KR100619052B1 - Hologram memory medium, recording apparatus therefor, and reproducing apparatus therefor - Google Patents

Abstract

In the optical system in which the reference light and the object light propagate on the same optical path, by using both spatial separation and polarization separation together, a hologram memory medium capable of realizing a large capacity while minimizing the influence of scattered light noise, and providing a recording apparatus and a reproducing apparatus For the purpose of

First and second recording layers for irradiating the object light and the reference light to record information of the object light as interference stripes, and having the recording layer between the recording surface side and the side opposite to the recording surface to change the polarization state of the incident light; By providing a phase difference film of 2, a hologram memory medium capable of realizing a large capacity while minimizing the influence of scattered light noise is provided.

Description

Hologram memory medium, recording apparatus therefor, and reproducing apparatus therefor}

1 is a configuration diagram of a hologram memory medium in the present embodiment.

2 is a configuration diagram of an optical system of the recording and reproducing apparatus in this embodiment.

3 is a configuration diagram of the upper surface in the present embodiment.

4 is a configuration diagram of the λ / 2 plate in the present embodiment.

5 is a diagram showing a recording operation in the recording and reproducing apparatus according to the present embodiment.

6 is a diagram showing a reproducing operation in the recording and reproducing apparatus according to the present embodiment.

7 is a diagram showing a write operation when the reflective layer of the hologram memory medium is changed.

8 is a diagram showing a reproduction operation when the reflective layer of the hologram memory medium is changed;

9 is a diagram showing the relationship between the amount of scattered light and the diffraction efficiency in the conventional example.

10 is a diagram showing the relationship between the numerical aperture and the hologram multiple number of the objective lens.

11 is a diagram showing a relationship between diffraction efficiency and hologram multiple numbers.

12 is a view showing an optical system of a conventional example.

<Description of the code>

One… Cover layer 2... Phase difference film A (λ / 4 film)

3... . Recording layer 4.. Phase difference film B (λ / 4 film)

5... Cholesteric liquid crystal filter 6. Color filter

7... Substrate 8.. Reflective layer

11... Semiconductor laser 12. Beam expander

13... Polarizing beam splitters 14a, 14b, 14c... λ / 4 plate

15... Spatial light modulator (SLM) 16. Condenser

17... Aperture 18... mirror

19... λ / 2 plate 20... Beam splitter

21... Analyzer 22... Image sensor

23... Objective

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a memory medium, and more particularly, to a hologram memory medium for recording information as interference fringes by object light and reference light, a recording device for recording information on the hologram memory medium, and a reproduction device for reproducing the recorded information. .

The hologram recording method of recording information on a recording medium using holography is performed by polymerizing a light (hereinafter referred to as object light) and a reference light having image information to be recorded in a hologram memory medium and writing the interference stripes into the hologram memory medium. Is executed.

When the recorded information is reproduced, the same reference light as the reference light used at the time of recording is irradiated to the hologram memory medium, and the recorded image information is reproduced by diffraction from the interference fringe. The hologram recording method is a method of recording interference fringes three-dimensionally by using the thickness direction of the hologram memory medium, and since two-dimensional image information can be multiplely recorded in the same spatial part, the surface 2 represented by CD or DVD is represented. A significant improvement in recording capacity is expected compared to the dimensional memory.

Such a hologram recording and reproducing apparatus belongs to an interferometer using interference of two light beams of an object light and a reference light beam. In the interferometer, it is very difficult to polymerize two lights in a stable state and various studies have been made until now. Among them, an optical system called a common optical path type interferometer has been used in devices such as minute step measurement.

In such an optical system, since two light to be polymerized are transmitted along the same optical path, the influence of optical path fluctuation due to disturbance such as vibration or agitation of air acts on the two light equally, and their effects cancel each other. Therefore, a stable device that is not affected by optical path fluctuations is realized. For example, a device called a Nomarski interferometer or a Normalsky microscope is widely used as a representative of such a device. In addition, in the common optical path type interferometer, two light beams are transmitted along the same optical path, so that the optical system can be simplified and downsized.

Fig. 12 is a schematic diagram of an optical system in a hologram recording and reproducing apparatus that takes advantage of such a common optical path (see, for example, US Patent No. 6108110). As shown in FIG. 12, a spatial light modulator (SLM) is disposed near the center of the optical system, and recording information converted into a two-dimensional digital image is displayed on the SLM. In this SLM, light subjected to light intensity modulation becomes object light with information.

A reference light is disposed outside the object light, and interference fringes are recorded by polymerizing these two lights in a hologram memory medium. At this time, the hologram memory medium is rotated a little to shift the position, thereby multiplexing information from the object light onto the hologram memory medium. At the time of reproduction, the light emitted from the SLM is completely blocked, and only the reference light is irradiated to the recorded interference fringe, and the image information reproduced from this interference fringe is received by a two-dimensional image sensor such as a CCD to reproduce the information.

As described above, in the hologram recording, a large number of image information can be recorded in the same portion on the hologram memory medium. Therefore, if the thickness of the hologram memory medium is increased, there is no upper limit in principle. However, in reality, the recording capacity of a hologram memory medium is limited by various factors, and scattered light generated in an optical element such as a lens or a hologram memory medium is a major problem.

In general, as the number of multiple images (the number of interference stripes) increases, the diffraction efficiency of the reproduced light diffracted in the individual interference stripes decreases drastically. On the other hand, when light is irradiated to an optical element such as a lens or a hologram memory medium, scattered light is generated due to the surface roughness of the optical element or the hologram memory medium or the nonuniformity of the material. It is practically impossible to eliminate all such scattered light, and there is not much scattered light mixed in the image sensor in the reference light. Such light interferes with detection of reproduction light having low diffraction efficiency as optical noise. Therefore, the upper limit of the finally recorded capacity is determined by the ratio (the so-called S / N ratio) of the light intensity of the reproduced light and the light intensity of the scattered light.

However, even in the optical system shown in FIG. 12, since the reference light and the object light are transmitted along the same optical system, the recording and reproducing apparatus is stable, and further miniaturization of the apparatus can be expected. However, since the scattered light easily enters the image sensor because it is a common optical path. There is a problem. Therefore, the capacity of recording capacity has not been achieved so far in the hologram recording / reproducing optical system of the common optical path type shown in FIG.

Fig. 10 is multiplied by the numerical aperture (NA) of the objective lens in the case where the capacity of information recorded assuming a hologram memory medium having the same recording area as the current CD is 0.2 terabyte, 0.5 terabyte, or 1 terabyte. The relationship between the number of holograms is calculated. When the numerical aperture of the general objective lens is about 0.5, the hologram multiple number when the recording capacity is 0.2 terabyte is expected to be about 400, about 1,000 at 0.5 terabyte, and about 2000 at 1 terabyte.

11 is a diagram showing a relationship between diffraction efficiency and hologram multiple numbers.

The diffraction efficiency (η) corresponds to the square of the M number (M #) representing the characteristics of the recording material divided by the multiple number (M) of the hologram. For example, the general M number of the hologram recording material is M # = 5. If the hologram multiple number (M) is M = 1000, the diffraction efficiency (η) is about η = 2.5 × 10 ^-5 , and when the hologram multiple number (M) is M = 2000, the diffraction efficiency (η) is η = 6.3 × It is estimated to be about 10 ^-6 .

FIG. 9 is a diagram showing the relationship between the amount of scattered light measured in the conventional hologram disk storage system shown in FIG. 12 and its diffraction efficiency (η). The diffraction efficiency η can be reduced only to η = 1 × 10 ⁻² , and a small diffraction efficiency of η = 1 × 10 ^−5, which is required for a terabyte equivalent recording capacity, could not be detected.

In the conventional method shown in FIG. 12, the reference light is disposed so that the object light occupies and surrounds the center of the optical system, and separation of the reference light and the object light has been spatially performed, but scattered light is literally propagated in all directions. Because of the components, it is very difficult to remove all scattered light by such spatial separation alone.

SUMMARY OF THE INVENTION The present invention provides a hologram memory medium capable of realizing a large capacity while minimizing the influence of scattered light noise by using polarization in addition to spatial separation in an optical system in which a reference light and an object light propagate on the same optical path. It is an object of the present invention to provide a recording apparatus and a reproduction apparatus.

In order to achieve the above technical problem, the present invention provides the following holographic memory medium, its recording apparatus and reproducing apparatus.

The invention according to claim 1 is provided with a recording layer for irradiating object light and reference light and recording information of the object light as an interference fringe, and on the recording surface side of the recording side and the side opposite to the recording surface with the recording layer therebetween. A hologram memory medium has been proposed which includes first and second retardation films arranged respectively to change the polarization state of incident light.

According to the present invention, the polarization states of the object light and the reference light are changed by the first and second retardation films arranged with the recording layer therebetween. Therefore, by reflecting only the object light in the reflective layer with the object light and the reference light until it is incident on the hologram memory medium and transmitting the second retardation film twice, interference stripes are formed by reflecting the object light and the reference light in the same polarization state. can do.

The invention according to claim 2 proposes a hologram memory medium, further comprising a reflective layer provided in contact with the second retardation film surface in the hologram memory medium according to claim 1.

The invention according to claim 3 proposes a hologram memory medium in the hologram memory medium according to claim 2, wherein the reflective layer selectively reflects only the object light.

According to the present invention, by providing the reflective layer in contact with the second retardation film, the polarization states of the object light and the reference light can be orthogonal to each other except the recording layer, and only the recording layer can be matched. In addition, by providing a function of reflecting only object light to the reflective layer, the object light and the reference light can be separated to minimize the influence of scattered light noise.

According to a fourth aspect of the present invention, there is provided a hologram memory medium according to claim 2, further comprising: a filter layer provided in contact with a surface opposite to a surface in contact with the second retardation film surface of the reflective layer and absorbing reference light. A holographic memory medium is proposed.

According to this invention, since the filter layer absorbs the reference light transmitted through the reflection layer, the object light and the reference light can be separated to minimize the influence of the scattered light noise.

The invention according to claim 5 proposes a hologram memory medium characterized by the shape of a disk in the hologram memory medium according to any one of claims 1 to 4.

According to the present invention, the shape of the disc can be recorded and reproduced on the hologram memory medium by the same mechanism as that of the recording and reproducing apparatus used in the conventional optical disc.

The invention according to claim 6 proposes a hologram memory medium characterized by the shape of a card in the hologram memory medium according to any one of claims 1 to 4.

According to the present invention, the hologram memory medium can be applied to various fields by making the shape of the card.

The invention according to claim 7 proposes a hologram memory medium, wherein the hologram memory medium according to any one of claims 1 to 4 has a tape shape.

According to the present invention, the hologram memory medium can be applied to various fields by making the tape shape.

The invention according to claim 8 records information in the hologram memory medium according to any one of claims 1 to 7, wherein the object light and the reference light are transmitted along the same optical system and the object light and the reference light are only inside the recording layer. The polarizing states of the same and the polarizing states of the object light and the reference light are orthogonal to each other except the recording layer.

The invention according to claim 9 reproduces the information recorded in the hologram memory medium according to any one of claims 1 to 7, wherein the object light and the reference light are transmitted along the same optical system and at the same time the object light is only inside the recording layer. And a polarization state of the reference light coincide with each other and the polarization states of the object light and the reference light are orthogonal to each other except the recording layer.

According to the present invention, since the polarization of the object light and the reference light is orthogonal in the parts other than the recording layer, and the scattered light generated from the reference light is the same polarized light as the reference light, the scattered light can be easily removed by a polarization separation element such as an analyzer. have.

Hereinafter, a hologram memory medium, a recording apparatus and a reproduction apparatus according to the present invention will be described in detail with reference to Figs.

As shown in FIG. 1, a hologram memory medium according to an embodiment of the present invention includes a cover layer 1, a phase difference film A (λ / 4 film) 2, a recording layer 3, and a phase difference film B (λ). / 4 film) 4, the cholesteric liquid crystal filter 5, the color filter 6, and the board | substrate 7 are comprised.

Here, the retardation film A (λ / 4 film) 2 and the retardation film B (λ / 4 film) 4 have left-sided circularly polarized light as S-polarized light, right-sided circularly polarized light as P-polarized light, and S-polarized light. Right-handed circularly polarized light converts P-polarized light into left-handed circularly polarized light. The recording layer 3 is made of a photosensitive material such as a photopolymer, for example, and records information of the object light as interference fringes by irradiating the object light and the reference light to the same portion.

The cholesteric liquid crystal filter 5 is composed of a cholesteric liquid crystal having a molecular arrangement having a helical periodic structure and is an optical element that selectively reflects only a wavelength determined by a spiral period. This characteristic also depends on the molecular design, but for example, in the right helical cholesteric liquid crystal material, the circularly polarized dichroism reflects all of the right circularly polarized light and transmits all the left circularly polarized light. Have.

The color filter 6 is an optical element that absorbs all the recording and reproduction light. The cover layer 1 is a protective layer for protecting the inside of the hologram memory medium, and the substrate 7 is a member forming the base of the hologram memory medium.

Next, an optical system of a recording and reproducing apparatus according to an embodiment of the present invention will be described with reference to FIG.

The optical system of the recording and reproducing apparatus according to the embodiment of the present invention includes a semiconductor laser 11 serving as a light source and a beam expander 12 which enlarges the beam diameter of the laser light emitted from the semiconductor laser 11 as shown in FIG. ), A polarizing beam splitter 13 for splitting incident light into two or more separate beams, and a λ / 4 plate 14a, 14b, 14c for changing the polarization state of the incident light. And a spatial light modulator (SLM) 15 for generating object light, a condenser lens 16 for condensing incident light, an aperture 17 having a circular hole at a focal point of the condenser lens 16, and an aperture A mirror 18 for reflecting the light passing through the light 17, a λ / 2 plate 19 for changing the polarization state of the incident light, a beam splitter 20 for dividing the incident light into two or more split beams, The analyzer 21 for removing the light component orthogonal to the reproduction light, the image sensor 22 for receiving the reproduction light, and the incident light The objective lens 23 forms an image on the recording layer 3 of the program memory medium. The light source may not be a semiconductor laser as long as it is a laser suitable for a wavelength sensitive to the recording material.

Next, the recording and reproducing operation of the information on the hologram memory medium will be described with reference to FIGS. 2 to 6.

In this embodiment, the semiconductor laser light 11 used for recording and reproducing information on the hologram memory medium is assumed to be linearly polarized light (S polarized light). The laser beam emitted from the semiconductor laser 11 is enlarged by the beam expander 12 and reflected by the polarized beam splitter (PBS) 13 to rotate right in the λ / 4 plate 14a. After conversion to polarized light, it enters a spatial light modulator (SLM) 15.

In this embodiment, as shown in Fig. 3, two object light and reference light are arranged on the image plane of the optical system. Furthermore, in FIG. 3, as an example, the object light occupies the center of the optical system and the reference light is disposed outside thereof. For example, the positional relationship between the object light and the reference light may be reversed. In addition, the object light shown in this figure occupies the inside of a rectangle, but even if it is circular, there is no problem at all.

The information to be recorded is previously converted into two-dimensional digital data in accordance with a predetermined encoding logic, and the image data is displayed on the SLM 15. In order to realize large multiplicity with shift multiplexing, the reference light needs to be a speckle beam subjected to random phase modulation or intensity modulation. In the example of FIG. 3, the diffusion is placed on the outside of the SLM 15. The speckle beam generated in the plate may be used as the reference light.

In order to generate the speckle beam, a specially designed optical element called a spatial phase modulator using a liquid crystal or a random phase plate may be used. The speckle beam generated in this area may be used as the reference light by using the same SLM 15 as the SLM 15 used for displaying the object light and displaying a random pattern on the outside of the object light.

As described above, when both the object light and the reference light are displayed on one SLM 15, and when the reflective liquid crystal display is used as the SLM 15, the SLM 15 itself has a function as a λ / 4 plate. (Lambda) / 4 board 14a arrange | positioned between 13 and SLM 15 becomes unnecessary.

If a Digital Micro-Mirror Device (DMD) is used as the SLM, this lambda / 4 plate is required to orthogonal to the polarization of the incident light.

In any way, the light reflected from the upper surface of the object light and the reference light becomes P-polarized light that is orthogonal to the incident polarization and passes through the PBS 13. This transmitted light passes through another λ / 4 plate 14b and is condensed by the condenser lens 16. At the focal position of the lens, a circular aperture 17 and a mirror 18 are arranged. This focal position is in the conjugate position with the focal position of the objective lens 23 in the hologram memory medium. Furthermore, the diaphragm 17 placed in the focal position removes unnecessary light such as high-dimensional diffraction light and scattered light generated by the SLM 15, and also serves to prevent the size of the hologram from becoming larger than necessary.

Since the light reflected by the mirror reciprocates the λ / 4 plate 14b, the polarized light is converted from P polarized light to S polarized light and then reflected by the PBS 13 to form an upper surface again at the position of conjugate with the SLM 15. In this upper surface position, if the arrangement of the reference light and the object light shown in Fig. 3 is taken as an example, a wave plate as shown in Fig. 4 is placed, and the polarizations of the reference light and the object light are orthogonal to each other. Further, in Fig. 4, as an example, the λ / 2 plate is arranged in the area of the object light and the portion of the reference light is a simple glass substrate, but this positional relationship is not a problem at all.

When the reference light and the object light transmitted through the wavelength plate pass through the lambda / 4 plate 14c disposed next, the object light is converted into, for example, left-turning circularly polarized light and reference light-turning circularly polarized light. In addition, the object light and the reference light pass through the beam splitter 20 and are condensed by the objective lens 23 in the hologram memory medium.

Next, a state in which an interference fringe is recorded in the hologram memory medium will be described, taking the polarization state as shown in FIG. 5 as an example.

The polarization of the object light incident on the hologram memory medium is left-rotating circularly polarized light (L), and S-polarized light in the recording layer (3) of the hologram memory medium is first transmitted by the phase difference film A (λ / 4 film) 2 transmitted therethrough. do. In addition, when the phase difference film B (λ / 4 film) 4 beneath it is transmitted, the light is converted to right-turn circularly polarized light R.

Furthermore, in FIG. 5, if the cholesteric liquid crystal material has a right spiral arrangement, all of the object light of the right-handed circularly polarized light R is reflected by the cholesteric liquid crystal filter 5, and again the phase difference film B (4). If it passes through, it is converted into P polarized light which is orthogonal to the time of incidence in the recording layer 3. On the other hand, the reference light incident on the hologram memory medium is a right-handed circularly polarized light (R) orthogonal to the polarization of the object light. When transmitted through the phase difference film A (2), the reference light becomes P-polarized light in the hologram memory medium. Therefore, since the light matches the polarization of the object light reflected from the cholesteric liquid crystal filter 5, the two lights interfere with each other and the interference fringes are recorded in the recording material constituting the recording layer 3.

The reference light transmitted through both the retardation film A (2) and the retardation film B (4) is converted into left-rotating circularly polarized light L. FIG. Since the cholesteric liquid crystal filter 5 has a property of transmitting the left-rotating circularly polarized light L, all the reference light is incident on the color filter 6 disposed under the cholesteric liquid crystal filter 5. This color filter 6 absorbs all incident reference light.

Next, the polarization state at the time of reproduction is demonstrated using FIG.

The reference light at the time of reproduction is exactly the same as at the time of recording, and when this light is irradiated to the interference fringes written in the hologram memory medium, the object light written at the time of recording in this interference fringe is reproduced by the diffraction phenomenon. The regenerated light is generated from the reference light of the right-handed circularly polarized light R. The polarized light of the regenerated light is equivalent to the polarization of the reference light reciprocating the phase difference film A (2). As a result, the reference light is emitted from the hologram memory medium. The left turn circular polarized light L is orthogonal to the polarized light.

This light is returned to the opposite side of the optical system shown in FIG. 2 at the time of incidence, passes through the objective lens 23, is reflected by the beam splitter 20, and is returned to linearly polarized light at the λ / 4 plate 14c. It passes through the analyzer 21 which transmits only this polarization component, and is received by the image sensor 22, such as CCD.

The reference light, which is not converted to the regenerated light, passes through the cholesteric liquid crystal filter 5 and is completely absorbed by the color filter 6 provided in the lower layer. Therefore, since there is no reference light propagating toward the image sensor on the detection side, generation of scattered light noise is further suppressed. The surface reflection component of the recording medium also remains orthogonal to the polarization of the reproduced light and is removed by the analyzer 21 placed in front of the image sensor 22.

According to the present embodiment, the scattered light noise is reduced by adopting a common optical path type optical system in which the reference light and the object light propagate on the same optical path, using spatial separation and polarization separation, and introducing a color filter that absorbs the reference light. The impact can be reduced as much as possible.

In the present embodiment, a hologram memory medium having a cholesteric liquid crystal filter selectively reflecting only object light as described above has been described as an example, but the same applies to a hologram memory medium using an aluminum film as a reflective layer as shown in FIGS. 7 and 8. The effect can be obtained.

The operation during recording and reproduction in this case will be described with reference to FIGS. 7 and 8. FIG. The polarization states of the object light and the reference light incident on the hologram memory medium are the same as in the above embodiment.

As shown in FIG. 7, the polarization of the object light incident on the hologram memory medium is left-rotating circularly polarized light L, and when transmitted through the phase difference film A (λ / 4 film) 2, S is recorded in the recording layer 3 of the hologram memory medium. It becomes polarized light. Further, the light is transmitted through the retardation film B (λ / 4 film) 4 below and converted into the right-turning circularly polarized light R, and then reflected by the reflective layer 8. The object light reflected by the reflective layer 8 passes through the retardation film B (λ / 4 film) 4 again, is converted into P polarized light, and is incident on the recording layer 3.

On the other hand, the polarization of the reference light incident on the hologram memory medium is the right-handed circularly polarized light R and transmitted through the retardation film A (λ / 4 film) 2 results in P-polarized light in the recording layer 3 of the hologram memory medium. Further, the light is transmitted through the phase difference film B (λ / 4 film) 4 below and converted into the left-rotating circularly polarized light L, and then reflected by the reflective layer 8. The object light reflected by the reflective layer 8 passes through the retardation film B (λ / 4 film) 4 again, is converted into S-polarized light, and is incident on the recording layer 3.

As a result, as illustrated in FIG. 7, the object light of the S-polarized light and the reference light of the S-polarized light interfere with each other to record the hologram Holo-S. In addition, the hologram (Holo-P) is recorded because the object light of P polarization and the reference light of P polarization interfere with each other.

When the hologram is reproduced, as shown in Fig. 8, when the reference light of the right-turning circularly polarized light R enters the hologram memory medium and passes through the phase difference film A (λ / 4 film) 2, the recording layer of the hologram memory medium ( In 3), P polarization is obtained. When this reference light is irradiated to Holo-P, the regenerated light from Holo-P passes through retardation film A (λ / 4 film) 2, is converted into left-rotating circularly polarized light L, and is incident on the optical system.

On the other hand, the reference light transmitted through the retardation film B (λ / 4 film) 4 is converted to left circularly polarized light L and then reflected by the reflective layer 8, and the reference light is again converted into the retardation film B (λ / 4 film) 4. The light is transmitted through the light and becomes S polarized light in the recording layer 3 of the hologram memory medium. When this reference light is irradiated with Holo-S, the regenerated light from Holo-S passes through the retardation film B (λ / 4 film) 4 twice and then passes through the retardation film A (λ / 4 film) 2. Is converted into left circularly polarized light L and is incident on the optical system. Therefore, even when the aluminum film is used as the reflective layer, the polarization states of the object light and the reference light can be orthogonal to each other except the recording layer, so that only the recording layer can be matched.

Although the embodiments of the present invention have been described in detail with reference to the drawings, specific configurations are not limited to these embodiments, and design changes and the like within the scope of the present invention are included. Although the foregoing description has been focused on the novel features of the invention as applied to various embodiments, those skilled in the art will appreciate that the apparatus and method described above without departing from the scope of the invention. It will be understood that various deletions, substitutions, and changes in form and detail of the invention are possible. Accordingly, the scope of the invention is defined by the appended claims rather than in the foregoing description. All modifications within the scope of equivalents of the claims are to be embraced within the scope of the present invention.

According to the present invention, the influence of scattered light noise, which is most likely to be a problem in the common optical path type optical system in which the reference light and the object light propagate on the same optical path, and the polarization of the object light and the reference light in other parts than the recording layer is orthogonal. In addition, by introducing a reflective layer that reflects only the object light and transmits the reference light and a color filter that absorbs the reference light, there is an effect that can be reduced as much as possible. In addition, the above structure has the effect that a large capacity of recording information can be realized while simplifying the optical system.

Claims (9)

A recording layer which irradiates the object light and the reference light and records the information of the object light as interference stripes; First and second retardation films disposed on the recording surface side and the side opposite to the recording surface of the recording layer with the recording layer interposed therebetween to change the polarization state of incident light; And And a reflective layer disposed in contact with a side opposite to the surface in contact with the recording layer of the second retardation film. The hologram memory medium of claim 1, wherein the reflective layer reflects both the object light and the reference light. The hologram memory medium of claim 1, wherein the reflective layer selectively reflects only the object light. The method of claim 3, And a filter layer disposed in contact with a surface opposite to a surface in contact with the second retardation film surface of the reflective layer to absorb the reference light. The hologram memory medium according to any one of claims 1 to 4, wherein the shape is in the form of a disk. The hologram memory medium according to any one of claims 1 to 4, wherein the shape is in the form of a card. The hologram memory medium according to any one of claims 1 to 4, wherein the shape is in the form of a tape. Information is recorded on the hologram memory medium according to any one of claims 1 to 7, Light source; A polarization beam splitter for polarizing incident light from the light source and splitting the incident light into two or more separate beams; A spatial light modulator for modulating the separated beam to generate object light and reference light; A λ / 2 plate that polarizes the object light so that the object light and the reference light are perpendicular to each other; And At least one λ / 4 plate for polarizing the object light and the reference light, The object light and the reference light are transmitted along the same optical system, and the polarization states of the object light and the reference light coincide only within the recording layer, and the polarization states of the object light and the reference light are orthogonal to each other except the recording layer. Holographic memory media recording device. Reproducing the information recorded in the hologram memory medium according to any one of claims 1 to 7, Light source; A polarization beam splitter for polarizing incident light from the light source and splitting the incident light into two or more separate beams; A spatial light modulator for generating reference light by modulating the separated beam; And At least one λ / 4 plate for polarizing the reference light, The reproduction light reproduced by the reference light and the reference light is transmitted along the same optical system, and the polarization states of the reference light and the reproduction light coincide only inside the recording layer, and the polarization states of the reference light and the reproduction light are orthogonal to each other except the recording layer. A holographic memory medium reproducing apparatus, characterized in that.

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