Today, along with the wider use of high-speed information networks and multimedia, it is increasingly necessary to have higher-density and higher-transfer-rate storage devices. Therefore, research and development into holographic memories with three-dimensional storage areas is being carried out to realize next-generation large-capacity memories. The mainstream in the world is the angle multiplexing method, however, it costs too much and its control is quite severe. In such situation, we study about shift multiplexing method because it costs not much and its control is easier than the angle multiplexing. In this experiment, we examined shift selectivity of track direction, radial direction and vertical direction of the medium. As a result, combining these different kinds of selectivity, we found a possible multiplexing way to achieve several tera bits per inch square density recording.
We examined the possibility of high-density recording using shift-multiplexed holographic memory with a spherical
reference beam. The use of a spherical reference beam is considered to make it possible to realize a multi-dimensional
multiplex system that uses the disk track direction (x-axis), radial direction (y-axis), and disk thickness direction (z-axis);
this would clearly improve the recording density when compared with the conventional angle multiplex recording. The
experimental results confirm the possibility of multiple recording by 3 dimensional medium shift. Furthermore, the
results indicate that a large capacity memory system of over 1 Tb/in2 can be obtained if a thick medium (about 1.5 mm)
The method to do an shift multiplexing by using spherical reference light was
examined. The density growth can be expected by overwriting the hologram using spherical
reference light. The hologram recording is carried out by shifting the block where the multiplexed
hologram was recorded. In addition, a further large capacity can be expected by using the
transmission type together with the reflection type hologram recording. In this paper, the result of
verifying fundamental proof of these methods was reported by the record reproduction experiment.
The memory system described herein can record multiple holograms by a simple shift of the
photopolymer film medium. The primary advantage of this method is that it enables the generation of
make a single, large capacity hologram because the corresponding optical system is simpler than the
transmission-type recording system, which has generally been studied to date. The experimental results
confirm the possibility of multiple recording by medium shift. Furthermore, the results indicate that a
large capacity memory system of over 1 Tb/in<sup>2</sup> can be obtained if a thick medium (about 1 mm) is used.