Abstract: A switching assembly selectively routes power received from upstream power distribution systems over power transmission lines to a downstream electrical load using data signals communicated to the assembly from the power distribution systems over the power transmission lines. The switching assembly monitors information in the data signals to determine conditions in the upstream power distribution systems. The switching assembly can use the conditions in the power distribution systems and monitored power feed characteristics of power received at the switching assembly to determine whether to command a switching mechanism to switch the power feed routed to the load. Power system conditions can be used to adjust tolerance thresholds against which power feed characteristics are compared to determine whether to command a switch. The switching assembly can include an interposer device that controls the switching mechanism based on analysis of data signals received over the power transmission line.

Abstract: A depth camera assembly (DCA) includes a structured light generator, an imaging device and a controller. The structured light generator illuminates a local area with a structured light pattern in accordance with emission instructions from the controller. The structured light generator comprises an illumination source, an acousto-optic device, and a projection assembly. The acousto-optic device generates a structured light pattern from an optical beam emitted from the illumination source. The projection assembly modifies a general intensity envelope of the structured light pattern in order for the structured light pattern to illuminate a larger section of the local area, and projects the modified structured light pattern into the local area. The imaging device captures of portions of the structured light pattern scattered or reflected from the local area. The controller determines depth information for the local area based at least in part on the captured images.

Abstract: The present invention relates to an apparatus for imaging an object. It is described to receive (110) by at least a portion of first pixels of a first area (A, A1, A2, A3, A4, A5, A6, A7, A8) of an X-ray detector (20) first radiation emitted by at least one X-ray source (30). The X-ray detector is configured such that X-ray radiation received by a pixel leads to the generation of signal in that pixel. A plurality of first signals representative of corresponding signals on the plurality of first pixels are stored (120) in at least one first plurality of storage nodes associated with the first area. Second radiation emitted by the at least one X-ray source (30) is received (150) by at least a portion of second pixels of a second area (B, B1, B2, B3, B4, B5, B6, B7, B8; C) of the X-ray detector. A plurality of second signals representative of corresponding signals on the plurality of second pixels are stored (190) in at least one second plurality of storage nodes associated with the second area.

Abstract: Data can be encoded in physical medium and represented by shapes having many various physical attributes. In various examples, data points are encoded and represented by the physical shape, color, size, and/or structure of objects. In one embodiment, holes in memory surface substrates represent data. Various attributes of such holes, including depth, profile size, profile shape, and/or angle can represent data.

Abstract: A minimized-thickness angular scanner of electromagnetic radiation includes an optical sandwich having a two-dimensional (2D) image source, and a scanning assembly that includes a first optic and a second optic, wherein at least one of the first optic and the second optic are oscillatorily translating. Translation of the optics provides for generation of a three-dimensional (3D) image, while the optical sandwich design provides for compact implementation of 3D displays.

Abstract: Data can be encoded in physical medium and represented by shapes having many various physical attributes. In various examples, data points are encoded and represented by the physical shape, color, size, and/or structure of objects. In one embodiment, holes in memory surface substrates represent data. Various attributes of such holes, including depth, profile size, profile shape, and/or angle can represent data.

Abstract: A system for analyzing a request for proposal. The system includes an associative memory including a plurality of data having a plurality of associations. The system also includes an input device in communication with the associative memory. The input device is configured to provide the request for proposal to the associative memory in a format understandable to the associative memory. The associative memory is configured to digest the request for proposal to be included within the plurality of data, wherein a digested request for proposal is formed. The system also includes an analyzer in communication with the associative memory. The associative memory is configured to analyze the digested request for proposal by receiving a query comprising one or more terms, creating relationships among the plurality of data in the associative memory based on the query, and returning an output that includes requirements or other attributes presented in the digested request for proposal based on the query.

Abstract: Data can be encoded in physical medium and represented by shapes having many various physical attributes. In various examples, data points are encoded and represented by the physical shape, color, size, and/or structure of objects. In one embodiment, holes in memory surface substrates represent data. Various attributes of such holes, including depth, profile size, profile shape, and/or angle can represent data.

Abstract: A minimized-thickness angular scanner of electromagnetic radiation includes an optical sandwich having a two-dimensional (2D) image source, and a scanning assembly that includes a first optic and a second optic, wherein at least one of the first optic and the second optic are oscillatorily translating. Translation of the optics provides for generation of a three-dimensional (3D) image, while the optical sandwich design provides for compact implementation of 3D displays.

Abstract: A data recording apparatus and method using three dimensional (3D) optical memory and an authentication apparatus and method using 3D optical memory are provided. The data recording apparatus includes a recording excitation light splitting unit, a condition storage unit, and a data recording unit. The recording excitation light splitting unit splits recording excitation light into first split light and second split light. The condition storage unit stores recording conditions including information about the waveforms, wavelengths and phases of the split light and information about an arrangement of reflection mirrors configured to reflect the split light. The data recording unit records storage data by making the split light incident on the 3D optical memory through the reflection mirrors under the recording conditions.

Abstract: A device for storing data includes a sequence generator configured to generate a first number sequence that is a pseudorandom number sequence, a cross-correlation unit configured to produce a second number sequence that is a cross-correlation between the first number sequence and a third number sequence, and a write and read unit configured to write the second number sequence in memory and read the second number sequence from the memory, wherein the cross-correlation unit is further configured to reconstruct the third number sequence by obtaining a cross-correlation between the first number sequence and the second number sequence read from the memory.

Abstract: A device for storing data includes a sequence generator configured to generate a first number sequence that is a pseudorandom number sequence, a cross-correlation unit configured to produce a second number sequence that is a cross-correlation between the first number sequence and a third number sequence, and a write and read unit configured to write the second number sequence in memory and read the second number sequence from the memory, wherein the cross-correlation unit is further configured to reconstruct the third number sequence by obtaining a cross-correlation between the first number sequence and the second number sequence read from the memory.

Abstract: The embodiments of this invention also describe to a data medium comprising a holographic memory carried on the medium, and a photonic crystal configured, firstly, to filter the light received from a broad-spectrum light source in order to select a frequency band of the said spectrum and secondly, to guide the light corresponding to the said selected frequency band so as to light the said holographic memory in a predefined direction.

Abstract: Methods and systems for equalizing a holographic image page and for compensating nonlinearity of a holographic data storage channel are disclosed. In one embodiment, a method for equalizing a holographic image page includes receiving the holographic image page and dividing the holographic image page into a plurality of local image regions. The method further includes generating a local alignment error vector for each local image region, computing a local finite impulse response kernel for each local image region according to the corresponding local alignment error vector, and adjusting misaligned pixels of each local image region using the corresponding local finite impulse response kernel.

Abstract: A method is provided for acquiring a reserved block in a holographic storage system. A symmetrical reference table is defined according to the characteristics of a known reference reserved block. Then, the differences between respective unit blocks and the reference reserved block are calculated according to the symmetrical reference table so as to determine total match scores for respective unit blocks. Consequently, the unit block having the highest match score is deemed as the reserved block.

Abstract: A hybrid optical and holographic data storage medium is disclosed. In addition, a method is disclosed to manage information using that optical and holographic data storage medium. The method reads information from the optical data storage layer before reading data from, or writing data to, the holographic data storage layer.

Abstract: [PROBLEMS] To provide a reconfiguration controller of an optically reconfigurable gate array for correctly and reliably writing various types of logical operation circuits of an optically reconfigurable gate array and performing high-speed logical operation by quickly starting up the circuits.

Abstract: An optical pickup for recording a hologram by using an angle multiplexing method. An optical beam is separated into two beams, a signal beam and a reference beam having different convergence/divergence degrees, by using an optical component such as a diffraction lens. The signal and reference beams are made incident upon the same objective, and the optical component or the objective lens is moved in a direction perpendicular to an optical axis, to thereby realize angle multiplex recording. If an optical information recording medium is inclined, the optical component or the objective lens is moved along the direction along which the optical information recording medium moved to change an angle of the reference beam incident upon the optical information recording medium and compensate for degradation of a reproduction signal.

Abstract: In holographic recording, it is important to form stably an interference fringe between a reference beam and a signal beam in a holographic storage medium. To suppress factors degrading stability of the interference fringe, such as fluctuation of atmospheric air, position displacement of optical components and the like during propagation of the reference and signal beams, an optical pickup and an optical information recording/reproducing apparatus adopt an optical system structure providing a higher proportion of optical components shared by the reference and signal beams optical path than conventional optical system structure. To increase the proportion of shared optical components, the signal beam and the reference beam pass through the PBS prism as parallel beams and a concave lens is placed on a reference beam path just before the objective lens.

Abstract: There is provided an optical information detecting method. The method includes: detecting an image of a source data page coded with balanced codewords by the use of 1:N (where N is greater than 1) excessive detection pixels; determining a distribution pattern of valid detection pixels and invalid detection pixels to be corrected in the detected image by the use of a light intensity distribution of the detected image; and dividing the detected image into balanced codeword detecting areas corresponding to the balanced codewords and sampling data of the balanced codeword detecting areas by the use of the determined distribution pattern and an optical distribution characteristic of the balanced codewords. Accordingly, it is possible to efficiently detect optical information by the use of a 1:N over-sampling method. Specifically, the distribution pattern of valid detection pixels and invalid detection pixels in the detected image of a data page can be properly used to sample a balanced code.

Abstract: The invention relates to proton-translocating retinal proteins which exhibit a photocycle which is retarded as compared with the wild type and whose all-trans retinal contents in the light-adapted and dark-adapted states do not differ from each other by more than 10%. The invention furthermore relates to a photochromic composition and to the use of the proton-translocating retinal proteins and the photochromic composition.

Abstract: A waveguide includes a cladding region that has a refractive index that is substantially uniform and surrounds a wave-guiding region that has an average index that is close to the index of the cladding. The wave-guiding region also contains a thin ring or series of rings that have an index or indices that differ significantly from the index of the cladding. The ring or rings enable the structure to guide light.

Abstract: Integrated control electronics for a holographic storage system that is adapted for controlling read/write logic in a holographic storage device. The control electronics may control beam steering devices, SLM devices, shutters, optical sensor arrays and lasers.

Abstract: Data hologram recycling systems, methods and computer program products are configured to arrange data for storage in the intermediate data storage as data segments which are replicas of holographic storage segments for destaging to the holographic data storage, and to determine retrieval for recycling of the destaged holographic storage segments to which aggregated requests for deletion are directed. The retrieval determination may be based on a plurality of policies.

Abstract: Provided is a hologram retrieval method and a holographic recording and reproducing apparatus for preventing an increase in SNR, a decrease in retrieval accuracy, or the retrieval itself from being made impossible, which would otherwise occur because of a small size of data used for retrieval. Digital information is recorded on a holographic recording medium as data pages DP formed of a two-dimensional bit map image with each page being multiplexed. The data page DP is divided into a plurality of equal data blocks DB11 to 13, DB21 to DB23, and DB31 to DB33, and each data block DB is provided with a data image that is encoded by an encoding method for providing a certain number of ON pixels within each data block DB. A spatial light modulator allows the to-be-retrieved data image to be encoded by the encoding method and displayed as block information on a retrieval data block associated with the data block, and a signal beam to be thereby modulated.

Abstract: Data for storage by holographic data storage is arranged in an intermediate data storage as data segments which are replicas of holographic storage segments. Files of data are aggregated into the data segments, and a destaging control determines the destaging of the data segments to the holographic data storage in accordance with a plurality of policies, such as whether a segment is full, a time threshold has been reached, or whether a threshold number of segments are “open”. The intermediate data storage may be arranged into a number of partitions at least equal to the number of sources having input to the data destaging system, the partitions comprising integral multiples of the data segments.

Abstract: A hologram recording medium includes a first element hologram and a second element hologram. On the first element hologram, main data is recorded such that the main data is converted into a two-dimensional image, object light of the two-dimensional image is interfered with recording reference light, and an interference fringe produced as a result of the interference is recorded on the first element hologram. On the second element hologram, simplified-form data representing the content of the main data using a smaller data size than the data size of the main data is recorded such that the simplified-form data is converted into a two-dimensional image, object light of the two-dimensional image is interfered with recording reference light, and an interference fringe produced as a result of the interference is recorded on the second element hologram.

Abstract: Data for storage by holographic data storage is arranged in an intermediate data storage as data segments which are replicas of holographic storage segments. Files of data are aggregated into the data segments, and a destaging control determines the destaging of the data segments to the holographic data storage in accordance with a plurality of policies, such as whether a segment is full, a time threshold has been reached, or whether a threshold number of segments are “open”. The intermediate data storage may be arranged into a number of partitions at least equal to the number of sources having input to the data destaging system, the partitions comprising integral multiples of the data segments.

Abstract: Disclosed herein is a data identification method for identifying, from within a readout signal from a recording medium on or in which user data of k bits are recorded using a recording modulation code wherein m bits from among n bits which compose one codeword have a value of “1” while the remaining n-m bits have another value of “0”, the data, n and m being integers including, a first step of delimiting the readout signal in a unit of a codeword and adding, with regard to one of the n-bit codewords obtained by the delimiting, an amplitude of the readout signal of the bits of “1” to 2k different codewords which may possibly be recorded and setting results of the addition as evaluation values, and a second step of finding a maximum value among the 2k evaluation values and outputting the maximum value as an evaluation result.

Abstract: Disclosed herein is a data identification method for identifying, from within a readout signal from a recording medium on or in which user data of k bits are recorded using a recording modulation code wherein m bits from among n bits which compose one codeword have a value of “1” while the remaining n-m bits have another value of “0”, the data, n and m being integers including, a first step of delimiting the readout signal in a unit of a codeword and adding, with regard to one of the n-bit codewords obtained by the delimiting, an amplitude of the readout signal of the bits of “1” to 2^k different codewords which may possibly be recorded and setting results of the addition as evaluation values, and a second step of finding a maximum value among the 2^k evaluation values and outputting the maximum value as an evaluation result.

Abstract: A hologram recording/reproducing device includes a laser light source emitting laser light; a spatial light modulator generating signal light and reference light from the laser light emitted from the laser light source, the signal light and the reference light traveling in a common light path; a first relay lens system including a first shielding plate at a focal position thereof and transmitting the signal light and the reference light generated by the spatial light modulator, the first shielding plate having a pinhole whose size is 1 to 2 times a Nyquist size; a phase modulating element disposed at a conjugate plane of the signal light and the reference light transmitted through the first relay lens system; an objective lens converging the signal light and the reference light transmitted through the phase modulating element on a hologram recording medium; and a light receiving system disposed between the phase modulating element and objective lens and receiving light returning from the hologram recording me

Abstract: An apparatus and method is disclosed wherein, even if the multiplicity in multiplexing of recording data is increased, positioning of data upon reproduction can be performed with a high degree of accuracy without decreasing the recording capacity. Interference fringes generated by interference of a light beam spatially optically modulated by a spatial light modulator on which a marker data page is displayed with reference light are recorded at a recording spot on a hologram recording medium. Similarly, interference fringes corresponding to recording data page are recorded at another recording spot on the hologram recording medium. The multiplicity of such marker data pages upon recording is set to a value with which recognition of markers upon reproduction can be performed with a high degree of accuracy so that, even if the multiplicity of the data pages is raised, positioning information of high accuracy can be obtained.

Abstract: A data writing and reading device is capable of writing and reading data with respect to a holographic storage medium. The data writing and reading device includes a light source which emits a laser beam, a focusing lens unit having a multi-focal lens which splits the laser beam into a reference beam and an object beam and projects the split beams to the storage medium so that an interference pattern between the reference and object beams can be written in the storage medium, and a photo detector for detecting the object beam when the object beam is reproduced in accordance with the holographic data with the incidence of the reference beam to the storage medium. With a simple hardware, data can be written to or read out from the holographic storage medium.

Abstract: A holographic recording and reconstructing apparatus includes a laser light source for emitting a laser beam, a beam splitting element for splitting the emitted laser beam into a signal beam and a reference beam, a light modulating element for modulating the signal beam, an optical system for collecting the modulated signal beam and the reference beam onto a reflection hologram recording medium at substantially the same location, a light detection element for detecting a reconstructed light beam from the hologram recording medium, and wavelength shifting means for shifting the wavelength of the laser beam used during reconstruction from the wavelength used during recording.

Abstract: Hologram recording devices and techniques can be employed to produce wide-field-of-view holograms. In one embodiment, a specialized lens is used to couple an object beam into a holographic recording material without substantially changing the angle of incidence of the object beam. When displayed, images from holograms recorded using technique can have a field-of-view greater than that of the object beam. In another embodiment, one or more aspheric reflective surfaces are used to couple an object beam into a holographic recording material at relatively steep angles.

Abstract: A complex objective lens composed of a hologram and an objective lens, capable of realizing stable and high-precision compatible reproducing/recording of a BD with a base thickness of about 0.1 mm for a blue light beam (wavelength ?1) and a DVD with a base thickness of about 0.6 mm for a red light beam (wavelength ?2). In an inner circumferential portion of the hologram, a grating is formed. The hologram transmits a blue light beam as 0th-order diffracted light without diffracting it, and disperses a red light beam passing through an inner circumferential portion as +1st-order diffracted light and allows it to be condensed by an objective lens. Because of this, the focal length of the red light beam becomes longer than that of the blue light beam, whereby a working distance is enlarged.

Abstract: A holographic ROM reader having a servo control is disclosed. The holographic ROM reader includes an objective lens for focusing light reflected from a storage medium, a pinhole plate provided with a pinhole, a diffraction grating, embedded into the pinhole of the pinhole plate, for diffracting the light focused by the objective lens to produce 0th order diffracted light, +1st order diffracted light and ?1st order diffracted light therethrough, a photo detector for detecting the amounts of the 0th order, the +1st order and the ?1st order diffracted light, and a servo controller for comparing an amount of light of an overlapped area of the 0th order diffracted light and the +1st order diffracted light with an amount of light of an overlapped area of the 0th order diffracted light and the ?1st order diffracted light to control the position of the objective lens to pass the light through a center of the diffraction grating if the amounts of light are not identical to each other.

Abstract: In an angle multiplexing holographic storage device, a movable beam splitter is used for splitting a source beam into an object beam and a reference beam. An encoding device is used for encoding the object beam with pixel data. A parabolic reflector differentially reflects the reference beam with the movement of the movable beam splitter. A holographic storage medium is arranged at the focal point of the parabolic reflector and made to lie in the optical path of the encoded object beam so that the differentially reflected reference beams encounter and interfere with the encoded object beam at the same site of the holographic storage medium to form and record various interference patterns.

Abstract: Disclosed is a multiplexing method and apparatus that allows holograms to be spatially multiplexed with partial spatial overlap between neighboring stacks of holograms. Each individual stack can additionally take full advantage of an alternate multiplexing scheme such as angle, wavelength, phase code, peristrophic, or fractal multiplexing, for example. An amount equal to the beam waist of the signal beam writing a hologram separates individual stacks of holograms. Upon reconstruction, a hologram and its neighbors will all be readout simultaneously. An filter is placed at the beam waist of the reconstructed data such that the neighbors that are read out are not transmitted to the camera plane. Alternatively, these unwanted reconstructions can be filtered out with an angular filter at an intermediate plane in the optical system that has a limited angular passband.

Abstract: Disclosed are optical systems and methods of producing obliquity corrected light beams, for example, holographic recording and retrieval systems that utilize an obliquity corrected reference beam. One method includes directing a light beam reflected from a prism mirror to a reference plane with an angle of incidence to the reference plane, wherein the prism mirror varies the width of the light beam according to the angle of incidence to the reference plane. The optical system may include a holographic data storage system and the reference plane may be associated with a holographic storage medium.

Abstract: Disclosed is a multiplexing method and apparatus that allows holograms to be spatially multiplexed with partial spatial overlap between neighboring stacks of holograms. Each individual stack can additionally take full advantage of an alternate multiplexing scheme such as angle, wavelength, phase code, peristrophic, or fractal multiplexing, for example. An amount equal to the beam waist of the signal beam writing a hologram separates individual stacks of holograms. Upon reconstruction, a hologram and its neighbors will all be readout simultaneously. An filter is placed at the beam waist of the reconstructed data such that the neighbors that are read out are not transmitted to the camera plane. Alternatively, these unwanted reconstructions can be filtered out with an angular filter at an intermediate plane in the optical system that has a limited angular passband.

Abstract: A holographic apparatus includes a mask for modulating a signal beam to generate a modulated signal beam; a conical prism, which has a cone portion and a base portion, for refracting a reference beam to generate a refracted reference beam, wherein the refracted reference beam interferes with the modulated signal beam in a holographic medium to thereby record data thereon, the base portion facing the holographic medium. The holographic apparatus can be miniaturized by a positional relationship between the conical prism and the holographic medium.

Abstract: A holographic system for storing data on an interference pattern in a hologram storage medium includes a light source for emitting a laser beam, a beam splitter, modulating means and a refractive material. The beam splitter divides the laser beam into a reference beam and a signal beam and the modulating means modulates the signal beam to generate a modulated signal beam. The refractive material refracts the reference beam to generate a refracted reference beam, wherein the refracted reference beam interferes with the modulated signal beam in the hologram storage medium to generate the interference pattern.

Abstract: The present invention discloses a recording medium comprising an improved doped Stoichiometric Lithium Niobate (SLN) crystal for high-speed holographic data storage. The improved doped SLN has an extremely high optical damage resistance of more than 145 kW/cm2 for power density of an incident laser beam along the c axis. The Recording time using the present improved doped SLN is advantageously very short and is about 1 second for a single hologram with a saturated diffraction efficiency of 28.7% at a recording laser beam density of 70 W/cm2. Reliable retrieval of a signal-image written at as low as 1 milliseconds has been performed in the Z-cut doped SLN. The present recording medium is an improved doped SLN of a Z-cut SLN crystal doped with Iron (Fe) and Terbium (Tb). The Terbium (Tb) content within the fluxed melts for growing the improved doped SLN ranges from 10 ppm to 140 ppm.

Abstract: An optical head comprises an integrated unit for recording and reproducing page data on a reflective recording medium, wherein the integrated unit includes recording and reproducing units each corresponding to a bit of data of the page data, wherein each of the recording and reproducing units has a light emitter for emitting an object beam and a reference beam, an optical switch for transmitting or blocking the object beam, and a detector. Each of the recording and reproducing units records a bit of data corresponding to a state indicating whether or not a hologram has been formed and reproduces a bit of data corresponding to a state indicating whether or not a reference beam has been received by the light receiver when a reference beam is emitted to a recording position. The integrated unit of the optical head records and reproduces page data on a recording medium by recording and reproducing bit data on the recording medium by each of the recording and reproducing units.

Abstract: In a holographic digital data storage system, holographic page data has at least two concentric patterns with the optical information arranged within an outermost pattern of at least two concentric patterns. Since at least two concentric patterns in the holographic page data are deformed into at least two elliptic patterns in the diffracted beam caused by irradiation of the reference beam, at least two elliptic patterns are extracted from the diffracted beam and then at least two elliptic patterns are estimated to generate at least two estimated concentric patterns. A compensated vector between said at least two elliptic patterns and said at least two estimated concentric patterns is used to reconstruct the optical information from the diffracted beam.

Abstract: A method of recording holograms includes: generating a first signal-beam from a signal-beam source and a first reference beam from a reference-beam source; recording a first hologram in a holographic medium from an interference between the first signal beam and the first reference beam; shifting the reference-beam source after the act of recording the first hologram; generating a second signal beam from the signal-beam source and a second reference beam from the reference-beam source after the act of shifting the reference-beam source following the recording of the first hologram; and recording a second hologram in the holographic medium from an interference between the second signal beam and the second reference beam.

Abstract: The present invention relates to a method and a system for the storage of data in the form of volume holograms which do not mutually overlap. The storage medium consists of a high-sensitive material in the form of a plate of thickness D, in which a single hologram is essentially shaped as a cylinder with the minimal possible cross-section. The signal light beam is modulated with data and directed onto the plate-shaped storage material by means of a lens or a conventional optical system, illuminating an area of the material which, for a given amount of data, is the smallest possible. To record a hologram, a reference light beam is used, incident upon the storage material either from the same direction as the signal beam, or opposite thereto. The hologram is only written in the portion where the signal and the reference beams overlap.

Abstract: The invention is directed to self-referenced holographic recording techniques that make use of a diffusive element. Self-referenced holography refers to holographic recording techniques in which a reference beam is created from a zero frequency Fourier component of a data encoded object beam. In accordance with the invention, a diffusive element can be positioned in a holographic recording system to create the reference beam from the zero frequency Fourier component of the data encoded object beam. Using a diffusive element to create a reference beam in self-referenced holography can provide advantages to the self-referenced holographic recording system.

Abstract: A plurality of holographic recording media are positioned one above the other on an optical substrate and contain conventional stationary or moving imagery or data sets such as binary data representative of for example written text. A plurality of memory address access media are alternately interleaved between the plurality of holographic recording media. The memory access media causes a pair of optical beams to create an interference pattern at particular hologram recording media layers causing that layer to be read out. The specific memory access media layer is selected by means of scanning the interference pattern spatially within the interrogation beam, or by means of scanning the interrogation beam in wavelength.