Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1998-09-28
2001-01-30
Huber, Paul W. (Department: 2753)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S112040, C369S178010, C369S258100
Reexamination Certificate
active
06181665
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a volume holographic data storage system; and, more particularly, to a volume holographic data storage system incorporating therein a storage device mounted thereon a plurality of storage media for increasing the amount of holograms to be stored thereinto.
DESCRIPTION OF THE PRIOR ART
As is well known, demands for optically storing a large amount of data, such as a motion picture film, have been increasing. Therefore, various types of volume holographic data storage (VHDS) systems incorporating therein a storage medium have been recently developed for realizing high density optical storage capabilities, wherein the storage medium is conventionally made of lithium niobate(LiNbO
3
) or strontium barium niobate(Sr
x
Ba
1-x
Nb
2
O
6
) and is used for three-dimensionally storing the data in the form of pages.
In
FIG. 1
, there is shown a prior art volume holographic data storage (VHDS) system
100
capable of storing multiple holograms. The VHDS system
100
comprises a laser
110
, a beam splitter
120
, a first and a second mirrors
130
,
132
, a spatial light modulator (SLM)
140
, an object lens
150
, a storage medium
160
and a charge coupled device (CCD)
170
. In the system
100
, a laser beam emitted from the laser
110
impinges onto the beam splitter
120
which is capable of partially reflecting the laser beam to thereby obtain a reference and a signal beams, wherein the reference beam is a portion of the laser beam transmitted through the beam splitter
120
and the signal beam is a remaining portion of the laser beam reflected from the beam splitter
120
. The reference beam enters into the storage medium
160
after being reflected by the first mirror
130
.
In the meantime, the signal beam enters into the SLM
140
which converts the signal beam impinged thereonto into a modulated signal beam after being reflected by the second mirror
132
, wherein the modulated signal beam carries data in the form of pages after passing through the SLM
140
. The modulated signal beam is focused on a recording area
162
of the storage medium
160
by the object lens
150
. Conventionally, the storage medium
160
is in the form of a rectangular cube. The storage medium
160
is arranged in such a way that a central point of the recording area
162
therein coincides with the focal point of the object lens
150
. In the storage medium
160
, the modulated signal beam interferes with the reference beam at the recording area
162
to thereby generate an interference pattern therebetween, wherein the interference pattern contains information of the modulated signal beam. The interference pattern is converted to an optical index pattern in the storage medium
160
whose refractive index changes in response to the interference pattern to thereby record the modulated signal beam into the recording area
162
of the storage medium
160
. If another page of data to be modulated by the SLM
140
is recorded on another recording area
162
of the storage medium
160
, the VHDS system
100
can record the data by using an angular or a spatial multiplexing.
To read the stored data, the modulated signal beam retrieved from the storage medium
160
enters the CCD
170
which is capable of detecting the power of the retrieved signal beam. The retrieved signal beam is generated by diffraction of the reference beam from the storage medium
160
.
In the above-described VHDS system
100
, as the amount of holograms to be stored into the storage medium
160
increases, the volume of the storage medium
160
becomes larger to provide a lot of recording areas for an angular multiplexing or a spatial multiplexing. However, it is very difficult to produce a large volume of the storage medium
160
such as a photorefractive crystal without containing any defect or foreign material therein. In case that a defect or a foreign material is contained in the storage medium
160
, it may generate a scattering noise or a distortion noise in the holograms, thereby making the reproduction of the holograms difficult.
SUMMARY OF THE INVENTION
It is, therefore, a primary object of the present invention to provide an improved volume holographic storage system capable of increasing the amount of holograms to be stored into a holographic storage medium.
In accordance with the present invention, there is provided a volume holographic data storage system for storing a plurality of holograms, the storage system comprising: a light source for generating a coherent light beam; a beam splitter for splitting the coherent light beam into a reference and a signal beams; a storage device for storing the holograms thereinto, the storage device including a base having a top surface and N number of storage media, N being a positive integer, larger than 1 each of the storage media being mounted on the top surface of the base and made of a photorefractive crystal; a pair of mirrors for directing the signal and the reference beams to a cross point formed by intersecting therebetween; and a controller for controlling the storage device in such a way that each of the storage media sequentially aligns with the cross point.
REFERENCES:
patent: 4458345 (1984-07-01), Bjorklund et al.
patent: 5007690 (1991-04-01), Chern et al.
patent: 2326735 (1998-12-01), None
Daewoo Electronics Co. Ltd.
Huber Paul W.
Pennie & Edmonds
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