Radiation imagery chemistry: process – composition – or product th – Holographic process – composition – or product
Reexamination Certificate
2000-11-09
2004-10-12
Angebranndt, Martin (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Holographic process, composition, or product
C430S002000, C430S019000, C359S010000, C359S024000
Reexamination Certificate
active
06803153
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for storing data in an optical storage medium, reading the data from the optical storage medium, retrieving the data from the optical storage medium, and also relates to the optical storage medium used for such data storing, reading and retrieving.
2. Discussion of the Related Art
A rewritable optical disk such as a phase change disk or a magneto-optical disk has already used widely. The storing density of the optical disk is larger than that of a general magnetic disk by at least one digit. However, it is still insufficient for digital storage of image information. To enhance the storing density, it is necessary to reduce the beam spot diameter to shorten the distance to the adjacent track or bit.
A DVD-ROM is put into practice by such development of technique. The DVD-ROM with 12 cm diameter can store 4.7 GByte data on one side. A writable/erasable DVD-RAM with 12 cm diameter can realize high-density storage of 5.2 GByte data on both sides, which is more than 7 times as large as the capacity of a CD-ROM and corresponds to the capacity of more than 3,600 floppy disks.
The optical disk has been improved to obtain higher density and larger capacity from year to year. However, since the optical disk stores the data in the two-dimensional surface, the storing density is restricted by the light diffraction limit and is nearing 5 Gbit/cm
2
. To obtain larger capacity, three-dimensional storage (volume holographic storage) further utilizing a depth direction is required.
Materials for the three-dimensional (volume holographic) optical storage medium are, for example, a photopolymer material, photoreactive material and the like. Since these materials change their refractive indexes by absorbing relatively week light beam, it is possible to use the change of the photo-induced refractive index for storing information. Therefore, these materials can be used for multiplexed holographic storage that realizes the larger capacity.
An example of high-density storage utilizing the photopolymer material is discussed in “SPIE Vol. 2514,355”. Shift-multiplexed holograms are stored in a disk, that is made from DuPont's 150-100 photopolymer and rotated, using a spherical wave as a reference beam. As a result, the storing density of 10 times as large as that of a CD currently used, 10 bit/&mgr;m
2
, is obtained.
An example of high-density storage using the photorefractive material is described in “OPTICAL ENGINEERING Vol. 34, 2193 (1995)”. It is reported that 20,000-page holograms are multiple-stored in Fe-doped LiNbO
3
crystal of the size of 10×10×22 mm, and thereby about 1-GByte data storage is achieved.
The holographic memory can store the large capacity of data as described above, and in addition, it can write and read the pieces of data disposed two-dimensionally. Accordingly, it is possible to perform high-speed data storing, reading, retrieving, correlation detection and transfer by using the holographic memory. Specifically, the following data retrieving method is disclosed by Japanese Patent Application Laid-Open No. 3-149660 (1991).
FIG. 26
shows a device for retrieval. A laser
101
emits a laser beam to read pieces of two-dimensional retrieving object data holographically stored from an optical memory
102
. A data pattern image is written to a spatial light modulator
103
of the optical address type. Two-dimensional retrieving data is written to a spatial light modulator
104
of the electric address type that is a liquid-crystal display (LCD) panel.
The spatial light modulator
104
is illuminated with a laser beam as a read beam from a laser
105
through an analyzer
106
. The polarization state of the beam is changed in accordance with the retrieving data, and the light transmitted through the spatial light modulator
104
is reflected off a half-mirror prism
107
. Then the light forms an image on a readout surface of the spatial light modulator
103
of the optical address type.
Thus, the polarization state of the read beam is modulated by the spatial light modulator
103
for each pixel in accordance with the retrieving object data The read beam illuminates a photodetecting array
109
through an analyzer
108
, and the photodetecting array
109
performs batch detection as to whether there is any read beam transmitted through the pixels. Thus the batch detection of matching between bits of the retrieving object data and those of the retrieving data is possible.
“Conjugate Image Plane Correlator with Holographic Disk Memory”, A. Kutanov and Y. Ichioka, OPTICAL REVIEW Vol. 1.3, No. 4, 1996, pp. 258-263 describes a data storage method and data correlation detecting method as follows.
FIG. 27
shows a device used in the storage method and correlation detecting method. In storing the data, two-dimensional data to be stored is displayed on a spatial light modulator
111
of the electric address type that is an LCD panel. A signal beam
112
having a two-dimensional amplitude modulation transmitted through the spatial light modulator
111
is Fourier transformed on a Fourier plane P
1
by a lens
113
and illuminates an optical memory
114
. At the same time, a reference beam
115
illuminates the optical memory
114
and the two-dimensional data is stored as a Fourier-transform hologram in the optical memory
114
.
In detecting correlation, the two-dimensional retrieving data is displayed on the spatial light modulator
111
of the electric address type, and in addition, a read beam
116
having conjugate relation with the reference beam
115
used in storing illuminates the optical memory
114
. The diffracted beam of the two-dimensional retrieving object data is read out from the hologram stored in the optical memory
114
, and the diffracted beam is transformed on a Fourier plane P
2
by the lens
113
. Then the beam illuminates the spatial light modulator
111
.
Accordingly, the transmitted beam from the spatial light modulator
111
is an optical product of the retrieving data and the retrieving object data. If the retrieving data and the retrieving object data match with each other, a strong correlation peak appears on a Fourier plane P
3
through a lens
117
. By detecting the peak, correlation between two-dimensional images can be found.
As an optical storage medium in which the hologram can be rewritten, an optical storage medium made of liquid crystal polymer is disclosed by Japanese. Patent Application Laid-Open No. 2-280116 (1990), and an optical storage medium made of a phase change material is disclosed by Japanese Patent Application Laid-Open No. 4-30192 (1991).
As described so far, attentions have recently been paid to the holographic memory to improve the memory capacity and processing speed, and the retrieving method discussed with reference to FIG.
26
and the storage method and the correlation detecting method discussed with reference to
FIG. 27
have been proposed. Furthermore, enhancement of the signal-to-noise ratio (SIN) has been researched to realize high-density storage.
However, the conventional retrieving method, storage method and correlation detecting method explained with reference to
FIGS. 26 and 27
have adopted a spatial light modulator of an amplitude (intensity) modulation type that is an LCD panel
104
or
111
. Therefore, the following problems have been caused.
As shown in
FIG. 28
, like the spatial lightmodulators
104
and
111
, an LCD for displaying data is constructed by forming a liquid crystal cell
124
containing a liquid crystal
121
and electrodes
122
and
123
on both sides of the liquid crystal
121
and disposing polarizers
126
and
127
on the outside of the liquid crystal cell. Dichromatic polarizers are used as the polarizers
126
and
127
because they can be downsized easily. However, since the transmittance of the dichromatic polarizer in the direction of transmission axis is as low as 70-80%, if two dichromatic polarizers are used together, 50% transmission loss is caused.
Therefore, i
Ishii Tsutomu
Kawano Katsunori
Nishikata Yasunari
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