JP4525308B2 - Hologram recording apparatus, hologram reproducing apparatus, hologram recording method, and hologram reproducing method - Google Patents

Description

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

Development of hologram recording devices that record data using holography is in progress.
In the hologram recording apparatus, two signal lights, which are intensity or phase-modulated (data superimposed) and reference light that is not modulated, 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, holograms are not necessarily formed at different locations on the hologram recording medium, and so-called multiple recording (angle multiplexing) is possible in which a plurality of holograms are formed at the same location (or overlapping region) of the hologram recording medium. .
Here, development of a holographic recording apparatus that increases the storage capacity by using phase correlation multiplexing, which is a type of multiplex recording, is underway (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 11-242424

Here, it is necessary to match the beam condensing positions at the time of recording and at the time of reproduction. For example, a tracking servo is added for positioning the hologram recording medium to the track.
In addition to alignment, it is necessary to match the angle of the reference beam with respect to the hologram recording medium during recording and during reproduction. For example, when a disk type is used as the hologram recording medium, the reference beam may be displaced in the rotational direction during recording and reproduction due to the influence of the eccentricity of the disk. This deviation in the rotational direction causes an error during recording and reproduction of the hologram.
In view of the circumstances as described above, an object of the present invention is to provide a hologram recording device, a hologram reproducing device, a hologram recording method, and a hologram reproducing method capable of matching the reference beam rotation directions during recording and reproduction. It is in.

  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 On the basis of the detection result of the detection mechanism, an optical system for condensing the hologram recording medium at substantially the same location of the hologram recording medium, a detection mechanism for detecting a rotation angle of the phase modulation element with respect to the hologram recording medium, A rotating mechanism for rotating the optical unit used or the hologram recording medium.

  The rotation angle of the phase modulation element with respect to the hologram recording medium is detected, and the optical unit or hologram recording medium using the phase modulation element is rotated based on the detection result. As a result, the rotation angle of the phase modulation element with respect to the hologram recording medium can be controlled, and the phase pattern of the reference light can be made to coincide between recording and reproduction.

(1) Here, the hologram recording medium may be a disk shape or a card shape.
Regardless of whether the hologram recording medium has a disk shape or a card shape, the rotational angle of the phase pattern of the reference light can be shifted.

(2) A second laser light source in which the hologram recording medium has a track for recording and reproduction, and a groove formed along the track, and the detection mechanism emits a second laser beam. A second optical system for irradiating the hologram recording medium with the second laser light emitted from the second laser light source, and a groove of the hologram recording medium emitted from the second optical system. And a light receiving means for receiving the laser light reflected at.
The reflected light from the groove can detect the rotation angle deviation of the reference light with respect to the hologram recording medium, and as a result, the deviation of the rotation angle of the phase pattern can be detected.

Here, the detection mechanism further includes a light splitting element that splits the second laser light emitted from the second laser light source into a plurality of laser lights, and the second optical system includes the light splitting. The plurality of laser beams emitted from the element are applied to the hologram recording medium, and the light receiving means is emitted from the second optical system and reflected by the grooves of the hologram recording medium. There may be a plurality of light receiving elements corresponding to.
By dividing the laser beam, it is possible to more reliably detect a shift in the rotation angle of the phase pattern of the reference beam.
As the means, it is preferable that the light splitting element splits the second laser light so that the plurality of laser lights are arranged so as to be inclined by about half of the groove before and after the center of the groove.
As another means, the light splitting element splits the second laser light so that the plurality of laser lights are arranged to be inclined between the center of the groove and adjacent grooves before and after the center. It may be a thing.

  B. The hologram reproducing apparatus according to the present invention includes a laser light source that emits laser light, a phase modulation element that performs phase modulation using the laser light emitted from the laser light source as reference light, and a reference light that is phase-modulated by the phase modulation element. An optical system that focuses light on the hologram recording medium, a detection mechanism that detects a rotation angle of the phase modulation element relative to the hologram recording medium, and an optical unit that uses the phase modulation element based on the detection result of the detection mechanism, or A rotation mechanism for rotating the hologram recording medium.

  The rotation angle of the phase modulation element with respect to the hologram recording medium is detected, and the optical unit or hologram recording medium using the phase modulation element is rotated based on the detection result. As a result, the rotation angle of the phase modulation element with respect to the hologram recording medium can be controlled, and the phase pattern of the reference light can be made to coincide between recording and reproduction.

  C. The hologram recording method according to the present invention includes a light branching step for branching laser light emitted from a laser light source into signal light and reference light, a light modulation step for modulating the signal light branched in the light branching step, A phase modulation step for phase-modulating the reference light branched in the light branching step with a phase modulation element, the signal light modulated in the light modulation step, and the reference light phase-modulated in the phase modulation step as an abbreviation for a hologram recording medium A condensing step for condensing at the same location, a detection step for detecting a rotation angle of the phase modulation element with respect to the hologram recording medium, and an optical unit using the phase modulation element based on a detection result in the detection step, or A rotation step of rotating the hologram recording medium.

  The rotation angle of the phase modulation element with respect to the hologram recording medium is detected, and the optical unit or hologram recording medium using the phase modulation element is rotated based on the detection result. As a result, the rotation angle of the phase modulation element with respect to the hologram recording medium can be controlled, and the phase pattern of the reference light can be made to coincide between recording and reproduction.

(1) The shape of the hologram recording medium may be a disc shape or a card shape.
Regardless of whether the hologram recording medium has a disk shape or a card shape, the rotational angle of the phase pattern of the reference light can be shifted.

(2) The hologram recording medium has a track for recording and reproduction, and a groove formed along the track, and the detecting step is a second laser emitted from a second laser light source. There may be provided an irradiation step of irradiating the hologram recording medium with light, and a light receiving step of receiving the laser light emitted in the irradiation step and reflected by the groove of the hologram recording medium.
The deviation of the rotation angle of the phase pattern of the reference light can be detected by the reflected light from the groove.

  D. A hologram reproducing method according to the present invention includes a phase modulation step of phase-modulating a phase modulation element using a laser beam emitted from the laser light source as a reference beam, and a reference beam phase-modulated in the phase modulation step as a hologram recording medium. A condensing step for condensing, a detection step for detecting a rotation angle of the phase modulation element with respect to the hologram recording medium, and an optical unit or the hologram recording using the phase modulation element based on a detection result in the detection step And a rotation step for rotating the medium.

  The rotation angle of the phase modulation element with respect to the hologram recording medium is detected, and the optical unit or hologram recording medium using the phase modulation element is rotated based on the detection result. As a result, the rotation angle of the phase modulation element with respect to the hologram recording medium can be controlled, and the phase pattern of the reference light can be made to coincide between recording and reproduction.

  As described above, according to the present invention, it is possible to provide a hologram recording apparatus, a hologram reproducing apparatus, a hologram recording method, and a hologram reproducing method capable of matching the rotation directions of the reference beam during recording and reproduction.

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 device 134, mirror 141, shielding plate 142, phase modulation device 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 (LiNbO3) can be used.
As the organic material, for example, a photopolymerization type photopolymer can be used. In the photopolymerization type photopolymer, in the initial state, 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 concentration of the monomer 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 the recording 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 a 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 five 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 that receives the return light and generates 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 generated from the light receiving element 157 to perform tracking control and focus control, and has 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. Recording 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 recording 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.
Note that the servo drive unit 158 operates based on the servo signal generated from the output signal of the light receiving element 157, thereby eliminating tracking and focus deviation. Details of this will be described later.

B. At the time of reproduction An outline of the operation of the hologram recording apparatus at the time of 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 a random phase pattern or a phase pattern or amplitude pattern having a certain regularity are given by the phase modulation element 143. A hologram is recorded on the hologram recording medium 101 by interference with the reference light. 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 diffraction efficiency is reduced by changing the phase pattern or amplitude pattern of the reference light.
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 in the same area (or adjacent areas).

[Servo mechanism]
As described above, the recording density can be greatly improved, but on the other hand, the influence of the deviation of the light collecting position during recording and during reproduction becomes large. For this reason, it is preferable to add a servo mechanism in the focus or tracking direction to the hologram recording medium 101.

Furthermore, in the phase correlation multiplexing method, a deviation in the rotation direction of the reference light during recording and during reproduction also affects the recording and reproduction characteristics.
FIG. 6 is a diagram showing the deviation in the rotational direction. As shown in this figure, the term “rotation” here refers to rotation about an axis perpendicular to the hologram recording medium 101.
This shift in the rotation angle causes a shift in the phase pattern formed on the hologram recording medium 101 by the phase modulation element 143, and affects the diffraction efficiency of the hologram formed on the hologram recording medium 101 during recording. As a result, the BER (Bit Error Ratio) is increased.

FIG. 7 is a graph showing the relationship between the amount of rotation about the center of the reference light and the diffraction efficiency.
As shown in FIG. 7, the diffraction efficiency is halved by rotation of about 0.1 [deg]. In view of the margin, it is considered that the angular deviation needs to be about one-fifth or less. It is difficult to adjust and fix the position and angle with this accuracy.
Therefore, in order to read the recorded information stably and accurately, it is preferable to use a servo in the rotation direction in addition to the focus servo and tracking servo.

Hereinafter, the servo operation of the hologram recording apparatus will be described.
A. Focus servo and tracking servo First, focus servo and tracking servo will be explained.
The laser beam (servo beam) emitted from the servo light source 151 is converted into parallel light by the collimator lens 152, divided into a plurality of parts by the grating 153, and enters the beam splitter 154. The servo beam passes through the beam splitter 154 and is reflected by the dichroic mirror 125. The servo beam reflected by the dichroic mirror 125 is focused by the objective lens 127 and applied to the hologram recording medium 101.

  The servo beam reflected by the reflection layer 105 of the hologram recording medium 101 passes through the objective lens 127, is reflected by the dichroic mirror 125, and enters the beam splitter 154. The servo beam is reflected by the beam splitter 154, narrowed by the condensing lens 155, and then astigmatism is generated by the cylindrical lens 156 and is incident on the light receiving element (photodetector) 157.

FIG. 8 is a schematic diagram showing the relationship between the servo beam and the groove 104 irradiated on the hologram recording medium 101.
As shown in the figure, the servo beam is divided by a grating 153 and irradiated to the groove 104 as a center beam C and a plurality of beams S1 to S4 sandwiching the center beam C. The grating 153 is composed of two sheets, and one sheet generates S1 and S2 beams, and the other sheet generates S3 and S4 beams.
These servo beams S <b> 1 to S <b> 4 are disposed so as to be inclined so that, for example, only half of the groove 104 is applied. The beams S1 and S2 and the beams S3 and S4 are tilted in opposite directions.
The position of the servo beam does not have to be arranged at the center of the recording / reproducing beam, and may be anywhere.

FIG. 9 is a schematic diagram illustrating details of the configuration of the light receiving element 157. As shown in the figure, the light receiving element 157 includes eight elements A to H. A beam S3 is incident on the element G, a beam S1 is incident on the element E, a beam C is incident on the elements A to D, a beam S2 is incident on the element F, and a beam S4 is incident on the element H.
The focus servo error signal and the tracking servo error signal are generated from the outputs PA to PH of the eight elements A to H by the following calculation.
Focus error signal: (PA + PC)-(PB + PD)
Tracking error signal: PE-PF
Based on these error signals, the coils 161 and 162 of the servo drive unit 158 drive the objective lens 127, whereby focus servo and tracking servo are performed.

FIG. 10 is a schematic diagram showing a drive mechanism that drives the optical unit 100 shown in FIGS.
As shown in the figure, the optical unit 100 is disposed on a feed stage 170, and a gear 171 is attached to one end. On the other side of the feed stage 170, a motor 172 and a gear 173 that reduces the rotation of the motor 172 are attached. Is done.
A shaft 175 is attached to the feed stage 170 so that the hologram recording medium 101 can be moved in the inner and outer peripheral directions (in the direction of the arrow 176) by a motor (not shown). A hologram recording medium 101 is disposed on these optical units 100 and is rotated by a spindle motor (not shown).
As a result, the hologram can be recorded and reproduced at an appropriate position on the hologram recording medium 101.

B. Next, control of the rotation direction of the optical unit 100 will be described. Here, a case where a disk-type hologram recording medium 101 is used as the hologram recording medium 101 will be described.
For example, when the disc-type hologram recording medium 101 is removed from the hologram recording apparatus and then set again, the track center of the disc-type hologram recording medium 101 does not coincide with the rotation center of the spindle motor, and so-called eccentricity occurs. This eccentricity occurs due to a deviation between the center hole and the center of the recording track during manufacture of the disk-type hologram recording medium 101, a mounting deviation when the disk-type hologram recording medium 101 is mounted on the spindle motor shaft, or the like.

FIGS. 11 to 14 are a schematic view and an enlarged view showing the relationship between the eccentricity and the angular deviation of the disc-type hologram recording medium 101, respectively.
The signal light and reference light emitted from the optical unit 100 form a beam spot (condensing region) BS on the hologram recording medium 101. The beam spot BS can move in the radial direction of the rotation center Cr of the spindle motor as the optical unit 100 moves.
11 to 14, the track center Ct of the disc-type hologram recording medium 101 does not coincide with the rotation center Cr of the spindle motor, resulting in eccentricity.

When the track center Ct of the disc-type hologram recording medium 101 is on the straight line L connecting the rotation center Cr of the spindle motor and the beam spot BS of the optical unit 100 as shown in FIGS. 11 and the enlarged view of FIG. 13, the inclination of the groove 104 does not occur.
On the other hand, the track center Ct of the disc-type hologram recording medium 101 is on the straight line L connecting the rotation center Cr of the spindle motor and the beam spot BS of the optical unit 100 as shown in FIGS. When there is not, the groove 104 is inclined as shown in the enlarged views in FIGS.
This is the above-described shift in the rotational direction, which is a shift in the phase pattern of the phase modulation element 143 at the time of hologram recording and reproduction, which affects the diffraction efficiency and makes it difficult to accurately reproduce information.

A method of detecting and correcting this rotational direction deviation will be described below.
FIG. 15 is a block diagram illustrating a control circuit 180 that controls the motor 172 based on a signal output from the light receiving element 157.
The control circuit 180 includes an arithmetic circuit 181, an error amplifier 182, a loop filter 183, and a motor drive circuit 184.
The arithmetic circuit 181 generates an error signal of rotational deviation by calculating the output of the light receiving element 157 as follows.
Rotating error signal: (PE + PF)-(PG + PH)
Note that the arithmetic circuit 181 may perform the calculation for generating the focus error signal and the tracking error signal described above.

FIG. 16 is a graph showing the relationship between the rotational direction deviation and the signal level of the rotational deviation error signal when the tracking servo is applied. FIG. 17 is a schematic diagram showing the relationship between the rotational deviation and the positions of the servo beams S1, S2, S3, S4, and C.
The disc-type hologram recording medium 101 is displaced in the rotational direction, and the positional relationship between the groove 104 and the servo beams S1, S2, S3, S4, and C is θ1 as shown in FIGS. 17 (a) to 17 (b). When the rotational deviation occurs, the signal level of the rotational deviation error signal shown in FIG. 16 increases from 0 to V1. Further, if the positional relationship between the groove 104 and the servo beams S1, S2, S3, S4, and C causes a rotational deviation of −θ1 as shown in FIGS. 17A to 17C, the rotational deviation error shown in FIG. The signal level of the signal decreases from 0 to -V1.

FIG. 18 is a schematic diagram showing a state in which the servo beams S1 to S4 are rotated so as to correspond to the angular deviation of the groove 104. FIG.
The angular deviation servo operation will be described below with reference to FIGS. 18, 15 and 10. FIG.
The rotation deviation error signal output from the arithmetic circuit 181 has characteristics necessary for servo operation by the error amplifier 182 and the loop filter 183, and the motor 172 is driven by the motor drive circuit 184.
The rotation of the motor 172 is transmitted to the gear 171 via the gear 173, and the optical unit 100 rotates around the objective lens 127.

When the rotational deviation of θ1 occurs as shown in FIG. 17B, the servo beams S1 to S4 are centered on the center beam C together with the hologram recording / reproducing laser beam as shown in FIG. 18B. Rotate in the direction of arrow 191. As a result, the relative positional relationship between the groove 104 and the servo beam is as shown in FIG. 18B, and is substantially the same as in FIG.
As shown in FIG. 17C, when −θ1 and a rotational deviation in the opposite direction to the above occur, the motor 172 rotates in the opposite direction and is shown in FIG. 18C together with the hologram recording / reproducing laser beam. Thus, the servo beams S1 to S4 also rotate in the direction of the arrow 192 around the center beam C. As a result, the relative positional relationship between the groove 104 and the servo beam is as shown in FIG. 18C, which is substantially the same as in FIG.
Since such a servo operation is performed, the recording hologram recording medium 101 and the optical unit 100 are kept from being displaced in rotation.

(In the case of the card type hologram recording medium 101)
The disk type hologram recording medium 101 has been described above. The case of the card type hologram recording medium 101 will be described below.
FIG. 19 is a schematic diagram showing a drive mechanism for driving the optical unit 100 shown in FIGS. 1 and 2 in the case of the card-type hologram recording medium 101a, and corresponds to FIG.
In the case of the card-type hologram recording medium 101, the optical unit 100 is the same as the disk-type hologram recording medium 101. The rotation mechanism of the optical unit 100 is also the same.

The card-type hologram recording medium 101a is disposed on the optical unit 100 and can be moved in two directions indicated by arrows 177 and 178 by a feed mechanism (not shown) to accurately access the recording / reproducing position. be able to.
The relationship between the groove 104 provided on the card-type hologram recording medium 101a and the servo signal detection beams S1, S2, S3, S4, and C applied to the groove 104 is similar to that in the case of the disk type in FIG. expressed.
Even in the case of the card-type hologram recording medium 101a, a certain degree of rotational displacement occurs when the card is attached. For this reason, rotation deviation is detected by a method similar to that of the disk type, and servo control can be performed by the control circuit 180 shown in FIG. As a result, it is possible to prevent the hologram recording medium 101 and the optical unit 100 from rotating.

(Tracking with 3 beams)
Next, another method for detecting the rotation deviation signal will be described.
In the detection of the rotational deviation signal described above, five laser beams are used, but it is also possible to carry out using three beams.
FIG. 20 is a schematic diagram showing the positional relationship between the three beams S 1, C, S 2 and the groove 104.
These three beams can be made by forming a single grating 153. Reflected light from the hologram recording medium 101a of this beam enters the light receiving element 157a.
FIG. 21 is a schematic diagram showing the internal configuration of the light receiving element 157a.
The light receiving element 157a includes six elements A to F. The beam S1 is received on the element E, the beam C is received on the elements A to D, and the beam S2 is received on the element F.

FIG. 22 is a block diagram illustrating a control circuit 180a that controls the motor 172 based on a signal output from the light receiving element 157a.
This control circuit includes an arithmetic circuit 181a, an error amplifier 182a, a loop filter 183a, and a motor drive circuit 184a.
The arithmetic circuit 181a generates an error signal of rotational deviation by calculating the output of the light receiving element 157a as follows.
Rotating error signal: (PE + PF) / PC
Note that the arithmetic circuit 181a may perform an operation for generating the focus error signal and the tracking error signal described above.

FIG. 23 is a graph showing the relationship between the rotational direction deviation and the signal level of the rotational deviation error signal when the tracking servo is applied.
When the disc-type hologram recording medium 101 is displaced in the rotational direction and the rotational relationship of θ1 occurs in the positional relationship between the groove 104 and the servo beams S1, C, and S2, the error signal of the rotational displacement shown in FIG. Increase to V1. Further, when a rotational deviation of −θ1 occurs in the positional relationship between the groove 104 and the servo beams S1, C, and S2, the rotational deviation error signal shown in FIG. 23 decreases from V0 to V2.

FIG. 24 is a schematic diagram showing a state in which the servo beams S1 to S4 are rotated so as to correspond to the angular deviation of the groove 104. FIG.
Hereinafter, the servo operation of the angle deviation will be described with reference to FIGS. 24, 23, 22 and 10. FIG.
The error amplifier 182a shown in FIG. 22 has two input terminals, one of which is an error signal of rotational deviation from the arithmetic circuit 181a, and the other input terminal is an error signal when there is no rotational deviation. The target value V0 of the same voltage is input.
The error amplifier 182a amplifies and outputs the voltage of these differences. This output is input to the loop filter 183a to have characteristics necessary for the servo operation, and the motor 172a for rotation correction is driven by the motor driving circuit 184a.

The rotation of the motor 172 is transmitted to the gear 171 via the gear 173, the optical unit 100 rotates around the objective lens 127, and the servo beams S1 and S2 are also centered on the center beam C together with the hologram recording / reproducing laser beam. Rotate in the direction of arrow 191.
As a result, the relative positional relationship between the groove 104 and the servo beam is as shown in FIG. 24B, and is substantially the same as in FIG.

Further, when a rotational deviation occurs in the opposite direction, a rotational deviation of −θ1 occurs, and the rotational deviation error signal shown in FIG. 16 decreases from V0 to V2.
The error amplifier 182a shown in FIG. 22 amplifies the voltage of the difference between the target value V0 and the error signal of the rotational deviation from the arithmetic circuit 181a, and the loop filter 183a has the characteristics necessary for the servo operation. Since this output has a voltage opposite to the previous voltage, the motor 172 for rotation correction rotates in the reverse direction by the next motor drive circuit 39.
As a result, the relative positional relationship between the groove 104 and the servo beam is as shown in FIG. 24C, and is substantially the same as in FIG.
Since such a servo operation is performed, the recording hologram recording medium 101 and the optical unit 100 are kept from being displaced in rotation.

(Another example of tracking)
Next, still another method for detecting the rotational deviation signal will be described.
FIG. 25 is a schematic diagram showing the relationship between the servo beam and the groove 104 irradiated on the hologram recording medium 101.
As shown in the figure, the servo beam is divided by a grating 153, and irradiated to the groove 104 as a center beam C and beams S1 and S2 sandwiching the center beam C.
These servo beams S1 and S2 are arranged, for example, at the center between adjacent grooves.
The position of the servo beam does not have to be arranged at the center of the recording / reproducing beam, and may be anywhere.

FIG. 26 is a schematic diagram illustrating details of the configuration of the light receiving element 157. As shown in the figure, the light receiving element 157 includes eight elements A to H. A beam S1 is incident on the elements E and F, a beam S2 is incident on the elements G and H, and a beam C is incident on the elements A to D.
The focus servo error signal and the tracking servo error signal are generated from the outputs PA to PH of the eight elements A to H by the following calculation.
Focus error signal: (PA + PC)-(PB + PD)
Tracking error signal: (PA + PD)-(PB + PC) or
((PA + PD)-(PB + PC))-N ((PF-PE) + (PH-PG)) ------- N is a constant Based on these error signals, the servo drive unit 158 The coils 161 and 162 drive the objective lens 127, whereby focus servo and tracking servo are performed.

A method of detecting and correcting this rotational direction deviation will be described below.
The control circuit for controlling the motor 172 based on the signal output from the light receiving element 157 is the control circuit 180 shown in FIG.
Here, the arithmetic circuit 181 generates an error signal of rotational deviation by calculating the output of the light receiving element 157 as follows.
Rotating error signal: (PF-PE)-(PH-PG)
Note that the arithmetic circuit 181 may perform the calculation for generating the focus error signal and the tracking error signal described above.

The relationship between the rotational direction deviation and the signal level of the rotational deviation error signal in the state where the tracking servo is applied is the graph shown in FIG.
FIG. 27 is a schematic diagram showing the relationship between the rotational deviation and the positions of the servo beams S1, S2, and C.
The disc-type hologram recording medium 101 is displaced in the rotation direction, and the positional relationship between the groove 104 and the servo beams S1, S2, and C is deviated by θ1 as shown in FIGS. 27 (a) to 27 (b). Then, the signal level of the rotation error signal shown in FIG. 30B increases from 0 to V1. Further, if the positional relationship between the groove 104 and the servo beams S1, S2, and C causes a rotational deviation of −θ1 as shown in FIGS. 27A to 27C, the rotational deviation error shown in FIG. The signal level of the signal decreases from 0 to -V1.

FIG. 28 is a schematic diagram illustrating a state in which the servo beams S1, S2, and C are rotated so as to correspond to the angular deviation of the groove 104. FIG.
The angular deviation servo operation will be described below with reference to FIGS. 28, 29, and 10. FIG.
The rotation deviation error signal output from the arithmetic circuit 181 has characteristics necessary for servo operation by the error amplifier 182 and the loop filter 183, and the motor 172 is driven by the motor drive circuit 184.
The rotation of the motor 172 is transmitted to the gear 171 via the gear 173, and the optical unit 100 rotates around the objective lens 127.

When the rotational deviation of θ1 occurs as shown in FIG. 27B, the servo beams S1 and S2 are centered on the center beam C together with the hologram recording / reproducing laser beam as shown in FIG. Rotate in the direction of arrow 191. As a result, the relative positional relationship between the groove 104 and the servo beam is as shown in FIG. 28B, and is substantially the same as in FIG.
As shown in FIG. 27C, when -θ1 and a rotational deviation in the opposite direction to the above occur, the motor 172 rotates in the opposite direction and is shown in FIG. 28C together with the hologram recording / reproducing laser beam. Thus, the servo beams S1 and S2 also rotate in the direction of the arrow 192 around the center beam C. As a result, the relative positional relationship between the groove 104 and the servo beam is as shown in FIG. 28C, which is substantially the same as in FIG.
Since such a servo operation is performed, the recording hologram recording medium 101 and the optical unit 100 are kept from being displaced in rotation.

The rotation deviation signal detection method according to this embodiment has the following effects in particular.
In the 5-spot method shown in FIG. 9, two gratings 153 are required, but in the 3-spot method according to this embodiment, only one grating is required.
Further, the error signal for the rotational deviation in the three-spot method shown in FIG. 21 is “Rotating error = (PE + PF) / so that the detection voltage value is not offset when the output power of the laser 151 changes. PC "is calculated and a divider is required (see the solid curve in FIG. 30A). On the other hand, in the three-spot method according to this embodiment, a slight gain variation can be tolerated, and therefore only “Rotating error = PE + PF” may be calculated (see the dotted curve in FIG. 30B). Of course, the calculation of “Rotating error = (PE + PF) / PC” may be performed (see the solid line of the dotted line in FIG. 30B).
Further, in the case of the three spots shown in FIG. 21, if the laser power is constant, the reference voltage in FIG. 22 is set to V0, so that control is performed so that V0 is always maintained even if a rotational deviation occurs. However, if the laser power changes (for example, when it becomes large as shown in the figure), if V0 is kept constant, a rotational deviation of θ2 occurs. On the other hand, in the case of the three-spot method according to the present embodiment, the target value is 0 V as shown in FIG. 29. Therefore, even if the laser power changes, the gain changes slightly but the rotational deviation does not occur. Be controlled.

In the above description, when there is a deviation in the rotation direction, the optical unit 100 is corrected by being rotated by the motor 172. However, the hologram recording medium 101 may be rotated. Further, the device to be rotated is not limited to the motor but may be another driving method, and may be a part of the optical unit 100 instead of the entire optical unit 100.
As described above, according to the present embodiment, the hologram signal can be recorded and reproduced satisfactorily even if there is a shift due to the shift in the rotation direction between the hologram recording beam and the hologram recording medium 101.

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 figure showing the shift | offset | difference in a rotation direction. It is a graph showing the relationship between the amount of rotation centering on the center of reference light, and diffraction efficiency. It is a schematic diagram showing the relationship between the servo beam irradiated to the hologram recording medium and the groove. It is a schematic diagram showing the detail of a structure of a light receiving element. It is a schematic diagram showing an example of the drive mechanism which drives an optical unit. It is the model showing the relationship between eccentricity of a disk type hologram recording medium, and an angle shift, and its enlarged view. It is the model showing the relationship between eccentricity of a disk type hologram recording medium, and an angle shift, and its enlarged view. It is the model showing the relationship between eccentricity of a disk type hologram recording medium, and an angle shift, and its enlarged view. It is the model showing the relationship between eccentricity of a disk type hologram recording medium, and an angle shift, and its enlarged view. It is a block diagram showing the control circuit which controls a motor based on the signal output from a light receiving element. It is a graph showing the relationship between the rotation direction deviation and the signal level of the rotation deviation error signal in a state where the tracking servo is applied. It is a schematic diagram showing the relationship between a rotation shift | offset | difference and the position of a servo beam. It is a schematic diagram showing the state which rotated the beam for servos corresponding to the angle shift of a groove. FIG. 11 is a schematic diagram showing a drive mechanism that drives the optical unit 100 shown in FIGS. 1 and 2 in the case of a card-type hologram recording medium, and corresponds to FIG. 10. It is a schematic diagram showing the positional relationship of three beams and a groove. It is a schematic diagram showing an example of the internal structure of a light receiving element. It is a block diagram showing an example of the control circuit which controls a motor based on the signal output from a light receiving element. It is a graph showing the relationship between the rotation direction deviation and the signal level of the rotation deviation error signal in a state where the tracking servo is applied. It is a schematic diagram showing the state which rotated the beam for servos corresponding to the angle shift of a groove. It is a schematic diagram showing the relationship between the servo beam irradiated to the hologram recording medium which concerns on another embodiment, and a groove. It is a schematic diagram showing the detail of a structure of the light receiving element which concerns on another embodiment. It is a schematic diagram showing the relationship between the rotation shift which concerns on another embodiment, and the position of the beam for servos. It is a schematic diagram showing the state which rotated the beam for servos corresponding to the angle shift of the groove | channel which concerns on another embodiment. It is a block diagram showing an example of the control circuit which controls a motor based on the signal output from the light receiving element concerning another embodiment. FIG. 30B is a graph showing the relationship between the rotational direction deviation and the signal level of the rotational deviation error signal in the state where the tracking servo according to another embodiment is applied (FIG. 30B). It is an example.

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 (11)

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 detection mechanism for detecting a rotation angle of the phase modulation element with respect to the hologram recording medium;
A rotation mechanism that rotates the phase modulation element or the hologram recording medium around an axis perpendicular to the hologram recording medium , based on a detection result of the detection mechanism;
A holographic recording apparatus comprising: The hologram recording apparatus according to claim 1, wherein the hologram recording medium has a disk shape or a card shape. The hologram recording medium has a track for recording and reproduction, and a groove formed along the track,
A second laser light source that emits a second laser light; and a second optical system that irradiates the hologram recording medium with the second laser light emitted from the second laser light source. Receiving a laser beam emitted from the second optical system and reflected by the groove of the hologram recording medium,
2. The hologram recording apparatus according to claim 1, wherein: The detection mechanism further includes a light splitting element that splits the second laser light emitted from the second laser light source into a plurality of laser lights,
The second optical system irradiates the hologram recording medium with the plurality of laser beams emitted from the light splitting element,
The light receiving means includes a plurality of light receiving elements corresponding to the plurality of laser beams emitted from the second optical system and reflected by grooves of the hologram recording medium;
The hologram recording apparatus according to claim 3. The said light splitting element divides | segments a said 2nd laser beam so that the said some laser beam may be arranged so that it may be inclined and it may be about half the groove before and after the center of a groove. Hologram recording device. The light splitting element splits the second laser light so that the plurality of laser lights are inclined and arranged between a groove center and a groove adjacent to the front and rear of the center. 4. The hologram recording device according to 4. A laser light source for emitting laser light;
A phase modulation element that phase-modulates laser light emitted from the laser light source as reference light;
An optical system for focusing the reference light phase-modulated by the phase modulation element on a hologram recording medium;
A detection mechanism for detecting a rotation angle of the phase modulation element with respect to the hologram recording medium;
A rotation mechanism that rotates the phase modulation element or the hologram recording medium around an axis perpendicular to the hologram recording medium , based on a detection result of the detection mechanism;
A hologram reproducing apparatus comprising: A light branching step for branching laser light emitted from the laser light source into signal light and reference light;
An optical modulation step for modulating the signal light branched in the optical branching step;
A phase modulation step of phase-modulating the reference light branched in the light branching step with a phase modulation element;
A condensing step of condensing the signal light modulated in the light modulation step and the reference light phase-modulated in the phase modulation step at substantially the same location of the hologram recording medium;
A detection step of detecting a rotation angle of the phase modulation element with respect to the hologram recording medium;
A rotation step of rotating the phase modulation element or the hologram recording medium around an axis perpendicular to the hologram recording medium based on a detection result in the detection step;
A hologram recording method comprising: The hologram recording method according to claim 8, wherein a shape of the hologram recording medium is a disk shape or a card shape. The hologram recording medium has a track for recording and reproduction, and a groove formed along the track,
The detection step includes an irradiation step of irradiating the hologram recording medium with a second laser beam emitted from a second laser light source, and a laser emitted in the irradiation step and reflected by a groove of the hologram recording medium. A light receiving step for receiving light,
The hologram recording method according to claim 8. A phase modulation step in which phase modulation is performed with a phase modulation element using laser light emitted from the laser light source as reference light;
A condensing step of condensing the reference light phase-modulated in the phase modulation step onto a hologram recording medium;
A detection step of detecting a rotation angle of the phase modulation element with respect to the hologram recording medium;
A rotation step of rotating the phase modulation element or the hologram recording medium around an axis perpendicular to the hologram recording medium based on a detection result in the detection step;
A hologram reproducing method comprising:

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