JP4609409B2 - Hologram recording / reproducing apparatus and hologram recording / reproducing optical apparatus - Google Patents

Description

  The present invention relates to a hologram recording / reproducing apparatus and a hologram recording / reproducing optical apparatus.

  In recent years, hologram recording / reproducing apparatuses have attracted attention as data storage devices. In the hologram recording apparatus, the recording operation is performed as follows. The signal light modulated according to the recording data and the predetermined reference light are generated by the laser light from the same light source, and these are irradiated to the hologram recording medium, so that the signal light and the reference light interfere in the hologram recording medium. To form a hologram (diffraction grating). In this way, the recording data is recorded as a hologram on the hologram recording medium. The hologram recorded here contains a very large amount of information. This hologram is called one page, and the recorded data is specified and managed for each page.

  In the hologram recording apparatus, the reproduction operation from the recorded hologram recording medium is performed as follows. Diffracted light (reproduced light) is generated by irradiating a hologram formed according to the above-described recording data with predetermined reference light. Since this diffracted light includes recording data for one page, the diffracted light can be received by a two-dimensionally arranged light receiving element and subjected to signal processing to reproduce the recorded data.

  The generation of the signal light and the reference light and the reception of the diffracted light described above are performed by a hologram recording / reproducing optical device (optical unit) configured by combining optical elements. One method of optical path design in the optical unit is a so-called coaxial method (for example, Non-Patent Document 1) in which signal light and reference light are arranged coaxially and the optical paths through which these light beams pass are common. See). As another method of designing an optical path in the optical unit, a two-beam method is known in which each light beam of signal light and reference light passes through another optical path.

  Also, as a technique for forming a large number of holograms on a hologram recording medium in order to improve the recording density, so-called multiplex recording in which a plurality of holograms are formed in the same region of the hologram recording medium is known (for example, (See Patent Document 1 and Non-Patent Document 1). At the time of such recording and reproduction, a technology for moving reference light and signal light or reference light (hereinafter collectively referred to as reference light / signal light) to a specific recording area of the hologram recording medium is eagerly desired. Has been.

  As a technique for controlling the relative position between the hologram recording medium and the reference light / signal light, a predetermined recording area is detected based on address information given to the hologram recording medium while moving the hologram recording medium little by little. After that, a technique is known in which recording / reproduction is performed by irradiating the reference light / signal light for a short time enough to be regarded as a stop.

As another technique, after detecting a predetermined recording area, a technique of performing recording / reproduction while moving the reference light / signal light in synchronization with the movement of the predetermined recording area of the hologram recording medium and following the movement. Known (see Patent Document 2, Patent Document 3, and Non-Patent Document 2).
Japanese Patent Laid-Open No. 11-242424 Japanese Patent No. 3639212 Japanese Patent No. 36552337 Nikkei Electronics January 17, 2005 issue P106-114 K. Hirooka et al “Development of a Coaxial type Holographic Disc Data Storage Evaluation System, Capable of 500-fps-Consecutive Writing and Reading” Optical Data Storage MA4, 2006, P12-P14, 23 April 2006

  However, in the technique of irradiating the reference light / signal light only for a short time, the optical output of the reference light / signal light must be increased. In addition, in the technique of causing the reference light / signal light to follow the movement of the hologram recording medium, in addition to requiring a complicated control mechanism, it is necessary to enhance the control technique. Therefore, the price of the hologram recording and / or hologram reproducing apparatus (hologram recording / reproducing apparatus) adopting such a technique has become expensive.

  The present invention solves such problems and uses a relatively low-cost laser diode having a general light output that is currently available on the market, and has a simple control mechanism, but is desired at high speed. An object of the present invention is to provide a hologram recording / reproducing technique that moves a light spot to a position, reads address information at a high speed, and arranges the light spot at a desired position to enable recording / reproduction.

  The hologram recording / reproducing apparatus of the present invention irradiates a hologram recording medium with signal light and reference light to record recording data as a hologram, and irradiates the hologram recorded on the hologram recording medium with reference light to obtain diffracted light. In the hologram recording / reproducing apparatus comprising servo means for reproducing recording data from the diffracted light, the servo means includes a focus servo unit that focuses a light spot on the hologram recording medium, and recording on the hologram recording medium. A tracking servo unit that arranges a light spot in a track direction that is perpendicular to the track formed on the surface, and a light spot in a tangential direction that is a direction along the track formed on the recording surface of the hologram recording medium. A tangential servo section to be arranged, and the tangential servo Bo portion, said by stationary hologram recording medium, by scanning the light spot in the tangential direction, reads the prerecorded address information in the holographic recording medium.

The hologram recording / reproducing optical apparatus of the present invention records signal data and reference light on a hologram recording medium to record recording data as a hologram, and irradiates the hologram recorded on the hologram recording medium with reference light to generate diffracted light. In the hologram recording / reproducing optical apparatus provided with servo means for reproducing the recording data from the diffracted light, the servo means includes a focus servo section that focuses a light spot on the hologram recording medium, and the hologram recording medium A tracking servo unit that arranges a light spot in a track direction that is orthogonal to a track formed on the recording surface of the recording medium, and a light beam in a tangential direction that is a direction along the track formed on the recording surface of the hologram recording medium. A tangential servo section for arranging spots, and the tangential Yarusabo portion, said by stationary hologram recording medium, by scanning the light spot in the tangential direction, reads the prerecorded address information in the holographic recording medium.

  In this hologram recording / reproducing apparatus or hologram recording optical apparatus, the hologram recording medium is stopped and the light spot is scanned in the tangential direction. Then, the address information recorded in advance on the hologram recording medium is read. In this way, the light spot can be moved to a desired position at high speed without moving the hologram recording medium. In this way, the recording / reproducing speed can be increased.

  According to the present invention, it is possible to provide a hologram recording / reproducing apparatus that can read and write address information at a high speed and move a light spot to a desired position and perform high-speed recording and reproduction while having a simple control mechanism.

  The hologram recording / reproducing apparatus or the hologram recording / reproducing optical apparatus (optical unit used for hologram recording / reproducing) of the present invention records the recording data as a hologram by irradiating the hologram recording medium with signal light and reference light, and records on the hologram recording medium. The hologram is provided with servo means for irradiating the hologram with reference light to obtain diffracted light and reproducing recorded data from the diffracted light. The servo means includes a focus servo unit that focuses the light spot on the hologram recording medium, a tracking servo unit that arranges the light spot in a track direction that is perpendicular to the track formed on the recording surface of the hologram recording medium, and a hologram A tangential servo unit that arranges a light spot in a tangential direction, which is a direction along a track formed on the recording surface of the recording medium, and the tangential servo unit stops the hologram recording medium to stop the light The spot is scanned in the tangential direction, and the address information recorded in advance on the hologram recording medium is read.

  In the embodiment, the servo means includes at least a focus servo unit, a tracking servo unit, and a tangential servo unit. Each servo unit includes an optical unit, a mechanism unit having an actuator that operates based on a signal from the optical unit, and a control unit that is interposed between the optical unit and the mechanism unit and controls the actuator of the mechanism unit. In the embodiment, the optical unit configuring the focus servo unit, the optical unit configuring the tracking servo unit, and the optical unit configuring the tangential servo unit are configured integrally. In the following description, the configuration of the optical unit belonging to each servo will be clarified by describing how the optical unit functions. In addition, the control unit is configured around the CPU, and the control units belonging to the respective servo units are configured integrally. By explaining how the control unit works, the configuration of the control unit belonging to each servo will be clarified.

  Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a schematic diagram of a hologram recording / reproducing apparatus that performs recording / reproduction using a hologram recording medium with a hologram recording / reproducing optical apparatus (optical unit) as a main part as a center.

  The hologram recording medium 48 used in the hologram recording / reproducing apparatus 1 shown in FIG. 1 has a disk shape (disc shape) similar to a compact disk (CD) or a digital versatile disk (DVD). Is provided with a hole for positioning the center of rotation. The hologram recording / reproducing apparatus 1 that performs recording / reproducing on such a hologram recording medium 48 includes the optical unit illustrated in FIG. 1 as a main component. Moreover, the control part 100 comprised by the electric circuit which is not shown in detail is provided, Furthermore, although not shown in figure, the mechanism part which shows one part in FIG. 1 is provided. The hologram recording / reproducing apparatus 1 is connected to an external device (not shown) via the control unit 100. Here, the external device is, for example, a host computer, a video display device (monitor), or the like.

(Outline of hologram recording / reproducing device)
The optical unit of the hologram recording / reproducing apparatus 1 shown in FIG. 1 forms an optical path through which a light beam passes. The optical unit includes a laser light source 10, an isolator 11, a shutter 12, a Fourier transform lens 13, a Fourier transform lens 14, a movable mirror 16a, a spatial modulator 19, a polarization beam splitter 20, a Fourier transform lens 21, a pinhole 22, and a Fourier transform lens. 24, polarization beam splitter 27, Fourier transform lens 121, pinhole 122, Fourier transform lens 124, grating 125, polarization beam splitter 70, quarter wavelength plate 26, objective lens unit 36 equipped with objective lens 28, Fourier transform lens 29, a mirror 30, a Fourier transform lens 31, an image sensor 32, a condenser lens 71, a cylindrical lens 72, and a servo photo detector 73. Here, the condensing lens 71, the cylindrical lens 72, and the servo photodetector 73 are optical components that function exclusively as part of a servo system that performs servo.

  Further, the rotation angle of the movable mirror 16a is controlled by the movable mirror actuator provided in the movable mirror unit 16 as a part of the mechanism portion shown in FIG. Is moved in the vertical direction (tangential direction) on the paper surface. Further, the track king movable unit 34 moves the Fourier transform lens 124, the grating 125, the polarization beam splitter 70, the quarter wavelength plate 26, and the objective lens unit 36 as a single unit by a small amount in the horizontal direction (radial direction) of the drawing sheet. It is made like that. The movement of the track king movable part 34 is performed using a movable part actuator 60 which is a part of the mechanism part. That is, the movable mirror actuator is a part of the embodiment that constitutes the mechanism unit of the tangential servo unit, and moves the light spot in the tangential direction. Moreover, the track king movable part 34 is a part of the embodiment constituting the mechanism part constituting the tracking servo part, and moves the light spot in the tracking direction.

  FIG. 2 is a diagram showing the objective lens unit 36. As shown in FIG. 2, the objective lens unit 36 includes an objective lens 28 and a rising mirror 129. The direction of the light beam from the quarter-wave plate 26 is changed by the rising mirror 129, and the light beam whose direction has been changed passes through the objective lens 28. Here, the movable range of the objective lens unit 36 is about 100 μm (micrometer), which corresponds to a minute amount of displacement of the high frequency component of the tracking servo.

  FIG. 3 shows a mechanism portion for rotating the hologram recording medium 48 and a mechanism portion for performing focus servo. The hologram recording medium 48 is mounted on the turntable 33 a by, for example, magnet chucking, and the turntable 33 a is fixed to the rotating shaft of the spindle motor 33. With such a structure of the mechanism portion, the hologram recording medium 48 is rotated by the driving force of the spindle motor 33. A focus actuator 55 is mounted between the spindle motor 33 and the spindle motor base 58 to change the distance between the hologram recording medium 48 and the spindle motor base 58 in the vertical direction (focus direction) in FIG. It is made to be able to let you. Further, the first gear 57 a that is fixed to the rotation shaft of the slide feed motor 56 and rotates together with the rotation shaft and the second gear 57 b that is fixed to the spindle motor base 58 mesh with each other, so that the slide feed motor 56 Along with the rotation, the hologram recording medium 48 can be moved in the left-right direction on the paper surface. Such a slide feed mechanism can move the hologram recording medium 48 in response to a large amount of displacement of the low frequency component of the tracking servo over a distance corresponding to the radius of the hologram recording medium 48. ing.

  That is, the focus actuator 55 is a part of the embodiment that constitutes the mechanism part that constitutes the focus servo part, and moves the hologram recording medium 48 in the focus direction with respect to the light spot. The spindle motor 33 is a part of the embodiment that constitutes the mechanism part of the tangential servo part, and moves the hologram recording medium 48 in the tangential direction with respect to the light spot. The slide feed motor 56 is a part of the embodiment that constitutes the mechanism part that constitutes the tracking servo part, and moves the hologram recording medium 48 in the tracking direction with respect to the light spot.

  The laser light source 10 includes, for example, a laser (so-called blue laser) having a laser beam wavelength of 405 nm (nanometer) and a laser (so-called red laser) having a laser beam wavelength of 660 nm. As a configuration, at least the light beam from the blue laser is allowed to pass through the external resonator type, and the optical axes are substantially aligned so that the laser beams of both wavelengths pass through the same optical path. Here, in order to make the optical axes coincide, for example, a laser in which a red laser and a blue laser are incorporated in one package is used, and the red light beam and the blue light beam pass through the external resonator type. Alternatively, the light beam from the red laser and the light beam from the blue laser that has passed through the external resonator type may be combined by a dichroic prism.

  The isolator 11 is for maintaining the single mode oscillation by preventing the return light from returning to the blue laser configured as an external cavity laser even when the return light is returned by reflection of a lens or the like. is there. The isolator 11 does not have a function of preventing laser light having a wavelength of 660 nm from returning to the red laser, but the light beam from the red laser is not originally in a single mode but is used as a servo system as described later. Therefore, even if the return light returns to the red laser, no major trouble occurs. Further, the return light of the laser beam having a wavelength of 660 nm does not affect the oscillation of the blue laser.

  The shutter 12 is an element for transmitting or blocking the light beam, and it is controlled by the signal from the control unit 100 whether the light beam is transmitted or blocked. The Fourier transform lens 13 and the Fourier transform lens 14 are for enlarging the diameter of the light beam. By enlarging the diameter of the light beam in this manner, a desired region of the spatial modulator 19, that is, the reference light region 19a and the signal light region 19b of the spatial modulator 19 shown in FIG. It is possible. The movable mirror 16a is displaced by the movable mirror actuator and scans the light beam in the tangential direction as described above.

  As shown in FIG. 4, the spatial modulator 19 displays a predetermined pattern on each of the reference light region 19a and the signal light region 19b, and spatially modulates the light beam to generate the reference light and the signal light. For example, a reflective ferroelectric liquid crystal is employed. The reflective ferroelectric liquid crystal is formed as a set of pixels that are divided into two-dimensionally fine sizes. The predetermined pattern described above is a combination of selecting whether to reflect or not reflect the light beam irradiated to each pixel, and this pattern form. Is controlled by the control unit 100, and for example, a pattern as shown in FIG. 4 can be displayed. 4 is a portion that reflects a light beam, and a black portion (hereinafter referred to as a black portion) is a portion that does not reflect a light beam. Here, the control unit 100 encodes the recording data as a binary block code so that “1” corresponds to a white portion and “0” corresponds to a black portion.

  The polarization beam splitter 20 reflects the light beam from the movable mirror 16a toward the spatial modulator 19, and the polarization direction of the reference light and signal light modulated by the spatial modulator 19 is π with respect to the incident light. / 2 is different and orthogonal, so that it is transmitted through the polarization beam splitter 20 and directed toward the Fourier transform lens 21.

  The Fourier transform lens 21 and the Fourier transform lens 24 are for forming a condensing point of the light beam. The pinhole 22 is disposed at the condensing point of the light beam, thereby shielding high-order diffracted light and improving the shape of the hologram recorded on the hologram recording medium 48. It is.

  The polarization beam splitter 27 directs reference light and signal light in the direction of the Fourier transform lens 121 and directs diffracted light, which will be described later, in the direction of the Fourier transform lens 29.

  The Fourier transform lens 121 and the Fourier transform lens 124 are for forming a condensing point of the light beam. The pinhole 122 is disposed at the condensing point of the light beam, thereby blocking higher-order diffracted light.

  The grating 125 functions as a diffraction grating that diffracts a light beam passing therethrough, and divides the main component of the light beam (red light beam) from the red laser incident on the grating 125 into three light beams. Each of them is collected by an objective lens and three spots are arranged at predetermined positions on the hologram recording medium to detect a signal used for tracking servo. Here, since the optical depth of the grating is an integer multiple of the wavelength of 405 nm, which is the wavelength of the blue beam, the blue light beam is not diffracted by the grating. The light beam that has passed through the grating 125 passes through the polarization beam splitter 70 and further passes through the quarter-wave plate 26.

  The quarter wavelength plate 26 is for converting the polarization of the blue light beam from linearly polarized light to circularly polarized light. The quarter wavelength plate 26 converts the circularly polarized light into linearly polarized light when the polarization of the blue light beam incident on the quarter wavelength plate 26 is circularly polarized. Therefore, the red light beam that has been circularly polarized is irradiated onto the hologram recording medium 48, and the return light from the hologram recording medium again passes through the quarter-wave plate, but the polarization plane of the blue light beam of the return light at this time Is perpendicular to the outgoing polarization plane by π / 2, and passes through the polarization beam splitter 70 having a wavelength-selective film toward the grating 125. Here, since the quarter-wave plate 26 has characteristics matched to the blue beam, the polarization plane of the red light beam is not π / 2 with respect to the outgoing polarization plane. For this reason, a part passes through the polarization beam splitter 70, but the rest is reflected by the polarization beam splitter 70 and travels toward the condenser lens 71. Since the red light beam is used for servo, it is not a problem that a part of the red light beam passes through the polarization beam splitter 70.

  The condensing lens 71 condenses the red light beam into a size with a diameter of several tens of μm that fits in the area of the light receiving surface of the servo photo detector 73. The cylindrical lens 72 generates astigmatism and is used to obtain a focus error signal used for focus servo by a so-called stigma method. The servo photo detector 73 is composed of a plurality of divided detectors, and each signal from the plurality of detectors is taken into the control unit 100 to obtain each of a tracking error signal, a focus error signal, and a tangential error signal. These error signals will be described later.

  The mirror 30 reflects the diffracted light from the Fourier transform lens 29 and guides it to the Fourier transform lens 31. The mirror 30 is used to bend the optical path through which the light beam passes to reduce the size of the optical unit. Yes. The Fourier transform lens 29 and the Fourier transform lens 31 are used to form a real image with the magnification adjusted on the image sensor 32. The image sensor 32 is an optical light receiving element represented by a seamos sensor (CMOS sensor), a charge-coupled device (CCD), etc., and a plurality of finely divided light receiving elements (pixels) are two-dimensionally arranged. An electric signal corresponding to the brightness of the diffracted light that is disposed and irradiates each light receiving element is detected by each pixel. The control unit 100 receives this electric signal and performs signal processing for reproducing recorded data.

(Outline of hologram recording medium)
Next, the hologram recording medium 48 will be briefly described with reference to FIG. The hologram recording medium 48 includes a protective layer 48a, a recording layer 48b, a gap layer 48c, a dichroic reflection layer 48d, a gap layer 48e, an aluminum reflection layer 48f, and a substrate 48g in order in the depth direction. The protective layer 48a is a plastic layer for protecting the recording layer 48b, and the recording layer 48b records holograms according to interference fringes generated by reference light and signal light, and refracts according to interference fringes. It is formed of an organic material or an inorganic material that causes a change in rate or transmittance. For example, photopolymer is frequently used as a material for the recording layer. The dichroic reflection layer 48d is a layer that reflects a blue light beam, which is indicated by a solid line in FIG. 5, and transmits a red light beam, which is indicated by a broken line in FIG. The aluminum reflecting layer 48f is disposed on the groove and pit formation surface, and is used for servo and access described later, so that the red light beam is reflected. The substrate 48g is made of plastic, and has a thickness of 0.6 mm (millimeters), for example, so as to maintain the overall shape of the hologram recording medium 48 with a thickness greater than the thickness of each layer described above. belongs to.

(Recording / playback operation)
In the hologram recording / reproducing apparatus 1 using the optical unit described above, the blue light beam is used for recording / reproducing, and the red light beam is used for servo. Hereinafter, the operation of recording using a blue light beam will be described, and the operation of reproduction using a blue light beam will be described.

  The optical action when recording is described. When the control unit 100 is set so that the blue light beam emitted from the laser light source 10 passes through the isolator 11 and the shutter 12 transmits the light beam, the blue light beam further passes through the shutter 12. Pass through. The diameter of the light beam is expanded by the Fourier transform lens 13 and the Fourier transform lens 14. The blue light beam is reflected by the movable mirror 16a, reflected by the polarization beam splitter 20, and applied to the spatial modulator 19. At this time, a pattern is displayed in both the reference light region 19a and the signal light region 19b of the spatial modulator 19. The incident angle of the movable mirror 16a with respect to the light beam is set by the control unit 100, and the incident angle of the blue light beam incident on the spatial modulator 19 is changed according to the change in the incident angle. Accordingly, the blue light beam composed of the reference light and the signal light emitted from the spatial modulator 19 has a slight angle with respect to the optical axis of each optical component in the optical path through which it passes.

  Thus, the blue light beam composed of the reference light and the signal light spatially modulated by the spatial modulator 19 is converted into the polarization beam splitter 20, the Fourier transform lens 21, the Fourier transform lens 24, the Fourier transform lens 121, and the Fourier transform lens 124. , The grating 125, the polarizing beam splitter 70, the quarter-wave plate 26, and the rising mirror 129 and then the objective lens 28. At this time, the incident angles of the reference light and the signal light with respect to the optical axis of the objective lens 28 are changed according to the incident angles with respect to the light beam of the movable mirror 16a as described above.

  With reference to FIG. 6, the operation when the incident angle of the reference light and the signal light with respect to the optical axis of the objective lens 28 is changed will be described. First, the reference light and the signal light form a real image on the front focal plane of the objective lens 28 as shown in FIG. The light beam modulated in each pixel of the spatial modulator 19 is incident on the objective lens 28 with a numerical aperture spread determined by the pixel size and wavelength of the spatial modulator 19, and each of the reference light and the signal light is a hologram. The light is condensed in the recording layer 48 b which is the hologram forming area of the recording medium 48. At this time, the objective lens has a telecentric relationship with the light emitted from each pixel, and the reference light and the signal light interfere with each other in the recording layer 48b to generate interference fringes. Then, for example, in the recording layer 48b formed using a photopolymer as a material, the monomer is changed to a polymer, and a hologram is formed in the recording layer as a change in refractive index corresponding to the interference fringes. At this time, when the direction of rotation of the movable mirror 16a changes, the incident angle of the blue light beam to the hologram recording medium 48 changes as shown by a solid line, a broken line, and an alternate long and short dash line in FIG. The position of the condensing point of the light beam at 48 is moved in the tangential direction. The objective lens 28 satisfies the sine condition, and the position of the hologram is changed depending on the incident angle of the movable mirror 16a, but the interference fringes are not changed depending on the incident angle. In FIG. 6, the tangential direction is the left-right direction of the page. Thus, by rotating the movable mirror 16a, the reference light and the signal light interfere with each other to change the position where the hologram is formed, and the position of the hologram can be adjusted while the hologram recording medium 48 is stationary. , Can be formed by moving.

  In the reproduction operation, the operation until the light beam reaches the spatial modulator 19 is the same as that in the case of performing recording, and thus the description thereof is omitted. In the reference light area 19a of the spatial modulator 19, the same pattern as when recording is displayed. On the other hand, in the signal light region 19b, all the pixels are black. That is, the signal light region 19a does not reflect the blue light beam, and as a result, no signal light is generated. In this way, only the reference light is generated, and the light beam is focused on the area where the hologram has already been formed (the area where the hologram has been formed) on the recording layer 48b of the hologram recording medium 48, as in the case of recording. Is irradiated.

  Diffracted light is generated by irradiating the hologram-formed region with the reference light, and the diffracted light reflected by the dichroic reflective layer 48d (see FIG. 5) disposed on the hologram recording medium 48 is returned to the objective lens 28 side again. Return to. Here, the dichroic reflection layer 48d is arranged on the farther side from the objective lens 28 than the recording layer 48b on which the hologram is formed, and it is possible to return the diffracted light generated in the recording layer 48b to the objective lens 28. Has been.

  After passing through the objective lens 28, the diffracted light passes through the quarter-wave plate 26, the polarization beam splitter 70, the grating 125, the Fourier transform lens 124, the pinhole 22, and the Fourier transform lens 121, and enters the polarization beam splitter 27. Diffracted light reaches. The diffracted light is reflected by the polarization beam splitter 27, changes the traveling direction, passes through the Fourier transform lens 29, the mirror 30, and the Fourier transform lens 31 to form an image on the image sensor 32. That is, an image corresponding to the reference light component included in the diffracted light is reproduced on the outer peripheral portion of the image sensor 32, and an image corresponding to the signal light component included in the diffracted light is reproduced on the inner peripheral portion of the image sensor 32. Played.

  Here, the image corresponding to the reference light component displayed on the image sensor 32 is an image corresponding to the white part and the black part displayed on the reference light region 19 a of the spatial modulator 19, and is displayed on the image sensor 32. The image corresponding to the signal light component is an image corresponding to the white part and the black part displayed in the signal light region 19 b of the spatial modulator 19. Here, since only the image corresponding to the signal light component is necessary for reproduction, the outer peripheral portion of the image sensor 32 that receives the image corresponding to the reference light component is intended only for reproduction. Is not required.

  Electric signals from a plurality of two-dimensionally arranged light receiving elements detected based on the brightness of the image corresponding to the signal light component included in the diffracted light from the image sensor 32 are taken into the control unit 100 and are received by the image sensor 32. The image (reproduced image) formed by the light rotation on the light receiving surface is detected as an electrical signal for each pixel of a minute size arranged two-dimensionally in the image sensor 32. This electrical signal is converted into a binary signal so that the image received by each pixel is associated with “1” when the image is brighter than the predetermined threshold and is associated with “0” when the image is darker than the predetermined threshold. After the conversion, the block code decoding process is performed, the modulated recording data for each block is decoded, and then the signal processing such as the ECC decoding process is performed, the recording data is decoded, and the recording data is transferred to the external device. Is sent out.

  As described above, the above-described recording and reproduction can be performed by using the fact that the position of the light beam can be changed by rotating the movable mirror 16a and the light spot that has focused the light beam in the tangential direction can be moved by a small amount. In operation, multiple recording can be performed in which holograms are recorded while overlapping. Such multiplexing using the movable mirror 16a is hereinafter referred to as beam position multiplexing. The beam position multiplexing is performed by the action of the servo, details of which will be described later.

  Next, the preformat of the hologram recording medium 48 will be described with reference to FIG. 7, and then the operation of the servo system that is the main part of the embodiment, in particular, the light spot is arranged at a desired location on the hologram recording medium. The operation of the access servo (addressing) will be described.

(Regarding preformatting of hologram recording media)
With reference to FIG. 7, the preformat of the hologram recording medium 48, which is closely related to the operation of the servo system, will be described. The preformat is formed as an aluminum reflective layer 48f and has information on the groove shape or the pit arrangement. The position of the light spot obtained by condensing the light beam on the hologram recording medium 48 is specified by the information on the groove shape or the pit arrangement, and the radial servo, tracking servo, and access servo are smoothly performed.

  As shown in FIG. 7, in the hologram recording medium 48, one track is composed of four grooves G1 to G4, pits Pa, and pits Pc. Here, the track is continuously formed in a spiral shape from the inner periphery to the outer periphery of the hologram recording medium 48. The groove G1 is provided for the purpose of avoiding the crosstalk between the pit Pa and the pit Pc, and the groove G2 and the groove G4 are provided for the purpose of preventing the crosstalk from the pit Pa and the pit Pc from occurring in the groove G3. It has been. The groove G3 is provided for the purpose of detecting a radial push-pull signal for tracking servo. The pit Pa is provided for the purpose of detecting a radial push-pull signal and address information, and the pit Pc is provided for the purpose of detecting a tangential push-pull signal, radial push-pull signal, and clock information.

  Therefore, the depth and width of the grooves G1, G2 and G4 are 110 nm and 0.6 μm, and the groove G3 has the depth and width of the groove capable of obtaining a radial push-pull signal. The depth and width of the groove of the groove G4 are 110 nm and 0.6 μm.

  The pit Pa and the pit Pc are formed as pits that are spatially synchronized in the tangential direction in order to obtain signals that are temporally synchronized with the address information and the clock information. The pit Pa has a pit depth at which the presence or absence of a pit can be detected as a sum signal to be described later and a radial push-pull signal can be detected as a difference signal. The pit Pc has a pit depth that can detect the presence or absence of a pit as a sum signal, detect a radial push-pull signal as a difference signal, and detect a tangential push-pull signal as a difference signal in another direction.

  Here, the length of the pit Pc in the tangential direction will be described. A tangential push-pull signal can be detected without any particular limitation on the length of pits (marks) or spaces (parts that are not pits). That is, since the tangential push-pull signal detects the edge of the pit in the tangential direction, it is naturally possible to detect the tangential error signal using the pit Pa. However, when the length of the pit or space is long, the information amount of the tangential push-pull signal decreases and the information amount of the clock information also decreases. That is, the information amount of the tangential push-pull signal is defined by the spatial frequency defined by the length of the pit or space and the cutoff frequency of the modulation transfer function (MTF) of the optical system. is there.

  If the spatial frequency of the pit Pa, which is a periodically repeated pit row, is significantly lower than the cutoff frequency of the modulation transfer function of the optical system, not only the fundamental spatial frequency component but also its harmonic components are As will be described later, the tangential error signal detected by using the servo photo detector 73 is not a sine wave, but is close to a square wave including harmonics. Is included only in the rising and falling portions of the signal close to the square wave.

  On the other hand, the fundamental component of the spatial frequency of the pit Pa is lower than the cutoff frequency of the modulation transfer function of the optical system expressed as the size of the light spot, but the harmonic component of the spatial frequency of the pit Pa is modulated by the optical system. If the transfer function is equal to or higher than the cut-off frequency, the tangential error signal detected using the servo photodetector 73 is a sine wave. Here, the main value of the sine wave is a bivalent function from −π / 2 (radian) to π / 2, but the change in the position in the tangential direction in consideration of the polarity of the sum signal obtained from the pit Pa. By obtaining a monovalent signal with respect to, and obtaining an extended tangential error signal with correction, the range of the tangential error signal can be expanded to a range from −π to π. From such a viewpoint, the pit length of the pit Pc and the length of the space are the same, and the length is such that only the fundamental wave of the spatial frequency of the pit Pc falls within the range of the cutoff spatial frequency of the optical system. Yes. In the embodiment, the pit (mark) length is 0.5 μm, the space length is 0.5 μm, and the repetition period is 1 μm.

  When the focus servo and tracking servo are appropriately performed, as shown in FIG. 7, the light spot is a light spot Sm as a main spot, a light spot Ss1 as a side spot, and a light spot Ss2 as a side spot. As arranged. Here, each light spot is generated as a result of the action of the grating 125 (see FIG. 1), and the light spot Sm as the main spot is a light spot generated by the 0th order light, and is a light spot as a side spot. Ss1 and light spot Ss2 are light spots generated by the primary light. Here, the separation distance between the three light spots in the tangential direction (the vertical direction of the paper surface in FIG. 7) and the tracking direction (the horizontal direction of the paper surface in FIG. 7 and the direction orthogonal to the direction along the track). The distance is adjusted in advance by adjusting the arrangement of the grating 125, the servo photo detector 73, and the like. The radial direction has a predetermined interval, the tracking direction has the light spot Sm at the center of the groove G3, and the light spot Ss1. The center is arranged so as to coincide with the center of the pit Pc, and the center of the light spot Ss2 coincides with the center of the pit Pa. Further, the hologram recording medium 48 is moved in the tangential direction with respect to the light spot according to the rotation of the spindle motor 33 (see FIG. 1), and the light spot is moved in the tangential direction according to the rotation of the movable mirror 16a. The relative positional relationship between the three light spots and the hologram recording medium 48 moves in the vertical direction on the paper surface.

  The three light spots described above are light spots generated from a red light beam (hereinafter, abbreviated as red light spots), and are recorded and reproduced light spots (hereinafter, blue light spots) generated from a blue light beam. The abbreviated as “light spot” means that the optical part related to the servo and the optical part related to the recording / reproducing are made up of shared parts, and the positions to be formed have a predetermined relationship. Become. In the embodiment, the center position of the light spot Sm, which is a red light spot, and the center position of the blue light spot are the same, but the center position of the light spot Ss1 and the center position of the blue light spot are the same. And the center position of the light spot Ss2 may match the center position of the blue light spot. Furthermore, the position of the center of one of the red light spots and the position of the center of the blue light spot may not coincide with each other and may have a predetermined positional relationship. The mutual relationship with the position of the blue light spot can be appropriately determined by adjusting the optical unit.

  FIG. 8 illustrates the relationship among the divided detectors A to L, which are the divided detectors constituting the servo photo detector 73, and the light spot Sm, the light spot Ss1, and the light spot Ss2. As shown in FIG. 8, the light spot Ss1 is detected by the division detector A, the division detector B, the division detector C, and the division detector D, and the light spot Sm is divided by the division detector E, the division detector F, the division detector G, and the division detector. The light spot Ss2 is detected by the split detector I, the split detector J, the split detector K, and the split detector L.

  Here, the radial push-pull signal obtained from the groove G3 detected using the light spot Sm is obtained by adding the signal from the divided detector E and the signal from the divided detector F, and from the added signal from the divided detector G. It is obtained by subtracting the signal and the signal from the division detector H. A focus error signal is obtained from the light spot Sm by the stigma method. The focus error signal is obtained by adding the signal from the division detector E and the signal from the division detector H, and dividing the signal by the added signal. It is obtained by subtracting the signal from the detector F and the signal from the divided detector G.

  The radial push-pull signal obtained from the pit Pc detected using the light spot Ss1 adds the signal from the divided detector A and the signal from the divided detector B, and divides the signal from the divided detector C from the added signal. It is obtained by subtracting the signal from the detector D. The tangential push-pull signal obtained from the pit Pc detected using the light spot Ss1 is obtained by adding the signal from the divided detector A and the signal from the divided detector C, and from the added signal from the divided detector B. The signal is obtained by subtracting the signal from the division detector D. Further, the clock information obtained from the pit Pc detected using the light spot Ss1 is obtained by adding the signal from the divided detector A, the signal from the divided detector B, the signal from the divided detector C, and the signal from the divided detector D. (Sum signal).

  The radial push-pull signal obtained from the pit Pa detected using the light spot Ss2 is obtained by adding the signal from the division detector I and the signal from the division detector J, and dividing the signal from the division detector K from the added signal. It is obtained by subtracting the signal from the detector L. The address information obtained from the pit Pa detected using the light spot Ss2 is obtained by adding the signal from the divided detector I, the signal from the divided detector J, the signal from the divided detector K, and the signal from the divided detector L. (Sum signal). Although not used in the embodiment, the signal from the division detector I and the signal from the division detector K are added, and the signal from the division detector J and the signal from the division detector L are added from the added signal. A tangential push-pull signal can be obtained by subtraction.

  As the tracking error signal, only the radial push-pull signal from the light spot Sm may be used, but a linear addition signal of the radial push-pull signal detected from each of the light spot Sm, the light spot Ss1, and the light spot Ss2 is used. Thus, a so-called differential push-pull (DPP) signal can be obtained, and a tracking error signal with a good signal-to-noise ratio (S / N) can be obtained while eliminating the influence of offset due to position movement.

  As the tangential error signal, a tangential push-pull signal obtained from the pit Pc detected using the light spot Ss1 can be used as it is.

  In the address information obtained from the pit Pa detected using the light spot Ss2, the pit Pa is formed as a variable length code. When decoding the address information, the address information may be decoded based on the clock information included in the pit Pa, and from the pit Pa based on the clock information obtained from the pit Pc detected using the light spot Ss1. The obtained address information may be decoded. When using the clock information included in the pit Pa, the positional deviation between the pit Pa and the pit Pc does not cause a problem, but the content of the clock information is small. Therefore, the clock information is extracted from the pit Pa. Therefore, the time constant of the low-pass filter of the phase-locked loop (PLL) is increased, and the accuracy of the clock information is lowered when the relative speed changes greatly. On the other hand, when obtaining clock information from the pits Pc, in addition to using the presence / absence of the pits Pc directly as clock information, a phase-locked loop can be used to eliminate the influence of false detection due to missing pits Pc, In this case, the time constant of the low-pass filter of the phase locked loop can be made small, and the accuracy of the clock information is good even when the relative speed changes greatly. Furthermore, if the time constant of the low-pass filter is made variable based on information detected from the pit Pa, a clock with even better quality can be obtained.

  The clock information obtained from the pits Pc detected using the light spot Ss1 spatially has finer information than the address (position) of the hologram recording medium 48 specified by the address obtained from the pits Pa. Therefore, the address of the hologram recording medium 48 can be specified more finely. The clock information obtained from the pit Pc detected using the light spot Ss1 represents the relative speed between the hologram recording medium 48 and the light spot in terms of time. Specifically, when the relative speed is high, the number of pits Pc per unit time (number of inversions) is calculated, and when the relative speed is low, the length of the pits Pc per unit time (inverts). The relative speed can be detected with high accuracy.

(About focus servo, tracking servo, tangential servo)
Each of the focus servo, the tracking servo, and the tangential servo includes an optical system that generates each of the focus error signal, the tracking error signal, and the tangential error signal, and a control unit 100 that processes each of these error signals. And a mechanism portion associated with each servo. Although how to detect each error signal and each mechanism unit has already been described above, the operation of each servo will be described focusing on the contents of processing in the control unit 100.

  The control unit 100 includes an A / D converter (not shown) that converts each error signal obtained as an analog signal into a digital signal, and a central processing unit (CPU) that processes each error signal converted into a digital signal. (Not shown), a random access memory (RAM) (not shown) that functions as a memory when the program is executed, a program that is a procedure processed by the CPU, and a read-only memory (ROM) in which predetermined constants are stored (Not shown)), a driver (not shown) as a power amplifier that receives a signal calculated by the CPU and drives a mechanism unit related to each servo is included as a main component.

  The focus servo will be described. After the focus error signal is taken into the A / D converter, the CPU performs phase compensation, and the phase-compensated signal is output to the servo driver. The output from the servo driver is applied to the focus actuator 55, and the servo in the focus direction operates to form a light spot on the recording layer 48b of the hologram recording medium 48. The so-called focus servo pull-in process is also performed under the control of the CPU. The positional relationship in the focus direction between the red light spot and the blue light spot is also determined in advance by adjusting the optical unit. As shown in FIG. 5, the red light spot has a condensing point on the aluminum reflecting layer 48f. In this case, the blue light spot has a condensing point on the dichroic reflection layer 48d.

  The tracking servo will be described. After the tracking error signal is taken into the A / D converter, it is decomposed into a low-frequency component and a high-frequency component by the CPU, and phase compensation is performed for each of them, and each phase-compensated signal is servoed. Output to the driver. The output from one servo driver is applied to the movable part actuator 60, and the tracking servo is performed in a minute range by moving the position of the light spot. The output from the other servo driver is applied to the slide feed motor 56, and the position of the hologram recording medium 48 is moved to perform tracking servo in a larger range. Then, as shown in FIG. 7, the light spot is arranged on the groove G3, the pit Pa, and the pit Pc.

  The tangential servo will be described. After the tangential error signal is taken into the A / D converter, the CPU performs phase compensation, and the phase-compensated signal is output to the servo driver. The output from the servo driver is applied with a movable mirror actuator to move the light spot, and the servo in the tangential direction works. Here, since the tangential error signal is obtained from the edge of the pit Pc, positioning with one pit accuracy is possible. In addition, when the polarity of the tangential error signal is switched alternately, the signal from both the front edge and the rear edge of the pit can be used effectively, and when the ratio of mark to space is equal, 1/2 pit Positioning with accuracy is possible. Furthermore, if the CPU generates an offset voltage and replaces the difference signal between the above-mentioned extended tangential error signal and the offset voltage with a tangential error signal, the control is performed with a precision within one pit. Spots can be placed. Such tangential servo with accuracy within 1 pit is very effective when performing beam position multiplex recording.

(About access servo)
An access servo using the above-described focus servo, tracking servo, and tangential servo will be described. The access servo is performed according to the following procedure. All access servos are controlled by the CPU of the control unit 100.

  Before explaining the details of the access servo, an outline of an access servo of 1 pit or more and an access servo of 1 pit or less will be explained. Positioning for one or more pits is performed as follows. An absolute address (position on the hologram recording medium 48) is detected from the pit Pa, details of which will be described later. The pit Pc indicates relative address information (position at the absolute address). After decoding an address from a plurality of sets of pits representing one address belonging to the pit Pa, the address of the hologram recording medium 48 is specified by the position of the last pit representing the address. That is, by decoding the address information from the pit Pa, the relative address can be specified by the information from the pit Pc every time an absolute address is obtained. Here, the absolute address information given to the hologram recording medium 48 is spatially discretely arranged, and the absolute address is obtained every 200 μm, for example, and the relative address obtained from the pit Pc is every 1 μm. Or, it is obtained every 0.5 μm.

  When the above-described beam position multiplex recording is used, if the distance between the holograms recorded on the hologram recording medium 48 is 0.5 μm, an access servo in this range is sufficient. For example, an access servo of about 0.05 μm is required. Arbitrary positioning in the tangential direction can be performed by combining the above-described focus servo, tracking servo, and tangential servo with the positioning with 1 pit accuracy and the positioning with accuracy within 1 pit. The procedure of the positioning process performed by the CPU will be described below.

(1-1) The red laser is emitted, the emission of the blue laser is stopped, and all pixels in the reference light region 19a and the signal light region 19b of the spatial modulator 19 are set as white portions. Further, the rotation of the hologram recording medium 48 is stopped by controlling the spindle motor 33.
(1-2) Perform focus servo. Perform tracking servo.
(1-3) The movable mirror actuator is controlled to swing the movable mirror 16a, for example, in the negative direction (direction in which the light beam is arranged as shown by the broken line in FIG. 6) to read the address information.
At this time, the tracking servo is intermittently turned on and off so that the tracking servo does not come off, and the movable mirror 16a is controlled to move when the tracking servo is off.
The maximum amplitude of the light spot is, for example, 200 μm from the center position (position where the light beam is arranged as shown by the solid line in FIG. 6). This amplitude is a range in which recording / reproducing characteristics are good when recording / reproducing is performed using a blue laser.
The address information is read and the address is decoded by shaking the movable mirror 16a within a range of 200 μm in the direction along the track (tangential direction). In this case, the decoding of the address is obtained as time-series “1” and “0” obtained by binarizing the sum signal of the divided detectors I to L corresponding to the arrangement of the pits Pa. The moving direction of 16a is determined. If the moving direction is negative, reverse time processing is performed to detect an address.

(1-4) After the address information is detected at the pit Pa and the absolute address is specified, the position of the pit belonging to the pit Pa where the address information starts (if the movable mirror 16a is swung in the forward direction, the address information The CPU calculates how many pits the desired position specified by the relative address information is deviated by the number of pits belonging to the pit Pc from the position of the pit belonging to the pit Pa that ends, and the number of pits for the deviation is calculated. Only while counting, the movable mirror 16a is further moved in the tangential direction. The pit is counted using a sum signal or a tangential push-pull signal.
Also at this time, tracking servo is intermittently performed.
(1-5) When the desired pit is reached, tangential servo is performed, and the operation of the access servo to the desired position specified by the absolute address information and the relative address information is completed.
At this time, by switching between positive and negative of the tangential error signal, it is possible to access with ½ pit accuracy which switches whether to perform tangential servo at the rising edge of the pit or to perform tangential servo at the falling edge of the pit.
In addition, when a desired position is specified with an accuracy within one pit of the pit Pc as in the case of beam position multiplexing, the CPU generates an offset corresponding to the position and sets the position in the tangential direction. Furthermore, control is performed with high accuracy.

  The above is the basic access operation, but the address read by shaking the movable mirror 16a within the range of 200 μm (the value converted to the position of the light spot, and the same applies below) is far from the desired position. If it is separated and cannot be covered within the range of the swing width of the movable mirror 16a, the desired position cannot be accessed by the above-described method. In this case, the CPU performs the processing from the following (2-5) following the above-described processing (1-3).

(2-5) The movable mirror actuator is controlled to swing the movable mirror 16a, for example, 200 μm in the negative direction. For example, if the current position of the movable mirror 16a is 150 μm in the negative direction, it is further shaken by 50 μm. The swing width obtained by the movable mirror 16a may be obtained by providing a sensor (not shown) on the movable mirror 16a to detect the rotation angle, and converted from the voltage applied to the movable mirror actuator. It may be.
(2-6) The number of tracks spaced in the tracking (radial) direction and the rotation angle of the hologram recording medium 48 calculated from the separation distance in the tangential direction are calculated from the position of the light spot on the current hologram recording medium 48. To do.
(2-7) If the range for positioning the light spot at the desired position is a range that can be covered by controlling the spindle motor 33, the spindle motor 33 can be controlled and the movable portion actuator 60 can be controlled to cover If it is within the range, the movable portion actuator 60 is controlled. Further, if the range is not covered unless the slide feed motor 56 is moved, the slide feed motor 56 is controlled to place the light spot on the desired track. After that, perform tracking servo.
Here, the number of tracks is determined by, for example, a radial push-pull signal detected from the division detector E to the division detector H, that is, the radial push-pull how many grooves G1 to G4 and pits Pa and Pc have been crossed. Measure by signal.
(2-8) When rotating the spindle motor 33, in the course of this rotation, when not rotating, the absolute address is read out by shaking the movable mirror 16a in the positive direction, and the desired absolute address, When the desired relative address is detected by the information from the pits Pa and Pc, the rotation of the spindle motor 33 is stopped.
(2-9) When the hologram recording medium 48 reaches the desired position with one pit accuracy with respect to the light spot, tangential servo is performed, and the operation of the access servo to the desired position is completed.
At this time, by switching between positive and negative of the tangential error signal, it is possible to switch between performing the tangential servo at the rising edge of the pit or performing the tangential servo at the falling edge of the pit. In addition, when a desired position is specified with an accuracy within one pit of the pit Pc as in the case of beam position multiplexing, the CPU generates an offset corresponding to the position and sets the position in the tangential direction. Furthermore, control is performed with high accuracy.

  After the light spot is arranged at a desired position by the above-described processing, recording / reproduction is performed by the following processing.

When recording a hologram continuously from a desired position (or reproducing recorded data continuously recorded from the desired position), (3-1) the following processing is performed for each pit Pc in one pit unit. The case where recording (or reproduction) is performed while shifting the position is shown. (4-1) The following processing shows the case where recording (or reproduction) is performed while shifting the position of the hologram in units of 1/2 pit of the pit Pc.
(5-1) The following processing shows a case where recording (or reproduction) is performed while shifting the position of the hologram with a finer accuracy of 1 pit or less which is not every ½ pit unit of the pit Pc.

(3-1) Perform tangential servo.
(3-2) Hologram recording (or reproduction of recorded data) is performed.
(3-3) The tangential servo is turned off and the movable mirror actuator is driven with a kick pulse.
By repeating (3-1) to (3-3), it is possible to perform continuous recording (or reproduction) in which the position is moved from the desired position in units of one pit of the pit Pc.

(4-1) Perform tangential servo.
(4-2) Hologram recording (or reproduction of recorded data) is performed.
(4-3) The tangential servo is turned off and the movable mirror actuator is driven with a kick pulse. Inverts the current polarity of the tangential error signal.
By repeating (4-1) to (4-3), it is possible to perform continuous recording (or reproduction) in which the position is moved from the desired position in units of ½ pit of the pit Pc.

(5-1) Perform tangential servo using the extended tangential error signal.
(5-2) Hologram recording (or reproduction of recorded data) is performed.
(5-3) Add the tangential servo offset to the previous offset.
If the amount of offset reaches the amount to move by one pit, the amount of offset is returned to zero.
By repeating (5-1) to (5-3), it is possible to perform continuous recording (or reproduction) in which the position is moved from the desired position by a minute amount within one pit of the pit Pc.

(About the movement speed profile of the actuator in the access servo)
The light spot in the above-described processes (1-1) to (1-5) or the processes (2-5) to (2-9) following the processes (1-1) to (1-4). A method for setting the speed profile will be described.

  In either case of rotating the spindle motor 33 or moving the movable mirror 16a, the moving speed profile of the actuator is important from the viewpoint of increasing the access speed. For example, if the speed of the disk when the hologram recording medium 48 is rotated by the spindle motor 33 to be adjusted to the desired address position is suddenly changed, harmful vibrations may occur and the desired position may not be stopped accurately. Get higher. The same applies to the control of the movable mirror 16a. Further, since the voltage of the power source for driving the actuator is a finite value, it is necessary to perform control in consideration of this point.

  Both the movable mirror 16a and the spindle motor 33 are secondary systems. For such a secondary system, the shortest time control to reach the target position in the shortest time using a drive source with a constant power supply voltage is bang-bang control (Bang Bang control) having one voltage switching point. This is a well-known matter in the control field. In this case, the velocity profile of the light spot moved by the actuator increases in speed in proportion to time and decreases in proportion to time.

  FIG. 9 shows a speed profile when the spindle motor 33 is rotated or when the movable mirror 16a is rotated. First, control of the spindle motor 33 will be described. The graph in FIG. 9A shows the moving speed Dut of the hologram recording medium 48 (disk) on the vertical axis and the time on the horizontal axis, and FIG. 9B shows the hologram recording medium 48 (disk). FIG. 9C shows the relationship between the voltage Vs applied to the spindle motor when the movement amount is small and time, and FIG. 9C shows the spindle motor when the movement amount of the hologram recording medium 48 (disk) is large. The relationship between the applied voltage Vs and time is shown.

  As shown in FIG. 9A, when the amount of movement of the hologram recording medium 48 is small, the speed is increased at a constant acceleration (first predetermined acceleration), and the same constant acceleration (first predetermined acceleration) as during acceleration is used. And a second predetermined acceleration in which the direction of acceleration is opposite), and the speed is reduced to reach the target position at zero speed. In this case, the first predetermined acceleration and the second predetermined acceleration are set to have the same absolute value. When the movement amount of the hologram recording medium 48 is large, the speed is increased at a constant acceleration (first predetermined acceleration), and the acceleration is smaller than the acceleration at the time of acceleration (the direction of acceleration is opposite to the first predetermined acceleration). The speed was reduced at the second predetermined acceleration) so that the target position was reached when the speed was zero. In this case, the absolute value of the first predetermined acceleration was set larger than that of the second predetermined acceleration.

  As shown in FIG. 9B, when the movement amount of the hologram recording medium 48 is small, it is assumed that the voltage for acceleration and the voltage for deceleration are equal, and the time T1 and the time T2 in this case are the same. The length is the same. As shown in FIG. 9C, when the movement amount of the hologram recording medium 48 is large, the acceleration voltage is larger than the deceleration voltage, and the time T3 in this case is set to the time T4. Shorter than that.

  The above-described bang-bang control, which is open-loop control, is difficult to absorb time-dependent changes in the mechanism unit and the optical unit, individual differences, and non-linearity of the mechanism unit. Even when the voltage shown in (C) is applied, the speed profile shown in (A) of FIG. 9 may not be obtained. In this case, feedback control by the following processing (6-1) is performed. You may make it have such a speed profile.

(6-1) A speed profile as shown in FIG. 9A is generated by the CPU every predetermined time.
(6-2) The relative velocity between the light spot and the hologram recording medium 48 every predetermined time is detected. When the speed is high, the relative speed is obtained by binarizing the sum signal of the signal from the divided detector A or the signal from the divided detector D into “1” and “0” and by the number of inversions every predetermined time. If it is detected and the speed is low, the length of “1” or “0” is measured and calculated. The sign of the speed of the light spot can be detected by determining the phase relationship between the sum signal of the signal from the division detector A or the signal from the division detector D and the tangential error signal by the CPU.
(6-3) At every predetermined time, a subtraction signal obtained by subtracting the speed obtained in (6-2) from the speed obtained in (6-1) indicated by the speed profile at that time is obtained, and the phase is added to this subtraction signal. The spindle motor 33 is driven by the spindle motor driver after compensation.
By repeating the processes from (6-1) to (6-3) every predetermined time, the speed profile generated by the CPU and the relative speed of the light spot exactly match.

  In either case of the above-described open loop control or feedback control, it is determined whether the spindle motor should be rotated positively or negatively, and the spindle motor 33 is controlled so that the desired position can be reached most quickly. .

  Next, control of the movable mirror 16a will be described. The control of the movable mirror 16a is exactly the same as the control of the spindle motor 33, but the hologram medium 48 is moved in the control of the spindle motor 33, whereas the light spot is moved in the control of the movable mirror 16a. However, when the moment of inertia of the hologram recording medium 48 increases, there is an advantage that a higher-speed access servo is possible.

  9, the magnitude of the moving speed Dut of the movable mirror 16a that moves the light spot and the magnitude of the voltage Vs applied to the movable mirror actuator are the same as those in the control of the spindle motor 33. It takes different values. 9A shows the moving speed Dut of the movable mirror 16a on the vertical axis and the time on the horizontal axis, and FIG. 9B shows the movable mirror when the moving amount of the movable mirror 16a is small. FIG. 9C shows the relationship between the voltage Vs applied to the actuator and time, and FIG. 9C shows the relationship between the voltage Vs applied to the movable mirror actuator and time when the moving amount of the movable mirror 16a is large. Is shown.

  As shown in FIG. 9A, when the amount of movement of the movable mirror 16a is small, the speed is increased at a constant acceleration (first predetermined acceleration), and the same constant acceleration (first predetermined acceleration and The speed is reduced at a second predetermined acceleration in which the direction of acceleration is opposite) to reach the target position at zero speed. In this case, the first predetermined acceleration and the second predetermined acceleration are set to have the same absolute value. When the moving amount of the movable mirror 16a is large, the speed is increased at a constant acceleration (first predetermined acceleration), and the acceleration is smaller than the acceleration at the time of acceleration (the direction of the acceleration is opposite to the first predetermined acceleration). (2 predetermined acceleration) to reduce the speed so that the target position is reached when the speed is zero. In this case, the absolute value of the first predetermined acceleration was set larger than that of the second predetermined acceleration.

As shown in FIG. 9B, when the moving amount of the movable mirror 16a is small, it is assumed that the voltage for acceleration and the voltage for deceleration are equal, and the time T1 and time T2 in this case are long. The same is true. As shown in FIG. 9C, when the moving amount of the movable mirror 16a is large , the voltage for acceleration is larger than the voltage for deceleration, and the time T3 in this case is set from the time T4. Was also short.

  The above-described bang-bang control, which is open-loop control, is difficult to absorb time-dependent changes in the mechanism unit and the optical unit, individual differences, and non-linearity of the mechanism unit. Even if the voltage shown in (C) is applied, the speed profile shown in (A) of FIG. 9 may not be obtained. In this case, feedback control by the following processing (7-1) is performed. You may make it have such a speed profile.

(7-1) A speed profile as shown in FIG. 9A is generated by the CPU every predetermined time.
(7-2) The relative speed between the light spot and the hologram recording medium 48 every predetermined time is detected. When the speed is high, the relative speed is obtained by binarizing the sum signal of the signal from the divided detector A or the signal from the divided detector D into “1” and “0”, and by the number of inversions every predetermined time. If it is detected and the speed is low, the length of “1” or “0” is measured and calculated. The sign of the speed of the light spot can be detected by determining the phase relationship between the sum signal of the signal from the division detector A or the signal from the division detector D and the tangential error signal by the CPU.
(7-3) For each predetermined time, a subtraction signal obtained by subtracting the speed obtained in (7-2) from the speed obtained in (7-1) indicated by the speed profile at that time is obtained. The movable mirror actuator is driven by the movable mirror driver after compensation.
By repeating the processes from (7-1) to (7-3) every predetermined time, the speed profile generated by the CPU and the relative speed of the light spot exactly match.

  In either case of the above-described open loop control or feedback control, it is determined whether the movable mirror 16a should be rotated positively or negatively, and the movable mirror actuator is controlled so that the desired position can be reached most quickly. It is said.

  In this way, the speed in the tangential direction is controlled according to time, and at the final stage of the access operation, immediately after stopping without causing unnecessary vibration by making the speed in the tangential direction zero, Hologram recording (or reproduction) is possible. Furthermore, since the speed is linearly increased / decreased with respect to time, the desired position can be reached in the shortest time. Further, when an access operation is performed by feedback control, it is affected by the characteristics of the mechanism unit, optical unit, etc. Stable access operation is possible without any problem.

  When accessing using the movable mirror 16a without rotating the hologram recording medium 48, the access time is shorter than any of the techniques shown in the background art, and the transfer rate of the recording data is higher than the conventional one. It can be.

  Further, for example, a mark for confirming the circumferential position is provided at a specific position on the innermost periphery of the hologram recording medium 48 to facilitate the specification of the position. After the hologram recording medium 48 is mounted on the turntable 33a, the reflected light of the blue laser The mark may be searched for to determine the circumferential position of the disk. Also in this case, the position information is read by the CPU, and the CPU controls various actuators as appropriate for accessing the desired position.

FIG. 10 shows another preformat of the hologram recording medium. In the preformat shown in FIG. 10, the recording density in the track direction can be further improved as compared with the preformat shown in FIG. Parts having the same configuration as in FIG. 7 are denoted by the same reference numerals. In the preformat shown in FIG. 10, the light spot Ss1 traces the pit Pc and the pit Pa, the light spot Sm traces the groove G3 and the groove G6, and the light spot Ss2 Trace the pit Pc. That is, the light spot Ss1 traces the pit Pc, the light spot Sm traces the groove G3 , the light spot Ss2 traces the pit Pa, and the light spot Ss1 traces the pit Pa. It is assumed that the light spot Sm traces the groove G6 and the light spot Ss2 alternately generates periods (second periods) in which the pits Pc are traced. Groove G3 and groove G6 have the same groove structure.

  In order to realize the arrangement of the light spot corresponding to each of the first period and the second period, the track jump is performed every time the relative position of the shining spot makes one round, but this control is performed by the CPU. Do it. In addition, the process of switching the signal from the division detector A or the operation of the division detector D and the operation of the division detector I or the division detector L is performed in synchronization with the switching between the first period and the second period. By using such a preformat, the recording density in the track direction can be improved.

  The hologram recording / reproducing apparatus 2 and the hologram recording / reproducing optical apparatus (optical unit) shown in FIG. 11 are hologram recording / reproducing apparatuses when a red laser and a blue laser are arranged in different packages. 11 differs from FIG. 1 in that a servo light source 68, a grating 61, a collimating lens 65, and a beam splitter 67 are provided, and there are no other differences.

  Similarly, the hologram recording / reproducing apparatus 3 and the hologram recording / reproducing optical apparatus (optical unit) shown in FIG. 12 are hologram recording / reproducing apparatuses when the red laser and the blue laser are arranged in different packages. 12 differs from FIG. 1 in that a movable mirror unit 116 having a servo light source 168, a grating 161, a collimating lens 165, a beam splitter 170, a condenser lens 171, a cylindrical lens 172, a servo photodetector 173, and a movable mirror 116a. There are no other differences. Further, the present invention is not limited to this, and various modifications can be made to the embodiment. For example, the reflection type ferroelectric liquid crystal may be DMD (Digital Mirror Device). Further, instead of the movable mirror unit 16, an element such as an acoustic polarization diffraction element (AOD) or an electro-optic beam scanner (EOD) may be used.

  In the embodiment described above, the hologram recording medium has been described as having a disk shape. However, the hologram recording medium of other shapes is not limited to the shape of the hologram recording medium, and all the embodiments described above are modified. It is possible to apply. For example, in a disk-shaped hologram recording medium, a hologram is formed in a desired area by rotational movement, and recorded data is reproduced from a hologram formed in the desired area, whereas the hologram recording medium is a rectangular card. In some cases, for example, the relative motion between the light beam and the hologram recording medium in two orthogonal directions is controlled to form a hologram in a desired area, and the recorded data is reproduced from the hologram formed in the desired area. It can be possible.

  The present invention is not limited to the embodiment described above. That is, the present invention can be implemented with various modifications within the scope of the technical idea of the present invention as well as the above-described modification regarding the shape of the hologram recording medium.

It is a schematic diagram centering on the optical part of a hologram recording / reproducing apparatus. It is a figure which shows an objective lens unit. It is a figure which shows the mechanism part which rotates a hologram recording medium, and the mechanism part which performs focus servo. It is a figure which shows the reference light area | region and signal light area | region of a spatial modulator. It is a schematic diagram which shows the structure of a hologram recording medium. It is a figure which shows typically the effect | action in the case of changing the incident angle with respect to the optical axis of the objective lens of reference light and signal light. It is a figure explaining the preformat of a hologram recording medium. It is a figure which shows the structure of the photodetector for servos. It is a figure which shows the speed profile of a spindle motor or a movable mirror. It is a figure explaining another preformat of a hologram recording medium. It is a schematic diagram centering on the optical part of another hologram recording / reproducing apparatus. It is a schematic diagram centering on the optical part of another hologram recording / reproducing apparatus.

Explanation of symbols

  1, 2, 3 Hologram recording / reproducing apparatus, 10 Laser light source, 11 Isolator, 12 Shutter, 13, 14, 21, 24, 29, 31, 121, 124 Fourier transform lens, 16a, 116a Movable mirror, 16, 116 Movable mirror Unit, 19 Spatial modulator, 19a Reference light region, 19b Signal light region, 20 Polarizing beam splitter, 22, 122 Pinhole, 26 Wave plate, 27 Polarizing beam splitter, 28 Objective lens, 30, 129 Mirror, 32 Image sensor, 33 Spindle motor, 33a Turntable, 34 Track moving part, 36 Objective lens unit, 48 Hologram recording medium, 48a Protective layer, 48b Recording layer, 48c, 48d Dichroic reflective layer, 48e Gap layer, 48f Aluminum new Reflective layer, 48 g substrate, 55 focus actuator, 56 slide feed motor, 57a, 57b gear, 58 spindle motor base, 60 movable part actuator, 61, 125 grating, 65, 165 collimating lens, 67, 170 beam splitter, 68, 168 Servo light source, 70 Polarizing beam splitter, 71, 171 Condensing lens, 72, 172 Cylindrical lens, 73, 173 Servo photo detector, 100 Control unit

Claims (3)

The hologram recording medium is irradiated with signal light and reference light to record recording data as a hologram, the hologram recorded on the hologram recording medium is irradiated with reference light to obtain diffracted light, and the recorded data is obtained from the diffracted light. In a hologram recording / reproducing apparatus comprising servo means for reproducing,
The servo means includes
A focus servo unit that focuses a light spot on the hologram recording medium;
A tracking servo unit that arranges a light spot in a track direction that is a direction orthogonal to a track formed on a recording surface of the hologram recording medium;
A tangential servo unit that arranges a light spot in a tangential direction that is a direction along a track formed on a recording surface of the hologram recording medium,
The tangential servo unit is
A hologram recording / reproducing apparatus, wherein the hologram recording medium is stopped, the light spot is scanned in a tangential direction, and address information recorded in advance on the hologram recording medium is read.   The tangential servo unit accelerates the light spot at a first predetermined acceleration, maintains the predetermined speed when reaching a predetermined speed, decelerates the light spot at a second predetermined acceleration, and 2. The hologram recording / reproducing apparatus according to claim 1, wherein the light spot is arranged at a desired position indicated by information. The hologram recording medium is irradiated with signal light and reference light to record recording data as a hologram, the hologram recorded on the hologram recording medium is irradiated with reference light to obtain diffracted light, and the recorded data is obtained from the diffracted light. In a hologram recording / reproducing optical device comprising servo means for reproducing,
The servo means includes
A focus servo unit that focuses a light spot on the hologram recording medium;
A tracking servo unit that arranges a light spot in a track direction that is orthogonal to a track formed on the recording surface of the hologram recording medium, and a tangential that is a direction along the track formed on the recording surface of the hologram recording medium A tangential servo unit that arranges a light spot in the direction,
The tangential servo unit is
A hologram recording / reproducing optical apparatus, wherein the hologram recording medium is stopped, the light spot is scanned in a tangential direction, and address information recorded in advance on the hologram recording medium is read.

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