JP4835847B2 - Information recording medium and information recording / reproducing apparatus - Google Patents

Description

  The present invention relates to an information recording medium and an information recording / reproducing apparatus, and more particularly to an information recording medium on which information is recorded by holography, and an information recording / reproducing apparatus for recording and / or reproducing information by a hologram method.

  Conventionally, holographic recording in which information is recorded on an information recording medium using holography is generally performed by superimposing an object beam carrying image information and a recording reference beam inside the information recording medium. This is done by writing a possible interference pattern on the information recording medium. At the time of reproducing information recorded on the information recording medium, image information is reproduced by diffraction by the interference pattern by irradiating the information recording medium with reference light for reproduction (for example, see Patent Document 1).

  In recent years, volume holography, in particular digital volume holography, has been developed in practical use for ultra-high density optical recording and has attracted attention. Volume holography is a holographic recording method in which an interference pattern is three-dimensionally written on an information recording medium by actively utilizing the thickness direction of the information recording medium. Volume holography is characterized in that the diffraction efficiency can be increased by increasing the thickness of the information recording medium, and the recording capacity can be increased by using multiple recording.

  Digital volume holography is a computer-oriented holographic recording method in which image information to be recorded is limited to a binarized digital pattern while using the same information storage medium and recording method as in volume holography.

  In digital volume holography, for example, image information such as an analog picture is once digitized and developed into two-dimensional digital pattern information, which is recorded as image information. At the time of reproduction of digital volume holography, the digital pattern information is read out and decoded, so that the original image information is restored and displayed. As a result, even if the SN ratio (signal-to-noise ratio) is somewhat poor at the time of reproduction, the original information is reproduced very faithfully by performing differential detection or encoding binary data and correcting errors. It becomes possible.

  As a holographic recording method, a method using an optical pickup device using a disk-shaped information recording medium is prominent, as in a CD (Compact Disk), a DVD (Digital Versatile Disk), and the like. The optical pickup device includes an optical system for recording information on the information recording medium and reproducing information from the information recording medium. In general, in an optical disk apparatus, focus servo and tracking servo are performed by making full use of an objective lens in an optical pickup apparatus while rotating a disk-shaped information recording medium.

  In the configuration of the optical pickup device as described above, when the disk-shaped information recording medium is bent or distorted, the incident angle of light applied to the information recording medium from the optical pickup device changes. CDs, DVDs, and the like have a structure that reads the intensity of reflected light from the pits as information, so that even if the incident angle changes, there is no major problem if the pits are irradiated with light.

  However, in the case of holographic recording, the interference pattern between the object beam and the recording reference beam is recorded during recording, and the diffraction between the reproduction reference beam and the interference pattern is reproduced during reproduction. For this reason, in the case of holographic recording, if the object beam and each reference beam are not incident at the same angle during recording and during reproduction, the wavefront with respect to the information recording medium differs during recording and during reproduction, and the SN ratio is high. It was extremely bad. Therefore, when holographic recording is put into practical use, means for correcting the relative inclination between the information recording medium and the optical pickup device is important.

  The conventional optical information recording apparatus translates the light beam of the storage light or the reproduction light incident on the objective lens in accordance with the relative inclination between the storage light or the reproduction light and the storage medium. Control is performed so that light is always incident on the information recording medium at the same angle (see, for example, Patent Document 2). Next, a conventional basic concept for correcting the relative inclination between the recording object light or reproduction reference light and the information recording medium will be described with reference to FIGS.

  FIG. 10 is a diagram showing a state of the light beams 3a to 3e irradiated to the recording layer of the information recording medium 2 by the objective lens 1. FIG. 10 to 13, light rays 3a to 3e are recording light or reproducing light. 12 and 13, the information recording / reproducing apparatus 2 that is not tilted is represented by a dotted line.

  As shown in FIG. 10, the parallel light flux composed of the light beams 3 a to 3 e becomes a convergent light beam when entering the objective lens 1 and converges toward the focal point f in the recording layer of the information recording medium 2. From a different viewpoint of this phenomenon, it can be seen that the light beams 3a to 3e are incident on the recording layer of the information recording medium 2 at different angles. That is, in FIG. 10, light rays 3a and 3b are incident on the recording layer of the information recording medium 2 from the left side, light rays 3c are incident from the front, and light rays 3d and 3e are incident on the right side. Therefore, the incident angle of the light beam incident on the recording layer of the information recording medium 2 can be changed depending on the position of the parallel light beam incident on the objective lens 1.

  FIG. 11 is a diagram showing a case where the information recording medium 2 is not inclined with respect to the objective lens 1 in FIG. As shown in FIG. 11, when the information recording medium 2 is not tilted, a parallel light beam composed of the light beams 3 b to 3 d may be used. That is, the parallel light flux composed of the light beams 3b to 3d may be incident on the recording layer from the front surface of the information recording medium 2, and information may be recorded or reproduced in the irradiation region 2r. In FIG. 11, the light rays 3a and 3e that are not used are represented by dotted lines.

  FIG. 12 is a diagram showing a case where the information recording medium 2 is inclined with respect to the objective lens 1 by an angle θ in FIG. As shown in FIG. 12, when the information recording medium 2 is tilted by the angle θ, a parallel light beam composed of the light beams 3a to 3c may be used. That is, the parallel light flux composed of the light beams 3a to 3c may be incident on the recording layer from the front of the tilted information recording medium 2, and information may be recorded or reproduced in the irradiation region 2s. In FIG. 12, light rays 3d and 3e that are not used are represented by dotted lines.

  FIG. 13 is a diagram showing a case where the information recording medium 2 is inclined with respect to the objective lens 1 by an angle −θ in FIG. 10. As shown in FIG. 13, when the information recording medium 2 is inclined at an angle of −θ, a parallel light beam composed of the light beams 3 c to 3 e may be used. That is, the parallel light flux composed of the light beams 3c to 3e may be incident on the recording layer from the front of the tilted information recording medium 2, and information may be recorded or reproduced in the irradiation region 2t. In FIG. 12, light rays 3a and 3b that are not used are represented by dotted lines.

  As apparent from FIGS. 10 to 13, the incident angles of the light beams 3 a to 3 e incident on the recording layer of the information recording medium 2 correspond to the distance from the center of the objective lens 1. Therefore, when the inclination of the information recording medium 2 is small, the light beam is incident on a position close to the center of the objective lens 1, and when the inclination of the information recording medium 2 is large, the light beam is incident on a position away from the center of the objective lens 1. Just do it. Thereby, the light rays 3 a to 3 e can be irradiated to the recording layer of the information recording medium 2 according to the inclination of the information recording medium 2.

  FIG. 14 is a side view showing a schematic configuration of a conventional optical information recording / reproducing apparatus 20. Referring to FIG. 14, an optical information recording / reproducing apparatus 20 includes a recording / reproducing light source 22, collimator lenses 24 and 32, a polarizing beam splitter 26, a spatial light modulator 28, a servo reading element 30, and a dichroic. A mirror 34, a relay lens 36, a mirror 38, a quarter-wave plate 40, an objective lens 42, and a photodetector 44 are provided.

  The optical information recording / reproducing apparatus 20 corrects the relative inclination between the recording object light or the reproducing object light and the information recording medium 11, records information on the information recording medium 11, and receives information from the information recording medium 11. Reproduce. The information recording medium 11 includes a circular transparent substrate 12, an information recording layer 13, a reflective layer 15, and a substrate 16. An information recording layer 13 is formed on the circular transparent substrate 12. A reflective layer 15 is formed on the information recording layer 13. A substrate 16 is formed on the reflective layer 15.

  The optical information recording / reproducing apparatus 20 includes a mirror 38 that directs the traveling direction of recording light or reproducing light toward the objective lens 42, and a drive device (not shown) that drives the mirror 38. By driving the mirror 38 with this driving device, the beam of recording light or reproducing light incident on the objective lens 42 can be translated. FIG. 14 shows the path of the light bundle when the mirror 38 is moved from the mirror 38h (dotted line).

  Here, in addition to the mirror 38, a half mirror, a 45-degree right angle prism, a pentagonal prism, or the like can be employed as an optical element that directs the traveling direction of the recording light or the reproduction light toward the objective lens 42. In particular, the pentagonal prism emits light with a precise 90-degree bend regardless of the angle at which light enters the effective surface, and the emitted image rotates like a 45-degree right angle prism. It is preferable because it does not reverse or reverse.

  Moreover, as a drive device which drives the mirror 38, a linear motor, a microactuator, etc. can be used suitably, for example. By moving the optical element such as the mirror 38 in the optical axis direction by this driving device, the beam bundle of the recording light or the reproducing light can be translated. In this case, since the movement distance of the optical element directly corresponds to the distance of the parallel movement of the light beam, the control becomes easy.

  As shown in FIG. 14, when the mirror 38 is moved from the position of the mirror 38h (dotted line), the light flux of the recording light or the reproduction light changes so as to enter from the moving direction (left side in FIG. 14). To do. As the moving distance of the mirror 38 increases, the change in the incident angle of the light beam also increases. Therefore, the recording light incident on the objective lens 42 is controlled by controlling the moving distance and moving direction of the optical element such as the mirror 38 according to the relative inclination between the recording light or the reproducing light and the information recording medium 11. Alternatively, the beam bundle of reproduction light can be translated. Thereby, the inclination of the information recording medium 11 can be corrected.

In addition, for example, in Patent Document 2, as a means for translating a beam of recording light or reproducing light incident on an objective lens, a method of driving a flat glass, a method of driving a relay lens, a recording light or A method of driving a reflecting element arranged at a focal position of a relay lens arranged in an optical path of reproduction light is described.
JP 11-311938 A JP 2005-32309 A

  However, in recording / reproduction using a hologram, not only the object light and each reference light are incident on the information recording medium at the same angle during recording but also the wavefronts of the object light and each reference light during recording / reproduction are the same. Otherwise, there is a problem that the SN ratio of the reproduced image is extremely deteriorated. More specifically, there is an effect of a difference in wavefront due to optical system tolerances and aberrations between apparatuses when information is reproduced by a reproducing apparatus different from the recording apparatus.

  SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an information recording medium and an information recording / reproducing apparatus capable of ensuring the commutability of the information recording medium while always keeping the wavefront of the light beam at the time of recording / reproducing information constant. It is.

According to a first aspect of the present invention, there is provided an information recording medium on which information is recorded by a hologram due to interference between an object beam carrying information and a reference beam not carrying information, the interference between the object beam and the reference beam. An information recording area in which information is written, and a hologram format area including a reference light hologram and an object light hologram , in which a standard image serving as a reference for wavefront control at the time of recording and reproduction by object light and reference light is recorded , It includes a hologram preformat area in which information for performing focus servo control and tracking servo control and address information for the information recording area are recorded.

According to a second aspect of the present invention, there is provided an information recording medium on which information is recorded by a hologram due to interference between an object beam carrying information and a reference beam not carrying information, the interference between the object beam and the reference beam. Information recording area in which information is written, and a reference image hologram and object light having a reference image serving as a reference for wavefront control during recording and reproduction using object light and reference light, and having address information for the information recording area A hologram format area including a hologram.

  Preferably, the reference light hologram and the object light hologram are multiplexed and recorded on the information recording medium.

According to the third aspect of the present invention, with respect to the information recording medium of the first aspect or the second aspect of the present invention described above due to interference between the object light carrying information and the reference light not carrying information. An information recording / reproducing apparatus that records and reproduces information , or records or reproduces information, and irradiates the information recording medium with light to record and reproduce information , or record or reproduce information. In a light source unit that performs servo reading operation of an information recording medium, a spatial light modulator that generates object light and reference light by carrying predetermined information in a part of light from the light source unit, and servo reading operation The reference image reproduced from the hologram for reference light and object hologram on the information recording medium is compared with the reproduced image reproduced from the information recording area of the information recording medium. A phase modulation optical element for controlling the wavefronts of the object light and the reference light irradiated on the information recording medium, and the reproduction light generated by the phase modulation optical element according to the comparison result in the processing circuit and the signal processing circuit. A photodetector that receives light and reproduces information recorded on the information recording medium.

Preferably, the light source unit includes a light source used for recording and reproduction of information with respect to the information recording medium , or recording or reproduction , and a servo reading element used for a servo reading operation before recording.

Preferably, servo read element comprises a light source for generating a servo light for reading embossed pits in hologram preformat area of the information recording medium, a light receiving unit that receives the light that came back through the embossed pit from the information recording medium Have

  Preferably, the phase modulation optical element is a liquid crystal element.

  According to the present invention, the wavefront of the light flux at the time of recording / reproducing information can always be kept constant and the commutability of the information recording medium can be secured.

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

[Embodiment 1]
(Structure of information recording medium)
FIG. 1 is a cross-sectional view schematically showing the structure of an information recording medium 100A according to Embodiment 1 of the present invention. Referring to FIG. 1, an information recording medium 100A of Embodiment 1 includes a reference light hologram 101, an object light hologram 102, a recording layer 103, circular transparent substrates 104a and 104b, a reflective layer 105, And a protective layer 106. A reflective layer 105 is formed on the circular transparent substrate 104b. A protective layer 106 is formed on the reflective layer 105. A recording layer 103 is formed on the protective layer 106. On the recording layer 103, a circular transparent substrate 104a is formed.

  That is, the information recording medium 100A has a structure in which the reflective layer 105, the protective layer 106, and the recording layer 103 are sandwiched between the circular transparent substrates 104a and 104b. The information recording medium 100A includes a hologram preformat area 107, a hologram format area 108, and an information recording area 109. The hologram format area 108 includes a reference light hologram 101 and an object light hologram 102.

  FIG. 2 is a top view schematically showing the structure of the information recording medium 100A according to Embodiment 1 of the present invention. Referring to FIG. 2, information recording medium 100 </ b> A has hologram preformat area 107, hologram format area 108, and information recording area 109 formed along track 200. As shown in FIG. 2, the information recording medium 100A has a circular shape, and is provided with a track 200 in a concentric or spiral shape. Note that the information recording medium 100 </ b> A of FIG. 1 is a schematic cross-sectional view along the track 200.

  As shown in FIGS. 1 and 2, a plurality of hologram preformat areas (address / servo areas) 107 are arranged at predetermined angular intervals in the radial direction on the reflective layer 105. A hologram format area 108 and an information recording area 109 are provided between the hologram preformat areas 107 adjacent in the circumferential direction. In the hologram preformat area 107, information for performing focus servo control and tracking servo control and address information for the information recording area 109 are recorded in advance by embossed pits. As information for performing tracking servo control, for example, a wobble pit can be used.

  The recording layer 103 is formed of a hologram recording material whose optical characteristics such as refractive index, dielectric constant, and reflectance change according to the intensity of the laser beam when irradiated with a laser beam for a predetermined time. For the recording layer 103, for example, a photopolymer HRF-600 manufactured by Dupont is used. In the hologram format area 108, two types of holograms, that is, a reference light hologram 101 and an object light hologram 102, are formed in advance when the information recording medium 100A is manufactured.

  The reference light hologram 101 is designed so that a predetermined reproduced image is obtained when the reference light is irradiated during recording and reproduction. The object light hologram 102 is designed so that a predetermined reproduced image can be obtained when irradiated with object light (non-modulated light beam) in a state where no information is carried. That is, the light beam (object light in a state in which no information is carried) applied to the object light hologram 102 of the first embodiment works as reference light in general hologram reproduction.

  As shown in FIG. 1, the reference light hologram 101 and the object light hologram 102 according to the first embodiment are separated from each other with a certain space therebetween. However, the reference light hologram 101 and the object light hologram 102 are not limited to this arrangement, and may be multiplexed, for example. Next, a description will be given of wavefront control of a light beam at the time of recording / reproduction when a reproduced image from the reference beam hologram 101 and the object beam hologram 102 is used as a reference image.

(Configuration and operation of information recording / reproducing apparatus)
3, 4, and 6 are side views showing a schematic configuration of information recording / reproducing apparatus 300 </ b> A according to Embodiment 1 of the present invention. 3, 4, and 6, the information recording / reproducing apparatus 300 </ b> A according to the first embodiment includes a recording / reproducing light source 301, collimator lenses 302 and 317, a polarization beam splitter 303, a spatial light modulator 304, Dichroic mirror 305, relay lenses 306a and 306b, mirror 307, phase modulation optical element 308, quarter wave plate 309, objective lens 310, objective lens actuators 311a and 311b, and photodetector 312, a signal processing circuit 313, a phase modulation optical element driving circuit 314, an actuator driving circuit 315, and a servo reading element 316.

  The information recording / reproducing apparatus 300A records information on the information recording medium 100A described with reference to FIGS. The information recording medium 100A includes a recording layer 103, circular transparent substrates 104a and 104b, and a reflective layer 105. 3, 4, and 6, the information recording medium 100 </ b> A is simply illustrated, and a configuration such as a pit is omitted.

  The recording / reproducing light source 301 generates a coherent linearly polarized light bundle, and for example, a semiconductor laser is used. The recording / reproducing light source 301 is advantageously shorter in wavelength in order to perform high-density recording, and it is preferable to employ a blue laser or a green laser. The collimator lens 302 converts the divergent light beam from the recording / reproducing light source 301 into a substantially parallel light beam. The polarization beam splitter 303 is configured to reflect or transmit linearly polarized light (for example, P-polarized light) generated from the recording / reproducing light source 301 and transmit or reflect linearly polarized light (for example, S-polarized light) perpendicular to the polarized light. Yes.

  The spatial light modulator (information expression means) 304 has a large number of pixels arranged in a lattice pattern, and determines whether or not each pixel rotates the polarization direction of the emitted light by 90 degrees with respect to the polarization direction of the incident light. It can be selected. As the spatial light modulator 304, for example, a reflection type liquid crystal element using the optical rotation of liquid crystal, excluding the polarizing plate on the incident / exit side, can be used. The spatial light modulator 304 constitutes object light generation means, recording reference light generation means, and reproduction reference light generation means.

  FIG. 5 is a schematic diagram showing an example of a specific configuration of the spatial light modulator 304 shown in FIGS. Referring to FIG. 5, a spatial light modulator 304 displays a modulation pattern 501 of information desired to be recorded at the center of the display pattern, and a modulation pattern 502 for generating recording reference light is formed in a ring shape around it. indicate. By displaying the modulation patterns 501 and 502 in this way, predetermined information can be carried on the incident light. Thereby, the object beam and the recording reference beam can be generated simultaneously.

  Returning to FIGS. 3, 4, and 6, the servo reading element 316 reads the embossed pit formed in the hologram preformat area (address / servo area) 107 of the information recording medium 100 </ b> A. The servo reading element 316 has a function of a light source (for example, a semiconductor laser) that generates servo light for reading embossed pits and a light receiving unit that receives light returned from the information recording medium 100A through the embossed pits. As a light source of the servo reading element 316, it is desirable to use a light source (for example, an infrared laser) having a wavelength different from that of the recording / reproducing light source 301 and not affecting the recording layer 103 of the information recording medium 100A.

  The collimator lens 317 makes the servo light from the servo reading element 316 substantially parallel and converges the light returned from the information recording medium 100 on the light receiving portion of the servo reading element 316. The dichroic mirror 305 reflects or transmits light having a wavelength generated from the recording / reproducing light source 301 and transmits or reflects light having a wavelength generated from the servo reading element 316. The relay lenses 306a and 306b are a pair of lens groups, and form an image displayed on the spatial light modulator 304 as a real image again. The mirror 308 directs the traveling direction of the recording light and the reproducing light toward the objective lens 310.

  The phase modulation optical element 308 controls the wavefront of the recording / reproducing light beam. The quarter-wave plate 309 changes the optical path difference of polarized light that vibrates in directions perpendicular to each other by a quarter wavelength. P-polarized light is converted into circularly polarized light by the quarter-wave plate 309. Circularly polarized light is converted to S-polarized light by the quarter-wave plate 309. The objective lens 310 converges the recording light and the reproduction light toward the information recording medium 100A. The recording light and the reproduction light are irradiated to a predetermined position of the information recording medium 100A by the objective lens 310.

  The photodetector 312 receives the reproduction light and reproduces the recorded information. The light detector 312 has a large number of light receiving elements arranged in a lattice pattern, such as a CCD array using a CCD (Charge Coupled Device), a CMOS sensor using a CMOS (Complementary Metal-Oxide-Semiconductor), and the like. Used. The signal processing circuit 313 compares a reference image reproduced from the reference light hologram 101 and the object light hologram 102 with a reproduced image and a reference image from an information recording medium 100A described later. The phase modulation optical element drive circuit 314 receives the signal from the signal processing circuit 313 and drives the phase modulation optical element 308. The actuator drive circuit 315 receives the signal from the signal processing circuit 313 and drives the objective lens actuators 311a and 311b.

<Servo action before starting recording / playback>
Next, with reference to FIG. 3, the servo action before the start of recording / reproduction using the information recording / reproducing apparatus 300A of the first embodiment will be described. The information recording / reproducing apparatus 300A in FIG. 3 shows a light path from a servo light source for reading pits when information is recorded on the information recording medium 100A described in FIGS.

  The servo light emitted from the servo reading element 316 is made substantially parallel light by the collimator lens 317 and reflected by the dichroic mirror 305. The reflected servo light passes through the relay lenses 306a and 306b, is reflected by the mirror 307, and is irradiated onto the information recording medium 100A by the objective lens 310. The servo light reflected by the reflective layer 105 of the information recording medium 100A has emboss pit information, and enters the servo reading element 316 along the same optical path. The light receiving unit of the servo reading element 316 can detect position information of the information recording medium 100A and the like from the received light. In addition, the relative inclination between the recording light or the reproduction light and the information recording medium 100A can be detected by the servo reading.

<Wavefront control method during recording and operation during recording>
Next, with reference to FIG. 4, the wavefront control method during recording using the information recording / reproducing apparatus 300A of Embodiment 1 and the operation during recording will be described. An information recording / reproducing apparatus 300A shown in FIG. 4 shows a path of recording light when information is recorded on the information recording medium 100A described with reference to FIGS.

  The light bundle emitted from the recording / reproducing light source 301 is converted into a substantially parallel light bundle by the collimator lens 302, reflected by the polarization beam splitter 303, and incident on the spatial light modulator 304. The spatial light modulator 304 selects whether or not to rotate the polarization direction by 90 degrees for each pixel, and displays the modulation patterns 501 and 502 described with reference to FIG. Accordingly, predetermined information can be carried on the incident light, and the object light and the recording reference light can be generated simultaneously.

<Control of wavefront performed before starting information recording>
Further, with reference to FIGS. 3 and 4, the wavefront control performed before the start of information recording will be described. The spatial light modulator 304 is, for example, a liquid crystal type spatial light modulator, and in this case, it is easy to control light transmission and blocking.

  First, the spatial light modulator 304 is controlled so that only the recording reference light region is transmitted and the recording object light region is blocked. The ring-shaped correction reference light generated as described above passes through the polarization beam splitter 303 and the dichroic mirror 305, and is reflected by the mirror 307 via the relay lenses 306a and 306b. The correction reference light reflected by the mirror 307 is converted from linearly polarized light to circularly polarized light by the quarter-wave plate 309 and irradiated to the information recording medium 100A by the objective lens 310. In the information recording medium 100A, the correction reference light is applied to the reference light hologram 101 in the information recording medium 100A. When the reference light for correction 101 is irradiated to the reference hologram 101, an image recorded in advance on the reference light hologram 101 is reproduced.

  Subsequently, the spatial light modulator 304 is controlled so that only the area of the recording object light is transmitted and the area of the recording reference light is blocked. The correction object light generated as described above passes through the polarization beam splitter 303 and the dichroic mirror 305, and is reflected by the mirror 307 through the relay lenses 306a and 306b. The correction object light reflected by the mirror 307 is converted from linearly polarized light to circularly polarized light by the quarter-wave plate 309 and irradiated onto the information recording medium 100A by the objective lens 310. In the information recording medium 100A, the object light for correction is applied to the object light hologram 102 in the information recording medium 100A. When the object light for correction 102 is irradiated onto the object hologram 102, an image previously recorded on the object light hologram 102 is reproduced.

<Reconstructed image detection from hologram for reference light>
Next, with reference to FIG. 6, description will be given of detection of a reproduced image from the reference light hologram 101 of the information recording medium 100A using the information recording / reproducing apparatus 300A of the first embodiment. The information recording / reproducing apparatus 300A in FIG. 6 shows the path of the reproduction light when reproducing information from the information recording medium 100A described in FIGS.

  The reproduced image from the reference light hologram 101 on the information recording medium 100A is converted by the quarter-wave plate 309 into linearly polarized light whose polarization plane is perpendicular to the linearly polarized light when the reproducing reference light is incident. Thereafter, the reproduction light is reflected by the mirror 307 and passes through the dichroic mirror 305 through the relay lenses 306a and 306b. The transmitted reproduction light is reflected by the polarization beam splitter 303 and received by the photodetector 312. The signal of the photodetector 312 is sent to the signal processing circuit 313.

  When there is an aberration in the optical system, or when the information recording medium 100A is relatively inclined with respect to the light beam, the reproduced image and the reference image recorded in the reference light hologram are changed due to the difference in wavefront. Correlation appears. The signal processing circuit 313 provides the phase modulation optical element drive circuit 314 and the actuator drive circuit 315 so that there is no correlation between the reference image of the reference light hologram 101 formed in advance in the information recording medium 100 and the reproduced image. Send a signal. The phase modulation optical element drive circuit 314 receives the signal from the signal processing circuit 313 and drives the phase modulation optical element 308. The actuator drive circuit 315 receives the signal from the signal processing circuit 313 and drives the objective lens actuators 311a and 311b.

  By the above driving, the correlation between the standard image and the reproduced image from the reference light hologram 101 can be eliminated in the signal processing circuit 313. In the information recording / reproducing apparatus 300A of Embodiment 1, a liquid crystal element is used as the optical element 308 for phase modulation.

  In the first embodiment of the present invention, an optical system is adopted in which the object light for recording information and the reference light are arranged coaxially. However, this optical system is only an example, and the present invention can be applied to the case where the light from the recording / reproducing light source 301 is divided and information is recorded by interference of two light beams. In this case, the wavefront of the reference light at the time of recording can be kept constant using the same method for the light beams of the object light and the reference light.

  In the above case, the object light is irradiated as a light beam in a state in which no information is carried. That is, the light beam (object light in a state in which no information is carried) applied to the object light hologram 102 of the first embodiment works as reference light in general hologram reproduction.

  As described above, the information recording / reproducing apparatus 300A of the first embodiment receives the reproduced images from the reference light hologram 101 and the object light hologram 102 in the information recording medium 100A and controls the wavefront before starting the information recording. . As a result, an assembly tolerance or the like occurs in the information recording / reproducing apparatus 300A, and even when the information recording / reproducing apparatus 300A has a wavefront difference or when the information recording medium 100A is relatively inclined with respect to the light beam, recording is possible. The wavefront of the reference light with respect to the information recording medium 100A at the time can be kept constant.

  The information recording / reproducing apparatus 300A records the information on the information recording / reproducing apparatus 100A after associating the wavefront at the time of recording with the reference images from the pre-formatted hologram 101 for reference light and the hologram 102 for object light. Do. When recording information, the spatial light modulator 304 generates reference light and object light carrying information, and irradiates the information recording medium 100A along the same optical path as described above. In the information recording medium 100A, the object light and the recording reference light interfere in the recording layer 103, and the interference pattern is recorded.

<Wavefront control method during reproduction and operation during reproduction>
Next, with reference to FIG. 4 again, the wavefront control method during reproduction using the information recording / reproducing apparatus 300A of Embodiment 1 and the operation during reproduction will be described. An information recording / reproducing apparatus 300A shown in FIG. 4 shows a path of reproduction light when information is reproduced from the information recording medium 100A described with reference to FIGS. As described above, the path of the reference light during reproduction is basically the same as that during recording. However, at the time of reproduction, a pattern for generating reproduction reference light is displayed in the modulation pattern displayed on the spatial light modulator 304, and reproduction reference light is generated.

  First, the spatial light modulator 304 is controlled so that only the recording reference light region is transmitted and the recording object light region is blocked. The ring-shaped correction reference light generated as described above passes through the polarization beam splitter 303 and the dichroic mirror 305, and is reflected by the mirror 307 via the relay lenses 306a and 306b. The correction reference light reflected by the mirror 307 is converted from linearly polarized light to circularly polarized light by the quarter-wave plate 309 and irradiated to the information recording medium 100A by the objective lens 310. In the information recording medium 100A, the correction reference light is applied to the reference light hologram 101 in the information recording medium 100A. When the reference light for correction 101 is irradiated to the reference hologram 101, an image recorded in advance on the reference light hologram 101 is reproduced.

  The reproduced image from the reference light hologram 101 on the information recording medium 100A is converted by the quarter-wave plate 309 into linearly polarized light whose polarization plane is perpendicular to the linearly polarized light when the reproducing reference light is incident. Thereafter, the reproduction light is reflected by the mirror 307 and passes through the dichroic mirror 305 through the relay lenses 306a and 306b. The transmitted reproduction light is reflected by the polarization beam splitter 303 and received by the photodetector 312. The signal of the photodetector 312 is sent to the signal processing circuit 313.

  When there is an aberration in the optical system, or when the information recording medium 100A is relatively inclined with respect to the light beam, the reproduced image and the reference image recorded in the reference light hologram are changed due to the difference in wavefront. Correlation appears. Similarly to the recording, the signal processing circuit 313 performs the phase modulation optical element driving circuit 314 so that there is no correlation between the reference image of the reference light hologram 101 formed in advance in the information recording medium 100 and the reproduced image. And sends a signal to the actuator drive circuit 315. The phase modulation optical element drive circuit 314 receives the signal from the signal processing circuit 313 and drives the phase modulation optical element 308. The actuator drive circuit 315 receives the signal from the signal processing circuit 313 and drives the objective lens actuators 311a and 311b.

  As described above, also in the generation of the reference light for reproduction, the wavefront is controlled before information is reproduced from the information recording medium 100A, as in recording. The reference light at the time of reproduction is applied to the reference light hologram 101, and a reproduction image is detected from the reference light hologram 101. As in the recording, the correlation between the reproduced image and the reference image of the reference light hologram 101 is checked, and the wavefront of the reproduction reference light is controlled in the same manner as in the recording.

  In the information recording / reproducing apparatus 300A of Embodiment 1, the reproduction images from the reference light hologram 101 and the object light hologram 102 in the information recording medium 100A are received before the information reproduction is started, and the wavefront is controlled. As a result, an assembly tolerance or the like occurs in the information recording / reproducing apparatus 300A, and even if the information recording / reproducing apparatus 300A has a wavefront difference or the information recording medium 100A is relatively inclined with respect to the light beam, reproduction is possible. The wavefront of the reference light with respect to the information recording medium 100A at the time can be kept constant.

  That is, by associating the reference image of the reference light hologram 101 with the wavefront of the reference light at the time of recording and reproduction, the wavefront at the time of recording and reproduction can be unified and information can be recorded and reproduced. As shown in FIG. 1, the reference light hologram 101 and the object light hologram 102 of the first embodiment are separately provided in the information recording medium 100A. However, the reference beam hologram 101 and the object beam hologram 102 are not limited to this arrangement, and may be multiplexed and recorded, for example.

  By the way, in the embodiments of the present invention, an apparatus for recording information on an information recording medium and / or reproducing information from the information recording medium has been described as an information recording / reproducing apparatus. However, this description is merely an example, and the above information recording / reproducing apparatus may be described separately as an information recording apparatus that records information on an information recording medium and an information reproducing apparatus that reproduces information from the information recording medium. Is possible.

  As described above, the information recording apparatus according to the first embodiment records information on the information recording medium having the preformatted hologram by the interference between the object beam carrying information and the reference beam not carrying information. A holographic information recording apparatus for irradiating a pre-formatted hologram with a light beam, a means for detecting a reconstructed image from the pre-formatted hologram, and an object light and a reference light based on the reconstructed light Means for controlling the wavefront during recording.

  According to Embodiment 1, the information recording apparatus can detect the image recorded on the preformatted hologram in the information recording medium and control the wavefronts of the object light and the reference light at the time of recording. become. In addition, the information recording medium having the pre-formatted hologram is recorded with an image serving as a reference for wavefront control at the time of recording the object light and the reference light, and a reference image for each of the object light and the reference light is reproduced. The wavefront of the light beam can be controlled. Further, since the preformatted hologram is multiplexed and recorded on the information recording medium, the recording area can be widened. Further, it becomes possible to control the wavefronts of the object light and the reference light at the time of recording by using a phase modulation type liquid crystal element.

  Also, the information reproducing apparatus according to Embodiment 1 reproduces information recorded as a hologram on an information recording medium having a preformatted hologram by interference between object light carrying information and reference light not carrying information. A holographic information reproducing apparatus for irradiating a pre-formatted hologram with a light beam, a means for detecting a reconstructed image from the pre-formatted hologram, and an object beam and a reference beam based on the reproduced beam. Means for controlling the wavefront during reproduction.

  According to the first embodiment, the information reproducing apparatus can detect the reference image recorded in the preformatted hologram, and can control the wavefront of the reference light during reproduction. In addition, the information recording medium having the pre-formatted hologram is recorded with a reference image for wavefront control at the time of reproduction of the object light and the reference light, and a reference image for each of the object light and the reference light is reproduced. The wavefront of the light beam can be controlled. Further, since the preformatted hologram is multiplexed and recorded on the information recording medium, the recording area can be widened. Further, it becomes possible to control the wavefront of the reference light during reproduction by using a phase modulation type liquid crystal element.

[Embodiment 2]
(Structure of information recording medium)
FIG. 7 is a cross-sectional view schematically showing the structure of an information recording medium 100B according to Embodiment 2 of the present invention. Referring to FIG. 7, the information recording medium 100B of Embodiment 2 includes a reference light hologram 801, an object light hologram 802, a recording layer 103, circular transparent substrates 104a and 104b, a reflective layer 105, And a protective layer 106. As in Embodiment 1, the information recording medium 100B has a structure in which the reflective layer 105, the protective layer 106, and the recording layer 103 are sandwiched between circular transparent substrates 104a and 104b.

  The information recording medium 100B includes a hologram format area 108 and information recording areas 109a and 109b, but unlike the first embodiment, does not include a hologram preformat area. The hologram format area 108 includes a reference light hologram 801 and an object light hologram 802. In the reference light hologram 801 and the object light hologram 802, holograms are formed in advance so that address information is also reproduced in addition to the reference image for wavefront control.

  FIG. 8 is a top view schematically showing the structure of an information recording medium 100B according to Embodiment 2 of the present invention. Referring to FIG. 8, information recording medium 100 </ b> B has hologram format area 108 and information recording area 109 formed along concentric or spiral track 200. The description of the same part as the information recording medium 100A of Embodiment 1 will not be repeated here.

(Configuration and operation of information recording / reproducing apparatus)
FIG. 9 is a side view showing a schematic configuration of an information recording / reproducing apparatus 300B according to Embodiment 2 of the present invention. Referring to FIG. 9, the information recording / reproducing apparatus 300B according to the second embodiment is different in that the servo reading element 316 and the collimator lens 317 are removed, and the recording / reproducing light source 301 is replaced with a recording / reproducing light source 301B. Different from the information recording / reproducing apparatus 300A of the first embodiment. Therefore, the description of the same parts as those in Embodiment 1 is not repeated here.

<Servo action before starting recording / playback>
With reference to FIG. 9, the servo action before the start of recording / reproduction using information recording / reproducing apparatus 300B of the second embodiment will be described. In the information recording / reproducing apparatus 300B of the second embodiment, light from the recording / reproducing light source 301B is used during servo. That is, the information recording / reproducing apparatus 300B in FIG. 9 shows the light path from the recording / reproducing light source 301B for reading pits when information is recorded on the information recording medium 100B described in FIGS. In addition to the light source used for recording / reproduction, the recording / reproducing light source 301B includes a light source (for example, a semiconductor laser) that generates servo light for reading address information, and light returned from the information recording medium 100B through the hologram format region 108. It has a function with the light-receiving part which receives light.

  In hologram recording, interference fringes are recorded when the sum of the energy densities of the object light and the reference light is higher than a threshold value that induces a change in the refractive index of the recording layer of the information recording medium. Therefore, in the information recording / reproducing apparatus 300B, only the reference light having a light intensity that does not induce a change in the refractive index of the recording layer 103 is used as the light emitted from the recording / reproducing light source 301B during servo.

  The reference light is applied to the reference light hologram 801 of the information recording medium 100B as in the first embodiment. The information recording / reproducing apparatus 300B compares the reproduced image from the reference light hologram 801 with the standard image, and controls the wavefront of the reference light. The reference light hologram 801 according to the second embodiment is designed so that a reference image for wavefront control and address information are reproduced. Therefore, at the same time that the reproduced image is correctly detected, address information is also detected by the light receiving unit of the recording / reproducing light source 301B. The information recording / reproducing apparatus 300B can record and reproduce information in a desired information recording area 109 with a hologram based on the generated address information after controlling the wavefront of the reference light in the same manner as in the first embodiment.

  As shown in FIG. 7, the reference light hologram 801 and the object light hologram 802 of the second embodiment are separately provided in the information recording medium 100B. However, the reference beam hologram 801 and the object beam hologram 802 are not limited to this arrangement, and may be multiplexed and recorded, for example.

  As described above, according to the second embodiment, the information recording apparatus can include address information in a reproduced image from a preformatted hologram. Further, it becomes possible to irradiate the pre-formatted hologram with object light and reference light, and to detect reproduced images for the respective light beams. Further, the wavefronts of the object light and the reference light can be controlled by comparing the standard image of the preformatted hologram with the reproduced image from the preformatted hologram.

  Further, according to the second embodiment, the information reproducing apparatus can include address information in a reproduced image from a preformatted hologram. Further, it becomes possible to detect the reproduced image by irradiating the pre-formatted hologram with the reference light. In addition, it is possible to control the wavefront of the reference light by comparing the reference image of the preformatted hologram with the reproduced image from the preformatted hologram.

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

It is sectional drawing which showed typically the structure of 100 A of information recording media by Embodiment 1 of this invention. 1 is a top view schematically showing the structure of an information recording medium 100A according to Embodiment 1 of the present invention. It is the side view which showed schematic structure of 300 A of information recording / reproducing apparatuses before the recording / reproducing by Embodiment 1 of this invention. It is the side view which showed the schematic structure of 300 A of information recording / reproducing apparatuses at the time of the recording or reproduction | regeneration by Embodiment 1 of this invention. FIG. 7 is a schematic diagram illustrating an example of a specific configuration of the spatial light modulator 304 illustrated in FIGS. It is the side view which showed schematic structure of 300 A of information recording / reproducing apparatuses at the time of the reproduction image detection by Embodiment 1 of this invention. It is sectional drawing which showed typically the structure of the information recording medium 100B by Embodiment 2 of this invention. It is the top view which showed typically the structure of the information recording medium 100B by Embodiment 2 of this invention. It is the side view which showed schematic structure of the information recording / reproducing apparatus 300B by Embodiment 2 of this invention. FIG. 3 is a diagram showing the state of light beams 3a to 3e that are irradiated onto the recording layer of the information recording medium 2 by the objective lens 1; FIG. 11 is a diagram illustrating a case where the information recording medium 2 is not inclined with respect to the objective lens 1 in FIG. 10. FIG. 11 is a diagram showing a case where the information recording medium 2 is inclined by an angle θ with respect to the objective lens 1 in FIG. 10. FIG. 11 is a diagram showing a case where the information recording medium 2 is inclined by an angle −θ with respect to the objective lens 1 in FIG. 10. It is the side view which showed the schematic structure of the conventional optical information recording / reproducing apparatus.

Explanation of symbols

  1, 42, 310 Objective lens, 2, 11, 100A, 100B Information recording medium, 2r, 2s, 2t Irradiation area, 3a-3e rays, 12, 104a, 104b Circular transparent substrate, 13 Information recording layer, 15, 105 Reflection Layer, 16 substrate, 20 optical information recording / reproducing device, 22, 301, 301B light source for recording / reproducing, 24, 32, 302, 317 collimator lens, 26, 303 polarization beam splitter, 28, 304 spatial light modulator, 30 servo reading Element, 34,305 Dichroic mirror, 36,306a, 306b Relay lens, 38,307 Mirror, 40,309 Quarter wave plate, 44,312 Photo detector, 101,801 Reference light hologram, 102,802 Hologram for object light, 103 recording layer, 106 protective layer, 107 Program preformat area, 108 hologram format area, 109, 109a, 109b information recording area, 200 tracks, 300A, 300B information recording / reproducing apparatus, 308 phase modulation optical element, 311a, 311b objective lens actuator, 313 signal processing circuit, 314 Phase modulation optical element drive circuit, 315 Actuator drive circuit, 316 Servo reading element, 501, 502 Modulation pattern.

Claims (7)

An information recording medium on which information is recorded by a hologram due to interference between object light carrying information and reference light not carrying information,
An information recording area in which information is written by interference between the object beam and the reference beam;
A hologram format region including a reference light hologram and an object light hologram , in which a standard image serving as a reference for wavefront control at the time of recording / reproduction with the object light and the reference light is recorded ,
An information recording medium comprising information for performing focus servo control and tracking servo control and a hologram preformat area in which address information for the information recording area is recorded. An information recording medium on which information is recorded by a hologram due to interference between object light carrying information and reference light not carrying information,
An information recording area in which information is written by interference between the object beam and the reference beam;
A reference image hologram having a reference image for wavefront control at the time of recording and reproduction by the object light and the reference light and having address information for the information recording area , and a hologram format area including the object light hologram An information recording medium comprising:   The information recording medium according to claim 1, wherein the reference light hologram and the object light hologram are multiplexed and recorded on the information recording medium. An information recording / reproducing apparatus for recording and reproducing information , or recording or reproducing information on an information recording medium according to claim 1 or 2, due to interference between an object beam carrying information and a reference beam not carrying information. And
A light source unit that records and reproduces information on the information recording medium or records or reproduces the information recording medium by irradiating the information recording medium with light, and performs a servo reading operation of the information recording medium;
A spatial light modulator that generates the object light and the reference light by carrying predetermined information in a part of the light from the light source unit;
With the reference image to be reproduced from the reference light holograms and the object light beam for hologram of the information recording medium in the servo read operation, the signal for comparison and a reproduction image reproduced from the information recording area of the information recording medium A processing circuit;
In accordance with the comparison result in the signal processing circuit, a phase modulation optical element that controls the wavefronts of the object light and the reference light irradiated on the information recording medium;
An information recording / reproducing apparatus comprising: a photodetector that receives reproduction light generated by the phase modulation optical element and reproduces information recorded on the information recording medium. The light source unit is
A light source used for recording and reproduction of information with respect to the information recording medium , or recording or reproduction ; and
The information recording / reproducing apparatus according to claim 4 , further comprising: a servo reading element used for a servo reading operation before recording. The servo reading element is:
A light source for generating the servo light for reading embossed pits in said hologram preformat area of the information recording medium,
The information recording / reproducing apparatus according to claim 5 , further comprising: a light receiving unit configured to receive light returned from the information recording medium through the embossed pits. The information recording / reproducing apparatus according to claim 4 , wherein the phase modulation optical element is a liquid crystal element.

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