Abstract: An optical system having at least one switched mirror for switching and routing at least one incident beam of electromagnetic radiation. The switched mirrors are controlled by a voltage source and based upon the desired controllability of the switched mirrors and wide range of switching and or routing of an optical signal can be effected. In addition by the selective placement of components with the optical system polarization effects can be controlled with the optical system to more effectively provide for subsequent signal transmission.

Abstract: A dioptric projection optical system projects an image of a first surface onto a second surface and includes a first lens group having a negative refractive power and arranged in an optical path between the first surface and the second surface, a second lens group having a positive refractive power and arranged in an optical path between the first lens group and the second surface, a third lens group having a negative refractive power and arranged in an optical path between the second lens group and the second surface, a fourth lens group having an aperture stop and arranged in an optical path between the third lens group and the second surface, and a fifth lens group having a positive refractive power and arranged in an optical path between the fourth lens group and the second surface, wherein lens components belonging to the dioptric projection optical system are formed of at least two types of fluorides, and wherein a clear aperture of a light beam in the projection optical system is at a relative maximum

Abstract: A holographic information storage and retrieval system provides an all-optical reversible method to fix information in doped or undoped photorefractive materials. The fixed information is sufficiently stable to provide long term archival storage over a period of decades or more and can be read out non-destructively by a coherent reference beam. Holograms recorded in a photorefractive material are fixed when the material is irradiated with incoherent ultraviolet light. Hence, the holograms are preserved indefinitely against erasure by a coherent beam and against dissipation in dark storage. Holograms, which are fixed in the photorefractive material with incoherent ultraviolet light, are. also erased with incoherent ultraviolet light, thus making the process reversible.

Abstract: A holographic recording medium comprising an amorphous host material which undergoes a phase change from a first to a second thermodynamic phase in response to a temperature rise about a predetermined transition temperature; a plurality of photo-sensitive molecular units embedded in the host material and which can be orientated in response to illumination from a light source; whereby said molecular units may be so orientated when said host material is at a temperature equal to or above said transition temperature but retain a substantially fixed orientation at temperatures below said transition temperature.

Abstract: Disclosed is a pretreatment method for a hologram recording medium used in the hologram recording method in which information signals loaded on signal beam are recorded by injecting coherent signal beam and reference beam to the hologram recording medium which is exposed to first light having first wavelength of ultraviolet band or short-wavelength visible light band in advance in order to generate light-induced absorption, wherein the coherent signal beam and reference beam each having longer wavelength than the first wavelength. The pretreatment method comprises subjecting the hologram recording medium to oxidation treatment prior to the irradiation of the first light has been completed.

Abstract: The present invention relates to an optical switch comprising a paraelectric photorefractive material, storing a hologram, possibly a latent hologram, whose reconstruction, or activation and reconstruction, is controllable by means of an applied electric field. The hologram may be formed by spatial modulation of the refractive index of the paraelectric photorefractive material, which arises from the quadratic electro-optic effect induced by the combined action of a spatially modulated space charge within the paraelectric photorefractive material and an external applied electric field. The present invention further relates to a switching network, such as a multistage network, for use in an optical communications system, incorporating at least one optical switch according to the invention.

Abstract: A holographic recording medium comprising an amorphous host material which undergoes a phase change from a first to a second thermodynamic phase in response to a temperature rise about a predetermined transition temperature; a plurality of photo-sensitive molecular units embedded in the host material and which can be orientated in response to illumination from a light source; whereby said molecular units may be so orientated when said host material is at a temperature equal to or above said transition temperature but retain a substantially fixed orientation at temperatures below said transition temperature.

Abstract: Improvements to the acquisition and replay systems for direct-to-digital holography and holovision are described. A method of recording an off-axis hologram includes: splitting a laser beam into an object beam and a reference beam; reflecting the reference beam from a reference beam mirror; reflecting the object beam from an illumination beamsplitter; passing the object beam through an objective lens; reflecting the object beam from an object; focusing the reference beam and the object beam at a focal plane of a digital recorder to form an off-axis hologram; digitally recording the off-axis hologram; and transforming the off-axis hologram in accordance with a Fourier transform to obtain a set of results. A method of writing an off-axis hologram includes: passing a laser beam through a spatial light modulator; and focusing the laser beam at a focal plane of a photorefractive crystal to impose a holographic diffraction grating pattern on the photorefractive crystal.

Abstract: Improvements to the acquisition and replay systems for direct-to-digital holography and holovision are described. A method of recording an off-axis hologram includes: splitting a laser beam into an object beam and a reference beam; reflecting the reference beam from a reference beam mirror; reflecting the object beam from an illumination beamsplitter; passing the object beam through an objective lens; reflecting the object beam from an object; focusing the reference beam and the object beam at a focal plane of a digital recorder to form an off-axis hologram; digitally recording the off-axis hologram; and transforming the off-axis hologram in accordance with a Fourier transform to obtain a set of results. A method of writing an off-axis hologram includes: passing a laser beam through a spatial light modulator; and focusing the laser beam at a focal plane of a photorefractive crystal to impose a holographic diffraction grating pattern on the photorefractive crystal.

Abstract: A two-color holographic recording apparatus reduces error signals possibly included in reproduced digital data signals. The two-color holographic recording apparatus has first, second and third light shutters for passing or blocking gate light, signal light and reference light incident on a recording medium respectively, and a controller for controlling the respective states of the first, second and third light shutters.

Abstract: A holographic information storage and retrieval system provides an all-optical reversible method to fix information in doped or undoped photorefractive materials. The fixed information is sufficiently stable to provide long term archival storage over a period of decades or more and can be read out non-destructively by a coherent reference beam. Holograms recorded in a photorefractive material are fixed when the material is irradiated with incoherent ultraviolet light. Hence, the holograms are preserved indefinitely against erasure by a coherent beam and against dissipation in dark storage. Holograms, which are fixed in the photorefractive material with incoherent ultraviolet light, are also erased with incoherent ultraviolet light, thus making the process reversible.

Abstract: A hologram recording medium, a hologram recording method and a recording and reproducing apparatus are capable of recording an interference pattern onto a volume holographic memory at high density.

Abstract: Disclosed is a storage medium which comprises strontium barium niobate single crystal containing europium and cerium as impurities. The material may be used in which the strontium barium niobate has a chemical formula: SrxBa1-xNb2O6 where x satisfies 0.25≦x≦0.75. Further, small amounts of cerium and europium are added to a main component comprised by strontium, barium, niobate and oxygen. The optical material can be used in various optical devices such as a holographic storage medium, a phase conjugate mirror and an optical amplifier.

Abstract: An optical information recording and reproducing apparatus, which detachably supports a holographic memory formed of a photorefractive crystal, includes a portion for supplying a coherent reference light beam at a first wavelength into the holographic memory; a portion for supplying a coherent signal light beam at the first wavelength, modulated in accordance with image data, into the memory to produce an optical interference pattern with the reference light within the memory; a portion for supplying a gate light beam at a second wavelength into the memory for activating or deactivating an index grating in accordance with the presence or absence of the optical interference pattern to enhance a photo-sensitivity of the memory; a detector for detecting diffraction light from the index grating of the memory by the irradiation of the reference light beam; and a portion for changing and regulating a light intensity of the gate light beam.

Abstract: A method for optimizing the interaction of a resonant material having generalized crystal symmetry with a beam or beams of radiation. The invention includes determining a special direction relative to the axes of crystal symmetry of the material and polarizing the interaction radiation beam along this direction. The polarized radiation beam is propagated through the material perpendicular to this special direction. The method and system are used in any application which involves the coherent interaction of optical radiation beams or fields with resonant ion-doped or molecular crystals of various types. Coherent interaction of optical radiation beams or fields with resonant ion-doped or molecular crystals of various types includes the phenomena of optical coherent transients, spectral hole burning, and spatial-spectral holography (also called time and space domain holography) and provides the basis for optical-electronic devices. Such applications include computer and communications networks.

Abstract: A system and method for generating a system are disclosed. The system includes a display device comprising a plurality of display regions, each region configured for displaying a color component of the image. A display controller is coupled to the display device and is operable to activate the regions of the display device to display portions of the image. A plurality of light directing devices are positioned to receive light from regions of the display device and direct light towards an image plane. The system further includes a light directing controller coupled to the light directing devices to direct light received thereby to different areas of the image plane. The areas of the image plane generally correspond to the different portions of the image displayed by the regions of the display device.

Abstract: A semiconductor laser with a rewritable wavelength stabilizer which comprises a laser mirror made of a grating written into a photorefractive material, in which the oscillation wavelength of the laser diode is determined by the period of the grating. This allows the refractive index of the grating to be changed by illuminating the photorefractive material after cooling thereof to a temperature at which most of the doped impurities form DX centers. The grating can be erased by heating the photorefractive material to a temperature at which most DX centers are ionized, which erases the grating. Thereafter the photorefractive material is cooled again to a temperature at which most impurities become DX centers, and a new grating can be written in the photorefractive material. The wavelength of the semiconductor laser can be changed repeatedly by erasing and rewriting the grating therein.

Abstract: An optical polarization apparatus for application to color displays for laptop computers and hand held computers, and other applications where it is advantageous to switchably control the polarization of monochromatic light. In a first preferred embodiment, the apparatus includes a first holographic optical device disposed between a source of randomly polarized light and a second holographic optical device that produces an output beam of plane-polarized light in a desired direction. The first optical device is a Bragg hologram that characteristically diffracts p-polarized light significantly more efficiently than s-polarized light. The first device splits the randomly polarized light into these two orthogonal components.

Abstract: An optical retro-reflective apparatus for application to reconfigurable displays for highway signs and other applications is disclosed. In a first preferred embodiment, the apparatus includes a retro-reflector such as a corner cube prism, three orthogonally arranged planer reflectors, or a plurality of either arranged as an array, or an array of micro-spheres or micro-prisms arranged as a corner-cube. In one embodiment, a holographic diffraction element is placed between a source of radiation such as visible light and one or more of the retro-reflectors. The diffraction element is made up of one or more stacked holographic devices in which pre-determined holographs are stored, operative to diffract a particular wavelength band of radiation (e.g. red, blue and green visible light). The hologram devices can be stacked and selectively deactivated so that the desired wavelength band (or color) to be diffracted is selected.

Abstract: A holographic storage medium, a method of manufacturing the holographic storage medium and a holographic storage device incorporating the storage medium. In one embodiment, the holographic storage medium includes: (1) first and second spaced-apart substrates, the first substrate being plastic and (2) a photopolymer core located between said first and second substrates and having a coefficient of thermal expansion such that said first and second substrates and said photopolymer core cooperate to respond substantially isotropically to a change in temperature.

Abstract: A method of producing a switchable hologram generally comprises providing a substrate comprised of a liquid crystal material and having two generally opposed surfaces and recording a plurality of holographic fringes composed of liquid crystal droplets in the substrate with one or more of the plurality of holographic fringes positioned such that a surface of the fringes is angled relative to one of the substrate surfaces. The substrate is subjected to an electrical field during recording of the holographic fringes. The electrical field varies across the surface of the substrate so that the liquid crystal droplets are all oriented generally in a common direction.

Abstract: A description is provided of an optical information recording and reproducing apparatus which detachably supports a volume holographic memory formed of a photorefractive crystal. The apparatus includes a portion for supplying a coherent reference light beam at a first wavelength into the volume holographic memory; a portion for supplying a coherent signal light beam at the first wavelength, modulated in accordance with image data, into the memory to produce an optical interference pattern with the reference light within the memory; a portion for supplying a gate light beam at a second wavelength into the memory for activating or deactivating an index grating in accordance with the presence or absence of the optical interference pattern to enhances a photo-sensitivity of the memory; and a detector for detecting diffraction light from the index grating of the memory by the irradiation of the reference light beam.

Abstract: Disclosed are a holographic optical element (HOE) and a method of producing the HOE. In one embodiment of the method, a substrate is provided which is capable of recording a hologram or diffraction gratings. This substrate is illuminated with a first pair of light beams and a second pair of light beams. The first pair of light beams intersect within the substrate. The second pair of light beams also intersect within the substrate. Additionally, the first pair of light beams intersect at a region within the substrate where the second pair of light beams intersect. Normally, each of the first pair of light beams comprises light of a first wavelength, and each of the second pair of light beams comprises light of a second wavelength, where the first wavelength is different from the second wavelength.

Abstract: Transmission and reflection type holograms may be formed utilizing a novel polymer-dispersed liquid crystal (PDLC) material and its unique switching characteristics to form optical elements. Applications for these switchable holograms include communications switches and switchable transmission, and reflection red, green, and blue lenses. The PDLC material of the present invention offers all of the features of holographic photopolymers with the added advantage that the hologram can be switched on and off with the application of an electric field. The material is a mixture of a polymerizable monomer and liquid crystal, along with other ingredients, including a photoinitiator dye. Upon irradiation, the liquid crystal separates as a distinct phase of nanometer-size droplets aligned in periodic channels forming the hologram. The material is called a holographic polymer-dispersed liquid crystal (H-PDLC).

Abstract: The invention relates to an optical element with variable optical properties, which ensures that the amount of light available is increased, and an optical device using the same. In a liquid crystal variable hologram element 3, polymer layers 18 and liquid crystal layers 19 are alternately arranged between transparent substrates 16 and 17, with liquid crystal particles 20 lining up in each liquid crystal layer 19. When voltages are applied on transparent electrodes 21 and 22, liquid crystal molecules 23 have their longitudinal directions oriented vertically with respect to the electrodes, so that the refractive index of the polymer layers 18 is substantially equal to that of the liquid crystal layers 19, resulting in no development of hologram. When the voltages are held off, the refractive index of the polymer layers 18 is different from that of the liquid crystal layers 19. This repetition gives rise to an interference fringe action, by which a hologram can be developed.

Abstract: A video display for two or three dimensions has a flat liquid-crystal screen 2 which ejects light from the plane at a selectable line 3. One or, in the case of a 3-D display, several video projectors 1 project a linear image into the plane from an edge. A complete image is written on the screen by addressing the line with appropriate images as it is scanned down the screen. To screen a three-dimensional image the video projectors, each projecting an image as seen at a slightly different angle, combine to constitute a three-dimensional display which produces a three-dimensional image that is one line high.

Abstract: A method and an apparatus for three-dimensional holographic display suitable for moving object display are disclosed. At least one hologram of a display target object is displayed on a display device, and a non-scattered light is irradiated onto the display device to produce a scattered light. Then the scattered light from the display device as an object light of the display target object and the non-scattered light as a reference light are irradiated simultaneously at different incident angles onto a photorefractive medium having a photorefractive effect, and interference fringes generated by the object light and the reference light are recorded in the photorefractive medium. Then, the three-dimensional image is displayed by irradiating only the non-scattered light onto the photorefractive medium so as to reproduce a holographic image corresponding to the interference fringes recorded in the photorefractive medium.

Abstract: A method for improving the quality of holographic images by reducing local noise in a holographic memory system is disclosed. The method is characterized by: storing a white reference image and a black reference image in the memory system, storing a series of data images in the memory system, applying a simple model based on a point-to-point of linear interpolation to the series of data images, the white reference image and the black reference image to provide a series of corrected data images having reduced noise.

Abstract: A non-volatile holographic recording method and system based on a doubly-doped photorefractive material. One embodiment of the holographic material is doped to have first and second types of dopants that are operable to produce charge carriers to a common band in response to radiation of a specified wavelengths. Charge carriers in the common band can migrate to a different spatial location. The dopants are also capable of recombining with charge carriers in the common band. The first type of dopants have a first dopant energy level below the band by a first energy gap greater than a second energy gap of a second dopant energy level of the second type of dopants below the common band. The first and second dopant energy levels are separated from each other so that their absorption bands to the common band are substantially separated. In addition, the first and second energy gaps should be much greater than the thermal energy k.sub.

Abstract: A volume hologram is created by exposing a volume holographic optical storage medium comprising a doped optically transparent glass matrix having a scattering coefficient of less than 10.sup.-5 cm.sup.-1 to an interference pattern created by intersecting a spatially modulated object beam with a reference beam, the object beam and the reference beam each having a wavelength of less than about 300 nm. The glass matrix may be doped with any of the following: (1) nanocrystalline semiconductor particles and an activator, (2) an alkaline earth sulfide, Sm ions, and an additional dopant selected from the group consisting of Eu ions and Ce ions, (3) ZnS and an additional dopant selected from the group consisting of Pb ions, Cu ions, and Mn ions and (4) Cu or Ce ions.

Abstract: A holographic grating is written into a photorefractive erasable holographic member and a light beam having a first wavelength which includes the joint power spectrum of a pair of joint images to be correlated is directed at the photorefractive member to partially erase the grating. A phase conjugate signal from the partially erased grating is then readout and Fourier transformed to produce the correlation output spots.

Abstract: A method and an apparatus for increasing detection signal-to-noise ratio, by reducing the effect of optical scatterers from a holographic storage medium, are disclosed. The method comprises the step of sensing the phase of scattered radiation and the subsequent step of writing the hologram data into the holographic storage medium. The image containing the hologram data is written with phase characteristics such that, during a subsequent hologram readout, the electric fields from the image and scatterers are 90 degrees out of phase. This optimum phase relationship greatly reduces the effect of scatter noise, thereby increasing signal-to-noise ratio and reducing bit-error-rate.

Abstract: Object rays and reference rays are projected to record interference fringes on a volume hologram comprising a material exhibiting a photoinducing refractive effect, and a reconstructed image is obtained by illuminating the volume hologram with reconstruction rays. When the wavelength .lambda..sub.1 of the object rays is longer than the wavelength .lambda..sub.2 of the reconstruction rays, the reconstruction is conducted by illuminating the volume hologram with a convergent spherical wave and when the wavelength .lambda..sub.1 of the object rays is shorter than the wavelength .lambda..sub.2 of the reconstruction rays, the reconstruction is conducted by illuminating the volume hologram with a diffused spherical wave.

Abstract: A method for dynamically refreshing a holographic data storage medium wherein data is stored in a plurality of data pages, each of which comprises a two dimensional pattern of pixel data. Each data page is stored by interfacing an image or a Fourier transform of the data page with a reference beam to form a holographic recording of the data page in the holographic medium. Pursuant to the method, all of the data pages are classified as either good pages, each of which was written into storage less than a threshold time ago related to the decay of the holographic recording, or empty pages available for writing, or self-erasing pages which are self-erasing with time. At sequential time intervals, the oldest good page is read which then becomes a self-erasing page, and its data is rewritten into an empty page which then becomes the youngest good page, and the oldest self-erasing page becomes an empty page.

Abstract: Apparatus which allows selection and generation of a variety of hologrammatic optical wavefronts. A device, which comprises a substrate layer of varying thickness and an electro optic layer, with a voltage dependent refractive index mismatch between the two, is used to modulate transmitted light, thus generating a hologrammatic wavefront. Said modulation can be changed by variation of an applied voltage and this changes the wavefront which is generated. The range of wavefronts which can be generated is defined by the distribution of substrate layer thicknesses across the device.

Abstract: The present invention is a method for optical data storage which enhances the contrast between ON and OFF pixels. The method comprises writing a two-dimensional image comprising a plurality of pixels into a recording medium with the exposure of individual ON pixels during the recording of the image. The ON pixels are then switched off and OFF pixels are switched on, and the phase of either the object beam or reference beam is changed. The process results in subtraction of residual signal from the OFF pixels.

Abstract: The present invention is a method for optical data storage which compensates for deterministic variations. The method comprises writing a two-dimensional image comprising a plurality of pixels into a recording medium while varying the exposure of individual ON pixels during the recording of the image to expose the weaker pixels more than brighter pixels.

Abstract: Ferroelectric materials are disclosed as reversible holographic recording media (25) for use in two-photon recording systems. The ferroelectric materials disclosed herein provide long-lived electronic states intermediate the ferroelectric material's valence and conduction bands. These intermediate states have a sufficiently long life (on the order of 1 to 100 milliseconds) that low-power continuous wave ("cw") lasers (1) can be used to record interference patterns on them. Thus, two-photon holographic recording systems are also disclosed which do not require high-power, short pulse length, mode-locked or Q-switched lasers. The disclosed two-photon holographic recording systems provide for absorption of a first photon which excites electrons of holographic recording media to an intermediate state. Thereafter, upon absorption of a second photon, the electrons are promoted to the media's conduction band where they are arranged according to the interference pattern provided by the recording system.

Abstract: A method and an apparatus for increasing detection signal-to-noise ratio of a holographic image by compensating for noise characteristics of a holographic storage medium are disclosed.

Abstract: An encryption method and apparatus for holographic data storage are disclosed. In a system using orthogonal phase-code multiplexing, data is encrypted by modulating the reference beam using an encryption key K represented by a unitary operator. In practice, the encryption key K corresponds to a diffuser or other phase-modulating element placed in the reference beam path, or to shuffling the correspondence between the codes of an orthogonal phase function and the corresponding pixels of a phase spatial light modulator. Because of the lack of Bragg selectivity in the vertical direction, the phase functions used for phase-code multiplexing are preferably one dimensional. Such phase functions can be one-dimensional Walsh functions. The encryption method preserves the orthogonality of reference beams, and thus does not lead to a degradation in crosstalk performance.

Abstract: In a hologram recording and reproducing apparatus including a hologram record element having a record unit formed by a photorefractive single crystal and a pair of electrodes provided on the record unit for applying a voltage to said record unit, and an optical system for impinging light onto an incident surface of the record unit, the record unit is made of a (100) wafer of Bi.sub.12 SiO.sub.20 or Bi.sub.12 GeO.sub.20 optical single crystal belonging to a cubic system, the light is made incident upon the (100) incident surface such that an optical axis of the incident light is inclined with respect to <100> axis of the optical single crystal by an angle .theta. of 30.degree.-60.degree.. The hologram record unit is immersed in an optically transparent and electrically insulating medium having a refractive index which differs from a refractive index of the optical single crystal by not larger than 0.

Abstract: An all optical photorefractive holographic joint transform correlator provides a first correlation plane output port using two-beam coupling, and a second correlation plane output port employing four-wave mixing. With appropriate input beam intensity ratios, the first port output is capable of high discrimination, while simultaneously the second port offers a low discrimination output.

Abstract: An optical interconnection network in which more than one communication can ccur at any give time is disclosed. The interconnection network can form part of a parallel computer, a fiber optic switching network, a massive video or data server or an asynchronous transfer mode (ATM) network. The network includes transmission network elements, reception network elements and a holographic storage element. The holographic storage element is located equidistant form all the transmission and reception network elements and stores therein a multiplicity of holograms. Each volume hologram is responsive to a different angle of incidence of wavelength.

Abstract: An optical head device uses a birefringent diffraction grating polarizer configured in a reflection type. The device includes a polarizing hologram element which reflects the light from a light source to a converging lens system and diffracts the polarized light returning from a recording medium. A total reflection film is formed on a surface of a diffraction grating which is provided periodically by an ion exchange region and a dielectric film on a surface of a crystal plate having optically anisotropic characteristics. A polarizing beam splitter film formed on a surface of the polarizing hologram element has reflectivity and transmissivity having dependency on the polarization of the incident light. In another form, a polarizing hologram element includes a polarizing hologram which has diffractive efficiency having dependency on polarization of incident light and a polarizing beam splitter film which has reflectivity and transmissivity having dependency on the polarization of the incident light.

Abstract: A multiphoton photorefractive holographic recording material includes an electro-optic host material doped with at least one lanthanide.

Abstract: Image derogating optical noise due to light scattering of an object under examination, embedded in a light scattering medium, is substantially reduced by passing a modulated signal laser beam through the scattering medium, and interfering the emerging signal with a coherent modulated reference beam to produce a hologram in a photorefractive member of the object, which in turn is read out of the crystal by a third unmodulated coherent beam to retrieve a clear image of the object. A smart pixel image convertor light valve may be substituted for the photorefractive member.

Abstract: A new photorefractive material comprises BaTiO.sub.3 double-doped with two dopant species, both of which have at least two valence states, with one of the dopant species (e.g., cerium) having an ionization level that is near the middle of the barium titanate bandgap and the other dopant species (e.g., rhodium) having an ionization level that is closer to the valence band edge of barium titanate, such that both dopant species are sensitive to visible light, but only one dopant species (the one closer to the valence band edge) is sensitive to infrared radiation. The double-doped BaTiO.sub.3 provides a unique combination of photorefractive properties, thereby improving its performance as a holographic storage medium. The double-doped barium titanate crystal is employed as a holographic recording element. The double-doped barium titanate crystal has a dark storage time at room temperature of several years or more and may be nondestructively read out at an infrared wavelength.

Abstract: Partially overlapping holograms are stored in a cylindrical volume holographic storage medium capable of rotation about and translation along its longitudinal axis. The reference and signal beams are mutually perpendicular, and each is perpendicular to the longitudinal axis. An index-matched housing encloses the medium laterally. An optional helically-varying optical axis (c-axis) orientation allows recording at constant angular intervals over a full revolution. Signals from stored pages are used to dynamically adjust the positioning of the medium relative to the light beams as the medium continuously spins at high velocity, and to control the access of the signal beam to the readout camera.

Abstract: The present invention describes a method for high capacity holographic data storage in photorefractive crystals. A doped ferroelectric crystal is used as a data storage medium. Prior to the recording, the crystal is depoled either thermally or electrically. Multiplexed photorefractive holograms are then recorded by illuminating the crystal in such a manner that domain screening of the photorefractive space-charge field occurs. The crystal is then repoled to enable the reading of the holograms stored within the crystal. Finally, any given hologram is readout by illuminating the crystal at the Bragg condition, which typically occurs while illuminating the crystal at the same angle and/or wavelength at which the hologram was recorded.

Abstract: This device comprises an optical source emitting a single-wavelength light beam. An index grating has been recorded in a holographic device by the interference of two plane light beams, both being beams at a single wavelength with one and the same determined value and being concurrent in the holographic device. The holographic device is illuminated by the light beam and delivers a single-wavelength beam whose radiation pattern has a limited angular passband. The wavelength of the reading beam may be different from that of the recording beams. Its orientation is then different from that of the beams.