Glenn Tavernia Sincerbox

Pixel-matched holographic data storage with megabit pages

Digital data-page holograms consisting of 1024 x 1024 arrays of binary pixels have been stored and subsequently retrieved with an optical exposure consistent with a data rate 1 Gbit /s. Each input pixel was precisely registered with a single detector pixel, and a raw bit-error rate as low as 2.4 x 10(-6) was demonstrated with global-threshold detection. To our knowledge, this is the first demonstration of the often-cited goal of holographic data storage of megabit data pages and a gigabit-per-second data rate.

A precision tester for studies of holographic optical storage materials and recording physics.

The design and the realization of an advanced precision optical test stand for evaluating materials and developing tools and techniques for holographic digital data storage are described. This apparatus allows studies of holographic recording materials and recording physics to be performed in the context of practical data storage. The system concept, its implementation, and its performance are described, and examples of holographic storage in photorefractive materials are discussed.

Diffraction characteristics of photoresist surface-relief gratings

Theoretical results from rigorous coupled-wave analysis are compared with experimental diffraction characteristics for holographically formed dielectric photoresist surface-relief gratings with deep grooves (greater than a grating period) and high diffraction efficiency (>85%). The angular selectivity (at a fixed wavelength) and the wavelength selectivity (at a fixed angle of incidence) are presented for both TE and TM incident polarizations. Modeling the gratings as a surface-relief modulated half-space and using rigorous coupled-wave analysis are shown to produce good general agreement with the experimentally measured diffraction characteristics.

Conservative arrays: multidimensional modulation codes for holographic recording

In holographic storage, two-dimensional arrays of binary data is optically recorded in a medium via an interference process. To ensure optimum operation of a holographic recording system, it is desirable that the patterns of 1s (light) and 0s (no light) in the recorded array satisfy the following modulation constraint: in each row and column of the array there are at least t transitions of the type 1/spl rarr/0 or 0/spl rarr/1, for a prescribed integer t. A two-dimensional array with this property is said to be a conservative array of strength t. In general, an n-dimensional conservative array of strength t is a binary array having at least t transitions in each column, extending in any of the n dimensions of the array. We present an algorithm for encoding unconstrained binary data into an n-dimensional conservative array of strength t. The algorithm employs differential coding and error-correcting codes. Using n binary codes-one per dimension-with minimum Hamming distance d/spl ges/2t-3, we apply a certain transformation to an arbitrary information array which ensures that the number of transitions in each dimension is determined by the minimum distance of the corresponding code.

Opto-optical light deflection

Light deflection is accomplished by diffraction from a transient index modulation established as a grating of variable frequency in an optical material by the interference of two controlling light beams. This device may be considered an opto-optical analog to an acoustooptical deflector, in that a change in angular deflection is created by altering the frequency of the diffraction grating. In this paper we report on a technique for altering the grating frequency by changing the wavelength of the control beams and the use of a novel optical system to maintain the Bragg condition over a wide range of frequencies. Configurations exhibiting very large angular deflections have been designed using a computer simulation and optimization program that allows minimization of the Bragg detuning. This new method of light deflection allows either discrete or continuous light scanning or modulation. A particular example using lithium niobate will be discussed which produces an 11.8 degrees deflection from a 0.027-micron wavelength change and with an angular detuning of lessthan +/-0.03 degrees. The use of other materials, inorganic, organic, and dispersive, will also be discussed.

A novel sensitized photochromic organic glass for holographic optical storage

A new class of photochromic glasses for use in irreversible holographic optical storage applications is described. The recording mechanism involves a triplet‐sensitized photoreaction of an organic chromophore. The materials are isotropic and red‐sensitive, and exhibit high diffraction efficiencies and long hologram lifetimes. The wavelength sensitivity can be adjusted by the choice of sensitizer; C60, sensitive in the red, is described here. Single digital data page recording and error‐free readout are demonstrated at a density of 0.5 Mb/cm2; multiplexing in a 150‐μm‐thick sample is also demonstrated.

Holographic storage: the quest for the ideal material continues

Abstract Throughout the 30-year history of holographic storage, an enormous number of material systems have been studied for use as the recording medium. In spite of the years and effort expended, the ideal material has not been identified and interest in holographic storage has waned. Recently, however, advances in both organic and inorganic photorefractive materials has rekindled interest in volume holography, not only for information storage but also as a technology that may be important for optical interconnects, neural networks and optical computing. Interest is further enhanced by continuing development in some of the enabling technologies, such as CCD arrays and spatial light modulators, necessary to make a viable storage product. After a brief introduction to holographic storage, this paper will concentrate on defining the systems requirements that drive material selection and review recent advances in photorefractive materials and techniques that address key issues. Included will be a discussion of multiplexing methods as well as various means to inhibit, or at least manage, destructive writing and reading. The paper will conclude with a discussion of the remaining critical issues as a focus for continued research and development.

Opto-optical light deflector

Light deflection is obtained by diffraction from a transient index modulation established as a grating of variable frequency by the interference of two light beams in an optical material. We describe a technique for altering the grating frequency by shifting only the wavelength of the control beams and the use of a novel optical system to maintain the Bragg condition over a wide range of frequencies in order to achieve light deflection without loss in efficiency. A computer simulation permits us to test various designs and to select the best configurations with emphasis on those that exhibit large angular deflections with minimum Bragg detuning. This new method of light deflection allows either discrete or continuous light scanning or modulation. The experimental results confirm the calculations and we have obtained angular deflection changes larger than 11 degrees from a wavelength shift smaller than 30 nm while maintaining the Bragg condition.

Polarization sensitivity of noise gratings recorded in silver halide volume holograms

The formation of holographic gratings in silver halide emulsions is limited by scattering from photosensitive grains embedded in these materials. The most serious consequence of this effect is a sharp reduction in the diffraction efficiency of a volume hologram reconstructed at the formation angle. This has been attributed to a noise grating, resulting from the interference between a beam illuminating the emulsion and scattered light. Although the presence of these gratings has previously been reported, their dependence on the relative orientation of the polarization of the construction and reconstruction beams has not been discussed. This report shows that the correct relative polarization orientation reduces the detrimental effects of these gratings and improves the efficiency of holograms formed in silver halide emulsions.

Near-infrared holography by two-photon photochemistry

The applicability of the technique of two-photon four-level photochemistry for the production of near-IR holograms is critically evaluated. Although the current best system (biacetyl in a polycyanoacrylate matrix) has low recording sensitivity, several applications of the material have been demonstrated. Hologram efficiencies of up to 70% recorded at 752 nm are shown. Recording of extended holographic images and production of holographic optical elements are demonstrated. Finally, we have recorded holograms directly with GaAlAs diode lasers.