JP2010027187A - Recording device, recording method, playback device, and hologram recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a reflection film for reflecting a playback image is conventionally provided in addition to a reflection film as a track forming layer in order to prevent deterioration in playback characteristics caused by noise light superimposed on a playback image of a hologram since a guide track for position control is formed, while a structure of a recording medium is complicated and a manufacturing cost is increased. <P>SOLUTION: The hologram is recorded around a center position between guide tracks. Since the hologram is not formed on the guide tracks, deterioration in the playback characteristics is suppressed and as a result, the reflection film for reflecting the playback image is not required and the playback image is reflected by the track forming layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a recording apparatus and a method for recording on a hologram recording medium in which a hologram corresponding to the signal light is formed by interference fringes of signal light and reference light and data is recorded. The present invention also relates to a reproducing apparatus for reproducing data recorded on the hologram recording medium. Furthermore, the present invention relates to a hologram recording medium on which data is recorded by forming a hologram corresponding to the signal light by interference fringes between the signal light and the reference light.

JP 2007-79438 A

For example, as disclosed in Patent Document 1, a hologram recording / reproducing method is known in which data recording is performed by forming a hologram using interference fringes between signal light and reference light. In this hologram recording / reproducing method, at the time of recording, a hologram recording medium is irradiated with signal light that has been subjected to spatial light modulation (for example, spatial light intensity modulation) according to the recording data and reference light that is different from the signal light. Then, data recording is performed by forming these interference fringes (holograms) on the recording medium.
At the time of reproduction, the reference light is irradiated to the recording medium. By irradiating the reference light in this way, diffracted light corresponding to the interference fringes formed as described above can be obtained. That is, a reproduced image (reproduced signal light) corresponding to the recorded data is thereby obtained. The reproduced image obtained in this manner is detected by an image sensor such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor, and the recorded data is reproduced.

FIGS. 21 and 22 are diagrams for explaining the hologram recording / reproducing method. FIG. 21 schematically shows the recording method, and FIG. 22 schematically shows the reproducing method.
21 and 22 show a recording / reproducing method in the case where a so-called coaxial method in which signal light and reference light are arranged on the same optical axis to perform recording is employed. Moreover, in these figures, the case where the reflection type hologram recording medium 100 provided with a reflecting film is used is illustrated.

  First, as shown in FIGS. 21 and 22, in the hologram recording / reproducing system, an SLM (spatial light modulator) 101 is used to generate signal light and reference light during recording and reference light during reproduction. Is provided. The SLM 101 includes an intensity modulator that performs spatial light intensity modulation (also simply referred to as intensity modulation) on the incident light for each pixel. The intensity modulator can be constituted by a liquid crystal panel, for example.

  First, at the time of recording shown in FIG. 21, by the intensity modulation of the SLM 101, signal light given an intensity pattern corresponding to recording data and reference light given a predetermined intensity pattern are generated. In the coaxial method, spatial light modulation is performed on incident light so that signal light and reference light are arranged on the same optical axis as shown in the figure. At this time, as shown in the figure, the signal light is generally arranged on the inner side and the reference light is arranged on the outer side.

  The signal light / reference light generated by the SLM 101 is applied to the hologram recording medium 100 via the objective lens 102. As a result, a hologram reflecting the recording data is formed on the hologram recording medium 100 by interference fringes between the signal light and the reference light. That is, data is recorded by forming this hologram.

  On the other hand, during reproduction, the SLM 101 generates reference light as shown in FIG. Then, the reference light is irradiated onto the hologram recording medium 100 through the objective lens 102.

  In this way, in response to the reference light being applied to the hologram recording medium 100, the recorded data is recorded by the diffractive action of the hologram formed on the hologram recording medium 100 as shown in FIG. A corresponding reproduced image is obtained. In this case, the reproduced image is guided to the image sensor 103 as reflected light from the hologram recording medium 100 through the objective lens 100 as shown.

  The image sensor 103 receives the reproduced image derived as described above in units of pixels, and obtains an electric signal corresponding to the amount of received light for each pixel, thereby obtaining a detection image for the reproduced image. Thus, the image signal detected by the image sensor 103 becomes a read signal for the recorded data.

  For confirmation, as can be understood from the description of FIGS. 21 and 22, in the hologram recording / reproducing method, recording data is recorded / reproduced in units of signal light. That is, in the hologram recording / reproducing system, one hologram (called a hologram page) formed by one-time interference between the signal light and the reference light is the minimum unit of recording / reproducing.

Here, consider that data is sequentially recorded on the hologram recording medium 100 in units of the hologram page.
In conventional CDs (Compact Discs) and DVDs (Digital Versatile Discs), the recording medium is a disk (disk), and data is recorded by forming marks while rotating the recording medium. Has been. At this time, a spiral or concentric guide groove (track) is formed on the recording medium, and marks are formed while controlling the beam spot position so as to trace on the track. Data is recorded at a predetermined position.

  Following this, also in the hologram recording / reproducing system, a spiral or concentric track is formed on the disc-shaped hologram recording medium 100, and the rotation-driven hologram recording medium 100 is sequentially irradiated with signal light and reference light. It is considered to adopt a method of forming a hologram page along a track by forming a hologram.

In this way, when a method of forming a hologram page at a position along the track is adopted, a recording servo / recording position such as a tracking servo for tracing the beam spot on the track and access control to a predetermined address is used. Control needs to be done.
In the conventional method, when controlling such a recording / reproducing position, a dedicated laser beam is irradiated. That is, laser light for recording / reproducing a hologram (laser light for irradiating signal light / reference light: laser light for recording / reproducing) and laser light for controlling the recording / reproducing position of the hologram ( And a method of separately irradiating position control laser light).
Conventionally, a hologram recording medium 100 having a structure as shown in FIG. 23 has been used in order to cope with a method of separately irradiating position control laser light.

As shown in FIG. 23, the conventional hologram recording medium 100 includes a recording layer 107 on which hologram recording is performed, and a position where address information and the like for position control are recorded by the concavo-convex cross-sectional structure on the substrate 111. The control information recording layer is formed separately.
Specifically, on the hologram recording medium 100, an antireflection film 105, a cover layer 106, a recording layer 107, a reflection film 108, an intermediate layer 109, a reflection film 110, and a substrate 111 are formed in order from the upper layer.
The antireflection film 105 is formed by applying an AR (Anti Refrection) coating.

The cover layer 106 is made of, for example, a plastic substrate or a glass plate, and is provided for protecting the recording layer 107.
For example, a photopolymer is selected as the material of the recording layer 107, and the recording / reproducing of the hologram by the recording / reproducing laser beam described above is performed.

  The reflection film 108 is irradiated with reference light from the recording / reproducing laser beam during reproduction, and when a reproduced image corresponding to the hologram recorded in the recording layer 107 is obtained, this is reflected as reflected light on the apparatus side. It is provided to return to

The substrate 111 and the reflective film 110 are provided for controlling the recording / reproducing position.
On the substrate 111, tracks for guiding the recording / reproducing position of the hologram in the recording layer 107 are formed in a spiral shape or a concentric shape. For example, a track is formed by recording information such as address information by a pit row.
A reflective film 110 is formed on the surface (front surface) of the substrate 111 on which the track is formed, for example, by sputtering or vapor deposition. The intermediate layer 109 formed between the reflective film 110 and the above-described reflective film 108 is an adhesive material such as a resin.

Here, with respect to the hologram recording medium 100 having the above-described cross-sectional structure, in order to appropriately perform position control based on the reflected light of the position control laser light, the position control laser light is The reflection film 110 having the uneven cross-sectional shape must be reached. In other words, from this point, the laser light for position control must pass through the reflective film 108 formed above the reflective film 110.
On the other hand, the reflective film 108 needs to reflect a laser beam for recording / reproduction so that a reproduced image corresponding to the hologram recorded on the recording layer 107 is returned to the apparatus side as reflected light.

Considering this point, in the conventional hologram recording / reproducing system, a laser beam having a wavelength different from that of the hologram recording / reproducing laser beam is used as the position controlling laser beam. For example, a blue-violet laser beam having a wavelength λ = 405 nm is used as a hologram recording / reproducing laser beam, and a red laser beam having a wavelength λ = 650 nm is used as a position control laser beam. Yes.
In addition, as a reflection film 108 formed between the recording layer 107 and the reflection film 110 on which the position control information is recorded, the recording / reproducing blue-violet laser light is reflected, and the position control red color is reflected. A reflective film having wavelength selectivity that transmits laser light is used.
With such a configuration, at the time of recording / reproducing, the laser beam for position control properly reaches the reflecting film 110, and the reflected light information for position control is properly detected on the apparatus side, The reproduced image of the hologram recorded on the recording layer 107 can be properly detected on the apparatus side.

FIG. 24 is a diagram schematically (mainly only an optical system) showing a configuration of a conventional recording / reproducing apparatus that performs recording / reproduction corresponding to the hologram recording medium 100 having the structure described above.
First, the recording / reproducing apparatus includes a first laser 115, a collimator lens 116, an SLM 101, a polarization beam splitter 117, a quarter wavelength plate as an optical system for irradiating signal light and reference light for hologram recording and reproduction. 119, an objective lens 102, and an image sensor 103 are provided.
The first laser 115 outputs, for example, the above-described blue-violet laser light having a wavelength λ = 405 nm as laser light for hologram recording / reproduction. The laser beam emitted from the first laser 115 enters the SLM 101 via the collimator lens 116.
As described above, the SLM 101 performs spatial light modulation on the incident light, thereby generating signal light and reference light during recording and generating reference light during reproduction.

The recording / reproducing laser beam subjected to spatial light modulation by the SLM 101 is transmitted through the polarization beam splitter 117 and then transmitted through a dichroic mirror 118 described later. Then, the recording / reproducing laser beam transmitted through the dichroic mirror 118 passes through the quarter-wave plate 119 and is then focused on the hologram recording medium 100 (recording layer 107) by the objective lens 102. .
Thus, during recording, interference fringes (holograms) between the signal light and the reference light are formed on the recording layer 107, and data recording is performed.

At the time of reproduction, a reproduction image corresponding to the hologram recorded on the recording layer 107 is obtained as reflected light from the reflective film 108 by irradiation of the reference light, and the reproduced image as the reflected light is the objective lens 102 → 1 / The light enters the polarizing beam splitter 117 via the four-wave plate 119 → the dichroic mirror 118. The polarization beam splitter 117 reflects the reproduced image obtained as the reflected light from the hologram recording medium 100 in this way and guides it to the image sensor 103 side.
In this way, during reproduction, the reproduced image from the hologram recording medium 100 is detected by the image sensor 103.

  In this case, the recording / reproducing apparatus is also provided with an optical system for irradiating position control laser light and detecting reflected light of the position control laser light. Specifically, the second laser 120, the collimator lens 121, the polarization beam splitter 122, the dichroic mirror 118, and the photodetector 123 are included.

The second laser 120 outputs, for example, the above-described red laser light having the wavelength λ = 650 nm as the position control laser light. The emitted light from the second laser 120 enters the dichroic mirror 118 via the collimator lens 121 → the polarization beam splitter 122.
The dichroic mirror 118 is configured to have wavelength selectivity such that the recording / reproducing laser beam from the first laser 115 is transmitted and the position controlling laser beam from the second laser 120 is reflected. Accordingly, the position control laser light transmitted through the polarization beam splitter 122 is reflected by the dichroic mirror 118 and guided to the quarter wavelength plate 119 side.
The laser light for position control via the quarter wavelength plate 119 is irradiated so as to be condensed on the reflection film 110 formed on the hologram recording medium 100 by the objective lens 102.

For confirmation, by providing the dichroic mirror 118 as described above, the laser beam for position control and the laser beam for recording / reproducing are synthesized on the same optical axis, and this synthesis is performed. The hologram recording medium 100 is irradiated with light through a common objective lens 102.
In other words, this is designed so that the beam spot of the laser beam for position control and the beam spot for recording and reproduction are formed at the same position. As a result, the position control as described below is performed. By performing the position control operation based on the laser beam for use, the hologram recording / reproducing position is controlled to be positioned on the track.

  As described above, the laser light for position control is irradiated onto the reflection film 110, so that reflected light corresponding to the recording information on the reflection film 110 is obtained. The light is guided to the polarization beam splitter 122 via the plate 119 → the dichroic mirror 118. The polarization beam splitter 122 reflects the reflected light of the position control laser light obtained through the dichroic mirror 118 in this way, and guides it to the photodetector 123.

  The photodetector 123 receives the reflected light of the position control laser light guided as described above, converts it into an electrical signal, and supplies it to the matrix circuit 124.

  The matrix circuit 124 includes a matrix calculation / amplification circuit for output signals from a plurality of light receiving elements as the photodetector 123, and generates necessary signals by matrix calculation processing. Specifically, a signal (reproduction signal RF) corresponding to a reproduction signal for the pit row formed on the reflective film 110, a focus error signal FE for servo control, a tracking error signal TE, and the like are generated.

Although not shown, the recording / reproducing apparatus is provided with an address detection circuit and a clock generation circuit for detecting address information and generating a clock based on the reproduction signal RF.
Further, a servo circuit is provided that controls the position of the laser spot for position control by controlling the position of the objective lens 102 and the like based on the address information and the tracking error signal TE. By controlling the beam spot position of the laser beam for position control by this servo circuit, the beam spot position of the laser beam for hologram recording / reproducing is moved to a required address, followed by a track, etc. You can do that. That is, this controls the recording / reproducing position of the hologram.

Here, as can be understood from the above description, in the conventional hologram recording / reproducing system, the hologram is recorded on the track.
For this reason, in the conventional hologram recording / reproducing system, a laser beam for position control with a different wavelength is separately irradiated together with a laser beam for recording / reproducing a hologram, and the hologram recording medium 100 has a hologram recording / reproducing function. In addition to the reflective film 108 for reflecting the laser beam for the purpose, a reflective film 110 for obtaining the reflected light of the laser light for position control (light reflecting the concave-convex cross-sectional shape for position control) is separately provided. Has been.

For confirmation, when recording a hologram on a track, it is important to prevent the unevenness of the track from being reflected in the reproduced image during reproduction. That is, when the unevenness of the track is reflected in the reproduced image, the reproduction characteristics are remarkably deteriorated.
Considering this point, in the conventional recording / reproducing system, as shown in FIG. 23, the hologram recording / reproducing light is reflected by the flat reflective film 108 having no unevenness. Accordingly, with respect to position control, laser light having a different wavelength is separately irradiated, and the reflective film 108 is given wavelength selectivity, and the position under the reflective film 108 is used for position control. A technique of providing a reflective film 110 having an uneven cross-sectional shape is employed.

However, the conventional hologram recording / reproducing system employing such a method has a problem that the structure of the recording medium is complicated in that two reflection films must be provided. The complexity of the structure leads to an increase in manufacturing cost.
Further, in the conventional hologram recording / reproducing system, it is necessary to use a reflective film (108) for recording / reproducing laser light having wavelength selectivity in order to transmit the position controlling laser light. Thus, a reflective film having wavelength selectivity is more expensive than a normal reflective film, and this also causes an increase in manufacturing cost of the recording medium.

Therefore, in the present invention, in view of the above problems, the recording apparatus is configured as follows.
That is, the recording apparatus of the present invention includes a recording layer on which data is recorded by forming a hologram corresponding to the signal light by interference fringes between the signal light and the reference light, and a recording position of the hologram in the recording layer. A recording apparatus that performs recording on a hologram recording medium having a track forming layer formed such that a plurality of guide tracks for guiding are arranged in at least one direction, the light source being emitted from the light source. Signal light generating means for generating the signal light by applying spatial light modulation to the recorded light according to the recording data.
In addition, a reference light generation unit that generates the reference light based on the light emitted from the light source is provided.
The hologram includes recording light irradiation means for irradiating the signal light and the reference light so that the hologram is formed around a center position between the guide tracks formed in the track forming layer. .

In the present invention, the reproducing apparatus is configured as follows.
That is, the reproducing apparatus of the present invention includes a recording layer on which data is recorded by forming a hologram corresponding to the signal light by interference fringes between the signal light and the reference light, and a recording position of the hologram in the recording layer A reproducing apparatus for reproducing a hologram recording medium having a track forming layer formed by arranging a plurality of guide tracks for guiding a track in at least one direction, the light source and a light source emitted from the light source Reference light generating means for generating the reference light based on the received light.
Further, an objective lens serving as an output end of the reference light with respect to the hologram recording medium is provided.
The reference light is guided to the objective lens, and the light obtained by spectrally dividing the light emitted from the light source or the light emitted from another light source different from the light source is used as the position control light. An optical system for guiding to the objective lens, wherein the distance between the optical axis of the reference light and the optical axis of the position control light in the arrangement direction of the guide tracks is ½ of the track pitch of the guide tracks And an optical system configured to guide the reference light and the position control light to the objective lens.
Further, it represents a position error of the light spot of the position control light with respect to the guide track, which is obtained when the position control light irradiated onto the hologram recording medium through the objective lens passes through the track forming layer. A spot position control unit is provided for controlling the position of the objective lens so that the light spot is positioned on the guide track based on the result of detecting the position error information.

In the present invention, the hologram recording medium is configured as follows.
That is, the hologram recording medium of the present invention includes a recording layer on which data is recorded by forming a hologram corresponding to the signal light by interference fringes between the signal light and the reference light, and a recording position of the hologram in the recording layer And a track forming layer formed so that a plurality of guide tracks are arranged in at least one direction.
The guide tracks in the track forming layer are formed with an interval larger than the width of the bottom surface of the hologram recorded in the recording layer.

As described above, the recording apparatus (recording method) of the present invention records the hologram with the center position between the guide tracks as the center. That is, the hologram is recorded so that the center of the hologram coincides with the center between the guide tracks.
According to this, even if the reflection film above the track formation layer, which has been conventionally required, is omitted and the reproduction image of the hologram is reflected by the reflection film on which the guide track is formed, the reproduction characteristics are remarkably high. Occurrence of a situation that gets worse can be prevented. That is, compared with the conventional case where a hologram is recorded on a guide track, it is possible to remarkably suppress the deterioration of reproduction characteristics.
As understood from this point, according to the present invention, the reflection film (reflection film 108 in FIG. 23) above the track formation layer, which is necessary for the conventional hologram recording medium, is omitted. In addition, a reflective film having wavelength selectivity can be eliminated.

At this time, if the hologram recording medium to be recorded is such that the guide track is formed with an interval equal to or larger than the bottom surface width of the hologram as in the hologram recording medium of the present invention, the hologram does not overlap the guide track. Can be recorded. That is, this makes it possible to completely prevent the reproduction characteristics from being deteriorated due to the hologram being recorded on the guide track.
In addition, even if the target hologram recording medium is a case where the distance between the guide tracks is narrower than the width of the bottom surface of the hologram, the central portion of the hologram can be prevented from overlapping the guide track. Compared to the conventional case where holograms are recorded, the deterioration of the reproduction characteristics is still suppressed.

As described above, according to the present invention, since the center of the hologram is recorded so as to coincide with the center position between the guide tracks, only one layer needs to be provided as the reflection film in the hologram recording medium. I can do it. Therefore, according to the present invention, the structure of the hologram recording medium can be simplified, and the manufacturing cost of the hologram recording medium can be reduced.
Conventionally, it has been necessary to use a wavelength selective film as a reflective film for reflecting the reproduced image of the hologram. However, according to the present invention, the reflective film needs to have wavelength selective. It can be with no. That is, also in this respect, the manufacturing cost of the hologram recording medium can be reduced.

  Further, according to the reproducing apparatus of the present invention, the hologram recorded so that the center is located at the center position between the guide tracks by the recording apparatus (recording method) of the present invention can be read appropriately.

  Further, according to the hologram recording medium of the present invention, it is possible to provide a hologram recording medium capable of recording a hologram such that the bottom surface of the hologram does not overlap the guide track.

Hereinafter, the best mode for carrying out the invention (hereinafter referred to as an embodiment) will be described.

<First Embodiment>
[Configuration of hologram recording medium]

FIG. 1 is a diagram showing a cross-sectional structure of a hologram recording medium HM as an embodiment of the present invention.
As shown in FIG. 1, the hologram recording medium HM of the present embodiment includes an antireflection film R-1, a cover layer R-2, a recording layer R-3, a reflection film R-4, and a substrate R in order from the upper layer. -5 is formed.
For the sake of confirmation, the “upper layer” and “lower layer” referred to here are the above-mentioned upper surface, with the surface on which light for recording / reproducing is incident as the upper surface and the surface opposite to the upper surface as the lower surface. The side is the upper layer, and the lower surface side is the lower layer.

  The antireflection film R-1 is formed by AR (Anti Refrection) coating and has a function of preventing unnecessary reflection of light. The cover layer R-2 is made of, for example, a plastic substrate or a glass plate, and is provided for protecting the recording layer R-3.

For example, a photopolymer is selected as the material of the recording layer R-3, and recording / reproduction is performed by laser light using the first laser 2 shown in FIG. 4 as a light source later.
In addition, the reflection film R-4 obtained a reproduction image corresponding to the interference fringes (hologram) recorded in the recording layer R-3 in response to the reference light irradiated with the laser beam at the time of reproduction. At this time, it is provided to return this to the recording / reproducing apparatus as reflected light.

  Here, a substrate R-5 is provided under the reflective film R-4. A track TR for guiding the recording / reproducing position of the hologram in the recording layer R-3 is formed on the substrate R-5 in a spiral shape or a concentric shape. In this case, the track TR is formed by recording information such as address information by a pit string as will be described later.

The reflective film R-4 is formed on the surface (front surface) of the substrate R-5 on which the track TR is formed, for example, by sputtering or vapor deposition. As a result, the reflective film R-4 is provided with an uneven cross-sectional shape reflecting the track TR formed on the substrate R-5.
In this regard, hereinafter, it is assumed that the track TR is formed on the reflective film R-4.

2 and 3 are plan views of the hologram recording medium HM. 2 and 3 show cross sections in the state where the upper layer side of the hologram recording medium HM is peeled off from the reflective film R-4.
First, as can be seen with reference to FIGS. 2 and 3, the hologram recording medium HM of the present embodiment has a disk shape (disk shape).

In the hologram recording medium HM, the track TR is formed in a spiral shape as shown in FIG. 2, for example.
Alternatively, as shown in FIG. 3, a plurality of tracks TR can be formed concentrically.

  For confirmation, in the spiral shape, the track TR can be regarded as one continuous track. However, when viewed in the radial direction, a plurality of tracks TR are formed as in the concentric shape. You can see that. In the case of a spiral shape, a recording start position (rotation angle) is determined for each round of one continuous track, and “each track” is delimited by the rotation angle.

Here, in the case of the present embodiment, the track TR is formed by a pit row in which address information and the like are recorded.
For example, the address information (position information) recorded by the pit row can include track number information and sector number information.
In the hologram recording medium HM in this case, for example, a serial number is assigned to each track TR, and the number information becomes track number information.
In the case of this example, a sector having a predetermined length is defined as a recording / reproducing unit, and the hologram recording medium HM is divided into a plurality of sectors. This sector is also given a serial number, and the number information is the sector number information.

  The track number information is stored, for example, at the head position in each sector. The sector number information is stored in each sector, for example, at a position following the track number information.

In the case of this example, the track TR is formed so that the pitch in the radial direction is constant over the entire surface of the disk. That is, the formation interval (pitch) of the tracks TR in the radial direction is constant.
The hologram recording medium HM of the present embodiment is characterized by the track pitch (arrangement interval of the tracks TR), which will be described later.

[Configuration of hologram recording / reproducing apparatus]

Next, the internal configuration of a recording apparatus as an embodiment for recording data corresponding to the hologram recording medium HM will be described with reference to the block diagram of FIG.
The recording apparatus of the present embodiment has a reproducing function as well as a recording function for the hologram recording medium HM. In this sense, hereinafter, the recording apparatus of the present embodiment is referred to as a recording / reproducing apparatus 1.

  First, in this embodiment, a so-called coaxial system is adopted as a hologram recording / reproducing system. That is, the signal light and the reference light are arranged on the same axis, and both are irradiated onto the hologram recording medium HM set at a predetermined position to form a hologram by interference fringes, and data is recorded. By irradiating the hologram recording medium HM with reference light, a reproduced image (reproduced signal light) of the hologram is obtained and the recorded data is reproduced.

  In FIG. 4, the recording / reproducing apparatus 1 is provided with a medium holding part (not shown) for holding the hologram recording medium HM. When the hologram recording medium HM is loaded in the recording / reproducing apparatus, the medium holding part As a result, the hologram recording medium HM is held in a state where it can be rotationally driven by the spindle motor 21. In the recording / reproducing apparatus 1, hologram pages are recorded / reproduced by irradiating the hologram recording medium HM thus rotationally driven with laser light using the first laser 2 as a light source.

The first laser 2 is, for example, a laser diode with an external resonator, and outputs so-called blue-violet laser light having a wavelength λ = 405 nm, for example. Hereinafter, laser light using the first laser 1 as a light source is referred to as first laser light.
The first laser light emitted from the first laser 2 is guided to the shutter 4 after passing through the collimator lens 3.

  The opening / closing operation of the shutter 4 is controlled by a control unit 29 described later, and blocks / passes incident light.

  The first laser light through the shutter 4 is guided to the galvanometer mirror 5 as shown in the figure. The galvanometer mirror 5 is provided in order to realize a so-called image stabilization function.

Here, the recording / reproducing apparatus 1 of the present embodiment records the hologram by irradiating the rotationally driven hologram recording medium HM with the signal light and the reference light.
At this time, in order to record a hologram as an interference fringe between the signal light and the reference light, a certain reaction time of the recording material in the recording layer R-3 is required. For this reason, in the system that performs rotational recording on the hologram recording medium HM, the laser beam is scanned so that the irradiation position of the signal light and the reference light is stationary at a certain position on the hologram recording medium HM for a certain time. Has been. Specifically, by changing the laser beam emission angle at a speed synchronized with the rotation speed of the hologram recording medium HM (rotation speed of the spindle motor 21), the irradiation spot of the signal light and the reference light is reflected on the hologram recording medium HM. It stays at a certain position for a certain time.

  The galvanometer mirror 5 changes the emission angle of the reflected light of the incident light based on the control by the control unit 29.

The light emitted from the galvanometer mirror 5 is reflected by the mirror 6 and guided to an SLM (spatial light modulator) 7.
The SLM 7 performs, for example, spatial light intensity modulation (also simply referred to as intensity modulation) as spatial light modulation on incident light. In this case, the SLM 7 is a reflection type, and a spatial light modulator such as a DMD (Digital Micromirror Device: registered trademark) or a reflection type liquid crystal panel is employed.
The SLM 7 modulates the intensity of incident light in units of pixels by changing the light intensity of each intensity modulation element based on the drive signal supplied from the modulation control unit 26 shown in the figure.

Here, in this embodiment, a coaxial method is adopted as a hologram recording / reproducing method. When the coaxial method is adopted, in the SLM 7, in order to arrange the signal light and the reference light on the same optical axis, each area as shown in FIG. 5 is set.
As shown in FIG. 5, in the SLM 7, a substantially circular area having a predetermined range including the center is set as the signal light area A2. A substantially annular reference light area A1 is set outside the signal light area A2 with a gap area A3 therebetween.
By setting the signal light area A2 and the reference light area A1, the signal light and the reference light can be irradiated so as to be arranged on the same optical axis.
The gap area A3 is defined as a region for preventing the reference light generated in the reference light area A1 from leaking into the signal light area A2 and becoming noise with respect to the signal light.

In FIG. 4, the modulation control unit 26 performs drive control on the SLM 7 to generate signal light and reference light during recording and only reference light during reproduction.
Specifically, at the time of recording, the modulation control unit 26 sets the pixels in the signal light area A2 in the SLM 7 to an on / off pattern corresponding to the supplied recording data, and the pixels in the reference light area A1 are predetermined predetermined. A drive signal for turning on / off the pattern and turning off all other pixels is generated and supplied to the SLM 7. By intensity modulation by the SLM 7 based on this drive signal, signal light and reference light that are arranged so as to have the same optical axis are obtained as light emitted from the SLM 7.
Further, at the time of reproduction, the modulation control unit 26 drives and controls the SLM 7 with a drive signal that turns the pixels in the reference light area A1 into the predetermined on / off pattern and turns off all other pixels. Only the reference light is generated.

  At the time of recording, the modulation control unit 26 generates an on / off pattern in the signal light area for each predetermined unit of the input recording data string, and thereby generates data for each predetermined unit of the recording data string. It operates so that the stored signal light is sequentially generated. As a result, data is sequentially recorded on the hologram recording medium HM in units of hologram pages (data units that can be recorded by one-time interference between the signal light and the reference light).

  The light subjected to spatial light modulation by the SLM 7 is guided to the polarization beam splitter 8. The polarization beam splitter 8 transmits the first laser beam guided from the SLM 7.

  The first laser light transmitted through the polarization beam splitter 8 is guided to the dichroic mirror 9. The dichroic mirror 9 is configured to transmit the first laser light and reflect a second laser light (light using the second laser 15 as a light source) described later. For this reason, the first laser light transmitted through the polarizing beam splitter 8 is transmitted through the dichroic mirror 9, reflected by the mirror 10 as shown in the figure, and after passing through the quarter wavelength plate 11, The hologram recording medium HM is irradiated through the objective lens 12 held by the biaxial mechanism 13.

  The biaxial mechanism 13 is directed to the direction in which the objective lens 12 is brought into and out of contact with the hologram recording medium HM (focus direction) and the radial direction of the hologram recording medium HM (direction perpendicular to the focus direction: tracking direction). And hold it displaceable. Further, a focus coil for driving the objective lens 12 in the focus direction and a tracking coil for driving in the tracking direction are provided.

  Here, according to the optical path described above, the laser light that has undergone spatial light modulation in the SLM 7 is irradiated onto the hologram recording medium HM via the objective lens 12, but the recording by the SLM 7 described above. Depending on the temporal spatial light modulation, signal light and reference light are generated. Accordingly, at the time of recording, the hologram recording medium HM is irradiated with the signal light and the reference light. As a result, a hologram is formed on the recording layer R-3 by interference fringes of these lights, and data is recorded. .

For confirmation, the shape of the hologram recorded on the hologram recording medium HM is shown in FIG. In FIG. 6, a part of the recording layer R-3 on which the hologram is recorded is extracted and shown.
As shown in FIG. 6, the hologram is recorded in a shape corresponding to the shape of the signal light applied to the recording layer R-3. Specifically, in this case, the signal light is condensed with the lower surface of the recording layer R-3 (the interface with the reflective film R-4) as the condensing surface. ) Is made smaller. At this time, the shape of the upper surface of the hologram is substantially circular according to the spot shape of the signal light formed on the upper surface of the recording layer R-3, and the shape of the bottom surface of the hologram is substantially square according to the pixel shape of the SLM7. To be shaped.

FIG. 7 shows a state of light obtained on the light collecting surface when the signal light and the reference light are irradiated. In FIG. 7, the light intensity is represented by a color density, and the dark color → light color represents light intensity small → large. The horizontal axis represents the distance in the x direction (radial direction of the hologram recording medium HM) from the optical axis center, and the vertical axis represents the distance in the y direction (direction perpendicular to the x direction: linear direction) from the optical axis center.
As shown in FIG. 7, in response to the irradiation of the signal light and the reference light at the time of recording, on the condensing surface, along with the substantially square light spot as the bottom surface of the hologram described above, Separate light spots are formed in the left and right directions.
At this time, the size (width) WH of the bottom surface of the hologram surrounded by the white frame in the figure is defined by the following equation.


WH = 2fλ / d (Equation 1)


In the above equation, f is the focal length of the objective lens, λ is the wavelength of the recording / reproducing light (in this case, the wavelength of the first laser light), and d is the size (width) of one pixel of the SLM.
Note that the pixel shape of the SLM is usually a square, and the width of the bottom surface of the hologram can be considered to be the same in the x and y directions.

Here, as can be seen with reference to FIG. 6, the light obtained on the light collection surface by the irradiation of the signal light and the reference light has a strong light intensity within a certain range including the center of the optical axis, and moves away from it. The light intensity gradually decreases, and a portion where the light intensity = 0 appears. Then, after the light intensity = 0, the light intensity increases again, and the above-mentioned vertical and horizontal spots appear.
The above equation defines the range from the center of the optical axis to the portion where the light intensity = 0 (the portion surrounded by a white frame in FIG. 6) as the hologram bottom surface.

Returning to FIG.
As described above, only the reference light is generated in the SLM 7 during reproduction. The reference light generated in this way is also applied to the hologram recording medium HM through an optical path similar to the optical path during recording described above.
In this way, when the hologram recording medium HM is irradiated with the reference light, a reproduced image is obtained by the diffraction action corresponding to the hologram recorded in the recording layer R-3. The reproduced image thus obtained is returned to the apparatus side as reflected light from the reflection film R-4 of the hologram recording medium HM.

  The reproduced image passes through the objective lens 12 → the quarter-wave plate 11 → the mirror 10, passes through the dichroic mirror 9, and enters the polarization beam splitter 8. The polarization beam splitter 8 is configured to reflect the reproduced image incident through the quarter-wave plate 11 as described above. The reproduced image reflected by the polarization beam splitter 8 is guided to the image sensor 14 as shown in the figure.

  The image sensor 14 is, for example, a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor. The image sensor 14 receives a reproduced image from the hologram recording medium HM guided as described above, and uses this as an electrical signal. To obtain an image signal. The image signal thus obtained reflects an on / off pattern (that is, a data pattern of “0” and “1”) given to the signal light at the time of recording. That is, the image signal detected by the image sensor 14 in this way corresponds to a read signal for data recorded on the hologram recording medium HM.

  The data reproduction unit 27 performs data identification of “0” and “1” for each pixel value of the SLM 7 included in the image signal detected by the image sensor 14 and a demodulation process of the recording modulation code as necessary. Etc. to reproduce the recorded data.

  In addition, the recording / reproducing apparatus 1 as the first embodiment shown in FIG. 4 has the recording / reproducing position of the hologram recording / reproducing operation performed using the first laser beam as described above. As an optical system for controlling, an optical system using a separate light source different from the first laser 2 is provided. Specifically, they are the second laser 15, the collimator lens 16, the polarization beam splitter 17, the condensing lens 18, and the photodetector 19 in the drawing.

The second laser 15 is configured to emit laser light having a wavelength different from that of the first laser light. Specifically, for example, red laser light having a wavelength of about 650 nm is output.
In this case, the wavelength difference between the first laser 2 and the second laser 12 is about 250 nm. By providing a sufficient wavelength difference in this way, the laser beam (second laser beam) using the second laser 15 as a light source is almost insensitive to the recording layer R-4 of the hologram recording medium HM. It will be a thing.

The second laser light emitted from the second laser 15 passes through the polarization beam splitter 17 through the collimator lens 16 and is then guided to the dichroic mirror 9.
As described above, the dichroic mirror 9 is configured to have wavelength selectivity such that the first laser light is transmitted and the second laser light is reflected. Accordingly, the second laser light transmitted through the polarizing beam splitter 17 is guided to the mirror 10 side as shown in the figure.
Thus, the second laser beam guided to the mirror 10 side is also irradiated onto the hologram recording medium HM through the same path as in the case of the first laser beam.
As can be understood from this, the dichroic mirror 9 has a function of synthesizing the first laser beam and the second laser beam and irradiating the hologram recording medium HM through the same objective lens 12. It is what. Further, due to the wavelength selectivity, the reproduction image of the hologram is also returned to the image sensor 14 and the second laser beam (position control light) is returned to the photodetector 19 independently.

  Here, when the hologram recording medium HM is irradiated with the second laser light as described above, the concavo-convex cross-sectional shape (track TR by the pit row) on the reflective film R-4 in the hologram recording medium HM is reflected. Reflected light is obtained. The reflected light from the reflective film R-4 also enters the dichroic mirror 9 via the objective lens 12 → the quarter wavelength plate 11 → the mirror 10 as in the case of the first laser light.

  The dichroic mirror 9 reflects the reflected light of the second laser light, and the reflected light is guided to the polarization beam splitter 17 side. The polarization beam splitter 17 reflects the reflected light of the second laser light from the hologram recording medium HM, and the reflected light is irradiated so as to be condensed on the detection surface of the photodetector 19 via the condenser lens 18. .

The photodetector 19 includes a plurality of light receiving elements, receives the reflected light from the hologram recording medium HM irradiated through the condenser lens 18 as described above, and obtains an electrical signal corresponding to the light reception result. That is, the reflected light information reflecting the uneven cross-sectional shape formed in the reflective film R-4 is thereby detected.
The reflected light information (reflected light signal) detected by the photodetector 19 is supplied to the matrix circuit 20.

The matrix circuit 20 includes a matrix calculation / amplification circuit for the output signals from the plurality of light receiving elements as reflected light signals from the photodetector 19, and generates necessary signals by matrix calculation processing.
For example, a signal (reproduction signal RF) corresponding to a reproduction signal for a pit string formed on the hologram recording medium HM, a focus error signal FE for servo control, a tracking error signal TE, and the like are generated.

  The reproduction signal RF output from the matrix circuit 20 is supplied to the address detection / clock generation circuit 28. The focus error signal FE and the tracking error signal TE are supplied to the servo circuit 25.

The address detection / clock generation circuit 28 detects address information based on the reproduction signal RF and performs a clock generation operation.
As for detection (reproduction) of address information, the track number information and sector number information described above are detected.
As the clock generation operation, an operation for generating a reproduction clock by performing PLL processing based on the reproduction signal RF is performed.
The address information detected (reproduced) by the address detection / clock generation circuit 28 is supplied to the control unit 29. Although not shown, the clock information is supplied as an operation clock for each necessary unit.

The spindle control circuit 22 controls the rotation of the spindle motor 21. As the rotation control (rotation control of the hologram recording medium HM) method of the spindle motor 21, for example, a CAV (Constant Angular Verlocity) method or a CLV (Constant Linear Verlocity) method can be adopted.
For confirmation, when the CLV method is adopted, the spindle control circuit 22 inputs information on the reproduction clock output from the address detection / clock generation circuit 28 described above as rotation control information, and the reproduction clock The rotation control of the spindle motor 21 is performed so that the period becomes a predetermined constant period.

The slide mechanism 24 holds the optical unit UN in the drawing so as to be slidable in the tracking direction (radial direction of the hologram recording medium HM). As shown in the figure, the optical unit UN includes a first laser 2, a collimator lens 3, a shutter 4, a galvano mirror 5, a mirror 6, an SLM 7, a polarization beam splitter 8, a dichroic mirror 9, a mirror 10, a quarter wavelength plate 11, The objective lens 12, the biaxial mechanism 13, the image sensor 14, the second laser 15, the collimator lens 16, the polarization beam splitter 17, the condensing lens 18, and the photodetector 19 are included.
The slide drive unit 23 includes a motor for driving the slide mechanism 24, and the slide mechanism 24 is configured to slide the optical unit UN based on the driving force of the motor.

The servo circuit 25 generates various servo signals for focus, tracking, and thread based on the focus error signal FE and the tracking error signal TE from the matrix circuit 20 described above, and performs a servo operation.
That is, a focus servo signal and a tracking servo signal are generated in accordance with the focus error signal FE and the tracking error signal TE, and these are supplied as drive signals (focus drive signal, tracking drive signal) of the biaxial mechanism 13, thereby generating two axes. The focus coil and tracking coil of the mechanism 13 are driven and controlled by drive signals corresponding to the servo signals. As a result, a tracking servo loop and a focus servo loop are formed by the photodetector 19, the matrix circuit 20, the servo circuit 25, and the biaxial mechanism 13.
The servo circuit 25 turns off the tracking servo loop in response to an instruction from the control unit 29 and outputs a jump pulse as the tracking drive signal, thereby executing a track jump operation.

  Also, the servo circuit 25 slides the slide mechanism 24 by the slide drive unit 23 based on the thread error signal obtained as the low frequency component of the tracking error signal TE, the seek operation control from the control unit 29, etc., and the optical unit UN Slide the whole.

  In addition, the servo circuit 25 also controls the start and stop of the spindle motor 21 based on instructions from the control unit 29.

Various operations of the servo system as described above are controlled by a control unit 29 configured by a microcomputer including, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like.
The control unit 29 performs overall control of the recording / reproducing apparatus 1 by executing each arithmetic processing / control processing based on a program stored in a required memory such as the ROM.

For example, the control unit 29 controls the recording / reproducing position of the hologram by controlling the operation of the servo system described above.
Specifically, when a certain data recorded on the hologram recording medium HM is to be reproduced, first, seek operation control to the target address is performed. That is, the servo circuit 25 is instructed to execute an access operation targeting the target address. Here, according to the above description, it is necessary to irradiate the reference light when reproducing the data (hologram) recorded on the hologram recording medium HM. For this reason, at the time of reproduction, along with the above-described seek operation control, the modulation control unit 26 executes the drive control operation of the SLM 7 corresponding to the reproduction described above, and causes the SLM 7 to generate reference light.

  For example, when data is recorded at a certain position on the hologram recording medium HM, an instruction is given to the servo circuit 25 to execute an access operation to the target address, and the modulation control unit 26 is made to record data. By instructing to start the drive control of the corresponding SLM 7, signal light is generated together with the reference light.

During recording, the opening / closing control of the shutter 4 described above is also performed. Furthermore, drive control for the galvanometer mirror 5 is also performed so that scanning of the laser beam is performed as an image stabilization function.
As control for the galvanometer mirror 5, the angle of the mirror is changed so that the emission angle of the laser beam is changed in a predetermined direction (a direction coinciding with the disk rotation direction) at a required speed, and then the mirror is returned in the reverse direction. This control is repeated. On the other hand, as a control for the shutter 4, the shutter 4 is opened during the beam emission angle control period (that is, the period when the spot is stationary on the medium: the recording period during which recording is performed on the hologram page), and the other periods are Control is performed so that the shutter 5 is closed.
For confirmation, according to the above control, a period during which the beam is not irradiated is provided between the recording periods of the holograms. It is intended to prevent unnecessary reaction parts from being formed between the recorded holograms.

At this time, the recording interval in the linear direction of each hologram (hologram page) is set so as to realize shift multiplex recording as shown in FIG. In this shift multiplex recording, holograms are recorded in such a manner that the bottom surfaces of the holograms are overlapped in the line direction.
In the recording / reproducing apparatus 1 of this embodiment, the recording interval of each hologram as the shift multiplex recording as shown in FIG. 8 is obtained, and the rotational speed of the hologram recording medium HM and the opening / closing time of the shutter 4 are obtained. And the scan angle of the laser beam in the galvanometer mirror 5 is set.

Here, for confirmation, in the coaxial method, a hologram recorded by irradiating a reference light given a certain spatial light modulation pattern irradiates the reference light given the spatial light modulation pattern. It can be played back. When multiplex recording is performed using this point, holograms are multiplex-recorded using reference lights each having a different spatial light modulation pattern, and at the time of reproduction, a hologram to be reproduced is selected among the multiplexed holograms. The reproduction is performed by irradiating the reference light having the same spatial light modulation pattern as when the hologram was recorded.
In the present embodiment, the reference light pattern changing operation at the time of reproduction in response to such shift multiplex recording being performed is realized by the control unit 29 giving a pattern instruction to the modulation control unit 26. Yes.

Further, at the time of reproduction, the control unit 29 performs control to scan the laser beam in the same manner as at the time of recording. That is, at the time of reproduction, the control unit 29 sequentially sets the reference light pattern to the same pattern as that at the time of recording the hologram to be reproduced by controlling the modulation control unit 26, and the reference light is reproduced every time one hologram page is reproduced. The mirror angle of the galvanometer mirror 5 is controlled so that the recording position of the target hologram is continuously irradiated for a predetermined time. At this time, similarly to the recording, the shutter 4 can be controlled to be closed during a period in which the laser beam is returned in the direction opposite to the disk rotation direction.

[Recording / reproducing method of this embodiment]

Here, as can be seen with reference to FIG. 1, in the present embodiment, as the reflective film of the hologram recording medium HM, one common reflective film R that reflects the hologram recording / reproducing light and the position control light is used. -4 only.
However, when such a hologram recording medium HM is to record a hologram at a position on the track TR as in the prior art, noise light is superimposed on the reproduced image due to the unevenness imparted to the reflective film R-4. As a result, the reproduction characteristics are remarkably deteriorated.
From this point, in the conventional hologram recording / reproducing system, as described above with reference to FIGS. 23 to 24, the laser light for hologram recording / reproducing and the laser light for position control with different wavelengths are used. In addition to the reflection film 110 provided with the irregularities associated with the formation of the track TR, a flat reflection film 108 is provided for returning the reproduced image of the hologram to the apparatus side. The film 108 is given wavelength selectivity (recording / reproducing light is reflected and position control light is transmitted). In other words, such a technique prevents the unevenness for position control from being reflected in the reproduced image.

However, when such a conventional method is adopted, it is necessary to provide two reflection films on the hologram recording medium, and the medium structure is complicated accordingly. In this respect, the conventional method causes an increase in manufacturing cost of the recording medium.
Further, as the reflective film (108) for obtaining the reproduced image, it is necessary to use a film having wavelength selectivity in order to transmit the position control laser beam. The film is more expensive than a normal reflective film, and this also causes an increase in medium manufacturing cost.

  Therefore, in the present embodiment, the hologram recording medium HM is provided with a common reflection film R-4 that reflects the hologram recording / reproducing light and the position control light, and the unevenness of the track TR is provided. In order to solve the problem of deterioration in reproduction characteristics due to superimposition of noise light on the resulting reproduced image, the following method is adopted.

  In the present embodiment, the hologram is not recorded at a position on the track TR as in the prior art, but is recorded between the tracks TR. More specifically, hologram recording is performed such that the center position of the hologram coincides with the center position between the tracks TR.

FIG. 9 is a diagram for explaining a recording method according to the present embodiment.
In FIG. 9, a track TR formed on the hologram recording medium HM, a beam spot (recording / reproducing spot SP1) of recording / reproducing light using the first laser 2 as a light source, and a second laser 15 as a light source. The relationship with the beam spot (position control spot SP2) of the position control light to be performed is schematically shown.

First, as a premise, the center (the optical axis of the second laser beam) of the position control spot SP2 is positioned at the center (one-dot chain line portion in the figure) of the track TR by the tracking servo.
Based on this premise, in order to record the hologram with the center position Ct-t between the tracks TR as the center, the hologram recording / reproducing spot SP1 has its center (light of the first laser 2). Is only required to be separated from the center of the position control spot SP2 by a distance corresponding to the arrangement interval of the tracks TR. Specifically, as shown in the figure, when the track pitch of the track TR is TP, the distance between the center of the recording / reproducing spot SP1 and the center of the position control spot SP2 (radial direction = the distance in the track arrangement direction) ) D1 may be TP / 2.
Thus, when the position control spot SP2 follows the track TR by the tracking servo, the center of the hologram recording / reproducing spot SP1 can always be at the center position Ct-t between the tracks TR.

  In the recording / reproducing apparatus 1 as the present embodiment shown in FIG. 4, the center of the recording / reproducing spot SP1 (the optical axis of the first laser beam) and the center of the position controlling spot SP2 (the second) The distance of the first laser beam incident on the objective lens 12 is set such that the distance in the arrangement direction of the track TR (the radial direction of the hologram recording medium HM) with respect to the optical axis of the laser beam is ½ of the track pitch. The relationship between the optical axis and the optical axis of the second laser light is adjusted. As a result, the recording / reproducing apparatus 1 can record the hologram around the center position Ct-t between the tracks TR.

  For the sake of confirmation, the track pitch TP in this case is based on the same position in the adjacent track TR as represented by the interval between the alternate long and short dash lines in FIG. It refers to the time interval. For example, as shown in FIG. 9, when the center position (center axis) of the track TR is considered as a reference, the track pitch TP is an interval between the center positions of the adjacent tracks TR. Alternatively, when the boundary position with the land on one side (for example, the right side) of the track TR is used as a reference, the distance between the boundary positions of the adjacent tracks TR is set.

FIG. 10 illustrates a specific method for adjusting the distance D1 in the arrangement direction of the track TR between the optical axis of the first laser beam and the optical axis of the second laser beam as described above to a predetermined distance. As shown in FIG. 4, a part (the dichroic mirror 9, the mirror 10, the quarter wavelength plate 11, and the objective lens 12) in the optical unit UN shown in FIG. 4 is extracted and shown.
As shown in FIG. 10, in the recording / reproducing apparatus 1 of the present embodiment, the incident positions of the first laser light (recording / reproducing light) and the second laser light (position control light) with respect to the dichroic mirror 9 Is adjusted so that the distance in the arrangement direction of the track TR between the optical axis of the first laser light and the optical axis of the second laser light incident on the objective lens 12 becomes a predetermined distance D1.

Here, according to the recording / reproducing apparatus 1 in which the separation distance between the optical axes of the first laser beam and the second laser beam is adjusted as described above, the hologram recording / reproducing spot SP1 even during reproduction. Follows the center position between the tracks TR. Specifically, for the reference light irradiated for reproducing the hologram at the time of reproduction, the spot SP1 can be traced around the center position Ct-t between the tracks TR.
Thereby, according to the recording / reproducing apparatus 1 of this Embodiment, the hologram recorded centering | focusing on the center position between tracks TR with the said recording method can be read appropriately.

For confirmation, in the case of the coaxial method, the optical axis of the first laser light (recording / reproducing light) is synonymous with the optical axis of the signal light and the optical axis of the reference light.

[Recording medium as the present embodiment]

In the present embodiment, there is also provided a hologram recording medium HM capable of recording so that the bottom surface of the hologram does not overlap the track TR.
In the hologram recording medium HM of the present embodiment, as shown in FIG. 11, the interval Dt-t between the tracks TR is set to be equal to or larger than the width WH of the bottom surface of the hologram. As is apparent from the figure, the distance Dt-t between the tracks TR corresponds to the width of the land portion between the tracks TR.

Here, the width WH of the bottom surface of the hologram is defined by [Formula 1] presented earlier. For example, as shown in FIG. 12, an aperture 32 for improving the recording density is provided. In some cases, the size of the bottom surface of the hologram will be determined depending on the size of the aperture 32. In FIG. 12, only the configuration in the optical unit UN is extracted and shown.
The aperture 32 is inserted into a position that becomes a Fourier plane (frequency plane: a plane from which an image similar to the light condensing surface of the medium is obtained) in the optical system as shown in the figure. In the example of FIG. 12, a relay lens system including relay lenses 30 and 31 is inserted between the SLM 7 and the polarization beam splitter 8, and an aperture 32 is inserted into a condensing surface of the relay lens system.
The aperture 32 limits the passage area of incident light on the Fourier plane, thereby limiting the size of the bottom surface of the hologram and improving the recording density.

In a system in which such an aperture 32 is used, the distance Dt-t between the tracks TR of the hologram recording medium HM is a value of the width (WH-ap) of the hologram bottom determined by the size of the aperture 32 (aperture size). It will be set according to. Specifically, the distance Dt-t between the tracks TR in this case is set to be equal to or larger than the width WH-ap of the bottom surface of the hologram.

[Effect of the embodiment]

The recording operation by the recording / reproducing apparatus 1 described above is performed on the hologram recording medium HM in which the interval Dt-t between the tracks TR is set as described above, so that the hologram does not overlap the track TR. Can be recorded.
According to this, in the case of adopting a medium structure in which recording / reproducing light is also reflected by a reflective film provided with unevenness for position control, reproduction characteristics deteriorate due to the hologram being recorded on the track TR. Can be completely prevented.

Here, even if the distance Dt-t between the tracks TR as the hologram recording medium HM is not equal to or larger than the width WH of the bottom surface of the hologram, according to the recording method of the present example described above, the track TR Compared with the conventional method of recording a hologram with respect to the upper position, it is still possible to suppress the deterioration of the reproduction characteristics.
Since the deterioration of the reproduction characteristics can be suppressed in this way, according to the recording method of the present embodiment, it is not necessary to provide two reflecting films as in the case of recording a hologram on the conventional track TR. Furthermore, it is not necessary to give wavelength selectivity to the reflective film. Therefore, according to the recording method of the present embodiment, the structure of the recording medium can be simplified and the manufacturing cost can be reduced.

Here, for confirmation, in order to realize a method of reflecting the hologram recording / reproducing light and the position control light by the common reflection film R-4, the hologram is not necessarily applied to the track TR. There is no need to ensure that they do not overlap completely. When the system is put to practical use, it is only necessary to obtain characteristics that are practically acceptable as reproduction characteristics. What is important here is that a hologram is not recorded on the track TR as in the prior art, and this makes it possible to suppress the superposition of noise light on the reproduced image. It is possible to realize a hologram recording medium in which the number is reduced to one.

<Second Embodiment>

Next, a second embodiment will be described.
In the first embodiment, a laser beam different from the recording / reproducing laser beam is separately irradiated as the position control laser beam. However, the second embodiment is a recording / reproducing laser beam. The laser light obtained by spectrally dividing the laser light is used as position control laser light.

FIG. 13 is a diagram for explaining the internal configuration of the recording / reproducing apparatus according to the second embodiment. The internal configuration of the optical unit UN included in the recording / reproducing apparatus of the second embodiment (and the spindle motor 21) is shown. The hologram recording medium HM) held in a state where it can be rotated is extracted and shown. In the recording / reproducing apparatus according to the second embodiment, the configuration other than the optical unit UN is the same as that shown in FIG. 4 described above, and a description thereof is omitted here.
Also, with regard to the configuration in the optical unit UN, the same reference numerals are given to the same parts as those already described with reference to FIG.

The optical unit UN in this case is different in the following points from the optical unit UN shown in FIG. First, in the recording / reproducing apparatus in this case, the second laser 15, the collimator lens 16, the polarization beam splitter 17, and the dichroic mirror 9 are omitted.
Then, a non-polarizing beam splitter 35 is inserted between the collimator lens 3 and the shutter 4, and a part of the first laser light transmitted through the non-polarizing beam splitter 35 is used as hologram recording / reproducing light. A part of the first laser beam reflected by the polarization beam splitter 35 is used as a laser beam for position control.

  In this case, the position control laser light obtained as the reflected light component of the non-polarizing beam splitter 35 is guided to the half mirror 38 via the mirror 36 → mirror 37. The half mirror 38 transmits a part of incident light and reflects a part thereof (transmittance 50%, reflectivity 50%). The position control laser light transmitted through the half mirror 38 is guided to a non-polarization beam splitter 39 inserted between the polarization beam splitter 8 and the mirror 10 as shown in the figure.

The non-polarizing beam splitter 39 reflects a part of the position control laser light guided as described above and guides the reflected light to the mirror 10. The non-polarizing beam splitter 39 transmits part of the recording / reproducing laser light incident via the polarizing beam splitter 8 and guides the transmitted light to the mirror 10.
By such a non-polarizing beam splitter 39, both the recording / reproducing laser beam and the position controlling laser beam are guided to the objective lens 13 through the mirror 10 → ¼ wavelength plate 11. Yes. That is, this makes it possible to form the recording / reproducing laser beam spot SP1 and the position controlling laser beam spot SP2 on the reflection film R-4 of the hologram recording medium HM.

Further, according to the above configuration, the reflected light (returned light) from the reflective film R-4 is guided to the non-polarizing beam splitter 39 via the objective lens 12 → the quarter wavelength plate 11 → the mirror 10. The return light guided in this way is partially transmitted by the non-polarizing beam splitter 39 and partially reflected. Thereby, a part of the return light of the recording / reproducing laser beam is guided to the polarization beam splitter 8 and irradiated to the image sensor 14.
A part of the return light of the position control laser light is guided to the half mirror 38 described above. The half mirror 38 reflects a part of the return light of the position control laser light, and the reflected light is guided to the condenser lens 18. Thus, the return light of the position control laser beam guided to the condensing lens 18 is irradiated so as to be condensed on the detection surface of the photodetector 19 by the condensing lens 18.

  With the configuration as described above, hologram recording / reproduction and recording / reproduction position control based on the detection result of the reflected light of the position control laser beam can be performed.

In the recording / reproducing apparatus of the second embodiment, the optical axis of the recording / reproducing laser beam obtained as the transmitted light of the non-polarizing beam splitter 35 and the position control obtained as the reflected light of the non-polarizing beam splitter 35 are used. The optical system is adjusted so that the separation distance (in this case, the distance in the track arrangement direction of the hologram recording medium HM) D1 of the laser beam from the optical axis is ½ of the track pitch TP of the track TR.
Thus, in this case as well, as in the case of the first embodiment, the hologram can be recorded with the center position Ct-t between the tracks TR as the center. In addition, the hologram recorded with the center position Ct-t between the tracks TR as the center can be properly reproduced.
Also in this case, if the hologram recording medium HM is set so that the distance Dt-t between the tracks TR is equal to or larger than the width WH of the bottom surface of the hologram, the bottom surface of the hologram does not overlap the track TR. Hologram recording can be performed.

  In this case, it is not necessary to separately provide a light source different from the light source of the recording / reproducing laser beam for position control. In other words, the device manufacturing cost can be reduced accordingly.

  In the recording / reproducing apparatus in this case, the adjustment of the separation distance D1 between the optical axes of the respective lights incident on the objective lens 12 is performed on the non-polarizing beam splitter 39 in the same manner as in the first embodiment. This can be realized by adjusting the respective incident positions of the recording / reproducing laser beam and the position controlling laser beam.

By the way, in the case of the recording / reproducing apparatus according to the second embodiment described above, the image sensor 14 is also irradiated with a part of the return light of the position control laser beam.
Considering this point, in the recording / reproducing apparatus of the second embodiment, the ratio of the transmittance / reflectance in the non-polarizing beam splitters 35 and 39 is, for example,
Non-polarizing beam splitter 35... Transmittance = 90%, reflectance = 10%
Non-polarizing beam splitter 39... Transmittance = 90%, reflectance = 10%
It is set to. That is, the transmittance is greatly increased with respect to the reflectance.
With this setting, the intensity of the return light of the position control laser light incident on the image sensor 14 is sufficiently weakened relative to the intensity of the return light (reproduction signal light) of the recording / reproduction laser light. In this respect, the deterioration of reproduction characteristics due to the return light of the position control laser beam during reproduction is suppressed.

In the case of the second embodiment, the half mirror 38 reflects not only the return light of the position control laser beam but also part of the return light of the recording / reproducing laser beam and guides it to the photodetector 19 side. However, since the reflected light component of the half mirror 38 is condensed by the condenser lens 18 and irradiated to the photodetector 19, the photodetector 19 is irradiated only with the return light of the position control laser beam. In this respect, position control based on the return light of the position control laser light can be appropriately performed.

<Third Embodiment>

The third embodiment corresponds to a so-called transmissive hologram recording medium (HM-t) that does not include a reflective film.
FIG. 14 shows a cross-sectional structure diagram of a transmissive hologram recording medium HM-t.
In FIG. 14, the hologram recording medium HM-t is also provided with an antireflection film R-1 as the uppermost layer and a cover layer R-2 as the lower layer. In this case, the hologram recording layer provided on the lower layer side of the cover layer R-2 is divided into an upper recording layer R-6 and a lower recording layer R-8 as shown in FIG. Between the layer R-6 and the recording layer R-8, a translucent film R-7 having a concavo-convex cross-sectional shape associated with the formation of the track TR is inserted. On the lower layer of the lower recording layer R-8, a substrate R-9 (functioning as a cover layer for the recording layer) that is not provided with an uneven cross-sectional shape is formed.

Here, as the transmission type hologram recording medium HM-t, as shown in FIG. 14, the hologram recording layer is divided into upper and lower parts with a translucent film R-7 as a track forming layer as a boundary. The structure to be made is common. This is because the recording density of the hologram can be improved.
In the case of the transmissive hologram recording medium HM-t, the hologram is formed (recorded) in a portion where the light beam (recording / reproducing light) in the figure overlaps the recording layers R-6 and R-8. That is, the hologram in this case is formed in a shape like an hourglass over the upper and lower recording layers R-6 and R-8.
At the time of reproduction, a reproduced image corresponding to the hologram recorded in accordance with the irradiation of the reference light is obtained. In this case, the reproduced image is a surface opposite to the surface on which the reference light is incident (substrate R- 9).

In the translucent film R-7, as in the reflection film R-4 of the hologram recording medium HM described with reference to FIGS. 1 to 3, the track TR is formed by forming a pit row in which address information is recorded. It is formed. Also in this case, the track TR is formed in a spiral shape or a concentric shape.
The translucent film R-7 transmits a part of incident light and reflects a part thereof. Thus, when the semi-transparent film R-7 is irradiated with position control laser light as will be described later, the position control laser light can be changed according to the unevenness as the track TR. It has become.

  Also in this case, the distance Dt-t between the tracks TR is set to be equal to or larger than the width WH of the bottom surface of the hologram. Thus, it is possible to provide a hologram recording medium that can be recorded so that the bottom surface of the hologram does not overlap the track TR.

FIG. 15 is a diagram for describing an internal configuration of a recording / reproducing apparatus as a third embodiment that performs recording / reproduction corresponding to the transmission-type hologram recording medium HM-t described above. In FIG. 15, the internal configuration of the optical unit UN provided in the recording / reproducing apparatus of the third embodiment (and the hologram recording medium HM-t held in a state where it can be rotationally driven by the spindle motor 21) is extracted. Show.
The configuration of the recording / reproducing apparatus of the third embodiment is the same as that shown in FIG. 4 except for the configuration of the optical unit UN. Also, with regard to the configuration in the optical unit UN, the same reference numerals are given to the same parts as those already described with reference to FIG.
Here, for convenience of illustration, the illustration of the shutter 4, the galvanometer mirror 5, and the mirror 6 is omitted, and the SLM 7 is shown as if it is a transmissive spatial light modulator (for example, a transmissive liquid crystal panel). However, the configuration of this part is actually the same as that shown in FIG.

In the optical unit UN in this case, the polarizing beam splitter 8 inserted between the SLM 7 and the dichroic mirror 9 is omitted and the quarter wavelength is compared with the optical unit UN shown in FIG. The plate 11 is also omitted.
In this case, in the optical unit UN, the hologram recording medium HM-t set at a predetermined position in the recording / reproducing apparatus is used as a boundary with respect to a position opposite to the position where the objective lens 12 is disposed. The condensing lens 40 held by the shaft mechanism 41 so as to be movable in the tracking direction and the focus direction is provided.
In this case, the recording / reproducing laser beam (first laser beam) and the position control laser beam (second laser beam) emitted from the objective lens 12 are translucent film R- formed on the hologram recording medium HM-t. A part of the light is transmitted at 7 and enters the condenser lens 41.
Then, the first laser light and the second laser light that have passed through the hologram recording medium HM-t and entered the condensing lens 41 in this way enter the dichroic mirror 42 via the condensing lens 41.

Similar to the dichroic mirror 9, the dichroic mirror 42 is configured to have wavelength selectivity for transmitting the first laser beam and reflecting the second laser beam. Thus, the first laser light passes through the dichroic mirror 42 and is irradiated to the image sensor 14 provided so as to receive the light transmitted by the dichroic mirror 42 as shown in the figure.
The second laser light passing through the condenser lens 41 is reflected by the dichroic mirror 42 and guided to the condenser lens 18 provided so that the reflected light from the dichroic mirror 42 is incident.
In this case, the photodetector 19 is provided at a position where the light collected by the condenser lens 18 is received. Thus, the photodetector 19 obtains a light reception signal for the second laser beam through the semitransparent film R-7 (track formation layer) of the hologram recording medium HM-t.

  Although not shown, the light reception signal of the photodetector 19 is supplied to the matrix circuit 20 in this case as well, and the matrix circuit 20 generates a tracking error signal TE and a focus error signal FE based on the light reception signal and outputs them to the servo circuit 25. To supply. The servo circuit 25 generates a tracking servo (drive) signal and a focus servo (drive) signal based on the tracking error signal TE and the focus error signal FE. In this case, the servo circuit 25 generates the tracking drive generated in this way. The biaxial mechanism 13 and the biaxial mechanism 41 are simultaneously driven and controlled by the signal and the focus drive signal. Thus, the objective lens 13 and the condensing lens 40 facing each other through the hologram recording medium HM-t move in conjunction with each other. In other words, as described above, the first laser beam and the second laser beam emitted from the objective lens 12 and transmitted through the hologram recording medium HM-t are incident on the condenser lens 41 as described above.

With the configuration as described above, hologram recording / reproduction corresponding to the transmission type hologram recording medium HM-t as shown in FIG. 14 and recording / reproduction based on the detection result of the reflected light of the position control laser beam are performed. Position control can be performed.
Also in the recording / reproducing apparatus of the third embodiment, as in the case of the first embodiment, the separation distance between the optical axis of the first laser beam and the optical axis of the second laser beam (this Also in this case, the optical system is adjusted so that the distance (D1) in the arrangement direction of the tracks TR) becomes 1/2 of the track pitch TP of the tracks TR.
In this case as well, the hologram can be recorded around the center position Ct-t between the tracks TR. In addition, the hologram recorded with the center position Ct-t between the tracks TR as the center can be properly reproduced.
Also in this case, if the hologram recording medium HM-t is set so that the distance Dt-t between the tracks TR is equal to or larger than the width WH of the bottom surface of the hologram, the bottom surface of the hologram does not overlap the track TR. Thus, hologram recording can be performed.

  In this case as well, the adjustment of the separation distance D1 between the optical axes of the respective lights incident on the objective lens 12 is performed by the recording / reproducing laser beam for the dichroic mirror 9, as in the case of the first embodiment. This can be realized by adjusting the respective incident positions of the position control laser light.

Here, the system using the transmission type hologram recording medium has a different problem from the case of the system using the reflection type hologram recording medium.
Specifically, in the case of a transmission-type hologram recording medium, a reflection film as a track forming layer is used as in the case of a reflection-type hologram recording medium because of the feature of detecting a reproduced image that is transmitted through the recording medium. A method of providing a reflective film (reflective film 108) for reflecting the reproduced image above the (reflective film 110 in FIG. 23) to prevent the reproduced image from being affected by the unevenness of the track forming layer is adopted. Can not be. That is, in this respect, in a system using a transmissive hologram recording medium, if it is assumed that a hologram is recorded on the track TR as in the prior art, the reproduced image is not affected by unevenness in the track forming layer. As a result, it has been impossible to adopt a configuration in which the track TR is formed on the recording medium and the recording / reproducing position control is performed.
For such a situation, according to the third embodiment described above, it is effective to deteriorate the reproduction characteristics due to the reproduction image of the hologram being transmitted through the translucent film R-7 as the track forming layer. Can be suppressed. That is, in this respect, according to the third embodiment, as a recording / reproducing system for the transmission hologram recording medium, a configuration is realized in which the recording / reproducing position is controlled by forming the track TR on the recording medium. It is something that can be done.

  15 illustrates the case where a light source different from the light source for recording / reproducing laser light is provided as the light source for position control laser light separately as in the case of the first embodiment. As in the case of the second embodiment, it is possible to obtain a recording / reproducing laser beam and a position controlling laser beam by splitting light from the same light source.

FIG. 15 illustrates the configuration in which the position control is performed based on the result of detecting the position control laser light transmitted through the translucent film R-7 of the hologram recording medium HM-t. Since a part of the incident light is reflected, the position can be controlled based on the result of detecting the reflected light from the translucent film R-7.
In that case, the dichroic mirror 42 shown in FIG. 15 is omitted. For example, a half mirror is provided between the dichroic mirror 9 and the collimator lens 16 as a configuration for extracting the reflected light of the position control laser light from the semitransparent film R-7, and the reflected light of the half mirror is provided. It is sufficient to provide the condenser lens 18 so that the light is incident, and to provide the photodetector 19 so that the light condensed by the condenser lens 18 is irradiated.

<Fourth embodiment>

The fourth embodiment corresponds to a case where a so-called two-beam method is adopted instead of the coaxial method adopted in each of the previous embodiments.
FIG. 16 is a diagram for explaining a hologram recording / reproducing method using the two-beam method, and a cross-sectional structure of the hologram recording medium HM, and signal light applied to the hologram recording medium HM in the case of the two-beam method. A mode with reference light is shown typically.

First, the signal light is irradiated in the same manner as in the coaxial system. That is, also in this case, the signal light is generated by being subjected to spatial light modulation according to the recording data by the spatial modulator, and then irradiated to the hologram recording medium HM as condensed light through the objective lens.
In the two-beam method, the reference light is not disposed on the same optical axis as the signal light, but is irradiated onto the recording medium at an angle different from that of the signal light. At this time, as the reference light, the recording medium is irradiated with the parallel light as shown in the drawing without passing through the objective lens.

  In the case of the two-beam method, changing the reference light irradiation angle corresponds to changing the spatial light modulation pattern of the reference light in the coaxial method. That is, in the case of the two-beam method, a hologram recorded by irradiating reference light at a certain irradiation angle at the time of recording can be read out by irradiating the reference light at the same irradiation angle at the time of reproduction. Is to multiplex-record holograms by making the irradiation angle of the reference light variable. In this sense, the two-beam method is also called an angle multiplexing method.

FIG. 17 is a diagram for explaining an internal configuration of a recording / reproducing apparatus as the fourth embodiment for performing recording / reproduction by the two-beam method.
In FIG. 17, the configuration in the optical unit UN included in the recording / reproducing apparatus according to the fourth embodiment (and the hologram recording medium HM held in a state where it can be rotationally driven by the spindle motor 21) is extracted. The other parts are the same as those of the recording / reproducing apparatus 1 shown in FIG.

First, also in the recording / reproducing apparatus in this case, the configuration of the optical system for irradiating the signal light is provided as in the case of FIG. Specifically, in the optical unit UN in this case, the first laser light emitted from the first laser 2 is transmitted through the collimator lens 3 → half mirror 45 (described later) → shutter 4 → galvanometer mirror 5 through the SLM 7. Is incident on.
In this case, a transmissive spatial light modulator is used as the SLM 7. The transmissive spatial light modulator can be realized by, for example, a transmissive liquid crystal panel.

  In this case, in the SLM 7, only signal light is generated by performing spatial light modulation in units of pixels with respect to incident light. That is, in this case, the modulation control unit 26 that performs drive control of the SLM 7 is a drive signal that sets the signal light area A2 of the SLM 7 to an on / off pattern according to the recording data and turns off all other areas during recording. Thus, each pixel of the SLM 7 is driven and controlled.

  Although the case where a transmissive spatial light modulator is used as the SLM 7 is illustrated here, it is of course possible to use a reflective spatial light modulator as shown in FIG.

  The configuration of the optical system after the SLM 7 is the same as that shown in FIG. Specifically, the light emitted from the SLM 7 is irradiated onto the hologram recording medium HM through the objective lens 12 and a reproduced image obtained through the objective lens 12 in response to the irradiation of the reference light is guided to the image sensor 14. The configuration (the polarizing beam splitter 8, the quarter wavelength plate 11, and the objective lens 12 in the figure) is provided in the same manner as in FIG.

  The recording / reproducing apparatus in this case is also provided with a configuration for performing position control based on irradiation of position control laser light using the second laser 15 as a light source. Specifically, the second laser 15, the collimator lens 16, the polarization beam splitter 17, the dichroic mirror 9, the condensing lens 18, the photodetector 19, and the biaxial mechanism 13 are provided in the same manner as in FIG.

In the recording / reproducing apparatus in this case, as a two-beam method, as an optical system for irradiating the hologram recording medium HM with reference light at an angle different from the signal light, a half mirror 45 and a galvanometer mirror in the figure 46 is provided.
The half mirror 45 is provided so as to be inserted between the collimator lens 3 and the shutter 4 as shown in the figure, for example. The half mirror 45 transmits a part of the first laser beam incident through the collimator lens 3 and reflects a part thereof (transmittance 50%, reflectivity 50%). A part of the first laser light transmitted through the half mirror 45 is guided to the shutter 4 as understood from the above description. On the other hand, a part of the first laser light reflected by the half mirror 45 is irradiated as reference light to the hologram recording medium HM after passing through the galvano mirror 46 as shown in the figure.
The galvanometer mirror 46 is provided in order to make the irradiation angle of the reference light variable in realizing the angle multiplex recording described with reference to FIG.

Here, in order to realize the recording method described in FIG. 16, in the recording / reproducing apparatus in this case, the irradiation range of the reference light is the irradiation range of the signal light in the recording layer R-3 of the hologram recording medium HM. The optical system is adjusted so as to overlap. Specifically, the irradiation range of the reference light in this case is sufficiently wide so that the entire movable range of the signal light irradiation position accompanying the position control of the objective lens 12 in the tracking direction can be covered.
At this time, according to the configuration shown in FIG. 17, the objective lens 12 and the galvanometer mirror 46 are provided in the same optical unit UN, and even if the entire optical unit UN is moved (sliding), such a signal is used. The relationship between the irradiation range of light and reference light is maintained. Thus, in this case, only the position control of the signal light spot based on the irradiation of the position control laser light is performed, and the hologram can be recorded at a desired position.

  For confirmation, the galvano mirror 5 is also provided in this case, and the image stabilization operation is performed. As can be understood from the description in the first embodiment, the spot of the signal light moves in the linear direction of the hologram recording medium HM depending on the image stabilization operation. From this point, the irradiation range of the reference light in this case is set so as to cover the movement range of the signal light spot in the linear direction.

  Here, although explanation by illustration is omitted, the control unit 29 in this case performs mirror angle control of the galvanometer mirror 46 so as to realize angle multiplex recording. Specifically, the mirror angle of the galvanometer mirror 46 is sequentially changed for each signal light irradiation period as a period for controlling the shutter 4 to the open state.

  In this case, the control unit 29 controls the mirror angle of the galvanometer mirror 46 so that the reference light is irradiated at the same irradiation angle as when the hologram to be reproduced is recorded. As a result, a reproduced image of the hologram to be reproduced can be selectively obtained, and each angle-multiplexed hologram can be reproduced appropriately.

For confirmation, in the case of the two-beam method, at the time of reproduction, 1) the position control light spot (that is, the readout position) is moved to the recording address of the hologram to be reproduced, and 2) the reproduction target is reproduced. The reference light is irradiated at the same irradiation angle as when recording the hologram. Accordingly, a reproduced image of the hologram to be reproduced is obtained.
At this time, the objective lens 12 is placed at a position where the reproduced image of the hologram to be reproduced can be incident as the position control of 1) is performed. In other words, the reconstructed image obtained by the irradiation of the reference light of 2) is appropriately guided to the image sensor 14 via the quarter wavelength plate 11 → the mirror 10 → the dichroic mirror 9 → the polarization beam splitter 8. It has come to be.

  As described above, the recording / reproducing apparatus shown in FIG. 17 is capable of recording / reproducing a hologram by the two-beam method and controlling the recording / reproducing position based on the detection result of the reflected light of the position control laser beam. It is said that.

In addition, in the recording / reproducing apparatus of the fourth embodiment shown in FIG. 17, the optical axis of the signal light irradiated through the objective lens 12 using the first laser 2 as a light source, and the second laser 15 A separation distance (in this case, a distance in the track arrangement direction of the hologram recording medium HM) D1 as a light source from the optical axis of the position control laser light irradiated through the objective lens 12 is 1 of the track pitch TP of the track TR. The optical system is adjusted to be / 2.
Thus, in this case as well, as in the case of the first embodiment, the hologram can be recorded with the center position Ct-t between the tracks TR as the center. In addition, the hologram recorded with the center position Ct-t between the tracks TR as the center can be properly reproduced.
Also in this case, if the hologram recording medium HM is set so that the distance Dt-t between the tracks TR is equal to or larger than the width WH of the bottom surface of the hologram, the bottom surface of the hologram does not overlap the track TR. Hologram recording can be performed.

  Here, in the recording / reproducing apparatus shown in FIG. 17, the adjustment of the separation distance D1 between the optical axes of the respective lights incident on the objective lens 12 is performed with respect to the dichroic mirror 9 according to the case of the first embodiment. This can be realized by adjusting the incident positions of the signal light and the position control laser light.

  In the above description, as a configuration example of the recording / reproducing apparatus when the two-beam method is adopted, the light source for obtaining the hologram recording / reproducing light and the position control light are obtained as in the first embodiment. However, instead of this, the configuration is such that the light from the same light source is dispersed to obtain the position control laser light as in the second embodiment. You can also.

In the above description, the case where the reflection type hologram recording medium HM is used as the hologram recording medium is exemplified, but the transmission type hologram recording medium HM-t as described in the third embodiment can also be used. .
As a recording / reproducing apparatus in that case, at least a configuration for detecting a reproduced image is provided on the opposite side of the hologram recording medium HM-t as described in the third embodiment.

[Modification]

As mentioned above, although each embodiment of this invention was described, as this invention, it should not be limited to the specific example demonstrated so far.
For example, in the description so far, the case where the track TR by the pit row is formed on the hologram recording medium HM is exemplified, but the track TR may be formed by a continuous groove (groove). At this time, by forming the groove so as to meander periodically, the position information can be recorded based on the meandering period information. In that case, on the recording / reproducing apparatus side, position information (address information) / clock is reproduced based on the result of detecting the information on the meandering period of the groove formed on the hologram recording medium HM.

Further, the recording of the position information can be performed not only by information on the pit row and the above-described meandering period of the groove but also by forming a mark row, for example.
Here, when position information is recorded by forming a mark row, the following two types of structures of the hologram recording medium HM can be considered.
One is to form a mark row directly on the reflective film R-4. In this case, the sectional structure of the hologram recording medium HM is, for example, the same as that shown in FIG. 1, the antireflection film R-1 → the cover layer R-2 → the recording layer R-3 → the reflection film R-4 → Each layer is formed in the order of the substrate R-5. For confirmation, the substrate R-5 in this case is not given an uneven cross-sectional shape.
The other is that a mark recording layer made of, for example, an organic (or inorganic) dye material or a phase change film is inserted, and position information is recorded by forming a mark on the mark recording layer. Specifically, in the case of a reflection type hologram recording medium, the mark recording layer is inserted between the recording layer R-3 and the reflection film R-4 (in this case also, the substrate R-5 has irregularities). Needless to say, you can't be given.) In the case of a transmissive hologram recording medium, for example, the mark recording layer is inserted into a position where the translucent film R-7 is formed.

In the description so far, the case where recording / reproduction is performed by rotationally driving the hologram recording medium has been exemplified. However, recording / reproduction for a desired position on the hologram recording medium by moving the optical unit UN side is performed. It is also possible to take a technique to do.
In that case, the hologram recording medium may have a rectangular shape instead of a disk shape. In addition, the track TR is not the spiral shape or the concentric shape described so far, but a plurality of linear tracks TR can be arranged.

For example, assuming that the hologram recording medium has a rectangular shape, a plurality of tracks TR extending in one direction (x direction) in the planar direction are arranged in the y direction (direction perpendicular to the x direction). Can do. In that case, the arrangement state of the tracks TR in the track forming layer is the same as that shown in FIG. Specifically, the direction indicated as the line direction in FIG. 9 corresponds to the x direction, and the direction indicated as the radial direction corresponds to the y direction.
Even in this case, each track TR is formed such that the distance Dt-t between the tracks TR is equal to or larger than the width WH of the bottom surface of the hologram, so that the bottom surface of the hologram does not overlap the track TR. A hologram recording medium capable of recording can be provided.

Further, when the hologram recording medium is not rotationally driven, the track TR can be formed in a lattice shape as shown in FIG.
In this case, multiple holograms are recorded in one square of the grating.
In this case, the interval between the tracks TR arranged in the x direction and the interval between the tracks TR arranged in the y direction may be set to be equal to or larger than the width WH of the bottom surface of the hologram.
This is a condition when the pixel shape of the SLM 7 is assumed to be a square. For example, when the pixel shape is a rectangle, the interval between the tracks TR in the x direction is x on the bottom surface of the hologram. The distance between the tracks TR in the y direction is equal to or greater than the width of the hologram bottom surface in the y direction.

In the above description, when controlling the recording / reproducing position of the hologram, the light from a light source separate from the light source of the recording / reproducing light is irradiated as the position control light, or obtained from the recording / reproducing light by spectroscopy. Although the case of irradiating light as position control light has been exemplified, it is also possible to adopt a configuration that realizes position control by irradiating only recording / reproducing light.
Here, as described above with reference to FIG. 7, on the condensing surface, as the light spot of the recording / reproducing light, along with the light spot corresponding to the bottom surface of the hologram (inside the white frame in FIG. 7: referred to as the main spot) Light spots (referred to as sub-spots) also appear in the upper, lower, left and right directions.
Using such a sub spot that appears on the side of the track TR in the arrangement direction, position control is performed so that the sub spot traces on the track TR as shown in FIG. 19, for example. Thereby, the main spot (corresponding to the bottom surface of the hologram) can be traced around the center position between the tracks TR.
For example, by adopting such a method, the position control can be performed together with the irradiation of the hologram recording / reproducing light without separately irradiating the position control light.

For confirmation, FIG. 20 shows the configuration of a recording / reproducing apparatus that also performs position control by irradiating only hologram recording / reproducing light with a method using such sub-spots.
In FIG. 20, only the configuration in the optical unit UN of the recording / reproducing apparatus (and the hologram recording medium HM held in a state where it can be rotated by the spindle motor 21) is extracted and shown. Other configurations are the same as those shown in FIG. 4 and are not shown.

As shown in the figure, in this case, a configuration for irradiating the hologram recording medium HM with position control light using the second laser 15 as a light source (second laser 15, collimator lens 16, polarization beam splitter 17, dichroic mirror 9). Is omitted.
On the other hand, a configuration for irradiating the hologram recording medium HM with recording / reproducing light using the first laser 2 as a light source via the objective lens 12 (first laser 2, collimator lens 3, shutter 4, galvano mirror 5, mirror 6) , SLM 7, polarizing beam splitter 8, mirror 10, quarter-wave plate 11, objective lens 12 held by biaxial mechanism 13 are provided in the same manner as in FIG.

  Here, according to such a configuration, the return light to the device side of the above-mentioned sub spot and the reproduced image obtained at the time of reproduction are polarized beam splitter via the objective lens 12 → the quarter wavelength plate 11 → the mirror 10. 8 is incident. The polarization beam splitter 8 reflects the return light and the reproduced image of the incident incident sub-spot.

In the recording / reproducing apparatus in this case, with respect to the return light / reproduced image of the secondary spot obtained as the reflected light of the polarization beam splitter 8 as described above, the return light of the secondary spot is detected by the photodetector 19, and the reproduced image is also obtained. An optical system for detection by the image sensor 14 is provided. Specifically, the mirror 50, the half mirror 51, and the collimator lens 18 in the figure.
The half mirror 51 transmits a part of the light incident through the polarizing beam splitter 8 → the mirror 50 and reflects a part thereof. The light transmitted through the half mirror 51 is irradiated to the image sensor 14 as shown in the figure. As a result, the reproduced image can be detected by the image sensor 14.
Further, the light reflected by the half mirror 51 is guided to the collimator lens 18 as shown in the figure, and is condensed on the detection surface of the photodetector 19. At this time, the arrangement position of the photodetector 19 is such that the sub-spot used for position control is on the track TR among the sub-spots appearing on the arrangement direction side of the track TR, and the return light spot of the sub-spot is the detection surface. It is adjusted so that it is located in the upper center part. As a result, position control (tracking servo) for tracing the secondary spot on the track TR is appropriately performed.

  For example, with such a configuration, it is possible to realize a technique in which position control is also performed only by irradiation of hologram recording / reproducing light.

Further, in the description so far, the case where the coaxial method is adopted is exemplified as the case where the signal light area A2 is set to be circular and the reference light area A1 is set to be ring-shaped accordingly. However, the shapes of the reference light area A1 and the signal light area A2 are not limited to these, and may be set to have other shapes such as a rectangular shape. It can be suitably applied.
Also, when the two-beam method is adopted, the shape of the signal light can be other than circular.

  In the above description, only the case where the recording apparatus of the present invention is configured as a recording / reproducing apparatus having a hologram reproducing function has been exemplified. However, of course, the recording apparatus is configured as a recording-only apparatus having no hologram reproducing function. You can also In this case, a configuration for detecting a reproduced image of the hologram (image sensor 14 and polarization beam splitter 8 in FIGS. 4 and 17, image sensor 14, polarization beam splitter 8, quarter wavelength plate 11 in FIG. 13, FIG. 15). In FIG. 20, the image sensor 14, the dichroic mirror 42, and in FIG. 20, the image sensor 14, the polarization beam splitter 8, the quarter wavelength plate 11, and the half mirror 51) can be omitted.

Further, the playback apparatus of the present invention can be applied to a playback-only apparatus that does not have a recording function.
For example, when the coaxial method is adopted, the configuration of the read-only device is the same as that shown in FIGS. 4, 13, and 15. However, in this case, the SLM 7 does not generate signal light according to the recording data.
Note that the reproduction-only apparatus does not irradiate the signal light but irradiates only the reference light. In this case, the sub-spot as shown in FIG. 7 is not formed. From this point, the reproduction-only device cannot be configured to perform position control by irradiation with only one light as described with reference to FIGS. In other words, the reproduction-only device adopts a configuration in which the light from the light source is dispersed or the position control light is separately generated and irradiated by providing a separate light source.

  Here, as a reproduction-only device when the coaxial method is adopted, in order to reproduce the hologram recorded so that the center is located at the center position Ct-t between the tracks TR, the spot of the reference light is What is necessary is just to make it locate in the center position Ct-t between tracks TR. For this reason, as a reproduction-only device when the coaxial method is adopted, the separation distance in the track TR arrangement direction between the optical axis of the reference light and the optical axis of the position control light is ½ of the track pitch of the track TR. It suffices if the optical system is adjusted so that

It is the figure which showed the cross-section of the hologram recording medium (reflection type) as embodiment. It is the figure which showed the example of formation of the guide track with respect to a hologram recording medium. It is the figure which showed the other example of formation of the guide track with respect to a hologram recording medium. It is the block diagram which showed the internal structure of the recording / reproducing apparatus as 1st Embodiment. It is a figure for demonstrating each area of the signal light area, reference light area, and gap area which are set to a spatial light modulator. It is a figure for demonstrating the shape of the hologram recorded on the hologram recording medium. It is the figure which showed the mode of the light obtained by a condensing surface when signal light and reference light were irradiated. It is a figure for demonstrating shift multiple recording. It is a figure for demonstrating the recording technique as embodiment. It is a figure for demonstrating the specific method for adjusting the separation distance in the track arrangement direction of the optical axis of recording / reproducing light, and the optical axis of position control light. It is the figure which showed the relationship between the space | interval between tracks, and the width | variety of the bottom face of the recorded hologram. It is the figure which showed the example of insertion of an aperture. It is a figure for demonstrating the internal structure of the recording / reproducing apparatus as 2nd Embodiment. It is the figure which showed the cross-section of the hologram recording medium (transmission type) as embodiment. It is a figure for demonstrating the internal structure of the recording / reproducing apparatus as 3rd Embodiment. It is a figure for demonstrating a two light beam system (angle multiplexing system). It is a figure for demonstrating the internal structure of the recording / reproducing apparatus as 4th Embodiment. It is the figure which showed the formation example of the track | truck as a modification. It is a figure for demonstrating the method of performing position control only by irradiation of recording / reproducing light. It is a figure for demonstrating the internal structure of the recording / reproducing apparatus which performs position control only by irradiation of recording / reproducing light. It is a figure for demonstrating the recording method of the data with respect to a hologram recording medium. It is a figure for demonstrating the reproduction | regeneration method of the data recorded on the hologram recording medium. It is the figure which showed the cross-section of the hologram recording medium as a prior art example. It is the figure which showed the internal structure of the recording / reproducing apparatus as a prior art example.

Explanation of symbols

  HM hologram recording medium (reflection type), HM-t hologram recording medium (transmission type), R-1 antireflection film, R-2 cover layer, R-3 recording layer, R-4 reflection film, R-5, R -9 substrate, R-6 upper recording layer, R-7 translucent film, R-8 lower recording layer, 1 recording / reproducing device, 2nd laser, 3,16 collimator lens, 4 shutter, 5,46 galvano Mirror, 6, 10, 36, 37, 50 Mirror, 7 SLM, 8, 17 Polarizing beam splitter, 9, 42 Dichroic mirror, 11 1/4 wavelength plate, 12 Objective lens, 13, 41 Biaxial mechanism, 14 Image sensor , 15 Second laser, 18 Condenser lens, 19 Photo detector, 20 Matrix circuit, 21 Spindle motor, 22 Spindle control circuit, 23 Slide drive unit, 24 Slide mechanism, 25 Servo circuit, 26 Change Control unit, 27 data reproducing unit, 28 an address detection and the clock generation circuit, 29 control unit, 30 and 31 a relay lens, 32 apertures, 35, 39 non-polarizing beam splitter, 38,45,51 a half mirror, 40 a condenser lens

Claims (11)

At least one recording layer for recording data by forming a hologram corresponding to the signal light by interference fringes between the signal light and the reference light, and a guide track for guiding the recording position of the hologram in the recording layer A recording apparatus for recording on a hologram recording medium having a track forming layer formed so that a plurality of lines are arranged in a direction,
A light source;
Signal light generating means for generating the signal light by applying spatial light modulation according to recording data to the light emitted from the light source;
Reference light generating means for generating the reference light based on the light emitted from the light source;
A recording apparatus comprising: a recording light irradiation unit configured to irradiate the signal light and the reference light so that the hologram is formed around a center position between the guide tracks formed in the track formation layer. The recording apparatus according to claim 1,
The recording light irradiation means
An objective lens serving as an output end of the signal light to the hologram recording medium;
The objective lens guides the signal light to the objective lens, and uses the light obtained by spectrally dividing the light emitted from the light source or the light emitted from another light source different from the light source as the position control light. And the distance between the optical axis of the signal light and the optical axis of the position control light in the arrangement direction of the guide tracks is ½ of the track pitch of the guide tracks. An optical system configured to guide the signal light and the position control light to the objective lens;
A position error representing a position error of the light spot of the position control light with respect to the guide track, which is obtained when the position control light irradiated onto the hologram recording medium through the objective lens passes through the track forming layer. And a spot position control unit that controls the position of the objective lens so that the light spot is positioned on the guide track based on the detection result of the information. The recording apparatus according to claim 2,
The signal light generation means and the reference light generation means are:
The signal light and the reference are obtained by performing spatial light modulation for generating the signal light and the reference light by a common spatial light modulator that performs spatial light modulation by entering light emitted from the light source, respectively. The light is generated so as to be arranged on the same optical axis. The recording apparatus according to claim 3,
The track forming layer is composed of a reflective film,
The spot position control unit in the recording light irradiation means is
The position of the objective lens is controlled based on the result of detecting the position error information by receiving the reflected light of the position control light from the reflective film. The recording apparatus according to claim 4,
Furthermore, a rotation driving means for rotating the hologram recording medium is provided. The recording apparatus according to claim 5, wherein
The guide track is formed of a pit row in which position information representing a position on the hologram recording medium is recorded,
Position information detection means for detecting the position information based on the reflected light of the position control light from the reflective film is further provided. The recording apparatus according to claim 2,
The track forming layer is composed of a translucent film,
The spot position control unit in the recording light irradiation means is
The position of the objective lens is controlled based on the result of detecting the position error information by receiving the position control light transmitted through the translucent film. The recording apparatus according to claim 1,
The recording light irradiation means
The hologram recording medium is irradiated with the reference light through an optical path different from an optical path for irradiating the hologram recording medium with the signal light. A recording layer on which data is recorded by forming a hologram corresponding to the signal light by interference fringes between the signal light and the reference light, and at least one guide track for guiding the recording position of the hologram in the recording layer A recording method for recording a hologram recording medium having a track forming layer formed so that a plurality of the recording medium is arranged in
A signal light generation procedure for generating the signal light by performing spatial light modulation according to the recording data on the light emitted from the light source;
A reference light generation procedure for generating the reference light based on the light emitted from the light source;
A recording light irradiation procedure for irradiating the signal light and the reference light so that the hologram is formed around a center position between the guide tracks formed in the track forming layer. A recording layer on which data is recorded by forming a hologram corresponding to the signal light by interference fringes between the signal light and the reference light, and at least a guide track for guiding the recording position of the hologram in the recording layer A reproducing apparatus for reproducing a hologram recording medium having a track forming layer formed so that a plurality of lines are arranged in one direction,
A light source;
Reference light generating means for generating the reference light based on the light emitted from the light source;
An objective lens serving as an output end of the reference light with respect to the hologram recording medium;
The objective lens is configured to guide the reference light to the objective lens, and to obtain light obtained by spectrally dividing the light emitted from the light source or light emitted from another light source different from the light source as position control light. And the distance between the optical axis of the reference light and the optical axis of the position control light in the arrangement direction of the guide tracks is ½ of the track pitch of the guide tracks. An optical system configured to guide the reference light and the position control light to the objective lens;
A position error representing the position error of the light spot of the position control light with respect to the guide track, which is obtained when the position control light irradiated onto the hologram recording medium through the objective lens passes through the track forming layer. And a spot position control means for controlling the position of the objective lens so that the light spot is positioned on the guide track based on a result of detecting information. A recording layer on which data is recorded by forming a hologram corresponding to the signal light by interference fringes between the signal light and the reference light;
A track forming layer formed such that a plurality of guide tracks for guiding the recording position of the hologram in the recording layer are arranged in at least one direction;
A hologram recording medium in which the guide tracks in the track forming layer are formed with an interval equal to or greater than the width of the bottom surface of the hologram recorded in the recording layer.