JP2005322382A - Hologram recording device and hologram recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hologram recording device and a hologram recording method, which can securely enhance the recording density onto a hologram recording medium by multiplex recording. <P>SOLUTION: The multiplex recording with respect to the depth direction of the hologram recording medium is performed by controlling the distance between a phase modulation element and the hologram recording medium, and the multiplex recording with respect to the direction along the surface of the hologram recording medium is performed by controlling the light convergence point. Because a reference light passes through the phase modulation element, the multiplex recording can be performed without largely varying the distance between the phase modulation element and the hologram recording medium and the light convergence point. The multiplex recording is performed by varying the distance with respect to two (or three) directions, and the recording density can be enhanced by combining the multiplex recording. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hologram recording apparatus that performs recording using a hologram, and a hologram recording method.

  Development of hologram recording devices that record data using holography is in progress.

  In the hologram recording apparatus, two modulated signal lights (data superimposed) and unmodulated reference light are generated from laser light, and these are irradiated to the same place on the hologram recording medium. As a result, the signal light and the reference light interfere on the hologram recording medium, a diffraction grating (hologram) is formed at the irradiation point, and data is recorded on the hologram recording medium.

  By irradiating the recorded hologram recording medium with reference light, diffracted light (reproduced light) is generated from the diffraction grating formed during recording. Since the reproduction light includes data superimposed on the signal light at the time of recording, the recorded signal can be reproduced by receiving this with a light receiving element.

  In order to record a large amount of information on the hologram recording medium, a large number of holograms may be formed on the hologram recording medium. In this case, the hologram is not necessarily formed at different locations on the hologram recording medium, and the hologram can also be formed at the same location (or overlapping region) of the hologram recording medium. This is so-called multiplex recording, and various systems such as an angle multiplex system, a wavelength multiplex system, and a rotation multiplex system have been proposed.

  For example, in the angle multiplexing method, the hologram is formed by changing the incident angle of the reference light at the same location on the hologram recording medium. By using the same reference light as that used during recording during reproduction, it is possible to obtain reproduction light and data corresponding to each of a plurality of holograms formed at the same location.

In addition, development of a hologram recording apparatus that aims to increase the recording capacity by using phase correlation multiplexing, which is a type of multiplex recording, has been underway (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 11-242424

  However, there is a limit to improving the recording density by the multiplexing method. In order to increase the recording density by multiplex recording, it is necessary to reduce the shift amount during recording (the shift amount corresponds to the amount of movement, angle change, wavelength change, etc. according to the multiplex recording method). If this shift amount is reduced, crosstalk is likely to occur between a plurality of recordings, and it is necessary to prevent crosstalk by some means. Further, reducing the shift amount brings difficulty in optical and mechanical design and manufacture.

  In view of the circumstances as described above, an object of the present invention is to provide a hologram recording apparatus and a hologram recording method capable of improving the recording density on a hologram recording medium by multiple recording more reliably.

  A. The hologram recording apparatus according to the present invention includes a laser light source that emits laser light, a light branching element that branches the laser light emitted from the laser light source into signal light and reference light, and a signal branched by the light branching element. A light modulating element for modulating light, a phase modulating element for phase modulating the reference light branched by the light branching element, a signal light modulated by the light modulating element, and a reference light phase-modulated by the phase modulating element An optical system for condensing light at substantially the same location of the hologram recording medium, a condensing position control mechanism for controlling a condensing position in a direction along the surface of the hologram recording medium, the phase modulation element, and the hologram recording medium And a distance control mechanism for controlling the distance between the two.

  Multiple recording in the depth direction of the hologram recording medium is controlled by controlling the distance between the phase modulation element and the hologram recording medium, and multiple recording in the direction along the surface of the hologram recording medium is performed by controlling the focusing position. Yes. Since the reference light passes through the phase modulation element, multiple recording can be performed without greatly changing the distance between the phase modulation element and the hologram recording medium and the light condensing position. Multiple recording can be performed by changing the distance in two (or three) directions, and the recording density can be improved by combining multiple recording.

  (1) Here, the condensing position control mechanism controls the condensing position in the direction along the surface of the hologram recording medium by driving the hologram recording medium, or the optical system and You may have an optical system drive mechanism which controls the condensing position to the direction along the surface of the said hologram recording medium by driving a phase modulation element.

  Multiple recording in the surface direction of the hologram recording medium can be performed by driving any one of the hologram recording medium, the optical system, and the phase modulation element.

  (2) The distance control mechanism drives the hologram recording medium to control the distance between the phase modulation element and the hologram recording medium, or the phase modulation element drives the phase modulation element. You may have an element drive mechanism which controls the distance of an element and the said hologram recording medium.

  Multiple recording in the depth direction of the hologram recording medium can be performed by driving either the hologram recording medium or the phase modulation element.

  (3) The hologram recording apparatus may further include a condensing angle control mechanism that controls an incident angle of the signal light and the reference light to the hologram recording medium.

  In addition to multiplex recording in the surface direction of the hologram recording medium and multiplex recording in the depth direction, angle multiplex recording is possible, and the recording density can be further improved.

  (4) The hologram recording apparatus may further include a rotation control mechanism that controls rotation of the phase modulation element with respect to the hologram recording medium.

  In addition to multiplex recording in the surface direction of the hologram recording medium and multiplex recording in the depth direction, angle multiplex recording is possible, and the recording density can be further improved.

  (5) The laser light source emits a second laser beam having a wavelength different from that of the laser beam, and the hologram recording apparatus branches the second laser beam into a second signal beam and a second reference beam. A second optical branching element, wherein the optical modulation element modulates the second signal light branched by the second optical branching element, and the phase modulation element includes the second light The second reference light branched by the branch element is phase-modulated, and the optical system is phase-modulated by the second signal light modulated by the second light modulation element and the second phase modulation element The second reference light may be condensed in the vicinity of the substantially same location of the hologram recording medium.

  In addition to multiplex recording in the surface direction of the hologram recording medium and multiplex recording in the depth direction, wavelength multiplex recording is possible, and the recording density can be further improved.

  (6) The hologram recording apparatus further includes a light intensity control mechanism that controls the light intensity of the signal light and the reference light collected at the condensing portion according to the accumulated amount of condensing at the condensing portion. Also good.

  The intensity of the recorded hologram can be improved by controlling the light intensity according to the remaining amount of the recording material (for example, a monomer in the case of an organic material).

  B. In the hologram recording method according to the present invention, the signal light modulated by the light modulation element and the reference light phase-modulated by the phase modulation element are condensed at substantially the same location of the hologram recording medium to perform angle multiplex recording. A recording step; a distance changing step for changing a distance between the hologram recording medium and the phase modulation element; a signal light modulated by the light modulation element; and a phase modulation element in which the distance between the hologram recording medium is changed And a second recording step of performing angle multiplex recording by condensing the phase-modulated reference light at the substantially same location of the hologram recording medium.

  By changing the distance between the hologram recording medium and the phase modulation element after the angle multiplex recording, the angle multiplex recording can be performed again, and the recording density can be improved.

  C. In the hologram recording method according to the present invention, the wavelength multiplexing recording is performed by condensing the signal light modulated by the light modulation element and the reference light phase-modulated by the phase modulation element at substantially the same location of the hologram recording medium. A recording step; a distance changing step for changing a distance between the hologram recording medium and the phase modulation element; a signal light modulated by the light modulation element; and a phase modulation element in which the distance between the hologram recording medium is changed And a second recording step of performing wavelength multiplexing recording by condensing the phase-modulated reference light at the substantially same location of the hologram recording medium.

  By changing the distance between the hologram recording medium and the phase modulation element after wavelength multiplex recording, wavelength multiplex recording can be performed again, and the recording density can be improved.

  D. In the hologram recording method according to the present invention, the signal light modulated by the light modulation element and the reference light phase-modulated by the phase modulation element are condensed at substantially the same location of the hologram recording medium to perform rotational multiplex recording. A recording step; a distance changing step for changing a distance between the hologram recording medium and the phase modulation element; a signal light modulated by the light modulation element; and a phase modulation element in which the distance between the hologram recording medium is changed And a second recording step of performing rotational multiplex recording by condensing the phase-modulated reference light at substantially the same location of the hologram recording medium.

  By changing the distance between the hologram recording medium and the phase modulation element after the rotational multiplex recording, the rotational multiplex recording can be performed again, and the recording density can be improved.

  E. In the hologram recording method according to the present invention, the signal light modulated by the light modulation element and the reference light phase-modulated by the phase modulation element are condensed on the hologram recording medium, and the condensing part is along the surface of the hologram recording medium. A first recording step for performing recording by moving in a different direction, a distance changing step for changing a distance between the hologram recording medium and the phase modulation element, a signal light modulated by the light modulation element, and the hologram recording Reference light phase-modulated by a phase modulation element whose distance to the medium is changed is condensed on the hologram recording medium, and recording is performed by moving the condensing part in a direction along the surface of the hologram recording medium. And a recording step.

  By changing the distance between the hologram recording medium and the phase modulation element after the multiple recording in the surface direction of the hologram recording medium, the multiple recording in the hologram recording medium surface direction can be performed again, and the recording density can be improved.

  F. The hologram recording method according to the present invention condenses the signal light modulated by the light modulation element and the reference light phase-modulated by the phase modulation element at a first location of the hologram recording medium, and the hologram recording medium and the A first recording step in which recording is performed by changing a distance from the phase modulation element; and a condensing location of the signal light and the reference light is changed from the first location in the direction along the surface of the hologram recording medium to the second location. A condensing part moving step for moving to a part; and condensing the signal light modulated by the light modulation element and the reference light phase-modulated by the phase modulation element on the second part of the hologram recording medium; and And a second recording step for performing recording by changing a distance between the hologram recording medium and the phase modulation element.

  After multiple recording in the depth direction of the hologram recording medium, the recording density is improved by moving the condensing position in the direction along the surface of the hologram recording medium and performing multiple recording in the depth direction of the hologram recording medium. Can be planned.

  G. In the hologram recording method according to the present invention, first signal recording is performed by condensing the signal light modulated by the light modulation element and the reference light phase-modulated by the phase modulation element on the first region of the hologram recording medium. A condensing region moving step of moving the condensing region of the signal light and the reference light to a second region that partially overlaps the first region, the signal light modulated by the light modulation element, and the And a second recording step for performing recording by condensing the reference light phase-modulated by the phase modulation element in the second region of the hologram recording medium with a stronger intensity than the first recording step. It is characterized by.

  The intensity of the recorded hologram can be improved by controlling the light intensity according to the remaining amount of the recording material (for example, a monomer in the case of an organic material).

  As described above, according to the present invention, it is possible to provide a hologram recording apparatus and a hologram recording method that can more reliably improve the recording density on a hologram recording medium by multiple recording.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram showing an optical unit 100 of a hologram recording apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing a state in which a part of the optical unit 100 is enlarged. In FIG. 2, illustration of a part of the optical element is omitted for easy understanding of the contents.

  As shown in FIGS. 1 and 2, the hologram recording apparatus records and reproduces information on a hologram recording medium 101 and includes an optical unit 100.

  The optical unit 100 includes a recording / reproducing light source 111, a collimating lens 112, a polarization beam splitter 113, a mirror 121, a pinhole 122, a spatial light modulator 123, a mirror 124, a dichroic mirror 125, a concave lens 126, an objective lens 127, and a Faraday element 131. 132, polarization beam splitter 133, imaging element 134, mirror 141, shielding plate 142, phase modulation element 143, servo light source 151, collimator lens 152, grating 153, beam splitter 154, condensing lens 155, cylindrical lens 156, A light receiving element 157 and a servo drive unit 158 are included.

  The hologram recording medium 101 has a protective layer 102, a recording layer 103, a groove 104, and a reflective layer 105, and is a recording medium that records interference fringes due to signal light and reference light.

  The protective layer 102 is a layer for protecting the recording layer 103 from the outside world.

  The recording layer 103 records the interference fringes as a change in refractive index (or transmittance), and any material that changes the refractive index (or transmittance) according to the intensity of light can be used. It can be used regardless of whether it is an organic material or an inorganic material.

As the inorganic material, for example, a photorefractive material whose refractive index changes according to the exposure amount by an electro-optic effect such as lithium niobate (LiNbO ₃ ) can be used.

  As the organic material, for example, a photopolymerization type photopolymer can be used. In the initial state of the photopolymerization type photopolymer, the monomers are uniformly dispersed in the matrix polymer. When this is irradiated with light, the monomer is polymerized at the exposed portion. As the polymer is formed, the monomer moves from the surroundings, and the monomer concentration changes depending on the location.

  As described above, when the refractive index (or transmittance) of the recording layer 103 changes in accordance with the exposure amount, interference fringes caused by interference between the reference light and the signal light are regarded as changes in the refractive index (or transmittance). Recording on the hologram recording medium 101 is possible.

  The hologram recording medium 101 is moved or rotated by a driving unit (not shown), and the image of the spatial light modulator 123 can be recorded as a number of holograms.

  Since the hologram recording medium 101 moves, recording / reproduction on the hologram recording medium 101 is performed along a track formed in the moving direction.

  The groove 104 is provided for performing servo control such as tracking and focusing on the hologram recording medium 101. That is, the groove 104 is formed along the track of the hologram recording medium 101, and the tracking servo and the focus servo are performed by controlling the condensing position and depth of the signal light so as to correspond to the groove 104. .

  The recording / reproducing light source 111 is a laser light source, and for example, a laser diode (LD) having a wavelength of 405 [nm] or an Nd-YAG laser having a wavelength of 532 [nm] can be used.

  The collimating lens 112 is an optical element that converts the laser light emitted from the recording / reproducing light source 111 into parallel light.

  The polarization beam splitter 113 is an optical element that splits the parallel light incident from the collimator lens 112 into signal light and reference light. The polarization beam splitter 113 emits s-wave signal light toward the mirror 121 and p-wave reference light toward the mirror 141.

  The mirrors 121, 124, and 141 are optical elements that reflect incident light and change its direction.

  The pinhole 122 is an optical element that reduces the beam diameter of the signal light.

  The spatial light modulator 123 is an optical element that superimposes data by spatially (in this case, two-dimensionally) modulating signal light. As the spatial light modulator 123, a transmissive liquid crystal element which is a transmissive element can be used. In addition, it is possible to use a reflection type element such as a DMD (Digital micro mirror), a reflection type liquid crystal, or a GLV (Grating Light Value) element for the spatial light modulator.

  The dichroic mirror 125 is an optical element for making light used for recording / reproducing (laser light from the recording / reproducing light source 111) and light used for servo (laser light from the servo light source 151) the same optical path. The dichroic mirror 125 transmits the recording / reproducing light from the recording / reproducing light source 111 in response to the difference in laser light wavelength between the recording / reproducing light source 111 and the servo light source 151, and the servo from the servo light source 151. Reflects light. The surface of the dichroic mirror 125 is subjected to a thin film treatment such that the recording / reproducing light is totally transmitted and the light used for servo is totally reflected.

  The concave lens 126 is a lens for making the convergence of the signal light different from the reference light. Since only the signal light passes through the concave lens 126, the condensing depth of the signal light and the reference light on the hologram recording medium 101 is different.

  The objective lens 127 is an optical element for condensing both the signal light and the reference light on the hologram recording medium 101.

  The Faraday elements 131 and 132 are optical elements for rotating the polarization plane. The polarization plane of the s-polarized light incident on the Faraday element 131 is rotated by 45 °, and is returned to the original s-polarized light by the Faraday element 132.

  The polarization beam splitter 133 is an optical element that reflects the return light (reproduction light) that is transmitted from the Faraday element 131 and reflected by the hologram recording medium 101 and returned from the Faraday element 132. This is realized by a combination of the Faraday elements 131 and 132 and the polarization beam splitter 133.

  The image sensor 134 is an element for inputting an image of reproduction light.

  The shielding plate 142 is an optical element for shielding a part of the reference light so as not to overlap with the signal light.

  The phase modulation element 143 is an optical element for giving the reference light a random phase or a certain phase pattern, and may be called a phase mask. For the phase modulation element 143, a ground glass, a diffuser, or a spatial phase modulator may be used. It is also possible to use a hologram element in which a phase pattern is recorded. Light having a phase pattern is generated by reproduction from the hologram element.

  The servo light source 151 is a light source for performing servo control such as tracking servo and focus servo, and emits laser light having a wavelength different from that of the recording / reproducing light source 111. The servo light source 151 is, for example, a laser diode, and uses, for example, 650 nm having low sensitivity with respect to the hologram recording medium 101 as an oscillation wavelength.

  The collimating lens 152 is an optical element that converts the laser light emitted from the servo light source 151 into parallel light.

  The grating 153 is an optical element for dividing the laser light emitted from the collimator lens 152 into three beams, and is composed of two elements. Laser light is divided for servo control.

  The beam splitter 154 is an optical element that transmits the laser light emitted from the grating 153 and reflects the return light that is reflected from the hologram recording medium 101 and returned.

  The condensing lens 155 is an optical element for condensing the return light from the beam splitter 154 on the light receiving element 157.

  The cylindrical lens 156 is an optical element for converting the beam shape of the laser light emitted from the condensing lens 155 from a circular shape to an elliptic shape.

  The light receiving element 157 is an element, such as a CCD, for receiving return light and outputting a tracking error signal for tracking servo control and a focus error signal for focus servo control.

The servo drive unit 158 is a drive mechanism for driving the objective lens 127 by the tracking error signal and the focus error signal from the light receiving element 157 to perform tracking control and focus control, and includes driving coils 161 and 162.
(Operation of hologram recording device)

Hereinafter, an outline of the operation of the hologram recording apparatus will be described.
A. When recording

  An outline of the operation of the hologram recording apparatus during recording will be described.

  The laser light emitted from the recording / reproducing light source 111 is converted into parallel light by the collimator lens 112 and split by the polarization beam splitter 113 into s-wave signal light and p-wave reference light.

  The signal light is reflected by the mirror 121, has a desired beam diameter by the pinhole 122, and is spatially intensity-modulated by the spatial light modulator 123. The laser light modulated by the spatial light modulator 123 passes through the Faraday element 131, the polarization beam splitter 133, and the Faraday element 132, is reflected by the mirror 124, and passes through the concave lens 126 that adjusts the focal point on the hologram recording medium 101. To do.

  Further, the reference light transmitted through the polarization beam splitter 113 is reflected by the mirror 141, and only the central portion of the beam is blocked by the shielding plate 142 to be formed into a desired beam shape. For this reason, it is not reflected by the mirror 124 and has the same optical path as the signal light.

  The objective lens 127 condenses the signal light and the reference light at substantially the same location on the hologram recording medium 101, so that interference fringes are formed on the hologram recording medium 101. As a result, the information spatially modulated by the spatial light modulator 123 is recorded on the hologram recording medium 101 as a hologram.

A servo signal is output from the light receiving element 157, and the servo drive unit 158 operates based on this servo signal, so that the tracking and focus deviations are eliminated. Details of this will be described later.
B. During playback

  An outline of the operation of the hologram recording apparatus during reproduction will be described.

  During reproduction, the signal light is blocked and only the reference light is incident on the hologram recording medium 101.

  The reference light emitted from the recording / reproducing light source 111 and transmitted through the polarization beam splitter 113 is reflected by the mirror 141, and only the central portion of the beam is blocked by the shielding plate 142. Thereafter, the reference light passes through the dichroic mirror 125 and becomes reference light having a phase pattern similar to that at the time of recording by the phase modulation element 143 and enters the hologram recording medium 101.

  When reference light having the same phase pattern as that at the time of recording enters the hologram recording medium 101, diffracted light (reproduced light) is generated from the hologram recorded on the hologram recording medium 101.

  The generated reproduction light follows an optical path opposite to that of the signal light, passes through the objective lens 127, the concave lens 126, and the dichroic mirror 125, and is reflected by the mirror 124.

The direction of polarization of the reproduction light reflected by the mirror 124 is rotated by the Faraday element 132. As a result, the reproduction light emitted from the Faraday element 132 is reflected by the polarization beam splitter 133 and converted into an electrical signal corresponding to the spatial two-dimensional data in the spatial light modulator 123 by the imaging element 134. The output from the image sensor 134 is binarized by a signal processing unit (not shown) and converted into time-series binarized data.
[Recording of hologram by phase modulation element 143]

  FIG. 3 is a schematic diagram showing a hologram recorded / reproduced by the hologram recording apparatus.

  As shown in FIG. 3, the signal light spatially modulated by the spatial light modulator 123, and the reference light to which a random phase pattern or a phase pattern having a certain regularity is given by the phase modulation element 143 Causes the hologram to be recorded on the hologram recording medium 101. A recorded hologram is reproduced by irradiating the hologram recording medium 101 with reference light having a phase pattern that coincides with that during recording (phase correlation multiplexing method).

  Here, multiple recording can be performed by shifting the hologram recording medium 101 or the phase modulation element 143 in the x direction or the y direction in FIG.

  When the hologram recording medium 101 or the phase modulation element 143 is shifted in the x direction or the y direction in FIG. 3, the phase pattern of the reference light changes and the diffraction efficiency decreases.

  4 and 5 are graphs showing the relationship between the shift amount in the x direction and the y direction and the diffraction efficiency.

  As shown in FIGS. 4 and 5, it can be seen that the diffraction efficiency becomes almost zero with a shift of several μm. Since the signal is not reproduced by a shift of several μm in the x direction or the y direction, if recording is performed with such a shift amount of pitch at the time of recording, the hologram is not diffracted from the adjacent recorded hologram. For this reason, it becomes possible to record several holograms at close locations.

  Multiple recording can also be performed by shifting the hologram recording medium 101 or the phase modulation element 143 in the z direction (the depth direction of the hologram recording medium 101) in FIG. Also at this time, the phase efficiency of the reference light changes, so that the diffraction efficiency decreases.

  FIG. 6 is a graph showing the relationship between the shift amount in the z direction (layer direction (depth direction)) and diffraction efficiency.

  As shown in the figure, the diffraction efficiency becomes almost zero with a shift amount of about 100 μm. Therefore, by shifting the phase modulation element 143 and the hologram recording medium 101 by about 100 μm, it is possible to multiplex-record a hologram even by shifting the layer direction (depth direction) of the hologram recording medium 101.

  Note that the relationship between the shift amount in the x, y, and z directions and the change in diffraction efficiency depends on the phase modulation element 143. The graphs of FIGS. 4 to 6 are experimental examples using a holographic diffuser as the phase modulation element 143.

  As described above, the hologram is formed on the hologram recording medium 101 by the interference between the reference light and the signal light on the hologram recording medium 101. At this time, the following can be used as the reference light and the signal light.

  As the reference light, one that forms either a real image or a Fourier image of the phase modulation element 143 on the hologram recording medium 101 can be used. Further, as the reference light, reference light in the Fresnel region that does not form a clear image on the hologram recording medium 101 can also be used.

  As the signal light, one that forms either a real image or a Fourier image of the spatial light modulator 123 on the surface of the hologram recording medium 101 can be used. Further, as the signal light, one that forms an image that is slightly defocused from the real image or Fourier image of the spatial light modulator 123 can be used.

  Data can be recorded by forming a hologram on the hologram recording medium 101 by appropriately combining the imaging states of such reference light and signal light.

  A recording order when information is recorded on the hologram recording medium 101 by shifting in the x, y, and z directions will be described. Here, a case where a card-type hologram recording medium 101 is assumed and a case where a disk-type hologram recording medium 101 is assumed will be described.

The following (1) to (3) are listed as the order of recording.
(1) Shift in the x and y directions with the card-type hologram recording medium 101 (in the case of the disk-type hologram recording medium 101, shift in the direction along the track) Make a record. Thereafter, the shift is made in the z direction (depth direction), and recording is performed on the entire surface of the hologram recording medium 101. Further, the recording is performed on the entire surface of the hologram recording medium 101 by shifting in the z direction (depth direction). These operations are repeated until the dynamic range (total recording capacity) of the hologram recording medium 101 is used up.
(2) After recording a certain range of area on the hologram recording medium 101, the area is shifted in the z direction (depth direction) and recorded in the same area again. After using up the dynamic range of the area, recording is performed in the next area in the same manner.
(3) Multiplexing in the z direction (depth direction) is performed first at one place, and then shifting in the x direction or y direction is performed again in the z direction (depth direction).

  The method (1) can be easily applied as a read-only recording medium (ROM) that the user does not plan to record. In addition, since the method (2) can be post-processed for each area, it can be easily applied to a write-once recording medium. The method (3) makes it easy to increase the density of one hologram recording medium 101 without wasting the dynamic range.

  When multiple holograms are recorded, the remaining amount of recording material (polymer in the case of organic materials) decreases as it is recorded later. For this reason, it is preferable to use a scheduling recording method in which the diffraction efficiency from each hologram is made constant by gradually increasing the recording energy when recording in the same place.

  At this time, various multiplex recording schedule methods can be considered by performing the shift in the x, y, and z directions in any order. Even when recording is performed at a constant energy, the diffraction efficiency from each hologram varies depending on the amount of recording material remaining when recording.

  As a basic scheduling method, there is a method of adjusting the recording energy in accordance with the amount of the recording material that is not exposed to the hologram recording area. As a specific example, FIG. 7 shows a case where the shift pitch is ¼ of the hologram size (diameter r).

  As shown in FIG. 7, four areas where holograms are recorded overlap. For this reason, the recording material in the area where the hologram is recorded decreases as the time shifts from the time of recording the first hologram to the time of recording the second, third, and fourth holograms. For this reason, it is preferable to increase the recording energy (light quantity) according to the number of times of recording. However, when the fourth and subsequent holograms are recorded, the remaining amount of the recording material in the area where the hologram is recorded is substantially constant, so that the recording may be performed with substantially the same energy as that for the fourth hologram recording.

  In the disk-type hologram recording medium 101, the first track can be recorded with the same energy, but when writing with the track pitch narrowed on the second round, it is necessary to perform schedule recording according to the remaining amount of the recording material. There is. Further, when recording in the layer direction, basically the recording is performed at the same location, and the recording by the above recording method is performed again with the recording energy corresponding to the remaining amount of the recording material not exposed in the first layer recording. This is the same when the number of times of recording in the layer direction is further increased.

  In the recording method (1), as described above, the recording energy is gradually increased in accordance with the track number (M / #) of the hologram recording medium 101 at the track writing start portion (unrecorded portion of the hologram recording medium 101). The recording energy is made uniform after the used portion of the hologram recording medium 101 becomes uniform. Further, when performing multiplex recording in the z direction (layer direction), recording is performed in accordance with the multiplicity of holograms written in the same place on the first layer. For example, if the multiplicity of the hologram written in the first layer is 100, the schedule recording for the second layer starts from the one corresponding to the 101st time, and the third layer starts from the schedule recording corresponding to the 201st time. It is to start.

  As the schedule recording corresponding to the recording order of the above (2), recording is performed on the area to be recorded using the same schedule recording method as in (1).

  Also in the recording method of (3) above, schedule recording in the z direction (layer direction) is first performed, and recording with energy corresponding to the amount of monomer remaining in the x and y direction (plane direction) shift is also performed. Do. In addition, when performing multiplex recording in the z direction (layer direction), recording from the surface of the hologram recording medium 101 to the inside, recording from the inside to the surface, and the like can be considered.

  Also, this multiple recording in the z direction (depth direction) can be used in combination with various other multiplexing methods.

  For example, it can be combined with angle multiplexing. Hologram multiplex recording is performed while changing the angle of the two incident lights with the signal light and the reference light in one recording area. Thereafter, the hologram recording medium 101 or the phase modulation element 143 is shifted in the depth direction (z direction), and multiple recording is performed while changing the angle of the incident light again. Multiple recording by shifting in the depth direction is possible until the dynamic range of the hologram recording medium 101 is exhausted.

  When only the angle multiplexing method is used, if the multiplicity is to be increased in one recording area, the angle pitch must be limited to the limit, or the range in which the angle can be changed must be widened. In the former, crosstalk between horizontal angle components becomes a problem by narrowing the angle shift pitch. In the latter case, it is conceivable that the diffraction efficiency changes due to the difference in angle components, making recording difficult, and mounting the angle adjusting mechanism difficult.

  On the other hand, by combining the multiplexing method in the z direction (depth direction) and the angle multiplexing method, a sufficient recording density can be obtained without giving a margin to the angle shift width and further taking a wide angle change range. Can be obtained.

  The same advantage can be considered when this method is combined with the wavelength multiplexing method or the rotation multiplexing method. With respect to the wavelength multiplexing method, it is possible to give a margin to the wavelength shift width as compared with the case where the wavelength multiplexing method is used alone. With respect to rotational multiplexing, it is possible to provide a margin for the angle shift to be rotated. As a result, the recording density can be increased.

  As described above, the recording density can be improved by combining the multiplexing method in the z direction (depth direction) with other multiplexing methods.

  For example, by combining with a multiplexing method in the x direction or y direction, the recording density is increased by multiplexing several to several tens in the z direction (depth direction) without reducing the shift pitch in the surface direction so much. be able to. For this reason, a certain amount of margin can be given to the shift pitch in the surface direction.

  In order to reduce the crosstalk by the multiplexing method in the surface direction, it is conceivable to use the phase modulation element 143 having a fine phase pattern. In this case, it is necessary to increase the alignment accuracy of the optical system. By shifting the hologram recording medium 101 or the phase modulation element 143 in the depth direction (z direction), the recording density can be increased by multiplex recording in the depth direction. Therefore, even with the phase modulation element 143 having a rough phase pattern, the recording density can be increased. It is possible to improve.

It is a schematic diagram showing the optical unit of the hologram recording device which concerns on one Embodiment of this invention. It is a schematic diagram showing the state which expanded a part of optical unit. It is a schematic diagram showing the hologram recorded and reproduced | regenerated by the hologram recording apparatus. It is a graph showing the relationship between the shift amount in the x direction and the diffraction efficiency. It is a graph showing the relationship between the shift amount in the y direction and the diffraction efficiency. It is a graph showing the relationship between the shift amount in the z direction and the diffraction efficiency. It is a schematic diagram showing an example of the state in which the area | region which records a hologram has mutually overlapped on the hologram recording medium.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Optical unit 101 Hologram recording medium 102 Protective layer 103 Recording layer 104 Groove 105 Reflection layer 111 Recording / reproducing light source 112 Collimating lens 113 Polarizing beam splitter 121 Mirror 122 Pinhole 123 Spatial light modulator 124 Mirror 125 Dichroic mirror 126 Concave lens 127 Objective lens 131 Faraday element 132, 133 Polarizing beam splitter 134 Imaging element 141 Mirror 142 Shielding plate 143 Phase modulation element 151 Light source 152 for servo Collimating lens 153 Grating 154 Beam splitter 155 Condensing lens 156 Cylindrical lens 157 Light receiving element 158 Servo drive unit 161 162 coil

Claims (14)

A laser light source for emitting laser light;
A light branching element for branching the laser light emitted from the laser light source into signal light and reference light;
An optical modulation element that modulates the signal light branched by the optical branching element;
A phase modulation element that phase-modulates the reference light branched by the light branching element;
An optical system that focuses the signal light modulated by the light modulation element and the reference light phase-modulated by the phase modulation element at substantially the same location of the hologram recording medium;
A condensing position control mechanism for controlling a condensing position in a direction along the surface of the hologram recording medium;
A distance control mechanism for controlling the distance between the phase modulation element and the hologram recording medium;
A holographic recording apparatus comprising: The said condensing position control mechanism has a medium drive mechanism which controls the condensing position to the direction along the surface of the said hologram recording medium by driving the said hologram recording medium. Hologram recording device. The said condensing position control mechanism has an optical system drive mechanism which controls the condensing position to the direction along the surface of the said hologram recording medium by driving the said optical system and a phase modulation element. Item 2. A hologram recording apparatus according to Item 1. The hologram recording apparatus according to claim 1, wherein the distance control mechanism includes a medium driving mechanism that controls a distance between the phase modulation element and the hologram recording medium by driving the hologram recording medium. The hologram recording apparatus according to claim 1, wherein the distance control mechanism includes an element driving mechanism that controls a distance between the phase modulation element and the hologram recording medium by driving the phase modulation element. A condensing angle control mechanism for controlling an incident angle of the signal light and the reference light to the hologram recording medium;
The hologram recording apparatus according to claim 1, further comprising: A rotation control mechanism for controlling rotation of the phase modulation element with respect to the hologram recording medium;
The hologram recording apparatus according to claim 1, further comprising: The laser light source emits a second laser beam having a wavelength different from that of the laser beam;
The hologram recording apparatus further comprises a second optical branching element that splits the second laser light into a second signal light and a second reference light,
The light modulation element modulates the second signal light branched by the second light branching element;
The phase modulation element phase-modulates the second reference light branched by the second light branching element;
The optical system receives the second signal light modulated by the second light modulation element and the second reference light phase-modulated by the second phase modulation element at the substantially same location of the hologram recording medium. Condensing in the vicinity,
2. The hologram recording apparatus according to claim 1, wherein: A light intensity control mechanism for controlling the light intensity of the signal light and the reference light collected at the condensing portion according to the accumulated amount of condensing at the condensing portion;
The hologram recording apparatus according to claim 1, further comprising: A first recording step of performing angle multiplexing recording by condensing the signal light modulated by the light modulation element and the reference light phase-modulated by the phase modulation element at substantially the same location of the hologram recording medium;
A distance changing step for changing a distance between the hologram recording medium and the phase modulation element;
Angle multiplexing recording is performed by condensing the signal light modulated by the light modulation element and the reference light phase-modulated by the phase modulation element whose distance from the hologram recording medium is changed at the substantially same location of the hologram recording medium. A second recording step to be performed;
A hologram recording method comprising: A first recording step of performing wavelength multiplexing recording by condensing the signal light modulated by the light modulation element and the reference light phase-modulated by the phase modulation element at substantially the same location of the hologram recording medium;
A distance changing step for changing a distance between the hologram recording medium and the phase modulation element;
Wavelength multiplexing recording is performed by condensing the signal light modulated by the light modulation element and the reference light phase-modulated by the phase modulation element whose distance from the hologram recording medium is changed at the substantially same location of the hologram recording medium. A second recording step to be performed;
A hologram recording method comprising: A first recording step of performing rotational multiplex recording by condensing the signal light modulated by the light modulation element and the reference light phase-modulated by the phase modulation element at substantially the same location of the hologram recording medium;
A distance changing step for changing a distance between the hologram recording medium and the phase modulation element;
Rotational multiplex recording is performed by condensing the signal light modulated by the light modulation element and the reference light phase-modulated by the phase modulation element whose distance from the hologram recording medium is changed at substantially the same location of the hologram recording medium. A second recording step to be performed;
A hologram recording method comprising: Recording is performed by condensing the signal light modulated by the light modulation element and the reference light phase-modulated by the phase modulation element onto the hologram recording medium, and moving the condensing part in a direction along the surface of the hologram recording medium. A first recording step;
A distance changing step for changing a distance between the hologram recording medium and the phase modulation element;
The signal light modulated by the light modulation element and the reference light phase-modulated by the phase modulation element whose distance from the hologram recording medium is changed are condensed on the hologram recording medium, and the condensing part is A second recording step for recording by moving in a direction along the surface;
A hologram recording method comprising: The signal light modulated by the light modulation element and the reference light phase-modulated by the phase modulation element are condensed on the first location of the hologram recording medium, and the distance between the hologram recording medium and the phase modulation element is changed. A first recording step for performing recording,
A condensing part moving step of moving the condensing part of the signal light and the reference light from the first part in the direction along the surface of the hologram recording medium to the second part;
The signal light modulated by the light modulation element and the reference light phase-modulated by the phase modulation element are condensed on the second location of the hologram recording medium, and the hologram recording medium and the phase modulation element A second recording step for recording by changing the distance;
A hologram recording method comprising:

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