JP2006302328A - Hologram recording apparatus and hologram reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hologram recording apparatus which can perform multi-layer recording using a comparatively simple servo system because the hologram recording apparatus does not requires a servo pattern nor sticking positioning accuracy as a result, and requires not so severe positioning accuracy for a depth direction. <P>SOLUTION: When hologram recording is performed for a target recording layer of a hologram recording medium 24, hologram recording is performed by moving the hologram recording medium 24 by a position control part 33 and a drive mechanism 32 at mechanical accuracy to a position at which interference information of signal light 11b and reference light 12b are recorded at the target recording layer based on position information of each recording layer. Also, when data is reproduced, the medium is moved to a position at which only reproduced light 13a generated from the target recording layer is passed through a diaphragm 27 by the position control part 33 and the drive mechanism 32. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hologram recording / reproducing apparatus, and more particularly to recording / reproducing when a hologram recording medium for hologram recording is a multilayer.

  Conventionally, during recording of hologram data storage, a hologram recording medium is arranged in an area where two light beams of signal light and reference light interfere, and the interference fringes of the two light beams are recorded on the hologram recording medium (for example, non-patent). Reference 1). At that time, in order to improve the recording density on the hologram recording medium, multiplex recording of holograms by various multiplexing methods such as an angle multiplexing method, a shift multiplexing method, a speckle multiplexing method, and a phase code multiplexing method is performed. .

  In the hologram recording apparatus using the angle multiplexing method, the hologram recording medium is irradiated with two light beams of signal light and reference light. Every time the signal light is spatially modulated (intensity modulated) by a data page displayed on a spatial modulator (SLM). In addition, by changing the incident angle (recording angle) of the reference light to the hologram recording medium, different recording information is multiplexed and recorded in the same recording area.

  In this angle multiplexing type hologram recording apparatus, the change angle of the reference beam recording angle is changed within a range of a maximum of several degrees, for example, in increments of 0.01 degrees (for example, slightly changed between 88 degrees and 92 degrees). ) If different recording information (data pages) in the same recording area are sequentially multiplexed and recorded, a plurality of different recording information such as 50 multiplexing can be recorded in the same recording area.

  On the other hand, a hologram reproducing apparatus paired with such a hologram recording apparatus reproduces recorded information multiplexedly recorded in the same recording area by gradually changing the angle of the surface of the hologram recording medium with respect to the reproduction reference light. It is configured. Here, the angle of the reproduction reference light with respect to the surface of the hologram recording medium in reproducing the hologram recording medium recorded by such an angle multiplexing method is appropriately referred to as “reproduction angle”. Further, for example, an angle serving as a reference for the reproduction angle, such as a reproduction angle when matching the normal line of the surface of the hologram recording medium, is appropriately referred to as a “reference reproduction angle”. According to this angle multiplexing type hologram reproducing apparatus, the reproduction information is reproduced by the reproduction angle by changing the reproduction angle slightly from the reference reproduction angle in accordance with the recording angle. can do.

  As described above, according to the angle multiplexing type hologram recording apparatus and hologram reproducing apparatus, a large number of recording information can be recorded in the same recording area for each recording angle of the reference light, and the multiplexed recording information can be separated from each other. Since it can be reproduced, the recording density and the recording capacity can be dramatically increased. In addition, since interference fringes are recorded in the thickness direction of the recording medium, the recording density increases as the thickness increases, ignoring optical problems.

  However, for example, even if the angle is multiplexed and the angle of 45 degrees is changed in increments of 0.01 degrees, the 450 multiplexing is the limit, and beyond that, the recording / reproduction becomes difficult optically no matter how much the thickness is increased. In addition, since the selectivity increases in the direction of increasing the thickness of the recording medium, it is possible to make finer increments of 0.01 degree increments. It becomes difficult to make a mechanism that can In addition, the better the angle selectivity is, the more planarity of the plane wave of the reference light is required.

  Similarly, in the speckle multiplex recording system, if the mechanical and optical restrictions can be ignored, the thickness can be increased by increasing the recording medium, and the recording density can be improved. An optical system that requires uniform light in the direction, and because of the increased selectivity, an accurate and minute recording medium positioning mechanism is required, and the reproducibility of recording medium mounting / removal is more difficult, even in theory Even if possible, the practicality becomes severe. For the above reasons, the recording density is theoretically higher than that of the current optical recording / reproducing apparatus and is said to be 1 terabyte or more, but it has not been put into practical use.

For this reason, as another capacity improvement means, there is a technique such as multilayering (see, for example, Patent Document 1).
IBM J.RES DEVELOP VOL.44 NO.3 MAY 2000 “Holographic data strage” JP 11-126335 A (page 5-8, FIG. 1)

  This multi-layer method is a technique aimed at increasing the storage capacity by using a plurality of recording layers in the thickness direction, but in this case, strict positioning accuracy is required also in the thickness direction, and recording is performed. Since position correction means (servo) is required at the time of playback and playback, a servo pattern is required for each layer of the media, and accuracy of the bonding positioning is required. .

  The present invention has been devised in view of the above circumstances, and the object of the present invention is that a servo pattern is unnecessary and does not require pasting positioning accuracy, and the positioning accuracy in the thickness direction is not so strict. An object of the present invention is to provide a hologram recording / reproducing apparatus capable of performing multi-layer recording / reproducing using a relatively simple servo system.

  In order to achieve the above object, the present invention provides a hologram recording apparatus for recording interference information of a reference light and spatially modulated signal light on a hologram recording medium having a plurality of recording layers, wherein the interference information is recorded on the plurality of recording layers. When recording on the target recording layer, the hologram recording medium is moved with mechanical accuracy to the position where the interference information is recorded on the target recording layer based on the position information of each recording layer. A recording medium position control means is provided.

  The present invention also provides a hologram recording apparatus for recording interference information between a reference light and a spatially modulated signal light on a hologram recording medium having a plurality of recording layers, the interference information being a target in the plurality of recording layers. A reference light movement control means for translating the reference light so that the interference information is recorded on the target recording layer based on the positional information of each recording layer when recording on the recording layer. It is characterized by.

  Further, the present invention irradiates reproduction reference light onto a hologram recording medium on which data is hologram-recorded on a plurality of recording layers, thereby receiving reproduction light generated from the hologram recording medium by an imaging means to obtain reproduction data. A hologram reproducing apparatus, wherein unnecessary light in the reproduction light is cut and unnecessary light removal means that passes only desired reproduction light and guides it to the imaging means, and target recording in the plurality of recording layers When reproducing the data recorded on the layer, the hologram recording medium is located at a position where only the reproduction light generated from the target recording layer passes through the unnecessary light removing means based on the positional information of each recording layer. And a recording medium position control means for moving the recording medium with mechanical accuracy.

  Further, the present invention irradiates reproduction reference light onto a hologram recording medium on which data is hologram-recorded on a plurality of recording layers, thereby receiving reproduction light generated from the hologram recording medium by an imaging means to obtain reproduction data. A hologram reproducing apparatus, wherein unnecessary light in the reproduction light is cut and unnecessary light removal means that passes only desired reproduction light and guides it to the imaging means, and target recording in the plurality of recording layers Reference light that translates the reference light so that only the desired reproduction light passes through the unnecessary light removal means based on the positional information of each recording layer when reproducing the data recorded on the layer. A movement control means is provided.

  As described above, in the present invention, when holographic recording is performed on the target recording layer of the hologram recording medium having a plurality of recording layers, each of the interference information of the signal light and the reference light is recorded at the position where the target recording layer is recorded. Based on the position information of the recording layer, the hologram recording medium is moved with mechanical accuracy, or the reference light is moved to the position of each recording layer so that the interference information is recorded on the target recording layer. By moving in parallel based on the information, a servo pattern is not required, the positioning accuracy of the recording medium is not required, and the positioning accuracy in the thickness direction does not need to be so strict, so a relatively simple servo system Can be used for multilayer recording.

  Further, when reproducing data from a target recording layer of a hologram recording medium having a plurality of recording layers, each recording layer is positioned at a position where only the reproduction light generated from the target recording layer passes through the unnecessary light removing means. The hologram recording medium is moved with mechanical accuracy based on the position information of the recording layer, or only the desired reproduction light passes through the unnecessary light removing means based on the position information of the recording layers. By moving the reference beam in parallel, a servo pattern is not required, the positioning accuracy of the recording medium is not required, and the positioning accuracy in the thickness direction does not need to be so strict. Multi-layer reproduction can be performed using the system.

  According to the present invention, when holographic recording is performed on a target recording layer of a hologram recording medium having a plurality of recording layers, each recording is performed at a position where interference information of signal light and reference light is recorded on the target recording layer. Based on the positional information of each recording layer, by moving the hologram recording medium with mechanical accuracy based on the positional information of the layer, or so that the interference information is recorded on the target recording layer By moving the reference beam in parallel, a servo pattern is not required, the positioning accuracy is not required, and the positioning accuracy in the thickness direction is not so strict, so a relatively simple servo system is used. Multi-layer recording can be performed, and when data is reproduced from a target recording layer of a hologram recording medium having a plurality of recording layers, reproduction generated from the target recording layer is performed. By moving the hologram recording medium to a position where only light passes through the unnecessary light removing means with mechanical accuracy based on position information of each recording layer, or only the target reproduction light is removed by the unnecessary light. By translating the reference light based on the positional information of each recording layer so as to pass through the means, a servo pattern is unnecessary, no bonding positioning accuracy is required, and positioning accuracy in the thickness direction is improved. Since it is not so strict, multilayer reproduction can be performed using a relatively simple servo system, multilayer recording can be performed even in hologram recording, and further increase in density of hologram recording can be easily achieved. it can.

  When hologram recording is performed on a target recording layer of a hologram recording medium having a plurality of recording layers, the interference information between the signal light and the reference light is recorded on the target recording layer based on the position information of each recording layer. The reference light is collimated based on the positional information of each recording layer by moving the hologram recording medium with mechanical accuracy or so that the interference information is recorded on the target recording layer. A position where only the reproduction light generated from the target recording layer passes through the unnecessary light removal means when the data is reproduced from the target recording layer of the hologram recording medium having a plurality of recording layers by moving Further, the hologram recording medium is moved with mechanical accuracy based on the position information of each recording layer, or only the target reproduction light passes through the unnecessary light removing means. On the basis of the position information of each recording layer, it was achieved by translating the reference light.

  FIG. 1 is a block diagram showing a configuration of a hologram recording / reproducing apparatus according to the first embodiment of the present invention. The hologram recording / reproducing apparatus includes a laser light source 20, a polarization beam splitter (PBS) 21, a spatial modulator 22, a signal light lens 23, a hologram recording medium 24, reproduction light lenses 25 and 26, a diaphragm 27 for cutting unnecessary light, From the lens 28 that forms an image of the light that has passed through the diaphragm 27 on the imaging device 29, the imaging device 29 such as a CCD or CMOS image sensor, the path changing mirrors 30 and 31, the drive mechanism 32 that moves the hologram recording medium 24, and the diaphragm 27. The light detector 34 detects the reflected light, the position control unit 33 that controls the position of the hologram recording medium 24, and the reference light angle correction unit 35 that changes the angle of the mirror 31.

  Next, the schematic operation of this embodiment will be described. The laser beam 10 emitted from the laser light source 20 is divided into a P wave 11 a and an S wave 12 a by the PBS 21. A laser light source 20 that generates a wavelength in the vicinity of visible light is generally used. The P wave 11a passes through the spatial modulator 22, is spatially modulated according to the data page displayed on the spatial modulator 22, and becomes signal light 11b. In general, the spatial modulator 22 is often a transmissive LCD panel, a reflective LCD panel, or a device used for an image display device such as DMD or GLV. The signal light 11 b is condensed on the recording area of the hologram recording medium 24 by the lens 23. Here, the hologram recording medium 24 does not necessarily intersect the optical axis of the signal light 11b perpendicularly.

  On the other hand, the path of the S wave 12a is changed by the mirrors 30 and 31, and the reference beam 12b is irradiated so as to cover the irradiation range of the signal light 11a of the hologram recording medium 24. The signal light 11b and the reference light 12b cause interference in the recording area of the hologram recording medium 24, and the interference information is recorded in the recording area. In the hologram recording method, by changing the angle of the mirror 31 by the reference light angle correction unit 35, the incident angle of the reference light 12b to the hologram recording medium 24 changes, and the wavefront information changes completely. Multiple recording is possible.

  Next, when the recording area of the hologram recording medium 24 is irradiated with only the same reference light 12b as that at the time of recording as the reproduction reference light 12b, diffracted light reflecting interference information recorded on the hologram recording medium 24 is generated, and the 4f system is It passes through the lenses 25 and 26 to be formed and becomes the reproduction light 13a and is condensed on the stop 27. The portion where the diffracted light is generated and the condensing portion of the stop 27 have a mirror image relationship, and the stop 27 removes light other than the 0th order light and light caused by crosstalk from the adjacent recording area, and has reproduction information. Only the light that passes through is passed, and this is further condensed by the lens 28 onto the image pickup device 29, and is photoelectrically converted by this image pickup device 29 to become reproduction data. At that time, the photodetector 34 detects the reflected light that cannot pass through the hole of the diaphragm 27, and based on this reflected light, the position control unit 33 controls the drive mechanism 32 to move the position of the hologram recording medium 24, Control is performed so that only desired reproduction light passes through the diaphragm 27. Accordingly, the diaphragm 27 removes information on the adjacent recording location and reproduction light generated from another recording layer generated from the hologram recording medium 24, and sends only light of a desired portion of the desired layer to the lens 28. Only the information of the desired layer is imaged on the imaging device 29.

  FIG. 2 is a cross-sectional view showing a configuration example of the hologram recording medium 24. The layer structure of the recording medium includes an intermediate layer 24c so as to sandwich the recording layers 24b and 24d that are actually recorded, and eliminates physical contact between 24b and 24d. There are also layers 24a and 24e for the covers 24b and 24d. For 24a, 24c, and 24e, for example, highly transparent materials such as polycarbonate and glass are used, but it is not necessary that they are the same material or the same thickness.

  FIG. 3 is a diagram showing the relationship among the signal light 11 b, the reference light 12 b, and each layer of the hologram recording medium 24 when data is recorded on the hologram recording medium 24. Reference numerals 24a and 24e denote protective layers, which do not cause any physical or chemical changes even when the reference light 12b or the reproduction light is applied. Reference numerals 24b and 24d denote hologram recording layers, which react to the reference light 12b or the signal light 11b. However, when the recording light 11b and the reference light 12b interfere with each other, it reacts and an interference fringe is recorded. Therefore, the laser light source 20, the PBS 21 or an ND filter is inserted between the laser light source 20 and the PBS 21 so that the hologram recording layers 24b and 24d have a light quantity that does not react with only the signal light 11b and the reference light 12b. As a result, the recording layer reacts in the portion 25 where the signal light 11b and the reference light 12b overlap to record interference fringes, but the portion that only hits the signal light 11b as in 26 does not react. Further, this layer structure is a case of two layers, but it is possible to further increase the number of layers by overlapping in the same manner.

  At the time of recording, the position control unit 33 controls two axes perpendicular to the optical axis of the signal light 11b and one axis in the focus direction as the direction of the hologram recording medium 24. In the case of two-beam angle multiplexing, the focus of the medium is controlled. Since the positional accuracy of the direction can be guaranteed by the mechanical accuracy, it is not necessary to perform feedback control using a servo pattern or the like, and the hologram recording medium 24 is positioned in advance at a position where the signal light is focused on the layer to be recorded. Even if the other two axes are moved at that time, even if the focus direction is shifted, the spot diameter is large and a deviation that affects writing is not generated. Therefore, in the example of FIG. 3, the position control unit 33 controls the drive mechanism 32 to determine the position of the hologram recording medium 24 in the focus direction so that the signal light 11b and the reference light 12b overlap at the position of the hologram recording layer 24d. In this case, interference fringes between the signal light 11b and the reference light 12b are generated at the hologram recording layer 24d. The amount of light of the interference fringes becomes a fringe at a portion that is partially different from a portion that is the sum of 11b and 12b. By adjusting the light amount setting and the hologram recording medium 24 in advance so as to react when the sum is reached, only the recording layer 24d is recorded. However, the signal light 11b and the reference light 12b do not overlap in the hologram recording layer 24b, which is a layer that is not desired to be recorded. Since the light amount is adjusted so that it does not react only with the signal light 11b and the reference light 12b, nothing is recorded on the hologram recording layer 24b.

  FIG. 4 is a diagram showing an optical path with respect to the hologram recording medium 24 during reproduction. When the hologram recording medium 24 is irradiated with the reference beam 12b, diffracted beams (reproduced beams) 43 and 44 are generated from the recorded portions 41 and 42 in the recording layers 24d and 24b. In this figure, for example, when only the information of the reproduction light 44 is desired, the position controller 33 controls the drive mechanism 32 to adjust the relative positional relationship between the hologram recording medium 24 and the optical systems 25 to 29 to reproduce the diaphragm 27. The hologram recording medium 24 is moved so that only the light 43 passes. In that case, since the reproduction light 43 is shielded by the diaphragm 27 as shown in the figure, only the desired reproduction light 44 is guided to the rear imaging device 29. That is, by moving the hologram recording medium 24 with respect to the diaphragm 27 so that the desired light enters, it is possible to remove the light of the undesired recording layer.

  According to the present embodiment, since the hologram recording is volume recording, when the recording layer of the hologram recording medium 24 is two layers, the interval between the recording layers 24b and 24d is in mm units. The servo for selecting whether to record to 24d may be mechanically accurate, and the recording can be performed simply by mechanically aligning the hologram recording medium 24 during recording with a simple control system that does not require a servo pattern. Selection control of the layers 24b and 24d can be performed. During reproduction, the reproduction recording layer can be selected simply by moving the position of the hologram recording medium 24 in the focus direction with mechanical accuracy. In this case, a simple control system can be used.

  Therefore, the conventional method requires high-precision control in the thickness direction using a servo pattern or the like, and the reference light and the recording light enter from the same optical axis. Inevitably, in the recording / reproducing method of the present embodiment in the case of two-beam angle multiplexing, the servo pattern is unnecessary, and the reference light and the recording light alone have a light quantity that does not react with the recording medium. It is possible to avoid exposure of the recording layer that does not occur.

  FIG. 5 is a block diagram showing a configuration of a hologram recording / reproducing apparatus 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. The hologram recording / reproducing apparatus does not require position control of the hologram recording medium 24 in the focus direction. For this purpose, the hologram recording / reproducing apparatus has a function of moving the mirror 30 parallel to the optical axis, and is controlled by the position control unit 33. Is provided with a focus adjustment unit 37 that moves the lens 28 or the imaging device 29 in the optical axis direction.

  Next, the operation of this embodiment will be described. If the optical thickness is sufficiently small and sufficient light can be collected even if there are two or more recording layers of the hologram recording medium 24, the recording medium moving means (the means for moving in the focus direction) is omitted. A mirror 30 that can be translated with respect to the optical axis is provided by a reference light translation mechanism 36. When the mirror 30 moves, the reference light 12b also moves in parallel. For example, as shown in FIG. 6, initially, when the reference beam 12b intersects the signal beam at the portion 250 of the recording layer 24d and data is recorded on the recording layer 24d, the mirror 30 translates to the left. The reference light 12b is translated in the direction of the arrow in FIG. 6, and the reference light 12b crosses the signal light (not shown) at the portion 251 of the recording layer 24b, and data is recorded on the recording layer 24b.

  Further, at the time of reproduction, it is selected by moving the mirror 30 to irradiate the reference light 12b to the recording layers 24b and 24d of the hologram recording medium 24 in the state 80 in FIG. 6 or 81. Thus, it is possible to select the reproduction light that passes through the diaphragm 27, and to guide the reproduction light from the target recording layer to the imaging device 29 to reproduce the desired data. In that case, a positional shift occurs in the focus direction, and there is a possibility that the imaging relationship with the imaging device 29 is shifted. Therefore, position adjustment is performed by moving either or both of the lens 28 and the imaging device 29 from the focus adjustment unit 37. When this method is used, the focus adjustment means by the drive mechanism 32 is unnecessary.

  According to the present embodiment, the selection servo to be recorded on which recording layer 24b, 24d and the data reproduction from which recording layer can be selected simply by moving the mirror 30 with mechanical accuracy. There are the same effects as those of the first embodiment.

  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 example in which the present invention is applied to the angle multiplexing hologram recording apparatus has been described. However, the present invention can be applied to all multiplexing systems such as shift multiplexing and phase code multiplexing to obtain the same effect. it can. Further, the present invention can be similarly applied to an in-line type in which two light beams of reference light and signal light are irradiated with one lens or a two-light beam type in which the light beams are separately irradiated.

1 is a block diagram showing a configuration of a hologram recording / reproducing apparatus according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view illustrating a configuration example of the hologram recording medium illustrated in FIG. 1. It is the figure which showed the relationship between the signal light in the case of recording data on a hologram recording medium, reference light, and each layer of a hologram recording medium. It is the figure which showed the optical path with respect to the hologram recording medium at the time of reproduction | regeneration. It is the block diagram which showed the structure of the hologram recording / reproducing apparatus which concerns on the 2nd Embodiment of this invention. FIG. 5 is a diagram showing an operation of selecting a recording layer to be reproduced by parallel movement of reference light.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Laser light source, 21 ... Polarization beam splitter (PBS), 22 ... Spatial modulator, 23 ... Signal light lens, 24 ... Hologram recording medium, 24a, 24e ... Protective layer, 24b, 24d ... ... Recording layer, 24c ... Intermediate layer, 25, 26 ... Reproducing light lens, 27 ... Aperture, 28 ... Lens, 29 ... Imaging device, 30, 31 ... Direction changing mirror, 32 ... Drive Mechanism: 33... Position control unit, 34... Photo detector, 35... Reference light angle correction unit, 36.

Claims (9)

A hologram recording apparatus for recording interference information between reference light and spatially modulated signal light on a hologram recording medium having a plurality of recording layers,
When recording the interference information on a target recording layer among a plurality of recording layers, the hologram recording medium is positioned at a position where the interference information is recorded on the target recording layer based on the position information of each recording layer. Including a recording medium position control means for moving the recording medium with mechanical accuracy.
A hologram recording apparatus characterized by that.   The recording medium position control means includes a position control unit in which position information of each recording layer of the hologram recording medium is set in advance, and a recording medium driving unit that moves the hologram recording medium in accordance with a control signal of the position control unit. The hologram recording apparatus according to claim 1. A hologram recording apparatus for recording interference information between reference light and spatially modulated signal light on a hologram recording medium having a plurality of recording layers,
When recording the interference information on a target recording layer among a plurality of recording layers, the reference light is used so that the interference information is recorded on the target recording layer based on positional information of each recording layer. Comprising reference beam movement control means for parallel translation;
A hologram recording apparatus characterized by that.   The reference light movement control means includes an optical system that translates the reference light, a position control unit in which position information of each recording layer of the hologram recording medium is set in advance, and the optical system according to a control signal of the position control unit The hologram recording apparatus according to claim 3, further comprising an optical system driving unit that moves the optical system.   4. The light quantity of the reference light and the signal light is adjusted so that each recording layer of the hologram recording layer is exposed only to interference fringes of the reference light and the signal light. The hologram recording apparatus described. A hologram reproducing apparatus for obtaining reproduction data by irradiating a hologram recording medium on which data is recorded on a plurality of recording layers with reproduction reference light, and receiving reproduction light generated from the hologram recording medium by an imaging means. ,
Unnecessary light removal means for cutting unnecessary light in the reproduction light and passing only desired reproduction light to the imaging means;
When reproducing data recorded on the target recording layer of the plurality of recording layers, only the reproduction light generated from the target recording layer based on the position information of each recording layer is the unnecessary light. Recording medium position control means for moving the hologram recording medium to a position passing through the removing means with mechanical accuracy,
A hologram reproducing apparatus comprising:   The recording medium position control means includes a position control unit in which position information of each recording layer of the hologram recording medium is set in advance, and a drive unit that moves the hologram recording medium in accordance with a control signal of the position control unit. The hologram reproducing apparatus according to claim 6. A hologram reproducing apparatus for obtaining reproduction data by irradiating a hologram recording medium on which data is recorded on a plurality of recording layers with reproduction reference light, and receiving reproduction light generated from the hologram recording medium by an imaging means. ,
Unnecessary light removal means for cutting unnecessary light in the reproduction light and passing only desired reproduction light to the imaging means;
When reproducing the data recorded on the target recording layer of the plurality of recording layers, only the desired reproduction light passes through the unnecessary light removing means based on the positional information of each recording layer. A reference light movement control means for translating the reference light as described above,
A hologram reproducing apparatus characterized by that.   The reference light movement control means includes an optical system that translates the reference light, a position control unit in which position information of each recording layer of the hologram recording medium is set in advance, and the optical system according to a control signal of the position control unit 9. The hologram reproducing apparatus according to claim 8, further comprising an optical system driving unit that moves the optical system.

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