Holographic Storage Technique Research Articles

Multiplexed holographic memory by use of fiber bundle referencing

We propose a volume holographic storage technique, in which a fiber bundle is used to guide the reference beam. Multiplexing is implemented by changing the incident direction of the laser beam upon the fiber bundle in the reference arm. In the technique, we make the system more compact by using a wedge prism to change the direction of the laser beam. This method has a large accessible angular scanning range and a large geometric storage bandwidth. Multiple images are stored in a LiNbO3:Fe crystal with an angular separation of 0.05° between successive holograms using a wedge prism with a deviation angle of 8°. This method is useful as a new image storage technique because of its compactness and simplicity.

Low-frequency relaxation processes in LiNbO3: Fe single crystals

The study of the complex dielectric function of LiNbO 3 :Fe single crystals over a wide range of Fe concentrations revealed the presence of well-defined low-frequency relaxations associated to the Fe ion. These resonances are very sensitive to heat treatment and doping. Such low-frequency relaxation processes in LiNbO 3 :Fe could be important for a better understanding of this material due to its large application in nonlinear optics and especially in holographic storage techniques.

Large-time-bandwidth-product correlation and holographic storage with an s.a.w. storage correlator

High-resolution (375 Hz) spectrum analysis has been performed by correlating long signals during the read-in process. In a ZnO-on-Si storage correlator a new holographic storage technique is demonstrated to achieve chirp compression with large compression ratio (?8000) and improved dynamic range.

Page-Oriented Associative Holographic Memory

Holographic memories are an attractive candidate for future large capacity parallel associative search storage systems. Parallel retrieval of stored data is essential to many data processing applications, yet electronic implementations of associative memories are very costly. A straightforward extension of more conventional holographic storage techniques can be used to implement an associative memory. The various output beams for a two-dimensional page associative store are analyzed and separated to provide the desired output function. A correlation-type associative memory is also analyzed and compared with the first system. Applications of these memories are discussed for complex search algorithms and also for the potential of associative data processing.

Tomosynthesis: A holographic method for variable depth display

A circular symmetric tomosynthetic arrangement has been investigated using holographic storage techniques. With a set of 24 single radiographs a 3D image of a human orbita region has been generated by image integration leading to a continuously variable depth display of arbitrary layers. The received resolution in a particular layer was about 3 1p/mm. An estimate will be given for the number of necessary radiographs to compare the blurr quality of discrete sample procedures in tomosynthesis with a continuous motion in tomography. Finally a short outline will be given for a possible real-time procedure.

Optical storage of digital information

Optical data storage provides a solution for the requirements of large read-write mass memories (capacity greater than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> bits) with small random access time (typically several μs) with high speed data transfer rates (0.1-1 Gbit/s). The well-known properties characteristic of holographic storage, including lensless stigmatic imaging capabilities and redundancy, make the holographic storage technique attractive. When using a two-dimensional storage medium, theoretical studies indicate that an information density on the order of 2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> bit/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> are obtainable, or a wavelength of 0.5 μm. Even if one used optical components (lenses, etc.) having transverse dimensions as large as 80 cm, such a system would be limited to a capacity of about 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> bits. To obtain larger capacities it will be necessary to use a 3-dimensional storage medium allowing superposition of the stored information. This could be obtained by varying the angle of the holographic reference beam. A practical system for realizing such a memory is presented here. The organization of the memory is compatible with the use of a reversible storage material. The read-write functions are realized using an acoustooptic deflector, which eliminates any mechanically moving parts. The organization permits the use of a second deflector to vary the reference angle and allows superposition of holograms [1]. Possible recording materials which could be used in such memories are ferroelectric crystals or ceramics. Experiments in our laboratory have demonstrated the possibility of electrically controlling the fixation and erasure of holograms in these materials [2].