JP2007149251A - Optical information recording/reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To strike a balance between the assurance of followability with recording medium movement and the compactness of an optical system. <P>SOLUTION: Reference and information lights are generated from a luminous flux emitted from a first laser light source by a space modulator 3, and information is recorded in the recording medium 12 of a moving state by using holography. During reproduction, only the reference light from the space modulator 3 is applied to the recording medium 12 to guide a reflected light to an image light receiving element 5. A luminous flux from a second laser light source is applied to the recording medium 12 to obtain a servo signal from the reflected light. At least one relay lens 8 of a relay optical system is moved in a direction vertical to an optical axis by the servo signal to execute moving direction following-up of the recording medium, and the position of merging the luminous flux from the second laser light source with the optical system from the first laser light source to the recording medium 12 is in space between at least one relay lens 8 and the space modulator 12. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical information recording / reproducing apparatus, and in particular, optical information for recording information on a recording medium on which information is recorded using holography and reproducing information from the recording medium on which information is recorded. The present invention relates to a recording / reproducing apparatus.

  A method of recording information on a recording medium using holography is performed by superimposing light having image information and reference light inside the recording medium and writing interference fringes generated at that time on the recording medium. At the time of reproduction, image information is reproduced by diffracting by interference fringes by irradiating the recording medium with reference light. In recent years, holographic memory has attracted attention in the field of practical use as ultra-high density data storage. In particular, image information is developed into two-dimensional digital pattern information, which is recorded on a disc-shaped recording medium similar to a CD or DVD using holography, and the information is reproduced from the recording medium. Optical disc memories that attract attention are attracting attention.

  As such a technique, for example, there is a recording / reproducing apparatus using a collinear holographic memory disclosed in Non-Patent Documents 1 and 2 below.

  The feature of this method is that information light and reference light are produced by the same spatial modulator, propagated along the same optical axis, and focused on a recording medium by an objective lens to record a hologram. Further, when only the reference light is generated from the spatial modulator and condensed on the recording medium, the information light is reproduced by diffraction from the recorded hologram.

  Normally, in such an optical disk memory, focus servo and tracking servo for eccentric tracking are performed in the same manner as CD and DVD.

  In addition, in the optical disk memory as described above, in order to record the rotating recording medium information, a very high output light source such as a Q switch laser is required for recording in a short time. When using a light source with an output typified by a semiconductor laser, it is necessary to change the light irradiation position according to the rotation in order to secure energy for recording.

  For example, the light irradiation position is caused to follow the light irradiation position by rotating the recording light source collimator perpendicularly to the optical axis (Patent Document 1 below).

  FIG. 6 shows a conventional optical information recording / reproducing apparatus disclosed in Patent Document 1.

The light from the recording / reproducing light source 32 includes a first collimator lens 33, a polarizing beam splitter 34, a spatial light modulator (information expression means) 35, a pair of relay lenses 36a and 36b, a dichroic mirror 37, and a quarter wavelength. It reaches the recording medium 31 through the plate 38 and the objective lens 39.
On the other hand, the light from the servo reading element 41 travels to the second collimator lens 42 and the dichroic mirror 37. The photodetector 43 receives the reproduction light and reproduces the recorded information.

  The servo reading element 41 detects position information of the recording medium 31 and moves the first collimator lens 33 following the movement of the recording medium 31 by the driving means 44. This is because the angle of the recording light incident on the polarization beam splitter 34 is changed so that the position of the light incident on the recording medium 31 is shifted to follow the movement of the recording medium 31 so that the information is placed at a normal position. This is for recording or reproducing information from a regular position.

In addition, there is one that uses two galvanometer mirrors arranged in an optical system to follow the tracking servo and the rotation position of the light irradiation position orthogonal thereto (Patent Document 2 below).
Proceedings of 35th Meeting on Lightwave Sensing Technology June, 2005 p.75-82 “Holographic Memory / Measurement and Nano-Control Technology Supporting HVDTM” NIKKEI ELECTRONICS 2005.1.17 p.105-114 “Achieving 200GB in the near-takeoff holographic media in 2006” Japanese Patent Laying-Open No. 2005-032306 JP 2004-022083 A

  However, the above conventional example has the following problems.

 In general, when the recording medium rotates with an eccentricity, the moving speed in the rotational direction at the light irradiation position changes according to the eccentricity even at a constant speed.

  On the other hand, in the conventional example in which the recording light source collimator is moved perpendicularly to the optical axis to rotate and follow the light irradiation position, the light emitted from the servo reading element is recorded on the recording medium by the recording light source collimator. Meet on the side.

  Therefore, in the conventional example as described above, the movement of the recording light source collimator has no effect on the light emitted from the servo reading element. There was a problem that the accuracy of.

  In the above conventional example in which the tracking servo and the light irradiation position orthogonal to the tracking servo are rotated and tracked using two galvanometer mirrors arranged in the optical system, the mirror near the recording medium must be rotated. Don't be. For this reason, in order to avoid positional interference with the focus servo driving means, there has been a problem that the apparatus becomes large in the vicinity of the recording medium.

  Alternatively, it is necessary to newly provide a mirror element in the optical system, and there is a problem that optical design is restricted.

  SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to achieve both ensuring of the follow-up performance for recording medium movement and compactness of the optical system.

  In order to solve the above problems, an optical information recording / reproducing apparatus of the present invention irradiates a spatial light with a light beam from a first laser light source, generates reference light and information light by the spatial modulator, and relay optical Information is recorded on a recording medium in a moving state using holography through a system, and the recording medium is irradiated with only reference light from the spatial modulator, and reflected light from the recording medium. It is assumed that the optical information recording / reproducing apparatus obtains a servo signal by reflected light by irradiating the image receiving element to the image light receiving element, reproducing information, irradiating the recording medium with a light beam from a second laser light source.

  In the optical information recording / reproducing apparatus, the servo signal causes at least one relay lens of the relay optical system to move in a direction perpendicular to the optical axis to follow the moving direction of the recording medium, and the second laser light source The position where the light beam from the light beam joins with the optical system from the first laser light source to the recording medium is between the at least one relay lens and the spatial modulator.

  According to the present invention, the relay lens is moved to follow the moving direction of the recording medium, and the light beam from the light source for obtaining the servo signal is merged between the moving lens and the spatial modulator. There is no element, and the tracking error can be accurately detected according to the movement of the relay lens, so that it is possible to ensure the tracking performance for the movement of the recording medium and the compactness of the optical system.

[Embodiment 1]
FIG. 1 is a diagram showing an optical path of an optical information recording / reproducing apparatus according to the first embodiment of the present invention.

  First, the optical path during recording will be described.

  A light beam emitted from a green LD (laser diode) 1 as a recording / reproducing light source, which is a semiconductor laser, is collimated by a collimator 2 and enters a spatial modulator 3.

  The spatial modulator 3 is composed of a liquid crystal element, and selects whether or not to rotate the polarization direction by 90 ° for each pixel using the optical rotation of the liquid crystal, and reflects it by the polarization beam splitter 4 after that. The predetermined information can be carried by the incident light flux depending on whether or not. By forming an information pattern to be recorded near the center of the light beam and forming a reference light pattern around the information pattern, information light and reference light can be generated simultaneously.

  The recording light beam composed of the information light and the reference light generated in this way passes through the polarization beam splitter 4 and a pair of relay lenses (consisting of a first relay lens 6 and a second relay lens 8), and is ¼ wavelength. The plate 9 converts linearly polarized light into circularly polarized light. At this time, the dichroic beam splitter 7 is transmitted. Thereafter, the recording light beam is deflected by the mirror 10 and is irradiated onto the hologram disk 12 as a recording medium by the objective lens 11.

  In the hologram disk 12, the information light and the reference light interfere with each other and the hologram is recorded. The hologram disk 12 is rotated by driving means.

  Here, although not shown, the hologram disk 12 includes a transparent substrate, a recording layer that absorbs the green wavelength and transmits the red wavelength, and a reflective layer as viewed from the light incident side, and the recording of the hologram is performed on the recording layer. The

  The movement of the reproduction light beam during reproduction is basically the same as during recording. However, at the time of reproduction, the pattern formed by the spatial modulator 3 is only a predetermined reference light pattern. At this time, the information light generation region 21 may be masked. When the reference light is applied to the hologram disk 12, it is diffracted by the recorded hologram, and reproduction light carrying information on the hologram is generated.

  This reproduction light is converted into a substantially parallel light beam by the objective lens 11 and converted into linearly polarized light orthogonal to the time of irradiation on the hologram disk 12 by the quarter wavelength plate 9. After that, the reproduction light passes through the polarization beam splitter 4 through the reverse optical path from the time of irradiation, and is received and reproduced by the CMOS sensor 5 which is an image light receiving element. At this time, the ambient light of the reproduction light that did not contribute to diffraction is shielded on the CMOS sensor 5.

  On the other hand, at the time of reading the servo signal and addressing signal, a light beam is emitted from the red LD 13 which is a light source for reading the servo signal and addressing signal. This light beam passes through the polarizing beam splitter 14, passes through the coupling lens 15, is reflected by the dichroic beam splitter 7, and becomes a substantially parallel light beam after passing through the relay lens 8. The light beam passes through the quarter-wave plate 9 and is deflected by the mirror 10, and is irradiated onto the hologram disk 12 by the objective lens 11.

  The servo signal and addressing signal reading light beam reflected by the reflection layer of the hologram disk 12 traces the same optical path in reverse with the information of the servo signal and addressing signal, and is reflected by the polarization beam splitter 14. To do. The reflected light flux passes through the sensor lens 16 and enters a PD (photodiode) 17 that is a light receiving element for servo signal and addressing signal, and the servo signal and addressing signal are reproduced. From this, a rotation direction tracking error signal is also obtained.

  By the way, in this embodiment, the relay lens 8 is reciprocated by the driving means 18 in the left-right direction (FIG. 1, a direction perpendicular to the paper surface) with respect to the optical axis. The driving means 18 performs feedback control in accordance with a servo signal reproduced from the light beam incident on the PD 17 to move the relay lens 8.

  For this control, in this embodiment, the servo signal and addressing signal reading optical system is combined with the recording / reproducing optical system before the optical path to the relay lens 8 which is a movable element, so that the relay lens 8 Signal detection according to movement is made possible.

  Here, the driving means 18 is a uniaxial actuator using a magnetic circuit.

  Incidentally, the focus servo and the tracking servo for the eccentric follow-up perform feedback control according to the servo signal reproduced from the light beam incident on the PD 17 as in the conventional CD and DVD. The tracking servo moves the carriage optical system 19 comprising the mirror 10 and the objective lens 11 in the direction of the arrow (left and right in the drawing), and the focus servo moves the objective lens 11 within the carriage optical system 19 in the direction of the arrow ( Move up and down in the paper).

  FIG. 2 schematically shows the optical system of the present embodiment.

  In FIG. 1, the spatial modulator 3 and the CMOS sensor 5 that is an image light receiving element are placed at a position away from the relay lens 6 at the focal length fr of the relay lens 6 (the focal length of the relay lens 8 is the same). Schematically, they are in the same position in FIG.

  The focal length of the objective lens is indicated by fo and not clearly shown in FIG. 1, but the interval between the spatial modulator 3, the CMOS sensor 5 as the image light receiving element, and the relay lens 6 is fr. The distance between the relay lenses 6 and 8 is twice fr, and the distance between the relay lens 8 and the objective lens is the sum of fr and fo.

  A broken line in FIG. 2 indicates an optical path when the relay lens 8 is placed at the center of the optical axis. That is, the Lee lens 6 and the relay lens 8 are on the same optical axis.

  On the other hand, the optical path when the driving unit 18 moves the relay lens 8 in the direction of the arrow (upward in the drawing) according to the rotation direction tracking error signal is indicated by a solid line. The rotation direction of the hologram disk 12 is the vertical direction in the drawing of FIG.

  In FIG. 2, when the relay lens 8 moves in the direction of the arrow from the direction indicated by the broken line, the light beam from the focal point of the relay lens 6 collected by the relay lens 8 is in contrast to the light beam indicated by the original broken line. Tilt and the incident light beam to the objective lens 11 are tilted. As a result, the information light and the reference light formed in the spatial modulator 3 are irradiated to a position different from the case where the irradiation position on the hologram disk 12 is also indicated by the broken line, and should be recorded following the rotation of the hologram disk 12. The normal position is irradiated.

  Further, since the optical path indicated by the solid line in FIG. 2 is also taken during reproduction, reproduction from a regular position on the hologram disk 12 can be performed.

  As described above, according to the present embodiment, it is possible to follow the movement of the recording medium without adding an element such as a mirror, and to detect the signal according to the movement of the movable element, thereby following the movement of the recording medium. Performance can be secured.

[Embodiment 2]
Next, a second embodiment will be described.

  FIG. 3 is a diagram showing an optical path of the optical information recording / reproducing apparatus according to the second embodiment of the present invention.

  The optical path for the recording / reproducing optical system, the servo signal, and the optical path for reading the addressing signal are the same as those in the first embodiment.

  Therefore, only differences from the first embodiment will be described.

  In this embodiment, the relay lens 8 is reciprocated up and down and left and right (FIG. 3, up and down direction in the drawing sheet, and perpendicular to the drawing sheet) with respect to the optical axis by the driving means 20. The drive means 20 performs feedback control according to a tracking error signal and a servo signal that is a rotation direction tracking error signal reproduced from a light beam incident on the PD 17 to move the relay lens 8.

  Here, the driving means 20 is a biaxial actuator using a magnetic circuit.

  As described above, since the tracking is also performed by the relay lens 8, in the first embodiment, the vicinity of the recording medium that is slightly enlarged due to the moving means (not shown) of the carriage optical system 19 becomes compact. Yes.

  Note that the optical path when the relay lens 8 is moved follows the solid line optical path in FIG. 2 when viewed from the cross sections in the radial direction and the rotational direction of the hologram disk.

  As described above, according to the present embodiment, it is possible to follow the movement of the recording medium without adding an element such as a mirror, and it is possible to detect the signal according to the movement of the movable element. Can be secured.

  Furthermore, it is possible to reduce the size of the device in the vicinity of the medium.

[Embodiment 3]
Next, the third embodiment will be described.

  FIG. 4 is a diagram showing an optical path of an optical information recording / reproducing apparatus according to the third embodiment of the present invention.

  The optical system optical path for recording / reproducing, the servo signal, and the optical system optical path for addressing signal reading are similar to those in the first and second embodiments.

  First, the difference between the optical path and the first and second embodiments will be described.

  In the present embodiment, the position where the servo signal and addressing signal reading optical system merges with the recording / reproducing optical system is different from the previous embodiment.

  A dichroic beam splitter 21 is disposed between the relay lens 6 and the recording / reproducing optical system polarization beam splitter 4.

  Further, in the servo signal and addressing signal reading optical system, the coupling lens 15 is eliminated from the first and second embodiments, and the relay lens 6 is also used as a collimating lens for the luminous flux from the red LD 13. Accordingly, the specifications of the sensor lens 22 have also been changed.

  Thus, in this embodiment, both the relay lens 6 and the relay lens 8 are movable. That is, the relay lens 6 is reciprocated by the driving means 23 in the left and right directions (FIG. 4, perpendicular to the paper surface) with respect to the optical axis. The relay lens 8 is reciprocated vertically by the driving means 24 with respect to the optical axis (FIG. 4, vertical direction in the drawing).

  Here, each of the driving means 23 and 24 is a uniaxial actuator using a magnetic circuit.

  The driving unit 23 performs feedback control according to the rotation direction tracking error signal reproduced from the light beam incident on the PD 17 to move the relay lens 6. The drive unit 24 performs feedback control according to a tracking error signal reproduced from the light beam incident on the PD 17 and moves the relay lens 8.

  FIG. 5 schematically shows an optical system according to the present embodiment when the relay lens 6 of the CMOS sensor 5 of the image light receiving element is moved.

  The case where the relay lens 6 is not moving is the same as that indicated by the broken line in FIG.

  On the other hand, the optical path when the driving unit 23 moves the relay lens 6 in the direction of the arrow (upward in the drawing) according to the rotation direction tracking error signal is indicated by a solid line. The rotation direction of the hologram disk 12 is the vertical direction in the drawing of FIG.

  In FIG. 5, when the relay lens 6 moves from the direction indicated by the broken line in the direction of the arrow, the light beam from the focal point of the relay lens 6 collected by the relay lens 8 is in contrast to the light beam indicated by the original broken line. Tilt and the incident light beam to the objective lens 11 are tilted. As a result, the information light and the reference light formed in the spatial modulator 3 are irradiated to a position different from the case where the irradiation position on the hologram disk 12 is also indicated by the broken line, and should be recorded following the rotation of the hologram disk 12. The normal position is irradiated.

  Further, since the optical path indicated by the solid line in FIG. 5 is also taken during reproduction, reproduction from a normal position on the hologram disk 12 can be performed.

  As described above, since tracking and rotation direction tracking are performed separately for the relay lens 6 and the relay lens 8, respectively, the second embodiment requires an actuator that moves in two directions and is technically difficult. On the other hand, in the present embodiment, each actuator is only required to move in one direction, which is easy to implement.

  As described above, according to the present embodiment, it is possible to follow the movement of the recording medium without adding an element such as a mirror, and to detect the signal according to the movement of the movable element. Can be secured.

  Furthermore, the size in the vicinity of the medium can be reduced, and its feasibility is high.

The figure which shows the optical path of the optical information recording / reproducing apparatus concerning 1st Embodiment Schematic diagram of optical system when one relay lens according to the present invention is moved The figure which shows the optical path of the optical information recording / reproducing apparatus concerning 2nd Embodiment The figure which shows the optical path of the optical information recording / reproducing apparatus concerning 3rd Embodiment Schematic diagram of the optical system when the other relay lens according to the present invention is moved The figure which shows the conventional optical information recording / reproducing apparatus disclosed by patent document 1

Explanation of symbols

1 ... Green LD
3. Spatial modulator 5. CMOS sensor (image light receiving element)
6, 8 ... Relay lens 7 ... Dichroic beam splitter 12 ... Hologram disc (recording medium)
13 ... Red LD
18, 20, 24 ... Driving means

Claims (4)

A spatial light modulator is irradiated with a light beam from the first laser light source, reference light and information light are generated by the spatial light modulator, guided to a recording medium via a relay optical system, and in a moving state using holography Information is recorded on the recording medium, only the reference light from the spatial modulator is irradiated onto the recording medium, the reflected light from the recording medium is guided to the image light receiving element, information is reproduced, and the second laser light source In the optical information recording / reproducing apparatus for irradiating the recording medium with the luminous flux and obtaining a servo signal by reflected light,
In accordance with the servo signal, at least one relay lens of the relay optical system is moved in the direction perpendicular to the optical axis to follow the moving direction of the recording medium, and the light flux from the second laser light source is changed to the first light source. An optical information recording / reproducing apparatus characterized in that a position where the optical system from the laser light source to the recording medium is joined is between the at least one relay lens and the spatial modulator.   The optical information recording / reproducing apparatus according to claim 1, wherein the laser light source is a semiconductor laser.   According to the servo signal, at least one of the relay lenses is moved in two directions perpendicular to the optical axis of the relay optical system in a direction perpendicular to each other, thereby following the rotational movement direction and decentering of the recording medium. The optical information recording / reproducing apparatus according to claim 1, wherein tracking is performed.   Two relay lenses constituting the relay optical system are used, and one of the relay lenses is moved in a direction perpendicular to the optical axis of the relay optical system by the servo signal. Rotational movement direction tracking is performed, and eccentric tracking is performed by moving the other relay lens in a direction perpendicular to the movement direction of the one relay lens in a direction perpendicular to the optical axis of the relay optical system. The optical information recording / reproducing apparatus according to claim 1.

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