JP2006164331A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device capable of satisfactorily correcting a spherical aberration caused by a difference in thickness between transparent substrates for optical recording media where the wavelengths of laser beams used for recording/reproducing are equal and the difference in thickness between the transparent substrates is large such as HD-DVD or blu-ray Disc, and selectively and compatibly recording/reproducing an information signal in the optical recording media. <P>SOLUTION: This device is provided with an objective lens 28 for converging a laser beam L emitted from a laser light source 21 on the signal recording layers of optical recording media 201a and 201c through a transparent substrate, an aperture limiting means 27 for limiting the numerical aperture of the objective lens 28, and a correction plate 29 inserted between the objective lens 28 and the optical recording media 201a and 201c. When recording/reproducing is executed in the blu-ray Disk 201a, the correction plate 29 is inserted without limiting the numerical aperture of the objective lens 28. When recording/reproducing is executed in the HD-DVD 201c, the numerical aperture of the objective lens 28 is limited to remove the correction plate 29. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical pickup device that can selectively perform recording, erasing, or reproduction on an optical recording medium having a transparent substrate having a significantly different thickness using a single laser light source.

  Conventionally, an optical recording medium such as a disk-shaped optical disk or a card-shaped optical card has been used. In these optical recording media, various information signals such as video information, audio information, computer data, and the like are recorded on a signal recording layer formed on a transparent substrate along a recording track formed in a spiral on the signal recording layer. Recorded. The information signal recorded on the signal recording layer is reproduced along the recording track by collecting and irradiating the signal recording layer with a light beam.

  This optical recording medium has been widely used in various fields in recent years because it can record information signals at a very high density and can select and reproduce desired information signals at high speed.

  As such an optical disc as an optical recording medium, for example, “CD” (Compact Disc: trade name), “DVD” (Digital Versatile Disc: trade name) and the like are already generally used. In “CD”, laser light having a wavelength of about 780 nm is condensed through an objective lens having a numerical aperture (NA) of about 0.45 and irradiated to a signal recording layer to record or reproduce an information signal. I do. In this “CD”, the laser beam is applied to the signal recording layer through a transparent substrate having a thickness of about 1.2 mm.

  In “DVD”, a laser beam having a wavelength of about 650 nm is condensed through an objective lens having a numerical aperture (NA) of about 0.6 and irradiated to a signal recording layer, and recording of an information signal or , Play. In this “DVD”, the laser beam is applied to the signal recording layer through a transparent substrate having a thickness of about 0.6 mm. The recording density of the information signal in this “DVD” is about 6 to 8 times that of “CD”. When the diameter of the disk substrate is set to 12 cm, which is equal to “CD”, The recording capacity is about 4.7 GB (gigabytes).

  Then, “blu-ray Disc” (trade name) and “HD-DVD” (High Definition DVD) have been proposed as those capable of recording information signals with higher density than those of “CD” and “DVD”. . In “blu-ray Disc”, a laser beam having a wavelength of 450 nm or less is condensed through an objective lens having a numerical aperture (NA) of about 0.85 and irradiated to a signal recording layer to record an information signal. Or perform playback. In this “blu-ray disc”, the laser beam is applied to the signal recording layer through a transparent substrate having a thickness of about 0.1 mm. The information signal recording capacity of this “blu-ray disc” is about 25 GB (gigabytes) per single-sided signal recording layer when the diameter of the disc substrate is 12 cm.

  In addition, in “HD-DVD”, a laser beam having a wavelength of 450 nm or less is condensed through an objective lens having a numerical aperture (NA) of about 0.65 and irradiated to a signal recording layer to record an information signal. Or perform playback. In this “HD-DVD”, the laser beam is applied to the signal recording layer through a transparent substrate having a thickness of about 0.6 mm. The recording capacity of the information signal in this “HD-DVD” is about 15 GB (gigabyte) per single-sided signal recording layer when the diameter of the disk substrate is 12 cm.

  By the way, in Patent Document 1, by using a composite objective lens composed of a hologram as a diffractive optical element and an objective lens as a refractive optical element, as described above, it corresponds to a blue light beam (wavelength 450 nm) and is transparent. Selectively for “blu-ray Disc” with a substrate thickness of about 0.1 mm and “DVD” for a red light beam (wavelength 650 nm) with a transparent substrate thickness of about 0.6 mm, There is described an optical pickup device which can perform recording and reproduction interchangeably.

  In the compound objective lens in this optical pickup device, as shown in FIGS. 22A to 22C, holograms 102A, 102B, and 102C are attached to the lower part (light source side) in the cylindrical lens holder 101. At the same time, the objective lens 103 is attached to the upper part (on the optical recording medium side) in the lens holder 101.

  The holograms 102A, 102B, and 102C in the compound objective lenses 100A, 100B, and 100C have an uneven shape ((a) in FIG. 22), a staircase shape ((b) in FIG. 22), or a sawtooth shape (see FIG. A plurality of diffraction gratings (c) in 22 are formed in a ring shape. In the holograms 102A, 102B, and 102C of the compound objective lenses 100A, 100B, and 100C, the blue light beam 104 that performs recording and reproduction on the “blu-ray Disc” 201a transmits a large amount of light without being diffracted, The red light beam 105 that performs recording / reproduction on the “DVD” 201b is diffracted in the inner peripheral region. As described above, since the diffraction characteristics of the holograms 102A, 102B, and 102C are wavelength-dependent, the use of the composite objective lenses 100A, 100B, and 100C allows the “blu-ray Disc” 201a and the “DVD” 201b to be transparent. Spherical aberration that occurs due to the difference in thickness of the substrate is corrected.

The optical pickup device having such compound objective lenses 100A, 100B, and 100C has a “blu-ray disc” 201a having a transparent substrate thickness of about 0.1 mm and a transparent substrate thickness of about 0.6 mm. A certain “DVD” 201b can be recorded and reproduced selectively and interchangeably.
JP 2004-71134 A.

  By the way, the wavelength of the laser beam used for recording and reproduction differs between the “blu-ray Disc” 201a and the “DVD” 201b. Therefore, by utilizing such a difference in wavelength, spherical aberration can be corrected by using different diffracted beams for each laser beam by diffraction in the hologram, as described in Patent Document 1. it can. Therefore, recording and reproduction can be performed on these “blu-ray Disc” 201a and “DVD” 201b by using one compound objective lens 100A, 100B, and 100C.

  Here, it is considered that the above-mentioned “HD-DVD” (High Definition DVD) is recorded and reproduced by an optical pickup device common to “blu-ray Disc”. In “HD-DVD” and “blu-ray Disc”, the wavelength of the laser beam used is approximately equal to about 405 nm, and the thickness of the transparent substrate and the numerical aperture (NA) of the objective lens are greatly different. That is, in “HD-DVD”, the thickness of the transparent substrate is around 0.6 mm and the numerical aperture (NA) of the objective lens is about 0.65, whereas in “blu-ray Disc”, the transparent substrate The objective lens has a numerical aperture (NA) of about 0.85.

  Therefore, even if an optical pickup configured for “blu-ray disc” is used to record or reproduce “HD-DVD”, spherical aberration caused by the difference in thickness of the transparent substrate. Is too large to record or play back. In addition, when an optical pickup configured for “HD-DVD” is used to record or reproduce “blu-ray disc”, spherical aberration caused by the difference in the thickness of the transparent substrate. Is too large to record or play back.

  Since “HD-DVD” and “blu-ray Disc” have the same wavelength of the laser beam used for recording and reproduction, different diffracted beams can be used for each laser beam by the hologram as described above. Therefore, it is impossible to correct spherical aberration using a hologram.

  It has been proposed to correct spherical aberration by changing the distance between the lenses forming the beam expander so that the laser light before entering the objective lens passes through the beam expander. Since “HD-DVD” and “blu-ray Disc” have a large difference in thickness of the transparent substrate, it is impossible to correct the spherical aberration by such a beam expander.

  Therefore, the present invention has been proposed in view of the above-mentioned circumstances, and the wavelengths of laser beams used for recording and reproduction are equal and transparent, such as “HD-DVD” and “blu-ray Disc”. Good spherical aberration caused by the difference in the thickness of the transparent substrate in the first optical recording medium and the second optical recording medium having a large difference in substrate thickness, or the third optical recording medium in which these are laminated. It is an object of the present invention to provide an optical pickup device which is capable of recording and reproducing information signals selectively and interchangeably with respect to each of these optical recording media.

  In order to solve the above-described problems and achieve the above object, an optical pickup device according to the present invention has any one of the following configurations.

[Configuration 1]
A first optical recording medium having a first signal recording layer on a transparent substrate, a second optical recording medium having a recording density lower than that of the first signal recording layer on a transparent substrate thicker than the transparent substrate of the first optical recording medium For at least two types of optical recording media of a second optical recording medium having a signal recording layer and a third optical recording medium integrally formed by stacking the first and second optical recording media An optical pickup device for selectively recording, erasing, or reproducing information signals, and a laser light source that emits laser light having a wavelength of 450 nm or less, and a numerical aperture of 0.75 or more that is emitted from the laser light source. An objective lens that irradiates the first or second signal recording layer through the transparent substrate with a focused light, an aperture limiting means that limits the numerical aperture of the objective lens, and an objective lens And a correction plate inserted between the optical recording medium and When recording, erasing or reproducing the first signal recording layer, the numerical aperture of the objective lens is not limited by the aperture limiting means, and the correction plate is interposed between the objective lens and the first optical recording medium. Is inserted, the sine condition is substantially satisfied, and the numerical aperture of the objective lens is limited by the aperture limiting means when recording, erasing, or reproducing the second signal recording layer. The sine condition is substantially satisfied by removing the correction plate from between the objective lens and the second optical recording medium.

  In this optical pickup device, as in “HD-DVD” and “blu-ray Disc”, the wavelength of the laser beam used for recording and reproduction is the same, and the difference in thickness of the transparent substrate is large. For the medium and the second optical recording medium, spherical aberration caused by the difference in thickness of the transparent substrate is corrected well, and information signals are recorded or reproduced selectively and interchangeably with respect to each of these optical recording media. It can be performed.

[Configuration 2]
In the optical pickup device having the configuration 1, a tilt detection unit that detects a tilt of the first optical recording medium with respect to the optical axis of the objective lens, and a correction plate tilt unit that tilts the correction plate with respect to the optical axis of the objective lens. The correction plate tilting means is characterized in that the occurrence of coma aberration is reduced by tilting the correction plate in accordance with the tilt amount of the first optical recording medium detected by the tilt detection means. .

  In this optical pickup device, coma generated in proportion to the third power of the numerical aperture (NA) of the objective lens is corrected. Therefore, even when the numerical aperture (NA) of the objective lens is large, coma aberration is corrected. Can be suppressed.

[Configuration 3]
In the optical pickup device having Configuration 1 or Configuration 2, when the correction plate has a refractive index substantially equal to that of the transparent substrates of the first and second optical recording media, the first optical recording medium is transparent. A parallel plane plate having a thickness corresponding to the difference between the thickness of the substrate and the transparent substrate of the second optical recording medium, and having a refractive index different from that of the transparent substrates of the first and second optical recording media. Is characterized by being a convex lens or a concave lens.

  In this optical pickup device, even when the refractive index of the correction plate is different from the transparent substrates of the first and second optical recording media, the spherical aberration caused by the difference in thickness of the transparent substrate can be corrected well. Can do.

[Configuration 4]
A first optical recording medium having a first signal recording layer on a transparent substrate, a second optical recording medium having a recording density lower than that of the first signal recording layer on a transparent substrate thicker than the transparent substrate of the first optical recording medium For at least two types of optical recording media of a second optical recording medium having a signal recording layer and a third optical recording medium integrally formed by stacking the first and second optical recording media An optical pickup device for selectively recording, erasing, or reproducing information signals, and a laser light source that emits laser light having a wavelength of 450 nm or less, and a numerical aperture of 0.75 or more that is emitted from the laser light source. An objective lens that irradiates the first or second signal recording layer through the transparent substrate with a focused light, an aperture limiting means that limits the numerical aperture of the objective lens, and an objective lens Correction inserted between the optical recording medium and the optical recording medium And a second correction plate that is thinner than the first correction plate inserted between the objective lens and the optical recording medium, and a tilt of the first and second optical recording media with respect to the optical axis of the objective lens. When the tilt detection means and the correction plate tilt means for tilting the first and second correction plates with respect to the optical axis of the objective lens are used for recording, erasing or reproducing the first signal recording layer, The numerical aperture of the objective lens is not limited by the aperture limiting means, and the first correction plate is inserted between the objective lens and the first optical recording medium, so that the sine condition is substantially satisfied. In addition, the correction plate tilting unit tilts the first correction plate in accordance with the tilt amount of the first optical recording medium detected by the tilt detection unit, thereby reducing the occurrence of coma aberration and the second signal recording. Record and erase layers Or, when performing reproduction, the numerical aperture of the objective lens is limited by the aperture limiting means, and the second correction plate is inserted between the objective lens and the second optical recording medium, so that the sine condition is substantially satisfied. The correction plate tilting means tilts the second correction plate in accordance with the tilt amount of the second optical recording medium detected by the tilt detection means, thereby reducing the occurrence of coma aberration. It is characterized by.

  In this optical pickup device, as in “HD-DVD” and “blu-ray Disc”, the wavelength of the laser beam used for recording and reproduction is the same, and the difference in thickness of the transparent substrate is large. For the medium and the second optical recording medium, spherical aberration caused by the difference in thickness of the transparent substrate is corrected well, and information signals are recorded or reproduced selectively and interchangeably with respect to each of these optical recording media. In addition, since coma aberration generated in proportion to the third power of the numerical aperture (NA) of the objective lens is corrected, even if the numerical aperture (NA) of the objective lens is large, the coma Occurrence of aberration can be suppressed.

[Configuration 5]
In the optical pickup device having Configuration 4, when the first and second correction plates have a refractive index substantially equal to that of the transparent substrates of the first and second optical recording media, A parallel plane plate having a thickness difference corresponding to the difference between the thickness of the transparent substrate and the transparent substrate of the second optical recording medium, and having a refractive index different from that of the transparent substrates of the first and second optical recording media In the case of having a convex lens or a concave lens.

  In this optical pickup device, even when the refractive indexes of the first and second correction plates are different from the transparent substrates of the first and second optical recording media, the spherical aberration caused by the difference in the thickness of the transparent substrate. Can be corrected satisfactorily.

  In the optical pickup device according to the present invention, the first optical recording medium and the second optical recording medium having the same wavelength of laser light used for recording and reproduction and a large difference in thickness of the transparent substrate are used. The spherical aberration caused by the difference in thickness can be satisfactorily corrected, and information signals can be recorded or reproduced selectively and interchangeably on these optical recording media.

  In the optical pickup device according to the present invention, the first optical recording medium and the second optical recording medium having the same wavelength of laser light used for recording and reproduction and a large difference in thickness of the transparent substrate are transparent. The spherical aberration caused by the difference in thickness of the substrate can be corrected well, and information signals can be recorded or reproduced selectively and interchangeably on each of these optical recording media. Since the coma generated in proportion to the third power of the numerical aperture (NA) is corrected, the occurrence of coma can be suppressed even when the numerical aperture (NA) of the objective lens is large.

  That is, the present invention provides a first optical recording medium such as “HD-DVD” and “blu-ray Disc” in which the wavelength of laser light used for recording and reproduction is equal and the difference in thickness of the transparent substrate is large. And the second optical recording medium or the third optical recording medium in which these are laminated, the spherical aberration caused by the difference in the thickness of the transparent substrate is corrected well, and selected for each optical recording medium. Therefore, it is possible to provide an optical pickup device that can record or reproduce information signals in a compatible manner.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an optical pickup device according to an embodiment of the invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a side view showing the overall configuration of an optical pickup device according to the present invention.

  As shown in FIG. 1, this optical pickup device is installed in an optical disk drive 10 so as to be movable in the radial direction of the optical disk in parallel with the main surface of the optical disk serving as an optical recording medium. In this optical disk drive device, any one of the optical disks as the first to third optical recording media can be selectively used.

  The optical disc as the first optical recording medium is, for example, a “blu-ray disc” based on the “blu-ray disc” standard, and is a signal recording formed on a thin transparent substrate of about 0.05 mm to 0.15 mm. Information signals can be recorded and reproduced with high density by a laser beam having a wavelength of 450 nm or less irradiated to the layer through a transparent substrate. The “blu-ray disc” has a thickness of about 1.2 mm, for example, by attaching a reinforcing plate.

  The optical disk as the second optical recording medium is, for example, “HD-DVD” based on the “HD-DVD” standard, and is about 0.55 mm to 0.65 mm thicker than the transparent substrate of the first optical recording medium. An information signal can be recorded and reproduced with high density by a laser beam having a wavelength of 450 nm or less irradiated to the signal recording layer formed on the transparent substrate through the transparent substrate. . In this “HD-DVD”, the thickness of the entire disk is, for example, about 1.2 mm by attaching the reinforcing plate.

  The third optical recording medium is configured by integrally laminating the signal recording layers of the first and second optical recording media, and the first and second optical recording media are provided for each signal recording layer. It can be handled in the same manner as the signal recording layer in the recording medium. This third optical recording medium is formed with a total disk thickness of about 1.2 mm.

  In the following description, a case where “blu-ray Disc” 201a is used as the first optical recording medium and “HD-DVD” 201c is used as the second optical recording medium will be described. Further, the third optical recording medium can be used by the same operation as when the first optical recording medium is used or when the second optical recording medium is used, and thus the description thereof is omitted. . However, the first to third optical recording media are not limited to disk-shaped optical disks, and for example, those configured as card-shaped optical recording media can also be used.

In the optical disc driving apparatus 10, “blu-ray disc” 201 a and “HD-DVD” 201 c are selectively mounted on a turntable 12 fixed to the shaft of the spindle motor 11. These “blu-ray disc” 201 a and “HD-DVD” 201 c are rotated together with the turntable 12 when the spindle motor 11 is driven. In this embodiment, the thickness _{t 1} of the transparent substrate "blu-ray Disc" 201a is adapted and 0.1 mm. In addition, the thickness _{t 2} of the transparent substrate of the "HD-DVD" 201c has been made and 0.6mm.

  The optical pickup device 20 is installed so as to be movable in the radial direction of the optical discs 201a and 201c while facing the optical discs 201a and 201c mounted on the turntable 12.

  The optical pickup device 20 includes a blue semiconductor laser 21 as a laser light source that emits laser light L having a wavelength of 450 nm or less corresponding to “blu-ray disc” 201a and “HD-DVD” 201c. In this embodiment, the reference wavelength of the laser light L emitted from the blue semiconductor laser 21 is, for example, 405 nm. The laser light L emitted from the blue semiconductor laser 21 is linearly polarized divergent light.

  The laser light L emitted from the blue semiconductor laser 21 passes through the grating 22 and is divided into three or more light beams, passes through the polarization-selective dielectric multilayer film 23a of the polarization beam splitter 23, and enters the collimator lens 24. Incident. The laser beam L is incident on the polarization selective dielectric multilayer film 23a in a P-polarized state and is transmitted through the polarization selective dielectric multilayer film 23a.

  The laser light L incident on the collimator lens 24 is converted into a parallel light beam by the collimator lens 24, deflected by 90 ° by the plane mirror 25 for raising, and incident on the phase plate 26. The phase plate 26 transmits the laser light L as circularly polarized light. As the phase plate 26, a plate that gives a phase difference of [λ / 4] (quarter wavelength) to the laser light L when the laser light L is transmitted can be used.

  The laser beam L that has passed through the phase plate 26 is incident on the objective lens 28 through an aperture limiting unit 27 that serves as aperture limiting means. When the “blu-ray Disc” 201a is used, the objective lens 28 collects the laser light L and transmits it through the correction plate 29, and passes through the transparent substrate of the “blu-ray Disc” 201a. Irradiate onto the signal recording layer 202a of the "blu-ray Disc" 201a. Further, when the “HD-DVD” 201c is used, the objective lens 28 condenses the laser light L, passes through the transparent substrate of the “HD-DVD” 201c, and transmits the “HD-DVD” 201c signal. Irradiation is performed on the recording layer 202c.

  The objective lens 28 has a numerical aperture (NA) of 0.75 or more corresponding to “blu-ray Disc” and a transparent substrate thickness “t2” (0.6 mm) of “HD-DVD”. Designed accordingly. The objective lens 28 is a lens in one group in which at least one of the first surface 28a on the laser light source side and the second surface 28b on the optical discs 201a and 201c side is aspherical. In this embodiment, the objective lens 28 is a single lens having a numerical aperture (NA) of 0.85, and both the first surface 28a and the second surface 28b are aspherical. , The laser beam L having a wavelength (λ) of 405 nm is optimized in an infinite conjugate manner. The distance between the objective lens 28 and the surface of the transparent substrate (the incident surface of the laser beam L) 203a of the “blu-ray disc” 201a, that is, the working distance is the thickness of the correction plate 29 inserted in the optical path. Except for this, it is about 0.57 mm.

  The objective lens 28 is held by a lens holder 37. A focus coil 38 and a tracking coil 39 are integrally attached to the outer periphery of the lens holder 37. The lens holder 37 is inserted in the optical axis direction (focus direction) of the objective lens 28 and the radial direction (tracking direction) of the optical disc perpendicular to the optical axis via a plurality of suspension wires (not shown) fixed to the outer periphery. It is supported movably. The focus coil 38 and the tracking coil 39 are positioned in a magnetic field formed by a permanent magnet (not shown), and when the drive current is supplied, the lens holder 37 is moved in the focus direction and the tracking direction. ing.

The correction plate 29 is a parallel flat plate formed of a transparent member having a refractive index equal to that of the transparent substrate of each of the optical discs 201a and 201c, for example, polycarbonate. The refractive index of polycarbonate is 1.62231 at a wavelength (λ) of 405 nm. The material forming the correction plate 29 may be a material having a refractive index close to that of polycarbonate, such as “SK14” having a refractive index of 1.61983 at a wavelength (λ) of 405 nm. The thickness of the correction plate 29 is a thickness corresponding to the difference between the thickness t ₁ of the transparent substrate of “blu-ray Disc” 201 a and the thickness t ₂ of the transparent substrate of “HD-DVD” 201 c, for example, It is 0.5 mm.

  The correction plate 29 is held by a holder 32 via a connecting member 35. The holder 32 is formed integrally with the support shaft 33. The support shaft 33 can be rotated by a drive motor 34. That is, the correction plate 29 can be moved and operated by the drive motor 34 between a position where it is inserted on the optical axis of the light emitted from the objective lens 28 and a position where it is removed from this optical axis. Yes. The correction plate 29 is inserted on the optical axis when the “blu-ray disc” 201a is used, and is removed from the optical axis when the “HD-DVD” 201c is used.

  In this optical pickup device 20, information to the signal recording layer 202a of the “blu-ray Disc” 201a or the signal recording layer 202c of the “HD-DVD” 201c is obtained by the laser light L condensed by the objective lens 28. Signal recording, erasure, or reproduction is performed.

  The laser light L (reflected light) reflected by the signal recording layers 202a and 202c is circularly polarized in the opposite direction to the forward light and re-enters the objective lens 28, and is converted into parallel light by the objective lens 28, thereby limiting the aperture. By passing through the phase plate 26 through the unit 27, it becomes linearly polarized light (S-polarized light) whose outgoing light and the polarization direction are orthogonal.

  The reflected light is deflected by 90 ° by the plane mirror 25, passes through the collimator lens 24, becomes convergent light, and returns to the polarization beam splitter 23. Since this reflected light is linearly polarized light (S-polarized light) whose polarization direction is orthogonal to the forward light, this polarized beam splitter 23 is reflected by the polarization selective dielectric multilayer film 25a and passes through the cylindrical lens 30. Then, the light is received by the photodetector 31. Then, the tracking error signal, the focus error signal, and the main data signal when the signal recording layer 202a of the “blu-ray Disc” 201a or the signal recording layer 202c of the “HD-DVD” 201c is reproduced by the photodetector 31. Is detected.

  In this optical pickup device, when the “blu-ray disc” 201a is used, the opening restriction by the opening restriction unit 27 is not performed, and the correction plate 29 is inserted into the optical path. In this optical pickup device, when the “HD-DVD” 201c is used, the opening restriction by the opening restriction unit 27 is performed, and the correction plate 29 is removed from the optical path.

  When the “blu-ray disc” 201a is used, the working distance (the second surface 28b of the objective lens 28 and the surface 203a of the transparent substrate of the “blu-ray disc” 201a that minimizes the spherical aberration with respect to the laser light L is used. (Distance between the incident surface of the laser beam L) is a distance obtained by adding the thickness of the correction plate to 0.5 mm and approximately 0.57 mm. When the “HD-DVD” 201c is used, the working distance that minimizes the spherical aberration with respect to the laser light L (the second surface 28b of the objective lens 28 and the surface 203c of the transparent substrate of the “HD-DVD” 201c). (Distance to (incident surface of laser beam L)) is about 0.57 mm.

  FIG. 2 is a plan view showing a liquid crystal pattern of a liquid crystal shutter used as an opening restricting portion.

  As shown in FIG. 2, the opening restricting portion 27 includes a liquid crystal shutter 27a having an annular pattern. In the opening restricting portion 27, the inner peripheral portion 27b is a region through which the laser light L is transmitted regardless of whether the “blu-ray disc” 201a or the “HD-DVD” 201c is used. The annular outer peripheral portion 27c around the inner peripheral portion 27b transmits the laser light L only when the “blu-ray Disc” 201a is used, and shields the laser light L when the “HD-DVD” 201c is used. It is an area. Note that such a liquid crystal shutter can be configured by a known technique.

  FIG. 3 is a cross-sectional view showing the operating principle of a liquid crystal shutter used as an aperture limiting portion.

  As shown in FIG. 3, the liquid crystal shutter 27a can be configured using, for example, a guest-host type liquid crystal 27d. By providing this guest-host type liquid crystal 27d between a pair of substrate glasses 27e, a liquid crystal shutter 27a is configured. An electrode (not shown) is provided between the substrate glass 27e and the guest-host type liquid crystal 27d. In the OFF state in which no voltage is applied to this electrode, as shown in FIG. 3A, the incident laser beam L is completely transmitted without being blocked, and the “blu-ray disc” 201a is used. Become. At this time, the numerical aperture (NA) of the objective lens 28 is 0.85.

  When the voltage is applied to the electrodes, as shown in FIG. 3B, the orientation direction of the guest-host type liquid crystal 27d changes, and the laser light L having a predetermined polarization direction is transmitted to the outer peripheral portion. Since the light is shielded at 27c, the state where the “HD-DVD” 201c is used, that is, the numerical aperture (NA) of the objective lens 28 is limited to 0.65.

  The aperture limiting unit 27 is not limited to the one using the liquid crystal shutter 27a as described above, and may be one using a mechanical aperture stop, for example. As such an aperture stop, the aperture may be limited by rotating each blade portion of a diaphragm mechanism composed of a plurality of blade portions, or a light shielding plate provided with a plurality of openings having different diameters may be orthogonal to the optical axis. The opening may be limited by switching the opening by moving in the direction of movement. Furthermore, the aperture limiting unit 27 may limit the aperture using a polarization-selective optical element.

  FIG. 4 is a side view showing the configuration of the objective lens and the correction plate.

  The objective lens 28 has a numerical aperture (NA) equal to the numerical aperture (0.85) when the “blu-ray Disc” 201a is used, and corresponds to the transparent substrate thickness t2 of the “HD-DVD” 201c. And optimized for infinite conjugates. As the glass material forming the objective lens 28, for example, “NBF1” (HOYA optical glass) can be used. The objective lens 28 is a lens of one group in which the first surface 28a on the laser light source side and the second surface 28b on the optical discs 201a and 201c side are both aspherical.

  The working distance WD1 between the second surface 28b of the objective lens 28 and the surface (incident surface of the laser beam L) 203a of the “blu-ray Disc” 201a is the thickness of the correction plate 29 as described above. Except for 0.5 mm, it is about 0.57 mm. This working distance WD1 is a combination of the distance WD11 from the second surface 28b of the objective lens 28 to the front surface of the correction plate 29 and the distance WD12 from the rear surface of the correction plate 29 to the surface 203a of the transparent substrate of the “blu-ray Disc” 201a. It becomes a thing.

  Further, the working distance WD2 between the second surface 28b of the objective lens 28 and the surface of the transparent substrate (incident surface of the laser beam L) 203c of “HD-DVD” 201c is equal to the working distance WD1 and approximately 0.57 mm. Degree. At this time, the correction plate 29 is removed from the optical path.

The aspherical shapes of the first surface 28a and the second surface 28b of the objective lens 28 can be expressed using a polynomial shown in the following [Equation 1].

In [Equation 1], Z is the distance from the apex of the first surface 28a or the second surface 28b of the objective lens 28, and C is the curvature (curvature: radius of the first surface 28a or the second surface 28b). Reciprocal), h is the height of the objective lens 28 from the optical axis, K is the conic constant, and A _{4 to} A ₁₂ are the fourth to twelfth aspheric coefficients.

Here, assuming that the angle of warp of the optical disk is α and the optical disk warps in a simple saddle shape, the surface runout amount L of the optical disk at the position of the distance R from the center of the optical disk is ].

  The warp angle of the optical disc is set to be within 0.3 ° in “DVD”. In the case of the bowl-shaped warp shape described above, the surface deflection of the optical disk is maximized at the outermost periphery. At this time, if the diameter of the optical disk is 120 mm, a surface runout of 0.3 mm may occur. In “blu-ray Disc” 201a and “HD-DVD” 201c, which have higher information recording density than “DVD”, the material forming the transparent substrate is a synthetic resin material. A warp angle similar to the case may occur. Therefore, in an optical disc having a maximum radius of 60 mm, such as “blu-ray disc” 201a and “HD-DVD” 201c, the working distance is preferably 0.3 mm or more in consideration of surface deflection of the optical disc.

In a single lens, the working distance WD is generally expressed as [Equation 3] below.

In this Formula 3, f is the focal length of the objective lens 28, R ₁ is the radius of curvature at the vertex of the laser light source side surface 28a of the objective lens 28, t is the center thickness of the objective lens 28, n is , D is the thickness of the transparent substrate of the optical disk, and N is the refractive index of the transparent substrate of the optical disk. The thickness d of the transparent substrate of the optical disk is 0.6 mm because the objective lens 28 is optimized for “HD-DVD” 201c. The material forming the transparent substrate of the optical disk is polycarbonate, and the refractive index N is 1.58 ≦ N ≦ 1.65 at a wavelength of 405 nm. Since the objective lens 28 is infinitely conjugate, it is a convex lens, and R ₁ must be a positive number (R ₁ > 0). The thickness of the objective lens 28 is a positive number (t> 0).

  If the sag angle of the first surface 28a of the objective lens 28 is large, it becomes difficult to produce a mold for producing the objective lens 28 by press molding. Therefore, the material forming the objective lens 28 has a refractive index n. It is necessary to reduce the sag angle by using a large material. Considering existing materials, it is desirable that the refractive index of the glass material used for the objective lens 28 is 1.65 ≦ n ≦ 2.1.

From the above conditions such as [Equation 3] and the working distance, the focal length f of the objective lens 28 needs to be 0.68 mm or more (f ≧ 0.68 mm). When the diameter of the light beam incident on the objective lens 28 is φ, there is a relationship expressed by the following [Equation 4].

  The larger the incident light beam diameter, the larger the optical components and the larger the optical pickup device 20 as a whole. Therefore, the light beam diameter φ incident on the objective lens 28 is desirably 10 mm or less (φ ≦ 10 mm). Since the numerical aperture (NA) of the objective lens 28 is 0.85, the focal length f of the objective lens 28 is desirably 5.89 mm or less (f ≦ 5.89 mm) from [Equation 4].

In addition, since the objective lens 28 may have a narrow field of view, it is desirable to design the objective lens 28 as a lens (abranate) having a characteristic in which on-axis aberrations and off-axis aberrations are well corrected. Furthermore, what is most important for facilitating the production of the objective lens 28 is to maximize the eccentricity tolerance between the first surface 28a and the second surface 28b. For general formula for obtaining the radius of curvature R ₁ of the first surface 28a of Abra Inert lenses such eccentricity tolerance is maximized, the applicant in Japanese Patent Application No. 2003-167188, discloses a [number 5] below is doing.

Further, in a double-sided spherical lens, a combination of radii that minimizes spherical aberration is known, and such a lens is called a best form lens. The radius of curvature R ₂ of the radius of curvature R ₁ and the second surface 28b of the first surface 28a, by fulfill the following [6], to reduce the deviation from the best form lenses, small spherical aberration can do.

From the above-mentioned conditions and [Expression 5] and [Expression 6], the radius of curvature R ₁ of the first surface 28a of the objective lens 28 is 0.46 mm to 7.12 mm (0.46 mm ≦ R ₁ ≦ 7. 12 mm), and the thickness t of the objective lens 28 is desirably 11.83 mm or less (t ≦ 11.83 mm).

In addition, when recording or reproducing with respect to the “blu-ray disc” 201a, it is necessary to insert the correction plate 29 in the optical path of the light emitted from the objective lens 28. The working distance WD1 is the sum of WD11 and WD12. In order to avoid a collision between the second surface 28b of the objective lens 28 and the front surface of the correction plate 29, the distance WD11 is preferably 0.1 mm or more, and when combined with the surface deflection of the optical disk, the working distance WD1 (= WD11 + WD12) Is more preferably 0.4 mm or more (WD1 ≧ 0.4 mm). At this time, the radius of curvature _{R 1} of the first surface 28a of the objective lens 28, 0.51 mm to _{7.12mm (0.51mm ≦ R 1 ≦ 7.12mm} ), the thickness t of the objective lens, 11.36Mm following It is desirable that (t ≦ 11.36 mm).

  In order to reduce the size of the optical pickup device, the light beam diameter φ of incident light on the objective lens 28 is desirably 5 mm or less (φ ≦ 5 mm), and the focal length f is 2.94 mm or less (f ≦ 2.94 mm) is desirable.

When the working distance WD1 is 0.3 mm or more (WD1 ≧ 0.3 mm), the radius of curvature R ₁ of the first surface 28a of the objective lens 28 is 0.46 mm to 3.25 mm (0.46 mm ≦ R ₁ ≦ 3). .25 mm), and the thickness t of the objective lens 28 is desirably 4.8 mm or less (t ≦ 4.8 mm). When the working distance WD1 is 0.4 mm or more (WD1 ≧ 0.4 mm), the curvature radius R ₁ of the first surface 28a of the objective lens 28 is 0.51 mm to 3.25 mm (0.51 mm ≦ R ₁ ≦ 3). .25 mm), and the thickness t of the objective lens 28 is desirably 4.44 mm or less (t ≦ 4.44 mm).

When "NBF1" (HOYA optical glass) is used as the glass material of the objective lens 28, the refractive index N of the objective lens 28 with respect to the laser beam L having a wavelength of 405 nm emitted from the blue semiconductor laser 21 is 1 .768895. Here, the specifications of the objective lens 28 designed to be optimized to infinite conjugate at a wavelength of 405 nm are shown in [Table 1] below.

[Table 2] below shows an example of the aspheric coefficients A _{4 to} A ₁₂ for forming the first surface 28a of the objective lens 28 into an aspheric surface using the above-described polynomial of [Equation 1].

Further, by using a polynomial of the equation (1), shown in the following an example of the aspherical coefficients A ₄ to A ₁₀ for forming the second surface 28b of the objective lens 28 to the aspherical Table 3.

The configuration of each optical element in the case of using the “blu-ray Disc” 201a in this optical pickup device is shown in [Table 4] below.

Further, the configuration of each optical element in the case of using “HD-DVD” 201c in this optical pickup device is shown in [Table 5] below.

  From these [Table 4] and [Table 5], in this embodiment, the radius of curvature at the apex of the first surface 28a of the objective lens 28 is 2.046517 mm, and the radius of curvature at the apex of the second surface 28b is − 11.90374 mm, the lens thickness between the first surface 28a and the second surface 28b of the objective lens 28 is 2.94 mm, and the distance WD11 from the second surface 28b of the objective lens 28 to the front surface of the correction plate 29 A working distance WD1 including a distance WD12 from the rear surface of the correction plate 29 to the surface of the “blu-ray Disc” 201a, and a working distance WD2 from the second surface 28b of the objective lens 28 to the surface of the “HD-DVD” 201c Are both approximately 0.57 mm.

  FIG. 5 is a graph showing an unsatisfactory sine condition and longitudinal aberration when the numerical aperture of the objective lens is 0.85.

  FIG. 6 is a graph showing the unsatisfactory sine condition and longitudinal aberration when the numerical aperture of the objective lens is 0.65.

  Further, as shown in FIGS. 5 and 6, the objective lens 28 has a sine condition for the laser light L corresponding to both “blu-ray Disc” 201a and “HD-DVD” 201c. Designed to satisfy.

  In FIG. 5, the vertical axis indicates the height of the light beam normalized with respect to the numerical aperture (NA) 0.85 of the objective lens 28 of the laser light L, and the horizontal axis indicates the amount of deviation (mm). In FIG. 6, the vertical axis indicates the height of the light beam normalized with respect to the numerical aperture (NA) 0.65 of the objective lens 28 of the laser light L, and the horizontal axis indicates the amount of deviation (mm). .

The aberration characteristics of the optical pickup device of this embodiment on the signal recording layer 202a of “blu-ray Disc” 201a and on the signal recording layer 202c of “HD-DVD” 201c are shown in Table 6 below.

  In this [Table 6], the on-axis aberration indicates the wavefront aberration when the laser beam L is incident parallel to the optical axis of the objective lens 28, and the image height characteristic is 0.3 ° with respect to the optical axis of the objective lens 28. The wavefront aberration when the tilted laser beam L is incident is shown, and the decentering characteristic shows the wavefront aberration when the decentering of the center of the first surface 28a and the second surface 28b of the objective lens 28 is 3 μm.

  As shown in FIGS. 5 and 6, the sine is approximately sine according to the numerical apertures (0.85 and 0.65) when using the “blu-ray Disc” 201a and when using the “HD-DVD” 201c. By designing the objective lens 28 so that the conditions are satisfied, as shown in [Table 6], the occurrence of coma aberration caused by the image height for both “blu-ray Disc” 201a and “HD-DVD” 201c. Can be suppressed. Further, spherical aberration can be suppressed by designing the longitudinal aberration so as to be almost no aberration in accordance with each numerical aperture.

  As described above, when performing recording or reproduction on two types of optical recording media having different thicknesses of the transparent substrate and corresponding numerical apertures (NA) of the objective lens with the laser light L having the same wavelength, the objective lens The design of 28 corresponds to a large numerical aperture for the numerical aperture, and corresponds to the transparent substrate on the thick side for the thickness of the transparent substrate, and a correction plate is inserted on the optical path of the outgoing light from the objective lens 28. By switching between the corrected state and the state in which the correction plate is removed from the optical path of the light emitted from the objective lens 28 and the numerical aperture of the objective lens 28 is limited by the aperture limiting means 27, both light beams are obtained by one optical system. Good recording and reproduction can be performed on the recording medium.

[Second Embodiment]
The optical pickup device can be configured to correct coma aberration that occurs when the optical disk is tilted (tilted) from a state perpendicular to the optical axis of the objective lens 28 by tilting the correction plate 29. it can.

  FIG. 7 is a side view showing a state when the “blu-ray disc” 201a is tilted from the normal position.

  When the “blu-ray Disc” 201 a is rotated on the turntable 12, the “blu-ray disc” 201 a is moved from the normal position indicated by the solid line in FIG. 7 to θ ° in one direction as indicated by the dotted line in FIG. It may tilt.

  FIG. 8 is a graph showing wavefront aberration that occurs when the “blu-ray Disc” 201a is tilted from the normal position.

  When the “blu-ray disc” 201a is tilted from the normal position, as shown in FIG. 8, the wavefront aberration increases substantially linearly as the tilt amount θ increases. Such wavefront aberration caused by the tilt of the “blu-ray Disc” 201a can be removed by tilting the correction plate 29 by a predetermined angle in the direction opposite to the tilt of the “blu-ray Disc” 201a. .

  FIG. 9 is a side view showing a state in which the correction plate 29 is tilted to correct the wavefront aberration when the “blu-ray disc” 201a is used.

  In this optical pickup device, as shown in FIG. 9, the correction plate 29 is integrated with the holder 32 around the connecting member 35 in the radial direction of the optical disc, the tracking direction, or any of these directions. Also, it can be tilted with respect to the optical axis of the objective lens 28. The correction plate 29 is tilted with respect to the optical axis of the objective lens 28 by a tilt adjusting mechanism 36 as shown in FIG.

  FIG. 10 shows the tilt of the correction plate 29 necessary for minimizing the wavefront aberration (wavefront aberration when the tilt amount θ ° is 0) with respect to the “blu-ray disc” 201a tilted by θ °. It is a graph which shows quantity psi.

  In this optical pickup device, as shown in FIG. 10, the wavefront aberration is obtained by making the tilt amount ψ ° of the correction plate 29 substantially proportional to the tilt amount θ ° of the “blu-ray disc” 201a. (Coma aberration) can be suppressed to about 0.005λrms. That is, if the “blu-ray disc” 201a tilt amount θ ° is known, the tilt amount ψ ° of the correction plate 29 necessary for suppressing the wavefront aberration can be obtained.

  FIG. 11 is a flowchart showing a process of tilting the correction plate 29 in order to correct coma aberration in the “blu-ray disc” 201a.

  In order to tilt the correction plate 29 in order to correct the coma aberration in the “blu-ray disc” 201a, first, as shown in FIG. The reflected light from “ray Disc” 201a is detected. As shown in FIG. 1, the disc tilt sensor 40 is provided in the optical pickup device and includes a light emitting unit (LED) 40a and a light receiving unit 40b. The light beam from the light emitting unit 40a is reflected by the signal recording layer 202a of the “blu-ray disc” 201a and reaches the light receiving unit 40b. When a tilt occurs in the “blu-ray disc” 201a, the position of the reflected light on the light receiving unit 40b deviates from the normal position. The tilt amount of the “blu-ray disc” 201a can be detected based on such a positional shift of the reflected light on the light receiving unit 40b.

  As shown in FIG. 11, in the second step (st2), the tilt direction of the “blu-ray Disc” 201a and the tilt amount θ ° are calculated from the positional deviation amount of the reflected light in the disc tilt sensor 40.

  In the third step (st3), the tilt amount ψ ° of the correction plate 29 is obtained from the tilt amount θ ° obtained in the second step (st2). As described above, the tilt amount θ ° of the “blu-ray disc” 201a and the tilt amount ψ ° of the correction plate 29 have a substantially proportional relationship. Can be obtained.

  In the fourth step (st4), a signal for setting the tilt direction of the correction plate 29 to be opposite to the tilt direction of the “blu-ray Disc” 201a (positive and negative is opposite) and the tilt amount is ψ ° is sent to the tilt adjusting mechanism 36. Supply.

  In the fifth step (st5), the tilt adjustment mechanism 36 tilts the correction plate 29 in a predetermined tilt direction by a predetermined tilt amount ψ ° based on the supplied signal.

  Note that the tilt direction of the “blu-ray disc” 201a may be any of the radial direction (radial direction) and the tangential direction (circumferential direction) of the “blu-ray disc” 201a. Further, the method for obtaining the tilt direction and the tilt amount of the “blu-ray Disc” 201a is not limited to the method using the disc tilt sensor as described above, and may be another method.

  By the way, the standard regarding the disc tilt of “blu-ray Disc” 201a is that the maximum tilt amount in the radial direction is ± 0.7 ° and the maximum tilt amount in the tangential direction is ± 0.3 °. Then, as shown in FIG. 10, the correction plate 29 may be easily tilted by ± 0.2 ° with a margin. Even if the correction plate 29 is tilted by 0.2 °, it is necessary that the correction plate 29 does not collide with the objective lens 28 and the “blu-ray disc” 201a. The size of the correction plate 29 is preferably 5 mm or more and 30 mm or less in view of the size of the objective lens 28 and the actuator on which the objective lens 28 is mounted. The distance between the second surface 28b of the objective lens 28 and the front surface of the correction plate 29 is the distance WD11 between the second surface 28b of the objective lens 28 and the front surface of the correction plate 29 shown in the first embodiment. It is necessary that the distance is equal to or more than 0.05 mm. The distance between the rear surface of the correction plate 29 and the laser light incident surface 203a of the “blu-ray disc” 201a is the same as the distance between the rear surface of the correction plate 29 and the “blu-ray disc” 201a shown in the first embodiment. It is necessary that the distance WD12 with respect to the laser beam incident surface 203a is equal to or greater than the distance obtained by adding 0.05 mm.

Therefore, it is desirable to secure 0.5 mm or more (0.5 mm ≦ WD1) as the working distance WD1, and if the light beam diameter φ of the incident light to the objective lens 28 is 10 mm or less (φ ≦ 10 mm), the objective The focal length f of the lens 28 is 0.88 mm to 5.89 mm (0.88 mm ≦ f ≦ 5.89 mm), and the curvature radius R ₁ of the first surface 28 a is 0.56 mm to 7.12 mm (0.56 mm ≦ 0.56 mm). R ₁ ≦ 7.12 mm), and the thickness t of the objective lens 28 is desirably 11.83 mm or less (t ≦ 11.83 mm).

Furthermore, it is desirable that the light beam diameter φ of the incident light to the objective lens 28 is 5 mm or less (φ ≦ 5 mm), and the focal length f of the objective lens 28 is 0.88 mm to 2.94 mm (0.88 mm ≦ 0.88). f ≦ 2.94 mm), the radius of curvature R ₁ of the first surface 28 a is 0.56 mm to 3.25 mm (0.56 mm ≦ R ₁ ≦ 3.25 mm), and the thickness t of the objective lens 28 is 4.8 mm. The following is desirable (t ≦ 4.8 mm).

[Third Embodiment]
FIG. 12 is a side view showing the configuration of the correction plate in this embodiment.

In this optical pickup device, as shown in FIG. 12, when a “blu-ray disc” 201a is used as a correction plate, it is inserted into the optical path between the objective lens 28 and the “blu-ray disc” 201a. The first correction plate 29a and the second correction plate 29b inserted into the optical path between the objective lens 28a and the “HD-DVD” 201c when the “HD-DVD” 201c is used. May be. The second correction plate 29b is thinner than the first correction plate 29a, and the difference between the thicknesses of the first and second correction plates 29a and 29b is the thickness of the transparent substrate of the “blu-ray Disc” 201a. This corresponds to the difference between t ₁ and the thickness t ₂ of the transparent substrate of “HD-DVD” 201c. That is, the difference of these correction plate 29a, the thickness of 29b is equivalent to the difference between the "blu-ray Disc" in 201a of the transparent substrate thickness _{t 1} and "HD-DVD" thickness _{t 2} of the transparent substrate 201c For example, 0.5 mm.

  The first and second correction plates 29a and 29b are parallel flat plates formed of a transparent member having a refractive index equal to that of the transparent substrate of each of the optical discs 201a and 201c, for example, polycarbonate.

  In this optical pickup device, when using either “blu-ray Disc” 201a or “HD-DVD” 201c, these optical discs are tilted (tilted) from a state perpendicular to the optical axis of the objective lens 28. ) Can be corrected by tilting the first or second correction plate 29a, 29b.

  The objective lens 28 has a numerical aperture (NA) of 0.85 when the “blu-ray Disc” 201a is used, as in the above-described embodiment. This objective lens 28 is designed to be optimized to infinite conjugate, corresponding to the thickness obtained by adding the thickness of the second correction plate 29b to the thickness t2 of the transparent substrate of “HD-DVD” 201c. ing. The thickness obtained by adding the thickness of the second correction plate 29b to the thickness t2 of the transparent substrate of “HD-DVD” 201c is equal to the thickness t1 of the transparent substrate of “blu-ray Disc” 201a. It is equal to the thickness of the correction plate 29a plus the thickness.

  These correction plates 29a and 29b are held by the holder 32 via the connecting member 35 as in the above-described embodiment. In the holder 32, the correction plates 29a and 29b are held adjacent to each other in parallel as shown in FIG. As shown in FIG. 1, the holder 32 is formed integrally with the support shaft 33. The support shaft 33 can be rotated by a drive motor 34. That is, each of the correction plates 29a and 29b is in a state where the first correction plate 29a is inserted on the optical axis of the emitted light from the objective lens 28 by the drive motor 34, and the second on the optical axis of the emitted light. The movable plate can be moved over the state in which the correction plate 29b is inserted. When using “blu-ray disc” 201a, the first correction plate 29a is inserted on the optical axis, and when using “HD-DVD” 201c, the second correction plate 29b is on the optical axis. Inserted.

  13A and 13B are side views showing the configuration of the objective lens and the correction plate in this optical pickup device.

  The distance WD11 from the second surface 28b of the objective lens 28 to the front surface of the first correction plate 29a and the surface of the transparent substrate “blu-ray Disc” 201a from the rear surface of the first correction plate 29a (incident surface of the laser light L) ) The working distance WD1 combined with the distance WD12 between 203a is about 0.55 mm as shown in FIG. 13A. Further, the distance WD21 from the second surface 28b of the objective lens 28 to the front surface of the second correction plate 29b and the surface of the transparent substrate “HD-DVD” 201c from the rear surface of the second correction plate 29b (incident incidence of the laser beam L). The working distance WD2 combined with the distance WD22 to the surface 203c is equal to the working distance WD1 and about 0.55 mm, as shown in FIG. 13B.

When “NBF1” (HOYA optical glass) is used as the glass material of the objective lens 28, the refractive index N of the objective lens 28 with respect to the laser light L having a wavelength of 405 nm emitted from the blue semiconductor laser 21 is 1. 768895. Here, the specification of the objective lens 28 designed to be optimized to infinite conjugate at a wavelength of 405 nm is shown in the following [Table 7].

Further, the aspherical shapes of the first surface 28a and the second surface 28b of the objective lens 28 can be expressed by using the polynomial shown in the above [Equation 1]. [Table 8] below shows an example of aspheric coefficients A _{4 to} A ₁₂ for forming the first surface 28a of the objective lens 28 into an aspheric surface using the polynomial of [Equation 1].

[Table 9] shows an example of aspheric coefficients A _{4 to} A ₁₀ for forming the second surface 28b of the objective lens 28 into an aspheric surface using the polynomial of [Equation 1].

The configuration of each optical element in the case of using the “blu-ray Disc” 201a in this optical pickup device is shown in [Table 10] below.

Further, the configuration of each optical element in the case of using “HD-DVD” 201c in this optical pickup device is shown in [Table 11] below.

  From these [Table 10] and [Table 11], in this embodiment, the radius of curvature at the apex of the first surface 28a of the objective lens 28 is 2.146645 mm, and the radius of curvature at the apex of the second surface 28b is − The lens thickness between the first surface 28a and the second surface 28b of the objective lens 28 is 3.1 mm, and the distance between the second surface 28b of the objective lens 28 and the front surface of the first correction plate 29a is 10.47725 mm. The working distance WD1 obtained by adding the distance WD11 and the distance WD12 from the rear surface of the first correction plate 29a to the surface of the “blu-ray Disc” 201a, and the front surface of the second correction plate 29b from the second surface 28b of the objective lens 28. And the working distance WD2 including the distance WD22 from the rear surface of the second correction plate 29b to the surface of the “HD-DVD” 201c are both approximately 0.55 m. It is.

  In this optical pickup device, the opening restricting portion 27 is provided as in the above-described embodiment.

  FIG. 14 is a graph showing the unsatisfactory sine condition and longitudinal aberration when the numerical aperture of the objective lens is 0.85.

  FIG. 15 is a graph showing an unsatisfactory sine condition and longitudinal aberration when the numerical aperture of the objective lens is 0.65.

  As shown in FIGS. 14 and 15, the objective lens 28 substantially satisfies the sine condition with respect to the laser light L, corresponding to both “blu-ray Disc” 201a and “HD-DVD” 201c. Designed to be

  In FIG. 14, the vertical axis indicates the height of the light beam normalized to the numerical aperture (NA) 0.85 of the objective lens 28 of the laser light L, and the horizontal axis indicates the amount of deviation (mm). In FIG. 15, the vertical axis indicates the height of the light beam normalized with respect to the numerical aperture (NA) 0.65 of the objective lens 28 of the laser light L, and the horizontal axis indicates the amount of deviation (mm). .

Table 12 below shows the aberration characteristics of the optical pickup device of this embodiment on the signal recording layer 202a of the “blu-ray disc” 201a and on the signal recording layer 202c of the “HD-DVD” 201c.

  In this [Table 12], the on-axis aberration indicates the wavefront aberration when the laser beam L is incident parallel to the optical axis of the objective lens 28, and the image height characteristic is 0.3 ° with respect to the optical axis of the objective lens 28. The wavefront aberration when the tilted laser beam L is incident is shown, and the decentering characteristic shows the wavefront aberration when the decentering of the center of the first surface 28a and the second surface 28b of the objective lens 28 is 3 μm.

  As shown in FIGS. 14 and 15, the sine is approximately sine according to the numerical apertures (0.85 and 0.65) when using the “blu-ray Disc” 201a and when using the “HD-DVD” 201c. By designing the objective lens 28 so as to satisfy the conditions, as shown in [Table 12], the occurrence of coma aberration caused by the image height for both “blu-ray Disc” 201a and “HD-DVD” 201c. Can be suppressed. Further, spherical aberration can be suppressed by designing the longitudinal aberration so as to be almost no aberration in accordance with each numerical aperture.

  The “blu-ray disc” 201a and the “HD-DVD” 201c may be tilted by θ ° in one direction from the normal position when being rotated on the turntable 12.

  FIG. 16 is a graph showing wavefront aberration that occurs when the “blu-ray Disc” 201a is tilted from the normal position.

  When the “blu-ray disc” 201a is tilted from the normal position, as shown in FIG. 16, the wavefront aberration increases substantially linearly as the tilt amount θ ° increases. The wavefront aberration caused by the tilt of the “blu-ray disc” 201a is removed by tilting the first correction plate 29a by a predetermined angle in the direction opposite to the tilt of the “blu-ray disc” 201a. be able to. In this optical pickup device, the first correction plate 29a is integrated with the holder 32 with the connecting member 35 as an axis, in the radial direction of the optical disc, in the tracking direction, or in any of these directions. It can be tilted with respect to the 28 optical axes. The first correction plate 29 a is tilted with respect to the optical axis of the objective lens 28 by the tilt adjustment mechanism 36.

  FIG. 17 shows the first correction plate necessary for minimizing the wavefront aberration (wavefront aberration when the tilt amount θ ° is 0) with respect to the “blu-ray disc” 201a tilted by θ °. It is a graph which shows tilt amount (psi) of 29a.

  In this optical pickup device, as shown in FIG. 17, the tilt amount ψ ° of the first correction plate 29a is approximately proportional to the tilt amount θ ° of the “blu-ray disc” 201a. The wavefront aberration (coma aberration) can be suppressed to about 0.005λrms. That is, if the “blu-ray Disc” 201a tilt amount θ ° is known, the tilt amount ψ ° of the first correction plate 29a necessary for suppressing the wavefront aberration can be obtained.

  FIG. 18 is a graph showing the wavefront aberration that occurs when the “HD-DVD” 201c is tilted from the normal position.

  When the “HD-DVD” 201c is tilted from the normal position, the wavefront aberration increases substantially linearly as the tilt amount θ increases as shown in FIG. The wavefront aberration caused by the tilt of the “HD-DVD” 201c can be removed by tilting the second correction plate 29b by a predetermined angle in the direction opposite to the tilt of the “HD-DVD” 201c. it can. In this optical pickup device, the second correction plate 29b is integrally formed with the holder 32 around the connecting member 35, in the radial direction of the optical disc, in the tracking direction, or in any of these directions. It can be tilted with respect to the 28 optical axes. The second correction plate 29 b is tilted with respect to the optical axis of the objective lens 28 by the tilt adjustment mechanism 36.

  FIG. 19 shows the second correction plate 29b necessary for minimizing the wavefront aberration (wavefront aberration when the tilt amount θ ° is 0) with respect to the “HD-DVD” 201c tilted by θ °. Is a graph showing the tilt amount ψ °.

  In this optical pickup device, as shown in FIG. 19, by making the tilt amount ψ ° of the second correction plate 29b substantially proportional to the tilt amount θ ° of the “HD-DVD” 201c, Wavefront aberration (coma aberration) can be suppressed to about 0.005λrms. That is, if the “HD-DVD” 201c tilt amount θ ° is known, the tilt amount ψ ° of the second correction plate 29b necessary for suppressing the wavefront aberration can be obtained.

  FIG. 20 is a flowchart showing a process of tilting the correction plates 29a and 29b to correct the coma aberration in the “blu-ray disc” 201a and the “HD-DVD” 201c.

  In order to tilt the correction plates 29a and 29b in order to correct the coma aberration in the “blu-ray disc” 201a and the “HD-DVD” 201c, as shown in FIG. 20, first, as a first step (st1) The disc tilt sensor 40 detects the reflected light from the “blu-ray disc” 201a or “HD-DVD” 201c. As shown in FIG. 1, the disc tilt sensor 40 is provided in the optical pickup device and includes a light emitting unit (LED) 40a and a light receiving unit 40b. Light rays from the light emitting unit 40a are reflected by the signal recording layers 202a and 202c of the “blu-ray disc” 201a or “HD-DVD” 201c and reach the light receiving unit 40b. When the “blu-ray disc” 201a or “HD-DVD” 201c is tilted, the position of the reflected light on the light receiving unit 40b deviates from the normal position. The tilt amount of the “blu-ray disc” 201a or “HD-DVD” 201c can be detected based on such a shift in the position of the reflected light on the light receiving unit 40b.

  Then, as shown in FIG. 20, in the second step (st2), the tilt direction of “blu-ray Disc” 201a or “HD-DVD” 201c is calculated from the amount of positional deviation of the reflected light in the disc tilt sensor 40. The tilt amount θ ° is calculated.

  In the third step (st3), the tilt amount ψ ° of the first or second correction plate 29a, 29b is obtained from the tilt amount θ ° obtained in the second step (st2). As described above, since the tilt amount θ ° of the “blu-ray disc” 201a and “HD-DVD” 201c and the tilt amount ψ ° of the correction plates 29a and 29b are substantially proportional, these The tilt amount ψ ° of each of the correction plates 29a and 29b can be obtained from the expression representing the relationship.

  In the fourth step (st4), the tilt direction of each of the correction plates 29a and 29b is set to the opposite direction of the tilt direction of “blu-ray Disc” 201a or “HD-DVD” 201c (positive and negative are opposite), and the tilt amount is set. A signal for ψ ° is supplied to the tilt adjustment mechanism 36.

  In the fifth step (st5), the tilt adjustment mechanism 36 tilts each correction plate 29a, 29b by a predetermined tilt amount ψ ° in a predetermined tilt direction based on the supplied signal.

  The tilt direction of “blu-ray Disc” 201a and “HD-DVD” 201c is the radial direction (radial direction) and circumferential direction (tangential direction) of “blu-ray Disc” 201a and “HD-DVD” 201c. ) Can be considered. Further, the method for obtaining the tilt direction and the tilt amount of “blu-ray Disc” 201a and “HD-DVD” 201c is not limited to the method using the disc tilt sensor as described above, and may be another method. .

[Fourth Embodiment]
In the optical pickup device according to the present invention, as described above, the material forming the correction plate 29 is desirably a material having a refractive index close to that of the transparent substrates of “blu-ray Disc” 201a and “HD-DVD” 201c. As long as it is such a material, it is not limited to polycarbonate, but may be another synthetic resin material or glass.

  When the correction plate 29 has a refractive index different from that of the transparent substrates of “blu-ray Disc” 201a and “HD-DVD” 201c, the correction plate 29 can be used as a plane parallel plate to correct spherical aberration. It cannot be performed sufficiently, and good recording or reproduction cannot be performed.

  Here, consider a case where the refractive index of the correction plate 29 is 1.55, which is smaller than the refractive indexes of the transparent substrates of “blu-ray disc” 201a and “HD-DVD” 201c. In this case, in the optical pickup device having the same configuration as that of the first embodiment described above, assuming that the shape of the correction plate 29 is also a parallel plane plate, recording and reproduction of “blu-ray Disc” 201a The spherical aberration that sometimes occurs is 0.068 λrms on the axis.

Therefore, in this case, in order to correct spherical aberration satisfactorily, the shape of the correction plate 29 must be changed. That is, spherical aberration can be reduced by making at least one of the surface (one surface) on the objective lens 28 side and the surface (two surfaces) on the optical disk side of the correction plate 29 spherical. The formation of each optical element with respect to the “blu-ray Disc” 201a when the two surfaces of the correction plate 29 are spherical is shown in Table 13 below.

  Assuming that the two surfaces of the correction plate 29 have a spherical shape and the correction plate 29 has a slightly convex lens shape, the axial aberration is 0.032 λrms as shown in [Table 13], and the spherical aberration is sufficiently reduced. Can be reduced.

  In this embodiment, for “HD-DVD” 201c, the correction plate 29 is removed from the optical path of the light emitted from the objective lens 28, so that each optical element in the case of using “HD-DVD” 201c. The configuration is as shown in Table 5 above.

  FIG. 21 is a graph showing a tilt amount ψ ° for tilting a correction plate with a refractive index of 1.55 to a minimum wavefront aberration with respect to a “blu-ray disc” 201a tilted by θ °. is there.

  In this optical pickup device, as shown in FIG. 21, the wavefront aberration is obtained by making the tilt amount ψ ° of the correction plate 29 substantially proportional to the tilt amount θ ° of the “blu-ray disc” 201a. (Coma aberration) can be suppressed to about 0.005λrms. That is, if the “blu-ray disc” 201a tilt amount θ ° is known, the tilt amount ψ ° of the correction plate 29 necessary for suppressing the wavefront aberration can be obtained. That is, coma aberration can be reduced by a procedure similar to the procedure shown in FIG.

  However, in this optical pickup device, when the tilt amount θ ° of the “blu-ray Disc” 201a increases, the coma aberration differs even when the correction plate 29 is tilted by ψ °, unlike the case where the correction plate 29 is a parallel substrate. Cannot be completely removed. For example, when the tilt amount θ ° of “blu-ray Disc” 201a is 1.2 °, the wavefront aberration is 0.035 λrms, and the coma aberration remains slightly.

  On the other hand, when the refractive index of the material forming the correction plate 29 is larger than the refractive index of the transparent substrate of the optical disk, the spherical aberration can be sufficiently reduced by making the shape of the correction plate 29 slightly concave. Can do. Also in this case, the wavefront aberration (coma aberration) is improved by making the tilt amount ψ ° of the correction plate 29 substantially proportional to the tilt amount θ ° of the “blu-ray disc” 201a. It can be corrected.

  Further, when the correction plate 29 has a concave lens shape or a convex lens shape, the concave lens shape or the convex lens shape may be a Fresnel lens or a diffractive surface shape.

1 is a side view showing an overall configuration of a first embodiment of an optical pickup device according to the present invention. FIG. 3 is a plan view showing a liquid crystal pattern of a liquid crystal shutter used as an aperture limiting portion in the first embodiment of the optical pickup device. FIG. 3 is a cross-sectional view showing the operation principle of a liquid crystal shutter used as an aperture limiting unit in the first embodiment of the optical pickup device. It is a side view which shows the structure of the objective lens and correction plate in 1st Embodiment of the said optical pick-up apparatus. 5 is a graph showing an unsatisfactory sine condition and longitudinal aberration when the numerical aperture of the objective lens is 0.85 in the first embodiment of the optical pickup device. 6 is a graph showing an unsatisfactory sine condition and longitudinal aberration when the numerical aperture of the objective lens is 0.65 in the first embodiment of the optical pickup device. FIG. 6 is a side view showing a state when the first optical recording medium is tilted from a normal position in the second embodiment of the optical pickup device. 6 is a graph showing wavefront aberration that occurs when the first optical recording medium is tilted from a normal position in the second embodiment of the optical pickup device. FIG. 6 is a side view showing a state in which a correction plate is tilted to correct wavefront aberration when the first optical recording medium is used in the second embodiment of the optical pickup device. 6 is a graph showing a tilt amount of a correction plate necessary for minimizing wavefront aberration with respect to the first optical recording medium in a tilted state in the second embodiment of the optical pickup device. 6 is a flowchart showing a process of tilting a correction plate in order to correct coma in the first optical recording medium in the second embodiment of the optical pickup device. It is a side view which shows the structure of the correction board in 3rd Embodiment of the said optical pick-up apparatus. It is a side view which shows the structure of the objective lens and correction plate in 3rd Embodiment of the said optical pick-up apparatus. It is a side view which shows the structure of the objective lens and correction plate in 3rd Embodiment of the said optical pick-up apparatus. 10 is a graph showing an unsatisfactory sine condition and longitudinal aberration when the numerical aperture of an objective lens is 0.85 in the third embodiment of the optical pickup device. 10 is a graph showing an unsatisfactory sine condition and longitudinal aberration when the numerical aperture of an objective lens is 0.65 in the third embodiment of the optical pickup device. 14 is a graph showing wavefront aberration that occurs when the first optical recording medium is tilted from the normal position in the third embodiment of the optical pickup device. FIG. 6 is a graph showing the tilt amount of the first correction plate necessary for minimizing wavefront aberration with respect to the tilted first optical recording medium in the third embodiment of the optical pickup device. FIG. is there. 10 is a graph showing wavefront aberration that occurs when the second optical recording medium is tilted from the normal position in the third embodiment of the optical pickup device. In the third embodiment of the optical pickup device, a graph showing the tilt amount of the second correction plate necessary for minimizing wavefront aberration with respect to the second optical recording medium in a tilted state. is there. 10 is a flowchart showing a process of tilting a correction plate in order to correct coma aberration in the first and second optical recording media in the third embodiment of the optical pickup device. 14 is a graph showing a tilt amount for tilting a correction plate to a minimum wavefront aberration with respect to a tilted first optical recording medium in the fourth embodiment of the optical pickup device. . It is the side view which showed the form of the conventional optical pick-up apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical disk drive device 11 Spindle motor 12 Turntable 20 Optical pick-up device 21 Blue semiconductor laser 27 Aperture limiter 28 Objective lens 29 Correction plate 29a First correction plate 29b Second correction plate 36 Tilt adjustment mechanism 40 Disc tilt sensor 201a “ blu-ray Disc "
201c "HD-DVD"
202a Signal recording layer 202c Signal recording layer 203a Laser beam incident surface 203c Laser beam incident surface

Claims (5)

A first optical recording medium having a first signal recording layer on a transparent substrate, a recording density lower than that of the first signal recording layer on a transparent substrate thicker than the transparent substrate of the first optical recording medium. At least two types of optical recording of a second optical recording medium having two signal recording layers and a third optical recording medium integrally formed by stacking the first and second optical recording media An optical pickup device that selectively records, erases, or reproduces information signals with respect to a medium,
A laser light source that emits laser light having a wavelength of 450 nm or less;
An objective lens having a numerical aperture of 0.75 or more and condensing and irradiating laser light emitted from the laser light source through the transparent substrate with respect to the first or second signal recording layer. When,
Aperture limiting means for limiting the numerical aperture of the objective lens;
A correction plate inserted between the objective lens and the optical recording medium,
When recording, erasing, or reproducing is performed on the first signal recording layer, the numerical aperture of the objective lens is not limited by the aperture limiting unit, and the objective lens and the first optical recording medium are not limited. By inserting the correction plate into the sine condition, the sine condition is substantially satisfied,
When recording, erasing, or reproducing is performed on the second signal recording layer, the numerical aperture of the objective lens is limited by the aperture limiting means, and the objective lens and the second optical recording medium are interposed between the objective lens and the second optical recording medium. By removing the correction plate from the optical pickup device, the sine condition is substantially satisfied. Tilt detecting means for detecting a tilt of the first optical recording medium with respect to the optical axis of the objective lens;
Correction plate tilting means for tilting the correction plate with respect to the optical axis of the objective lens,
The correction plate tilting unit reduces the occurrence of coma aberration by tilting the correction plate according to a tilt amount of the first optical recording medium detected by the tilt detection unit. Item 5. The optical pickup device according to Item 1. When the correction plate has a refractive index substantially equal to that of the transparent substrates of the first and second optical recording media, the thickness of the transparent substrate of the first optical recording medium and the transparency of the second optical recording medium. A parallel flat plate having a thickness corresponding to a difference from the thickness of the substrate, and having a refractive index different from that of the transparent substrates of the first and second optical recording media, becomes a convex lens or a concave lens. The optical pickup device according to claim 1, wherein the optical pickup device is an optical pickup device. A first optical recording medium having a first signal recording layer on a transparent substrate, a recording density lower than that of the first signal recording layer on a transparent substrate thicker than the transparent substrate of the first optical recording medium. At least two types of optical recording of a second optical recording medium having two signal recording layers and a third optical recording medium integrally formed by stacking the first and second optical recording media An optical pickup device that selectively records, erases, or reproduces information signals with respect to a medium,
A laser light source that emits laser light having a wavelength of 450 nm or less;
An objective lens having a numerical aperture of 0.75 or more and condensing and irradiating laser light emitted from the laser light source through the transparent substrate with respect to the first or second signal recording layer. When,
Aperture limiting means for limiting the numerical aperture of the objective lens;
A first correction plate inserted between the objective lens and the optical recording medium;
A second correction plate that is thinner than the first correction plate inserted between the objective lens and the optical recording medium;
Tilt detecting means for detecting a tilt of the first and second optical recording media with respect to the optical axis of the objective lens;
Correction plate tilting means for tilting the first and second correction plates with respect to the optical axis of the objective lens;
When recording, erasing, or reproducing is performed on the first signal recording layer, the numerical aperture of the objective lens is not limited by the aperture limiting unit, and the objective lens and the first optical recording medium are not limited. When the first correction plate is inserted into the first optical recording medium, the sine condition is substantially satisfied, and the correction plate tilt means detects the tilt amount of the first optical recording medium detected by the tilt detection means. And reducing the occurrence of coma by tilting the first correction plate according to
When recording, erasing, or reproducing is performed on the second signal recording layer, the numerical aperture of the objective lens is limited by the aperture limiting unit, and a second gap is formed between the objective lens and the second optical recording medium. By inserting the second correction plate, the sine condition is substantially satisfied, and the correction plate tilting means is in accordance with the tilt amount of the second optical recording medium detected by the tilt detection means. An optical pickup device characterized in that the coma aberration is reduced by tilting the second correction plate. When the first and second correction plates have a refractive index substantially equal to that of the transparent substrates of the first and second optical recording media, the thickness of the transparent substrate of the first optical recording media and the second A parallel flat plate having a thickness difference corresponding to the difference between the thickness of the transparent substrate of the optical recording medium and having a refractive index different from that of the transparent substrates of the first and second optical recording media, The optical pickup device according to claim 4, wherein the optical pickup device is a convex lens or a concave lens.

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