Patent Application
20090279153
This application is a Continuation of International Application Serial No. PCT/JP2007/051147, filed Jan. 25, 2007.
The present invention relates to a hologram recording/reproducing apparatus, a hologram recording/reproducing method and a hologram recording medium for recording holograms and reproducing holograms.
A conventional hologram recording/reproducing apparatus is disclosed in Patent Document 1, for example. In this hologram recording/reproducing apparatus, a laser beam emitted from a laser beam source is split by a beam splitter into a recording beam and a reference beam. The recording beam is modulated by a spatial light modulator and then a hologram recording medium is exposed to the modulated beam while simultaneously the reference beam is irradiated so as to interfere with the recording beam. The recording beam and the reference beam are arranged to have the same polarizing direction considering optical conditions such as coherency. The hologram recording/reproducing apparatus employs a method called shift multiplex recording method in which pages, which is units of recording, are partially overlapped in recording. As described in “Background Art” in the Patent Document 1, the apparatus of this type typically forms a bit-pattern hologram (data portion) corresponding to information to be recorded and markers each of which indicates respective one of the four corners of the hologram. In reproducing, the markers are used to specify the position of the data portion to be read out.
Patent Document 1: Japanese Laid-open Patent Publication No. 2005-99283
However, in hologram recording with a recording beam and a reference beam having the same polarizing direction, when the hologram is reproduced, it is known that a beam scattering region is generated at the both sides outside the hologram with directivity of the polarizing direction of the reference beam same as that of the recording beam. The beam scattering region is caused by diffracted beams due to noise grating. If optical intensity of the beam scattering region is relatively high and the markers are overlapped by the beam scattering region, the markers are not able to be detected at all, whereby read out error occurs because the data portion cannot be read out. In the above-described conventional hologram recording/reproducing apparatus, no measures have been taken about such a beam scattering region.
The present invention has been proposed under the above-described circumstances. It is, therefore, an object of the present invention to provide a hologram recording/reproducing apparatus and a hologram recording/reproducing method capable of avoiding errors in reading even if a beam scattering region appears.
In order to solve the above-described problems, the present invention makes use of the following technical means.
According to the first aspect of the present invention, there is provided a hologram recording/reproducing apparatus for recording a hologram by emitting a recording beam modulated by a spatial light modulator and a reference beam having a same wavelength as the recording beam onto a hologram recording medium so that the beams overlap each other to interfere with each other, and for reproducing the hologram by exposing the hologram recording medium storing the hologram to the reference beam to generate diffracted light and receiving the diffracted light by an imaging device, wherein the spatial light modulator is controlled so as to form a data area corresponding to information to be recorded and a plurality of mark areas for detecting a position of the data area in the hologram recording medium in recording of the hologram, the mark areas being formed at positions not to be overlapped by a beam scattering region which may be generated along a polarizing direction of the reference beam on an outward side of the data area.
According to the second aspect of the present invention, there is provided a hologram recording/reproducing apparatus for recording a hologram by emitting a recording beam modulated by a spatial light modulator and a reference beam having a same wavelength as the recording beam onto a hologram recording medium so that the beams overlap each other to interfere with each other, and for reproducing the hologram by exposing the hologram recording medium storing the hologram to the reference beam to generate diffracted light and receiving the diffracted light by an imaging device, wherein the spatial light modulator is controlled so as to form a data area corresponding to information to be recorded and a plurality of mark areas for detecting a position of the data area in the hologram recording medium in recording of the hologram, and wherein the hologram recording/reproducing apparatus further comprises a polarizer on an optical path of at least one of the recording beam and the reference beam, the polarizer being utilized for matching polarizing direction of the recording beam and the reference beam in recording, and for determining the polarizing direction so as not to cause any of the mark areas to be overlapped by a beam scattering region which may appear along the polarizing direction of the reference beam on an outward side of the data area.
Preferably, the spatial light modulator forms the mark areas adjacent to the data area.
Preferably, the hologram recording/reproducing apparatus is capable of performing multiple recording of holograms including the data area and the mark areas by using an angular multiple method, a wavelength multiple method, a shift multiple method, a speckles multiple method or a phase code multiple method.
Preferably, the spatial light modulator forms the data area in a polygonal shape and the mark areas at a plurality of positions from which corners of the data area are locatable.
According to the third aspect of the present invention, there is provided a hologram recording/reproducing method for recording a hologram by emitting a recording beam modulated by a spatial light modulator and a reference beam having a same wavelength as the recording beam onto a hologram recording medium so that the beams overlap each other with polarizing direction of the beams being matched to interfere with each other, and for reproducing the hologram by exposing the hologram recording medium storing the hologram to the reference beam to generate diffracted light and receiving the diffracted light by an imaging device, wherein the spatial light modulator is controlled so as to form a data area corresponding to information to be recorded and a plurality of mark areas adjacent to the data area for detecting a position of the data area in the hologram recording medium in recording of the hologram, the mark areas being formed at positions not to be overlapped by a beam scattering region which may be generated along a polarizing direction of the reference beam on an outward side of the data area.
According to the fourth aspect of the present invention, there is provided a hologram recording/reproducing method for recording a hologram by emitting a recording beam modulated by a spatial light modulator and a reference beam having a same wavelength as the recording beam onto a hologram recording medium so that the beams overlap each other to interfere with each other, and for reproducing the hologram by exposing the hologram recording medium storing the hologram to the reference beam to generate diffracted light and receiving the diffracted light by an imaging device, wherein the spatial light modulator is controlled so as to form a data area corresponding to information to be recorded and a plurality of mark areas adjacent to the data area for detecting a position of the data area in the hologram recording medium in recording of the hologram, and polarizing direction of the recording beam and the reference beam are matched, and the polarizing direction of at least one of the recording beam and the reference beam is determined so as not to cause any of the mark areas to be overlapped by a beam scattering region which may appear along the polarizing direction of the reference beam on an outward side of the data area.
According to the fifth aspect of the present invention, there is provided a hologram recording medium to be used in a hologram recording/reproducing apparatus for recording a hologram by emitting a recording beam modulated by a spatial light modulator and a reference beam having a same wavelength as the recording beam onto a hologram recording medium so that the beams overlap each other to interfere with each other, and for reproducing the hologram by exposing the hologram recording medium storing the hologram to the reference beam to generate diffracted light and receiving the diffracted light by an imaging device, wherein a data area corresponding to information to be recorded and a plurality of mark areas for detecting a position of the data area are formed in recording of the hologram in the hologram recording medium, the mark areas being formed at positions not to be overlapped by a beam scattering region which may be generated along a polarizing direction of the reference beam on an outward side of the data area.
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
As illustrated in
The hologram recording medium B has a recording layer 91 between two transparent protective layers 90, so that light can reach the recording layer 91 from both sides. In the recording layer 91, a recording beam S and a reference beam R intersect with each other at predetermined angles and interfere with each other, whereby holograms each having a different interference fringe pattern in accordance with the crossing angle are recorded. In reproducing, as indicated by long-and-short-dash lines, the hologram recording medium B is exposed to a reference beam R′ traveling from the opposite side to that in recording. The reference beam R′ is conjugate to the recording reference beam R. In the recording layer 91, therefore, the reference beam R′ makes interference with recorded holograms, and a diffracted beam D (see
The light source 1, which is e.g. a semiconductor laser device, emits a laser beam as a coherent beam in recording and reproducing. The collimator lens 2 converts the laser beam from the beam source 1 into a parallel light. The parallel light which comes out of the collimator lens 2 is guided to the half mirror 3. The half mirror 3 splits the incoming parallel light into a recording beam S which travels to the spatial light modulator 5, and reference beams R, R′ which travel on their own routes to the recording or the reproducing galvanometer mirrors 9, 11 respectively. Thus, the reference beams R, R′ always have the same wavelength as the recording beam S. Further, the recording beam S and the reference beams R, R′ have the same polarizing direction. The beam expanders 4A, 4B are provided by combination lenses, and direct the recording beam S to the spatial light modulator 5 while increasing the diameter of the recording beam S.
The spatial light modulator 5, which is e.g. a transmissive liquid-crystal display device, modulates a beam which incomes in recording into a recording beam S which has a two-dimensional pixel pattern. The recording controller 20 controls the spatial light modulator 5 for generating different holograms in accordance with information which is to be recorded.
Specifically, as illustrated in
According to the data pixel area G0, a data area H0 is formed in an area of the hologram corresponding to this, and according to the mark pixel areas G1, mark areas H1 are formed at four corners of the data area H0 in an area of the hologram corresponding to this. The mark areas H1 are used as indices indicating position of the data area H0, and also used to store address information. The address information includes, for example, information for determining the incident angles of the reference beams R, R′. In recording, the recording beam S and the reference beam R are arranged to have a matched polarizing direction, so that both of the beams have a vertical polarization for example. Alternatively, the beams may be arranged to have a horizontal polarization. The four mark areas H1 are formed not to be overlapped by a line (hereinafter referred to as “polarization line”) p extending in the polarization direction of the recording beam S and passing through the center of the data area H0. That is, at the spatial light modulator 5, the mark pixel areas Glare formed at locations which are determined from a positional relationship between the data pixel area G0 and the polarization line p. Although the mark pixel areas G1 are formed adjacent to the data pixel area G0 in the present embodiment, the mark pixel areas G1 may be formed at a predetermined distance from the data pixel area G0. Further, although the data pixel area G0 is a rectangle in the present embodiment, it may be a polygon, such as a triangle, a hexagon, and so on.
Back to
In reproducing, the reference beam R′ is guided via the fixed mirror 8C to the reproducing galvanometer mirror 11. The reproducing galvanometer mirror 11 varies the incident angle of the reference beam R′ relative to the unit recording area T in reproducing. The galvanometer mirror 11 is so arranged that the reference beam R′ impinges on the hologram recording medium B from the opposite side to that in recording. After being emitted from the reproducing galvanometer mirror 11, the reference beam R′ is a conjugate beam which travels in the opposite direction to that in recording, and this reference beam R′ passes by the relay lenses 12A, 12B and reaches the hologram recording medium B. The reference beam R′ for reproducing is also arranged to have a matched polarizing direction with the polarizing direction of the recording beam S and the reference beam R. In the reproducing process, the spatial light modulator 5 is controlled so that the unit recording areas T is not exposed to the recording beam S.
As illustrated in
In a hologram reproducing process described above, a beam scattering region N may be generated with directivity of the polarizing direction of the reference beam P′ at both sides outward of the hologram. The beam scattering region N is caused by diffracted beams due to noise grating, and generated along the polarization line p. The beam scattering region N overlaps partially the data pixel pattern P0, but does not overlap any of the four mark pixel patterns P1. Therefore, the mark pixel patterns P1 can be surely detected, and the data pixel pattern P0 corresponding to the data area H0 can be obtained by specifying at least the position of the data area H0. In other words, the mark pixel areas G1 formed in the spatial light modulator 5 is configured to be positioned not to overlap the polarization line p, taking the beam scattering region N to generate in reproducing into consideration.
The other layout patterns for the data pixel area G0 and the mark pixel areas G1 include various layout patterns in which none of the mark pixel areas G1 overlap the polarization line p and the location of the data pixel area G0 is specified by the mark pixel areas G1, as illustrated in
Next, recording and reproducing operation performed by the hologram recording/reproducing apparatus A will be described below.
First, in recording, as illustrated in
In this process, the recording beam S is modulated by the spatial light modulator 5 into light which corresponds to the data pixel area G0 and the mark pixel areas G1. Thus, a data area H0 and mark areas H1 corresponding to the data pixel area G0 and the mark pixel areas G1 are recorded in multiple in a unit recording area T of the hologram recording medium B. The mark areas H1 are formed at four corners of the data area H0 without overlapping the polarization line p.
Next, in reproducing, as illustrated in
In this process, when the incident angle of the reference beam R′ becomes equal to the incident angle of recording, the imaging device 13 detects the mark pixel patterns P1 corresponding to the mark areas H1 located at the four corners of the data area H0. At this time, the imaging device 13 unavoidably detects the beam scattering region N. However, since the mark pixel patterns P1 are in the positions not overlapping the beam scattering region N, the four mark pixel patterns P1 are detected reliably.
Once the mark pixel patterns P1 are detected in this way, the position of the data area H0 is determined, and the exposure position or the incident angle of the reference beam R′ is adjusted finely based on the determined position. Therefore, the imaging device 13 is able to read the data pixel pattern P0 corresponding to the data area H0. By repeating the series of operations described above, the information is read out in the form of data pixel pattern P0 from a plurality of data areas H0 stored in multiple recording.
Therefore, with the hologram recording/reproducing apparatus A according to the present embodiment, it is possible to read the mark areas H1 reliably even if a beam scattering region N is generated by diffracted light due to so-called noise grating during the reproduction operation. This makes possible to specify the location of the data area H0 for reading out, avoiding errors in reading in the reproducing operation.
The other embodiments can include hologram recording/reproducing apparatuses as illustrated in
The hologram recording/reproducing apparatus A1 in
In this hologram recording/reproducing apparatus A1, which performs multiplex recording by such variable wavelength control, the spatial light modulator 5 forms mark pixel areas G1 at the position not overlapping the polarization line p (see
The hologram recording/reproducing apparatus illustrated in
In this hologram recording/reproducing apparatus, which records holograms by the shift multiplex method, the spatial light modulator 5 forms mark pixel areas G1 at the position not overlapping the polarization line p (see
The hologram recording/reproducing apparatus A2 illustrated in
In this hologram recording/reproducing apparatus A2, which performs multiple recording by variable control of the speckle size, the spatial light modulator 5 forms mark pixel areas G1 at the positions not overlapping the polarization line p (see
Further, if phase modulation devices are provided instead of the diffuser plates 10C, 12C, the phase code multiple method is performed. In the phase code multiple method, reading errors can be avoided in reproduction by forming mark pixel areas G1 at the positions not overlapping the polarization line p.
The hologram recording/reproducing apparatus A3 illustrated in
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2007/051147 | Jan 2007 | US |
| Child | 12507643 | US |
