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)
is used.
A major barrier to the practical use of holographic memories is deterioration of reconstructed signals due to
shrinkage of the medium. It is reported that a photopolymer medium shrinks mainly in the thickness direction
during recording or as a result of variations in ambient temperature, and the optimal reconstruction angle shifts
and deteriorates. To avoid the influence of medium shrinkage, we propose co-axial, dual-reference-beam
recording and reconstruction. The recording and reconstruction characteristics of this method were examined
through simulation and experiments, and the results confirmed that in holographic multiplex recording, the
reference-beam angle is not affected by medium shrinkage, and stable recording and reconstruction are achieved.
Holographic memory systems have been widely researched since 1963. However,
the size of the drives required and the deterioration of reconstructed data resulting from
shrinkage of the medium have made practical use of a hologram memory difficult. In light of
this, we propose a novel holographic recording/reconstructing system: a dual-reference beam
reflection system that is smaller than conventional systems such as the off-axis or co-axis
types, and which is expected to increase the number of multiplexing in angle multiplexed
recording. In this multiplex recording system, two laser beams are used as reference beams,
and the recorded data are reconstructed stably, even if there is shrinkage of the recording
medium. In this paper, a reflection holographic memory system is explained in detail. In
addition, the change in angle selectivity resulting from shrinkage of the medium is analyzed
using the laminated film three-dimensional simulation method. As a result, we demonstrate
that a dual-reference beam multiplex recording system is effective in reducing the influence
of medium shrinkage.
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