JP2005235312A - Recording and reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recording/reproducing apparatus which can realize recording/reproducing of a signal optimum for a hologram memory being a large capacity recording medium with a simple constitution. <P>SOLUTION: In the recording/reproducing apparatus, by which an object light and a reference light are emitted from the same facial direction of an optical recording medium and the information of the object light is subjected to shift multiplex recording on the optical recording medium as interference fringes and also the reference light is emitted to the recorded interference fringes to reproduce the information by a diffracted light. The recording/reproducing operation of the signal optimum for the hologram memory can be realized by an optical unit mechanically fixing the positional relation between an objective lens for converging the object light to the recording medium and a wave face conversion means for converting the wave face of the reference light to a non-planar wave and by a movement means for moving the optical unit. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a recording / reproducing apparatus that records information on a hologram memory medium and reproduces the recorded information.

  In recent years, rewritable optical discs such as phase change type and magneto-optical type are widely used as information recording media. In order to further increase the recording density of these optical discs, techniques such as reducing the beam spot diameter and shortening the distance between adjacent tracks or adjacent bits are required.

  As described above, the density of optical discs is increasing year by year. However, since the above optical disc records data in a plane, the recording density is limited to the diffraction limit of light, and physical recording of high density recording is performed. Approaching the limit. Therefore, in order to further increase the capacity, three-dimensional (volume type) multiplex recording including the depth direction is required.

  Therefore, a hologram memory having both a large capacity derived from a three-dimensional multiple recording area and a high speed derived from a two-dimensional batch recording / reproducing system has attracted attention as a next-generation computer file memory. Hologram memory, for example, irradiates a recording medium formed by sandwiching a recording layer made of a photopolymer or the like between two glass plates with object light corresponding to recording information and reference light, and is generated by both lights The recorded interference fringes are recorded as a change in the refractive index of the recording material, and when reproducing information, only the reference light is irradiated to the recorded interference fringes and optical information corresponding to the recorded information is extracted. It is.

Since this hologram memory can multiplex-record a plurality of two-dimensional data in the same area, it has been attracting attention as a terabyte memory having a huge recording capacity while having the same shape as a CD or the like. As for a recording / reproducing apparatus for such a holographic memory, for example, as shown in Patent Document 1, a method of multiplex recording by changing the angle of reference light on a recording medium has been proposed.
JP 2000-338846 A

  However, according to the technique described in Patent Document 1, since it is necessary to respectively control the rotation of a pair of wedge-shaped prisms for large-capacity recording, two rotation driving units are required, and the apparatus becomes complicated. There is a problem of increasing the size.

  Therefore, the present invention has been made in view of the above-described problems, and provides a recording / reproducing apparatus capable of realizing optimum recording / reproduction of a signal in a hologram memory as a large-capacity recording medium with a simple configuration. Objective.

  According to the first aspect of the present invention, object light and reference light are irradiated from the same plane direction of the optical recording medium, and information on the object light is shift-multiplexed and recorded as interference fringes on the optical recording medium. A recording / reproducing apparatus that reproduces information by diffracted light by irradiating the interference fringes with the reference light, and an objective lens for condensing the object light on the recording medium and a wavefront of the reference light in a non-planar wave The recording / reproducing apparatus is characterized by comprising an optical unit that mechanically fixes the positional relationship with the wavefront converting means for converting the optical unit and a moving means for moving the optical unit.

  According to the present invention, the moving means moves the objective lens for condensing the object light and the wavefront converting means for converting the wavefront of the reference light into a non-planar wave, so that interference fringes are formed at an arbitrary position on the recording medium. Can be generated.

The invention according to claim 2 proposes a recording / reproducing apparatus according to claim 1, wherein the wavefront converting means spatially and randomly converts the phase of the reference light. ing.
According to the present invention, since the phase of the reference beam is spatially randomly converted, there is no correlation between the reference beams when creating each hologram during shift multiplex recording, and reproduction without crosstalk is possible during reproduction. It becomes.

According to a third aspect of the present invention, there is provided a recording / reproducing apparatus according to the first aspect, wherein the wavefront conversion means spatially and randomly converts the amplitude of the reference light. doing.
According to the present invention, since the amplitude of the reference beam is spatially randomly converted, there is no correlation between the reference beams when creating each hologram during shift multiplex recording, and reproduction without crosstalk is possible during reproduction. It becomes.

According to a fourth aspect of the present invention, there is provided a recording / reproducing apparatus according to the first aspect, wherein the wavefront converting means spatially and randomly converts the traveling direction of the reference light. doing.
According to the present invention, since the traveling direction of the reference beam is spatially randomly converted, there is no correlation between the reference beams when creating each hologram during shift multiplex recording, and reproduction without crosstalk is performed during reproduction. It becomes possible.

The invention according to claim 5 proposes a recording / reproducing apparatus according to claim 1, wherein the wavefront converting means is a wavefront converting means for converting the reference light into a spherical wave. doing.
According to the present invention, since the reference light is converted into a spherical wave, there is no correlation between the reference light when creating each hologram during shift multiplex recording, and reproduction without crosstalk is possible during reproduction.

According to a sixth aspect of the present invention, in the recording / reproducing apparatus according to the first aspect, the wavefront converting means performs optical processing for converting the wavefront of the reference light into a non-planar wave on the front side and the back side of the substrate. Has been proposed.
According to the present invention, since the optical processing for converting the wavefront of the reference light into a non-planar wave is performed on the front side and the back side of the substrate, the spatial random degree of the reference light can be increased without increasing the number of components. .

The invention according to claim 7 relates to the recording / reproducing apparatus according to claim 1, and includes at least two wavefronts including the same wavefront conversion means among the wavefront conversion means described in claims 2 to 5. There has been proposed a recording / reproducing apparatus in which conversion means is arranged in the optical path of the reference light.
According to this invention, since at least two of the wavefront conversion means described in claims 2 to 5 including the same wavefront conversion means are arranged in the optical path of the reference light, the space of the reference light Randomness can be increased.

According to an eighth aspect of the present invention, there is provided a recording / reproducing apparatus according to any one of the first to seventh aspects, wherein the wavefront converting means is configured by a hologram. ing.
According to the present invention, since the wavefront conversion means is constituted by a hologram, the wavefront conversion means can be thinned.

According to the present invention, it is possible to provide a recording / reproducing apparatus suitable for multiplex recording and reproduction of multiplex recorded information with a simple configuration.
In addition, the objective lens that condenses the object light and the wavefront conversion means that converts the wavefront of the reference light into a non-planar wave can be moved together, so if only the object light is controlled, it is optimal for the reference light irradiation position. If effective control can be performed, there is an effect.
In addition, since the wavefront conversion means has a function of converting the phase, amplitude and traveling direction of the reference light at random, and a function of converting the reference light into a spherical wave, there is an effect that a good reproduction signal can be obtained. .

  Hereinafter, a recording / reproducing apparatus according to an embodiment of the present invention will be described in detail with reference to FIGS.

  As shown in FIG. 1, a recording / reproducing apparatus according to an embodiment of the present invention includes a hologram recording medium 1, a spindle motor 2, an optical pickup 3, a feed motor 4, a signal processing IC 5, and a CPU (CPU: Central Processing Unit) 6 and a driver IC 7.

  The hologram recording medium 1 is a recording medium formed by sandwiching a recording layer made of a photopolymer or the like as a recording material between a substrate made of a glass plate or the like and a reflection layer, and includes object light and reference light corresponding to recorded information. Is recorded on the recording area, and the interference fringes generated by both lights are recorded as a change in the refractive index of the recording material. When reproducing information, the recorded interference fringes are irradiated only with reference light, and optical information corresponding to the recorded information is extracted.

The spindle motor 2 is a drive device for rotating the hologram recording medium, for example, at a constant linear velocity when the hologram recording medium has a disk shape, and the rotation speed and the like are controlled by the output of the driver IC 7.
The optical pickup 3 includes a laser light source using a semiconductor laser, an objective lens driven by a collimator lens, a focus actuator or a tracking actuator, optical components such as a polarization beam splitter, and a two-dimensional light detection array as a light receiving element. ing.

The feed motor 4 is a mechanism for sending the optical pickup from the inner periphery to the outer periphery of the hologram recording medium 1, for example, and controls the position of the optical pickup 3 by a drive signal of the tracking actuator.
The signal processing IC 5 generates a reproduction signal based on the amount of light returned from the hologram recording medium 1 incident on the two-dimensional photodetection array, and detects a focus error signal (FE) that detects a defocus of the irradiation laser in the optical pickup 3. Is generated by the astigmatism method based on the amount of return light obtained by the light receiving element in the optical pickup 3, and a tracking error signal (TE) for detecting a track shift of the irradiation laser in the optical pickup 3 is further pushed, for example. Generated by the pull method or the like. Further, based on the generated FE and TE, a focus drive signal (FODRV) and a tracking drive signal (TRDRV) are generated.

The CPU 6 controls the entire apparatus based on a control program stored in a ROM (ROM: Read Only Memory) or the like. In the present invention, various servo operations are controlled in the operation of recording and reproducing information on the hologram recording medium 1.
The driver IC 7 receives the focus drive signal (FODRV), the tracking drive signal (TRDRV), or the spindle control signal generated in the signal processing IC 5 and amplifies them to a desired size. Alternatively, it is supplied to a spindle motor or the like. The feed motor drive signal generated from the tracking drive signal (TRDRV) is amplified to a desired magnitude, and then supplied to the feed motor.

Various methods have been proposed as a method for recording information on the hologram recording medium. Of these, a shift multiplexing method will be described as a typical recording method with reference to FIG.
The shift multiplexing method is a method of recording information on the recording layer of the hologram recording medium 1 while shifting the information recording area little by little. In order to perform the recording by the shift multiplexing method, it is necessary to make the reference light a spherical wave, or make the phase, amplitude, traveling direction, etc. spatially random.

  Specifically, the shift multiplexing method will be described with reference to FIG. 4. First, the object light 33-1 (information 1) is irradiated to a certain region, and similarly, the position irradiated with the object light 33-1 is referred to. The light 34-1 is irradiated to interfere with these, and the interference fringes 35-1 are recorded in volume. Next, the recording position is shifted by shifting the irradiation spot by a small amount. Similarly, the object beam 33-2 (information 2) and the reference beam 34-2 are irradiated to the same position to cause interference. Volume stripes 35-2 are recorded. Thereafter, information is multiplexed and recorded while sequentially shifting the recording position little by little.

  In the reproduction operation of information recorded by the shift multiplexing method, the position of the recorded interference fringe 35-1 is irradiated with the reference light 34-1 and only from the interference fringe 35-1 recorded at that position by the reference light. Diffracted light can be obtained. Therefore, the two-dimensional data of information 1 can be reproduced by using the reference beam 34-1.

  In this example, only the shift multiplexing in the X direction has been described, but similarly, the same shift multiplexing recording can be performed in the Y direction. Therefore, enormous multiplex recording is possible by performing shift multiplex recording in the X direction and Y direction together.

Next, using FIG. 2 and FIG. 3, the operation and configuration of the optical system of the present invention corresponding to the recording and reproduction of information on the hologram recording medium, particularly the shift multiplexing method will be described.
The light emitted from the semiconductor laser 11 in the optical pickup 3 (for example, S-polarized light) is converted into parallel light by the lens 12, and the polarization plane is rotated by a half wavelength plate (λ / 2 plate) 13. , P-polarized light and S-polarized light components. Among these, the P-polarized light is transmitted through the polarization beam splitter (PBS) 14, the polarization plane is further rotated in the λ / 2 plate 15, and is again separated into P-polarized light and S-polarized light components.

  The separated S-polarized light is reflected by a polarization beam splitter (PBS) 16 and converted into two-dimensional data by a spatial light modulator (SLM) 17. The converted two-dimensional data is transmitted through the λ / 2 plate 18 in the S-polarized state and is condensed near the recording layer 31 of the hologram recording medium 1 by the objective lens (OL) 19. This light becomes object light 50.

  On the other hand, the light that has been transmitted through the λ / 2 plate 13 and converted into S-polarized light is reflected by the PBS 14, and has a light-condensing function and / or a wavefront conversion that spatially randomizes the phase and / or amplitude of the light beam. The element 42 converts the wavefront into a non-plane wave. The light converted into the non-plane wave is deflected by the wedge prism 41 and is irradiated from the same side as the object light in the vicinity of the recording layer 31 on the hologram recording medium 1 irradiated with the object light. This becomes the reference beam 51.

  In the recording layer 31 of the hologram recording medium 1 irradiated with the object light 50 and the reference light 51, the object light 50 and the reference light 51 interfere with each other, and interference fringes are volume-recorded. The light amounts of the object light 50 and the reference light 51 can be arbitrarily set by rotating the λ / 2 plates 13 and 15 around the optical axis. Therefore, the light amounts of the object light 50 and the reference light 51 may be arbitrarily selected so that the interference fringe pattern becomes the clearest.

Here, the wavefront conversion element 42 is an optical element having an optical function of randomizing the reference light. Hereinafter, the details will be described with reference to FIG.
As described above, in order to realize shift multiplex recording, it is necessary to make the wavefront of the reference light completely random in the light beam or to make it a spherical wave. This is because information before and after the shift is reproduced at the same time if the recorded data in the overlapping area before and after the shift has a correlation with the wavefront of the reference light before and after the shift.

  The wavefront conversion element 42 in this embodiment has a function of spatially and randomly converting the wavefront of the reference light in phase, amplitude, and traveling direction, and one example thereof is irregularly arranged as shown in FIG. The black, gray, and white regions have regions with optically different thicknesses. Therefore, the light transmitted or reflected through these regions is converted into spatially random light by the optical action of these thicknesses.

  Moreover, in each area | region of black, gray, and white, each area | region can also be comprised so that the transmittance | permeability or reflectance of light may differ. Also in this case, the light transmitted or reflected through these regions is converted into light having a random amplitude or intensity spatially by the optical action due to the difference in transmittance or reflectance.

  Further, in each of the black, gray, and white regions, each region may have an angle that makes an incident angle or a reflection angle different with respect to transmitted light or reflected light. Also in this case, light transmitted or reflected through these regions is converted into light whose traveling direction is spatially random due to the optical action due to the difference in incident angle or reflection angle.

  In this embodiment, each example has been described in three stages of black, gray, and white. However, the smaller the level and the smaller the area of each region, the more random the light phase, amplitude, etc. Therefore, crosstalk during reproduction due to multiple recording is reduced.

  Furthermore, as shown in FIG. 6, for example, black, gray, and white regions 42-1 having optically different thicknesses are provided irregularly on one surface of the glass substrate 42, and irregularly disposed on the other surface. By providing the black, gray, and white regions 42-2 having different transmittances disposed in the plane, a single optical element can convert a plane wave into light with random phases and amplitudes.

Further, by using a hologram, the light flux of the reference light can be randomized. FIG. 3 shows the configuration of the optical system when a hologram 43 is used as a wavefront conversion element. The case where the hologram 43 is used as a wavefront conversion element will be described with reference to FIGS. 7 is, for example, light transmitted or reflected by the wavefront conversion element 42 illustrated in FIG. 5 or light transmitted through a lens.
Using this light as object light, a hologram 63 is produced in which interference fringes are recorded by interference with the reference light 62. Then, as shown in FIG. 8, when the hologram 63 is irradiated with the reference light 65, the light beam is spatially irregularly transmitted, that is, transmitted or reflected through an optical element that changes the phase or amplitude (intensity) or the traveling direction of the light beam. Light or light 64 transmitted through the lens is generated in the direction of the arrow in the figure.

  The random light 64 is a light beam that is equivalent to the random light 61 and whose traveling direction is opposite. Further, in order to combine the function of the hologram as a wavefront conversion element, the luminous flux of the object beam 61 is spatially irregular, that is, transmitted or reflected through an optical element and a lens that change both phase and amplitude (intensity). The hologram 43 may be produced by interfering with the reference light 62 and recording interference fringes as the light.

  Thereby, as shown in FIG. 8, when the hologram 63 is irradiated with the reference light 65, the combined random light 64 is generated in the direction of the arrow in the figure. The random light 64 is a light beam that is equivalent to the random light 61 and whose traveling direction is opposite. In addition, during mass production of holograms, mass production is possible at low cost with good reproducibility by transferring the hologram pattern to a mold and further transferring it to glass, resin or the like.

  Next, when reproducing the recording data, the λ / 2 plate 13 is rotated around the optical axis, and the light emitted from the semiconductor laser 11 is reflected by the PBS 14 as only the S-polarized light. That is, only the reference light that is S-polarized light is applied to the interference fringes formed in the recording area of the recording layer 31 of the hologram recording medium 1.

  The light diffracted by the recording layer 31 is reflected by the reflective film layer 32 of the hologram recording medium 1, enters the OL 19, is converted into a parallel light beam, and is then converted into P-polarized light by the λ / 2 plate 18. The converted P-polarized light passes through the SLM 17 and the PBS 16 and is condensed on the two-dimensional light detection array 21 by the condenser lens 20 to reproduce the two-dimensional data.

  However, at the time of signal reproduction, the SLM 17 needs to be in a totally transmissive state or be out of the optical path. Further, the λ / 2 plate 18 needs to rotate the optical axis at 45 degrees with respect to the S-polarized light. In the present embodiment, the configuration of the hologram recording medium 1 includes the substrate 30, the recording film layer 31, and the reflection layer 32. However, the configuration of the hologram recording medium is not limited to this.

  Further, the optical system in the present embodiment has a position of the objective lens 19 for condensing the object light 50 on the recording layer 31 of the hologram recording medium 1 and the wavefront conversion element 42 for converting the wavefront of the reference light 51 into a non-plane wave. Since the optical unit 22 having a structure in which the relationship is mechanically fixed is provided, the condensing position of the reference light 51 can be accurately controlled by controlling the condensing position of the object light 50.

  In the present embodiment, after recording the interference fringes 35-1, the optical unit 22 can be moved by a predetermined amount, and the recording / reproducing operation can be continued sequentially. Since the optical unit 22 is built in the optical pickup 3, the optical unit 22 can be moved by a predetermined amount by controlling the feed motor 4. Therefore, highly accurate positioning control can be realized with respect to the object light and the reference light without using a special control mechanism.

  Therefore, according to this embodiment, the objective lens for condensing the object light and the wavefront conversion means for converting the wavefront of the reference light into a non-plane wave can be moved together. Optimal control can also be performed on the irradiation position. In addition, since the wavefront conversion means has a function to convert the phase, amplitude and traveling direction of the reference light at random, and a function to convert the reference light to a spherical wave, there is little influence of crosstalk during playback and good playback A signal can be obtained.

  As described above, the embodiments of the present invention have been described in detail with reference to the drawings, but the specific configuration is not limited to these embodiments, and includes design changes and the like within a scope not departing from the gist of the present invention. It is. For example, in the present embodiment, it has been described that the optical pickup is moved to record or reproduce information on the hologram recording medium. However, the present invention is not limited to this. For example, when the recording medium has a card shape, the optical pickup May be fixed and the movement of the hologram recording medium may be controlled.

It is a block diagram of the recording / reproducing apparatus in a present Example. It is a block diagram of the optical system in a present Example. It is a figure which shows the modification of the optical system in a present Example. It is a conceptual diagram of a shift multiplexing system. It is the figure which showed the wavefront conversion element in a present Example. It is the figure which showed the other form of the wavefront conversion element in a present Example. It is a figure which shows the effect | action of the light at the time of using a hologram as a wavefront conversion element. It is a figure which shows the effect | action of the light at the time of using a hologram as a wavefront conversion element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Hologram recording medium, 2 ... Spindle motor, 3 ... Optical pick-up, 4 ... Feed motor, 5 ... Signal processing IC, 6 ... CPU, 7 ... Driver IC, DESCRIPTION OF SYMBOLS 11 ... Semiconductor laser, 12 ... Lens, 13, 15, 18 ... 1/2 wavelength plate, 14, 16 ... Polarizing beam splitter, 17 ... Spatial light modulator, 19 ... Objective lens, 20 ... Condensing lens, 21 ... Two-dimensional detection array, 22 ... Optical unit, 30 ... Substrate, 31 ... Recording layer, 32 ... Reflective layer, 41 ...・ Wedge prism, 42... Wavefront conversion element, 43... Wavefront conversion hologram, 50... Object light, 51.

Claims (8)

The object light and the reference light are irradiated from the same plane direction of the optical recording medium, and information on the object light is shift-multiplexed and recorded as interference fringes on the optical recording medium, and the reference light is applied to the recorded interference fringes. A recording / reproducing apparatus for reproducing information by irradiating and diffracting light,
An optical unit that mechanically fixes the positional relationship between an objective lens that focuses the object light on the recording medium and a wavefront conversion unit that converts the wavefront of the reference light into a non-planar wave;
A recording / reproducing apparatus comprising a moving means for moving the optical unit.   The recording / reproducing apparatus according to claim 1, wherein the wavefront converting unit spatially and randomly converts the phase of the reference light.   The recording / reproducing apparatus according to claim 1, wherein the wavefront converting unit spatially and randomly converts the amplitude of the reference light.   The recording / reproducing apparatus according to claim 1, wherein the wavefront conversion unit spatially and randomly converts the traveling direction of the reference light.   2. The recording / reproducing apparatus according to claim 1, wherein the wavefront converting means is wavefront converting means for converting the reference light into a spherical wave.   2. The recording / reproducing apparatus according to claim 1, wherein the wavefront converting means performs optical processing for converting the wavefront of the reference light into a non-planar wave on the front side and the back side of the substrate.   The at least two wavefront conversion means including the same wavefront conversion means among the wavefront conversion means described in claims 2 to 5 are arranged in the optical path of the reference light. Recording / reproducing apparatus described in 1. 8. The recording / reproducing apparatus according to claim 1, wherein the wavefront converting means is constituted by a hologram.

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