Abstract: A method of holographic recording in a photorefractive medium wherein stored holograms may be retrieved with maximum signal-to noise ratio (SNR) is disclosed. A plurality of servo blocks containing position feedback information is recorded in the crystal and made non-erasable by heating the crystal. The servo blocks are recorded at specific increments, either angular or frequency, depending whether wavelength or angular multiplexing is applied, and each servo block is defined by one of five patterns. Data pages are then recorded at positions or wavelengths enabling each data page to be subsequently reconstructed with servo patterns which provide position feedback information. The method of recording data pages and servo blocks is consistent with conventional practices. In addition, the recording system also includes components (e.g.

Abstract: A holographic article and method for forming permits the party producing the final document to print the holographic image directly on the final document thereby permitting such party to retain and maintain control of its own embossing shim on which the hologram has been formed and which is utilized for embossing the holographic image on the document. A film upon which a holographic image can be directly stamped upon the final document includes a layer of metal having a thickness in the range of 20 millimicrons to 100 millimicrons, a lacquer coating having a thickness in the range of 0.5 microns to 3 microns and a heat activatible adhesive. The metal layer lacquer coating and heat activatible adhesive are caused to be adhered to the substrate forming the final document during a stamping operation which releases said metal layer, lacquer coating and heat activatible adhesive from a plastic carrier film to which had initially been applied.

Abstract: Apparatus for the simultaneous parallel recording of holograms on a dynamic volume medium. Directed along a recording axis is a polychromatic source image which has multiple component images to be recorded in the dynamic volume medium. Each component image of the polychromatic source image has a separate frequency. Directed along a reference axis is a polychromatic reference beam having a plurality of monochromatic reference components with each reference component having a separate wavelength. Positioned upstream from the volume on the reference axis is a prism which angularly multiplexes the reference components to provide a plurality of monochromatic reference beams which are directed at angular offsets from the reference axis to the medium. Each of the reference beams has a wavelength which is identical to the wavelength of only one of the monochromatic component images of the polychromatic source image.

Abstract: A two-photon process for writing to a holographic recording medium comprising a photorefractive material doped with an excitation dopant selected from rare earth ions and an ionization dopant selected from transition metal ions or rare earth ions.

Abstract: Holograms within an array are recorded and/or read out by use of a reference/read out beam produced by illumination of a phase mask.

Abstract: A method and system are disclosed for dynamically refreshing angle-multiplexed holograms stored in a photorefractive medium. In accordance with the invention the photorefractive medium is simultaneously exposed to a plurality of reference beams. Each reference beam is oriented at an angle corresponding to an angle at which a hologram was previously stored within the photorefractive medium. The frequency and duration of the reference beams are regulated such that each reference beam enhances the diffraction efficiency of an associated hologram, stored at the angle corresponding to the angle of the reference beam. Each reference beam is preferably at a frequency different from the frequency of the other reference beams so as to avoid the generation of plane-wave holograms due to interference between the multiple reference beams.

Abstract: A method and apparatus are provided for reducing speckle noise in images read out from holographic memories. An image recorded in the memory is read out using a multiple component readout beam, with each component having the same horizontal orientation but a different vertical orientation. Because the Bragg effect is pronounced only in the horizontal direction, the readout beam components all access the same stored image. Each readout beam component is set to oscillate at a slightly different frequency such that the smallest frequency difference is greater than the reciprocal of the output detector response time. The multiple oscillating readout beam components can be produced by an acoustooptic deflector driven by a wideband electrical signal. The memory readout comprises multiple reconstructions of the desired image, with each image reconstruction oscillating at a slightly different optical frequency.

Abstract: The invention is embodied in a method of recording successive holograms in a recording medium, using at least a fan of M waves along at least a first axis with a separation angle between adjacent waves and directing the fan of M waves as a reference beam along a reference beam path onto the recording medium, successively modulating a wave with a succession of images to produce a succession of signal beams along a signal beam path lying at a propagation angle relative to the reference beam path so that the signal and reference beams intersect at a beam intersection lying within the medium, the beam intersection having a size corresponding to beam areas of the reference and signal beams, producing a succession of relative displacements in a direction parallel to the first axis between the recording medium and the beam intersection of the signal and reference beam paths in synchronism with the succession of signal beams, each of the displacements being less than the size of the intersection whereby to record suc

Abstract: A method and system for searching for a given sequence in a data base having a multitude of reference sequences stored or identified therein. In accordance with this method, a light beam is modulated with patterns representing the reference sequences, and with a pattern representing the given sequence, and a correlation signal is generated representing the correlation of the reference and given sequences.Optical diffraction patterns may be used to represent the given and reference sequences. In one embodiment, a multitude of first diffraction patterns, each one representing the given sequence, are formed in an optical medium, and a light beam is modulated with each of those multitude of diffraction patterns to form a multi-channel signal beam. Each channel of that beam is then modulated with a respective one second diffraction pattern representing one of the reference sequences to form a multi-channel correlation beam.

Abstract: The invention is embodied in an optical memory having a holographic recording medium capable of storing respective holograms in respective storage spots, the memory including a coherent collimated reference beam and an information-bearing object beam illuminating the recording medium, a segmented optical array including a stack of plural segmented optical sub-arrays, each of the segmented optical sub-arrays including an array of generally parallel optical strips, each optical strip having a strip length extending parallel to the optical strips, respective optical strips of all of the sub-arrays providing an optical path for the reference beam to respective recording spots in the holographic recording medium whenever the reference beam is incident within the strip length, two optical strips in different sub-arrays with optical paths to the same recording spot being separated by at least an out-of-plane multiplexing difference angle subtended by paths of the reference beam to the two optical strips, a reference

Abstract: An optical data storage system is disclosed in which information is encoded and decoded in the spectrally resolved optical properties of the storage medium. An optical storage medium scatters an incident light excitation into both elastic and inelastic light beams. The inelastically scattered light serves as an optical data storage channel, whereby the inelastic light scattering properties of the medium are modulated in accordance with the information to be encoded or decoded. The elastically scattered light is also used as a data channel as in conventional optical storage systems, as well as for control functions. By increasing the optical processing gain, relatively weak inelastic scattering channels may provide a signal:noise ratio sufficient for storage applications. Furthermore, incorporation of a plurality of independently addressable inelastic scattering channels increases the storage density of the medium.

Abstract: A holographic storage assembly is provided which utilizes a large holographic storage media (36) disposed between two reflecting surfaces (40) and (42). An optics system (44) is disposed between the two reflecting surfaces (40) and (42) is operable to generate both a reference beam (58) and a data beam (50). The data beam (50) and reference beam (58) are generated on a virtual spot plane (100), which is then imaged from the surface of the reflecting surface (42) onto the much larger surface of the media (36). This is operable to record an interference grating at a storage location (56). During a playback operation, a reconstructed data beam (64) is generated and reflected from the surface of the mirror (40) onto a detector (68) in the deflector system (44).

Abstract: A tape cartridge (12) is provided for storing holographic recordings in a longitudinal holographic storage media tape (14). The tape (14) is comprised of a thin holographic storage media such as a photopolymer. A laser (54) is operable to generate a coherent light beam, which is then positioned on a given row of storage regions (42) on the surface of the tape (14). A positioning/angle multiplexing device (90) is operable to both position a reference beam (60) and a data beam (62) onto a select one of the storage regions in a given row on the surface of the tape (14). The tape (14) is incremented a row at a time for each scan operation wherein both the reference and the data beams during a Write operation, and only the reference beam during the playback operation, are moved along a given row. The spinning polygon mirror (56) is utilized to provide both positioning along a given row and angle multiplexing in a select storage region, with the optic system removing the angular information from the data beam (62).

Abstract: An optical memory stores data in an optical data layer capable of selecting altering light such as by changeable transmissivity. Data is organized into a plurality of regions or patches (called pages) in which each page contains a field of data spots storing binary data as the presence or absence of a hole. The data is illuminated by controllable light sources and an array of single element diffractive imaging lenslets, one for each data page, projects the image onto a common array of light sensors. By selective illumination of each data page, one of the single element lenslets images the selected data page of holes onto the light sensors. By selecting a hole size and using a certain range of restricted acceptance angle grooves on the diffractive elements, the data image is optimized for a single diffractive element lens.

Abstract: A modulator apparatus for modulating arrays of input data V.sub.in to be stored in a holographic recording medium is disclosed wherein the final output data array V.sub.out has frequent transitions from light to dark and from dark to light in either dimension across the data page and has the total amount of illuminated regions throughout the entire data page held constant. These two constraints are achieved by a first set of control arrays obtained from two fixed sets of m.times.n binary arrays {A.sub.0, A.sub.1, . . . , A.sub.n } and {B.sub.0, B.sub.1, . . . , B.sub.m } which in turn are obtained from fixed sets of binary control vectors {a.sub.0, a.sub.0, a.sub.1, . . . , a.sub.n }, {b.sub.0, b.sub.1, . . . , b.sub.m }, respectively. The control vectors a.sub.0, a.sub.1, . . . , a.sub.n any n+1 fixed elements of the inverse mapping, .phi. .sup.1 (C.sub.1), of the (t-2) error-correcting code C.sub.1 of length m. The control vectors b.sub.0, b.sub.1, . . . , b.sub.

Abstract: A method for encoding and decoding digital data for storage in a holographic medium (12). Digital data, consisting of binary data (B.sub.i) or grey scale data (A.sub.i), is encoded in bit groups or digit groups (B.sub.k, A.sub.k) containing at least k=1 bits or digits, respectively, by assigning to each bit group (B.sub.k) one reference bit (B.sub.r) and to each digit group (A.sub.k) two reference digits (A.sub.r1, A.sub.r2), assigning the bits of group (B.sub.k) to information bits (B.sub.j), assigning the digits of group (A.sub.k) to information digits (A.sub.j), assigning the reference bit (B.sub.r) and information digits (B.sub.j) to a reference pixel (P.sub.r) and information pixels (P.sub.j) chosen from pixels (24) of a holographic signal modulator (18), and assigning the reference digits (A.sub.r1, A.sub.r2) and information digits (A.sub.j) to reference pixels (P.sub.r1, P.sub.r2) and information pixels (P.sub.j) chosen from pixels (24) of the holographic signal modulator (18).

Abstract: Disclosed is a spatial multiplexer for use with a holographic storage medium, and an information storage system employing the spatial multiplexer. The spatial multiplexer directs a reference beam of optical radiation onto the storage medium, the storage medium having (n) rows and (m) columns of storage locations. The spatial multiplexer includes an array of (n times m) discrete reflector elements each having a linear shape. The discrete reflector elements are disposed in a parallel arrangement with one another upon a substrate, and each has a different angular orientation with respect to the storage medium. A deflection of the reference beam by an angle multiplexer changes the angle of incidence of the reference beam on the storage medium, which provides multiple angles required for angle multiplexing a plurality of superimposed holograms within a single storage location.

Abstract: New methods are presented for multiplexing volume holograms in electrooptic materials. Multiple volume holograms can be superimposed in a medium and be individually addressed by tuning the underlying refractive index of the medium or the crystal parameters, while keeping the external parameters (wavelength, angles) fixed. According to the presented methods, the refractive index and crystal parameters of the material can be varied via the electrooptic, elastooptic or piezoelectric effects, alone or in combination with each other, by tuning the value of an applied electric field, or by tuning an applied mechanical stress, or by changing the material temperature. Volume holograms that have been multiplexed by either wavelength or angle or electric field or mechanical stress or temperature can be individually addressed by any one of the same five parameters. Additionally, selective, updatable fixing and erasing of volume holograms in photorefractive media is described.

Abstract: An optical memory is disclosed in which data is stored in an optical data layer capable of selectively altering light such as by changeable transmissivity, reflectivity, polarization, and/or phase. The data is illuminated by controllable light sources and an array of multi-surface imaging lenslets project the image onto a common array of light sensors. Data is organized into a plurality of regions or patches (called pages) and by selective illumination of each data page, one of the lenslets images the selected data page onto the light sensors. Light in the data image pattern strikes different ones of the arrayed light sensors, thereby outputting a pattern of binary bits in the form of electrical data signals.

Abstract: An optical cache memory architecture is utilized that has the advantages of fast access time, high bandwidth and high density. The optical cache memory architecture stores data holographically with greatly reduced crosstalk and distortions. The memory architecture uses the beam fanning effect present within a high gain photorefractive crystal to eliminate the so-called Bragg degeneracy.

Abstract: The correlation speed and storage capacity of an optical disk-based correlator is enhanced by employing a thick (several hundred micron) photo- polymeric film (or other thick holographic media) on the disk as the recording media to permit volume holography and angular multiplexing of holograms in each spot on the disk. For example, if 100 holograms are multiplexed at one spot, 100 1-dimensional correlation functions can be read in parallel off of the disk while illuminating it with a single input image. The diffraction of the image beam by the recorded holographic patterns occurs at the holograms in the disk.

Abstract: A hologram system comprises two volume holograms on two separate substrates which are cemented together with an optical cement. The two volume holograms are manufactured with identical Bragg planes. The two volume holograms are oriented with respect to one another such that the Bragg planes are optically aligned. The result is that the two volume holograms operate as a single thicker volume hologram wherein the Bragg angle sensitivity is greatly increased.

Abstract: A multidimensional optical storage medium is provided for storing a plurality of holographic images representative of data. An interrogation network generates a search argument including a target data field to be simultaneously searched for over at least a segment of the optical storage medium. The interrogation network couples the search argument into the optical storage medium and extracts a set of address fields at which data fields in the storage medium that match the target data field of the search argument are stored.

Abstract: A high density rapid access data storage device employs a volume of field-oriented bacteriorhodopsin in a polymer medium, and contained in a vessel that can be accurately displace in three dimensions. X-axis and Y-axis laser illumination systems each converge a beam in the respective direction at a location at which a particular bit cell is to have a "1" or "0" recorded or is to be interrogated. Both laser systems are pulsed on at one wavelength to write a "1" or at a second wavelength to write a "0". After writing, a cleaning step is carried out by actuating the laser systems non-simultaneously at the other of the wavelengths to remove any undesired photochemistry from adjacent bit cells. A read cycle involves actuating two or four lasers, and then discriminating the "1" or "0" state from the electrical signal generated by the medium.

Abstract: In processes of holography using bacteriorhodopsin-based recording media, it is essential to design the signal-to-noise ratio to be as favorable as possible. This is achieved by recording the hologram using circularly polarized light and reconstructing the hologram by using linearly polarized light, specific beam components being selected as a function of polarization in the beam path of the reconstructed hologram. The process is suitable both for purely holographic applications and also for other processes which include one or more intermediate or partial steps involving holography.

Abstract: A method and apparatus for erasing an array of electrically erasable EPROM cells that avoids overerasure and allows programming or erasure of individual cells are provided. An erase line for each column of the array applies erase potential to the erase node of each cell in the column, provided that the erase node is connected to the erase line by a transistor controlled by a row select line. A sense amplifier determines when each cell begins to conduct and disconnects that cell from its erase line. By selecting a particular row, and then applying erase potential only to selected erase lines, a pattern of erased and programmed cells can be created in each row. The pattern differs from row to row depending on which erase lines have erase potential applied when that row is selected. Bias differences between erase and read modes assure that the erased cells, which have gone slightly into depletion, are not in depletion in normal operation.

Abstract: A memory cell array (100) of an EPROM includes a first data memory region (1a), a second data memory region (1b), a 2M code memory line (2a) and a 1M code memory line (2b). When both the first and the second data memory regions (1a, 1b) are normal, the EPROM may be used as a 2M bit EPROM, in which case a device code indicating that the EPROM is a 2M bit EPROM is read out from the 2M code memory line (2a). When a defective portion is present in one of the first and the second data memory regions (1a, 1b), the EPROM may be used as a 1M bit EPROM, in which case a device code indicating that the EPROM is a 1M bit EPROM is read out from the 1M code memory line (2b).

Abstract: A parallel optical information processing system includes an information inputting part which produces a coherent optical beam spatially modulated by input image information. A rewritable hologram memory carries a plurality of stored images as holograms so that the holograms are overlapped with each other, the rewritable hologram memory being written with image information when illuminated by a recording optical beam. An image reproducing part is supplied with the input image information, and produces reproduced image information from the rewritable hologram memory. A hologram synthesizing part synthesizes a synthetic hologram in response to the reproduced image information. A hologram recording part records the synthetic hologram in the rewritable hologram memory through the recording optical beam.

Abstract: A plurality of reflective diffusing holographic memory elements (16) is positioned on a memory plate (14). An array (24) of detectors (22) faces at least one of the memory elements. A laser (26) illuminates the selected memory element and the data stored therein is reflected onto the array for reading. A new memory element may be illuminated or may be brought into interrogation position.

Abstract: A finely detailed defraction grating is applied to an object as an identifier or tag which is unambiguous, difficult to duplicate, or remove and transfer to another item, and can be read and compared with prior readings with relative ease. The exact pattern of the defraction grating is mapped by diffraction moire techniques and recorded for comparison with future readings of the same grating.

Abstract: A programmable semiconductor memory apparatus comprises a memory cell array, a data sense circuit for reading data from the memory cell array, and a bus line connected to a common node of a plurality of bit lines forming the memory cell array and to the data sense circuit, a circuit for storing an identifying code for identifying the programmable semiconductor memory apparatus is connected to the bus line, thereby enabling the identifying code to be read externally.

Abstract: The holographic manufacture of Compact Discs has three stages namely mastering, production of the sub-master holograms and replication. In the production stage, a holographic plate, spacer and master transparency are positioned against a prism, and then illuminated with split beams from a laser in order to record a hologram, at the plate, of the master transparency. The resultant hologram of the plate is then mass replicated on polycarbonate or photochromic discs to produce compact Discs compatible to conventional Compact Disc players.

Abstract: A low noise system and method for both amplifying and retroreflecting an information-bearing probe beam employs a two-wave mixer in conjunction with a pseudoconjugating element. The probe beam is amplified by two-wave mixing in a photorefractive medium, while the pseudoconjugator is arranged to retroreflect the amplified probe beam back through the photorefractive medium such that optical distortions imposed upon the beam during the amplifying pass are compensated, yielding an output with a high signal-to-noise ratio. Various types of pseudoconjugating elements may be used.

Abstract: An associative memory system incorporating a hologram, a spatial light modulator (SLM) and thresholding components in a feedback loop to derive an enhanced reference beam for use in reconstructing a stored image. In a preferred embodiment, the SLM includes a liquid crystal light valve (LCLV). A polarizing thresholding analyzer device provides adjustable thresholding. An enhanced thresholded reference beam thereby derived is sent back to the hologram for readout and the stored image is reconstructed at the output plane of the system. In an alternative embodiment, two spatial light modulators and two feedback loops are provided in a resonator configuration.

Abstract: An associative memory system is provided which is a hybrid of optical and electronic components. In the preferred embodiment, a Fourier transform hologram is used to convolve a reference beam with correlated input images and stored object images. An electronic iteration loop is provided which is used to derive an enhanced reference beam for use in matching and enhancing the associative memory of the hologram with the object input plane image. The iteration loop of electronic components comprises a vidicon which receives the correlation plane image and provides that image in the form of an electronic signal to an electronic thresholding device or image processor. The image processor is capable of viewing the data at the rate of 30 frames per second and is used in the preferred embodiment to threshold the data with reference to the greatest amplitude portion of the correlation spot provided to the vidicon.

Abstract: Associative holography memory apparatus is disclosed which employs a hologram, two phase conjugate mirrors, and a two-wave mixing contra-directional coherent image amplifier. The mirrors and amplifier are arranged to form a conjugate resonator whereby the output image from the apparatus tends to converge to that stored image most closely associated with an input image. Alternate embodiments are described which employ a multiple storage and erasure hologram, and which employ only a single phase conjugate mirror.

Abstract: Associative holography memory apparatus is disclosed which employs a hologram and two phase conjugate mirrors. The mirrors are arranged to form a conjugate resonator whereby the output image from the apparatus tends to converge to that stored image most closely associated with an input image. Alternate embodiments are described which employ a multiple storage and erasure hologram, and which employ only a single phase conjugate mirror.

Abstract: An apparatus and method for infrared imaging is disclosed in which a pattern of infrared radiation is detected and stored in uniformly distributed localized states in a semiconductor. Photoemission of charge carriers from the localized states occurs only at locations where infrared photons interact with the carriers. When desired, a uniform electric field applied to the semiconductor allows for coherent transport of a pattern of remaining carriers in a direction substantially perpendicular to an outer surface to which the image is transported. A portion of the transported pattern of charge may be emitted from the outer surface of the semiconductor and utilized to produce an optical or electrical pattern corresponding to the incident infrared pattern.

Abstract: Information is stored by a process involving the steps of(1) sensitizing a recording medium comprising a two-photon, four-level material by exposing said medium to flood illumination with ultra-violet or visible light, and then(2) exposing the sensitized medium simultaneously to two beams of coplanar laser irradiation intersecting within said recording medium to create a microscopic interference pattern.

Abstract: The apparatus includes a frequency selective memory having a storage material for storing frequency holes in at least two spatial dimensions and a frequency dimension. Interference patterns are stored in the memory such that each complete interference pattern is found in the spatial dimensions while the series of interference patterns is in the frequency dimension. A laser beam is directed onto the surface of the memory to read the memory. By changing the electric field across the storage material, subsequent interference patterns are shifted in the frequency dimension into resonance with the laser beam thereby changing the interference pattern detected. The interference patterns may be a series of holographic interference patterns which would provide as an output a series of three dimensional images, or they may be a series of gratings which would provide a laser beam which scans in a spatial dimension as an output.

Abstract: A rotating disc-shaped carrier upon which have been recorded audio, video or computer data in holographic form, a method for forming such a carrier, and an apparatus for reading such a carrier is disclosed. A beam of coherent radiation is spatially modulated in a prescribed way, this beam then illuminating one radial of a rotating carrier upon which has been recorded a series of holograms in the form of a spiral track or series of concentric tracks. The holograms are elongated in a direction perpendicular to movement of the rotating carrier and overlap in directions both parallel and perpendicular to such movement, the amount of overlap in the perpendicular direction being inversely proportional to the amount of overlap in the parallel direction such that data storage density remains constant across the surface of the rotating carrier. The sequentially illuminated holograms generate a series of signal images which vary in amplitude, width, spatial frequency, azimuth or position relative to a centerline.

Abstract: The arrangement for displaying deformations of deformable structures by holographic interferometry, in which the interferogramme of the object is obtained by double exposure for an object subjected to periodic deformation or by prolonged exposure by comparison with the period of vibration for a vibrating object, comprises a recording electro-optical, photoconductive crystal to which is applied an electrical field substantially orthogonal to the mean direction of the fringes. The interferogramme is viewed in an image plane or recorded in a memory tube where it is desired to memorize the information because readout destroys the information. The arrangement can be made compact by integration of the displaying means in an enclosure. In that case, the source furnishes a reference beam and an object beam which are respectively directed towards the enclosure and the object by optic cables.

Abstract: The invention relates to the acousto-optical imagery of objects transmitting ultrasonic waves; an optical image diffracted by the action of an ultrasonic wave is detected by coherent detection in an electro-optical and photoconductive holographic recording material under an applied field by holographic recording of the interferences between the diffracted order to be imaged formed by the optical wave of pulsation .omega..sub.o +.omega..sub.s (or .omega..sub.o -.omega..sub.S) and an optical reference wave having the same pulsations. Imagery is effected in real time by restoration of the object wave by a reading wave having the same pulsation as the reference wave.

Abstract: A holographic playback system comprises a turntable adapted to support a record disk which contains a series of holograms recorded along convoluted spiral tracks. Each of the holograms represents a pattern of data bits and synchronization bit, and an optical system for directing a laser beam to the record disk, whereby the laser beam is diffracted by the interference fringes of the hologram to reconstruct the image of the pattern of data and synchronization bits. The turntable is driven so that the holograms are successively shifted in location with respect to the laser beam and illuminated by the beam. A solid-state image sensor is provided which includes a plurality of charge storage type sensing elements each positioned to receive the reconstructed image of each data bit and a non-charge storage type sensing element positioned to receive the reconstructed image of the synchronization bit.

Abstract: A holographic data storage system for the storage and retrieval of data which includes in combination input means adapted to produce a number of coherent beams; wavefront matching means comprising at least one cylindrical lens for facilitating the discrimination of date; a storage medium adapted to store a number of data tracks, and capable of movement in a plane perpendicular to the plane of incidence; stepping means which is adapted to direct the number of beams produced by the input means on to the storage medium in a manner whereby a number of data tracks are recorded or retrieved, and read out means capable of controllable selective retrieval of date.

Abstract: A verification system utilizing a holographic memory defined by a multiplicity of individual holograms on a photographic strip arranged side by side in elongate, parallel, hologram channels of substantially equal length. A holographic index on the strip identifies the information stored in each channel. The memory is a holographic record of binary spot patterns of multi-digit numbers which are sequentially recorded. The spot pattern for any given number may extend over one or more holograms to fully utilize the available recording space. Data compression is employed to reduce or eliminate the recordation of digits which are identical to corresponding digits of a preceding number to thereby reduce the memory bulk. A given number to be verified is entered in a keyboard and stored, the index is searched and the appropriate memory channel is then searched for a match of the given number with a number in the memory by producing and detecting images from the recorded holograms.

Abstract: An optoelectronic memory comprising the following elements placed one after another in succession downstream the original beam from the source of electromagnetic radiation: a means for scanning the original beam, which is electrically connected to an address register, a means for splitting the original beam into m beams forming a scan pattern and a focusing lens. The focusing lens is followed by n beam splitters whose number along each beam direction is equal. The memory also comprises .vertline.n+1.vertline. information memory plates each being positioned at a focal distance from the focusing lens and carrying m memory modules arranged upon the surface facing the beam.

Abstract: A byte of binary data to be stored is recorded as a synthetic Fourier transform hologram of the byte of data. A time varying control signal representing the synthetic hologram is used to intensity modulate a coherent light beam as the beam scans transversely across a photosensitive recording film. The amplitudes of different spatial frequencies in the data band are differently altered to compensate for signal to noise roll-off over the data band. The thus compensated signals are also modified to compensate for nonlinear gain characteristics. The thus modified signals are processed to provide the modulating control signal. During the readout process an inverse Fourier transformation is performed optically on the light diffracted by the synthetic hologram in order to produce the original byte of data in the form of an optical intensity pattern. This pattern is transversely distributed on an array of photosensitive detectors which converts the optical intensity pattern to an electrical data signal.

Abstract: The holographic recording system comprises a pair of aligned first and second Fourier transforming lenses, a holographic beam splitter having a series of random phase illumination holograms at a front focal plane of the first lens and arranged to move in a given direction to successively receive a light beam for deffracting it into a zero-order diffracted beam and a first-order diffracted array of sampled, phase shifted beams, and a mask having a first and second apertures disposed at the Fourier transform plane of the first lens. A page composer having electrooptical transducers is positioned in the second aperture to receive the first-order diffracted array of beams to spatially optically modulate the incident beams in accordance with one of successive groups of binary signals.

Abstract: A holographic optical memory utilizes an optical heterodyne technique to significantly increase the signal-to-noise ratio during the readout stage of operation. A light source provides a coherent light beam which is split into a readout beam and a local oscillator beam. The readout beam is directed to one of the holograms stored in the memory medium and a portion of the readout beam is diffracted by the hologram to form a reconstructed image of the bit pattern stored in the hologram at the reconstructed image plane. The local oscillator beam is superimposed with the diffracted portion of the readout beam. An optical frequency translator is positioned in either the readout beam or the local oscillator beam to cause the beams to have different optical frequencies. Therefore, when the two beams are superimposed, a beat frequency signal is produced. An array of detectors is positioned at the reconstructed image plane to receive the superimposed beams.