JP4882802B2 - Hologram recording apparatus and hologram reproducing apparatus - Google Patents

Description

  The present invention relates to a hologram recording apparatus that records information on a recording medium using holography. The present invention also relates to a hologram reproducing apparatus that reproduces information from a recording medium on which hologram information is recorded.

  Hologram recording that records information on a recording medium using holography has been conventionally proposed. Hologram recording can be performed by superimposing signal light having a two-dimensional light intensity modulation pattern modulated according to user data information and reference light having a predetermined light intensity pattern inside the recording medium. This is done by writing interference fringes on the recording medium. This hologram recording is performed by various multiplex recording methods such as an angle multiplex method, a shift multiplex method, a wavelength multiplex method, a phase code multiplex method, and the like, and information can be multiplexed and recorded at the same position or overlapping areas of the recording medium. Therefore, it is said that ultra-high density optical recording becomes possible, and has attracted attention.

  FIG. 7 is a diagram for explaining the configuration of a conventional hologram recording medium 100 (see Patent Document 1) used for performing hologram recording. As shown in FIG. 7, a hologram recording medium 100 includes a hologram layer 102 as an information recording layer on which information is recorded using volume holography on one surface of a transparent substrate 101 formed of polycarbonate or the like, and a reflective film 103. And the protective layer 104 are laminated in this order. At the boundary between the hologram layer 102 and the protective layer 104, a plurality of address / servo areas 105 serving as positioning areas extending in the radial direction are provided at predetermined angular intervals, and a sector shape between adjacent address / servo areas 105 is formed. A section is a data area 106.

  The hologram recording medium 100 is provided with a positioning area (address / servo area 105) in which information for positioning the irradiation position of signal light (same for information light), recording reference light, and reproduction reference light is recorded. Therefore, it is possible to accurately position the light for recording or reproduction. Therefore, when holographic recording is performed using the hologram recording medium 100, the irradiation position of the information light and the reference light can be accurately positioned, and information can be multiplexed and recorded at the correct position. Also, when reproducing the hologram recording medium 100 on which information is recorded, since the irradiation position of the reference light can be accurately positioned, information can be reproduced with high reproduction quality.

  However, in the case of the hologram recording medium disclosed in Patent Document 1, only one volume hologram is formed in the thickness direction of the recording medium, which is not efficient in terms of recording capacity. For this reason, Patent Document 2 introduces a hologram recording medium on which information is recorded using holography, which can record information at a higher density.

FIG. 8 is an explanatory diagram showing a configuration of the hologram recording medium 200 introduced in Patent Document 2. As shown in FIG. As shown in FIG. 8, the hologram recording medium 200 is laminated in the thickness direction, and information is recorded by an interference pattern due to interference between signal light carrying information and recording reference light, and reproduction reference light is also transmitted. A plurality of information recording layers 201 for generating reproduction light corresponding to recorded information when irradiated, and positioning of signal light, recording reference light, and reproduction reference light with respect to each information recording layer 201 And a positioning layer 202 used for the purpose. Therefore, the hologram recording medium 200 can record a plurality of information in the thickness direction of the recording medium, and can record information at a higher density.
Japanese Patent Laid-Open No. 10-124872 Japanese Patent Laid-Open No. 11-126335 JP 2006-243243 A

  However, in the case of the hologram recording medium 200 having the configuration shown in Patent Document 2, since a plurality of layers in which one information recording layer 201 is sandwiched between two positioning layers 202 are stacked, information that can be recorded in the thickness direction is recorded. If the number is increased, there is a problem that the thickness of the hologram recording medium 200 is increased. In addition, since the number of the information recording layers 201 is plural, there is a problem that the production of the hologram recording medium is expensive.

  In consideration of such points, the present inventors are studying the development of a hologram recording medium 1 as shown in FIG. 9, for example. FIG. 9 is a schematic cross-sectional view of the hologram recording medium 1 studied by the inventors when cut along the radial direction. First, the configuration of the hologram recording medium 1 will be described.

  As shown in FIG. 9, the hologram recording medium 1 includes a first positioning layer 3a, a gap layer 4a, a second positioning layer 3b, a gap layer 4b, a dichroic mirror layer 5, and a gap layer 4c on a disk-shaped substrate 2. The hologram recording layer 6 and the protective layer 7 are stacked in this order.

  The first positioning layer 3 a and the second positioning layer 3 b are used when reproducing signal light and reference light used when performing hologram recording on the hologram recording medium 1 or information recorded on the hologram recording medium 1. It is a layer used for positioning the irradiated position of the reference light. Each of the first positioning layer 3 and the second positioning layer 3b is formed with a track TR made of, for example, a groove. Each track TR is formed with a mark indicating a position where the signal light and the reference light are irradiated.

  The track TR formed in the positioning layers 3a and 3b is formed, for example, concentrically with respect to the center of the substrate 2 formed in a disk shape (another form may be, for example, a spiral shape). Absent). Further, the tracks TR formed on the first positioning layer 3a and the second positioning layer 3b are at the same position when the hologram recording medium 1 is viewed from above.

  A reflective film using, for example, Al, Ag, Au, or an alloy thereof is formed on the first positioning layer 3a and the second positioning layer 3b. Note that at least the reflection film formed on the second positioning layer 3b does not reflect all red laser light (servo laser light) incident on the hologram recording medium 1, but reflects only a part thereof. It is a semi-reflective film.

  The gap layers 4a to 4c constituting the hologram recording medium 1 have a role of forming a gap having a predetermined thickness between the layers and do not hinder the incidence of light. The material constituting the gap layers 4a to 4c is not particularly limited. For example, materials such as glass, plastics such as polycarbonate and polyimide, and ultraviolet curable acrylic resins are used.

  The hologram recording layer 6 is a layer on which information is recorded by an interference pattern due to interference between signal light and reference light. The hologram recording layer 6 is made of a material whose optical characteristics such as a refractive index, a dielectric constant, and a reflectance change according to the intensity of light when irradiated with light. For example, a photopolymer is used.

  The dichroic mirror layer 5 reflects the green laser light (reference light and signal light) incident from the protective layer 7 side and transmits the red laser light. That is, the dichroic mirror layer 5 reflects green laser light used for recording / reproducing on the hologram recording medium 1 before reaching the positioning layers 3a and 3b. On the other hand, the red laser beam used for positioning (servo) of the signal light and the reference light reaches the positioning layers 3a and 3b.

  Note that the configuration of the dichroic mirror layer 5 may be changed as appropriate depending on the type of laser light used for recording and reproduction of the hologram recording medium 1.

  The protective layer 7 protects the hologram recording layer 6 and is made of a material that does not prevent light from entering. The material constituting the protective layer 7 is not particularly limited, and for example, materials such as glass, plastics such as polycarbonate and polyimide, and ultraviolet curable acrylic resins are used.

  Thus, in the hologram recording medium 1, the two positioning layers of the first positioning layer 3a and the second positioning layer 3b are separately formed. For this purpose, the positioning layers 3a and 3b are used to position the irradiation positions of the signal light and the reference light so that multiple recording can be performed in the thickness direction of the hologram recording medium 1 in addition to the multiple recording by shift multiplexing. It can be performed well and information can be recorded at high density. The holographic recording medium 1 studied by the present inventors can perform multiplex recording in the thickness direction of the holographic recording medium only by providing one holographic recording layer 6.

  Although the case where the number of positioning layers is two is shown here, if the number of positioning layers is three or more, higher information density can be achieved.

  By the way, when information is multiplexed and recorded in the thickness direction of the hologram recording medium 1, reference light is irradiated to a plurality of holograms recorded in the thickness direction of the hologram recording layer 6 during reproduction. Since the angle formed by the reference light with respect to the hologram is different from the angle formed by the reference light with respect to the hologram that is not the reproduction target, it is theoretically possible to reproduce the information only for the hologram to be reproduced. . This will be described below with reference to the description in Patent Document 2.

First, with reference to FIG. 10, the relationship between the relief in a hologram (volume hologram) and the incident angle to it will be described. Consider a case where light 303 having a wavelength λ ₀ is incident on a hologram 301 having a thickness T in which a relief 302 is formed with a period Λ as shown in FIG. 10 at an angle θ _i with respect to the relief 302.

Note that the refractive index distribution n (x) in the direction x orthogonal to the relief 302 in the hologram 301 is expressed by the following equation.
n (x) = n ₀ + n ₁ sin (K · x)
However, K = 2π / Λ.

At this time, the diffraction intensity I ₁ of the first-order diffracted light by the hologram 301 is obtained by the following equation.
I ₁ = (κT · (sinσ / σ)) 2
However,
κ = πn ₁ / λ ₀
σ = (1/4) · √ (Q ² (1-2α) ² +4 (2κT) ² )
Q = 2πλ ₀ T / n ₀ Λ ²
α = (− 1/2) · (sin θ _i / sin θ _B )
It is.

Θ _B is a Bragg angle and satisfies the following equation.
2Λsinθ _B = λ ₀ / n ₀

Here, when λ ₀ ≈0.5 μm, Λ≈λ ₀ , T≈50 Λ, n ₁ ≈1 / 100, cos θ _B ≈1, n ₀ ≈1.5, the diffraction intensity I ₁ is given by It becomes like this.

I ₁ ≈ ((πn ₁ T / λ ₀ ) Sinc (πλ ₀ Tδ / 2n ₀ Λ ² )) ²
sin θ _i = sin (θ _B + δ)
Sinc (x) = sinx / x

Here, δ represents a deviation from the Bragg angle. Further, with δ = 0 as the center, the separation width is a width from δ when the diffraction intensity I ₁ is first 0 on the negative side to δ when the diffraction intensity I ₁ is first 0 on the positive side. Δ is given by the following equation.
Δ = 4n ₀ Λ ² / λ ₀ T

  From the above, it can be seen that in the hologram 301, reproduction light is obtained only when the light 303 is incident on the relief 302 near the Bragg angle. Accordingly, each hologram recorded in the thickness direction on the hologram recording layer 6 of the hologram recording medium 1 generates reproduction light only when the reference light is irradiated at an angle near the same angle as the reference light at the time of recording. It can be seen that it is possible to reproduce information only from the hologram to be reproduced.

  However, as a result of studies by the present inventors, when information is multiplexed and recorded in the thickness direction of the hologram recording medium 1, crosstalk noise occurs between holograms that are multiplexed and recorded in the thickness direction, and the S / N of the reproduced image As a result, it was found that a good reproduced image could not be obtained. This point is considered to be a phenomenon that occurs even in the hologram recording medium 200 having the configuration shown in Patent Document 2, even if there is a difference in the degree of degradation of the reproduced image.

  In the shift multiplexing method, there is a conventional report on a technique for suppressing the influence of crosstalk between tracks (see Patent Document 3). However, regarding the influence of crosstalk that occurs when information is multiplexed and recorded in the thickness direction of the hologram recording medium, there has been no report so far, and countermeasures have not been studied. Further, the hologram recording medium studied by the present inventors has a structure that has not been reported so far, and it is not known that the influence of the crosstalk becomes a problem.

  In view of the above points, an object of the present invention is to provide hologram recording for performing hologram recording so that information can be recorded in a multiplex manner in the thickness direction of the hologram recording medium, and a good reproduced image can be obtained by reducing the influence of crosstalk. Is to provide a device. Another object of the present invention is to provide a hologram reproducing apparatus capable of reproducing information with high quality from a hologram recording medium on which a hologram is recorded as described above.

  In order to achieve the above object, the present invention provides a hologram recording apparatus for recording the information on a hologram recording medium by an interference pattern due to interference between a reference light and a signal light carrying information, wherein the hologram recording medium records information. A hologram recording medium having only one hologram recording layer to be positioned, and having a plurality of positioning layers on one surface side of the hologram recording layer for positioning the irradiation positions of the reference light and the signal light, A first light source that emits light and light serving as the signal light, the oscillation wavelength of which is variable, a condensing lens that condenses the reference light and the signal light on the hologram recording medium, and a condensing lens. From the actuator that moves in the thickness direction of the hologram recording medium, a second light source that emits light having a wavelength different from that of the first light source, and the second light source A light detection unit that receives the reflected light reflected by the positioning layer and a wavelength change control unit that controls a change in the wavelength of the light emitted from the first light source, from the light detection unit Using this information, the actuator moves the condenser lens and moves the irradiation position of the reference light and the signal light, thereby recording information in the thickness direction in a multiplexed manner and moving the irradiation position. The wavelength change control unit changes the wavelength of the light emitted from the first light source, and information recorded in a multiplexed manner in the thickness direction is recorded using light of different wavelengths. It is a feature.

  According to this, the hologram recording medium has a plurality of positioning layers for positioning the irradiation positions of the reference light and the signal light, and using this positioning layer, information can be recorded in a multiplexed manner with high accuracy in the thickness direction of the hologram recording medium. . And since information recorded in multiple directions in the thickness direction of the hologram recording medium is recorded using light of different wavelengths (reference light and signal light), the influence of crosstalk is reduced on the information in the thickness direction. Thus, information can be recorded so that a good reproduced image can be obtained.

  In order to achieve the above object, the present invention provides a hologram recording apparatus for recording the information on the hologram recording medium by an interference pattern due to interference between the reference light and the signal light carrying the information. The information recorded in multiple in the thickness direction is recorded by using light of different wavelengths.

  According to this, since information recorded in a multiplexed manner in the thickness direction of the hologram recording medium is recorded using light of different wavelengths (reference light and signal light), the information in the thickness direction is crosstalked. Information can be recorded so as to reduce the influence and obtain a good reproduced image.

  In the hologram recording apparatus having the above-described configuration, the hologram recording medium includes a hologram recording layer for recording the information, and a positioning layer for positioning an irradiation position of the reference light and the signal light. In addition, by using the positioning layer, information may be recorded multiple times in the thickness direction.

  According to this, when information is recorded in a multiplex manner in the thickness direction of the hologram recording medium, the information can be recorded so that an even better reproduced image can be obtained because the recording in the thickness direction can be performed with high accuracy.

  In the hologram recording apparatus having the above-described configuration, the hologram recording medium includes only one hologram recording layer, and at least one positioning layer is provided on one surface side of the hologram recording layer. It is good to be.

  According to this, the thickness of the hologram recording medium can be reduced and the cost can be further reduced, and information can be recorded in multiple directions in the thickness direction of the hologram recording medium. Information can be recorded so that a good reproduction image can be obtained by reducing.

  According to the present invention, in the hologram recording apparatus having the above-described configuration, the reference light and the signal light are emitted, the first light source whose oscillation wavelength is variable, and the reference light and the signal light are converted into the hologram. A condensing lens that condenses on a recording medium, an actuator that moves the condensing lens in the thickness direction, and a wavelength change control unit that controls a change in the wavelength of light emitted from the first light source, When the condenser lens is moved by the actuator and the irradiation position of the reference light and the signal light is moved, information is recorded in multiple in the thickness direction, and the wavelength is changed when the irradiation position is moved. The change control unit may change the wavelength of light emitted from the first light source.

  According to this, for example, a hologram recording apparatus having a collinear optical system that makes signal light and reference light incident from the same optical axis direction can record information in multiple directions in the thickness direction of the hologram recording medium. Furthermore, it is possible to record the information in the thickness direction so that a good reproduced image can be obtained by reducing the influence of crosstalk.

  According to the present invention, in the hologram recording apparatus configured as described above, the hologram recording medium includes a positioning layer for positioning an irradiation position of the reference light and the signal light, and has a wavelength different from that of the first light source. A second light source that emits light; and a light detection unit that receives reflected light emitted from the second light source and reflected by the positioning layer, and using information from the light detection unit, By moving the irradiation position, information may be recorded in multiple in the thickness direction.

  According to this, it is possible to easily realize a configuration in which information is multiplexed and recorded in the thickness direction of the hologram recording medium using the positioning layer. Also in this case, it is possible to record the information in the thickness direction so as to reduce the influence of crosstalk and obtain a good reproduced image.

  The present invention is also a hologram reproducing apparatus for reproducing a hologram recording medium on which information is recorded by the hologram recording apparatus having the above-described configuration, and when reproducing information recorded in a multiplexed manner in the thickness direction, The information is reproduced by using the reference light.

  According to this, information in the thickness direction recorded so as to obtain an excellent reproduced image by reducing the influence of crosstalk can be reproduced with high quality.

  According to the present invention, it is possible to multiplexly record information in the thickness direction of the hologram recording medium, and in the case of multiplexly recording information in the thickness direction, it is possible to obtain a good reproduced image by reducing the influence of crosstalk. Thus, a hologram recording apparatus capable of recording information can be provided. Further, according to the present invention, it is possible to provide a hologram reproducing apparatus capable of reproducing information with high quality from the hologram recording medium on which information is recorded as described above.

  Embodiments of the present invention will be described below in detail with reference to the drawings. However, the embodiment shown here is an example, and the present invention is not limited to the embodiment shown here.

  FIG. 1 is a block diagram showing a configuration of a hologram recording / reproducing apparatus functioning as a hologram recording apparatus and a hologram reproducing apparatus of the present embodiment. The hologram recording / reproducing apparatus 21 of the present embodiment is provided so that the hologram recording medium 1 shown in FIG. 9 can be recorded and reproduced. Hereinafter, the configuration of the hologram recording / reproducing apparatus 21 will be described.

  Reference numeral 22 denotes a spindle motor, and the hologram recording medium 1 is chucked by a chuck portion (not shown) provided at the tip of the spindle motor 22 and thereby rotated during recording and reproduction. The rotation control of the spindle motor 22 is performed by a spindle motor drive circuit 23.

  Reference numeral 24 denotes an optical pickup, which makes it possible to record information by irradiating the hologram recording medium 1 with signal light and reference light, and irradiating the hologram recording medium 1 with reference light. Thus, the information recorded on the hologram recording medium 1 can be reproduced. FIG. 2 is a schematic diagram showing the configuration of the optical system of the optical pickup 24 provided in the hologram recording / reproducing apparatus 21. In the present embodiment, a so-called collinear optical system is used in which signal light and reference light are incident from the same optical axis direction.

  As shown in FIG. 2, the optical pickup 24 includes a first light source 41, a shutter 42, a collimator lens 43, a spatial light modulator 44, a reflection mirror 45, a first beam splitter 46, a dichroic prism 47, and the like. An objective lens 48, a detection lens 49, a two-dimensional image sensor 50, a second light source 51, a second beam splitter 52, and a photodetector 53.

  The first light source 41 is a wavelength tunable laser provided so that the wavelength of emitted laser light can be changed. In this embodiment, an Nd-YAG laser that emits green laser light having a wavelength of 532 nm is used as the laser element. The amplitude of the wavelength changed by the first light source 41 is at least 1 nm, and the wavelength is changed within a range in which information is recorded on the hologram recording layer 6 of the hologram recording medium 1. The command regarding the change of the wavelength of the first light source 41 is performed by the system control unit 31 (see FIG. 1), which will be described later.

  The first light source 41 is not limited to this, and can be changed as appropriate without departing from the object of the present invention. That is, for example, the laser element may be a semiconductor laser that emits a blue (precisely blue-violet) laser beam having a wavelength of 405 nm.

  The shutter 42 appropriately switches between the passage and shielding of the laser light emitted from the first light source 41. Thereby, the irradiation timing of the signal light and reference light irradiated to the hologram recording medium 1 is controlled. The collimating lens 43 converts the laser light emitted from the first light source 41 into parallel light.

  At the time of recording, the spatial light modulator 44 modulates light intensity on the center side of incident light according to page data (two-dimensional data) generated by a recording information processing unit 25 (see FIG. 1) described later. The signal light having the two-dimensional light intensity modulation pattern is taken out. The outer peripheral side of the incident light is extracted as reference light having a predetermined light intensity pattern without performing light intensity modulation according to page data. FIG. 3 is a diagram schematically showing the configuration of the laser light that has passed through the spatial light modulator 44. As shown in FIG. 3, the laser light that has passed through the spatial light modulator 44 has a configuration in which signal light is present at the center and reference light is present around the signal light.

  During reproduction, the spatial light modulator 44 extinguishes the portion from which the signal light is extracted during recording, and prevents the laser light from being extracted. For the portion from which the reference light is extracted during recording, a laser beam having the same light intensity pattern as that during recording is extracted as the reference light. That is, at the time of reproduction, only the reference light having a donut shape is extracted by the spatial light modulator 44.

  As the spatial light modulator 44 that exhibits the above functions, an electro-optic element, a magneto-optic element, a device controlled using liquid crystal, a so-called DMD (Digital Micromirror Device; registered trademark), or the like is used.

  The reflection mirror 45 reflects the laser beam sent from the spatial light modulator 44 and sends it to the first beam splitter 46. The first beam splitter 46 reflects the laser beam sent from the reflection mirror 45 and guides it to the hologram recording medium 1 side, and transmits the reflected light reflected by the hologram recording medium 1 to provide a two-dimensional image to be described later. Guide to the sensor 50 side. The dichroic prism 47 transmits the green laser light emitted from the first light source 41 and reflects the red laser light emitted from the second light source 51 described later.

  The objective lens 48 has a function of collecting signal light and reference light (during recording) or reference light (during reproduction). At the time of recording, the interference fringes formed by the interference between the signal light collected by the objective lens 48 and the reference light are changed as the refractive index change or the transmittance change in the hologram recording layer 6 of the hologram recording medium 1 (see FIG. 9). This change in refractive index or transmittance acts as a diffraction grating. On the other hand, during reproduction, the reference light collected by the objective lens 48 is diffracted by the diffraction grating written in the hologram recording layer 6 and is emitted from the hologram recording medium 1 as reproduction light.

  In this embodiment, since the reproduction light is reflected by the dichroic mirror layer 5 (see FIG. 9), it is extracted from the hologram recording medium 1 as reflected light.

  The objective lens 48 is mounted on an actuator 54, and the actuator 54 causes the objective lens 48 to move in the focus direction (direction parallel to the thickness direction of the hologram recording medium 1) and the tracking direction (radius of the hologram recording medium 1). In a direction parallel to the direction). This makes it possible to correctly position and irradiate the signal light and the reference light at desired positions on the hologram recording medium 1.

  As the configuration of the actuator 54, for example, similarly to an objective lens actuator used for an optical disc such as a CD or a DVD, a configuration using a magnet and a coil can be used. For the configuration of such an objective lens actuator, Since it is known, its description is omitted here.

  The reproduction light extracted from the hologram recording medium 1 passes through the objective lens 48, the dichroic prism 47, and the first beam splitter 46 in this order, and is detected by the detection lens 49, for example, a two-dimensional image sensor including a CCD image sensor, a CMOS image sensor, or the like. To 50. The two-dimensional image sensor 50 sends an image signal to a reproduction information processing unit 26 (see FIG. 1), which will be described later, whereby the page data recorded on the hologram recording medium 1 is reproduced.

  The second light source 51 is, for example, a semiconductor laser that emits red laser light. The reason why the laser light emitted from the second light source 51 is red is that the laser light emitted from the second light source 51 uses the positioning layers 3a and 3b (see FIG. 9) formed on the hologram recording medium 1. This is because the above-described signal light and reference light positioning (servo) can be performed, and it is desired that the laser light be insensitive to the photopolymer used for the hologram recording layer 6.

  The second beam splitter 52 transmits the laser light emitted from the second light source 51 and is condensed from the second light source 52 through the objective lens 48 onto the positioning layers 3 a and 3 b of the hologram recording medium 1. The reflected red return light is reflected and guided to the photodetector 53. The photodetector 53 receives the red laser beam reflected by the positioning layers 3a and 3b of the hologram recording medium 1 and converts it into an electric signal. With this signal, servo control, which will be described later, control of movement of the objective lens 48 for recording information in the thickness direction of the hologram recording medium 1, and the like are performed.

  Returning to FIG. 1, the light source driving circuit 34 includes a first light source driving circuit that controls the first light source 41 and a second light source driving circuit that controls the second light source 51. The first light source 41 and the second light source The laser power 51 is controlled. Further, as described above, the first light source 41 is a wavelength tunable laser, and the first light source driving circuit controls the laser wavelength emitted from the first light source 41 according to a command from the system control unit 31.

  The recording information processing unit 25 includes an ECC encoder and an SLM (spatial light modulator) driver (not shown). The ECC encoder performs error correction encoding on main data input from the outside using a predetermined encoding method. The SLM driver drives the spatial light modulator (SLM) 44 according to page data formed based on data sent from the ECC encoder.

  Since the spatial light modulator 44 is also used when reproducing the hologram recording medium 1 as described above, the SLM driver appropriately drives the spatial light modulator 44 not only during recording but also during reproduction.

  The reproduction information processing unit 26 includes an image signal processing unit and an ECC decoder (not shown). The image signal processing unit performs binarization processing on the image signal sent from the two-dimensional image sensor 50. The ECC decoder performs error correction decoding processing on the binarized signal data. As a result, the page data recorded on the hologram recording medium 1 is reproduced.

  The servo detection circuit 27 generates a focus error signal, a tracking error signal, and the like based on the signal sent from the photodetector 53. Note that the focus error signal and the tracking error signal can be generated using a technique similar to a known technique for obtaining a focus error signal and a tracking error signal in an optical disc such as a CD or a DVD.

  The generated focus signal and tracking signal are sent to the servo drive circuit 28 and the slide motor drive circuit 29. Further, the servo detection circuit 27 obtains information on the reflectance of the reflected light reflected by the positioning layers 3 a and 3 b from the electrical signal sent from the photodetector 53, and transmits this information to the system control unit 31.

  The servo drive circuit 28 controls the actuator 54 (see FIG. 2) based on the focus error signal and the tracking error signal, and performs servo control of the focus direction and tracking direction of the objective lens 48. The slide motor drive circuit 29 controls a drive device (not shown) that moves the optical pickup 24 in the radial direction of the hologram recording medium 1 based on the tracking error signal and a command from the system control unit 31.

  By the control by the servo drive circuit 28 and the slide motor drive circuit 29, the objective lens 48 is appropriately positioned at a desired position, and the irradiation positions of the signal light and the reference light can be correctly positioned.

  Based on a command from the system control unit 31, the shutter drive circuit 30 controls switching between passage and shielding of the laser light (green) at the position of the shutter 42 (see FIG. 2). The system control unit 31 determines the timing of irradiating the signal light and the reference light (at the time of recording) or the reference light (at the time of reproduction) based on the information regarding the reflectance transmitted from the servo detection circuit 28 described above. .

  The system control unit 31 controls the entire system of the hologram recording / reproducing apparatus 21 in addition to the functions described above. As described above, the wavelength of the laser light emitted from the first light source 41 is not constant, and the wavelength of the laser light emitted from the first light source 41 is changed by a command from the system control unit 31. Thus, the system control unit 31 functions as a wavelength change control unit that controls a change in the wavelength of the laser light emitted from the first light source 41. Details of the case where the system control unit 31 functions as a wavelength change control unit will be described below.

  The system control unit 31 includes a ROM (Read Only Memory) 32 and a RAM (Random Access Memory) 33. The ROM 32 stores various parameters and operation programs necessary for the system control unit 31 to perform various processes. The RAM 33 is used as a work area by the system control unit 31 and is a storage area for various necessary information.

  Next, an example of a method for recording / reproducing on the hologram recording medium 1 using the hologram recording / reproducing apparatus 21 will be described. First, a method for recording on the hologram recording medium 1 will be described with reference to FIG. FIG. 4 is a schematic diagram for explaining a recording method by the hologram recording / reproducing apparatus 21.

  When performing hologram recording on the hologram recording medium 1, the hologram recording medium 1 is rotated by the spindle motor 22 (see FIG. 1), and the red laser light is constantly emitted from the second light source 51 (see FIG. 2). Servo control (focus servo control, tracking servo control) of the objective lens 48 is performed using the second positioning layer 3b. Then, multiplex recording is performed by shifting the recording position by a predetermined amount along the track with respect to the previous recording position (multiplex recording by a so-called shift multiplex method). At this time, the shift amount is, for example, about 10 μm, and is set to be equal to or smaller than the spot size formed by the signal light and the reference light.

  Hologram recording is performed while performing servo control using the track TR of the second positioning layer 3b. When hologram recording is completed along all the tracks TR of the second positioning layer 3b, the first positioning layer 3a is then moved to the next position. A command is issued from the system control unit 31 (see FIG. 1) so as to start the servo control used. In the present embodiment, when the servo control by the second positioning layer 3b is switched to the servo control by the first positioning layer 3a, a command is issued from the system control unit 31 to the servo drive circuit 28 (see FIG. 1). The position of the objective lens 48 is moved by the actuator 54, and servo control using the first positioning layer 3a is started.

When the system control unit 31 issues a command to start servo control by the first positioning layer 3a, almost simultaneously with the laser beam emitted from the first light source 41, the laser beam having the wavelength λ ₀ previously used. A command is sent to the light source drive circuit 34 (more precisely, the first light source drive circuit) so as to change the laser beam to the laser beam having the wavelength λ ₁ . Then, the light source drive circuit 34 to which the command is sent changes the wavelength of the laser light emitted from the first light source 41, and then the servo control using the track TR of the first positioning layer 3a is performed while the hologram is being performed. Recording starts.

  Note that the timing at which the system control unit 31 sends a command to the light source drive circuit 34 is not limited to the timing of the present embodiment. Laser emitted from the first light source 41 during the period from the end of hologram recording while performing servo control by the second positioning layer 3b to the start of hologram recording while performing servo control by the first positioning layer 3a Any timing may be used as long as the wavelength of light is changed.

  As described above, in the hologram recording / reproducing apparatus 21 of the present embodiment, the hologram recording medium is moved by moving the position of the objective lens 48 in the thickness direction of the hologram recording medium 1 in addition to the so-called shift multiplexing method. The information can be multiplexed and recorded in the thickness direction of the hologram recording medium 1 by moving the irradiation position of the reference light and the signal light with respect to 1.

  When the positioning layers 3a and 3b used for servo control are changed in the configuration in which information can be multiplexed and recorded in the thickness direction of the hologram recording medium 1, light that becomes reference light and signal light is emitted accordingly. The wavelength of the first light source 41 is changed. Therefore, the difference between the interference patterns recorded in the thickness direction of the hologram recording medium 1 can be made clearer. Therefore, during reproduction, it is possible to reduce the influence of crosstalk generated between holograms recorded in the thickness direction of the hologram recording medium 1 and obtain a good reproduced image.

  In changing the wavelength of the laser light emitted from the first light source 41, the amount of change may be 1 nm or more. If the wavelength is changed by 1 nm or more, it is possible to reduce the influence of crosstalk generated between holograms recorded in the thickness direction of the hologram recording medium 1 and obtain a good reproduced image. In a wavelength multiplex system in which information is recorded at the same position, it is generally said that multiplex recording is performed by changing the wavelength by 2 nm or more. However, in the case of this embodiment, the irradiation position of the reference light and the signal light is moved in the thickness direction of the hologram recording medium 1 to multiplex record information, and an effect can be obtained by changing the wavelength by 1 nm or more. it can.

When reproducing the information recorded on the hologram recording medium 1, the hologram recording medium 1 is rotated by the spindle motor 22 so that the red laser light is always emitted from the second light source 51, and the second positioning layer 3b Servo control is performed. Information is reproduced while irradiating reference light having the same laser wavelength (λ ₀ ) as when recording on the hologram recording medium 1.

  When the servo control using the track TR of the second positioning layer 3b is performed, the information recorded on the hologram recording medium 1 is reproduced, and the information is reproduced along all the tracks TR of the second positioning layer 3b. Next, a command is issued from the system control unit 31 (see FIG. 1) so as to start servo control using the first positioning layer 3a. In the present embodiment, when the servo control by the second positioning layer 3b is switched to the servo control by the first positioning layer 3a, a command is issued from the system control unit 31 to the servo drive circuit 28 (see FIG. 1). The position of the objective lens 48 is moved by the actuator 54, and servo control using the first positioning layer 3a is started.

When the system control unit 31 issues a command to start the control by the first positioning layer 3a, the laser beam emitted from the first light source 41 is almost the same as the laser beam having the wavelength λ ₀ previously used. A command is sent to the light source drive circuit 34 (more precisely, the first light source drive circuit) so as to change the laser light to the wavelength λ ₁ . Then, the wavelength of the laser light emitted from the first light source 41 is changed by the light source driving circuit 34 to which the command has been sent, and the servo control using the track TR of the first positioning layer 3a is performed, while the hologram recording medium Playback of the information recorded in 1 is started.

  As described above, the hologram recording / reproducing apparatus 21 of the present embodiment can reproduce the hologram information recorded by the so-called shift multiplexing method and move the position of the objective lens 48 in the thickness direction of the hologram recording medium 1. By moving the irradiation position of the reference light with respect to the hologram recording medium 1, it is possible to reproduce information that is multiplexed and recorded in the thickness direction of the hologram recording medium 1.

  When information recorded in the thickness direction of the hologram recording medium 1 is reproduced, the information is reproduced in the thickness direction of the hologram recording medium 1 in order to reproduce the information by changing the wavelength of the reference light in accordance with the recording. Information can be reproduced with high quality.

  In this embodiment, the hologram recording is performed according to the tracks TR formed on the first positioning layer 3a after the hologram recording is performed according to all the tracks TR formed on the second positioning layer 3b. The present invention is not limited to this, and various modifications can be made without departing from the object of the present invention.

  That is, for example, after hologram recording is performed according to the track TR formed on the first positioning layer 3a, hologram recording may be performed according to the track TR formed on the second positioning layer 3b. Further, for example, a configuration may be adopted in which hologram recording is performed while switching between servo control by the first positioning layer 3a and servo control by the second positioning layer 3b for each track.

  Further, in the above, the case of the hologram recording / reproducing apparatus capable of recording / reproducing with respect to the hologram recording medium 1 as shown in FIG. 9 has been described. However, the present invention is not limited to the apparatus for recording and reproducing the hologram recording medium 1 shown in FIG. 9, and various modifications can be made without departing from the object of the present invention.

  That is, for example, the present invention can also be applied to a hologram recording medium as shown in FIG. 5 and an apparatus that performs recording and reproduction with respect to the hologram recording medium shown in FIG. 5 and 6 are diagrams for explaining another embodiment of the present invention, and the same reference numerals are given to the same components as those in the above-described embodiment.

  First, the embodiment shown in FIG. 5 will be described. The hologram recording medium shown in FIG. 5 is provided with only one positioning layer 3 unlike the hologram recording medium 1 (see FIG. 9) shown above. Even with such a hologram recording medium, information can be recorded in a multiplexed manner in the thickness direction of the hologram recording medium as follows. Since information can be recorded in the thickness direction in a multiplex manner, the information recorded in the thickness direction in a multiplexed manner is used for the information recorded in the thickness direction by using different wavelengths of light (reference light and signal light). It becomes possible to record. That is, as in the case of the above-described embodiment, high-quality recording / reproduction is possible in the thickness direction of the hologram recording medium.

  A method of recording information in multiple directions in the thickness direction using the hologram recording medium 1 shown in FIG. 5 will be described. First, hologram recording is performed by controlling the objective lens 48 so that the focus of the red laser light emitted from the second light source 51 is aligned with the positioning layer 3. Next, a constant bias voltage is applied to the voltage value given to the actuator 54 in order to adjust the focus position of the objective lens 48 first. In this way, the position of the objective lens 48 moves by a predetermined amount, and the irradiation positions of the reference light and the signal light are shifted by a predetermined amount. For this reason, information can be recorded in multiple directions in the thickness direction of the hologram recording medium.

  Next, the embodiment shown in FIG. 6 will be described. The hologram recording medium shown in FIG. 6 differs from the hologram recording medium 1 (see FIG. 9) described above in that a plurality of hologram recording layers 6a and 6b are provided, and the hologram recording layers 6a and 6b and the positioning layers 3a and 3b are provided. Are arranged alternately. In such a hologram recording medium, hologram recording is performed on the hologram recording layer 6a while performing servo control of the objective lens 48 using the positioning layer 3a, and holograms are performed while performing servo control of the objective lens 48 using the positioning layer 3b. It is possible to perform hologram recording on the recording layer 6b. That is, information can be recorded in a multiplexed manner in the thickness direction of the hologram recording medium. For this reason, it becomes possible to record holograms using information having different wavelengths (reference light and signal light) with respect to information recorded in a multiplexed manner in the thickness direction, and in the same way as in the above-described embodiment, holograms can be recorded. High-quality recording / reproduction is also possible in the thickness direction of the recording medium.

(Other)
In the embodiment described above, the case where the number of positioning layers is one or two has been described. However, the present invention is not limited to this, and the number of positioning layers may be three or more. I do not care.

  Further, in the above-described embodiment, the reflection type configuration in which the light irradiated to the hologram recording medium is reflected to record and reproduce information is shown, but the present invention is not limited to this. The present invention can also be applied to a transmissive configuration.

  Furthermore, in the embodiment described above, the collinear method is used for the optical system of the hologram recording / reproducing apparatus (the hologram recording apparatus and the hologram reproducing apparatus). However, the present invention is not limited to the case of the collinear method, but can also be applied to a configuration employing a two-beam method in which signal light and reference light are incident on the hologram recording medium from different directions.

According to the hologram recording apparatus and hologram reproducing apparatus of the present invention, high-density and high-quality recording / reproduction can be realized. Therefore, the present invention is useful in the field of hologram devices for recording information on a hologram recording medium and reproducing information from a hologram recording medium.

These are block diagrams which show the structure of the hologram recording / reproducing apparatus of this embodiment. These are the schematic diagrams which show the structure of the optical system of the optical pick-up with which the hologram recording / reproducing apparatus of this embodiment is provided. These are the figures which showed typically the structure of the laser beam which passed through the spatial light modulator with which the optical pick-up of this embodiment is provided. These are the schematic diagrams for demonstrating the recording method by the hologram recording / reproducing apparatus of this embodiment. These are explanatory drawings for demonstrating other embodiment of this invention. These are explanatory drawings for demonstrating other embodiment of this invention. These are explanatory drawings for demonstrating the structure of the conventional hologram recording medium. These are explanatory drawings for demonstrating the structure of the conventional hologram recording medium. These are schematic sectional drawing at the time of cutting along the radial direction the hologram recording medium which the present inventors are examining. These are explanatory drawing for demonstrating the relationship between the relief in a hologram, and the incident angle with respect to it.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hologram recording medium 3a 1st positioning layer 3b 2nd positioning layer 6 Hologram recording layer 21 Hologram recording / reproducing apparatus (hologram recording apparatus and hologram reproducing apparatus)
31 System controller (wavelength change controller)
41 First light source 48 Objective lens (condenser lens)
51 Second light source 53 Photo detector (light detection unit)
54 Actuator

Claims (7)

In the hologram recording apparatus for recording the information on the hologram recording medium by an interference pattern due to interference between the reference light and the signal light carrying the information,
The hologram recording medium has only one hologram recording layer for recording information, and has a plurality of positioning layers for positioning the irradiation positions of the reference light and the signal light on one surface side of the hologram recording layer. A hologram recording medium,
A first light source that emits light serving as the reference light and the signal light, the oscillation wavelength of which is variable;
A condensing lens for condensing the reference light and the signal light on the hologram recording medium;
An actuator that moves the condenser lens in the thickness direction of the hologram recording medium;
A second light source that emits light having a wavelength different from that of the first light source;
A light detector that receives reflected light emitted from the second light source and reflected by the positioning layer;
A wavelength change control unit that controls a change in wavelength of light emitted from the first light source;
With
Using the information from the light detection unit, moving the condenser lens by the actuator, moving the irradiation position of the reference light and the signal light, multiplexly recording information in the thickness direction,
When the irradiation position is moved, the wavelength change control unit changes the wavelength of the light emitted from the first light source, and the information recorded in multiple in the thickness direction depends on the difference in the position in the thickness direction. the hologram recording apparatus characterized by being recorded with light of different wavelengths. In the hologram recording apparatus for recording the information on the hologram recording layer of the hologram recording medium by an interference pattern due to interference between the reference light and the signal light carrying the information,
It is provided so that information can be recorded in multiple directions in the thickness direction of one hologram recording layer ,
The hologram recording apparatus, wherein the information recorded in the thickness direction is recorded by using different wavelengths of light depending on the position in the thickness direction . The holographic recording medium may further include a positioning layer for positioning the irradiation position before Symbol reference light and the signal light,
3. The hologram recording apparatus according to claim 2, wherein information is multiplexed and recorded in the thickness direction by using the positioning layer.   4. The hologram recording according to claim 3, wherein the hologram recording medium has only one hologram recording layer, and at least one positioning layer is provided on one surface side of the hologram recording layer. apparatus. A first light source that emits light serving as the reference light and the signal light, the oscillation wavelength of which is variable;
A condensing lens for condensing the reference light and the signal light on the hologram recording medium;
An actuator for moving the condenser lens in the thickness direction;
A wavelength change control unit that controls a change in wavelength of light emitted from the first light source;
With
By moving the condenser lens by the actuator and moving the irradiation position of the reference light and the signal light, information is recorded in a multiplexed manner in the thickness direction,
The hologram recording apparatus according to claim 2, wherein the wavelength change control unit changes a wavelength of light emitted from the first light source when the irradiation position is moved. The hologram recording medium has a positioning layer for positioning the irradiation position of the reference light and the signal light,
A second light source that emits light having a wavelength different from that of the first light source;
A light detection unit that receives reflected light emitted from the second light source and reflected by the positioning layer;
6. The hologram recording apparatus according to claim 5, wherein information is multiplexedly recorded in the thickness direction by moving the irradiation position using information from the light detection unit. A hologram reproducing apparatus for reproducing a hologram recording medium on which information is recorded by the hologram recording apparatus according to claim 1,
When reproducing information recorded in multiple directions in the thickness direction, information is reproduced using reference lights having different wavelengths depending on the position in the thickness direction .