Geoffrey W. Burr

System metric for holographic memory systems

We introduce M/# as a metric for characterizing holographic memory systems. M/# is the constant of proportionality between diffraction efficiency and the number of holograms squared. Although M/# is a function of many variables in a holographic recording system, it can be measured from the recording and erasure of a single hologram. We verify experimentally that the diffraction efficiency of multiple holograms follows the prediction of M/# measured from a single hologram.

Thermal Fixing of 10,000 Holograms in LiNbO3:Fe

We discuss thermal fixing as a solution to the volatility problem in holographic storage systems that use photorefractive materials such as LiNbO(3):Fe. We present a systematic study to characterize the effect of thermal fixing on the error performance of a large-scale holographic memory. We introduce a novel, to our knowledge, incremental fixing schedule to improve the overall system fixing efficiency. We thermally fixed 10,000 holograms in a 90 degrees -geometry setup by using this new schedule. All the fixed holograms were retrieved with no errors.

Angle and space multiplexed holographic storage using the 90" geometry

The 90-degrees geometry - with reference and signal beams entering orthogonal crystal faces - is used to angularly multiplex up to 500 holograms at each of 8 spatially multiplexed locations in a LiNbO3 crystal. A segmented mirror array and a 2D mechanical scanner are used to perform both angular and spatial multiplexing. We show that this mirror array can be used with non-mechanical angle scanners, providing for holographic storage in multiple locations with no moving parts.

Effect of the oxidation state of LiNbO3:Fe on the diffraction efficiency of multiple holograms

We show that the oxidation state of Fe in LiNbO(3) has two competing effects on the diffraction efficiency of multiple holograms in 90 degrees -geometry holographic storage. For crystals with moderate absorption, the saturation space-charge field is larger after high-temperature reduction treatment. However, reduction also increases absorption, which reduces the overall diffraction efficiency. We develop a theoretical model that predicts achievable diffraction efficiency as a function of oxidation state, doping level, photovoltaic field, crystal length, and region of beam overlap. We compare this model with experimental results for achievable diffraction efficiency and erasure-time constant.

Large-scale volume holographic storage in the long interaction length architecture

We describe a page-formatted random-access holographic memory designed to store up to 160,000 holograms. The memory consists of 16 vertically spaced locations, each containing 10,000 holograms, which in turn are organized as 10 fractal-multiplexed rows of 1000 angularly-multiplexed holograms. A segmented mirror array is used to enable random access to any of the stored holograms within the access time of a non-mechanical angle scanner such as an acousto-optic deflector. Using a mechanical scanner with such a mirror array, we demonstrate storage of 10,000 holograms at a single location of the system, as well as simultaneous storage and recall of holograms at 6 locations, including the highest and lowest of the 16 locations.

Spatially and angle-multiplexed holographic random access memory

A 3-D holographic optical memory is described that combines spatially and angularly multiplexed storage to yield a storage capacity of approximately 1012 bits in a crystal with volume less than 100 cm3. A non-mechanical scanning mechanism, consisting of acoustooptic deflectors and a segmented mirror, retrieves any stored hologram in a time equal to the acoustic delay through the aperture of the acoustooptic deflector.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Large-scale rapid access holographic memory

We describe a page-formatted random-access holographic memory capable of storing up to 160,000 holograms. A segmented mirror array allows a 2D angle scanner to provide access to any of the stored holograms. High-speed random access can be achieved with a nonmechanical angle scanner. We demonstrate holographic storage and high-speed retrieval using an acousto- optic deflector.

Magnetically actuated MEMS scanning mirror

A 4 mm by 5 mm, magnetically actuated scanning MEMS mirror is fabricated by integration of bulk silicon micromachining and magnetic thin film head techniques. Large mirror deflection angles (0 - 70 degree(s)) are achieved. The MEMS mirror is demonstrated as a laser beam scanner in both conventional and compact holographic data storage system configurations.

Large-Scale Holographic Memory - Experimental Results

We present experimental results of a page-formatted random-access holographic memory capable of storing up to 1012 bits of information. Up to 500 holograms were angularly multiplexed at each of 8 spatially multiplexed locations, using a mechanical scanner and a segmented mirror array.

Large-scale Holographic Memory: Experiment Results

We describe a holographic optical memory capable of storing up to 10^12 bits of information. The stored information nis retrieved in blocks or pages, each consisting of n10^3 x 10^3 bits. Each page can be accessed randomly in napproximately 100 µsec with an experimentally measured SNR nof 816.8, and a projected probability of error of n10^(-28).