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 method for optical data storage and/or retrieval using an optical data storage medium having a spatially-modulated refractive index that can be altered locally with optical methods. Data can be written at a plurality of depths throughout the volume of the medium using a write beam and relatively simple and inexpensive optical components. The write beam stores data locally by physical distortion of the medium at discrete storage locations. The alterations can be detected as variations in the reflectivity of the storage locations using a retrieval beam.

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: Digital data bits are stored at storage locations at plural depths within a holographic medium of a holographic storage disk in the form of 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: 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: 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: 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: An optical data storage system and method comprising a photopolymer medium having generally a polymerizable monomer, an active binder, a first, hologram recording polymerization initiator, and a second, data writing polymerization initiator. The monomer is preferably a cationic ring-opening monomer. The hologram recording polymerization initiator preferably comprises a sensitizer and photoacid generator which initiate a first polymerization in the medium which defines a format hologram. The format hologram recording is carried out via interference of a signal and reference beam, with the sensitizer being specific for the wavelength(s) of the signal and reference beams. The hologram recording polymerization is only partial and does not consume all of the monomer present in the photopolymer medium.

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).