JP5017957B2 - Hologram recording / reproducing apparatus and hologram recording / reproducing method - Google Patents

Description

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

  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 onto the hologram recording medium to interfere the signal light and the reference light 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. One hologram recorded here contains a very large amount of information. This one hologram is called one page, and the recording 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. Reproduction light (diffracted light) is generated by irradiating the hologram formed according to the above-described recording data with predetermined reference light. Since this reproduction light includes recording data for one page, the reproduction light can be received by a two-dimensionally arranged light receiving element and subjected to signal processing to reproduce the recording data.

  The generation of the signal light and the reference light and the reception of the reproduction light described above are performed by an 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 this time, if there is an undesired amount of deviation from a predetermined position where the hologram is to be formed, the characteristics of recording / reproduction (recording or reproduction and recording and reproduction) deteriorate. It is necessary to strictly manage the relative position between the light beam from the optical unit used for the recording and the hologram recording medium.

The techniques for managing the relative position between the light beam and the hologram recording medium are roughly classified into the following three techniques. The first technique fixes the position of the light beam from the optical unit, stops after moving the hologram recording medium, forms a hologram by irradiating the light beam, and moves the hologram recording medium again. This is a so-called stop-and-go method in which the process of stopping and repeating the hologram formation is repeated. The second technique includes a follow-up period in which the movement of the light beam from the optical unit and the movement of the hologram recording medium are both performed, and the movement of both is controlled to cause the light beam to follow a specific region in the hologram recording medium. The so-called asking method (see Patent Document 2) is provided. The third technique is a so-called angle multiplexing method that stops the movement of the hologram recording medium and changes the hologram forming area by changing the incident angle of the reference light. The fourth technique is a technique in which a hologram is formed by irradiating a light beam in a pulsed manner for a very short time such that the hologram recording medium cannot be regarded as moving while moving the hologram recording medium. In addition to the third technique, any of the above-described four systems is a technique suitable for multiplexing, and can be applied to both recording and reproduction.
Japanese Patent Laid-Open No. 11-242424 Japanese Patent No. 3639212 Nikkei Electronics January 17, 2005 issue P106-114

  Of the three techniques for managing the relative position between the light beam and the hologram recording area shown in the background art, the third technique is exclusively adopted by the two-beam method, and the fourth technique is required for a laser light source. The light output exceeds that of an actual laser light source. In a recording / reproducing apparatus having an optical unit adopting a coaxial method, the first technique and the second technique are exclusively used. However, when the first technique is employed, the time for setting the relative position becomes long, resulting in a problem that the time required for recording and reproduction becomes long. Further, in the second technique, the movement of the light beam and the hologram recording medium must be performed in synchronization, the control mechanism and control technique are complicated, and the price of the apparatus is also expensive. It was.

  The present invention solves such a problem in a recording / reproducing apparatus having an optical unit adopting a coaxial method, and has a simple mechanism and enables a high-speed recording / reproducing apparatus and a simple recording / reproducing apparatus. It aims to provide a method.

  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 reproduction light. Then, in the hologram recording / reproducing apparatus for reproducing the recording data from the reproduction light, a laser light source for emitting a light beam, and spatially modulating the light beam to generate reference light and signal light arranged coaxially A spatial modulator, an objective lens for condensing the reference light and the signal light on the hologram recording medium, and incidence of the reference light and the signal light incident on the objective lens with respect to the optical axis of the objective lens A movable mirror that changes the angle, and the rotation angle of the movable mirror is different when the movement of the hologram recording medium is stopped. Each time a fixed angle is set, a plurality of holograms corresponding to the recording data are recorded on the hologram recording medium, and the hologram is recorded each time the movable mirror is rotated at different predetermined angles. The recorded data is reproduced from each of the above.

  In this hologram recording / reproducing apparatus, the laser light source emits a light beam. The spatial modulator performs spatial modulation on the light beam to generate reference light and signal light that are arranged coaxially. The objective lens focuses the reference light and the signal light on the hologram recording medium. The movable mirror changes the incident angle of the reference light and the signal light incident on the objective lens with respect to the optical axis of the objective lens. Then, in a state where the movement of the hologram recording medium is stopped, a plurality of holograms corresponding to the recording data are recorded on the hologram recording medium every time the rotation angle of the movable mirror is different from each other. Recorded data is reproduced from each of the plurality of recorded holograms each time the rotation angle is set to a different predetermined angle.

In the hologram recording / reproducing method of the present invention, recording data is recorded as a hologram by irradiating the hologram recording medium with signal light and reference light, and reproducing light is obtained by irradiating the hologram recorded on the hologram recording medium with reference light. Then, in the hologram recording / reproducing method for reproducing the recording data from the reproduction light, a light beam is emitted from a laser light source, the light beam is spatially modulated, and the reference light and the signal light are arranged coaxially. The reference light and the signal each time the hologram recording medium stops moving and the reference light incident on the objective lens and the signal light have different incident angles with respect to the optical axis of the objective lens. A plurality of holograms corresponding to the recording data are recorded on the hologram recording medium by condensing light on the hologram recording medium, and the objective The recorded data is reproduced from each of the plurality of holograms recorded on the hologram recording medium every time the reference light and the signal light incident on the lens are incident on the optical axis of the objective lens at different angles. To do.

  In this hologram recording / reproducing method, a light beam is emitted from a laser light source, spatial modulation is applied to the light beam, and the reference light and the signal light are arranged coaxially. Each time the movement of the hologram recording medium is stopped and the incident angles of the reference light and the signal light incident on the objective lens with respect to the optical axis of the objective lens are changed to different predetermined angles, the reference light and the signal light are transmitted to the hologram recording medium. A plurality of holograms corresponding to the recording data are recorded on the hologram recording medium. Each time the incident angle of the reference light and signal light incident on the objective lens with respect to the optical axis of the objective lens is changed to different predetermined angles, the recorded data is reproduced from each of the plurality of holograms recorded on the hologram recording medium.

  According to the present invention, in a recording / reproducing apparatus having an optical unit adopting a coaxial method, a hologram recording / reproducing apparatus that enables high-speed recording / reproducing while having a simple mechanism is provided, and a simple recording / reproducing method is provided. Can be provided.

  Hereinafter, embodiments of the present invention 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 an optical unit as a main part of the apparatus as a center.

  The hologram recording medium 48 has a disk shape (disc shape) similar to a CD (compact disk) or a DVD (digital versatile disk). And a hole for positioning the center of rotation.

  A hologram recording / reproducing apparatus 1 that performs recording / reproducing on such a hologram recording medium includes the optical unit illustrated in FIG. 1 as a main component. Moreover, the control part 50 comprised with the electric circuit which is not shown in detail is provided, Furthermore, all are provided with the mechanism part which is not shown in figure. The hologram recording / reproducing apparatus 1 is connected to an external device (not shown) via the control unit 50. Here, the external device is, for example, a computer CPU (Central Processing Unit) or a video display device (monitor). When the external device is a CPU, connection with the CPU is made via a bus line.

  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 mirror 18, a spatial modulator 19, a polarization beam splitter 20, a Fourier transform lens 21, a pinhole 22, A Fourier transform lens 24, a quarter wavelength plate 26, an objective lens 28, a Fourier transform lens 29, a mirror 30, a Fourier transform lens 31, and an image sensor 32 are provided.

  Here, the Fourier transform lens 24, the quarter-wave plate 26, and the objective lens unit 36 are moved integrally in the horizontal direction (radial direction) of the paper surface as a movable portion 34. The movable portion 34 is moved by using a slide feed motor 37 which is a part of the mechanism portion. The objective lens unit 36 includes an objective lens 28, a rising mirror (not shown), and an objective lens actuator (not shown) as a mechanism unit. The objective lens actuator is configured to move the objective lens 28 in a direction perpendicular to the paper surface (focus direction). Further, the movable mirror 16a is provided in the movable mirror unit 16, and a movable mirror actuator 16b constituting a mechanism unit transmits a light beam that passes through the objective lens 28 and is applied to the hologram recording medium 48 in a vertical direction (tanger). (In the local direction).

  The laser light source 10 is an external resonator type laser (for example, the resonance wavelength is in the range of 405 nm (nanometer) ± 3 nm) that can change the wavelength of the laser beam. The isolator 11 is for preventing return light from returning to the laser light source 10 configured as an external resonator type laser and stabilizing the oscillation of the laser light source 10. The shutter 12 is an element for transmitting or blocking the light beam, and whether the light beam is transmitted or blocked is controlled by a signal from the control unit 50. The Fourier transform lens 13 and the Fourier transform lens 14 are for expanding the diameter of the light beam and irradiating the entire surface of the spatial modulator 19 with the light beam. The movable mirror 16a is displaced by the movable mirror actuator 16b and scans the light beam in the tangential direction as described above. The mirror 18 changes the direction of the light beam and irradiates the spatial light modulator 19 with the light beam. The spatial modulator 19 is for obtaining a reference light and a signal light by applying a spatial modulation to the light beam. For example, a DMD (digital mirror device) is adopted. The polarization beam splitter 20 transmits reference light and signal light and reflects reproduction light.

  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, and is used to shield higher-order diffracted light. The quarter wavelength plate is for converting linearly polarized light into circularly polarized light. The objective lens 28 is for condensing the light beam on the hologram forming area of the hologram recording medium 48. The Fourier transform lens 29 and the Fourier transform lens 31 are used to form a real image with an adjusted magnification on the image sensor 32. The mirror 30 is for guiding the light beam to the image sensor 32 by changing the direction of the light beam. The image sensor 32 is an optical light receiving element typified by a CMOS sensor (Seamos sensor), a CCD (Charge Coupled Device), etc., and a plurality of finely divided light receiving elements are two-dimensionally arranged. The electric signals from the respective light receiving elements can be detected separately.

  Further, the hologram recording / reproducing apparatus has the above-described slide feed motor 37 for moving the entire movable portion 34 in the radial direction and the spindle motor 33 for rotating the hologram recording medium 48. The rotation axis of the spindle motor 33 is fixed to a turntable (not shown), and a hole (see reference numeral 48a in FIGS. 4 and 7) arranged at the center of the hologram recording medium 48 is positioned on the turntable, thereby recording the hologram. Medium 48 is rotated.

  The recording operation in the hologram recording / reproducing apparatus 1 using the optical unit described above will be described below, and then the reproducing operation will be described.

  When recording is performed, the laser light source 10 emits a light beam having a predetermined intensity. If the light beam passes through the isolator 11 and the control unit 50 is set so that the shutter 12 transmits the light beam, the light beam further passes through the shutter 12. The diameter of the light beam is expanded by the Fourier transform lens 13 and the Fourier transform lens 14. Then, the light beam is reflected by the movable mirror 16 a, further reflected by the mirror 18, and irradiated on the spatial modulator 19. Here, the incident angle of the movable mirror 16a with respect to the light beam is set by the control unit 50, and the incident angle of the light beam incident on the spatial modulator 19 is changed according to the change of the incident angle. Finally, the incident angles of the reference light and the signal light incident on the objective lens 28 with respect to the optical axis of the objective lens 28 are changed. The effect obtained by changing the incident angle of the light beam incident on the spatial modulator 19 will be described later in detail.

  The light beam incident on the spatial modulator 19 undergoes spatial modulation. The spatial modulator 19 is composed of DMD. The angle of each of the two-dimensionally arranged micromirrors constituting the DMD is controlled by the control unit 50, and an angle that reflects the light beam in the direction of the polarization beam splitter 20 ("1" angle), and the light beam One of the angles corresponding to the two states is maintained such that the angle is not reflected in the direction of the polarization beam splitter 20 ("0" angle). The micromirrors are classified into two groups: micromirrors belonging to the reference light region 19a (see FIG. 2) and micromirrors belonging to the signal light region 19b (see FIG. 2). Each of the micromirrors belonging to the reference light area 19a is a predetermined reference expressed by a combination of “1” and “0” stored in a storage area of the control unit 50, for example, a RAM (Random Access Memory). Depending on the light pattern, the angle “1” is maintained at the “1” angle, and the angle “0” is maintained at the “0” angle.

  Similarly, each of the mirrors belonging to the signal light region 19b is set to “1” according to the recording data in units of pages expressed by a combination of “1” and “0” output from the control unit 50. In this case, the angle is maintained at the “1” angle, and when it is “0”, the angle is maintained at the “0” angle. Here, the recording data is encoded as modulation recording data which is a block code. For example, one block of the modulation recording data is associated with the area of 16 micromirrors in 4 rows and 4 columns, A 16: 3 code is used in which three of the sixteen have a “1” angle.

  FIG. 2 is a diagram showing the angle state of each micromirror of the spatial modulator 19, where the color portion of the paper surface (hereinafter referred to as a white portion) in FIG. 2 is the “1” angle, and the black color portion (hereinafter referred to as the white portion). (Referred to as a black portion) corresponds to the “0” angle. The donut-shaped portion of the outer peripheral portion shown in FIG. 2 is the reference light region 19a, and the circular region inside thereof is the signal light region 19b. In the signal light region 19b, the “1” angle and the “0” angle of the micromirror are maintained according to the recording data pattern as shown by polygons. Here, it is sufficient that the spatial modulator 19 has an area including the reference light region 19a and the signal light region 19b, and the outside of the donut-shaped reference light region 19a is not required.

  In this way, the light beam in which the reference light that has undergone spatial modulation in the reference light region 19a of the spatial modulator 19 and the signal light that has undergone spatial modulation in the signal light region 19b are arranged coaxially is a polarization beam splitter. 20 passes through the Fourier transform lens 21, the pinhole 22, and the Fourier transform lens 24, and higher-order diffracted light is removed. Further, after the light beam passes through the quarter-wave plate 26, the traveling direction of the light beam directed in the horizontal direction of the paper surface is changed from the back surface direction of the paper surface to the front surface direction of the paper surface by a rising mirror (not shown). Is done. Then, each of the reference light and the signal light is collected by the objective lens 28 on the recording layer which is a hologram forming region of the hologram recording medium 48, and the reference light and the signal light interfere with each other to generate interference fringes. Then, for example, in a hologram forming region 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.

  Here, in order to focus the light beam on the hologram forming area of the hologram recording medium 48, a focus servo is used, which will be described later. Further, the technique related to the procedure for recording holograms in page units is a main part of the embodiment, and will be described later in detail.

  The operation of the optical unit when performing reproduction will be described below. 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 region 19a of the spatial modulator 19, the "1" angle and the "0" angle of the micromirror are maintained at the same angle as when recording is performed. That is, as will be described later, the same reference light used for recording is also used for reproduction. On the other hand, in the signal light region 19b, all the micromirrors have a “0” angle. That is, 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) in the recording layer of the hologram recording medium 48 as in the case of recording. Irradiated.

  The reproduction light is generated by irradiating the hologram-formed region with the reference light, and the reproduction light reflected by the reflection film disposed on the hologram recording medium 48 returns to the objective lens 28 side again. Here, the reflection film of the hologram recording medium 48 is disposed on the side farther from the objective lens 28 than the recording layer on which the hologram is formed, and the reproduction light generated in the recording layer can be returned to the objective lens 28. It is said that.

  The reproduction light passes through the objective lens 28 and then passes through the quarter wavelength plate, and the polarization direction is converted from circularly polarized light to linearly polarized light. Then, the reproduction light passes through the Fourier transform lens 24, the pinhole 22, and the Fourier transform lens 21 and reaches the polarization beam splitter 20. At this time, the polarization direction of the reproduction light converted to the linearly polarized light is shifted by π / 2 with respect to the polarization direction of the reference light. For this reason, the reproduction light cannot pass through the polarization beam splitter 20, is reflected by the polarization beam splitter 20, changes the traveling direction, and passes through the Fourier transform lens 29, the mirror 30, and the Fourier transform lens 31. Thus, an image is formed on the image sensor 32. This image is formed in the same form as displayed on the spatial modulator 19 during recording in FIG. That is, an image corresponding to the reference light component included in the reproduction light is reproduced on the outer peripheral portion, and an image corresponding to the signal light component included in the reproduction light is reproduced on the inner peripheral portion.

  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 required 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.

  The electrical signals from the plurality of light receiving elements arranged in two dimensions, which are detected based on the brightness of the image corresponding to the signal light component included in the reproduction light from the image sensor 32, are taken into the control unit 50, and the bright part is detected. A signal such as “1”, converted to a binary signal having a dark portion “0”, then decoded block data, decoded modulated data for each block, and then decoded ECC. Processing is performed, the recording data is decoded, and the recording data is sent to the external device.

  Next, the function of the movable mirror 16a for changing the incident angle of the light beam incident on the spatial modulator 19 will be described with reference to FIG. In FIG. 3, the optical components that form the optical path from the movable mirror 16 a to the objective lens 28 are omitted except for the spatial modulator 19 in order to show the principle. The movable mirror 16a is rotated so that the position of the condensing point of the light beam on the hologram recording medium 48 moves in the tangential direction. In FIG. 3, the tangential direction is the horizontal direction of the paper. That is, as shown in FIG. 3, when the incident angle θ of the light beam incident on the objective lens 28 is changed with respect to the optical axis by rotating the movable mirror 16a, the condensing point depends on the incident angle θ. Moves in the tangential direction.

  In this way, by rotating the movable mirror 16a, the position of the condensing point of the light beam is moved, for example, every 3 μm (micrometer) while the hologram recording medium 48 is stationary, so that the focal position is reached. A plurality of holograms formed at different positions can be recorded.

  Here, desirable characteristics of the objective lens 28 will be described. In the hologram recording / reproducing apparatus 1 of the embodiment, the spatial modulator 19 and the reflection surface of the hologram recording medium 48 are arranged on the focal planes before and after the objective lens 28. When the incident angle of the light beam with respect to the optical axis of the objective lens 28 is θ, the moving distance of the Fourier image on the reflection surface of the hologram recording medium 48 is expressed by the product of the focal length f of the objective lens 28 and Sinθ. At this time, when the objective lens 28 has a characteristic satisfying the sine condition, the Fourier image is merely moved in the tangential direction, and the fringe and the like are not changed. In the embodiment, it was confirmed that normal recording and reproduction can be performed within a range of ± 70 μm. When the sine condition is not satisfied, normal recording / reproducing characteristics deteriorate. That is, the range of change of the condensing point at which recording and reproduction can be performed becomes small.

  Moreover, the optical part of the hologram recording / reproducing apparatus 1 shown in FIG. 1 has a telecentric characteristic. Since it has telecentric characteristics, the light beam spatially modulated by the spatial modulator 19 can form a real image at the front focal position of the objective lens 28. The optical unit shown in FIG. 1 has an optical path separation distance between the reflection surface of the spatial modulator 19 and the Fourier transform lens 21, an optical path separation distance between the Fourier transform lens 21 and the pinhole 22, and a pinhole 22. The distance between the four optical paths, that is, the distance between the optical paths between the lens and the Fourier transform lens 24 and the distance between the optical paths between the Fourier transform lens 24 and the front focal plane of the objective lens 28 is a telecentric system. Are arranged as follows. The pinhole is used as an aperture.

  Various multiplexing systems in the embodiment will be described. The multiplexing method described below can be used in either recording or reproduction operations. Moreover, it is possible to arbitrarily combine two or more of any multiplexing systems. Hereinafter, these will be described in order.

(Beam position multiplexing)
As described above, shift multiplex recording can be performed by rotating the movable mirror 16a. Such shift multiplexing using the movable mirror 16a is hereinafter referred to as beam position multiplexing. Here, a general term of a recording method in which holograms are multiplexed in the direction of the surface on which the hologram of the hologram recording medium is formed is called a shift multiplex recording method. In addition, performing such recording is referred to as performing shift multiplexing. The term shift multiplexing is also a commonly used term.

  In the present application, when a hologram is recorded at a position where the condensing point is shifted in the range of 2 μm to 3 μm in the tangential direction, the crosstalk between the holograms is a level at which no problem occurs in recording and reproduction. The inventors of this invention (hereinafter abbreviated as the inventors) have found out through experiments. As described above, the inventors have also found that normal recording and reproduction can be performed within a range of ± 70 μm when the characteristics of the optical system including the objective lens 28 satisfy both telecentric and sine conditions. Therefore, in the case of performing shift multiplex recording every 3 μm with a margin, the multiplexable page, which is the number of pages capable of beam position multiplexing by rotating only the movable mirror 16a without moving the hologram recording medium 48. The number N1 is represented by Equation 1.

N1 = 70 (μm) × 2 ÷ 3 (μm)
= 46 ... (Formula 1)

  FIG. 4 schematically shows how a hologram is formed in the hologram formation region 48 b of the hologram recording medium 48. In this example, a plurality of holograms are recorded on the hologram forming region 48b so as to overlap each other. More specifically, after the hologram 48b1 is formed, the hologram 48b2 is formed so as to overlap with the hologram 48b3 and the hologram 48b4. That is, beam position multiplex recording is performed in the tangential direction (circumferential direction). In this embodiment, since the characteristics of the objective lens 28 satisfy the sine condition, 46 holograms can be recorded at intervals of 3 μm from the hologram 48b1 to the hologram 48b46 (not shown). In FIG. 4, the adjacent holograms are recorded so as to overlap each other. However, the adjacent holograms may be recorded so as to be separated from each other by a distance that does not overlap each other.

  Here, according to the experiment, the time required to move the movable mirror 16a by 3 μm on the reflection film of the hologram recording medium 48 by rotating the movable mirror 16a was about 3 mSec (millisecond). In order to record the recording data, the reference light area 19a of the spatial modulator 19 configured as a DMD can be made the same even if the recording data for each page changes, but at least the micro area of the signal light area 19b. A “1” angle and a “0” angle must be set for each page of the mirror. The time required for this is smaller than 5 μSec (microseconds) and 3 mSec for multiplexing the beam position of the movable mirror 16a, and the time required to record one page is the time for one page of the movable mirror 16a. The time of movement and the time of irradiating the hologram recording medium with the light beam to form the hologram are almost dominated.

  Here, the time until preparation for recording / reproduction is completed is referred to as preparation time. In this example, a time for setting a micromirror to a “1” angle and a “0” angle for each page is set to 5 μSec and a movable mirror 16a. The preparation time is 3.005 mSec, which is the sum of the time 3 mSec set for beam position multiplexing. Further, the time (laser irradiation time) during which the light beam is irradiated to record the hologram for one page on the hologram recording medium depends on the properties of the recording layer of the hologram recording medium, and is used in the embodiment. In the polymer example, the average was about 1 mSec.

  In reproduction, the laser irradiation time is necessary to obtain reproduction light by irradiating a light beam and obtain an electric signal necessary for reproduction of the hologram from the image sensor 32 irradiated with the reproduction light. This time depends on the characteristics of the image sensor 32 and the hardware and processing procedure for signal processing. In addition to this, in reproduction, in the case of pattern multiplexing, which will be described later, as preparation time before laser irradiation, time for setting the reference light region 19a is required, and after reproduction after laser irradiation. After an electrical signal corresponding to an image formed on the image sensor 32 is detected as a post-reproduction processing time that is a processing time, a predetermined time is required for a block code decoding process, an ECC decoding process, and the like. In the embodiment, the laser irradiation time at the time of reproduction was 0.3 mSec on average.

  Here, the preparation time at the time of recording and reproduction differs depending on which of the multiplexing methods to be described later is employed, or in which order the various multiplexing methods are combined. In addition, when the preparation time for recording is short, the preparation time for reproduction is generally short. On the other hand, the laser irradiation time depends on the characteristics of the medium of the hologram recording medium during recording, and is proportional to the number of pages to be recorded, and is not dependent on the difference in multiplexing method. The irradiation time depends on the performance of the image sensor 32 during reproduction, is proportional to the number of pages to be recorded, and is not dependent on the difference in multiplexing method.

  As described above, in both the recording operation and the reproducing operation, the processing of the recording data for one page is about 3 mSec of the rotation time for one page of the movable mirror 16a. When this time is compared with the recording / reproducing time realized when the technique shown in the background art is employed, the following results are obtained.

  When compared with the stop-and-go method described as the first technology of the background art, the movable mirror 16a having a smaller rotational moment than the hologram recording medium 48 is controlled, so that the recording and reproducing speed is greatly increased. To improve. For example, the time required to move the disc-shaped hologram recording medium 48 having a diameter of 12 cm by 3 μm while fixing the position of the light spot is 200 mSec according to the experimental value.

  In the Asking method described as the second technique of the background art, a movable mirror similar to the movable mirror 16a can be used for moving the light beam (light spot). This is equivalent to the technology of the embodiment. However, in the Asking method, it is necessary to synchronize the amount of rotation of the movable mirror and the amount of movement of the hologram recording medium 48, and the mechanism and circuit for controlling the synchronization are extremely complicated compared to this embodiment. It becomes.

  In comparison with the angle multiplexing method that can be used in the two-beam method described as the third technique of the background art, the mechanism for angle multiplexing is used for angle multiplexing in the two-beam method. Since a movable mirror having substantially the same structure as the above and having substantially the same movable speed can be used, it has a recording / reproducing speed equivalent to that in the angle multiplexing system. In other words, the hologram multiple recording speed, which has been thought to be impossible in the conventional coaxial method, can be realized in the coaxial method by the newly adopted beam position multiplexing method. Is.

  Here, the movable mirror actuator 16b for driving the movable mirror 16a may be one that uses an electromagnetic force constituted by a combination of a coil and a magnet, or one that uses an electrostatic force constituted by a piezo element or the like. The rotation amount of the movable mirror 16a may be controlled by a feed forward method or a feedback method using a position sensor.

  As shown in Expression 1, the value of the multiplexable page number N1 is 46. Therefore, when pages of 46 or less are continuously written, the recording / reproducing speed is high speed that could not be realized by the conventional coaxial method. However, when 46 or more pages are continuously recorded and reproduced, other techniques must be employed in addition to multiplexing in the tangential direction. Here, when a technique for moving the hologram recording medium 48 is added, the recording / reproducing speed is greatly reduced. FIG. 5 shows a hologram recording / reproducing apparatus in which two movable mirrors are arranged in the optical path in order to solve such a problem and further increase the number of multiplexable pages.

  In the hologram recording / reproducing apparatus 2 shown in FIG. 5, the configuration and operation of the optical components denoted by the same reference numerals as those in the hologram recording / reproducing apparatus 1 are the same, and thus the description thereof is omitted. The difference between the hologram recording / reproducing apparatus 2 and the hologram recording / reproducing apparatus 1 is that the hologram recording / reproducing apparatus 2 further includes a movable mirror 17a in addition to the movable mirror 16a. Here, the movable mirror 17a moves the light spot condensed on the hologram recording medium 48 in a radial direction which is a direction orthogonal to the tangential direction.

  With reference to FIG. 6, how a hologram is formed using the hologram recording / reproducing apparatus 2 will be described. FIG. 6 schematically shows how a hologram is formed in the hologram forming region 48 c of the hologram recording medium 48. In this example, a plurality of holograms are recorded in the hologram forming area 48c so as to overlap each other in the two-dimensional direction. Specifically, the hologram 48c1.1, the hologram 48c1.2, the hologram 48c1.3, the hologram 48c1.4, the hologram 48c1.33 (not shown), the hologram 48c2.1, the hologram 48c2.2, and the hologram 48c2.3. , Hologram 48c2.4, hologram 48c2.33 (not shown), hologram 48c3.1, hologram 48c3.2, hologram 48c3.3, hologram 48c3.4, hologram 48c3. Further, 48c3.33 (not shown), and finally, hologram 48c33.1, hologram 48c33.2, hologram 48c33.3, hologram 48c33.4, hologram 48c33.33, and tangential direction and tracking, all not shown. It is formed so as to overlap every 3 μm in any direction. That is, beam position multiplexing is performed in the tangential direction (circumferential direction). In addition, in the radial direction (radial direction), beam position multiplexing is performed with the hologram 48c33.1, the hologram 48c33.2, the hologram 48c33.3, the hologram 48c33.4, and the hologram 48c33.33. The number of holograms that can be superposed is 1089, which is a value obtained by writing 33 and 33. In FIG. 6, the adjacent holograms are recorded so as to overlap each other. However, the adjacent holograms may be recorded so as to be separated from each other by a distance that does not overlap each other.

  Here, it is assumed that 33 can be recorded in each of the tangential direction and the radial direction, and the number is smaller than 46 in the case of recording only in the tangential direction. The reason is that when both the movable mirror 16a and the movable mirror 17a are moved, normal recording and reproduction are performed within a range of ± 70 μm from the position (initial position) where the incident angle θ with respect to the optical axis of the light beam is zero. It depends on what has been confirmed. In other words, when the area to be recorded in a quadrangle is a quadrangle, the distance between the four corner positions of the quadrangle and the initial position is an allowable range up to 70 μm, so the hologram recording medium 48 is not moved. When the movable mirror 16a and the movable mirror 17a are rotated to multiplex holograms in the quadrangular area, the number of pages that can be multiplexed N2, which is the number of pages that can be multiplexed in the beam position, is expressed by Equation 2.

N2 = [{(70 (μm) × 2) √2} / 3 (μm)] ²
= 1089 (Equation 2)

  Equation 2 calculates the number of holograms that can be recorded in a square having a diagonal length of 140 μm. However, when the hologram forming area is not a quadrangle but a circle, that is, the hologram recording medium 48 is moved. If the movable mirror 16a and the movable mirror 17a are rotated and the hologram is multiplexed in a circular area under the same recording / reproducing conditions, the number of pages that can be multiplexed N3 is the number of pages that can be multiplexed in the beam position. This is shown in FIG.

N3 = 1089 × π / 2
= 1710 (Equation 3)

  Here, it is possible to arbitrarily select how the light beam is scanned by rotating the movable mirror 16a and the movable mirror 17a. For example, after the light spot on the hologram recording medium 48 is scanned in the tangential direction by the movable mirror 16a, the light spot is shifted by 3 μm in the radial direction by the movable mirror 17a, and the light spot is scanned again in the tangential direction. A hologram may be formed in the region. After the light spot on the hologram recording medium 48 is scanned in the radial direction by the movable mirror 17a, the light spot is shifted by 3 μm in the tangential direction by the movable mirror 16a, and the light spot is again formed. A hologram may be formed in the entire region by repeating scanning in the radial direction, or the entire region may be scanned at random.

  Here, when the hologram forming area is a quadrangular shape, the maximum movement range of the light spot on the hologram recording medium 48 is 99 μm (140 (μm) √2). On the other hand, when the hologram forming area is circular, the amount of movement in the tangential direction changes according to the amount of displacement of the light spot on the hologram recording medium 48 from the initial position in the radial direction. That is, at the initial position in the radial direction, the maximum movement range of the light spot in the tangential direction is 140 μm. As the position in the radial direction deviates from the initial position, the maximum movement range of the light spot in the tangential direction decreases. When the position in the radial direction deviates 140 μm from the initial position, the maximum light spot in the tangential direction The movement range of is zero. Such control of the maximum movement range is performed by the control unit 50. The displacement amount in the tangential direction with respect to the displacement amount in the tracking direction is stored as a storage table in the control unit 50, and the control unit 50 controls the movable mirror 16a and the movable mirror 17a with reference to this storage table.

  According to the hologram recording / reproducing apparatus 2, compared with the hologram recording / reproducing apparatus 1, the number of holograms that can be multiplexed can be greatly increased. In both the recording operation and the reproduction operation, the preparation time, which is the time required to prepare for recording / reproduction for one page, is dominated by the rotation time of the movable mirror 16a, and is about 3 mSec. . In actual recording / reproduction, the recording time is the time obtained by adding the laser irradiation time in recording and reproduction and the post-reproduction processing time in reproduction as described above.

(Pattern multiplexing)
Another hologram multiplexing method that does not move the hologram recording medium 48 will be described. In the reference light region 19a shown in FIG. 2, the recording data is correctly reproduced from the reproducing light so that the setting at the time of reproducing the “1” angle and the “0” angle of the micromirror is the same as the setting at the time of recording. It is a condition for. That is, the reference light at the time of recording is the same as the reference light at the time of reproduction. Here, if the setting of the micromirror is partially different between the recording time and the reproducing time, the reproduction characteristics of the recorded data will be deteriorated depending on the degree of the difference, and the micro light in the reference light area 19a at the time of recording will be deteriorated. When there is no shared portion of the spatial position where the “1” angle of the mirror and the “1” angle of the micromirror in the reference light region 19a at the time of reproduction are arranged, the recorded data is reproduced from the recorded hologram Can not be. Here, the case where the mutual forms of the plurality of reference light regions 19a do not have a common “1” angle at all such spatially identical positions is referred to as “reference light region is uncorrelated”. .

  When a plurality of holograms are formed in the same region using each of the aspects of the plurality of reference light areas 19a in which the reference light areas 19a are uncorrelated with each other, depending on the reference light area 19a of one specific aspect, The recorded data cannot be reproduced from a hologram other than the hologram recorded using the reference light region 19a of the one specific mode. In other words, holograms can be multiplexed and recorded in the same area as many as the number of reference light areas 19a that can be uncorrelated with each other. In the embodiment, the number of two-dimensional divisions of the reference light region 19a is 5010. As an example in this case, nine types of reference light regions 19a that are uncorrelated with each other can be selected. In such a case, even if the hologram is multiplexed and recorded nine times in the same area, the recorded data for 9 pages can be reproduced if the reproduction is performed while changing the aspect of the reference beam area 19a. This type of multiplexing is called pattern multiplexing.

  When DMD was used as the spatial modulator 19, according to the experiment, the time (preparation time) for switching the aspect of the reference light region 19a was 5 μSec. Also, since the laser irradiation time for one page is about 1 mSec on average, a recording speed of 1.005 mSec per page can be obtained when using pattern multiplexing. In the case of reproduction, since the laser irradiation time is about 0.3 mSec, a reproduction speed of about 0.305 mSec per page can be obtained.

(Phase correlation multiplexing)
Instead of changing the aspect of the reference light region 19a, an optical member that changes the phase is arranged in the optical path through which the reference light passes, and by having a plurality of phase aspects, the hologram can be similarly recorded in the same region.

  An example of the optical member having a plurality of phases is a liquid crystal element. A liquid crystal element used in a normal display device or the like has a property that a molecular direction changes in a plane parallel to a substrate and a polarization direction of light passing therethrough changes. Therefore, a light beam is irradiated onto the board surface formed of such a liquid crystal element, and is further transmitted through the polarizing plate, thereby causing brightness and darkness in the pixels of the display device. However, liquid crystal elements used as optical members having a plurality of phases have different properties. For example, when no voltage is applied, the molecular direction is in-plane, and when a voltage is applied, the molecular direction is perpendicular to the surface. Since the liquid crystal molecules have strong birefringence, this change in molecular direction can give a phase change to the light beam.

  Such an optical member has already been widely sold in the market under the name of a programmable phase modulation unit or the like. In such a programmable phase modulation unit, a time of about 10 μSec is sufficient to change the phase mode. Such a programmable phase modulation unit employs a transmission type that transmits a light beam and changes the phase mode, and a reflection type that reflects the light beam and changes the phase mode.

  In the case of using a reflection type programmable phase modulation unit, in FIG. 1, if the reflection type programmable phase modulation unit is disposed in place of the mirror 18 at the same position as the mirror 18 is disposed, the phase modulation is received. The light beam from the programmable phase modulation unit is irradiated onto the spatial modulator 19 and phase correlation multiplexing can be performed. Even in this case, the control unit 50 changes the phase of the programmable phase modulation unit. In the embodiment, there are nine types of phases. Further, in the recording operation, the programmable phase modulation unit has one of the reference light region 19a and the signal light region 19b of the spatial modulator 19, or both the reference light region 19a and the signal light region 19b. By applying phase modulation to the portion of the light beam that irradiates the region, the effect of phase correlation multiplexing can be obtained. In the reproduction operation, the light that irradiates the reference light region 19a of the spatial modulator 19 By applying phase modulation to the beam portion, the effect of phase correlation multiplexing can be obtained.

(Wavelength multiplexing)
Multiple recording can also be performed by performing recording and reproduction by changing the wavelength of the laser from the laser light source 10. That is, when a plurality of holograms are formed in the same region by changing the wavelength of the laser, the recorded data is reproduced only from the holograms recorded using the wavelengths. For this purpose, the light beam from the laser light source 10 must be capable of changing the wavelength. The laser light source 10 will be described below.

  A laser light source 10 according to the embodiment will be described with reference to FIG. The laser light source 10 includes a multi-mode laser diode 111, a collimating lens 112, a grating 113, a mirror 114, and a wavelength detection detector 115 as optical members. The mirror 114 and the grating 113 are fixed, and are rotatable about a rotation axis 127 in the direction indicated by an arrow in the drawing. Here, a line where an extension line of the grating surface 113a and the mirror surface 114a intersects is a rotation axis 127.

  Further, the rotation mechanism includes a gear mechanism 141b, a gear mechanism 141c, and a motor 141a. That is, the gear mechanism 141b is fixed to the mirror 114 and the grating 113, and the gear mechanism 141c is arranged so as to mesh with the gear mechanism 141b. The gear mechanism 141c is connected to the rotation shaft of the motor 141a. Accordingly, the mirror 114 and the grating 113 can be rotated around the rotation axis 127 while keeping the angle formed between the grating surface 113a and the mirror surface 114a constant according to the rotation of the motor 141a.

  Moreover, the laser control part 160 for controlling the motor 141a is provided. The laser control unit 160 includes, as hardware, a RAM, a ROM, an interface with an external circuit (for example, an A / D converter (analog / digital converter), a D / A converter (digital / analog converter), and a power amplifier. ) And CPU, and a microcomputer having software stored in the ROM and describing the processing procedure to be processed by the CPU.

  The operation of the laser light source 10 shown in FIG. 7 will be described. The light beam 120 emitted from the laser diode 111 is converted into parallel light by the collimator lens 112, and the light beam 121 converted into parallel light is converted by the grating 113 into primary light that is diffracted light directed in different directions for each wavelength. To emit. The grating 113 diffracts in a different direction for each wavelength. Among these primary lights, there is also primary light returning to the laser diode 111, and primary light in the direction returning to the laser diode 111 is applicable. The wavelength becomes dominant, and the laser diode 111 oscillates at a single mode at that wavelength. Most of the light is reflected as if the grating 113 is a mirror and is emitted as a zero-order light beam 122 and finally as a zero-order light beam 124.

  Changing the angle of the grating 113 with respect to the laser diode 111 can change the wavelength of the laser beam. However, since the emission direction in the 0th-order light direction also changes, a mirror 114 that moves in cooperation with the grating 113 is employed. Yes. The light beam 122 from the grating 113 is also reflected by the mirror 114, so that the direction of the emitted light of the light beam 124 is always constant.

  In order to achieve the purpose of oscillating the laser at a desired frequency, a wavelength detection detector 115, a laser controller 160, a motor 141a, a gear mechanism 141b, and a gear mechanism 141c are arranged. That is, the motor 141a, the gear mechanism 141b, and the gear mechanism 141c function as a rotation mechanism for changing the wavelength of the laser beam, and the wavelength detection detector 115 and the laser control unit 160 have a function of detecting the wavelength of the laser beam. It is what has.

  About 5% of the light beam 122 reflected by the grating 113 passes through the mirror 114 and irradiates the wavelength detection detector 115. At this time, the irradiation position of the light beam 123 on the wavelength detection detector 115 is changed by the rotation of the grating 113 and the mirror 114. The wavelength detection detector 115 is configured as a two-divided detector arranged in a direction that captures the change in the irradiation position.

  And the control part 50 performs the following processes and makes the wavelength of the light beam 124 a desired thing. First, a difference signal which is an electric signal of a difference between electric signals detected from the two detectors 115a and 115b is detected. Next, the difference signal is converted into the wavelength of the laser light with reference to a conversion table stored in a predetermined area of the RAM. Next, an error wavelength, which is a wavelength error between the desired wavelength of the light beam and the current wavelength of the light beam 123 referenced from the conversion table, is calculated. Next, the error wavelength is multiplied by a gain and frequency correction is performed to optimize the control system. This optimization of the control system is a common technique. Further, after the digital signal is converted into an analog signal by the D / A converter, power amplification is performed and a motor drive signal Smd is output to the motor 141a.

  In this way, feedback is configured, and the motor 141a is controlled so that the error wavelength becomes zero. As a result, the positions of the grating 113 and the mirror 114 are controlled so as to always emit a desired wavelength. Here, the rotational moment when the grating 113 and the mirror 114 are rotated can be reduced as the grating 113 and the mirror 114 are reduced in size, and is much smaller than the rotational moment of the hologram recording medium 48, for example, 3 mSec. The wavelength of the laser can be changed in a certain amount of time.

  According to the result of the experiment, when the thickness of the recording layer of the hologram recording medium 48 is set to 0.6 mm (millimeter), the wavelength of the light beam from the laser light source 10 is changed in the range of 6 nm and multiplexed five times. Was possible.

(Example of multiplexing combinations)
The number of pages that can be recorded / reproduced can be increased by combining two or more of the above-described beam position multiplexing, pattern multiplexing, phase multiplexing, and wavelength multiplexing to obtain a synergistic multiplexing effect. In this case, in order to increase the recording / reproducing speed, it is desirable to combine the recording / reproducing speeds in descending order. In the following, description will be given with examples tried in the experiment.

(Combination of pattern multiplexing and unidirectional beam position multiplexing)
Multiple pattern recording is performed nine times in the same pattern multiple area. Since the required time was 5 μSec per page, it was about 45 μSec, and 9 pages were recorded.
The position of the light spot is shifted by 3 μm by the beam position multiple movable mirror 16a and recording is performed 46 times. The time for shifting by 3 μm was 3 mSec.
The number of pages recorded in this case is 414 pages, and the preparation time for recording is
It is 3.045 (mSec) x 46 = 140.07 (mSec).
If the laser irradiation time necessary for forming the hologram by irradiating the light beam to the hologram medium is added to this, the laser irradiation time per page is approximately 1 mSec, so the preparation time for recording and the laser irradiation time The recording time expressed as the sum of
140.07 + 414 = 554.07 (mSec).

On the other hand, the recording time when the processing order of pattern multiplexing and beam position multiplexing is switched, beam position multiplexing is performed first, and pattern multiplexing is performed later is shown below.
If pattern multiplexing is set while shifting the position for beam position multiplexing, the time for pattern multiplexing does not need to be added, so the preparation time for recording is
(3 (mSec) × 46) × 9 = 1242 (mSec)
If the laser irradiation time necessary for forming the hologram by irradiating the light beam to the hologram medium is added to this, the laser irradiation time per page is approximately 1 mSec, so the preparation time for recording and the laser irradiation time The recording time expressed as the sum of
1242 + 414 = 1656 (mSec).
Here, the preparation time for beam position multiplexing recording is greater than the preparation time for pattern multiplexing recording, and the pattern multiplexing process with a shorter preparation time for recording is performed before the beam position multiplexing process. It turns out that the time required for recording becomes shorter.

(Combination of pattern multiplexing and two-way beam position multiplexing)
Multiple pattern recording is performed nine times in the same pattern multiple area. Since the required time was 5 μSec per page, it was about 45 μSec, and 9 pages were recorded.
The position of the light spot is shifted by 3 μm by the beam position multiple movable mirror 16a and the movable mirror 17a and recorded 1089 times. The time for shifting by 3 μm was 3 mSec.
In this case, the number of recorded pages is 9801, and the preparation time for recording is
It is 3.045 (mSec) * 1089 = 3316.005 (mSec).
If the laser irradiation time necessary for forming the hologram by irradiating the light beam to the hologram medium is added to this, the laser irradiation time per page is approximately 1 mSec, so the preparation time for recording and the laser irradiation time The recording time expressed as the sum of
3316.005 + 9801 = 131117.005 (mSec).

On the other hand, the recording time when the processing order of pattern multiplexing and beam position multiplexing is switched, beam position multiplexing is performed first, and pattern multiplexing is performed later is shown below.
If pattern multiplexing is set while shifting the position for beam position multiplexing, the time for pattern multiplexing does not need to be added, so the preparation time for recording is
3 (mSec) × 1089 × 9 = 29403 (mSec)
If the laser irradiation time necessary for forming the hologram by irradiating the light beam to the hologram medium is added to this, the laser irradiation time per page is approximately 1 mSec, so the preparation time for recording and the laser irradiation time The recording time expressed as the sum of
29403 + 9801 = 39204 (mSec).
Here, preparation time for beam position multiplexing recording> preparation time for pattern multiplexing recording, and even when a combination of two-way beam position multiplexing and pattern multiplexing is employed, the preparation time for recording It can be seen that the time required for recording is shortened when the shorter pattern multiplexing process is performed before the beam position multiplexing process.

(Combination of pattern multiplexing and wavelength multiplexing)
Multiple pattern recording is performed nine times in the same pattern multiple area. Since the required time was 5 μSec per page, it was about 45 μSec, and 9 pages were recorded.
The wavelength-multiplexed laser light source 10 shifts the wavelength of the light beam little by little in the range of 6 nm and records five times. The time for shifting the wavelength once was 3 mSec.
The number of pages recorded in this case is 45 pages, and the preparation time for recording is
3.045 (mSec) × 5 = 15.225 (mSec).
If the laser irradiation time necessary for forming the hologram by irradiating the light beam to the hologram medium is added to this, the laser irradiation time per page is approximately 1 mSec, so the preparation time for recording and the amount of 45 pages The recording time represented by the sum of the laser irradiation time of
15.225 + 45 = 60.225 (mSec).

On the other hand, the recording time when the processing order of pattern multiplexing and wavelength multiplexing is switched is shown below.
If pattern multiplexing is set while shifting the position for wavelength multiplexing, the time for pattern multiplexing does not need to be added, so the preparation time for recording is
3 (mSec) × 45 = 135 (mSec)
If the laser irradiation time necessary for forming the hologram by irradiating the light beam to the hologram medium is added to this, the laser irradiation time per page is approximately 1 mSec, so the preparation time for recording and the amount of 45 pages The recording time represented by the sum of the laser irradiation time of
135 + 45 = 180 (mSec).
Here, the preparation time for wavelength-multiplexed recording is greater than the preparation time for pattern-multiplexed recording, and the pattern multiplexing process with a shorter preparation time for recording is performed before the wavelength-multiplexed process. It can be seen that the time required for recording is shortened.

(Combination of pattern multiplexing, wavelength multiplexing, and one-way beam position multiplexing)
Multiple pattern recording is performed nine times in the same pattern multiple area. Since the required time was 5 μSec per page, it was about 45 μSec, and 9 pages were recorded.
The wavelength-multiplexed laser light source 10 shifts the wavelength of the light beam little by little in the range of 6 nm, and multiplex recording is performed five times. The time for shifting the wavelength once was 3 mSec.
The position of the light spot is shifted by 3 μm by the beam position multiple movable mirror 16a and recording is performed 46 times. The time for shifting by 3 μm was 3 mSec.
In this case, the number of recorded pages is 2070, and the preparation time for recording is
(3 (mSec) +3.045 (mSec) × 5) × 46
= 839.5 (mSec).
If the laser irradiation time necessary for forming the hologram by irradiating the light beam onto the hologram medium is added to this, the laser irradiation time per page is about 1 mSec, so the preparation time for recording and 2070 pages The recording time represented by the sum of the laser irradiation time of
839.5 + 2070 = 29099.5 (mSec).

On the other hand, the recording time when processing proceeds in the order of beam position multiplexing, wavelength multiplexing, and pattern multiplexing is shown below.
If wavelength multiplexing and pattern multiplexing are set while shifting the position for beam position multiplexing, it is not necessary to add the time for wavelength multiplexing and pattern multiplexing, so the preparation time for recording is
3 (mSec) × 9 × 5 × 46 = 6210 (mSec).
If the laser irradiation time necessary for forming the hologram by irradiating the light beam onto the hologram medium is added to this, the laser irradiation time per page is about 1 mSec, so the preparation time for recording and 2070 pages The recording time represented by the sum of the laser irradiation time of
6210 + 2070 = 8280 (mSec).
Here, preparation time for wavelength multiplexing recording = preparation time for beam position multiplexing recording> preparation time for pattern multiplexing recording, and processing for pattern multiplexing with a shorter preparation time for recording is performed. It can be seen that the time required for recording is shorter when processing is performed prior to wavelength multiplexing and beam position multiplexing.

(Combination of pattern multiplexing, wavelength multiplexing, and two-way beam position multiplexing)
Multiple pattern recording is performed nine times in the same pattern multiple area. Since the required time was 5 μSec per page, it was about 45 μSec, and 9 pages were recorded.
The wavelength-multiplexed laser light source 10 shifts the wavelength of the light beam little by little in the range of 6 nm and records five times. The time for shifting the wavelength once was 3 mSec.
The position of the light spot is shifted by 3 μm by the beam position multiple movable mirror 16a and recorded 1089 times. The time for shifting by 3 μm was 3 mSec.
In this case, the number of recorded pages is 49,005 pages, and the preparation time for recording is
(3 (mSec) +3.045 (mSec) × 5) × 1089
= 19847 (mSec).
If the laser irradiation time necessary for forming the hologram by irradiating the light beam to the hologram medium is added to this, the laser irradiation time per page is approximately 1 mSec, so the preparation time for recording and 49005 pages The recording time represented by the sum of the laser irradiation time of
19847 + 49005 = 68852 (mSec).

On the other hand, the recording time when processing proceeds in the order of beam position multiplexing, wavelength multiplexing, and pattern multiplexing is shown below.
If wavelength multiplexing and pattern multiplexing are set while shifting the position for beam position multiplexing, it is not necessary to add the time for wavelength multiplexing and pattern multiplexing, so the preparation time for recording is
3 (mSec) × 1089 × 9 × 5 = 147015 (mSec).
If the laser irradiation time necessary for forming the hologram by irradiating the light beam to the hologram medium is added to this, the laser irradiation time per page is approximately 1 mSec, so the preparation time for recording and 49005 pages The recording time represented by the sum of the laser irradiation time of
147015 + 49005 = 196020 (mSec).
Here, preparation time for wavelength multiplexing recording = preparation time for beam position multiplexing recording> preparation time for pattern multiplexing recording, and processing for pattern multiplexing with a shorter preparation time for recording is performed. It can be seen that the time required for recording is shortened when processing is performed prior to processing of wavelength multiplexing and beam position multiplexing in two directions.

  The above-described example is the preparation time for the case of recording, but the preparation time for the case of reproduction is substantially the same. In all the multiplexing methods described above, it is possible to expand the multiplex recording area by moving the hologram recording medium 48. In this case, for example, the hologram recording medium 48 is moved by 140 μm and moved to the next area. In this case, the recording time can be shortened by setting the initial position of the movable mirror 16a, the initial position of the movable mirror 17a, the initial wavelength of the laser light source 10 and the like while the hologram recording medium 48 is moving.

  The above-described example is only one example. In short, the above-described example is performed by giving priority to a multiplexing method that does not require time. For example, a preparation time for recording of a multiplexing method (beam position multiplexing) in which each of a plurality of holograms is recorded and reproduced each time the movable mirror is rotated, and a reference light region of the spatial modulator are uncorrelated with each other In the case of comparing the preparation time for recording of a multiplexing method (pattern multiplexing) in which each of a plurality of holograms is recorded and reproduced in an overlapping manner every time the change is made, the preparation time for recording is more One of the short processes is performed first. As another example, the preparation time for the recording of the multiple method (beam position multiplexing) in which each of the plurality of holograms is recorded and reproduced each time the movable mirror is rotated, and the wavelength of the light beam from the laser light source. If the preparation time for recording in a multiplexing method (wavelength multiplexing) in which each of a plurality of holograms is recorded and reproduced in a different manner is compared, one process with a shorter preparation time for recording is performed. This is done first. Therefore, if the order that does not take time in the future changes due to technological advancement, the order of which processing should be performed first may be changed. By recording in this order, the recording speed can be increased when recording data of the same capacity.

  Further, in the combination of pattern multiplexing, wavelength multiplexing, and one-way beam position multiplexing, a method of not multiplexing in the radial direction (radial direction) is adopted. This method is advantageous for additional writing because it is easy to irradiate post-processing light only on the recorded portion.

  As shown in the above-described recording results, even during reproduction, the laser irradiation time for irradiation with the light beam and the post-reproduction processing time depend on the number of pages to be reproduced. It does not depend on the order in which they are combined.

  By using any of the above-described beam position multiplexing, pattern multiplexing, phase multiplexing, and wavelength multiplexing, multiple recording and / or multiplexing can be performed at a speed that is not comparable to the stop-and-go method conventionally used in the coaxial method. Playback from the recording area becomes possible. Here, in a normal data storage device, since data is exchanged in units of finely divided files, the burst transfer rate is important. From this point, the amount of recording data that can be accessed at one time is sufficient. is there. However, by arbitrarily combining two or more of the above-described multiplexing techniques, it is possible to record and reproduce a larger amount of recording data.

  Further, in the asking method conventionally employed in the coaxial method, the movement of the movable mirror and the movement of the hologram recording medium 48 must be synchronized, and the mechanism and control thereof are extremely complicated. In the various multiplexing methods, it is not necessary to synchronize with the rotation of the hologram recording medium 48, so that the mechanism can be simplified.

(Other variations)
As a modification of the embodiment, FIG. 8 shows a hologram recording / reproducing apparatus 3 when the spatial light modulator is a ferroelectric liquid crystal 25. Since the difference between the hologram recording / reproducing apparatus 3 and the hologram recording / reproducing apparatus 1 is that the spatial modulator is the ferroelectric liquid crystal 25, the description of the other components is the same as that in the hologram recording / reproducing apparatus 1. A description thereof will be omitted. The time required for switching the light and dark of the ferroelectric liquid crystal 25 is about 100 μs, and the switching time is longer than that of the DMD, but is much shorter than the moving time of the hologram recording medium 48.

(Replenishment explanation of hologram recording medium and servo system)
Although it is obvious to those skilled in the art, in order to make sure, the structure of a general hologram recording medium and a general servo system will be supplementarily described.

  The hologram recording medium 48 has a protective layer, a recording layer, a groove, and a reflective layer in order in the depth direction. The protective layer is a layer for protecting the recording layer, and the recording layer is for holographic recording of interference fringes generated by the reference light and the signal light as a change in refractive index or transmittance. It is formed of an organic material or an inorganic material in which a change in refractive index or transmittance occurs according to the strength of the film. For example, photopolymer is frequently used as a material for the recording layer.

  The hologram recording medium 48 is provided with a groove, and a predetermined track can be accurately traced by this groove. Further, address information for specifying the irradiation position of the light beam of the hologram recording medium 48 is added, and it is general that the address groove by modulating the above-mentioned groove also uses these functions.

  The servo system will be described with reference to FIG. The central portion of the servo system is a servo optical system 150 that partially uses the movable portion 38 as an optical portion for recording and reproduction. The light beam from the servo optical system 150 condenses the reference light and the signal light at a position in the appropriate depth direction of the hologram recording medium 48, and the reference light and the signal in the track direction along the track based on the address groove. A light beam consisting of light is accurately traced. The servo optical system 150 also reads out an address signal indicating a position on the disk. The servo light source 126 is a laser light source similar to the laser light source 10, but emits a light beam having a wavelength different from that of the light beam from the hologram recording / reproducing laser light source 10, for example, a red laser light source is used. Has been. The light beam from the servo light source 126 is reflected by the dichroic mirror 125, collected by the objective lens 28, and irradiated onto the hologram recording medium 48.

  Here, the path of the light beam from the servo light source 126 and the path of the light beam from the laser light source 10 for hologram recording / reproduction have a mutual relationship depending on the arrangement of optical components at the time of designing the optical system. Therefore, if the light beam from the servo light source 126 is positioned with respect to the hologram recording medium 48, the light beam composed of the reference light and the signal light can be positioned with respect to the hologram recording medium 48 as described above. It has been made. Therefore, the positioning in the beam position multiplexing can be performed not only by the feed forward method but also by detecting the return light from the address groove by the servo optical system 150.

  The servo optical system 150 includes a servo light source 126, a grating 127 for dividing the laser light emitted from the servo light source 126 into a plurality of beams, a collimating lens 128 for converting the laser light into parallel light, and a collimating lens 128. A beam splitter 129 that transmits the emitted laser light and reflects the return light that is reflected and returned from the hologram recording medium 48, a condensing lens 130 that condenses the return light from the beam splitter 129, and a condensing lens The cylindrical lens 131 that converts the beam shape from the circular shape to the elliptical shape, the return light from the cylindrical lens 131 is received, a tracking error for tracking servo control, a focus error for focus servo control, and an address signal Each containing It is formed from the servo photodetector 132 which outputs a detector signal comprising a signal.

  The detector signal is calculated by the control unit 50, the signal for focus servo is detected by the stigma method, processed by the control unit 50, and output to the focus actuator arranged in the objective lens unit 36. The light beam is focused on the recording layer of the hologram recording medium 48. The detector signal is calculated by the control unit 50, and the tracking servo signal is detected by the push-pull method and processed by the control unit 50 to control the movable mirror actuator 16b and the slide feed motor 37. The detector signal is calculated by the control unit 50, and a signal for spindle servo is detected from the high frequency component of the push-pull signal and processed by the control unit 50 to control the spindle motor 33.

  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 the hologram recording / reproducing apparatus which concerns on embodiment. It is a figure which shows the reference light area | region and signal light area | region of a spatial modulator. It is a figure explaining the function of a movable mirror. It is a figure which shows typically the hologram formed in a hologram formation area. It is a schematic diagram centering on the optical part of the hologram recording / reproducing apparatus which concerns on embodiment. It is a figure which shows typically the hologram formed in a hologram formation area. It is a figure which shows a laser light source. It is a schematic diagram centering on the optical part of the hologram recording / reproducing apparatus which concerns on embodiment. It is a figure for demonstrating a servo system.

Explanation of symbols

1, 2, 3 Hologram recording / reproducing device, 10 Laser light source, 11 Isolator, 12 Shutter, 13, 14, 21, 24, 29, 31 Fourier transform lens, 16, 17 Movable mirror unit, 16a, 17a Movable mirror, 16b, 17b Movable mirror actuator, 18 mirror, 19 Spatial modulator, 19a Reference light region, 19b Signal light region, 20 Polarizing beam splitter, 22 Pinhole, 25 Ferroelectric liquid crystal, 26 1/4 wavelength plate, 28 Objective lens, 30 Mirror, 32 Image sensor, 33 Spindle motor, 34, 38 Movable part, 36 Objective lens unit, 37 Slide feed motor, 48 Hologram recording medium, 48b, 48c Hologram formation area, 48b1, 48b2, 48b3, 48b4, 48c1.1, 48c1.2, 48 c1.3, 48c1.4, 48c2.1, 48c2.2, 48c2.3, 48c2.4, 48c3.1, 48c3.2, 48c3.3, 48c3.4, hologram, 50 controller, 111 laser diode 112 collimating lens, 113 grating, 113a grating surface, 114 mirror, 114a mirror surface, 115 wavelength detection detector, 115a, 115b detector, 120, 121, 122, 123, 124 light beam, 125 dichroic mirror, 126 light source for servo, 127 Grating, 127 Rotating shaft, 128 Collimating lens, 129 Beam splitter, 130 Condensing lens, 131 Cylindrical lens, 132 Servo photodetector, 141a Motor, 141b Gear mechanism, 141c gear mechanism, 141b gear mechanism, 141c gear mechanism, 150 servo optical system, 160 laser controller

Claims (6)

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 reproduction light, and the recording data is obtained from the reproduction light. In the hologram recording / reproducing apparatus to reproduce,
A spatial modulator that spatially modulates the light beam to generate reference light and signal light arranged coaxially;
An objective lens for condensing the reference light and the signal light on the hologram recording medium;
A movable mirror that changes an incident angle of the reference light and the signal light incident on the objective lens with respect to an optical axis of the objective lens,
In a state where the movement of the hologram recording medium is stopped,
Each time the movable mirror is rotated at different predetermined angles, a plurality of holograms corresponding to the recording data are recorded so that some of the holograms adjacent to different positions of the hologram recording medium overlap each other. ,
A hologram recording / reproducing apparatus that reproduces the recording data from each of the plurality of recorded holograms each time the movable mirror is rotated at different predetermined angles.   The rotation angle of the movable mirror is controlled so that the hologram formed later is superimposed on the previously formed hologram and recorded at the overlapping position, and the reproduction light is obtained from each of the holograms recorded at the overlapping position. The hologram recording / reproducing apparatus according to claim 1.   The hologram recording / reproducing apparatus according to claim 1, wherein the movable mirror is rotated within a range in which the objective lens satisfies a sine condition.   Each time the reference light regions of the spatial modulator for generating the reference light are made uncorrelated with each other, the hologram is recorded at an overlapping position, and the reference light regions of the spatial modulator are uncorrelated with each other. 2. The hologram recording / reproducing apparatus according to claim 1, wherein the recording data is reproduced from each of the overlapped position-recorded holograms for each of the above aspects.   Each time the wavelength of the light beam from the laser light source is changed, the hologram is recorded at the overlapping position, and each time the wavelength of the light beam is changed, the recorded data is reproduced from each of the overlapping recorded holograms. The hologram recording / reproducing apparatus according to claim 1. 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 reproduction light, and the recording data is obtained from the reproduction light. In the hologram recording / reproducing method for reproducing,
A light beam is emitted from a laser light source,
Spatial modulation is performed on the light beam, and the reference light and the signal light are arranged coaxially,
The movement of the hologram recording medium is stopped,
Each time the reference light incident on the objective lens and the signal light are incident on the optical axis of the objective lens at different angles, the reference light and the signal light are condensed on the hologram recording medium and A plurality of holograms corresponding to the recording data are recorded so that some of the holograms adjacent to different positions of the hologram recording medium overlap each other,
The recording data from each of the plurality of holograms recorded on the hologram recording medium each time the reference light incident on the objective lens and the signal light are incident on the optical axis of the objective lens at different angles. Hologram recording / reproducing method for reproducing

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