JP2008015180A - Information recording medium and information recording/reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an information recording medium that can be easily positioned with respect to an optical system and attains spatial filtering highly precisely, and to provide an information recording/reproducing device therefor. <P>SOLUTION: The holographic recording medium 10 comprises substrates 1A, 1B, thin films 2, 3 and a holographic recording material layer 4. The thin films 2, 3 include a single or multilayer optical multiple interference film inducing optical multiple interference. Changes in the optical multiple interference in the thin films 2, 3 are caused by changes in a complex refractive index of the optical multiple interference film according to changes in incident light. This type of thin films is generally called as a super-resolution film. In the holographic recording medium 10, the thin film 2 is set to reflect or absorb light at an intensity higher than P1, while the thin film 2 is set to reflect or absorb light at an intensity lower than P2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an information recording medium and an information recording / reproducing apparatus, and more specifically to an information recording medium used for a holographic memory and the information recording / reproducing apparatus.

  Holographic memory is attracting attention as a next-generation large-capacity memory. In holographic storage, signal light and reference light are collected by a Fourier transform lens, interfered inside the information recording medium, and information is recorded as three-dimensional interference fringes. Information is superimposed on the signal light by two-dimensional page data. The holographic memory has been studied and developed by many companies and research institutes because it has a possibility of being able to read a large capacity and at a high speed as compared with a conventional optical disk.

  Write-once holographic memory using photopolymer as the main recording material is expected to be applied to applications that require large capacity, such as medical data, underground exploration data, and data backup of large-capacity storage. Problems with the holographic memory include improving the basic characteristics of the recording medium and effectively utilizing the volume of the recording medium. Effective use of the volume of the recording medium means that the dynamic range of the recording medium is fully utilized to perform multiplex recording and improve the recording density.

  As a technique for effectively using the dynamic range of a recording medium, a hologram recording / reproducing apparatus described in Patent Document 1 is disclosed. This conventional hologram recording / reproducing apparatus will be described with reference to the next figure.

  FIG. 4 is a diagram showing a schematic configuration of a conventional hologram recording / reproducing apparatus 200. Referring to FIG. 4, hologram recording / reproducing apparatus 200 includes a two-dimensional spatial light modulator 106, a lens 107, and a mask 110 formed on a glass plate 120. The hologram recording / reproducing apparatus 200 records information on the recording medium 100 and reproduces information recorded on the recording medium 100.

  Light emitted from a light source (not shown) and collimated is separated into object light PA and reference light PC. The object light PA enters the two-dimensional spatial light modulator 106 and is converted into the object light PAd optically two-dimensionally modulated corresponding to the recording medium 100. This two-dimensionally modulated object beam PAd is optically Fourier transformed by the lens 107. This two-dimensional Fourier transform image is projected onto a mask 110 in which a material that reflects or absorbs light is distributed in the two-dimensional plane of the glass plate 120.

  Of the two-dimensionally modulated object light PAd, the object light PAt component is transmitted through the mask 110, and the object light PAr component is reflected by the mask 110. As a result, the object light PAd is converted by the mask 110 into new object light PD that does not include a specific spatial frequency component of the original object light PA. The recording medium 100 is irradiated with the new object light PD and the reference light PC from another path. As a result, interference fringes between the object light PD and the reference light PC are formed on the recording medium 100 and recorded as a hologram.

  Here, the specific spatial frequency component indicates a component other than the component contributing to hologram formation in the Fourier transform image of the object beam PAd modulated by the two-dimensional spatial light modulator 106. The specific frequency component may include both a DC component and a high frequency component. In the hologram recording / reproducing apparatus 200 shown in FIG. 4, the DC component of the Fourier transform image of the object light PAd two-dimensionally modulated by the mask 110 is removed to obtain new object light PD.

With the configuration described above, the hologram recording / reproducing apparatus 200 can record information by irradiating the recording medium 100 with only the spatial frequency component contributing to the formation of interference fringes and causing it to interfere with the reference light PC. Thereby, the dynamic range of the recording medium 100 can be effectively utilized.
JP 2004-198816 A

  When the mask 110 that removes the DC component included in the Fourier transform image of the object beam PAd is disposed in the vicinity of the recording medium 100 as in the hologram recording / reproducing apparatus 200 of FIG. 4, the mask 100 is moved according to the movement of the optical system. There was a need to adjust or move. For example, if the wavelength of the light source is 532 nm, the focal length of the lens 107 is 10 mm, the pixel pitch of the two-dimensional spatial light modulator 106 is 5 μm, and the number of pixels is 1000 × 1000, the Fourier transform image of the signal light that does not contribute to interference recording The two-dimensional distribution range of the low frequency component is a square having a side of about 1 μm. For this reason, the positional adjustment accuracy between the optical system and the mask 110 and the recording medium 100 is on the order of submicrons, and the adjustment becomes very difficult.

  Originally, when spatial filtering is performed using the mask 110, it is desirable to perform filtering on the Fourier transform image of the signal light that has been completely spatial frequency transformed. However, in the hologram recording / reproducing apparatus 200 of FIG. 4, since the material that reflects or absorbs light is formed on the surface of the glass plate 120, the mask 110 cannot be disposed on the Fourier plane that generates the Fourier transform image. For this reason, there is a problem that the spatial frequency conversion is not complete and accurate spatial filtering cannot be performed.

  SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an information recording medium and an information recording / reproducing apparatus thereof that can easily adjust the position of the optical system and perform spatial filtering with high accuracy.

  The present invention provides an information recording medium on which information is recorded by a hologram, and a holographic recording material layer on which information is recorded, and a specific refractive index of incident light by changing a complex refractive index according to a change in incident light. An optical multiple interference film that transmits the spatial frequency component.

  Preferably, the optical multiple interference film includes a first film that reflects or absorbs light having a light intensity greater than the first light intensity.

  Preferably, the optical multiple interference film includes a second film that reflects or absorbs light having a light intensity smaller than the second light intensity.

  Preferably, the optical multiple interference film includes a first film that reflects or absorbs light having a light intensity greater than the first light intensity, and a second film that reflects or absorbs light having a light intensity smaller than the second light intensity. Including a membrane.

Preferably, the optical multiple interference film reflects or absorbs a direct current component of incident light.
Preferably, the optical multiple interference film reflects or absorbs a high frequency component of incident light.

  Preferably, the optical multiple interference film transmits a predetermined component having a spatial frequency corresponding to a Fourier transform image or a Fresnel transform image of incident light.

Preferably, the optical multiple interference film is formed of a super-resolution film.
According to another aspect of the present invention, a holographic recording material layer on which information is recorded, and optical multiplexing that transmits a predetermined spatial frequency component of incident light by changing a complex refractive index in accordance with a change in incident light. An information recording / reproducing apparatus that records information on an information recording medium including an interference film and / or reproduces information recorded on the information recording medium.

  According to the present invention, position adjustment with the optical system is easy, and spatial filtering can be performed with high accuracy.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  FIG. 1 is a sectional view showing a configuration of a holographic recording medium 10 according to an embodiment of the present invention. Referring to FIG. 1, a holographic recording medium 10 includes substrates 1A and 1B, thin films 2 and 3, and a holographic recording material layer 4. A holographic recording material layer 4 is formed on the substrate 1B. A thin film 3 is formed on the holographic recording material layer 4. A thin film 2 is formed on the thin film 3. On the thin film 2, a substrate 1A is formed.

  The thin films 2 and 3 include a single layer or a plurality of layers of optical multiple interference films that cause optical multiple interference. The change in the optical multiple interference in the thin films 2 and 3 is caused by the change in the complex refractive index of the optical multiple interference film in accordance with the change in the incident light. Such a thin film is generally called a super-resolution film, and is described in, for example, Japanese Patent Application Laid-Open Nos. 2001-189033 and 2005-18964.

  If the above super-resolution film is used, for example, a multiple interference film is designed so that light is reflected at room temperature, and light is emitted only when light having an intensity exceeding a certain threshold is irradiated. It can be transmitted. Specifically, when light having an intensity exceeding a certain threshold is irradiated, the light is absorbed by the film, and a complex refractive index change corresponding to the light intensity is generated in the super-resolution film. The change in the refractive index causes a change in multiple interference, and light can be transmitted only in a portion exceeding the threshold value of the irradiated light energy.

  In the holographic recording medium 10 of FIG. 1, the thin film 2 is set to reflect or absorb light having a light intensity greater than P1, and the thin film 3 is set to reflect or absorb light having a light intensity smaller than P2. To do. Thereby, as will be described later with reference to FIG. 3, the holographic recording medium 10 can transmit only light having a light intensity between P1 and P2. The thin films 2 and 3 can also be realized by a single thin film.

  FIG. 2 is a diagram showing a schematic configuration of the information recording / reproducing apparatus 20 according to the embodiment of the present invention. With reference to FIG. 2, the information recording / reproducing apparatus 20 includes a light source 5, a collimating lens 6, a spatial light modulator 7, and an objective lens 8. The information recording / reproducing apparatus 20 records information on the holographic recording medium 10 and reads out and reproduces information from the holographic recording medium 10.

  The light emitted from the light source 5 is converted into parallel light Pa by the collimator lens 6 and then enters the spatial light modulator 7. The parallel light Pa incident on the spatial light modulator 7 is first spatially divided into the signal light Pb and the reference light Pc, and two-dimensional information is superimposed only on the signal light Pb. The signal light Pb and the reference light Pc are condensed inside the holographic recording medium 10 by the objective lens 8. Thereby, information is recorded on the holographic recording medium 10.

  FIG. 3 is a diagram showing the light intensity distribution with respect to the spatial frequency of the signal light Pb modulated by the spatial light modulator 7. FIG. 3 shows a Fourier transform image of the signal light Pb modulated by the spatial light modulator 7.

  As shown in FIG. 3, the signal light Pb has a DC component Pdc having a high intensity in the vicinity (central part) of the spatial frequency of zero, and interference components Pf1 corresponding to the pixel pitch of the spatial light modulator 7 on both sides thereof. , Pf2. Here, the DC component Pdc is a component that does not contribute to the recording of light on which signals are not superimposed, that is, information, and simply consumes the dynamic range of the holographic recording medium 10. On the other hand, the interference components Pf1 and Pf2 are components that contribute to information recording on the holographic recording medium 10.

  Therefore, in the holographic recording medium 10, as described above, the thin film 2 is set to reflect or absorb light having a light intensity greater than P1, and the thin film 3 is set to reflect or absorb light having a light intensity smaller than P2. Yes. Thereby, the holographic recording medium 10 can transmit only light having a light intensity between P1 and P2.

  As a result, as shown in FIG. 3, the holographic recording medium 10 can reflect or absorb most of the DC component Pdc that does not contribute to information recording, and interference components Pf1 and Pf2 that contribute to information recording. Can be transmitted. Also, high-frequency components that do not contribute to information recording can be reflected or absorbed by setting the light intensities P1 and P2 so that the light intensity peaks other than the shaded area in FIG.

  As described above, the holographic recording medium 10 can be irradiated with only the interference component that contributes to the information recording in the signal light Pb, and the DC component and the high-frequency component that do not contribute to the information recording can be reflected or absorbed. Thereby, position adjustment with an optical system becomes easy and spatial filtering can be performed accurately. As a result, the dynamic range of the holographic recording medium 10 can be effectively utilized.

  In the above embodiment, the Fourier transform image of the signal light Pb has been described. However, for example, the signal light Pb can also be described using a Fresnel transform image. In the above-described embodiment, the coaxial transmission type holographic recording in which the signal light Pb and the reference light Pc are collected by the same objective lens 8 is described as an example of the recording optical system. An information recording / reproducing apparatus using a two-beam interference optical system of a type may be used.

  As described above, according to the embodiment of the present invention, in a holographic recording medium that records information by Fourier-transforming and coherently coherent reference light and signal light, light having a light intensity greater than the first light intensity. It has the thin film which reflects. The first light intensity is set to a value that reflects all or part of the direct current component of the Fourier transform image of the signal light. For this reason, it is possible to remove all or part of the direct current component that is not necessary for forming the interference fringes in the signal light. This is preferable because the dynamic range of the holographic recording medium can be effectively utilized.

  According to an embodiment of the present invention, the holographic recording medium includes a single-layer or multiple-layer optical multiple interference film that causes optical multiple interference, and the change in the optical multiple interference of the thin film depends on the incident light intensity. It is caused by the change of the complex refractive index of the optical multiple interference film. If the thin film is formed on the surface of the holographic recording medium, it is possible to remove all or part of the direct current component contributing to recording in the Fourier transform image of the signal light. This eliminates the need to arrange a mask or the like outside and eliminates the need to adjust the position of the optical system, the mask, and the recording medium, which is preferable.

  According to the embodiment of the present invention, the holographic recording medium has a thin film that reflects light having a light intensity greater than the first light intensity, and has a light intensity smaller than the second light intensity. It also has a thin film that reflects light. Note that these thin films can be realized by a single thin film. As described above, not only all or part of the DC component included in the Fourier transform image of the signal light but also all or part of the high frequency component included in the Fourier transform image of the signal light can be removed. . As a result, signal light including only a spatial frequency component contributing to the formation of interference fringes can be generated, which is preferable.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

It is sectional drawing which showed the structure of the holographic recording medium 10 by embodiment of this invention. It is the figure which showed schematic structure of the information recording / reproducing apparatus 20 by embodiment of this invention. It is the figure which showed light intensity distribution with respect to the spatial frequency of the signal beam | light Pb modulated by the spatial light modulator. FIG. 6 is a diagram showing a schematic configuration of a conventional hologram recording / reproducing apparatus 200.

Explanation of symbols

  1A, 1B substrate, 2, 3 thin film, 4 holographic recording material layer, 5 light source, 6 collimating lens, 7 spatial light modulator, 8 objective lens, 10 holographic recording medium, 20 information recording / reproducing apparatus, 100 recording medium, 106 Two-dimensional spatial light modulator, 107 lens, 110 mask, 120 glass plate, 200 hologram recording / reproducing apparatus.

Claims (9)

An information recording medium on which information is recorded by a hologram,
A holographic recording material layer in which the information is recorded;
An information recording medium comprising: an optical multiple interference film that transmits a specific spatial frequency component of the incident light by changing a complex refractive index according to a change of the incident light.   The information recording medium according to claim 1, wherein the optical multiple interference film includes a first film that reflects or absorbs light having a light intensity greater than the first light intensity.   The information recording medium according to claim 1, wherein the optical multiple interference film includes a second film that reflects or absorbs light having a light intensity lower than the second light intensity. The optical multiple interference film is:
A first film that reflects or absorbs light having a light intensity greater than the first light intensity;
The information recording medium according to claim 1, further comprising: a second film that reflects or absorbs light having a light intensity smaller than the second light intensity.   The information recording medium according to claim 1, wherein the optical multiple interference film reflects or absorbs a direct current component of the incident light.   The information recording medium according to claim 1, wherein the optical multiple interference film reflects or absorbs a high-frequency component of the incident light.   The information recording medium according to claim 1, wherein the optical multiple interference film transmits a predetermined component having a spatial frequency corresponding to a Fourier transform image or a Fresnel transform image of the incident light.   The information recording medium according to claim 1, wherein the optical multiple interference film is formed of a super-resolution film.   An information recording / reproducing apparatus for recording information on the information recording medium according to claim 1 and / or reproducing information recorded on the information recording medium.

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