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Stx Aprilis, Inc. filed Critical Stx Aprilis, Inc.
Publication of WO2009051775A1 publication Critical patent/WO2009051775A1/fr

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Classifications

    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
    • G11B7/0065—Recording, reproducing or erasing by using optical interference patterns, e.g. holograms
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/13—Optical detectors therefor
    • G11B7/131—Arrangement of detectors in a multiple array
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1362—Mirrors

Definitions

  • Holographic data storage facilitates the recording of information volumetrically at substantially high areal densities compared to other data storage technology that utilize removable media. For instance, values in the range of about 200 to 500 Gbits/inch 2 have already been demonstrated.
  • CD, DVD, and Blu-ray optical storage technology are limited to one to few layers with storage density of less than about 0.45, 2.6 and 16 Gbits/inch 2 per layer, respectively, and magnetic tape is limited to 1 to 2 layers at less than about 1 Gbit/inch 2 per layer.
  • volume holographic storage can also provide massive parallel search capability through the use of optical correlation methods based upon two-dimensional (2 -D) cross- correlation between two images at a hardware level, such as disclosed by B. J. Goertzen et al., Volume holographic storage for large relational databases, Optical Engineering, 35(7), pp. 1847-1853, 1995.
  • the previously disclosed apparatuses for optical correlation-based search of information stored as volume holograms require the use of a plurality of independent storage volumes, or require rotation of the storage volume and/or the object or reference beams, or require an optical system comprising a separate detector which operates as a correlation plane detector that is located along the optical axis of the incident Reference light used to record the holograms.
  • the correlation plane detector is used for measuring the intensity of a signal produced by an optical correlation of a search argument with the information that was previously stored as one or more holograms, wherein said holograms may be recorded so as to be multiplexed co-locationally in a storage location or volume, or multiplexed in partially or substantially overlapping storage locations or volumes, or multiplexed in a plurality of independent spatially separated volumes, or combinations thereof.
  • previously described devices do not provide a compact, simple holographic media drive capable of performing writing, reading and content-search operations.
  • a requirement for two separate and distinct detectors, one for reconstruction of the content information stored as holograms and the other for detecting search results for presence of said information, can result in a holographic system design that is substantially more complex and costly, unnecessarily redundant in circuitry, and requires more space and power for operation.
  • the present invention relates to holographic drive architecture and methods of use thereof.
  • the present invention can be used to read, record or search holographic data recorded by employing various multiplexing methods such as in-plane shift, out-of-plane shift, planar-angle, azimuthal (peristrophic), tilt (out-of-plane angle), wavelength, phase, spatial, or combinations thereof.
  • the present invention eliminates the requirement for a second distinct detector by using the data-readout detector for both address and content recall.
  • the present invention is an apparatus for writing, reading or content-searching holographic data.
  • the apparatus comprises a spatial light modulator (SLM) configured to generate a search argument beam in a content search mode or an object beam in a write mode; a first lens element, disposed in the optical path of the search argument beam or the object beam, configured to direct the search argument beam or the object beam at a selected storage location in a holographic recording media (HRM); an optical element configured to direct a reference beam at the selected storage location in the HRM in a read mode or write mode.
  • the object beam and the reference beam interact at the selected storage location in the HRM, thereby generating an interference pattern.
  • the search argument beam is directed at the selected storage location in the HRM, thereby generating a correlation signal beam in the event of a non-zero correlation.
  • the reference beam is directed at the selected storage location in the HRM, thereby generating a reconstructed object beam.
  • the apparatus further includes a detector configured to detect the correlation signal beam or the reconstructed object beam; and a second lens element, disposed in the optical path of the reconstructed object beam or the correlation signal beam, configured to direct the correlation signal beam or the reconstructed object beam at the detector.
  • the present invention is an apparatus for writing, reading or content-searching holographic data.
  • the apparatus comprises a spatial light modulator (SLM) configured to generate an object beam in a write mode or a search argument beam in a content search mode; a first lens element, disposed in the optical path of the object beam or the search argument beam, configured to direct the object beam or the search argument beam at a selected storage location in a holographic recording media (HRM); and an optical element configured to direct a reference beam at the selected storage location in the HRM in a read mode or write mode.
  • SLM spatial light modulator
  • HRM holographic recording media
  • an optical element configured to direct a reference beam at the selected storage location in the HRM in a read mode or write mode.
  • the object beam and the reference beam interact at the selected storage location in the HRM, thereby generating an interference pattern.
  • the search argument beam is directed at the selected storage location in the HRM, thereby generating a correlation signal beam in the event of a non-zero correlation
  • the reference beam is directed at the selected storage location in the HRM, thereby generating a reconstructed object beam.
  • the apparatus further includes a readout detector configured to detect the reconstructed object beam; a second lens element, disposed in the optical path of the reconstructed object beam, configured to relay the reconstructed object beam to the readout detector; a correlation detector configured to detect the correlation signal beam; and a reflector, disposed in the optical path of the correlation signal beam, configured to redirect the correlation signal beam at the correlation detector.
  • the present invention is a method of operating a device configured to at least read and content-search holographically stored information, said device comprising a detector.
  • the method comprises: generating a search argument beam; directing the search argument beam at a selected storage location in a holographic recording media (HRM) having holographically stored information recorded thereon; and if one or more correlation signal beams are generated: directing the one or more correlation signal beams at the detector; and detecting the one or more correlation signal beams.
  • HRM holographic recording media
  • the method comprises: generating a reference beam; directing the reference beam at a selected storage location in the holographic recording media (HRM) having holographically stored information recorded thereon, thereby generating a reconstructed object beam; directing the reconstructed object beam at the detector; and detecting the reconstructed object beam.
  • HRM holographic recording media
  • the present invention is a method of operating a device configured to at least read and content-search holographically recorded data, said device comprising a detector.
  • the method comprises: generating a search argument beam; directing the search argument beam at a storage location in a holographic recording media (HRM) having holographically stored information recorded thereon; and if one or more correlation signal beams are generated: directing the one or more correlation signal beams at a first reflector and a second reflector, said first and second reflectors configured together to direct the correlation signal beams at the detector; and detecting the correlation signal beams.
  • HRM holographic recording media
  • the method comprises: generating a reference beam; directing the reference beam at the selected storage location in the holographic recording media (HRM) having holographically stored information recorded thereon, thereby generating a reconstructed object beam; directing the reconstructed object beam at the detector without reflecting from the first or the second reflectors; and detecting the reconstructed object beam.
  • HRM holographic recording media
  • the present invention is a method of operating a device configured to at least read and content-search holographically stored information, said device comprising a readout detector and a correlation detector.
  • the method comprises: generating a search argument beam; directing the search argument beam at a selected storage location in a holographic recording media (HRM) having holographically stored information recorded thereon; and if one or more correlation signal beams are generated: directing the one or more correlation signal beams at a reflector, thereby redirecting the correlation signal beams at the correlation detector; and detecting the one or more correlation signal beams.
  • HRM holographic recording media
  • the method comprises: generating a reference beam; directing the reference beam at the selected storage location in the HRM having holographically stored information recorded thereon, thereby generating a reconstructed object beam; directing the reconstructed object beam at the detector, without reflecting said reconstructed object beam from the reflector; and detecting the reconstructed object beam.
  • a single detector is used to detect both the reconstructed object beam and the correlation signal beam.
  • FIG. IA is a schematic representation of a process of recording an interference patter between two coherent beams.
  • FIG. IB is a schematic representation of a process of content searching of a recorded hologram using an information-encoded search argument beam.
  • FIG. 2 is a schematic diagram of a 4-f holographic system.
  • FIG. 3 is a schematic diagram of one embodiment of a device of the present invention.
  • FIG. 4 is a schematic diagram of another embodiment of a device of the present invention being operated in reading mode.
  • FIG. 5 is a schematic diagram of another embodiment of a device of the present invention being operated in reading mode.
  • FIG. 6 is a schematic diagram of the device shown in FIG. 4 being operated in a content search mode.
  • FIG. 7 is a schematic diagram of another embodiment of a device of the present invention.
  • FIG. 8 is a schematic diagram showing a detail of the embodiments shown in FIGs. 5-7.
  • FIG. 9 is a schematic diagram showing a detail of the embodiments shown in FIGs. 4-6.
  • FIG. 10 is a perspective view of a device suitable for practicing the present invention.
  • FIG. 11 is a diagram illustrating a superpixel indexing scheme employed by an embodiment of the present invention.
  • Optical correlation search in volume holographic data storage systems can be carried out using a conventional 4-f recording/reading geometry among others.
  • FIG. IA is a schematic representation of a process of recording an interference pattern between two coherent beams in a material.
  • FIG. IB is a schematic representation of a process of content searching of a recorded hologram using an information-encoded search argument beam.
  • SLM Spatial Light Modulator
  • the spatial 2-D Fourier spectrum of dl(xl,yl) is obtained at the back focal plane of the said lens yielding Dl(x2,y2).
  • An additional reference wave Rl (x2, y2), coherent with the laser beam path used to form the object beam, is propagated so as to interfere with the 2-D Fourier spectrum of the 2-D data page signal, Dl, of a first modulated data page.
  • a holographic recording medium placed at or near the Fourier plane records, within the volume of the media, a signal or wavefront representing the interference pattern formed between Rl and Dl .
  • the term "near” refers herein to a distance before or after the Fourier plane, wherein said distance can be up to about 30% of the value of the focal length of the lens.
  • the interference pattern signal has the intensity represented by
  • the recording in one class of recording material, occurs by way of photopolymerization reactions that create chemical segregation of chemical structures having different refractive indices thereby forming a microstructure that exhibits refractive index modulation corresponding to presented interference pattern.
  • Other classes of materials are contemplated for use as recording materials, such as ,by way of example, photorefractive crystals, materials comprising photochromic compounds, photorefractive polymers, and the like.
  • the second and the third data pages each is a signal having amplitude represented as D2(x2, y2) and D3(x2, y2), respectively.
  • a search pattern signal also referred to herein as a search argument signal
  • s(xl ,yl ) displayed on a search pattern encoding device such as an SLM
  • the 2-D Fourier transform S(x2,y2) is presented to the locations of one or more recorded holograms in the media positioned at or near the back focal plane of the lens.
  • the signal S(x2,y2) is multiplied (diffracted) by the structure formed from the interference pattern signal having intensity
  • the present invention also contemplates structures formed from an interference pattern signal having intensity
  • the multiplied image H(x2,y2) is relayed by a second Fourier transform lens, such as,by way of example, in a 4-f imaging system, two signals result, the correlation of s(xl,yl) and d(xl,yl) and the convolution of s(xl,yl) and d(xl,yl) plus an attenuated search signal.
  • the resultant signal will be a modified form of H(x2,y2).
  • a parallel search can preferably be executed when a plurality of holograms storing information are recorded co-locationally in a storage location.
  • the correlation of a search argument with a plurality of co-locationally multiplexed holographic gratings can produce a plurality of search result optical signals simultaneously.
  • the intensity of each said optical signal is related to the strength of the correlation between the search argument and the information stored as holograms.
  • the plurality of holograms storing information are recorded using at least dual multiplexing methods, so as to provide for increasing the degree of parallel search of the stored information by increasing the number of co- locationally multiplexed holograms in a storage location.
  • Certain embodiments of the apparatuses and methods described herein eliminate the requirement for a second distinct detector by using the content readout detector for both Address and Content recall.
  • Typical systems include a spatial light modulator (SLM) (1), that encodes the incident light beam (19) from light incident upon SLM (1) from a source such as a laser (not shown) to generate object beam (20), lens elements (2) and (3) that have common optical axis (25) and are located at distances of focal length fl and f2 from the SLM (1) and digital detector (4), respectively, and the media (5) that may be a disk, card, cube, cylinder or other suitable form factor and which comprises, by way of example, substrates (6) and (7) that may be optional, and a recording material (8) that may, by way of example, be a photopolymerizable material, photorefractive material, photochromic material, combinations thereof and the like.
  • SLM spatial light modulator
  • Media (5) having active material without substrates for recording holograms is also contemplated by the present invention.
  • the generated object beam (2) for recording is depicted as amplitude modulated pattern.
  • the said object beam for recording may be phase modulated, such as by 0, Il phase or other suitable phase modes.
  • Figure 2 depicts recording of transmission holograms, the present invention is not restricted to transmission holograms.
  • Other suitable recording geometries are also contemplated such as for reflection holograms, wherein the Object and Reference beams are incident to the media from directions that are oriented with respect to opposing sides of the media, or for recording holograms in 90 degree geometry whereby the angle between the Object beam (20) and the Reference beam (10) is equal to 90 degrees.
  • optical recording/reading imaging systems are also contemplated, such as 6-f or 8-f systems or the like that may be used for improved Signal-to-Noise (SNR) for content retrieval, or other systems that are non 4-f (i.e. fl ⁇ f2) and which, by way of example, can provide for magnification or demagnification that may be used to match pixel dimensions corresponding to one or more pixels of the SLM to pixel dimensions of one or more pixels of the digital detector (i.e. CMOS), or phase conjugate systems, and the like.
  • SNR Signal-to-Noise
  • CMOS digital detector
  • phase conjugate systems and the like.
  • an aperture element (15) may be located at or near the front surface of the media (5), so as to restrict the illuminated region at a storage location such that the areal density is optimized with respect to bit-error-rate (BER) and other parameters.
  • Aperture element (see element (15) in FIG. 3) may alternatively be integral to the media, such as a layer or surface of the media that may, by way of example, be electrically or magnetically active, such as due to an electroclinic effect from a surface or intermediate layer, and may be addressable for different locations across the area of the media.
  • FIG. 2 are a group of positions of a reference beam, depicted as bounded by beam (9) and beam (10). This group of positions includes angles between beams (9) and (10).
  • Reference beam (9) and beam (10) are separated by angle ⁇
  • Reference beam (9) is depicted to represent a reference beam that is separated by angle increment, ⁇ , from the incident angle of reference beam (10) with respect to the optical axis (25)of signal beam (20).
  • reference beam (9) can lie in a plane formed by reference beam (10) and optical axis (25) or, alternatively, can lie out of this plane.
  • Plane (21) is the Fourier transform plane of lens element (2). Specifically, FIG.
  • FIG. 3 is a schematic diagram of one embodiment of an apparatus of the present invention suitable for writing and/or reading a holographic recording media (HRM), as well as content-searching holographic information recorded in an HRM.
  • the device shown in FIG. 3 comprises SLM 1, lens elements 2 and 3, readout detector 4 for detecting reproduced holograms, optical element 32 (which can be a reflector or a mirror, e.g., an ellipsoidal mirror), and correlation detector 55.
  • Lens elements 2 and 3 can each include one or more lenses or any other optical elements suitable for refracting, reflecting or diffracting light beams.
  • optical axis (25) may be folded to provide for further compactness of the optical system or for other desirable features such as incorporation of optical relay systems, in which case, for example, the optical axis of lens element (2) may be folded so as to be oriented at an angle of 90 degrees from the optical axis of lens element (3) and may be folded again if desirable for the optical system.
  • HRM 5 which includes a first aperture element 15, depicted as a front aperture element, a second aperture element 16, depicted as a rear aperture element, and wherein HRM 5 comprises recording material 8.
  • First aperture element 15 and second aperture element 16 can include a reflecting surface.
  • FIG. 3 schematic represents all three possible modes of operation of the device shown.
  • beam 19 is encoded by SLM 1 into Object beam 20, which can also be a search argument beam during searching operations.
  • Object beam 20 intersects and overlaps with a coherent Reference beam (10), that is at an angle ⁇ with respect to optical axis (25), at the recording material (8) of HRM (5).
  • Any known method of holographic image multiplexing can be employed during the recording operation, which, by way of example, can be multiplexing methods such as shift, planar-angle, azimuthal (peristrophic), out-of- plane tilt, wavelength, phase, spatial, or combinations thereof.
  • Reference beam 10 is directed at HRM 5, thereby generating reconstructed Object beam 20', relayed or imaged at readout detector 4 by lens element 3.
  • Optical element (32) and aperture element (16) are depicted in the said writing and/or reading embodiments to reflect the transmitted or undiffracted Reference beam (10') light, respectively, such that it can exit the optical system during recording or reading operations, or otherwise not be propagated by lens element (3) to detector (4) during reading operations.
  • rear surface 161 of the rear aperture element (16) may be blackened or otherwise darkened to prevent said light (10') from entering media (5) or from being propagated by lens element (3) to detector (4).
  • the said transmitted or undiffracted Reference beam (10') not impinge upon the media (5) so as to re-enter the recording material (8) or be redirected into the detector (4).
  • encoded beam 20 is a search-argument beam, which generates correlation signal beam 10' upon diffracting from a hologram recorded in HRM 5.
  • Correlation signal beam 10' reflects off of optical element (reflector) 32, is redirected to second aperture element 16, which, in the embodiment shown, includes a reflector, and is thereby directed at correlation detector 55.
  • correlation detector 55 can be mounted so that its working surface is orthogonal to a working surface of readout detector (4).
  • FIG. 4 An alternative embodiment of a device of the present invention is shown in FIG. 4.
  • This embodiment includes a flip mirror 35.
  • Flip mirror 35 can be mounted directly behind HRM 5 along the line of the forward-propagating direction of Reference beam 10 (i.e. beam 10')
  • Flip mirror 35 operates to redirecting the correlation signal beams to a correlation signal detector 55.
  • Flip mirror 35 can be a flat reflector surface, or curved reflector surface, or can comprise a grouping of segmented facets that are each reflecting surfaces and can have inclination angles with respect to a flat surface.
  • Flip mirror 35 can be moved by actuator or other motive device or otherwise operated to be positioned into a reflecting position for redirecting correlation signal beams to correlation detector 55 during searching operation.
  • correlation signal detector 55' can be used instead of correlation detector 55.
  • Correlation detector 55' is disposed alongside readout detector 4 and is an extension of readout detector 4, as shown schematically in FIG. 4.
  • correlation signal detector 55' and readout detector 4 may be integrated into a larger detector element.
  • This larger detector element can comprise detector elements for reading operations and, separately, detector elements for searching operations, wherein the types and/or shapes of detector elements for the two operations may be different.
  • FIG. 5 and FIG. 6 Another embodiment of a device of the present invention is shown in FIG. 5 and FIG. 6.
  • This embodiment of the device can used for reading, writing, or content-searching holographically stored information.
  • the device shown in FIG. 5 and FIG. 6 can employ a single detector to both detect a reconstructed holographic image and to detect one or more correlation signals.
  • the device shown in FIG. 5 and FIG. 6 comprises SLM 1, lens elements 2 and 3, readout detector 4 for detecting reproduced holograms, and optical element 32 (which can be a reflector or a mirror, e.g., an ellipsoidal mirror). Also shown is beam dump 36.
  • Optical element 31 which can be a reflector (a mirror) is movable and can be slidably disposed in the optical path of beam 20' and/or reflected portions of beam 10'. (See below the discussion of FIG. 6 for more details.)
  • Lens elements 2 and 3 can each include one or more lenses or any other optical elements suitable for refracting, reflecting or diffracting light beams.
  • HRM 5 which includes a first aperture element 15, a second aperture element 16, and recording material 8.
  • Second aperture element 16 can include a reflecting surface.
  • FIG. 5 illustrates the use of the depicted device in the reading operation mode. It is understood that the reading operation mode can be employed to read holographically stored information recorded using various multiplexing methods or combinations thereof.
  • reference beam 10 is directed at HRM 5 at an angle ⁇ to optical axis of 25 of the device, thereby generating reconstructed object beam 20', which is relayed to detector 4 by lens element 3.
  • Undiffracted Reference beam 10' is reflected from optical element (mirror) 32, is thereby redirected at second aperture element 16, which, in the embodiment shown, includes a reflector, and is then directed to beam dump 36.
  • second aperture element 16 can comprise the beam dump, in which case, it does not operate to redirect the once reflected light from optical element 32.
  • FIG. 6 illustrates the use of the same device for operation of content searching mode (also referred to as "address retrieval mode").
  • SLM 1 encodes beam 19, thereby generating a search argument beam 22.
  • Search argument beam 22 is relayed by lens element 2 at a selected storage location in HRM 5 having holographically stored information.
  • search argument beam 22 at least partially diffracts, thereby creating correlation signal beam 10'.
  • the undiffracted portion of search argument beam 22, shown as beam 22' passes through HRM 5 and is blocked from propagating toward detector 4 by optical element 31. As shown in FIG.
  • element 31 can be moved into the optical path of search argument beam 22 (and, correspondingly, into the optical path of undiffracted portion 22' of beam 22) during the search mode operation.
  • a group of correlation signals 10' generated by the correlation of the image of search argument beam 22 with the holographically stored information content in a group of multiplexed holograms stored in a selected storage location, can be relayed simultaneously by lens element (3) to detector (4) as a group of beams 10".
  • a parallel search of holographically stored information with search argument beam 22 is provided.
  • correlation signal beam 10' the diffracted portion of search argument beam 22 is shown as correlation signal beam 10'.
  • Correlation signal beam 10' is directed at reflector 32 (shown in FIG. 6 as an ellipsoidal mirror) and is then redirected at element 31.
  • Element 31 includes reflector 33 that is configured to redirect correlation signal beam 10' at lens element 3.
  • Lens element 3, in rum relays correlation signal beam 10' (as beam 10") to detector 4.
  • reflector element (32) can be rotated or tilted slightly when in the Address Retrieval (i.e. content-search) mode, thereby providing for the correlation signal beam to be directed towards reflective element (31).
  • FIG. 7 Another embodiment of a device that can be used to practice the present invention is shown schematically in FIG. 7.
  • the device of FIG. 7 is similar to the device shown in FIG. 5 and FIG. 6 and comprises SLM 1 that encodes beam 19, thereby generating a search argument beam 22.
  • Search argument beam 22 is directed by lens element 2 at HRM 5.
  • search argument beam 22 at least partially diffracts by interaction with HRM 5, thereby creating correlation signal beam 10'.
  • the undiffracted portion of search argument beam 22, shown as beam 22' passes through HRM 5 and is blocked from propagating toward detector 4 by optical element 31.
  • FIG. 7 is similar to the device shown in FIG. 5 and FIG. 6 and comprises SLM 1 that encodes beam 19, thereby generating a search argument beam 22.
  • Search argument beam 22 is directed by lens element 2 at HRM 5.
  • HRM 5 a successful search operation
  • search argument beam 22 at least partially diffracts by interaction with HRM 5, thereby creating correlation signal beam 10'.
  • element 31 can be moved into the optical path of search argument beam 22 (and, correspondingly, into the optical path of undiffracted portion 22' of search argument beam 22).
  • the diffracted portion of search argument beam 22 is shown as correlation signal beam 10'.
  • Correlation beam 10' is directed at reflector 32 and is then redirected at element 31.
  • reflective element 32 shown in FIG. 7 is a flat or segmented mirror.
  • Reflective element 32 of FIG. 7 can be rotated or tilted to accommodate correlation signal beams 10' generated during content search operations of holographically stored information recorded using various multiplexing techniques.
  • the reflective surface (33) and the reflective element (32) each comprise planar surfaces that are shown as inclined with respect to the optical axis (25), such as can be used for dual multiplexed holograms recorded co-locationally in a storage location using planar-angle in combination with tilt multiplexing methods.
  • a group of correlation signals 10' generated by the correlation of the image of search argument beam 22 with the holographically stored information in a group of multiplexed holograms in a selected storage location in HRM 5, can be relayed simultaneously by lens element (3) to detector (4) as a group of beams 10", thereby providing for parallel search of the holographically stored information with search argument beam 22.
  • element 31 can include reflector 33 which is configured to redirect correlation signal beam 10' at lens element 3.
  • Lens element 3 in turn, relays correlation signal beam 10' to detector 4 as beam 10".
  • optical elements (31) and (32) may be combined into one optical element
  • elements (32) and (31) are mirrors.
  • the devices shown include lens elements (2) and (3), which may each comprise a grouping of optical components (i.e. elements) and may optionally be coated for anti reflection properties, wherein the numerical aperture of lens elements (2) and (3) are typically in the range of about 0.2 to 0.8.
  • optical axis (25) may be folded to provide for further compactness of the optical system or for other desirable features such as to incorporate optical relay systems, in which case, by way of example, the optical axis of lens element (2) may be folded so as to be oriented at an angle of 90 degrees from the optical axis of lens element (3) and may be folded again if desirable for the optical system.
  • the recording material (8) may be located at intermediate distances from the Fourier transform plane of lens element (2), such as for recording at fractional Fourier transform planes.
  • the media (5) may be rotated about the shown y-axis to angles such that the recording plane of the media (5) is non parallel to the x-y plane and non perpendicular to the optical axis (25), such as for purposes of reducing the slant angle of recorded holograms.
  • Preferred embodiments may feature a 4-f type optical recording/reading geometry for 1 : 1 imaging that utilizes dual multiplexing methods comprising, by way of example, planar-angle and azimuthal multiplexing or planar-angle and tilt (out-of-plane angle) multiplexing.
  • optical recording/reading geometries are also contemplated, such as 6-f or 8-f optical recording/reading systems or the like that may be used for improved Signal-to-Noise (SNR) for content retrieval (see Waldman and Butler in WO 2004/112045 A2, the entire teachings of which are incorporated herein) or others that are non 4-f (i.e./ / ⁇ fi) and which, by way of example, can provide for magnification or demagnification that may be used to match pixel dimensions corresponding to one or more pixels of the SLM to pixel dimensions of one or more pixels of the digital detector (i.e. CMOS), or phase conjugate systems, and the like.
  • SNR Signal-to-Noise
  • CMOS digital detector
  • phase conjugate systems and the like.
  • FIG. 5 can be used to modify the traditional 4-f optical recording/reading geometry such as depicted in FIG. 2 so as to operate in three distinct modes: Recording mode, Address Retrieval mode (i.e. content-based search or "content search"), and Content Retrieval mode (i.e. address-based search).
  • Recording mode i.e. content-based search or "content search”
  • Content Retrieval mode i.e. address-based search
  • the Recording (or write) mode provides for the recording of object information or data in a holographic media (5) shown in FIG. 5 and is also applicable to the device shown in FIG. 3. Recording is carried out by presenting the media with an encoded Object beam (20), propagated by lens element (2) from SLM (1), and a Reference beam (10), also from a light source such as a laser (not shown). Reference beam (10) is shown to be incident at an oblique external angle ⁇ with respect to optical axis (25) of the depicted 4-f system, said Object and Reference beams are substantially coherent and are directed to the media so as to overlap in the volume of the recording location and thereby form an interference pattern in said volume.
  • optical element (31) of the present invention is not present in the optical path while the system operates in Recording mode but can be moved in or out of the optical path for different operating modes of the system.
  • optical element (32) is a reflector that may or may not be present during Recording mode.
  • the construction and placement of optical element (32) should preferably not interfere with recording of holograms in the traditional 4-f geometry or other suitable optical recording geometries.
  • Preferred embodiments provide for the Reference beam (10) to escape the optical system once it has passed through HRM (5) during recording mode, and, consequently, the construction and placement of optical element (32) should provide for ability of Reference beam (10) to exit from the optical system during Recording mode.
  • said exit of the reference beam (10) during recording is provided by the use of a rear (second) aperture element (16) located at or near the rear surface of the media (5).
  • the undiffracted reference beam 10" (see FIG. 5) is reflected from optical element (32) and becomes incident on the rear surface of the rear aperture element (16).
  • Rear surface 161 of aperture element (16) reflects the light at an angle such that the undiffracted Reference beam 10' light can exit the system during recording or otherwise not be propagated by lens element (3) to detector (4).
  • beam dump 36 can be eliminated.
  • rear surface 161 of the rear (second) aperture element (16) may be blackened or otherwise darkened to prevent undiffracted beam 10' from entering recording material (8) of media (5) or from being propagated by lens element (3) to detector (4).
  • undiffracted reference beam 10' may reflect from optical element (32) to aperture element (16), or to another light absorbing element located between reflector (32) and media (5), such that (16) or the alternative light absorbing element can operate to absorb the light or otherwise prevent it from re-entering the recording material (8) of media (5).
  • second aperture element (16) or the light absorbing element may alternatively be integral to the media, such as a layer or surface of the media that may, by way of example, be electrically or magnetically active, such as due to an electroclinic effect from a surface or intermediate layer, and may be addressable for different locations across the area of the media.
  • the undiffracted reference beam 10' not impinge upon the media (5) so as to re-enter the recording material (8) or be redirected into the detector (4).
  • the reflective optical element (32) may be constructed with apertures.
  • the placement, size, and shape of the apertures in reflective optical element (32) can be determined by the angle of the incident Reference beam (10) for all multiplexed holograms.
  • the apertures provide for the undiffracted Reference beam 10' to exit the system during Recording mode or otherwise not be propagated or redirected by lens element (3) to detector (4).
  • undiffracted beam 10' can be collected by a beam trap 36.
  • FIG. 5 depicts the optical paths of the beams as they appear during the operation of the shown device in the reading mode (also known as Content-Retrieval mode).
  • FIG. 3 shows a device having a similar optical architecture.
  • the reference beam (10) is incident on the media (5) at a storage location at an incident angle ⁇ , with respect to optical axis (25), consistent with the incident angle of the Reference beam (10) during recording of the one or more holograms in the storage location.
  • the Reference beam angle 6? during Recording mode may be different for each hologram recorded in a storage location such as for the case of planer-angle multiplexing.
  • the Reference beam angle ⁇ during Content Retrieval mode will also be different for each different hologram reconstructed in said storage location.
  • the Reference beam angle # during Content Retrieval mode may not be different for each hologram recorded in a storage location, such as when dual multiplexing methods are used.
  • Retrieval mode may be adjusted to optimally achieve the Bragg condition, so as to compensate for (i) volume shrinkage of the holograms such as may occur for holograms recorded in photopolymerizable materials or (ii) temperature changes between when the hologram(s) was recorded and reconstructed for Content retrieval or (iii) change in wavelength of the laser from the wavelength at the time of recording the hologram(s), or change in tilt of the media with respect to the Reference beam (10) at the time of recording the hologram(s) such as may occur when the media is removable from the system, or combinations thereof.
  • the reference wave diffracts from the Bragg-matched grating in the holographic media thereby reconstructing the Fourier spectrum of the recorded object.
  • optical elements (31) and (32) can be identical to the requirements stated above for the recording mode.
  • optical elements (31) and (32) are both inserted into the optical system used for holographic data storage as shown, by way of example, in FIG. 6.
  • Address Retrieval is implemented by presenting a storage location(s) in the media with a search argument propagated by lens element (2) from SLM (1).
  • the search argument is encoded by SLM (1) and depicted as bounded by ray bundle (22) in
  • the search argument encoded by the SLM (1) may comprise a grouping of pixels arranged in a contiguous manner over an array equal to the entire SLM array size of m rows by n columns of the m x n SLM.
  • the search argument may comprise a grouping of contiguous pixels arranged in an area that is less than the entire m x n array size of the SLM, such as depicted by bounded rays (22) in FIG. 6.
  • the pixels may be arranged in a contiguous manner in complete rows or columns but in fewer than m rows and/or n columns, or, alternatively, may be arranged in a contiguous manner but in incomplete rows and columns.
  • the search argument encoded by m x n SLM (1) may comprise a grouping of pixels arranged in a non-contiguous manner.
  • the smallest area fraction of the m x n array size of SLM (1) that may be used for the search argument can be influenced by the manner in which the holograms are recorded, for example amplitude-modulated holograms and phase modulated holograms may have different size of the smallest area of the search argument usable for content searching mode of operation.
  • the resultant signal-to-noise characteristics of the cross-correlation noise, as well as the multiplexing methods used in recording can also affect the smallest usable area of the search argument usable for content searching mode of operation.
  • the Fourier spectrum of the search argument is formed by the transform lens element (2).
  • the transformed image of the search argument is directed (relayed) towards a storage location on the media comprising at least one recorded hologram, wherein the at least one hologram may be located at the Fourier plane of lens element (2) or, alternatively, at a fractional Fourier plane.
  • a storage location comprises a plurality of multiplexed holograms, and even more preferably a plurality of co-locationally multiplexed holograms such as by combination of planar-angle and tilt multiplexing or planar-angle and azimuthal multiplexing wherein storage locations are additionally spatially multiplexed.
  • Each hologram(s) in the selected storage location of the media that is illuminated with the said image of the search argument and which comprises content correlating at least in part with the search argument, diffracts light in a direction and having a wavefront consistent with its own reference beam orientation and wavefront used during recording of the said hologram(s).
  • An array of search generated Reference beams is produced from the multiplexed holograms when correlation of the stored information in the holograms occurs with the image of the search argument, each said search generated Reference beam(s) having intensity proportional to the extent of the correlation of the image of said search argument and the information content of the hologram(s), as well as the size of the search argument.
  • Said array may be 1-D, such as when single multiplexing methods (e.g.
  • planar-angle multiplexed are used to record the holograms, or optionally may be 2- D, such as when dual multiplexing methods (see above described methods such as planer-angle in combination with azimuthal or planar-angle in combination with tilt) are used to record the holograms.
  • the said array of search generated Reference beams reflects off element (32) and is directed towards the surface of optical element (31).
  • optical element (31) operates to redirect the array of search generated Reference beams through the inverse Fourier transform lens element (3) towards the detector (4).
  • FIG. 6 shows schematically, for simplicity, one of the said array of correlation signal beams (10') that corresponds to the correlation signal from one of the multiplexed holograms in the selected storage location, said correlation signal propagated through lens element (3) and relayed towards the detector (4) as correlation signal beams (10")-
  • a grouping of said correlation signals generated by the correlation of the image of the search argument with the information content in a grouping of multiplexed holograms in the selected storage location, can be propagated simultaneously through lens element (3) so as to be directed simultaneously to the detector (4).
  • the rear surface of optical element (31) (i.e. the surface facing lens element 3) is constructed so that the array of search generated reference beams is reflected by element (31) towards lens element (3) so as to remain spatially separated and optionally focused on the detector (4).
  • detector (4) will detect a grouping of resolved correlation signal(s) (10"), each corresponding to a hologram recorded with a different reference beam.
  • the spatially separated array of correlation signal beams may not all be ideally focused on detector (4). This effect is due to the increased path length resulting from introduction of optical elements (31) and (32) into the optical configuration. However, all beams in such an array will intersect the detection plane of detector (4).
  • a plurality of correlation signal beams, diffracted from a storage location having a large multiplexing factor for its recorded holograms, can all be simultaneously detected using one short-time pulse of light, such as from a pulsed laser.
  • one short-time pulse of light such as from a pulsed laser.
  • the rear surface of optical element (31) (i.e. the surface facing lens element 3) can include a reflective surface (33) having curvature and can be contiguous or segmented. Segmented surface is preferred for the apparatus of the present invention for dual multiplexed holograms recorded co-locationally in a storage location using planar-angle in combination with azimuthal multiplexing methods.
  • reflective surface (33) is a surface having curvature when reflective element (32) comprises a surface having curvature, or said surface (33) is a surface having a grouping of surfaces each having curvature when reflective element (32) comprises a surface having curvature, or said surface (33) comprises a grouping of planar surfaces on a surface having curvature when said element (32) comprises a segmented surface having a grouping of planar surfaces on a surface having curvature, or said surface (33) is a planar surface when said element (32) comprises a planar surface.
  • reflective surface (33) can be a convex or concave curved surface or aspherical surface when reflective element (32) comprises a concave elliptical surface or ashperical surface.
  • the correlation signal beams (10') directed from reflective element (32) having concave elliptical surface will focus at a position(s) located prior to focal position F2 of the elliptical surface, namely before reflective surface (33), wherein the distance between the focus position of the said Reference beam(s) (l ⁇ ')and position F2 is dependent upon planar angle ⁇ (i.e. larger planar angles ⁇ will exhibit larger divergence at F2; see Waldman et al. in WO 2004/0066035 A2, the entire teachings of which are incorporated herein).
  • reflective surface (33) is a segmented surface having a grouping of concave curvatures so as to compensate for divergence of search generated Reference beam(s) (10') incident upon reflective surface (33) of optical element (31) at position F2 from reflective element (32) having ellipsoidal surface, thereby providing a means to redirect and focus Reference beam(s) (10') onto detector (4).
  • the front surface 34 of optical element (31) that is behind and adjacent to media (5) preferably also operates to deflect or otherwise redirect the undiffracted object beam (22') towards rear surface 161 of aperture element (16).
  • the undiffracted object beam (22') can exit the system during Address Retrieval (i.e. content search) mode, or otherwise not be propagated by lens element (3) to detector (4).
  • Rear surface 161 of aperture element 16 can be a light absorbing or light trapping surface that operates to absorb or trap the undiffracted object beam (22').
  • aperture element 16 can be reflective and thereby can direct the undiffracted object beam (22') to another light absorbing element, (not shown in FIG.
  • the inner surface of reflective element (32) preferably has two focal positions.
  • the first focal position (Fl) is located in the media at or near the recording plane, and the second focal position (F2) is located in the vicinity of reflective surface (33) such that the array of correlation signal beams are reflected so as to be spatially separated and focused on the detector (4) (not shown in FIG. 9).
  • the exact position of the second focal position F2 depends upon the structure of the rear reflective surface of optical element (31).
  • a preferred embodiment of the reflector element (32) having two focal positions is depicted in FIG. 9.
  • the ellipsoidal surface of element 32 may be contiguous, as shown, or alternatively segmented having a grouping of planar surfaces on a surface having curvature.
  • correlation signal beam (10') can be redirected by reflective element (32) towards its focal position F2 and onto reflective surface (33), and then be redirected towards lens element (3) so as to be focused on detector (4) as correlation signal (10').
  • reflective surface (33) can comprise a grouping of planar surfaces oriented so as to be inclined with respect to the optical axis (25).
  • reflector element (32) comprises a planar surface and reflective surface (33) can comprise a planar surface that is inclined with respect to optical axis (25), such as can be used for dual multiplexed holograms recorded co-locationally in a storage location using planar- angle in combination with tilt multiplexing methods.
  • FIG. 10 shows an example of a device suitable for practicing the present invention having inner surface 35 of element (32) shaped as an ellipsoidal surface.
  • HRM is not shown for simplicity in FIG. 10, a storage location would be located at about focal point Fl of ellipsoidal mirror 32.
  • each correlation signal beam (10') corresponding to a correlation signal generated by the diffraction of search argument beam 22 from one of a group of the multiplexed holograms in the selected storage location.
  • the correlation signal beams (10') are diffracted from a grouping of dual multiplexed co-locational holograms.
  • Each hologram that diffracts beam 10' comprises content that matches with at least a portion of the image encoded in search argument beam (22).
  • the array of content search beams (10') is redirected by inner surface 35 of ellipsoidal mirror 32 to second focal position (F2).
  • focal point F2 is located on the surface of element 31 facing optical element 3.
  • correlation signal beams (10') are simultaneously directed from the optical element (31) to lens element (3) that relays said beams as a grouping of beams 10" to detector (4) in a manner that allows any number of beams 10' in the array to remain spatially separated and simultaneously focused on detector (4). This, in turn, eliminates the need for rotation of either the HRM or search argument beam (22) with respect to the one another.
  • Detectors suitable for use in the practice of the present invention can be a 2-D detector of CMOS or CCD type, diode detectors, magneto-optical elements, or any other detector types that can be suitably arranged to rapidly resolve and detect optical signals.
  • the detector is a 2-D detector comprising an array of individual detector elements such as pixels. Groups of contiguous pixels along a row or a column can also be referred to as "superpixels". Superpixels can also be contiguous grouping of pixels arranged into both columns and rows. In one embodiment, shown schematically in FIG.
  • each row of superpixels corresponds to a value of azimuthal or tilt multiplexing angle ⁇ selected from a sequence ⁇ , ⁇ j+i, ⁇ j+2, $+ 3 ... ⁇ j +q
  • each column of superpixels corresponds to a value of planar-angle multiplexing angle # selected form a sequence ⁇ ⁇ , ⁇ ⁇ +- ⁇ , ⁇ ⁇ + 2 , #+ 3 ... ⁇ ,+ p .
  • the detector includes a plurality of indexed detector elements, each said detector element assigned a set of indices, each set of indices corresponding to a set of one or more multiplexing parameters of at least one hologram recorded in the selected storage location.
  • the multiplexing parameters include angles, wavelengths, location shifts and any other parameter of a holographic recording that can be used for multiplexing
  • the methods of the present invention include detecting the correlation signal beam by the detector element having a selected set of indices; and based on the selected set of indices, computing the set of one or more multiplexing parameters of the hologram recorded in the selected storage location that corresponds to the correlation beam being detected.
  • the present invention can be especially advantageously used for parallel content searching of holographically stored information recorded using various multiplexing techniques. These multiplexing techniques will now be generally described.
  • the Reference beam (10) in FIG. 2 can be incident at an oblique angle ⁇ with respect to optical axis (25), where ⁇ is selected from one or more of a grouping of angles about the shown y-axis that are perpendicular to the y-axis and where the optical axis (25) is also perpendicular to thejy-axis.
  • Multiplexing of holograms in a storage location is therefore based upon selection of at least one value of the angle ⁇ that is directed along a line on the interaction plane, said plane defined herein as containing the Reference beam (10) and the optical axis (25) of the Object beam
  • FIG. 2 schematically depicts zl ⁇ to represent a range of planar Reference beam angles, ⁇ , that may be used for planar-angle multiplexing in one or more storage locations.
  • the Reference beam (10) can be incident at angles inclined (i.e. tilted out of plane) with respect to the aforementioned interaction plane defined for planar-angle multiplexing, wherein said tilted angles are directed along a line on a plane that is perpendicular to the said interaction plane and said angles are selected from one or more of a grouping of angles that are non perpendicular to the shown y- axis and thus inclined with respect to the angles selected for planar-angle multiplexing.
  • the Reference beam (10) can be incident at angles selected from one or more of a grouping of azimuthal angles about the shown optical axis (25), such angles being along a line on a plane that contains the optical axis (25) but where said plane is rotated about the optical axis (25) with respect to the aforementioned interaction plane.
  • Recording a grouping of two or more holograms in a storage location, each with a plane wave Reference beam having different azimuthal angle, is sometimes referred to as peristrophic multiplexing (see Pu et al. in US 5,483,365, the entire teachings of which are incorporated herein) or azimuthal multiplexing (see Trisnadi et al.
  • Such combinations of two or more angles can also include pairs of angles wherein ⁇ is combined with a zero value of the tilt angle ⁇ or of the azimuthal angle ⁇ .
  • spatial multiplexing wherein each storage location is shifted in its position along the media in one or more directions with respect to the other locations such that the storage locations are non overlapping, can be combined with any suitable above referred to multiplexing method or combinations of methods (see Burr et al. in Opt. Communications, Vol. 117, Nos. 1-2, pp. 49-55, 19995, and Pu and Psaltis in Applied Optics Vol. 35, No. 14, pp. 2389-2398, 1996, the entire teachings of which are incorporated herein by reference).
  • Combinations of spatial multiplexing independently with planar-angle or tilt or azimuthal or shift mutiplexing, or wavelength mutiplexing, or phase multiplexing, or correlation multiplexing is also a dual multiplexing method, and combinations with at least two of other multiplexing methods can also be implemented.
  • reference beam (10) may be a spherical wave or a fan of planar- waves, in which case the term "multiplexing" means shift multiplexing and is achieved by small movements of HRM 5 relative to reference beam 10 (see G. Barbastathis et al. in Applied Optics, Vol. 35, pp. 2403-2417, 1996, the entire teachings of which are incorporated herein by reference).
  • the positions of successively or skip sorted shift multiplexed holograms, that are immediate neighbors in their locations, are shifted in accordance with their shift Bragg selectivity so as to be substantially overlapped in one or more directions.
  • the maximum multiplexing number is directly related to the thickness of the recording material. Shift multiplexing may be implemented in the in-plane mode or out-of-plane mode, such as described for planar-angle and tilt multiplexing, respectively, and the modes may also be combined.
  • the holograms are stored utilizing at least a dual multiplexing method to achieve advantageous large multiplexing factors, said methods, by way of example, described above.
  • Said at least dual multiplexed holograms may be recorded in manner such that the signal beam for recording is amplitude modulated.
  • the signal beam for recording may be phase modulated, such as by 0, ⁇ phase or other suitable phase modes.
  • FIG. 2 depicts recording of transmission holograms, the present invention is not restricted to transmission holograms.
  • Other suitable recording geometries are also contemplated such as for reflection holograms, wherein the Object and Reference beams are incident to the media from directions that are oriented with respect to opposing sides of the media, or for recording holograms in 90 degree geometry whereby the angle between the Object beam (20) and the Reference beam (10) is equal to 90 degrees.
  • dual multiplexed holograms are recorded co- locationally in storage locations that are abutting, substantially overlapping, partially overlapping, spaced apart or are disposed in the HRM by a combination of these techniques.
  • the arrangements of the storage locations can be along arcuate tracks, wherein these tracks may be abutting, overlapping or spaced apart in a radial, helical or other suitable arrangement.
  • the storage locations can be arranged in rows or columns or combinations thereof.
  • the dual multiplexing embodiments of planar-angle in combination with azimuthal, or planar- angle in combination with tilt, in a manner such that the multiplexed holograms are stored co-locationally provide for a substantial advantage in search speed and efficiency.
  • the co-locationally multiplexed holograms can be searched in parallel without physically redirecting a search argument beam or moving of the HRM.
  • the dual multiplexed holograms are recorded co- locationally in one or more storage locations by rotation of the reference beam only (see Trisnadi et al. in US 5,638,194 and Waldman et al. in WO 2004/0066035 A2, the entire teachings of which are incorporated herein by reference) rather than rotation of the reference beam and object beam together.
  • presenting a search argument to a storage location in HRM 5 can result in generating a correlation signal from all co-locationally recorded holograms simultaneously.
  • the direct optical correlation search rate for presence of content matching the search argument is on the order of 5El 1 GBytes/sec.
  • the present invention is a holographic drive that can implement the aforementioned multiple (e.g. dual) multiplexing methods and achieve similarly large multiplexing factors in relatively thin material, such as material having thickness of 0.5 mm.
  • the devices and methods of present invention advantageously provide for similarly fast optical correlation search rates for holograms recorded co-locationally in relatively thinner media, such as material having thickness of 0.5 mm. In all cases, if the multiplexed holograms are recorded co-locationally in each storage location, then in Address Retrieval (i.e.
  • all of the possible reference beam angles or combinations of angles and/or wavelengths used for each storage location be generated by the optical system simultaneously for the array of correlation signal beams diffracted by the holograms in each storage location.
  • all of the combinations of ⁇ and ⁇ or ⁇ can simultaneously diffract as the correlation signal beams that can be directed to the detector. Since the detector is two-dimensional, the array of the correlation signal beams corresponding can be detected simultaneously rather than successively.
  • the detected signals can, by way of example, be analog or digital signals that can be pre-normalized to distinguish whether a signal represents a correlation signal, and, further, to take into consideration expected intensity differences such as due to optical geometry, value of the Reference beam angle, diffraction efficiency of the holograms, and the like.

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Abstract

La présente invention concerne un appareil et un procédé pour écrire, lire ou rechercher le contenu de données holographiques. Dans un mode réalisation, l'appareil qui est un capteur unique est utilisé pour détecter à la fois un faisceau d'objets reconstruits généré par la diffraction d'un faisceau de référence en un emplacement sélectionné dans un support d'enregistrement holographique (HRM) et un faisceau de signaux de corrélation généré par la diffraction d'un faisceau d'arguments de recherche en un emplacement de stockage sélectionné dans un HRM.
PCT/US2008/011844 2007-10-18 2008-10-17 Système optique et procédé pour une recherche adressable de contenu et une récupération d'informations dans un système de stockage de données holographiques WO2009051775A1 (fr)

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