Abstract: Ionic and impurity concentrations in a photorefractive holographic storage medium are optimized such that electronic and ionic Debye numbers match an expected grating wave number K, at fixing and recording temperatures, respectively. Simultaneous and sequential recording and fixing are evaluated. The photovoltaic effect is reduced, subject to response time and absorption constraints, by matching reduced and oxidized impurity concentrations.

Abstract: A dynamic multiple-wavelength filter which selects at least one wavelength from a beam of radiation incident on a Stratified volume Holographic Optical Element (SVHOE) in accordance with the Bragg condition. The SVHOE has a number n of grating layers i and a hologram of a grating vector K.sup.i is recorded in each grating layer i. A number n-1 of buffer layers are interposed between grating layers i such that the layers SVHOE presents an alternating structure of grating and buffer layers. The filter has a diffraction efficiency control, preferably based on the ECD effect, for selectively varying the diffraction efficiency .eta. in at least one grating layer i to select from the beam of radiation a narrow bandwidth centered about Bragg wavelength .lambda..sub.B.sup.i of grating layer i.

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 storage system and method having separate, independent format hologram writing and data writing mechanisms to allow optimization of data writing separately from format hologram recording. In its most general terms, the invention comprises an optical medium having a first, photoactive material responsive to a first, format hologram recording condition, and a second photo-active material, responsive to a second data writing condition, which is dispersed or dissolved in the first photoactive material. The second photoactive material may additionally be “erasable” under a third, erasing condition. The second photoactive material is preferably in the form of microparticles, microdroplets or microcapsules which are dispersed throughout the first photoactive material.

Abstract: An optical storage system and method having separate, independent format hologram writing and data writing mechanisms to allow optimization of data writing separately from format hologram recording. In its most general terms, the invention comprises an optical medium having a first, photoactive material responsive to a first, format hologram recording condition and a second photo-active material, responsive to a second, data writing condition, which is dispersed or dissolved in the first photoactive material. The second photoactive material may additionally be “erasable” under a third, erasing condition. The second photoactive material is preferably in the form of microparticles, microdroplets or microcapsules which are dispersed throughout the first photoactive material.

Abstract: A method for coded-wavelength multiplexing according to which a signal waves S.sub.i (r) is recorded in a holographic medium in a counter-propagating geometry using corresponding writing reference waves R.sub.i (r). The method involves selecting discrete wavelengths .lambda. and encoding reference wave vectors .rho..sub.l which make up writing reference waves R.sub.i (r) such that the writing reference waves R.sub.i (r) at each wavelength .lambda. are orthogonal. The stored signal waves S.sub.i (r) are reconstructed in the form of reconstruction waves A.sub.c (.sigma.) with reconstruction reference waves R.sub.c (r) selected from among the writing reference waves R.sub.i (r). In the event of angular multiplexing of the reference wave vectors .rho..sub.l, it is possible to use one reference wave to produce a number of reconstruction waves A.sub.c (.sigma.) and generate a mosaic of desired holographic pages.

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 hologram with a dynamically controlled diffraction efficiency and enhanced signal-to-noise ratio is recorded in ferroelectric photorefractive materials, such as strontium barium niobate (Sr.sub.x Ba.sub.1-x Nb.sub.2 O.sub.6) (SBN), BSTN, SCNN, PBN, BSKNN, BaTiO.sub.3, LiNbO.sub.3, KNbO.sub.3, KTN, PLZT and the tungsten bronze family. The diffraction efficiency of the hologram is dynamically controlled by applying an electric field along the polar axis of the ferroelectric photorefractive recording medium. Electrically controlled diffraction is used in conjunction with hologram fixing and operation of the material at a temperature in the vicinity of or above its Curie temperature to additionally provide prolonged, low-noise readout. The general methods for recording and reconstructing a hologram (or a set of multiplexed holograms) using these techniques is disclosed.

Abstract: Rare earth doped ferroelectric materials are disclosed as reversible holographic recording medium (25) for use in two-photon recording systems. Such rare earth elements provide long-lived electronic states intermediate the ferroelectric material's valence and conduction bands. In some cases, these rare earth intermediate states have a sufficiently long life 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. Rather, the disclosed holographic recording systems employ cw lasers such as diode lasers. The rare earth dopants include praseodymium, neodymium, dysprosium, holmium, erbium, and thulium. These dopants provide ions having 4f excited states that give rise to absorptions in the near infra-red and visible spectral regions and typically have lifetimes on the order of 0.1 to 1 milliseconds.