Abstract: A positive unit magnification reflective head is used to back-reflect a primary light beam, for storing reflection microholograms at the coincident foci of the primary and reflected beams. Imaging the primary beam focus onto itself at positive unit magnification allows increasing system tolerance to tilts and transverse misalignments between the primary and reflective heads. Holograms are stored at multiple depths in a holographic storage medium. Tunable-focus primary and reflective heads are positioned on opposite sides of the storage medium. The reflective head images each storage location onto itself at positive unit magnification. Suitable reflective heads include: two lenses in an f-2f-f configuration and a planar mirror; a lens and a corner cube; a thin lens and a thick lens with a coated reflective back surface; and a thin lens and a back-coated gradient-index (GRIN) lens.

Abstract: An improved focus error signal generator device and an optical data delivery and detection system including an optical lens disposed in the path of a return read beam and a birefringent plate disposed in the path of the return beam of light after the optical lens, wherein the birefringent plate provides for a first and second focal plane of corresponding first and second polarization. A pinhole is disposed in the path of the return read beam after the birefringent plate and in close proximity to first and second focal planes. A polarizing beam splitter is positioned after the second focal plane and serves to split the return read beam into two light beams of first and second polarization. First and second detectors are disposed in the path of corresponding first and second polarization light beams. The detectors are connected to the inputs of an electrical differencing circuit that has an output to an optical head servo system.

Abstract: An improved focus error signal generator device including two optical lenses in series; a birefringent optical lens followed by a standard optical lens, the lenses being disposed in the path of a return read beam wherein the birefringent optical lens has a first and second focal plane. A pinhole is disposed in the path of the return read beam in close proximity to the first and second focal planes. A polarizing beam splitter is positioned after the second focal plane and serves to split the return read beam into two light beams of polarization associated with the first and second focal planes. First and second detectors are positioned so as to read the two light beams signals output from the polarizing beam splitter and the detectors are connected to an electrical differencing circuit having an output to an optical head servo system.

Abstract: A focus error signal generator device and an optical data delivery and detection system including an optical lens disposed in the path of a return read light beam, and first and second polarizers of corresponding first and second polarizations having corresponding first and second pinholes formed therein wherein the polarizers are spaced apart, disposed in the path of the read light beam after the optical lens. A polarizing beam splitter is disposed in the path of the read light beam after the second polarizer and serves to split the read light beam into a first light beam of first polarization and a second light beam of second polarization. First and second light beams are received by corresponding first and second optical detectors and an electrical differencing circuit having inputs to the first and second detectors and an output to an optical head servo system.

Abstract: Digital data bits are stored at storage locations at plural depths within a holographic storage medium as selective, localized alterations in a format hologram. Micro-localized regions of a reflection format hologram extending throughout the medium are deleted by focusing a high-power laser beam at desired storage locations. The deletion regions have a lower reflectivity than the surrounding parts of the format hologram. Tunable-focus storage and retrieval heads, as well as dynamic aberration compensators, are used for multi-depth access. Storage and retrieval may each be achieved with a single head.

Abstract: An apparatus and a method for loading and unloading a flying lens relative to the surface of an optical storage media is provided. The apparatus is comprises a flying lens, a movable optical module for supporting and positioning the lens, and a ramp that slidably engages the movable optical module to load and unload the flying lens. The flying lens is loaded, or moved into a position close to the surface of the moving optical storage media, when the speed is sufficient that aerodynamic forces prevent contact between the flying lens and the storage media. The flying lens is unloaded before the storage media slows or stops and is held in a parked position by the ramp. During the loading and unloading the alignment integrity of the optical path is maintained.

Abstract: A positive unit magnification reflective head is used to back-reflect a primary light beam, for storing reflection microholograms at the coincident foci of the primary and reflected beams. Imaging the primary beam focus onto itself at positive unit magnification allows increasing system tolerance to tilts and transverse misalignments between the primary and reflective heads. Holograms are stored at multiple depths in a holographic storage medium. Tunable-focus primary and reflective heads are positioned on opposite sides of the storage medium. The reflective head images each storage location onto itself at positive unit magnification. Suitable reflective heads include: two lenses in an f-2f-f configuration and a planar mirror; a lens and a corner cube; a thin lens and a thick lens with a coated reflective back surface; and a thin lens and a back-coated gradient-index (GRIN) lens.

Abstract: A pair of compensation lenses which provide an adjustable amount of spherical aberration. Each compensation lens has an external surface and an internal surface. The internal surfaces face each other and define an air gap spacing between them. The external surfaces are preferably planar. The internal surfaces are purely aspheric and therefore have an absence of spherical power and an absence of spherical curvature. The amount of spherical aberration compensation is determined by adjusting an air gap spacing between the internal surfaces. The spherical aberration provided by the lenses can be negative, positive, or zero. For compensation of negative spherical aberration present when focusing light into a data storage medium, the compensation lenses should provide positive spherical aberration. The absence of spherical power characteristic of the compensation lenses allows them to be located far from an objective lens which requires spherical aberration compensation.

Abstract: A focus error signal generator device including first and second optical lenses disposed in the respective paths of first and second light beams derived from the return read beam wherein the first and second optical lens have corresponding points of focus, and first and second detectors disposed in the corresponding paths of the first and second light beams located after the points of focus. First and second pinholes are disposed in the corresponding paths of the first and second light beams after the corresponding optical lens and before the corresponding detector, and an electrical differencing circuit having inputs to the first and second detectors and an output to an optical head servo system.

Abstract: A holographic storage and retrieval system for use in co-propagating or counter-propagating geometries having a common optical relay for guiding a signal beam and a reference beam along a common optical axis to a holographic medium to write a hologram therein. The optical relay has an object region imaging quality such that at least 65% and preferably at least 80% of the nominal luminous energy from object pixels is encompassed or "ensquared" by the corresponding image pixels. Additionally, the optical relay has a high total numerical aperture (N.A.) of about 0.83, a pixel N.A. of approximately 0.04 for the signal beam. The system of the invention can be used with holographic storage media in the form of disks, tapes or bulk holographic crystals.

Abstract: The holographic storage and retrieval system according to the present invention comprises one convex reflector and one concave reflector having the same optical axis. The reflective surfaces of the two reflectors are opposite each other. The concave reflector is normally larger than the convex reflector. The holographic storage medium is positioned at the focal surface of the concave reflector. The spherical reflector system according to the present invention has nearly ideal performance off-axis: high bandwidth, low aberration imaging is permitted at a number of radial and axial locations. Thus, multiple SLM/CCD pairs can be placed off-axis to access the same storage medium and implement multiple interconnects.

Abstract: Two lenses separated by an air gap provide spherical aberration compensation and focusing of a light beam to a focal point inside a data storage medium. The thickness of the air gap determines the amount of spherical aberration compensation provided. The distance between the lens pair and storage medium determines the depth of the focal point within the storage medium. The internal surfaces of the lenses which define the air gap are preferably planar. The external surfaces of the lenses are aspheric to provide accurate focusing and positive spherical aberration. The air gap between the lenses may also be formed by curved internal surfaces, in which case it is best for the focus lens to have a concave internal surface. The apparatus and method of the present invention reduces the number of optical components required for an optical data reading/writing device.

Abstract: A method for holographic data storage comprises the step of formatting a page with calibration marks as well as data patterns representing data. The page is then stored in a holographic storage medium. A method for holographic data retrieval comprises the step of detecting locations of the calibration marks. A mathematical function is fitted to the locations, and the function is used to compensate for distortion in the detected image of the page. In the preferred embodiment, the calibration marks are also used to generate an inverse point spread function that is used to digitally sharpen the detected image of the page. In the preferred embodiment, the data patterns are dispersed throughout the page by an interleaving algorithm, so that subsequent data patterns are not stored consecutively in the page.

Abstract: The data encoder (e.g. an amplitude spatial light modulator, ASLM) in a volume holographic storage system is rotated by 45.degree. relative to the normal to the plane of the reference and signal beams, such that the near-Fourier transform pattern of the encoder at the medium has an X-shape. The encoder rotation allows tight packing of spatial multiplexing subvolumes in a rectangular array, and provides for uniform spatial frequency filtering in a perpendicular geometry.

Abstract: A DMD illumination coupler, and a method of improving the wavefront quality of a transmitted illumination beam over the prior art using the invented DMD illumination coupler are disclosed. The invented DMD illumination coupler comprises an angularly selective reflective thin film. The invented DMD illumination coupler has the characteristics of high optical quality and cost effectiveness. The application of the invented DMD illumination coupler in holographic systems is also discussed.

Abstract: Digital data bits are stored as discrete-level reflection microholograms in a multi-depth digital optical data storage system. Reference and signal beams are incident in a counterpropagating geometry on opposite faces of a tape. The reflection microholograms are stored at the coinciding focus of the reference and signal beams. The holograms are stored at the diffraction limit of high-N.A. optics, and have relatively high grating frequencies and small sizes. Dynamic aberration compensators correct for the depth-varying spherical aberration imparted to the beams by the medium. Multiple mutually-incoherent lasers are used for parallel storage and retrieval to increase data transfer rates. Achievable densities and signal-to-noise ratios are substantially higher than for index-perturbation or transmission hologram storage methods.

Abstract: A holographic data storage apparatus having no readout lens. The apparatus has a spatial light modulator (SLM), a focusing element such as a lens, a holographic data storage material and a spatial light detector such as a CCD. The lens is located between the SLM and CCD such that the SLM is imaged onto the CCD (i.e. the positions of the SLM, lens, and CCD satisfy the lens equation). The holographic storage material is located between the lens and CCD. Preferably, the storage material is located centered upon a Fourier plane of the lens. In this case, the apparatus also has a phase mask located adjacent to the SLM. Alternatively, the storage material is located a distance away from the Fourier plane or is not centered on the Fourier plane. In yet another embodiment, the holographic storage material is located in contact with the CCD.

Abstract: A pair of compensation lenses which provide an adjustable amount of spherical aberration. Each compensation lens has an external surface and an internal surface. The internal surfaces face each other and define an air gap spacing between them. The external surfaces are preferably planar. The internal surfaces are purely aspheric and therefore have an absence of spherical power and an absence of spherical curvature. The amount of spherical aberration compensation is determined by adjusting an air gap spacing between the internal surfaces. The spherical aberration provided by the lenses can be negative, positive, or zero. For compensation of negative spherical aberration present when focusing light into a data storage medium, the compensation lenses should provide positive spherical aberration. The absence of spherical power characteristic of the compensation lenses allows them to be located far from an objective lens which requires spherical aberration compensation.