JP2010073229A - Optical pickup device and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin optical pickup device that reduces astigmatism even when degree of convergence and divergence of light is large in a multi-layer disk by solving the problem that, when the degree of convergence and divergence of light is changed by moving a collimator to correct base material depth error of an optical disk, astigmatism occurs when BD light is transmitted through a rising mirror for DVD, and to provide an optical disk device. <P>SOLUTION: The optical pickup device includes: a collimator 50 converting light emitted from a light source to divergence light or convergence light; and an objective lens 54 converging light transmitted through the collimator 50 on an optical disk 55. A first prism 51 and a second prism 52 are arranged in an optical path between the collimator 50 and the objective lens 54 at an angle of approximately 45 degrees. Two prisms 51, 52 have a wedge shape having different directions. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical pickup device and an optical disc apparatus that perform at least one of recording and reproduction of information on an optical disc or an optical card.

  Optical disks that are one of the application fields of the present invention include CD, DVD, and BD (Blu-ray Disc). From the viewpoint of user convenience, it is required to record and reproduce these three types of optical disks with one optical disk device.

  When classified by focusing on the thickness of the optical disk device, it can be divided into a half height drive having a thickness of 42 mm, a slim drive having a thickness of 12.7 mm, and an ultra slim drive having a thickness of 9.5 mm. In particular, in slim drives and ultra slim drives, the optical paths of CD, DVD, and BD are partially shared in order to make the apparatus small and thin.

  For example, as disclosed in Japanese Patent Application Laid-Open No. 2005-174485, as shown in FIG. 11, light of three wavelengths of CD, DVD, and BD is guided to a collimator 100 to be a common optical path, and the wavelength selective mirror 101 performs CD The light of the DVD is reflected and the light of the BD is transmitted, so that each light path is separated. The light of CD and DVD is reflected at 90 degrees by the wavelength selective mirror 101 and guided to the objective lens 103 for CD and DVD, and the light of BD is transmitted through the wavelength selective mirror 101 and 90 by the rising mirror 102. It is reflected at a time and guided to the objective lens 104 for BD. The wavelength selective mirror may be constituted by a cubic prism 111 (see FIG. 12) as disclosed in, for example, Japanese Patent Laid-Open No. 2006-120306.

On the other hand, in recent years, multi-layer discs with higher density than BD have been proposed. For example, as disclosed in Japanese Patent Application Laid-Open No. 2006-40456, there is an optical disc in which a recording film on which a signal is recorded has four layers or eight layers. Since the recording layers of such a multi-layer disc are separated by an intermediate layer, the thickness from the surface of the optical disc, that is, the base material thickness differs depending on the recording / reproducing layer. Although spherical aberration occurs due to this substrate thickness error, it can be corrected by moving the collimator 100 and changing the light incident on the objective lens into convergent light or divergent light.
JP 2005-174485 A JP 2006-120306 A JP 2006-40456 A

  As shown in FIG. 11, the BD light passes through the movable collimator 100 to become convergent light or divergent light, and then passes through the wavelength selective mirror 101. When the wavelength-selective mirror 101 is formed of a flat plate, astigmatism occurs when light that is not parallel passes through the inclined flat plate. This is because the flat plate is inclined, so that there is a difference in optical path length between the meridional direction and the spherical direction. In the case of a two-layer disc, this astigmatism is small and does not cause a problem because the degree of convergence and divergence of light transmitted through the collimator is small. However, when a substrate thickness error such as an eight-layer disk increases, it is necessary to move the collimator to increase the degree of convergence and divergence of light. As a result, the light transmitted through the inclined flat plate has a large astigmatism, and normal recording and reproduction of the multilayer disk cannot be performed.

  As shown in FIG. 12, when the wavelength selective mirror is configured by the cubic prism 111, astigmatism does not occur because the cubic prism 101 is not tilted even if the light convergence / divergence degree changes. However, since the volume is larger than that of the wavelength selection mirror 101 configured by the flat plate shown in FIG. 11, it is difficult to configure a slim drive or an ultra slim drive by increasing the size of the apparatus. Further, the lens holder that holds the objective lens 103 and the objective lens 104 needs to be thinned to avoid interference with the cubic prism, and there is a problem that the rigidity of the lens holder cannot be maintained.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a small and thin optical pickup device that prevents astigmatism even if the degree of convergence and divergence of light transmitted through a collimator changes. To do.

  The present invention has been made to solve the above-described problems. A light source, a movable condensing lens that converts light emitted from the light source into divergent light or convergent light, and light transmitted through the condensing lens. An objective lens for condensing the optical disc on the optical disc, and having two prisms arranged in an inclined manner in the optical path between the condenser lens and the objective lens, the two prisms having a wedge shape with different directions. This is an optical pickup device.

  According to the present invention, astigmatism is corrected by two wedge-shaped prisms having different directions even when the degree of convergence and divergence of the light transmitted through the collimator changes, the size of the apparatus can be increased without increasing the size of the apparatus. Multi-layer discs such as layers and eight layers can be stably recorded and reproduced.

  The invention described in claim 1 is a light source, a movable condensing lens that converts light emitted from the light source into divergent light or convergent light, and an objective that condenses the light transmitted through the condensing lens onto an optical disk. And an optical pickup device having two lenses, each having two prisms arranged in an inclined manner in an optical path between the condenser lens and the objective lens, wherein the two prisms have a wedge shape with different directions. It is characterized by. As a result, even if the degree of convergence and divergence of the light transmitted through the condenser lens changes, the difference in optical path length between the meridional direction and the ball-missing direction of the light transmitted through the two prisms becomes equal. Can be suppressed.

  The invention described in claim 2 is characterized in that it has two prisms arranged at an angle of approximately 45 degrees in the optical path between the condenser lens and the objective lens. As a result, even if the degree of convergence and divergence of the light transmitted through the condenser lens changes, the difference in optical path length between the meridional direction and the ball-missing direction of the light transmitted through the two prisms becomes equal. Can be suppressed.

  According to a third aspect of the present invention, the two prisms include a first prism and a second prism, and light that has passed through the first prism passes through the first surface of the second prism, and the second prism again. The light is reflected from the second surface of the second prism so as to be emitted from one surface. As a result, even if the degree of convergence and divergence of the light transmitted through the condenser lens changes, the optical path length difference between the meridional direction and the spherical missing direction of the light transmitted through the first prism and the second prism becomes equal. Generation of point aberration can be suppressed. Further, since the second prism also has a function of a rising mirror that guides light to the condenser lens, a new member for correcting astigmatism is not required.

  The invention according to claim 4 is characterized in that the wavelength of the light emitted from the light source is approximately 405 nm. Thereby, recording or reproduction can be performed on an optical disc compatible with a Blu-ray disc or a multilayer disc.

  The invention according to claim 5 is characterized in that the numerical aperture of the objective lens is approximately 0.85. Thereby, recording or reproduction can be performed on an optical disc compatible with a Blu-ray disc or a multilayer disc.

  The invention according to claim 6 further includes: a second light source that emits light having a wavelength different from that of the light source; and a second objective lens that condenses light having a wavelength of the second light source on an optical disc, and the two prisms. At least one of which has a wavelength selection film, and reflects the light of the wavelength of the second light source transmitted through the condenser lens by the wavelength selection film and guides it to the second objective lens. Thereby, recording or reproduction can be performed on an existing optical disc corresponding to DVD or CD.

  The invention according to claim 7 is characterized in that the wavelength of the light emitted from the second light source is approximately 660 nm or approximately 780 nm. Thereby, recording or reproduction can be performed on an existing optical disc corresponding to DVD or CD.

  The invention according to claim 8 is characterized in that an apex angle of the first prism is larger than an apex angle of the second prism. As a result, even if the degree of convergence and divergence of the light transmitted through the condenser lens changes, the optical path length difference between the meridional direction and the spherical missing direction of the light transmitted through the first prism and the second prism becomes equal. Generation of point aberration can be suppressed.

  The invention according to claim 9 is characterized in that the two prisms have different refractive indexes and are joined. As a result, even if the degree of convergence and divergence of the light transmitted through the condenser lens changes, the difference in optical path length between the meridional direction and the ball-missing direction of the light transmitted through the two prisms becomes equal. Can be suppressed. In addition, the apparatus can be easily downsized.

  The invention described in claim 10 is characterized in that a hologram is provided in at least one of the two prisms. Thereby, the number of parts can be reduced and the cost can be suppressed.

  The invention according to claim 11 is characterized in that at least one of the two prisms changes a polarization state of the light. Thereby, the number of parts can be reduced and the cost can be suppressed.

  The invention described in claim 12 further includes a front light detector, wherein the two prisms transmit a part of the light transmitted through the condenser lens and receive the light with the front light detector. Accordingly, since the prism has a wedge shape, stray light generated by internal reflection becomes non-parallel to the light transmitted through the prism, so that interference can be prevented and stable front light can be detected.

  A thirteenth aspect of the present invention is an optical disc apparatus comprising the optical pickup according to the first to twelfth aspects. Thereby, recording or reproduction can be performed on an optical disc compatible with a Blu-ray disc, a DVD, and a CD.

  The invention according to claim 14 is characterized in that the optical disc apparatus records or reproduces an optical disc having a thickness from 40 μm to 140 from the surface of the optical disc to the recording surface. Thereby, recording or reproduction can be performed on an optical disc corresponding to the multilayer disc.

(Embodiment 1)
FIG. 1 is a schematic diagram showing an optical pickup device according to an embodiment of the present invention.

  In FIG. 1, reference numeral 1 denotes a short-wavelength optical unit that emits a short-wavelength laser. Light emitted from the short-wavelength optical unit 1 has a wavelength of 400 nm to 415 nm. In this embodiment, light of about 405 nm is emitted. It was configured as follows. In general, light having the above-described laser wavelength is blue to purple. In the present embodiment, a light source unit 1a that emits a short-wavelength laser, a signal detection light-receiving unit 1b that receives light reflected from the optical disk 2, and a light amount of light emitted from the light source unit 1a are monitored. The light receiving unit 1c, the optical member 1d, and a holding member (not shown) that holds these constituent members in a predetermined positional relationship are included. The light source unit 1a is provided with a semiconductor laser element (not shown) mainly composed of GaN or GaN, and light emitted from the semiconductor laser element is incident on the optical member 1d, and the incident light Part of the light is reflected by the optical member 1d and enters the light receiving portion 1c. Although not shown, a circuit for converting light into an electric signal by the light receiving unit 1c and adjusting the intensity of light emitted from the light source unit 1a to a desired intensity based on the electric signal is provided. . Further, most of the light emitted from the light source unit 1a is guided toward the optical disc 2 through the optical member 1d. The light reflected by the optical disk 2 is incident on the light receiving unit 1b through the optical member 1d. The light receiving unit 1b converts light into an electrical signal, and generates an RF signal, a tracking error signal, a focus error signal, and the like from the electrical signal. In the optical member 1d, a hologram 1e for separating the reflected light from the optical disc 2 is provided so that a focus error signal can be obtained.

  In this embodiment, in order to reduce the size of the optical pickup device, the optical pickup device is configured as one short wavelength optical unit including the light source unit 1a, the light receiving units 1b and 1c, and the optical member 1d. At least one of 1c may be configured to be separated from the short wavelength optical unit 1 or configured as a separate unit, or the optical member 1d may be configured to be separated from the short wavelength optical unit 1 and configured as a separate unit.

  Reference numeral 3 denotes a long wavelength optical unit that emits a long wavelength laser. The light emitted from the long wavelength optical unit 3 has a wavelength of 640 nm to 800 nm, and emits a single type of light or a plurality of types of light. A plurality of light beams having wavelengths are emitted. In the present embodiment, a light beam having a wavelength of about 660 nm (red: for example for DVD) and a light beam of about 780 nm (for infrared: for example, for CD) are emitted. In the present embodiment, a light source unit 3a that emits a long-wavelength laser, a signal detection light-receiving unit 3b that receives light reflected from the optical disc 2, and a light amount of light emitted from the light source unit 3a are monitored. The light receiving portion 3c, the optical member 3d, and a holding member (not shown) that holds these constituent members in a predetermined positional relationship are included. The light source unit 3a is provided with a semiconductor laser element (not shown). This semiconductor laser element is composed of a monoblock (monolithic structure), and a light flux (red) having a wavelength of about 660 nm from the monoblock element. And a light beam (infrared) of about 780 nm is emitted. In the present embodiment, a monoblock element emits two light beams, but a single block element may emit two light beams. A plurality of light beams emitted from the semiconductor laser element are incident on the optical member 3d, and a part of the incident light is reflected by the optical member 3d and enters the light receiving unit 3c. Although not shown, a circuit for converting light into an electric signal by the light receiving unit 3c and adjusting the intensity of light emitted from the light source unit 3a to a desired intensity based on the electric signal is provided. . Further, most of the light emitted from the light source unit 3a is guided toward the optical disc 2 through the optical member 3d. The light reflected by the optical disk 2 is incident on the light receiving unit 3b through the optical member 3d. The light receiving unit 3b converts light into an electrical signal, and generates an RF signal, a tracking error signal, a focus error signal, and the like from the electrical signal. The optical member 3d is provided with a hologram 3e that separates the reflected light from the optical disc 2 into a plurality of pieces and guides them to a predetermined location on the light receiving unit 3b in order to generate a focus error signal for CD. .

  In this embodiment, in order to reduce the size of the optical pickup device, the optical pickup device is configured as one long wavelength optical unit 3 including the light source unit 3a, the light receiving units 3b and 3c, and the optical member 3d. , 3c may be configured to be separated from the long wavelength optical unit 3 or may be configured as a separate unit. Alternatively, the optical member 3d may be configured to be separated from the long wavelength optical unit 3 and configured as a separate unit.

  Reference numeral 4 denotes a beam shaping lens through which light emitted from the short wavelength optical unit 1 and reflected light from the optical disk 2 pass. The beam shaping lens 4 is preferably made of glass with little deterioration due to the passage of a short wavelength laser. In the present embodiment, the beam shaping lens 4 is made of glass. However, the beam shaping lens 4 can be made of other materials as long as the material is less deteriorated by the passage of the short wavelength laser. is there. The beam shaping lens 4 increases the utilization efficiency of light emitted from the short wavelength laser, astigmatism of the short wavelength laser, and astigmatism generated in the optical path from the short wavelength optical unit 1 to the optical disc 2. It is provided for the purpose of canceling. For the purpose of the beam shaping lens 4, the light reflected from the optical disk 2 may be incident on the short wavelength optical unit 1 without going through the beam shaping lens 4, but the reflected light from the optical disk 2 is optically arranged. In this embodiment, the light is incident on the short wavelength optical unit 1 through the beam shaping lens 4. In the present embodiment, the beam shaping lens 4 is used so as to reduce the astigmatism of short wavelength light. However, a beam shaping prism or a beam shaping hologram may be used instead.

  Further, convex portions 4a and concave portions 4b are respectively provided at both ends of the beam shaping lens 4, and the light emitted from the short wavelength optical unit 1 is first incident on the convex portions 4a and emitted from the concave portions 4b. The shaping lens 4 is arranged.

  Reference numeral 5 denotes an optical component, and the optical component 5 is arranged at the tip of the beam shaping lens 4 on the optical path and arranged on the concave portion 4b side of the beam shaping lens 4. That is, the light emitted from the short wavelength optical unit 1 enters the optical component 5 through the beam shaping lens 4, is guided to the optical disc 2, and the light reflected from the optical disc 2 is the optical component 5 and the beam shaping lens. Then, the light enters the short wavelength optical unit 1 through 4. The optical component 5 is provided with a hologram and has at least the following functions. That is, it is a function of separating the light reflected from the optical disc 2 into a predetermined light flux so as to mainly generate a tracking error signal. As described above, the hologram 1e provided in the optical member 1d is separated into a plurality of light beams to generate a focus error signal, and the optical component 5 generates a tracking error signal into a plurality of light beams. To separate.

  Furthermore, the optical component 5 may be provided with a function of functioning as a RIM intensity correction filter that attenuates the amount of light at a substantially central portion of short-wavelength light. Further, the optical component 5 is separated into two parts, and one optical component 5 has a function of separating the light reflected from the optical disc 2 into a predetermined light beam so as to mainly generate a tracking error signal. The optical component 5 can also have a function of a RIM intensity correction filter.

  Reference numeral 6 denotes a relay lens through which long-wavelength light emitted from the long-wavelength optical unit 3 passes. The relay lens 6 is made of a transparent member such as resin or glass. The relay lens 6 is provided to efficiently guide the light emitted from the long wavelength optical unit 3 to the rear member. Further, by providing the relay lens 6, the long wavelength optical unit 3 can be arranged on the beam splitter 7 side, so that the apparatus can be reduced in size.

  Reference numeral 7 denotes a beam splitter. In the beam splitter 7, at least two transparent members 7b and 7c are joined, and one inclined surface 7a is provided between the transparent members 7b and 7c. A wavelength selection film is provided on the inclined surface 7a. A wavelength selective film is directly formed on the inclined surface 7a of the transparent member 7c into which the light emitted from the short wavelength optical unit 1 enters, and resin or glass is formed on the inclined surface 7a of the transparent member 7c on which the wavelength selective film is formed. The transparent member 7b is joined via a joining material such as.

  The beam splitter 7 has a function of reflecting the short wavelength light emitted from the short wavelength optical unit 1 and transmitting the light emitted from the long wavelength optical unit 3. That is, the light emitted from the short wavelength unit 1 and the light emitted from the long wavelength unit 3 are guided in substantially the same direction.

  A collimator 8 is movably held. The collimator 8 is attached to a slider 8b, and the slider 8b is movably attached to a pair of support members 8a provided substantially in parallel. A lead screw 8c provided with a helical groove is provided so as to be substantially parallel to the support member 8a, and a protrusion entering the groove of the lead screw 8c is provided at the end of the slider 8b. A gear group 8d is coupled to the lead screw 8c, and a drive member 8e is provided in the gear group 8d. The driving force of the driving member 8e is transmitted to the lead screw 8c through the gear group 8d, and the lead screw 8c is rotated by the driving force, and as a result, the slider 8b moves along the supporting member 8a. That is, the collimator 8 can be moved in the direction approaching or moving away from the beam splitter 7 depending on the difference in the driving direction or the driving speed of the driving member 8e, and the speed of the movement, etc. Can be adjusted.

  Various motors and the like are preferably used as the drive member 8e, and it is particularly preferable to use a stepping motor as the drive member 8e. That is, by adjusting the number of pulses sent to the stepping motor, the amount of rotation of the lead screw 8c is determined, and as a result, the amount of movement of the collimator 8 can be easily set.

  In this way, by adopting a configuration in which the collimator 8 is moved closer to or away from the beam splitter 7, the spherical aberration can be easily adjusted. In other words, since the spherical aberration of the short-wavelength light can be adjusted by the position of the collimator 8, the first recording layer provided on the short-wavelength optical disc and a depth different from that of the first recording layer. Each of the provided second recording layers can be configured to effectively perform at least one of recording and reproduction.

  Since the long wavelength and short wavelength light incident from the beam splitter 7 is transmitted to the collimator 8, it is made of glass or preferably a short wavelength light resin (a resin that does not deteriorate or hardly deteriorate due to a short wavelength). The collimator 8 also transmits short wavelength or long wavelength light reflected by the optical disc 2.

  In the present embodiment, the collimator 8 is moved by the driving member 8e as a configuration for correcting the spherical aberration of the short wavelength light. However, the collimator 8 may be moved by other configurations. However, the spherical aberration of light having a short wavelength may be adjusted using other means.

  Reference numeral 9 denotes a rising mirror, which is provided with a wavelength selection film 9b on the surface on which the light emitted from each of the units 1 and 3 is incident, and reflects most of the long wavelength light emitted from the long wavelength optical unit 3. In addition, it has a function of transmitting almost all of the short wavelength light emitted from the short wavelength optical unit 1.

  Reference numeral 10 denotes an objective lens for a long wavelength laser. The objective lens 10 condenses the light reflected from the rising mirror 9 on the optical disk 2. Although the objective lens 10 is used in the present embodiment, the objective lens 10 may be configured by other condensing means. As a matter of course, the light reflected from the optical disk 2 passes through the objective lens 10. The objective lens 10 is made of a material such as glass or resin.

  Reference numeral 11 denotes an optical component provided between the objective lens 10 and the raising mirror 9. The optical component 11 is compatible with the optical disc 2 of DVD (light having a wavelength of approximately 660 nm) and CD (light having a wavelength of approximately 780 nm). In addition, an aperture filter for realizing a necessary numerical aperture, a polarization hologram that reacts to light having a wavelength of about 660 nm, and a quarter wavelength member (preferably a quarter wavelength plate) are provided. . The optical component 11 includes a dielectric multilayer film, a diffraction grating aperture means, and the like. A polarization hologram applies polarization to light of approximately 660 nm (separates light having a wavelength of approximately 660 nm into light for tracking error signals and focus error signals). Further, the quarter wavelength member rotates the polarization direction of the return path with respect to the forward path of light having a wavelength of approximately 660 nm and approximately 780 nm by approximately 90 degrees.

  Reference numeral 12 denotes a rising mirror that almost reflects short-wavelength light. The rising mirror 12 is provided with a reflective film.

  Reference numeral 13 denotes an objective lens, and the objective lens 13 condenses the light reflected from the rising mirror 12 on the optical disk 2. Although the objective lens 13 is used in the present embodiment, it may be constituted by other condensing means. As a matter of course, the light reflected from the optical disk 2 passes through the objective lens 13. The objective lens 13 is made of glass or resin, but when the objective lens 13 is made of resin, it is preferably made of a short-wavelength light resin (a resin that does not deteriorate or hardly deteriorate due to a short wavelength). Composed.

  Reference numeral 14 denotes an achromatic diffraction lens provided between the objective lens 13 and the raising mirror 12, and the achromatic diffraction lens 14 has a function of correcting chromatic aberration. The achromatic diffractive lens 14 is provided with a quarter wavelength member that acts on short wavelength light. As this quarter-wave member, a quarter-wave plate that rotates the polarization direction of light that has passed twice (in the forward path and the return path) by approximately 90 degrees is preferably used. The achromatic diffractive lens 14 is provided so as to cancel and reduce chromatic aberration caused by each optical component through which light having a short wavelength passes. An achromatic diffractive lens is basically formed by forming a desired hologram on the lens, and the correction degree of chromatic aberration can be determined by adjusting at least one of the grating pitch of the hologram and the radius of curvature of the lens. is there. The diffractive lens 14 is made of resin such as plastic or glass. In the case of using a resin or the like, the resin is preferably composed of a short-wavelength light resin (a resin that does not deteriorate or hardly deteriorate due to a short wavelength).

  The specific arrangement of the optical system configured as described above will be described below with reference to FIG.

  FIG. 2 actually shows an example in which the optical configuration shown in FIG. 1 is embodied. The shape and the like of the members shown in FIG. 1 are slightly different, but the functions are almost the same.

  Reference numeral 15 denotes a base, to which the above-described members are attached so as to be fixed or movable. The base 15 is made of a metal or metal alloy material such as zinc, zinc alloy, aluminum, aluminum alloy, titanium, or titanium alloy, and is preferably made using a die casting method or the like from the viewpoint of mass production. The base 15 is movably held by an optical pickup module as shown in FIGS.

  Reference numeral 16 denotes a lens holder on which the two objective lenses 10 and 13 are mounted. Reference numeral 17 denotes a suspension for suspending the lens holder 16. Reference numeral 18 denotes a suspension holder for fixing the end portions of the plurality of suspensions 17. 21 and 22 are shafts that enable the base to move in the radial direction. Reference numeral 25 denotes a spindle motor on which the optical disk 2 is placed.

  3 and 4, reference numeral 20 denotes a frame, to which shafts 21 and 22 arranged substantially in parallel are attached to the frame 20, and a base 15 is movably attached to the shafts 21 and 22. Further, on the opposite side of the shaft 22 from the shaft 21 side, a screw shaft 23 provided with a helical groove is attached to the frame 20 so as to be rotatable in parallel with the shafts 21 and 22. Although not shown in detail, a member provided integrally or separately on the base 15 is engaged with a groove provided on the screw shaft 23. The screw shaft 23 meshes with a gear group 24 a that is rotatably provided on the frame 20, and the gear group 24 a meshes with the feed motor 24. Accordingly, when the feed motor 24 is rotated, the gear group 24a is rotated, and the screw shaft 23 is rotated accordingly. As the screw shaft 23 is rotated, the base 15 reciprocates in the arrow direction shown in FIG. be able to. At this time, in the present embodiment, the feed motor 24 is disposed substantially parallel to the screw shaft 23. Further, the optical disk 2 is mounted on the frame 20, and a spindle motor 25 for rotating the optical disk 2 is attached by a method such as screwing or bonding.

  Further, as shown in FIG. 3, a control board 26 is provided separately from the frame 20, and the control board 26 and the base 15 are electrically joined, for example, via a flexible board 29. Further, the control board 26 is also electrically connected to the spindle motor 25 by a member not shown. The control board 26 is provided with a connector 27 for electrical connection with the control board 26 provided in the optical disc apparatus. A flexible board or the like (not shown) is inserted into the connector 27 for electrical connection. .

  Further, as shown in FIG. 4, a frame cover 30 for the purpose of protecting members may be provided at least on the side facing the optical disc 2 in the frame 20. A through hole 31 is provided in the frame cover 30, and at least the objective lenses 10 and 13 on the base 15 are exposed from the through hole 31, and a spindle motor 25 protrudes a predetermined amount. 3 and 4, the frame 20 is provided with an attachment portion 20a for fixing to other members, and screws or the like are inserted into the attachment portion 20a to attach the frame 20 to other members.

  In FIG. 2, a base 15 includes a short wavelength optical unit 1, a long wavelength optical unit 3, a beam shaping lens 4, an optical component 5, a relay lens 6, a beam splitter 7, a support member 8a, a lead screw 8c, and a gear group 8d. , The drive member 8e, the raising mirrors 9 and 12, etc. are bonded using an organic adhesive such as a photo-curing adhesive or an epoxy adhesive, or a metal adhesive such as solder or lead-free solder is used. Or are attached using a method such as screwing, fitting, or press-fitting.

  The lead screw 8c and the gear group 8d are rotatably attached to the base 15.

  Reference numeral 17 denotes a suspension holder. The suspension holder 17 is attached to the base 15 by various joining methods via a yoke member, and the lens holder 16 and the suspension holder 17 are coupled via a plurality of suspensions 18. The lens holder 16 is supported so as to be movable within a predetermined range with respect to the base 15. The lens holder 16 is provided with objective lenses 10 and 13 and an optical component 11, an achromatic diffraction lens 14, and the like. When the lens holder 16 is moved, the lens holder 16 and the objective lenses 10 and 13 and the optical component 11 and color The eraser diffractive lens 14 also moves.

  The objective lens 13 is disposed slightly shifted from the radial direction of the spindle motor 25. Since the track direction of the optical disk 2 changes between the inner and outer peripheral sides of the optical disk 2 due to the movement of the base 15, a tracking servo system using one beam is adopted. On the other hand, since the objective lens 10 is disposed in the radial direction of the spindle motor 25, a tracking servo using three beams such as the DPP method and the three beam method is employed.

  This embodiment will be described in detail with reference to FIG.

  The prism 51 and the prism 52 are disposed at an angle of approximately 45 degrees in the optical path between the collimator 50 and the objective lens 54, and have a wedge shape with different directions. The apex angle θ1 of the prism 51 is 4.2 degrees and the thickness is 1 mm, the apex angle θ2 of the prism 52 is 2.4 degrees and the thickness is 0.8 mm, and the material is BK7 of optical glass, and the distance between the prism 51 and the prism 62 is 3. 5 mm. The prism 51 is provided with a wavelength selection film 51a that reflects DVD and CD light and transmits BD light. The DVD and CD light reflected by the prism 51 enters the objective lens 53. On the other hand, the BD light transmitted through the prism 51 is transmitted through the transmission surface 52a of the prism 52, is reflected by the reflection surface 52b of the prism 52, and is transmitted through the transmission surface 52a of the prism 52 again. 54. When the BD light is parallel light, the apex angles of the prism 51 and the prism 52 are determined so that the beam diameter D1 after passing through the collimator 50 and the beam diameter D2 before entering the BD objective lens 54 are equal. .

  The optical disk 55 is a multi-layer disk having four or eight recording films on which signals are recorded. Since each recording layer is separated by an intermediate layer, the thickness from the surface of the optical disk, that is, the thickness of the base material differs depending on the recording / reproducing layer. The spherical aberration caused by the substrate thickness error is corrected by moving the collimator 50 and changing the degree of convergence and divergence of the light incident on the BD objective lens 54.

  Next, correction of astigmatism caused by the degree of convergence and divergence of light will be described. In FIG. 5, the BD light that has passed through the collimator 50 passes through the prism 51, passes through the transmission surface 52a of the prism 52, and is reflected by the reflection surface 52b. At this time, since the prism 51 has a wedge shape, the optical path lengths of the light transmitted above the prism 51 and the light transmitted below are different as seen from the drawing. Therefore, the difference in optical path length is corrected by a wedge-shaped prism 52 having a direction different from that of the prism 51. As a result, astigmatism is corrected. In the prism 52, since the light passes through the transmission surface 52a, is reflected by the reflection surface 52b, and passes through the transmission surface 52a again, the optical path length in the prism 52 is about twice the optical path length in the prism 51. . Accordingly, the angle of θ2 with respect to θ1 is about half.

  FIG. 6 shows astigmatism with respect to the substrate thickness. Here, the objective lens for BD shows the case where the design base material thickness is 0.0875 mm. FIG. 6A shows a case where the apex angles of the prism 51 and the prism 52 are 0 degrees, that is, equivalent to a conventional flat plate. Astigmatism does not occur when the substrate thickness is 0.0875 mm, that is, when the BD light is parallel light. However, when the substrate thickness is different and the BD light becomes convergent light or divergent light, astigmatism occurs due to the difference in the optical path length between the meridional direction and the spherical missing direction by transmitting through a flat plate inclined at 45 degrees. . When the substrate thickness error is small with a two-layer disc, the degree of convergence and divergence can be small, so this astigmatism is not a problem of about 1 mλ. However, in the case of an eight-layer disc, the substrate thickness error is about four times larger than that of a two-layer disc, so it is necessary to increase the degree of convergence and divergence of light transmitted through the collimator. Astigmatism generated thereby becomes as large as about 20 mλ, and normal recording and reproduction of a multilayer disc cannot be performed.

  FIG. 6B shows astigmatism that occurs in the embodiment of the present invention. The generation of astigmatism is corrected by equalizing the optical path lengths of the meridional direction and the spherical direction of the light transmitted through the two prisms by the prisms 51 and 52 having different directions. As a result, good recording and reproduction can be performed even on an optical disk having a large substrate thickness error from 40 μm to 140 μm, such as an 8-layer disk.

  6C, when the apex angle of the prism 51 is 1 degree and the apex angle of the prism 52 is 5 degrees, FIG. 6D shows the apex angle of the prism 51 is 5 degrees and the apex angle of the prism 52 is 2.9. Is the case of degrees. In both cases, the directions of the prisms are different from each other. In the case of parallel light, the beam diameter D1 after passing through the collimator 50 and the beam diameter D2 before entering the objective lens 54 are equal. However, astigmatism occurs due to the difference in substrate thickness.

  As described above, according to the embodiment of the present invention, by appropriately selecting the apex angles of the prism 51 and the prism 52, even if the degree of convergence and divergence of the light transmitted through the collimator changes, the optical path length difference between the meridional direction and the spherical direction Therefore, the generation of astigmatism can be suppressed.

  The apex angle of the prism is not limited to this embodiment, and is preferably 1 to 6 degrees because it depends on the thickness of the prism, the inclination of the prism, the positional relationship between the two prisms, and the wavelength. The apex angle may be selected so that the difference in the optical path length between the meridional direction and the spherical notch direction when the degree of convergence and divergence of the light passing through the collimator changes is equal.

  For example, if the cubic prism 111 shown in FIG. 12 is used instead of the prism 51, the cubic prism 101 is not tilted, so that astigmatism does not occur. However, since the volume is larger than that of the prism 51 of the embodiment of the present invention, the apparatus becomes large and it is difficult to configure a slim drive or an ultra slim drive. Further, the lens holder that holds the objective lens 103 and the objective lens 104 needs to be thinned in order to avoid interference with the cubic prism 111, and there is a problem that the rigidity of the lens holder cannot be maintained. Furthermore, since the cubic prism 111 is configured by bonding two triangular prisms 111 a and 111 b together, there is a problem that the material cost is higher than that of the single prism 51. The prism 51 and the prism 52 of the embodiment of the present invention are also a DVD and CD rising mirror and a BD rising mirror, respectively, and do not require a new member for correcting astigmatism.

  Further, as shown in FIG. 7, a front photodetector 70 may be provided in the present embodiment. A part of the light of CD and DVD passes through the surface 51 a of the prism 51, passes through the prism 52, and is received by the front light detector 70. Based on the amount of light detected by the front light detector 70, the amount of light collected from the optical disk 55 is controlled by feeding back the intensity of light emitted from the light source.

  When the prism 51 is formed of a flat plate as in the conventional example, there is a problem that interference occurs due to reflection inside the flat plate, and the light amount detection becomes unstable in the front light detector 70. On the other hand, in the embodiment of the present invention, since the prism 51 has a wedge shape, the stray light generated by the internal reflection becomes non-parallel to the light transmitted through the prism 51, so that interference is prevented and the detected light quantity is stabilized. The same applies to the BD light. A part of the light is transmitted through the surface 52b of the prism 52 and received by the front light detector 70. Since the prism 52 has a wedge shape, interference is prevented and the amount of light detected by the front light detector 70 is stable. Although the embodiment shown in FIG. 1 has two front light detectors of the light receiving portion 1c and the light receiving portion 3c, the embodiment shown in FIG. 7 can detect three lights of CD, DVD and BD with one front light detector 70. As a result, the number of parts is reduced.

  Further, in the present embodiment, the case of correcting astigmatism in the BD has been described. However, the present invention is not limited to this and can be applied to recording media of various standards such as a DVD and a next-generation memory.

(Embodiment 2)
FIG. 8 shows a schematic diagram of the present embodiment.

  The prism 61 and the prism 62 are disposed at an angle of 45 degrees in the optical path between the collimator 50 and the objective lens 54, and have a wedge shape with different directions. The prism 51 has an apex angle of 4 degrees and a thickness of 1 mm, and the prism 62 has an apex angle of 4 degrees and a thickness of 1 mm, and the material thereof is BK7 of optical glass. The prism 61 is provided with a wavelength selection film 61a that reflects DVD and CD light and transmits BD light. The DVD and CD light reflected by the prism 61 enters the objective lens 53. On the other hand, the BD light transmitted through the prism 61 is transmitted through the prism 62 and guided to the objective lens 54 by the rising mirror 63. When the BD light is parallel light, the apex angles of the prism 61 and the prism 62 are determined so that the beam diameter D1 after passing through the collimator 50 and the beam diameter D2 before entering the objective lens 54 are equal.

  In the present embodiment, as in the first embodiment, astigmatism is corrected by the prism 61 and the prism 62 having different directions as shown in FIG. 6B. As a result, good recording and reproduction can be performed even on an optical disk having a large base material thickness error such as an 8-layer disk.

  As described above, according to the embodiment of the present invention, by appropriately selecting the apex angles of the prism 61 and the prism 62, the difference in the optical path length between the meridional direction and the ball-missing direction can be obtained even if the convergence / divergence degree of the light transmitted through the collimator changes. Therefore, the generation of astigmatism can be suppressed.

  In the present embodiment, since the BD light is transmitted through the prism 61 and the prism 62, the angle of θ2 is substantially the same as θ1.

  The apex angle of the prism is not limited to this embodiment. For example, when both the prism 61 and the prism 62 have a thickness of 0.5 mm, the apex angle is preferably 3.7 degrees. The apex angles of the prism 61 and the prism 62 are preferably 1 to 6 degrees because they depend on the thickness of the prism, the inclination of the prism, the positional relationship between the two prisms, and the wavelength. The apex angle may be selected so that the difference in the optical path length between the meridional direction and the spherical notch direction when the degree of convergence and divergence of the light passing through the collimator changes is equal.

  In the embodiment of the present invention, the prism 62 is disposed between the prism 61 and the rising mirror 63. However, like the prism 67 in FIG. May be provided.

  Furthermore, a hologram that generates a tracking error signal by separating the light reflected from the optical disk 2 into a predetermined light beam may be provided on the end surface 67a of the prism 67. Alternatively, the end face 67a may be provided with a function of a wavelength plate that changes the polarization direction of light by fine processing such as nanoimprinting. Or you may provide the RIM intensity | strength correction filter which attenuates the light quantity of the approximate center part of the light of BD on the end surface 67a. Thereby, the number of parts can be reduced and the cost can be suppressed.

  Further, in the embodiment of the present invention, the two prisms are disposed separately, but as shown in FIG. 10, the prism is composed of a prism 64 and a prism 65 made of materials having different refractive indexes. You may do it.

  In the present embodiment, the case of correcting astigmatism of BD light has been described. However, the present invention is not limited to this and can be applied to recording media of various standards such as a DVD and a next-generation memory.

1 is a schematic diagram showing an optical pickup device according to an embodiment of the present invention. The figure which shows the optical pick-up apparatus in one embodiment of this invention The figure which shows the module which mounts the optical pick-up apparatus in one embodiment of this invention The figure which shows the module which mounts the optical pick-up apparatus in one embodiment of this invention The figure which shows a part of optical system in one embodiment of this invention Diagram showing astigmatism against substrate thickness error The figure which shows a part of optical system in one embodiment of this invention The figure which shows a part of optical system in one embodiment of this invention The figure which shows a part of optical system in one embodiment of this invention The figure which shows a part of optical system in one embodiment of this invention A diagram showing part of a conventional optical system A diagram showing part of a conventional optical system

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Short wavelength optical unit 3 Long wavelength optical unit 7 Beam splitter 8a Support member 8c Lead screw 8d Gear group 8e Drive member 9,12 Raising mirror 10,13 Objective lens 21,22 Shaft 23 Screw shaft 50 Collimator 51, 52, 61 , 62, 64, 65, 67 Prism 53, 54 Objective lens 55 Optical disk 63 Rising mirror 67 Joint prism 70 Front light detector

Claims (14)

A light source, a movable condensing lens that converts light emitted from the light source into divergent light or convergent light, and an objective lens that condenses the light transmitted through the condensing lens onto an optical disc,
An optical pickup device having two prisms arranged in an inclined manner in an optical path between the condenser lens and the objective lens, wherein the two prisms have a wedge shape with different directions. 2. The optical pickup device according to claim 1, further comprising two prisms disposed at an inclination of approximately 45 degrees in an optical path between the condenser lens and the objective lens. The two prisms include a first prism and a second prism, and the light transmitted through the first prism is transmitted through the first surface of the second prism and is emitted from the first surface again. The optical pickup device according to claim 1, wherein the optical pickup device reflects the second surface of the second prism. 2. The optical pickup device according to claim 1, wherein the wavelength of light emitted from the light source is approximately 405 nm. 2. The optical pickup device according to claim 1, wherein the numerical aperture of the objective lens is approximately 0.85. The light source further includes a second light source that emits light having a wavelength different from that of the light source, and a second objective lens that condenses light having the wavelength of the second light source on an optical disc, and at least one of the two prisms is wavelength-selective. 2. The optical pickup device according to claim 1, further comprising a film that reflects light having a wavelength of the second light source transmitted through the condenser lens by the wavelength selection film and guides the light to the second objective lens. . The optical pickup device according to claim 6, wherein the wavelength of the light emitted from the second light source is approximately 660 nm or approximately 780 nm. The optical pickup device according to claim 3, wherein an apex angle of the first prism is larger than an apex angle of the second prism. The optical pickup device according to claim 1, wherein the two prisms have different refractive indexes and are joined. The optical pickup device according to claim 1, wherein a hologram is provided in at least one of the two prisms. The optical pickup device according to claim 1, wherein at least one of the two prisms changes a polarization state of the light. The optical pickup device according to claim 1, further comprising a front light detector, wherein the two prisms transmit a part of the light transmitted through the condenser lens and receive the light with the front light detector. An optical disc apparatus comprising the optical pickup according to claim 1. 14. The optical disk apparatus according to claim 13, wherein the optical disk apparatus records or reproduces an optical disk having a thickness from 40 μm to 140 from the surface of the optical disk to a recording surface.

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