JP2005310308A - Hologram recording and reproducing device and hologram recording and reproducing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To continuously and smoothly perform multiplex data recording and reproduction on a hologram recording medium. <P>SOLUTION: At the time of recording, a recording/reproducing controller 20 records interference fringes between reference light 200 obtained by fixing the angle of a mirror 13 to a first prescribed value and signal light 100 in all stacks on a hologram recording medium 12 and then fixes the angle of the mirror 13 to a second prescribed value to repeat the same operation. At the time of reproducing, the recording/reproducing controller 20 reproduces data from all stacks on the hologram recording medium 12 by using reference light of the same radiation angle and then changes the radiation angle of reference light to repeat the same operation. Since a servo controller 19 continuously rotates the hologram recording medium 12 by a spindle motor 17 in this case, a conventional mechanical control of repeating stop and go is unnecessary, so that data can be continuously and smoothly recorded/reproduced on the hologram recording medium 12 with multiplex angles. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hologram recording / reproducing apparatus and method, and more particularly, to an order of multiplex recording / reproducing data on a hologram recording medium.

  In recent years, holographic technology has been rapidly developed for the practical application of holographic memory, which is attracting attention as a candidate for powerful storage that competes with next-generation and next-generation optical discs. Thus, a hologram recording / reproducing system for recording / reproducing a large amount of data has been proposed (see, for example, Non-Patent Document 1).

  In such a hologram recording / reproducing system, a method called multiple recording is used to improve the recording density. This is to record a large number of independent data pages in the same recording area of the hologram recording medium. Typical multiplex recording methods include angle multiplex recording, shift multiplex recording, phase modulation multiplex recording, speckle multiplex, etc. It has been known.

  FIG. 6 is a schematic diagram showing a general configuration of a hologram recording / reproducing apparatus of an angle multiplex recording system. After the intensity of the coherent laser light emitted from the laser light source 1 is adjusted by the ND filter 2 and the polarization plane thereof is adjusted by the half-wave plate 3, the beam expander 4 makes parallel light. The laser light that has become the parallel light is incident on the mirror 6 via the shutter 5, the optical path is changed, the light is incident on the beam splitter 7, and is branched into the signal light 100 and the reference light 200.

  The signal light 100 is incident on the mirror 9 through the shutter 8, and the path is changed by the mirror 9 and is incident on the spatial light modulator 10. The signal light 100 is intensity-modulated by the spatial light modulator 10 displaying the data page, and the modulated signal light 100 is condensed on the hologram recording medium 12 by the signal light optical system 11. On the other hand, the reference light 200 is incident on the mirror 13 whose angle of the reflecting surface can be changed, is reflected at a certain angle to change the optical path, and then enters the 4f reference optical system 14. The light is focused on the hologram recording medium 12. As a result, the signal light 100 and the reference light 200 are superimposed in the hologram recording medium 12, and the interference fringes (holograms) formed as a result are recorded on the hologram recording medium 12.

  At that time, if the angle of the reflecting surface of the mirror 13 is changed each time the data page displayed on the spatial light modulator 10 is changed, the angle at which the reference light 200 is incident on the hologram recording medium 12 is changed, and the hologram A plurality of data pages are multiplexed and recorded in the same recording area (stack) of the recording medium 12.

  In order to reproduce the data recorded on the hologram recording medium 12, diffracted light generated by irradiating the hologram recording medium 12 with the same reproduction reference light as the reference light 200 (herein referred to as reference light 200) is used. The incident light is incident on the reproduction light optical system 15, and this diffracted light is imaged on the imaging device 16 by the reproduction light optical system 15.

  The imaging device 16 photoelectrically converts the received diffracted light, and the obtained light reception signal is analyzed and reproduced as image data. At the time of this reproduction, similarly to the time of recording, by changing the incident angle of the reference beam 200 with respect to the hologram recording medium 12 by rotating the mirror 13, it is possible to sequentially reproduce the image data multiplexedly recorded in one recording area. it can.

  FIG. 7 is a diagram for explaining a conventional order of reproducing data recorded by angle multiplexing. Holograms that are angle-multiplexed in a recording area (referred to as stack 1) of the hologram recording medium 12 are reproduced in order by changing the irradiation angle (1 to 5) of the reproduction reference light 200 and read out, for example, hologram recording The medium 12 is rotated and moved to the next stack 2, and here, the operation of changing the irradiation angle (7 to 12) of the reproduction reference beam 200 and sequentially reproducing is repeated.

In the phase modulation multiplexing method, reference light having various phases is generated by optical phase modulation of the reference light with a spatial light modulator with all optical components fixed, and interference with signal light is performed for each reference light. In this method, data is multiplexed and recorded in the same recording area of the hologram recording medium. By sequentially irradiating the hologram recording medium recorded by this phase modulation multiplexing method with reference light having the same phase as that at the time of recording, it is possible to sequentially reproduce the image data multiplexedly recorded in one recording area. In this case, the reproduction order is such that the irradiation angle of the reference light is constant and the optical phase modulation method of the reference light is changed in the same manner as at the time of recording to irradiate the data recorded in the same recording area in order. .
IBM J.RES DEVELOP VOL 44 NO.3 MAY 2000 `` Holographic data storage ''

  However, in the reproduction method in which the data recorded in a multiple recording area as described above is read sequentially by changing the irradiation angle and phase modulation of the reference light, and then the data is sequentially read from the next recording area in the same manner. In particular, in the case of the angle multiplexing method, when two different mechanical operations such as movement of the recording area for rotating the hologram recording medium and change in the angle of the reference light are repeated in a short cycle, for example, when a moving image or the like is read continuously Therefore, it is necessary to control mechanically repeatedly performing Stop and Go, and considering the inertia of the hologram recording medium, it is difficult to perform such mechanical control smoothly, and therefore, data can be read continuously and smoothly. Becomes very difficult. Such a problem also occurs when data is recorded on a hologram recording medium by, for example, phase modulation multiplexing.

  The present invention has been devised in view of the above circumstances, and an object of the present invention is to provide a hologram recording / reproducing apparatus and a hologram recording / reproducing method capable of continuously and smoothly multiplexing and reproducing data on a hologram recording medium. It is to provide.

  In order to achieve the above object, the present invention provides a hologram recording apparatus for performing multiple recording of interference fringes of signal light and reference light on the same recording stack on a disk-type hologram recording medium by changing the characteristics or irradiation angle of the reference light. When the interference fringes between the signal light and the reference light having a certain characteristic or a certain irradiation angle are recorded one by one on all the stacks or designated stacks on the hologram recording medium, the characteristic or irradiation angle of the reference light is changed. Recording control means for repeating the recording operation, and servo control means for moving the target recording stack to a position where the recording control means can record interference fringes on the target recording stack on the disk-type hologram recording medium; It is characterized by comprising.

  The present invention also relates to a hologram reproducing apparatus for reproducing data recorded in a multiplexed manner on a plurality of recording stacks on a disk-type hologram recording medium, wherein reference light having a certain characteristic or a certain irradiation angle is all transmitted on the hologram recording medium. A reproduction control unit that repeats the reproduction operation by changing the characteristics or irradiation angle of the reference light after sequentially irradiating the stack or a set range of stacks and reproducing data from each stack, and the disc-type hologram Servo control means for moving the target recording stack from the target recording stack on the recording medium to a position where data is reproduced by the reproduction control means is provided.

  The present invention also relates to a hologram recording method for recording multiple interference fringes of signal light and reference light on the same recording stack on a disk-type hologram recording medium by changing the characteristics of the reference light or the irradiation angle. Alternatively, after the interference fringes are recorded by sequentially accessing all the stacks on the disk-type hologram recording medium or the set range of stacks using the reference light and the signal light having a certain irradiation angle, the characteristics of the reference light or The above recording operation is repeated while changing the irradiation angle.

  The present invention also relates to a hologram reproducing method for reproducing data recorded on a plurality of recording stacks on a disk-type hologram recording medium, wherein reference light having a certain characteristic or having an irradiation angle is applied to the disk-type hologram recording medium. All the above stacks or stacks in a set range are sequentially irradiated to reproduce all data from each stack, and then the above reproduction operation is repeated by changing the characteristics of the reference light or the irradiation angle. .

  As described above, in the present invention, after performing recording / reproduction of data on all stacks on a disk-type hologram recording medium or a set range of stacks using reference light having a certain characteristic or a certain irradiation angle, Since the above-described recording operation is repeated by changing the reference light, data can be recorded / reproduced while the disk-type hologram recording medium is continuously rotated, and the control for repeating mechanical Stop and Go is reduced and the data is reduced. Recording and reproduction can be performed continuously and smoothly.

According to the present invention, after performing recording / reproduction of data on all stacks on a disc-type hologram recording medium or a set range of stacks using a reference light having a certain characteristic or a certain irradiation angle, the reference light By repeating the above recording operation by changing the characteristics and the irradiation angle, it is possible to reduce the control of repeating mechanical Stop and Go and to record and reproduce data continuously and smoothly.
Further, since it becomes easy to continuously read data recorded by the angle multiplexing method from the rotating hologram recording medium, the transfer rate can be increased.
In addition, when Stop and Go is repeated as in the conventional case, mechanical wear accumulates, so that mechanical accuracy is deteriorated and parts themselves are easily broken. However, since mechanical control is smooth, Mechanical durability and accuracy can be maintained, and BER deterioration due to mechanical accuracy can be avoided.
In addition, since the recording time interval between the hologram recorded with the reference beam with the first irradiation angle and the hologram recorded with the reference beam with the second irradiation angle becomes long, the previously written hologram It is no longer obstructed by the generation of the hologram to be written, and the S / N of the reproduction data can be improved.

  For the purpose of continuously and smoothly recording and reproducing data on a hologram recording medium, all or a set range of stacks on a disk-type hologram recording medium using a reference beam having a certain characteristic or irradiation angle is used. After recording / reproducing data, the above recording operation is repeated by changing the characteristics and irradiation angle of the reference light.

FIG. 1 is a schematic diagram showing the configuration of the main part of a hologram recording / reproducing apparatus according to the first embodiment of the present invention. However, the same parts as those in the conventional example will be described with the same reference numerals. The hologram recording / reproducing apparatus includes a spatial light modulator 10 that modulates the intensity of signal light 100, a lens 11 of a signal light optical system, a disk-type hologram recording medium 12 that records a hologram, and a reflection surface angle that changes the path of reference light 200. A variable mirror 13, 4f-type lenses 14-1 and 14-2 of the reference light optical system, a lens 15 of the reproduction light optical system, and an imaging device 1 that photoelectrically converts the reproduction image to obtain reproduction data
6. Spindle motor 17 for rotating the hologram recording medium 12, feed mechanism 18 for moving the hologram recording medium 12 in the radial direction, servo controller 19 for driving and controlling the spindle motor 17 and the feed mechanism 18, hologram recording accompanying hologram recording / reproduction It has a recording / reproduction control device 20 that generates servo information of the medium 12 and controls the angle of the mirror 13, and multiplex-records and reproduces holograms on the hologram recording medium 12 by an angle multiplexing method.

  Next, the reproduction operation of the present embodiment will be described with reference to the flowchart of FIG. First, it is assumed that data is multiplexed and recorded on the hologram recording medium 12 by, for example, three stacks 1 to 3 as shown in FIG.

  When the reproducing operation is started (step S1), the recording / reproducing control device 20 causes the reflected light of the mirror 13 to enter the hologram recording medium 12 at the initial predetermined angle (in FIG. (The incident angle) is controlled (step S2), and the spindle motor 17 or the feed mechanism 18 is operated via the servo control device 19 so that the reference beam 200 irradiates the target stack. Then, the stack 1) can be accessed (step S3). Thereafter, when the stack 1 is irradiated with the reference beam 200 at an angle indicated by reference numeral 1 in FIG. 3, a hologram diffracted beam 300 in which the reference beam 200 at the time of recording is multiplex-recorded at this angle is generated. Data is reproduced by forming an image on the imaging device 16 with the lens 15 (step S4).

  Next, it is determined whether or not the stack designated to be reproduced has been reproduced once at the reference light angle set this time. If not, the process returns to step S3 and the target stack to be reproduced next (stack 2 in this case). (This is done by driving the spindle motor 17 and the feed mechanism 18 in the same manner as described above). Thereafter, when the stack 2 is irradiated with the reference beam 200 at an angle indicated by reference numeral 1 in FIG. 3, a hologram diffracted beam 300 in which the reference beam 200 at the time of recording is multiplex-recorded at this angle is generated. Data is reproduced by forming an image on the imaging device 16 with the lens 15 (step S4).

  Thereafter, the same is applied, and when the stack designated for reproduction is reproduced once at the reference light angle set this time, the processes in steps S3 to S5 are repeated, and all the stacks are reproduced once at the reference light angle set this time. (Here, stacks 1 to 3), it is determined in step S6 whether or not the reproduction angle of the reference beam 200 has been changed to all designated angles. As a result, when reproduction is not performed with all angles changed, the process returns to step S2, and the angle of the reflection surface of the mirror 13 is controlled to the next predetermined angle (in FIG. 3, reference numerals 4, 5, and 6). At an angle, the incident light 200 enters the hologram recording medium 12) and moves to the target stack (here, stack 1). Subsequent operations are the same as described above, and the processing from step S3 to step S5 is repeated until the stack designated to be reproduced this time is reproduced once at the reference light angle set this time. Thereafter, the processing from step S1 to step S6 is performed until the stack is irradiated with reference light at all angles designated at this time in step S6, and data is read out from all stacks designated for reproduction. Is read out, the reproduction operation is terminated (step S7). In FIG. 3, only three stacks 1 to 3 are shown for explanation, but in reality, a large number of stacks are spread on the hologram recording medium 12. In the reproduction order of this example, the number of times of changing the angle of the reference beam 200 for reproduction is remarkably reduced, so that reproduction from the hologram recording medium 12 can be smoothly performed as compared with the conventional method.

  According to the present embodiment, after reproducing a hologram of a stack (for example, stack 1) irradiated with the hologram recording medium 12 with a reference light 200 at a certain angle for reproduction, the adjacent stack (for example, After illuminating the stack 2) to read the holograms, and subsequently reproducing each recorded hologram by irradiating each stack with the reference light 200, and reproducing the data of all the stacks designated for reading, By changing the irradiation angle of the reproduction reference light 200 and repeating the same reproduction, the reproduction reference light 200 can be fixed at a certain angle and the period of data reproduction can be extended. Since the control only needs to continuously rotate the hologram recording medium 12 and operate the feeding mechanism 18 as necessary, so-called Stop and G Since o can be reduced, data of the hologram recording medium 12 recorded by angle multiplexing can be read continuously and smoothly.

  In particular, when the hologram recording medium 12 is continuously rotated, there is a problem that the reproduction data is blurred. However, if the reference light 200 for reading is irradiated in a flash manner using a pulse laser or the like at the timing of reading data from a certain stack, the blurring occurs. Data can be reproduced without any problem. Further, since the hologram is recorded by being subjected to Fourier transform on the hologram recording medium 12, even if the stack moves, the image does not move, and it can be said that blurring hardly occurs from that point.

  In the above embodiment, the reproduction order when reproducing the data recorded on the hologram recording medium 12 by angle multiplexing has been described. However, the order at the time of recording data on the hologram recording medium 12 by angle multiplexing is also the reproduction order. Similarly, after the hologram generated by irradiating the hologram recording medium 12 with the reference light 200 at a certain angle and interfering with the signal light 100 is recorded on a certain stack (for example, stack 1), it is recorded on the adjacent stack (for example, stack 2). A hologram generated by irradiating the reference light of the same angle and interfering with the signal light 100 is recorded, and similarly, the hologram is recorded using the reference light of the same angle on different stacks, and data is recorded on all stacks. After that, by changing the irradiation angle of the reference beam 200 and repeating the same recording, the mechanical control burden is reduced and angle multiplexing is performed. It can be continuously and smoothly record data.

  Further, since it becomes easy to continuously read data recorded by the angle multiplexing method from the rotating hologram recording medium 12, an increase in the transfer rate can be expected. In addition, when Stop and Go is repeated as in the past, wear accumulates mechanically, so that it is considered that mechanical accuracy is deteriorated and parts themselves are likely to break down. The scheme is considered advantageous. Further, since the machine accuracy can be kept high for the reasons described above, it is possible to avoid the deterioration of BER due to the machine accuracy.

  Also. In the case of this method, considering a hologram that is angle-multiplexed at the same location, the time from when the hologram is written at the first angle to when it is written at the second angle (hereinafter the same) becomes longer. In view of the fact that a certain amount of time is required from when the hologram (interference fringes) of the reference beam 200 is exposed until the hologram is actually recorded on the recording medium 12, the recording order of this embodiment is Since the next hologram is written after the refractive index distribution of the first hologram is stabilized, the previously written hologram is not obstructed by the generation of the next written hologram. It can be expected that a good reproduction image can be obtained.

  FIG. 4 is a plan view showing a hologram recording medium for explaining a hologram recording / reproducing method according to the second embodiment of the present invention. However, the same parts as those in the first embodiment will be described with the same reference numerals. In the hologram recording medium 12 of the present embodiment, the recording / reproducing area is divided into a plurality of zones such as a first zone and a second zone (not physically divided but divided according to a recording / reproducing standard). ) Although two zones are shown in FIG. 4 for convenience, it is assumed that the zones are actually divided into n zones.

  Next, the operation of the present embodiment will be described. In the present embodiment, the same recording order or reproduction order as in the first embodiment is applied to each zone. For example, as shown in FIG. 5A, first, reproduction reference light is irradiated onto the hologram recording medium 12 at a first angle to reproduce data from all stacks in the first zone, and then for reproduction. The hologram recording medium 12 is irradiated with the reference light at the second angle and data is reproduced from all the stacks of the first zone, and the reproduction reference light is changed at all angles to change the first zone. When data is read from all the stacks, the process proceeds to the next second zone as shown in FIG. 5B, and the above operation is repeated. The playback order of these zones does not necessarily have to be played back in order from the first zone to the nth zone. After playing the first zone, the third zone is played, and then the eighth zone. Can be played as needed. The recording order is the same, and the first zone of the hologram recording medium 12 is recorded using the reference light that irradiates the first zone at the first angle, and the data is recorded in the first zone. The data is multiplexed and recorded in the same recording area by using the reference light that irradiates the second zone at the second angle. In this way, when the multiplex recording of the data in the first zone using the angle multiplex method is completed using all the reference light whose angles are changed, the multiplex recording is performed in another zone in the same manner.

  According to the present embodiment, if the size of each zone is large to some extent, the mechanical control of repeating Stop and Go is reduced as in the first embodiment, so that the hologram recording medium recorded by angle multiplexing is reduced. 12 can be reproduced continuously and smoothly, and data can be recorded on the hologram recording medium 12 continuously and smoothly by angle multiplexing.

  In the present embodiment, the disc-type hologram recording medium 12 is divided into concentric zones. However, the method of dividing the zones is not limited to this, but the basics for smooth reproduction. It is advantageous to take a large zone for reading continuously at the same angle. However, in the case of a system that records and reproduces only on a part of the hologram recording medium and uses other parts later (recordable type), the recording zone is post-processed such as cure, and so on. In this case, it is efficient to set a zone size according to the data amount because the recording density is lowered while the severity is fixed low.

  In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the summary, it can implement also with another various form in a concrete structure, a function, an effect | action, and an effect. For example, in the above embodiment, the procedure for recording / reproducing data to / from the hologram recording medium 12 by angle multiplexing has been described. However, the recording / reproducing procedure of the present invention is adopted regardless of the method of recording data on the hologram recording medium 12 in a multiplexed manner. This will have the same effect. For example, in order to reproduce data recorded by phase modulation multiplexing, the hologram of one stack is read by irradiating the hologram recording medium with phase-modulated reference light for reproduction, and then the same phase modulation is applied to the adjacent stack. The hologram is read by irradiating the reference beam 200, the hologram is reproduced from each stack in the same manner with the same phase-modulated reference light, and the data of all the stacks designated for reading are reproduced. Similar reproduction may be repeated by changing the phase modulation method of the reference beam 200 for reproduction.

It is the schematic which showed the structure of the principal part of the hologram recording / reproducing apparatus which concerns on the 1st Embodiment of this invention. 3 is a flowchart showing a reproducing operation of the hologram recording / reproducing apparatus shown in FIG. It is a perspective view explaining the reproducing operation of the hologram recording / reproducing apparatus shown in FIG. It is the top view which showed the hologram recording medium for demonstrating the hologram recording / reproducing method which concerns on the 2nd Embodiment of this invention. It is a figure explaining the reproduction | regeneration operation | movement of the hologram recording / reproducing apparatus shown in FIG. It is the schematic which showed the conventional structure of the hologram recording / reproducing apparatus of an angle multiplex recording system. It is a figure explaining the conventional order which reproduces the data recorded by angle multiplexing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Spatial light modulator, 11, 14-1, 14-2, 15 ... Lens, 12 ... Hologram recording medium, 13 ... Mirror, 16 ... Imaging device, 17 ... Spindle motor, 18 ... Feed mechanism, 19 ... servo control device, 20 ... recording / reproduction control device.

Claims (18)

A holographic recording apparatus that multiplex-records interference fringes of signal light and reference light on the same recording stack on a disk-type hologram recording medium by changing the characteristics or irradiation angle of the reference light,
When the interference fringes between the signal light and the reference light having a certain characteristic or a certain irradiation angle are recorded one by one on all the stacks on the hologram recording medium or the set range, the characteristic or irradiation angle of the reference light Recording control means for repeating the above recording operation by changing
Servo control means for moving the target recording stack to a position where interference fringes can be recorded by the recording control means on the target recording stack on the disk-type hologram recording medium;
A holographic recording apparatus comprising:   2. The hologram recording apparatus according to claim 1, wherein the servo control means performs control to continuously rotate the disk-type hologram recording medium during recording of the interference fringes by the recording control means.   2. The hologram recording apparatus according to claim 1, wherein the stack of the set range belongs to a divided area (zone) set on a recording surface on the disc-type hologram recording medium.   The hologram recording apparatus according to claim 1, wherein data is multiplexed and recorded on the same recording stack on the disk-type hologram recording medium by changing an irradiation angle of the reference light.   2. The hologram recording apparatus according to claim 1, wherein data is multiplexed and recorded on the same recording stack on the disk-type hologram recording medium by changing a phase modulation method of the reference light. A hologram reproducing device for reproducing data recorded in a plurality of recording stacks on a disk-type hologram recording medium,
When the reference light having a certain characteristic or a certain irradiation angle is sequentially irradiated to all the stacks on the hologram recording medium or the stack in a set range and data is reproduced from each stack, the characteristics or the irradiation angle of the reference light is changed. Reproduction control means for changing and repeating the reproduction operation;
Servo control means for moving the target recording stack from a target recording stack on the disk-type hologram recording medium to a position where data is reproduced by the reproduction control means;
A hologram reproducing apparatus comprising:   7. The hologram reproducing apparatus according to claim 6, wherein the servo control means performs control to continuously rotate the disk-type hologram recording medium during reproduction of the interference fringes by the reproduction control means.   7. The hologram recording apparatus according to claim 6, wherein the set range stack belongs to a divided region (zone) set on a recording surface on the disk-type hologram recording medium.   7. The hologram reproducing apparatus according to claim 6, wherein data is multiplexed and recorded on the recording stack on the disk-type hologram recording medium by an angle multiplexing method.   7. The hologram reproducing apparatus according to claim 6, wherein data is multiplexed and recorded on the recording stack on the disk-type hologram recording medium by a phase modulation method. A hologram recording method in which interference fringes of signal light and reference light are multiplexed and recorded on the same recording stack on a disk-type hologram recording medium by changing the characteristics or irradiation angle of the reference light,
The interference fringes are recorded by sequentially accessing all the stacks on the disc-type hologram recording medium or the set range of stacks using the reference light and the signal light having a certain characteristic or a certain irradiation angle. A hologram recording method, wherein the recording operation is repeated while changing the characteristic or irradiation angle.   12. The hologram recording method according to claim 11, wherein the stack in the set range belongs to a divided area (zone) set on a recording surface on the disc-type hologram recording medium.   The hologram recording method according to claim 11, wherein data is multiplexed and recorded on the same recording stack on the disk-type hologram recording medium by changing an irradiation angle of the reference light.   The hologram recording method according to claim 11, wherein data is multiplexed and recorded on the same recording stack on the disk-type hologram recording medium by changing a phase modulation method of the reference light. A hologram reproduction method for reproducing data recorded in a multiplexed manner on a plurality of recording stacks on a disk-type hologram recording medium,
A reference beam having a certain characteristic or a certain irradiation angle is sequentially irradiated to all stacks on a disk-type hologram recording medium or a set range of stacks, and all data is reproduced from each stack. A hologram reproducing method, wherein the reproducing operation is repeated while changing an irradiation angle.   16. The hologram reproducing method according to claim 15, wherein the stack in the set range belongs to a divided area (zone) set in a recording surface on the disc-type hologram recording medium.   16. The hologram reproducing method according to claim 15, wherein data is multiplexed and recorded on the recording stack on the disk-type hologram recording medium by an angle multiplexing method.   16. The hologram reproducing method according to claim 15, wherein data is multiplexed and recorded on the recording stack on the disk-type hologram recording medium by a phase modulation method.

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