JP2007328902A - Objective lens apparatus, optical pickup device, optical disk driving apparatus, and method of driving objective lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an objective lens apparatus which attains reduction of thickness and can handle recording mediums of three different kinds of formats, and to provide an optical pickup device, an optical disk driving apparatus, and a method of driving objective lenses thereof. <P>SOLUTION: The objective lenses 21, 22 and 23 for a BD, a DVD and a CD corresponding respectively to the three disk formats are provided individually. Thus, the objective lenses 21, 22 and 23 can be held by a lens holder 26 while the positions of the focusing directions of the respective objective lenses 21, 22 and 23 are varied relatively according to their working distances. When the respective objective lenses 21, 22 and 23 are held respectively at optimal positions in the focusing directions, the objective lens apparatus whose thickness is reduced is obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical pickup device that performs at least one of optically recording a signal on an optical recording medium and reproducing the recorded signal, an objective lens device mounted on the optical pickup device, and an objective lens driving method About.

  Conventionally, as an objective lens mounted on an optical pickup compatible with three formats such as BD (Blu-ray Disc (registered trademark)), DVD (Digital Versatile Disc), and CD (Compact Disc), the following objectives are used. There is a lens (for example, see Patent Documents 1 and 2).

  In the optical pickup of Patent Document 1, a first objective lens (24) that focuses laser light with a wavelength of 400 to 410 nm on a BD (100c) and a wavelength of 650 to 780 nm on a CD (100b) or DVD (100a). A second objective lens (25) for condensing the laser light is held by the movable block (12). In Patent Document 1, in order to reduce the thickness of the pickup, for example, as shown in FIG. 7, the working distance (working distance: WD) of each disk (100), that is, the distance from the disk to the objective lens is considered. Thus, the neutral position of the movable block (12) in the focusing direction is determined. This is because the objective lenses corresponding to CD and DVD are two-wavelength compatible objective lenses, and in this case, the focal lengths are almost the same. It is natural that the focal length is the same because of the compatible objective lens. Although the focal length is the same, the thickness of the cover layer on the disk surface is different between CD and DVD, so that the neutral position of the working distance must be considered as described above. As a result, the neutral position of the focus stroke (position away from each disk by the working distance) is different for each of CD and DVD. As a result, the total focus stroke (total stroke) that must be secured as an optical pickup is increased by the difference in neutral position.

  The “focus stroke” here is a range in which the objective lens moves by driving the actuator. In Patent Document 1, in order to support three formats including BD, the neutral position of the objective lens corresponding to BD is designed to be located at the center between the neutral positions of the CD and DVD. As a result, thinning in the focus direction is realized.

  On the other hand, in Patent Document 2, a three-wavelength compatible objective lens corresponding to the above three formats is used.

Japanese Patent Laying-Open No. 2005-302163 (paragraphs [0060] and [0061], FIG. 7) JP 2005-293770 A (paragraph [0038])

  Although the optical pickup disclosed in Patent Document 1 is thinned, as described above, a difference in working distance (ΔWD) due to different neutral positions of the CD and DVD is generated. Remains.

  In Patent Document 2, the difference in optical path length in air (Δ cover thickness / refractive index of the cover layer) corresponding to the difference in thickness of the cover layers of BD, DVD, and CD is the same as the three-wavelength compatible objective. This is the difference in the center position of the lens focus stroke (difference in neutral position). Therefore, in this design, the stroke amount becomes large, which is contrary to the reduction in thickness.

  In Patent Document 1, the two-wavelength compatible objective lens has a constant focal length as described above, but the NA (Numerical Aperture) is different for each laser beam used for DVD and CD. In this case, the beam diameter becomes unnecessarily large. That is, the effective diameter of the laser beam for CD passing through the two-wavelength compatible objective lens is different from that of the laser beam for DVD. In particular, as in Patent Document 2, in the case of a three-wavelength compatible objective lens, in the case of a BD having the largest NA, the beam diameter is further increased and the objective lens is also enlarged. As a result, the effective beam diameter necessary for the optical system becomes unnecessarily large for DVD and BD having a larger NA, and in this respect, the configuration is not suitable for thinning.

  In view of the circumstances as described above, an object of the present invention is an objective lens device, an optical pickup device, an optical disk drive device, and an optical pickup device that can be applied to recording media of three different formats and can be thinned. The objective is to provide a driving method of the objective lens.

  In order to achieve the above object, the objective lens device according to the present invention can be focused on a disk-shaped first optical recording medium having a first cover layer having a first thickness. The first objective lens having a numerical aperture of 1 and the second cover layer having a second thickness larger than the first thickness can be condensed onto a disc-shaped second optical recording medium. A second objective lens having a second numerical aperture smaller than the first numerical aperture, and a third cover layer having a third thickness larger than the second thickness and a third cover layer. A third objective lens having a third numerical aperture smaller than the second numerical aperture, and the first, second and third objective lenses. And a lens holder that is integrally held.

  In the present invention, first, second, and third objective lenses corresponding to the first, second, and third optical recording media are provided. Therefore, according to the working distance of each objective lens, the position of each objective lens in the focus direction can be relatively changed and held by the lens holder. If each objective lens is held at an optimum position in the focus direction, it is possible to realize a thinner objective lens device and an optical pickup device on which the objective lens device is mounted.

  Further, the provision of the first, second, and third objective lenses can solve the problem that the lens becomes large like a conventional compatible objective lens. This contributes to thinning of the objective lens device.

  The phrase “can be condensed” means that the signal can be recorded or reproduced.

  In the present invention, the first objective lens has a first focal length and a first lens principal point, and the second objective lens has a second focal length and a second lens principal. The third objective lens has a third focal length and a third lens principal point, and the lens holder is the first objective lens of the held first objective lens. A first focal length difference (A) that is a difference between the second focal length and the first focal length in the focus direction from the lens principal point, the second thickness, and the first thickness. The second lens principal point is located at a distance corresponding to a difference (A−D) from the first air equivalent cover thickness difference (D) which is the optical path length in air corresponding to the difference between The second objective lens is held so that the third focal length and the third focal length from the first lens principal point in the focus direction are arranged. The second focal length difference (C) that is the difference between the first focal lengths and the second air that is the optical path length in the air corresponding to the difference between the third thickness and the first thickness. The third objective lens is held so that the third lens principal point is disposed at a position corresponding to a difference (C−F) from the medium conversion cover thickness difference (F). As a result, the initial position in the focus direction of each objective lens (hereinafter referred to as “focus initial position” or “stroke center position”) is fixed by the lens holder. That is, the neutral position described in Patent Documents 1 and 2 is constant for each objective lens, and the difference between the neutral positions can be made zero. Thereby, it is possible to reduce the thickness of the objective lens device and the optical pickup device on which the objective lens device is mounted.

  In the present invention, the difference in thickness between the first cover layer, the second cover layer, and the third cover layer is replaced with the optical path length in air in advance, and the initial focus position of each objective lens. Is offset. Therefore, the difference between them is converted to air and expressed as “the optical path length in the air”.

  In the above invention, the lens holder is a difference between the first focal length and the second focal length in a focus direction from the second lens principal point of the held second objective lens. And a first air equivalent cover thickness difference (−D) that is an optical path length in the air corresponding to the difference between the first thickness and the second thickness. The first objective lens is held such that the first lens principal point is disposed at a position corresponding to a difference (A-D), and the second lens principal point Corresponding to the difference between the third thickness and the second thickness in the focus direction, the third focal length difference (B) that is the difference between the third focal length and the second focal length. In the position away from the third air equivalent cover thickness difference (E), which is the optical path length in the air, by a distance corresponding to the difference (B−E), the third As lens principal point is placed, to hold the third objective lens, it is substantially identical to the invention that. That is, in the present invention, the second lens principal point of the second objective lens is set as the reference position.

The same applies to the case where the third lens principal point of the third objective lens is set as the reference position. In this case, the lens holder is separated from the third lens principal point of the held third objective lens. Corresponds to the difference between the first focal length and the third focal length in the focus direction, the second focal length difference (−C) that is the difference between the first focal length and the third focal length, and the difference between the first thickness and the third thickness. The first lens principal point is arranged at a position separated by a distance corresponding to a difference (F-C) from a second air-converted cover thickness difference (-F) that is an optical path length in the air. As described above, the first objective lens is held, and the third focal length difference (the difference between the second focal length and the third focal length in the focus direction from the third lens principal point ( -B) and the third air equivalent, which is the optical path length in air corresponding to the difference between the second thickness and the third thickness. To a position apart a distance corresponding to the difference between the bar thickness difference (E) (E-B), as the second lens principal point is arranged to hold the second objective lens,
In the present invention, at least two of the first, second and third objective lenses are formed by integral molding. Thereby, the space | interval of the said at least 2 objective lens can be narrowed, and an objective lens apparatus can be reduced in size. In addition, the integral molding improves the mounting position accuracy and tilt accuracy of the at least two objective lenses when the objective lens device is manufactured. In particular, when the first to third objective lenses are integrally molded, the effect becomes remarkable.

  In the present invention, the first numerical aperture is 0.8 to 0.9, the second numerical aperture is 0.6 to 0.7, and the third numerical aperture is 0.45 to 0.55. . That is, the present invention describes that the first optical recording medium is BD, the second optical recording medium is DVD or HD (High Definition) DVD, and the third optical recording medium is CD.

  In the present invention, the third objective lens is different from the first objective lens and the second objective lens in the first objective lens, the second objective lens, the third objective lens, and the lens holder. Is disposed at a position close to the vibration antinode of the vibration system when the mechanical vibration system including An objective lens having a larger numerical aperture has a shorter focal length, and the recording density of an optical recording medium that is a target for collecting light by the objective lens increases. The higher the recording density, the higher the accuracy required for focusing servo and tracking servo. Therefore, the objective lens having a large numerical aperture is arranged at a position farther from the antinode of the vibration system so as not to be affected by the vibration system as much as possible, and the third objective lens having the smallest numerical aperture is It is arranged at a position close to the belly. Thereby, a signal recording error or a reproduction error can be prevented.

  The resonance of the vibration system here means at least one of resonance in the focus direction and resonance in the tracking direction.

  In the present invention, the third objective lens is disposed between the first objective lens and the second objective lens. The vibration system including the lens holder often has an antinode at the center. Therefore, with the configuration of the present invention, signal recording errors or reproduction errors can be prevented.

  In the present invention, the lens holder includes a required minimum stroke range of the second objective lens and a required minimum stroke range of the first objective lens within a required minimum stroke range of the third objective lens. As described above, the first, second and third objective lenses are held. The necessary minimum stroke is a distance corresponding to an allowable amount of surface blur of the corresponding optical recording medium. According to the configuration of the present invention, it is possible to reduce the thickness of the objective lens device and the optical pickup device on which the objective lens device is mounted.

  In the present invention, the working distance of the second objective lens and the third objective lens is 0.2 to 0.5 mm.

  In the present invention, the objective lens device is provided in the lens holder, and includes the first, second, or third optical recording medium and at least one of the first, second, and third objective lenses. It further includes a protector for preventing contact.

  In the present invention, the protector is provided on the outer peripheral side in the radial direction of the first, second, or third optical recording medium in the lens holder. For example, an annular rib is provided at least on the inner periphery of the CD. Therefore, according to this invention, it can prevent that the rib and protector contact.

  In the present invention, at least one of the first, second and third objective lenses has a self-aperture part. This eliminates the need for high positioning accuracy compared to the case where an aperture is provided in the lens holder as in the prior art. In particular, an integrated objective lens in which at least two of the first, second, and third objective lenses are integrally molded, and the integrated objective lens may have a self-aperture part.

  An optical pickup device according to the present invention includes a first laser beam having a first wavelength, a second laser beam having a second wavelength longer than the first wavelength, and a first laser beam longer than the second wavelength. The first laser beam is collected on a disk-shaped first optical recording medium having a light source that emits a third laser beam having a wavelength of 3 and a first cover layer having a first thickness. A first objective lens having a first numerical aperture, and a disc-shaped second light having a second cover layer having a second thickness larger than the first thickness. The second laser beam can be condensed on a recording medium, and a second objective lens having a second numerical aperture smaller than the first numerical aperture, and a second thicker than the second thickness. The third optical recording medium having a third cover layer having a thickness of 3 is provided on the third optical recording medium having the third shape. A third objective lens capable of condensing laser light and having a third numerical aperture smaller than the second numerical aperture is integrated with the first, second and third objective lenses. A lens holder for holding, and an actuator for driving the lens holder are provided.

  In the present invention, the “light source” may be a separate light source that emits each laser beam, or at least two of the three laser beams are physically configured as one structure. A light source may be used. The “first wavelength” is, for example, 400 to 410 nm, the “second wavelength” is, for example, 650 to 660 nm, and the “third wavelength” is, for example, 770 to 830 nm, but is not limited to these ranges.

  An “actuator” is a drive mechanism that drives a lens holder to drive each objective lens at least in the tracking direction and the focus direction for recording or reproducing a signal. For example, an actuator that is driven by a driving principle such as an electromagnetic action, an electrostatic action, or a piezoelectric action may be used.

  In the present invention, ΔST1 is a difference between the stroke center positions of the first and second objective lenses in the focus direction by the actuator, and an optical path length in air corresponding to the difference between the first and second thicknesses. In the case of L1, the lens holder holds the first and second objective lenses so as to satisfy ΔST1 <L1. Alternatively, in the present invention, the difference between the center positions of the strokes of the second and third objective lenses in the focus direction by the actuator is ΔST2, and the optical path in air corresponding to the difference between the second and third thicknesses. When the length is L2, the lens holder holds the second and third objective lenses so as to satisfy ΔST2 <L2. Alternatively, ΔST3 is a difference between the center positions of the strokes of the third and first objective lenses in the focus direction by the actuator, and L3 is an optical path length in air corresponding to the difference between the third and first thicknesses. In this case, the lens holder holds the third and first objective lenses so as to satisfy ΔST3 <L3.

  In the present invention, the optical pickup device has a plate shape or a triangular prism shape, is disposed so as to face the first objective lens, and transmits the first laser light emitted from the light source to the first objective lens. And a mirror for reflecting the first laser beam so as to be incident on the mirror. Since the first objective lens having the largest numerical aperture needs to be a lens having a large power in order to realize a large numerical aperture, the thickness in the focus direction is increased unless a special lens is used. In this case, as in the present invention, if the mirror is plate-shaped or triangular prism-shaped, a space in the focus direction of the first objective lens can be secured, and the first objective lens can be appropriately used even if the thickness is large. Can be arranged at various positions. In this case, the mirrors incident on the second and third objective lenses may be plate-shaped or triangular prism-shaped, or may be realized by a prismatic prism or the like as will be described later.

  In the present invention, the optical pickup device is disposed so as to face the second objective lens, transmits the first laser light out of the first laser light and the second laser light, and transmits the second laser light. The first dichroic mirror that reflects the laser beam so as to be incident on the second objective lens, and the first, second, and third laser beams are disposed so as to face the third objective lens. And a second dichroic mirror that transmits the first and second laser beams and reflects the third laser beam so as to be incident on the third objective lens. Thereby, an objective lens device in which the first, second and third objective lenses are arranged in a row can be realized.

  In the present invention, the optical pickup device is provided in the prism including the first dichroic mirror and the second dichroic mirror, and changes the polarization state of the first, second, and third laser beams. And a wave plate. In particular, since the wavelength plate of the third laser beam is provided on the prism, it is not necessary to provide a wavelength plate in the vicinity of the mirror that reflects the first laser beam. That is, for example, it is not necessary to secure a space for the first wavelength plate for laser light in the vicinity of the first objective lens, which contributes to a reduction in the thickness of the optical pickup device.

  An optical disk drive apparatus according to the present invention includes a first optical recording medium having a first cover layer having a first thickness, a second thickness having a second thickness greater than the first thickness. A disk-shaped second optical recording medium having a cover layer or a disk-shaped third optical recording medium having a third cover layer having a third thickness larger than the second thickness is rotationally driven. It is possible to condense on the rotation drive mechanism and the optical recording medium, and it is possible to condense on the first objective lens having the first numerical aperture and the second optical recording medium, The second objective lens having a second numerical aperture smaller than the first numerical aperture, and the third optical recording medium can be condensed, and a third objective lens smaller than the second numerical aperture can be condensed. A third objective lens having a numerical aperture and the first, second and third objective lenses; The first and second rotationally driven by the rotational drive mechanism using the lens holder integrally holding the actuator, the actuator for driving the lens holder, and the first, second or third objective lens. Or a recording / reproducing processor for recording a signal on the third optical recording medium or reproducing the recorded signal. “Recording / reproducing processor” means a member, function, processing circuit, or the like necessary for recording or reproducing a signal.

  According to the objective lens driving method of the present invention, a disc-shaped first optical recording medium having a first cover layer having a first thickness is collected by a first objective lens having a first numerical aperture. And a second numerical aperture smaller than the first numerical aperture in a disk-shaped second optical recording medium having a second cover layer having a second thickness greater than the first thickness. Condensing with a second objective lens having a second objective lens, and a disc-shaped third optical recording medium having a third cover layer having a third thickness greater than the second thickness. Condensing with a third objective lens having a third numerical aperture smaller than the numerical aperture, and holding the first, second and third objective lenses together for signal recording or reproduction Driving the lens holder.

  As described above, according to the present invention, it is possible to realize a reduction in thickness corresponding to recording media of three formats.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic perspective view of an optical disk drive apparatus according to an embodiment of the present invention. FIG. 2 is a schematic plan view showing an optical pickup device mounted on the optical disk drive device 50 of FIG.

  The optical disk drive 50 is an optical disk (CD, CD-ROM, CD-R / RW, DVD, DVD-ROM, DVD ± R / RW, DVD-RAM, BD, BD-ROM, BD-R) as an optical recording medium. / RE, HD DVD, etc.) is a device that records and plays back information. The optical disc 1 may have a single signal recording layer or a plurality of signal recording layers. Hereinafter, the optical disc 1 may be referred to as “BD100”, “DVD200”, and “CD300”. For convenience, these three optical discs or four optical discs including an optical disc such as an HD DVD are collectively referred to as “optical disc”. 1 ”.

  The optical disk drive device 50 includes, for example, a disk clamper 3 on which the optical disk 1 is mounted, an optical pickup device 6 on which an optical system to be described later is mounted, and a housing 7 that accommodates these.

  The disc clamper 3 is provided with a chucking mechanism for holding the optical disc 1. Thereby, the optical disc 1 is mounted on the disc clamper 3 and can be rotated.

  The optical pickup device 6 includes a moving base 4, an optical system 30 mounted on the moving base 4, and an actuator 8 that drives a condensing device (objective lens device) 20 described later. The moving base 4 is connected to a rotating shaft of a feed motor (not shown in FIG. 2), and can slide in the radial direction of the optical disc 1 along guide shafts 5 provided at both ends. The direction in which the moving base 4 moves is generally referred to as a radial direction. A direction orthogonal to the radial direction is generally called a tangential direction. The actuator 8 is a biaxial actuator that performs drive control such as focus servo and tracking servo by displacing the objective lens device 20 in the focusing direction and the tracking direction. However, the present invention is not necessarily limited to the case of two axes, and a triaxial actuator that can displace the objective lens device 20 also in the direction of the relative tilt angle (tilt angle) between the objective lens device 20 and the optical disc 1 is provided. It may be provided.

  FIG. 3 is a block diagram showing a configuration of the optical disk drive device 50 shown in FIG.

  As shown in FIG. 2, the optical disk drive 50 includes a spindle motor 9, a feed motor 10, a system controller 11, a servo control circuit 12, a preamplifier 13, a signal modulator / demodulator in addition to the optical pickup device 6 described above. And an ECC (error correction code) unit 14, an interface 15, a D / A converter and A / D converter 16, an audio / visual processing unit 17, an audio / visual signal input / output unit 18, and a laser control unit. 19.

  The spindle motor 9 is a motor for rotationally driving the optical disc 1. The disk clamper 3 and the spindle motor 9 constitute a rotational drive mechanism.

The feed motor 10 is a motor for moving the moving base 4 shown in FIG. 1 in the radial direction of the optical disc 1. Thereby, the system controller 11 in which the optical pickup device 6 is moved in the radial direction of the optical disc 1 is provided for the entire optical disc driving device 50 and for individual control such as signal processing and servo control.

  The servo control circuit 12 generates a focus servo signal and a tracking servo signal based on signals (focus error signal and tracking error signal) obtained from the preamplifier 13 and sends these signals to the optical pickup device 6 and the feed motor 10.

  The preamplifier 13 generates a focus error signal, a tracking error signal, and an RF signal) from the signal obtained by the optical pickup device 6.

  The signal modulator / demodulator and ECC (error correction code) unit 14 demodulates the RF signal, demodulates the recording signal, and performs error correction coding processing. For example, ECC is added to the recording signal, and error correction is performed on the reproduction signal (RF signal).

  The interface 15 exchanges signals with the external computer 27.

  The D / A converter and the A / D converter 16 convert the reproduction signal from a digital signal to an analog signal, and convert the recording signal from an analog signal to a digital signal.

  The audio / visual processing unit 17 and the audio / visual signal input / output unit 18 exchange audio signals and video signals with external devices.

  The laser control unit 19 controls the output and wavelength of the semiconductor laser mounted on the optical pickup device 6 according to recording and reproduction, the type of the optical disc 1 and the like.

  The optical disk drive device 50 configured as described above rotates the optical disk 1 by the spindle motor 9 and drives and controls the feed motor 10 in accordance with a control signal from the servo control circuit 12. As a result, the optical disc driving device 50 moves the optical pickup device 6 to a position corresponding to a desired recording track of the selected signal recording layer of the optical disc 1, so that the selected signal recording layer of the optical disc 1 is moved. Record and play back information.

  Referring to FIG. 2, the optical system 30 includes a one-wavelength laser diode 90, a laser coupler 92, a photodetector 93, a first adjustment lens 99, a λ / 2 plate 96, a first polarization beam splitter 94, and a second polarization. A beam splitter 95, a second adjustment lens 97, a mirror 98, a grating 24, a collimator lens 84, and the objective lens device 20 are provided.

  The one-wavelength laser diode 90 emits a laser beam having a wavelength of 400 to 410 nm (hereinafter referred to as a first laser beam) corresponding to the BD100. The laser coupler 92 has a laser beam having a wavelength of 650 to 660 nm corresponding to the DVD 200 (hereinafter referred to as a second laser beam) and a laser beam having a wavelength of 770 to 830 nm corresponding to the CD 300 (hereinafter referred to as a third laser beam). And a light emitting / receiving element for receiving the second and third laser beams.

  The photodetector 93 detects the return light from the optical disk 1 of the first laser light. The second adjustment lens 97 adjusts the beam diameter for the photodetector 93 to suitably detect the return light. The mirror 98 guides the first laser light emitted from the second adjustment lens 97 to the photodetector 93.

  The collimator lens 84 converts the laser light having each wavelength transmitted or reflected by the first polarization beam splitter 94 into parallel light. The collimator lens 84 is supported by the lens holder 51, and both ends of the lens holder 51 are supported by a pair of guide shafts 52 extending in the optical axis direction. The lens holder 51 is movable in the optical axis direction by being engaged with the lead screw 55 of the drive motor 54. The collimator lens 84 is driven to rotate the lead screw 55 of the drive motor 54, so that the lens holder 51 is moved in the optical axis direction, the thickness error of the surface cover layer of the optical disc 1, and the surface cover layer of the multilayer disc. While correcting the spherical aberration caused by the difference, even when the wavelength of the laser used for recording / reproduction differs according to the format of the optical disc 1, the optimum collimator position can be obtained.

  FIG. 4 is a side view of the periphery of the objective lens device included in the optical system 30 of the optical pickup device 6 shown in FIG. The optical system 30 further includes a rising prism 86, a rising mirror 83, a first λ / 4 plate 87, and a second λ / 4 plate 85.

  The rising prism 86 transmits the first laser light transmitted through the collimator lens 84 and raises the second and third laser lights transmitted through the collimator lens 84 to the optical disc 1 side. That is, the rising prism 86 reflects the second and third laser beams so that the second and third laser beams are incident on the DVD objective lens 22 and the CD objective lens 23. The raising mirror 83 raises the first laser light transmitted through the collimator lens 84 and the raising prism 86 to the optical disc 1 side, and causes the first laser light to enter the BD objective lens 21. Reflects laser light.

The first λ / 4 plate 87 converts the polarization directions of the second and third laser beams raised by the raising prism 86 from linearly polarized light to circularly polarized light. The first λ / 4 plate 87 is an integrated type for CD and DVD, but is not an integrated type, and may be provided individually as shown in FIG. 21, for example.
Similarly, the second λ / 4 plate 85 converts the polarization direction of the first laser light transmitted through the rising prism 86 from linearly polarized light to circularly polarized light.

  The rising prism 86 has a wavelength-dependent separation film, and has reflection and transmission film characteristics according to the order of the corresponding objective lenses. However, as will be described later, when the DVD objective lens 22 is used as an HD DVD objective lens, the wavelengths of the laser light for BD and HD DVD are the same. What is necessary is just to set suitably the ratio of reflection and transmission.

  The one-wavelength laser diode 90 emits the first laser beam from the light emitting unit toward the first polarization beam splitter 94. The laser light emitted from the one-wavelength laser diode 90 is substantially S-polarized with respect to the first polarizing beam splitter 94 by the grating 24 having the function of a λ / 2 plate for the first laser light. It is rotated to become. The first laser beam is further split by the grating 24 into three beams for generating a tracking error signal by the differential push-pull method, and then incident on the first polarization beam splitter 94.

  Here, since the position of the objective lens is offset in the tangential direction from the center of the spindle motor 3, the phases of the push-pull signals by the main and sub spots in the differential push-pull method are shifted. In order to avoid this, for example, as disclosed in Japanese Patent Application Laid-Open No. 2004-318957, the grating 24 generates astigmatism in the 45-degree direction at the secondary spot to suppress the push-pull signal amplitude due to the secondary spot. Also good.

  FIG. 5 is a perspective view showing the laser coupler 92. In FIG. 5, members such as a package covering the laser coupler 92 are not shown. The laser coupler 92 includes, for example, a silicon chip 103 provided with photodetectors 101 and 102 that detect return light of the second and third laser beams in the surface region. A photodiode chip 109 is mounted on the silicon chip 103, and a two-wavelength laser diode 104 is mounted on the photodiode chip 109.

  The two-wavelength laser diode 104 is usually attached to the silicon chip 103 via a photodiode chip 109 in which a PIN photodiode 108 is provided in the surface region when used exclusively for reproduction. The PIN photodiode 108 provided in the photodiode chip 109 monitors laser light emitted from the rear surface of the two-wavelength laser diode 104 for the purpose of controlling the output of the two-wavelength laser diode 104.

  In the case of recording / reproducing, a photodetector for laser power monitoring (not shown) provided on the silicon chip 103 is used. This photodetector corresponds to a light receiving part (27) for monitoring as described in, for example, FIG. 2, FIG. 7, FIG. 9, etc. of Japanese Patent No. 3438482. Such a laser power monitoring photodetector monitors a component of the laser light emitted from the front surface of the two-wavelength laser diode 104 that is not used for focusing on the optical disc 1 (for example, a component transmitted through the prism 105). .

  On the silicon chip 103, a prism 105 having an inclined end surface 105a that reflects the second and third laser beams emitted from the two-wavelength laser diode 104 at substantially right angles is mounted. The laser light reflected by the inclined end surface 105 a proceeds toward the second polarization beam splitter 95. On the other hand, the return light reflected by the signal recording surface of the optical disc 1 passes through the inclined end surface 105a of the prism 105, passes through the prism 105, and is detected by the photodetectors 101 and 102 as described above.

  Referring to FIG. 2, the first and second polarization beam splitters 94 and 95 each have a wavelength selection function. That is, the first and second polarizing beam splitters 94 and 95 are elements that transmit or reflect according to the wavelength of incident laser light. For example, an optical thin film having a predetermined configuration is provided on the joint surfaces 94a and 95a of the prism. It is constituted by being done. Thereby, the first polarization beam splitter 94 transmits the second and third laser beams regardless of the polarization state, and transmits or reflects the first laser beam according to the polarization state. Similarly, the second polarization beam splitter 95 transmits the second and third laser beams regardless of the polarization state, and transmits or reflects the first laser beam according to the polarization state.

  More specifically, the first polarization beam splitter 94 emits light from the one-wavelength laser diode 90 and is joined when the incident angle of the first laser light converted into S-polarization by the grating 24 is the design center value. The total amount of light is reflected by the surface 94a toward the collimator lens 84 side. The first polarization beam splitter 94 is designed such that the incident angle of the return light of the first laser beam reflected by the signal recording surface of the optical disc 1 and made P-polarized by the second λ / 4 plate 85 is the design center value. At this time, the entire amount of light is transmitted to the second polarizing beam splitter 95 side.

  The λ / 2 plate 96 is provided between the first polarizing beam splitter 94 and the second polarizing beam splitter 95. Therefore, the returned first laser light converted to P-polarized light that has passed through the first polarizing beam splitter 94 is again converted to S-polarized light and is incident on the second polarizing beam splitter 95. When the incident angle of the first laser beam converted to S-polarized light is the design center value, the second polarizing beam splitter 95 reflects the entire amount of light by the joint surface 95a as in the case of the first polarizing beam splitter 94. The return light reflected by the joint surface 95 a is incident on the light receiving surface of the photodetector 93 via the second adjustment lens 97 and the mirror 98.

  The objective lens device 20 includes a BD objective lens 21 that converges the first laser beam on the signal recording surface of the optical disc 1, a DVD objective lens 22 that converges the second laser beam on the signal recording surface of the optical disc 1, and It has a CD objective lens 23 for converging the third laser beam on the signal recording surface of the optical disc 1, and a lens holder 26 for holding these BD, DVD and CD objective lenses 21, 22, and 23 integrally. . The lens holder 26 is preferably made of, for example, a resin, but may be a light metal such as aluminum, or may be made of other materials.

  In this way, the objective lenses 21, 22 and 23 for BD, DVD and CD respectively corresponding to the three disc formats are individually provided, so that the objective lenses 21, 22 and 23 are set to their working distances. Accordingly, the positions of the objective lenses 21, 22 and 23 in the focus direction can be relatively changed and held by the lens holder 26. And if each objective lens 21, 22, and 23 is each hold | maintained in the optimal position in a focus direction, the objective-lens apparatus made thinner can be implement | achieved. The optimum holding position of each objective lens 21, 22 and 23 will be described later.

  In addition, by providing the BD, DVD and CD objective lenses 21, 22 and 23 individually, it is possible to solve the problem that the lens becomes large like a conventional compatible objective lens. This contributes to thinning of the objective lens device. This will be described in detail later.

  In the present embodiment, the lens design for the BD, DVD, and CD objective lenses 21, 22 and 23 can be made individually. For example, aberrations can be individually considered for each of the objective lenses 21, 22, and 23, and an optimum lens design corresponding to each laser beam having three different wavelengths becomes possible.

  The rising mirror 83 is a prism-shaped mirror having a triangular prism shape, and is arranged to face the BD objective lens 21. Since the BD objective lens 21 having the largest NA needs to be a lens having a large power in order to realize a large numerical aperture, the thickness in the focus direction becomes thick unless a special lens is used. In this case, if the raising mirror 83 has a triangular prism shape, a space in the focus direction of the BD objective lens 21 can be secured, and the BD objective lens 21 is disposed at an appropriate position even if the thickness is large. Can do. For the above purpose, the raising mirror 83 may of course have a plate shape.

  The rising prism 86 typically includes a first dichroic mirror 86a and a second dichroic mirror 86b as the separation film. The first dichroic mirror 86a is disposed so as to face the DVD objective lens 22. The first dichroic mirror 86a transmits the first laser light of the first and second laser lights, and transmits the second laser light to the DVD objective lens. The light is reflected so as to enter the lens 22. The second dichroic mirror 86b is disposed so as to face the CD objective lens 23, and transmits the first and second laser beams out of the first, second, and third laser beams. Is reflected so as to enter the CD objective lens 23.

  As described above, the rising prism 86 is provided with the first λ / 4 plate 87 and the second λ / 4 plate 85 as wave plates. In particular, since the second λ / 4 plate 85, which is a third wavelength plate for laser light, is provided on the rising prism 86, it is not necessary to provide a wavelength plate in the vicinity of the rising mirror 83. . That is, for example, it is not necessary to secure a space for the second λ / 4 plate 85 in the vicinity of the BD objective lens 21, which contributes to the thinning of the optical pickup device 6.

  In the optical system 30 as described above, the first laser light emitted from the one-wavelength laser diode 90 is polarized by the λ / 2 plate function of the grating 24 after the forward magnification is adjusted via the coupling lens 99. When the direction is rotated and emitted, the S polarization component is reflected by the joint surface 94a of the first polarization beam splitter 94, and a part of the P polarization component is transmitted. The amount of laser light is monitored. The reflected first laser light passes through the collimator lens 84 that can remove the spherical aberration of the BD 100 in combination with the BD objective lens 21 by adjusting the position, and further passes through the objective lens 21. It converges on the signal recording surface 100b through the cover layer 100a of the BD100. The return laser beam reflected by the signal recording surface 100 b of the BD 100 is converted by the λ / 4 plate 85 into a direction in which the polarization direction is orthogonal to the forward path, and is P-polarized with respect to the first polarization beam splitter 94. It is incident in the state and transmits all the light. The returned first laser beam that has transmitted the entire amount of light is converted into a direction in which the polarization direction is orthogonal by the λ / 2 plate 96 provided immediately before the second polarization beam splitter 95 and is incident in the state of S polarization. As a result, the total amount of light is reflected by the joint surface 95 a of the second polarizing beam splitter 95 and converges on the light receiving surface of the photodetector 93.

  Further, the second or third laser light emitted from the laser coupler 92 is transmitted through the second polarizing beam splitter 95, the λ / 2 plate 96, and the first polarizing beam splitter 94 in the entire amount of light. The second or third laser light transmitted through the entire amount of light passes through a collimator lens 84 set so as to be in an optimum position with respect to the DVD 200 or the CD 300 according to the respective emission point and wavelength, and further, the DVD objective. The light passes through the lens 22 or the CD objective lens 23 and converges on the signal recording surface 200b or 300b through the cover layer 200a or 300a of the DVD 200 or CD 300, respectively. The returned second or third laser beam reflected by the signal recording surface 200b or 300b of the DVD 200 or CD 300 returns to the laser coupler 92 through the same optical path as the forward path, and enters the inclined end surface 105a of the prism 105. The light passes through and converges on the photodetectors 101 and 102.

  In the present embodiment, the differential push-pull method is used as an example of the tracking servo method, but other known methods may be used. The optical system 30 is configured to selectively transmit or reflect only the first laser beam. For example, the light source, the photodetector, and the polarization separation films (bonding surfaces) of the first and second polarization beam splitters 94 and 95 are used. 94a and 95a) may be configured such that only the second laser beam is selectively transmitted or reflected.

  FIG. 6 shows the respective φ (effective diameter) (mm), f (focal length) (mm), NA of the CD objective lens 23, DVD objective lens 22, and BD objective lens 21 according to the present embodiment. It is the table | surface which showed. FIG. 7 is a table showing t (thickness) (mm) of each of the cover layers 300a, 200a, and 100a of the CD 300, the DVD 200, and the BD 100. Regarding φ and f, the values in this table are merely examples and are values that vary depending on the size of the objective lens. As for CD, NA = 0.45 to 0.50 is generally used for reproduction only, and NA = 0.50 to 0.55 is generally used for recording and reproduction. Also for DVDs, NA = 0.60 to 0.65 is generally used for reproduction only, and NA = 0.65 to 0.70 is generally used for recording and reproduction. As for BD, currently NA is generally about 0.85, but in the future, considering various conditions, an appropriate NA will be selected in the range of about 0.80 to 0.90 like CD and DVD. It is thought that it will do. Also for t, the values in this table are standard values, and may differ from these values, such as in the case of variations and multilayer discs. Hereinafter, the thickness of the BD cover layer is t1, the thickness of the DVD cover layer is t2, and the thickness of the CD cover layer is t3 (see FIG. 4).

  As shown in FIG. 4, the lens principal points of the objective lenses 21, 22 and 23 for BD, DVD and CD are the first lens principal point 21a, the second lens principal point 22a and the third lens principal point. Let it be point 23a. The lens principal point is the optical center of the lens and is the center point that defines the focal length f. The objective lenses 21, 22, and 23 for BD, DVD, and CD have a first focal length f1, a second focal length f2, and a third focal length f3, respectively.

Here, the difference between the first focal distance f1 and the second focal distance f2 is Δfa (= f2−f1),
The difference between the second focal length f2 and the third focal length f3 is Δfb (= f3-f2),
A difference between the third focal length f3 and the first focal length f1 is Δfc (= f3−f1).
Further, the difference in thickness between the cover layers 100a and 200a of the BD 100 and the DVD 200 is represented by Δta (= t2−t1),
The difference between the thicknesses of the cover layers 200a and 300a of the DVD 200 and the CD 300 is expressed as Δtb (= t3−t2),
A difference in thickness between the cover layers 300a and 100a of the CD 300 and the BD 100 is represented by Δtc (= t3−t1).

  In the example shown in FIG. 6, Δfa = 0.385, Δfb = 0.380, and Δfc = 0.765. Further, Δta = 0.5, Δtb = 0.6, and Δtc = 1.1.

  The optical path difference L1 of the laser light in the air corresponding to Δta, the optical path difference L2 of the laser light in the air corresponding to Δtb, and the optical path difference L3 of the laser light in the air corresponding to Δtc are as follows. It can be expressed by a formula.

L1 = Δta / refractive index of cover layer (1)
L2 = Δtb / refractive index of cover layer (2)
L3 = Δtc / refractive index of cover layer (3)
When the cover layer of BD100, DVD200, and CD300 is, for example, polycarbonate resin, the refractive index is approximately 1.6. In the example shown in FIG.
L1 = 0.5 / 1.6≈0.31 (4)
L2 = 0.6 / 1.6≈0.38 (5)
L3 = 1.1 / 1.6≈0.69 (6)
It becomes.

  When a cover layer different from polycarbonate is used for the objective lenses 21, 22 and 23 for BD, DVD and CD, and when the refractive index is different, naturally, L1, L2 and L3 are respectively Different from the value.

  The reason for converting the optical path length with air is that the difference in thickness between the cover layers 100a, 200a and 300a is replaced with the optical path length in the air, and the initial focus positions of the objective lenses 21, 22 and 23 are offset in advance. This is because the purpose of this embodiment is. The initial focus position is the stroke center position of the lens holder 26 by the actuator 8. The present embodiment has a feature that all the differences in the stroke center positions can be made zero in the objective lenses 21, 22 and 23 for BD, DVD and CD.

Here, the above formulas (1), (2), and (3) can be considered to represent, for example, a difference in stroke center position of an optical pickup using a conventional two-wavelength compatible objective lens. That means
(A) In the case of Formula (1), a form composed of a compatible objective lens for BD and DVD and an objective lens for independent CD is assumed. In this case, since the objective lens for CD is independent, the stroke center can be set freely. However, since a compatible objective lens is used for BD / DVD, the difference Δta in the thickness of the cover layer is set in the air. The converted optical path difference L1 remains as a stroke center difference.
(B) In the case of Formula (2), a form composed of compatible objective lenses for DVD and CD and an independent objective lens for BD is assumed. In this case, since the objective lens for BD is independent, the center of the stroke can be set freely. However, since the compatible objective lens is used for DVD / CD, the thickness difference Δtb of the cover layer is set in the air. The converted optical path difference L2 remains as a stroke center difference.
(C) In the case of the formula (3), a form constituted by a compatible objective lens for BD and CD and an independent objective lens for DVD is assumed. In this case, since the objective lens for DVD is independent, the stroke center can be set freely. However, since the compatible objective lens is used for BD / CD, the difference Δtc in the thickness of the cover layer is set in the air. The converted optical path difference L3 remains as a stroke center difference.

  As will be described below, in the present embodiment, the difference in stroke between the objective lenses 21, 22 and 23 can be made smaller than in any of the conventional methods such as the above (a) to (c). Specifically, the objective lenses 21, 22, and 23 for BD, DVD, and CD are held by the lens holder 26 at the following positions.

  The lens holder 26 holds the BD objective lens 21 at a predetermined position in the focus direction. The predetermined position may be anywhere, but this predetermined position becomes the reference position. A distance corresponding to the difference between Δfa and L1 described above from the first lens principal point 21a serving as the reference position, that is, Δfa−L1 = 0.385−0.31 = 0.075, and a focus direction (a focus direction away from the optical disc 1). The objective lens 22 for DVD is held by the lens holder 26 so that the second lens principal point 22a is arranged at a position separated by a). The focal length is taken into account because the BD objective lens 21, the DVD objective lens 22, and the CD objective lens 23 are individually provided and have different focal lengths.

  Similarly, the third lens principal point 23a is located at a position away from the first lens principal point 21a serving as the reference position by Δfc−L3 = 0.765-0.69 = 0.075 in the focus direction (the focus direction away from the optical disc 1). The CD objective lens 23 is held by a lens holder.

  As a result, the maximum value (ΔST) of the difference between the stroke center positions of the objective lenses 21, 22, and 23 can be set to zero by the lens holder, so that the movable range of the objective lens device 20 can be reduced. can do. As a result, the optical pickup device 6 and the optical disk drive device 50 can be reduced in thickness.

  The above “maximum value” refers to the difference between the center positions of the strokes of the BD objective lens 21 and the DVD objective lens 22, the difference between the stroke center positions of the DVD objective lens 22 and the CD objective lens 23, In addition, it means the largest value among the three differences in the difference between the center positions of the strokes of the CD objective lens 23 and the BD objective lens 21.

In the case of this example, the effective diameters of the respective objective lenses 21, 22 and 23 are almost equal. The relationship between effective diameter φ, NA and focal length f is
φ = 2 × NA × f
It becomes. Therefore, as in Patent Document 1 or 2, when a compatible objective lens is used, f is fixed, so that the effective diameter increases with the ratio of NA. However, if a compatible objective lens is not used as in this embodiment, the effective diameter of a BD or DVD having a large NA is unnecessarily large, and there is no disadvantage in reducing the size and thickness of the optical pickup. In the present embodiment, this is an effect resulting from the configuration in which the three objective lenses 21, 22, and 23 are independent and the focal length can be selected.

  Further, in this embodiment, the optical pickup device 6 can be thinned without using a special rising prism (31) as shown in FIG. 2 of JP-A-2005-100513.

  In the present embodiment, the objective lens device 20 is not particularly heavy because the three objective lenses 21, 22, and 23 are provided independently. Compared to the case where a huge lens such as a three-wavelength compatible objective lens is used, the three objective lenses 21, 22 and 23 can be reduced in size, so the total mass does not change much.

  In addition, since there is a large difference in the stroke center position in the conventional compatible objective lens, it is necessary to pass a DC current when displacing from the reference center position to the other center position. A design that takes into account skew fluctuations was also necessary. However, in this embodiment, since there is no difference in the stroke center position or it is sufficiently small, there is no need to flow a large DC current, and there is no need to design in consideration of sensitivity fluctuations and skew fluctuations. As a result, an optical pickup device having high performance and high reliability can be designed.

As described above, it is most preferable to set the maximum value ΔST of the difference between the stroke center positions of the objective lenses 21, 22, and 23 to zero, but it is not necessarily required to be zero. In the present embodiment, when the difference between the stroke center positions of the BD objective lens 21 and the DVD objective lens 22 is ΔST1,
ΔST1 <L1 (7)
It is preferable that the BD objective lens 21 and the DVD objective lens 22 are held by the lens holder 26 so as to satisfy the above.

Alternatively, similarly, when the difference between the stroke center positions of the DVD objective lens 22 and the CD objective lens 23 is ΔST2,
ΔST2 <L2 (8)
It is preferable that the DVD objective lens 22 and the CD objective lens 23 are held by the lens holder 26 so as to satisfy the above.

Alternatively, similarly, when the difference between the stroke center positions of the CD objective lens 23 and the BD objective lens 21 is ΔST3,
ΔST3 <L3 (9)
It is preferable that the CD objective lens 23 and the BD objective lens 21 are held by the lens holder 26 so as to satisfy the above.

  When (7), (8) and (9) are applied to the example shown in FIGS. 6 and 7, the value of L1≈0.31 in the above equation (4) is the smallest value. Therefore, it is most preferable to satisfy Expression (7).

  Even if the stroke center positions of the BD objective lens 21 and the DVD objective lens 22 are deviated by, for example, about 0.1 mm from the stroke center position of the CD objective lens 23, the effect on the performance and thinning of the actuator 8 can be obtained. , ΔST is almost the same as when zero. In other words, BD and DVD have less warpage standards for discs than CDs, and have less surface blurring. The standard of surface blur is a maximum of ± 0.3 mm for BD, a maximum of ± 0.4 mm for DVD, and a maximum of ± 0.5 mm for CD. That is, even if the BD objective lens 21 or the DVD objective lens 22 deviates by 0.1 mm from the stroke center position of the CD objective lens 21, it is within the CD stroke range where the amount of surface blur is the largest. is there.

  FIG. 8 is a plan view showing an optical pickup device according to another embodiment of the present invention. FIG. 9 is a side view of the periphery of the objective lens device of the optical pickup device 106. In the following description, the same members, functions, and the like of the optical pickup device 6 according to the embodiment shown in FIGS. 2 and 4 will not be described or will be mainly described.

  In the objective lens device 35 of the optical pickup device 106, a DVD objective lens 32 and a CD objective lens 33 are integrally molded to constitute a DVD / CD objective lens unit 34 (integrated objective lens). In this case, the DVD and CD objective lenses 32 and 33 may be made of resin or glass. The DVD / CD objective lens unit 34 and the BD objective lens 21 are separate bodies, and these objective lenses are integrally held in a lens holder 36. According to such a configuration, the distance between the two objective lenses 32 and 33 can be narrowed, and the objective lens device 35 and the optical pickup device 106 can be reduced in size. In addition, the integral molding improves the mounting position accuracy and tilt accuracy of the two objective lenses 32 and 33 when the objective lens device 35 is manufactured.

  As described above, the DVD and CD objective lenses 32 and 33 are not limited to be integrally molded, and the BD and CD objective lenses may be integrally molded, and the DVD may be independent. Furthermore, as shown in FIGS. 26A and 26B, all objective lenses for BD, DVD, and CD may be integrally molded. According to such a configuration, the interval between the three objective lenses can be narrowed, and the objective lens device 35 and the optical pickup device 106 can be reduced in size. In addition, the integral molding further improves the mounting position accuracy and tilt accuracy of the three objective lenses when the objective lens device 35 is manufactured.

  FIG. 10 is a plan view showing an optical pickup device according to still another embodiment of the present invention. 11A is a cross-sectional view taken along the line AA in FIG. 10, and FIG. 11B is a cross-sectional view taken along the line BB in FIG. In the objective lens device 40 of the optical pickup device 206, the BD lens 21 and the CD objective lens 23 are arranged in the radial direction of the optical disc 1. Further, the CD objective lens 23 and the DVD objective lens 22 are arranged so as to be aligned in the tangential direction (tangential direction) of the optical disc 1, and these BD, DVD and CD objective lenses 21, 22 and 23 are integrated. In particular, it is held by the lens holder 46.

  In the optical pickup device 206, for example, the arrangement of the one-wavelength laser diode 90 and the laser coupler 92 is reversed in accordance with the arrangement of the objective lenses 21, 22, and 23, as compared with the configuration illustrated in FIG. 2. In addition, necessary condenser lenses 41, mirrors 42, and the like are also provided.

  In the present embodiment, according to the design items such as the configuration and arrangement of each component constituting the objective lens device 40, or according to various design items of the optical disk drive device on which the optical pickup device 206 is mounted. Like the objective lens device 40, the arrangement of the objective lenses 21, 22 and 23 can be designed. For example, in FIG. 10, the arrangement of the BD objective lens 21 and the CD objective lens 23 may be opposite to each other, or the arrangement of the CD objective lens 23 and the DVD objective lens 22 may be opposite to each other. . Alternatively, the arrangement of the BD objective lens 21 and the DVD objective lens 22 may be reversed. It is also possible to arrange the objective lenses 21, 22 and 23 so as to be obliquely arranged in a line with respect to the radial direction.

  FIG. 12 is a side view showing an objective lens device according to still another embodiment of the present invention, and is a diagram showing an objective lens device in which a BD objective lens is arranged in the center. In this example, the CD objective lens 23, the BD objective lens 21, and the DVD objective lens 22 are held by the lens holder 26 in a line from the side near the light source (not shown). In this case, as shown in FIG. 4, the rising prism 86 and the rising mirror 83 may be arranged, but in FIG. 12, one rising prism 75 may be arranged. A λ / 4 plate 76 is disposed between the rising prism 75 and the objective lenses 21, 22, and 23.

  The present invention is not limited to the embodiment described above, and various modifications are possible.

  The optical path of the optical system 30 shown in FIGS. 2 and 4 is an example in which some of the optical paths of the first, second, and third laser beams are common. However, the optical system 30 may be configured such that the optical paths of the first, second, and third laser beams are independent of each other.

  The DVD objective lens 22 of the objective lens device 20 shown in FIG. 4 can also be used as an HD DVD objective lens. In other words, in the optical pickup device 6, the three objective lenses 21, 22, and 23 can correspond to four formats of optical disks. DVD and HD DVD have substantially the same NA and cover layer thickness, which are important for objective lens design. Therefore, for example, by using a wavelength-selective hologram, the DVD objective lens 22 can be used as an HD DVD objective lens.

  FIG. 13 is a perspective view showing an objective lens device according to still another embodiment of the present invention.

  In the objective lens device 45 according to the present embodiment, the lens holder 56 is arranged such that the DVD objective lens 22, the CD objective lens 23, and the BD objective lens 21 are arranged in this order from the side closer to the light source such as the laser coupler 92. Thus, these objective lenses 21, 22, and 23 are held. A coil 39 for driving the lens holder biaxially or triaxially is attached to the end of the lens holder 56. Hereinafter, the BD objective lens 21, the DVD objective lens 22, and the CD objective lens 23 may be collectively referred to as objective lenses 21 to 23.

  Here, a mechanical vibration system including the BD objective lens 21, the DVD objective lens 22, the CD objective lens 23, and the lens holder 56 is considered. The CD objective lens 23 is disposed at a position closer to the antinode of vibration of the vibration system when the vibration system resonates than the other two objective lenses. In the example shown in FIG. 13, the CD objective lens 23 is disposed near the center of the lens holder 56. In the present embodiment, an example in which the CD objective lens 23 and the DVD objective lens 22 are integrally molded as shown in FIG. 8 is shown. However, the objective lenses 21 to 23 may be separate from each other, or may be a lens unit in which all of the objective lenses 21 to 23 as shown in FIGS. 26 (A) and 26 (B) are integrally molded. Good.

  FIG. 14A is a diagram simulating resonance in the focus direction (Z-axis direction) of the vibration system. FIG. 15A is a graph showing the resonance peak in FIG. 14A for each of the objective lenses 21 to 23. In this case, the resonance frequency (secondary) was 27 kHz. FIG. 14B is a diagram simulating resonance in the tracking direction (X-axis direction) of the vibration system. FIG. 15B is a graph showing the resonance peak in FIG. 14B for each of the objective lenses 21 to 23. In this case, the resonance frequency (secondary) was 22 kHz. 14A and 14B, it can be seen that the center of the lens holder is an antinode of resonance in the focus direction and the tracking direction.

  The objective lens with a larger NA can narrow the focused spot, and the recording density of the optical disc 1 becomes higher, while the depth of focus becomes smaller. As a result, the higher the recording density, the higher the accuracy required for focusing servo and tracking servo. Therefore, the BD objective lens 21 or the DVD objective lens 22 having a large NA is disposed at a position farther from the resonance antinode so as not to be affected by the vibration system as much as possible, and the CD objective lens 23 having the smallest NA. Is arranged at a position near the antinode of resonance. As a result, signal recording or reproduction errors caused by the objective lenses 21 to 23 can be prevented. In a thin optical disk drive, the spindle motor 9 is often used at a maximum rotation speed of about 5000 to 6000 rpm (corresponding to about 24 × speed for CD, about 8 × speed for DVD, and about 5 × speed for BD). However, this embodiment is effective because a highly accurate servo is required particularly when recording or reproducing at such a high speed.

  In the case of the present embodiment, as shown in FIG. 16, the objective lens device 45 is arranged on the moving base 4 as follows. When the optical pickup device 156 is not in operation, the objective lens device 45 is configured so that the CD objective lens passes through the center line E passing through the center of the optical disc 1 when the optical disc 1 is held by the disc clamper 3 (see FIG. 1). 23 is located. Alternatively, as shown in FIG. 17, the objective lens device 45 may be arranged so that the CD objective lens 23 is located at a position shifted from the center line E when the optical pickup device 256 is not operating. .

  Depending on the shape of the lens holder 56 and the arrangement of the coil 39, the position of the antinode of the resonance is not always near the center of the lens holder 56. For example, when the objective lenses 21 to 23 are arranged in the order shown in FIG. 4 or FIG. 12, the CD objective lens 23 may be arranged at a position closest to the resonance antinode of the vibration system. . The gist of the present embodiment is that the CD objective lens 23 is arranged at the antinode of resonance of the vibration system. At the time of manufacturing the objective lens device, the position of the antinode of resonance of the vibration system may be set intentionally.

  In the objective lens device 45 shown in FIG. 13, a protector 37 is provided on the upper surface of the lens holder 56. The protector 37 has a function of preventing the optical disc 1 and at least one of the three objective lenses 21 to 23 (particularly, the upper end surfaces of the objective lenses 21 to 23) from coming into contact with each other. That is, the height of the upper end surface of the protector is set to be higher than the heights of the upper end surfaces 21b, 22b, and 23b of the objective lenses 21 to 23.

  For example, two protectors 37 are provided in the tangential direction (Y-axis direction), but may be one or any other arrangement. The material of the protector 37 is resin, rubber, metal or the like, but may be other materials.

  FIG. 18 is a perspective view showing an objective lens device including a protector according to another embodiment. The protector 38 according to the present embodiment is provided on the outer peripheral side in the radial direction of the optical disc 1 and is not provided on the inner peripheral side. That is, the protector 38 is provided from the substantially center position of the upper surface of the lens holder 66 to the outer peripheral side in the radial direction. Thereby, it can prevent that the protector 38 and the cyclic | annular rib (not shown) formed in the inner peripheral part of CD contact. In addition, the height of this rib is set to 0.4 mm at maximum according to the standard.

  In FIG. 18, the protector 38 is provided in the radial direction from the substantially center position of the upper surface of the lens holder 66 to the outer peripheral side. However, if the protector 38 does not contact the rib on the inner peripheral portion of the CD, the lens holder 66 is provided. It may be provided at any position.

  The concept of the objective lens device 45 shown in FIG. 13 may be applied to the objective lens devices 35 and 40 shown in FIG. 8 or FIG. 10, or may be applied to objective lens devices according to other embodiments described later. May be applied.

  Next, another embodiment of the arrangement of the relative heights of the BD objective lens 21, the DVD objective lens 22, and the CD objective lens 23 will be described. FIG. 19 is a diagram illustrating the minimum required stroke (minimum required focus stroke) and WD of the objective lenses 21 to 23. In FIG. 19, the size of the objective lenses 21 to 23 is small for each dimension value (unit: [mm]).

  In the present embodiment, the required minimum stroke ranges of the BD objective lens 21 and the DVD objective lens 22 are included in the required minimum stroke range of the CD objective lens 23. The WD of each objective lens 21 to 23 is set. The necessary minimum stroke is a distance corresponding to the allowable surface shake amount (standard value) of the optical disc 1. For example, the minimum required stroke of the CD objective lens 23 is a CD allowable surface blur amount ± 0.5 mm (maximum 1.0 mm). The minimum required stroke of the DVD objective lens 22 is an allowable surface blur amount of DVD ± 0.4 mm (maximum 0.8 mm). The required minimum stroke of the BD objective lens 21 is an allowable surface blur amount of BD ± 0.3 mm (maximum 0.6 mm). That is, the gist of the present embodiment is that the required minimum stroke range of each of the objective lenses 22 and 21 for DVD and BD is within the range of the allowable surface deflection of CD, which is the longest required minimum stroke ± 0.5 mm. As included, the lens holder 56 holds the objective lenses 21 to 23. According to such a configuration, at the time of manufacturing the objective lens device, the height of each of the objective lenses 22 and 21 for DVD and BD can be arranged while achieving a reduction in thickness within a range of ± 0.5 mm. Can be set freely.

  In the present embodiment, the WDs of the objective lenses 21 to 23 are 0.2 mm, 0.4 mm, and 0.4 mm, respectively.

  FIG. 20 is a diagram showing WD of a conventional objective lens compatible with CD and DVD. As can be seen from this figure, since the compatible objective lens 79 is used, the necessary minimum stroke of the objective lens must be increased, and the WD is increased accordingly. In the case of CD, WD is 0.7 mm, and in the case of DVD, WD is 0.33 mm. As described in Patent Document 1, since there is a difference (ΔWD) between the two WDs, the neutral position of the compatible objective lens 79 differs between the two disks 200 and 300. Therefore, the space for that must be secured, and the movable range of the objective lens device to be secured becomes large.

  FIG. 21 is a diagram showing another embodiment of an objective lens device in which a CD objective lens and a DVD objective lens are integrally molded as shown in FIGS. In the integrally molded DVD / CD objective lens unit 134, the upper end surface 23b of the CD objective lens 23 and the upper end surface 22b of the DVD objective lens 22 are set to the same height. Further, if the upper end surface 21b of the BD objective lens 21 is set to the same height as the upper end surfaces 23b and 22b of the DVD / CD objective lens unit 134, the manufacture is facilitated, and the protector 37 or 38 is also arranged. In addition, the possibility of a collision with each optical disc 1 can be minimized.

  The WD of the DVD / CD objective lens unit 134 is set to 0.2 to 0.5 mm. In the example shown in FIG. 21, the WD is 0.4 mm.

  The lower limit value 0.2 mm will be described. In the case of a CD, an annular rib having a maximum size of 0.1 mm is provided on the outer periphery of the CD. Further, since the cover layer thickness is 1.2 ± 0.1 mm, it is assumed that a CD having a cover layer thickness of 1.3 mm is used as the CD having the thickest cover layer. Therefore, the objective lens is moved to the 1.3 mm disk by 0.06 (≈0.1 / 1.6), which is the distance equivalent to 0.1 mm, which is the difference between 1.2 mm and 1.3 mm. It approaches the disc. Accordingly, a minimum WD of 0.1 + 0.06 = 0.16 mm is required only under the condition of avoiding a collision with the outer peripheral rib. Further, considering the tilt of the disc when the CD (or DVD) is chucked by the chucking mechanism, the tilt of the DVD / CD objective lens unit 134 held by the lens holder 66, etc., 0.16 mm + ( 0.02-0.04 mm) = 0.2 mm.

  The upper limit value 0.5 mm will be described. The difference between the cover layer thicknesses of CD and DVD is 1.2−0.6 = 0.6 mm. When this is converted into air, it is 0.36 (≈0.6 / 1.6). By adding 0.36 to the above lower limit value 0.2 mm and rounding down, 0.5 mm can be obtained.

  In this way, when the WD of the DVD / CD objective lens unit 134 is set, the WD of the BD objective lens 21 is different in the necessary minimum stroke (one side) of the BD objective lens 21 and the CD objective lens 23. In consideration of .2 mm, in the example shown in FIG. 21, the WD of the DVD / CD objective lens unit 134 is 0.4 mm, whereas the WD of the BD objective lens 21 is 0.2 mm.

  FIG. 22 is a perspective view showing a lens holder to which, for example, the DVD / CD objective lens unit 134 and the BD objective lens 21 are attached. The DVD / CD objective lens unit 134 is mounted in the recess 57, and the BD objective lens 21 is mounted in the recess 58.

  For example, when the objective lens device 45 is manufactured, first, the DVD / CD objective lens unit 134 is fitted into the recess 57. The skew values in the radial direction and tangential direction of the DVD / CD objective lens unit 134 at this time are used as a reference. The operator adjusts the skew in the tangential direction of the BD objective lens 21 so that the skew in the tangential direction of the BD objective lens 21 matches the reference skew value of the DVD / CD objective lens unit 134. The radial direction of the BD objective lens 21 can be adjusted during recording or reproduction by a biaxial or triaxial actuator without skew adjustment.

  The state of this skew adjustment is shown in FIG. FIG. 24 is a cross-sectional view of the BD objective lens 21 during skew adjustment. For example, the skew adjustment is performed by adjusting the height of one pin 72 of the adjusting tool having the two pressing pins 72 and 73.

  Thus, since the DVD / CD objective lens unit 134 is large, skew adjustment is easier when the skew of the BD objective lens 21 is adjusted than when the skew adjustment of the DVD / CD objective lens unit 134 is performed. become.

  At least one of the objective lenses 21 to 23 according to the above embodiments may have a self-aperture section. This eliminates the need for high positioning accuracy compared to the case where an aperture is provided in the lens holder as in the prior art.

  In particular, the DVD / CD objective lens units 34 and 134 may have a self-aperture part. FIG. 25 is a diagram showing a DVD / CD objective lens unit having self-aperture sections 122a and 123a. In the example of FIG. 25, as described in Japanese Patent Laid-Open No. 2000-30278, the DVD / CD objective lens unit 234 has a curved surface indicated by a predetermined function, so that annular self-aperture portions 122a and 123a are formed. The

  Typically, laser light incident within a predetermined radius from the radial direction (Y-axis direction) of the CD objective lens 123 (or DVD objective lens 122) converges on the pits of the CD 300 (or DVD 200) (convergence). Light α). The laser light incident on the self-aperture part 123a (or 122a) outside the predetermined radius is emitted as light that does not contribute to the recording / reproducing process even if it is parallel light β, divergent light, or convergent light. That is, even if there is no aperture separate from the conventional objective lens, the DVD / CD objective lens unit 234 has an aperture function. Thereby, size reduction or thickness reduction of an objective-lens apparatus is realizable.

  When apertures for the CD and DVD objective lenses 23 and 22 are provided in the lens holder, respectively, as in the prior art, the center of each aperture and the center of each of the CD and DVD objective lenses 23 and 22 are provided. It is difficult to match (the position of the optical axis). On the other hand, in the present embodiment, the CD and DVD objective lenses 123 and 122 of the DVD / CD objective lens unit 234 have the self-aperture portions 123a and 122a, respectively.

  The self-aperture sections 122a and 123a are not limited to those defined by curved surface functions. Any form may be used as long as the laser light is emitted as parallel light or diverges.

1 is a schematic perspective view of an optical disk drive device according to an embodiment of the present invention. It is a typical top view which shows the optical pick-up apparatus mounted in the optical disk drive device of FIG. It is a block diagram which shows the structure of the optical disk drive device shown in FIG. FIG. 4 is a side view of an objective lens device included in the optical system of the optical pickup device shown in FIG. 3. It is a perspective view which shows a laser coupler. It is the table | surface which each showed (phi) (effective diameter), f (focal length), and NA of the objective lens for CD which concerns on this Embodiment, for DVD, and for BD. It is the table | surface which showed the thickness of each cover layer of CD, DVD, and BD. It is a top view which shows the optical pick-up apparatus which concerns on other embodiment of this invention. It is a side view of the periphery of the objective lens apparatus of the optical pick-up apparatus shown in FIG. It is a top view which shows the optical pick-up apparatus which concerns on another another embodiment of this invention. (A) is the sectional view on the AA line in FIG. 10, (B) is sectional drawing on the BB line. It is a side view which shows the objective lens apparatus which concerns on another embodiment of this invention, and is a figure which shows the objective lens apparatus by which the objective lens for BD was arrange | positioned in the center. It is a perspective view which shows the objective-lens apparatus which concerns on another embodiment of this invention. (A) is the figure which simulated the resonance of the focus direction of a vibration system. (B) is a diagram simulating resonance in the tracking direction of the vibration system. (A) is the graph which showed the resonance peak in FIG. 14 (A) for every objective lens. (B) is the graph which showed the resonance peak in FIG.14 (B) for every objective lens. It is a schematic diagram which shows the example of the initial position of the objective lens apparatus shown in FIG. It is a schematic diagram which shows the other example of the initial position of the objective lens apparatus shown in FIG. It is a perspective view which shows the objective lens apparatus provided with the protector which concerns on other embodiment. It is a figure which shows the required minimum stroke and WD of each objective lens. It is a figure which shows WD of the compatible objective lens of the conventional CD and DVD. FIG. 10 is a diagram showing another embodiment of an objective lens device in which a CD objective lens and a DVD objective lens as shown in FIGS. 8 and 9 are integrally formed. It is a perspective view which shows the lens holder with which the DVD / CD objective lens unit and the objective lens for BD are mounted | worn. It is a figure which shows the mode of the skew adjustment of the objective lens for BD shown in FIG. It is sectional drawing of the objective lens for BD at the time of the skew adjustment. It is a figure which shows the DVD / CD objective lens unit which has a self-aperture part. (A) is a perspective view showing an objective lens in which three objective lenses are integrally molded. (B) is the side view.

Explanation of symbols

f1: First focal length f2: Second focal length f3: Third focal length Difference in cover layer thickness: Δta, Δtb, Δtc
L1, L2, L3 ... Optical path length 1 ... Optical disc (100 ... BD, 200 ... DVD, 300 ... CD)
6, 106, 206, 156, 256 ... Optical pickup device 8 ... Actuator 21 ... BD objective lens 21a ... First lens principal point 22, 32 ... DVD objective lens 22a ... Second lens principal point 23, 33 ... Objective lens 23a ... Third lens principal point 35, 40, 45 ... Objective lens device 26, 36, 46, 56, 66 ... Lens holder 34, 134, 234 ... DVD / CD objective lens unit 50 ... Optical disk drive device 100a, 200a, 300a ... cover layer

Claims (22)

A first objective lens having a first numerical aperture that can be focused on a disk-shaped first optical recording medium having a first cover layer of a first thickness;
A second optical recording medium having a second cover layer having a second thickness greater than the first thickness can be condensed onto a second optical recording medium having a second thickness smaller than the first numerical aperture. A second objective lens having a numerical aperture of
A third optical recording medium having a third cover layer having a third thickness larger than the second thickness can be focused on a third optical recording medium having a third thickness smaller than the second numerical aperture. A third objective lens having a numerical aperture of
An objective lens device comprising: a lens holder that integrally holds the first, second, and third objective lenses. The objective lens device according to claim 1,
The first objective lens has a first focal length and a first lens principal point;
The second objective lens has a second focal length and a second lens principal point;
The third objective lens has a third focal length and a third lens principal point;
The lens holder is
A first focal length difference (A) that is a difference between the second focal length and the first focal length in the focus direction from the first lens principal point of the held first objective lens; Only the distance corresponding to the difference (AD) from the first air equivalent cover thickness difference (D), which is the optical path length in air corresponding to the difference between the second thickness and the first thickness. Holding the second objective lens so that the second lens principal point is arranged at a distant position;
A second focal length difference (C) that is a difference between the third focal length and the first focal length in the focus direction from the first lens principal point, the third thickness, and the At a position separated by a distance corresponding to the difference (C−F) from the second air equivalent cover thickness difference (F) which is the optical path length in air corresponding to the first thickness difference, the third The objective lens device is characterized in that the third objective lens is held such that the lens principal points are arranged. The objective lens device according to claim 1,
An objective lens device, wherein at least two of the first, second and third objective lenses are formed by integral molding. The objective lens device according to claim 1,
The first numerical aperture is 0.8 to 0.9;
The second numerical aperture is 0.6 to 0.7,
3. The objective lens device according to claim 3, wherein the third numerical aperture is 0.45 to 0.55. The objective lens device according to claim 1,
The third objective lens is
Compared with the first objective lens and the second objective lens, a mechanical vibration system including the first objective lens, the second objective lens, the third objective lens, and the lens holder resonates. An objective lens device, wherein the objective lens device is disposed at a position close to a vibration antinode of the vibration system. The objective lens device according to claim 5,
The objective lens device, wherein the third objective lens is disposed between the first objective lens and the second objective lens. The objective lens device according to claim 1,
The lens holder includes a required minimum stroke range of the second objective lens and a required minimum stroke range of the first objective lens within a required minimum stroke range of the third objective lens. An objective lens device that holds the first, second, and third objective lenses. The objective lens device according to claim 1,
An objective lens device, wherein a working distance of the second objective lens and the third objective lens is 0.2 to 0.5 mm. The objective lens device according to claim 1,
A protector provided on the lens holder for preventing the first, second, or third optical recording medium from contacting at least one of the first, second, and third objective lenses; An objective lens device further comprising the objective lens device. The objective lens device according to claim 9, wherein
The objective lens device according to claim 1, wherein the protector is provided on an outer peripheral side in the radial direction of the first, second, or third optical recording medium in the lens holder. The objective lens device according to claim 1,
At least one of the first, second, and third objective lenses has a self-aperture unit. The objective lens device according to claim 1,
An integral objective lens in which at least two of the first, second and third objective lenses are integrally molded;
The integrated objective lens has a self-aperture part. The objective lens device according to claim 3,
The objective lens device, wherein the first, second and third objective lenses are formed by integral molding. A first laser beam having a first wavelength; a second laser beam having a second wavelength longer than the first wavelength; and a third laser having a third wavelength longer than the second wavelength. A light source that emits light;
The first laser light can be focused on a disk-shaped first optical recording medium having a first cover layer having a first thickness, and has a first numerical aperture. Objective lens,
The second laser beam can be focused on a disc-shaped second optical recording medium having a second cover layer having a second thickness that is thicker than the first thickness, A second objective lens having a second numerical aperture less than the numerical aperture of 1;
The third laser beam can be condensed on a disc-shaped third optical recording medium having a third cover layer having a third thickness greater than the second thickness, A third objective lens having a third numerical aperture smaller than 2;
A lens holder for integrally holding the first, second and third objective lenses;
An optical pickup device comprising: an actuator for driving the lens holder. The optical pickup device according to claim 14,
When the difference between the center positions of the strokes of the first and second objective lenses in the focus direction by the actuator is ΔST1, and the optical path length in air corresponding to the difference between the first and second thicknesses is L1. The lens holder is
ΔST1 <L1
An optical pickup device that holds the first and second objective lenses so as to satisfy the above. The optical pickup device according to claim 14,
When the difference between the center positions of the strokes of the second and third objective lenses in the focus direction by the actuator is ΔST2, and the optical path length in air corresponding to the difference between the second and third thicknesses is L2. The lens holder is
ΔST2 <L2
An optical pickup device that holds the second and third objective lenses so as to satisfy the above. The optical pickup device according to claim 14,
The difference between the center positions of the strokes of the third and first objective lenses in the focus direction by the actuator is ΔST3, and the optical path length in air corresponding to the difference between the third and first thicknesses is L3. The lens holder is
ΔST3 <L3
An optical pickup device that holds the third and first objective lenses so as to satisfy the above. The optical pickup device according to claim 14,
The first laser beam has a plate shape or a triangular prism shape, is disposed so as to face the first objective lens, and the first laser light emitted from the light source is incident on the first objective lens. An optical pickup device further comprising a mirror for reflecting the laser beam. The optical pickup device according to claim 18, wherein
The first objective lens is disposed so as to face the second objective lens, transmits the first laser beam out of the first laser beam and the second laser beam, and transmits the second laser beam to the second objective lens. A first dichroic mirror that reflects the light so as to enter the lens;
The first objective lens is disposed so as to face the third objective lens, transmits the first laser beam and the second laser beam among the first, second and third laser beams, and transmits the third laser beam to the first objective lens. And a second dichroic mirror that reflects the light so as to be incident on the third objective lens. The optical pickup device according to claim 19,
A prism including the first dichroic mirror and the second dichroic mirror;
An optical pickup device further comprising: a wave plate provided on the prism and changing a polarization state of the first, second, and third laser beams. A disk-shaped first optical recording medium having a first cover layer having a first thickness, and a disk-shaped second optical recording medium having a second cover layer having a second thickness greater than the first thickness. A rotational drive mechanism for rotationally driving the optical recording medium or a disk-shaped third optical recording medium having a third cover layer having a third thickness greater than the second thickness;
A first objective lens capable of focusing on the optical recording medium and having a first numerical aperture;
A second objective lens that can be focused on the second optical recording medium and has a second numerical aperture smaller than the first numerical aperture;
A third objective lens that can be focused on the third optical recording medium and has a third numerical aperture smaller than the second numerical aperture;
A lens holder for integrally holding the first, second and third objective lenses;
An actuator for driving the lens holder;
Using the first, second, or third objective lens, a signal is recorded on the first, second, or third optical recording medium that is rotationally driven by the rotational drive mechanism, or the recorded signal is reproduced. An optical disc driving apparatus comprising: a recording / reproducing processing unit. Condensing light onto a disk-shaped first optical recording medium having a first cover layer having a first thickness by a first objective lens having a first numerical aperture;
A second optical recording medium having a second cover layer having a second thickness larger than the first thickness has a second numerical aperture smaller than the first numerical aperture. Condensing with an objective lens;
The third optical recording medium having a third cover layer having a third thickness larger than the second thickness has a third numerical aperture smaller than the second numerical aperture. Condensing with an objective lens;
A method of driving an objective lens, comprising: driving a lens holder that integrally holds the first, second, and third objective lenses for recording or reproducing signals.