JP2005063572A - Optical pickup and optical disk playback device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup capable of easily correcting astigmatism for a plurality of light sources, and an optical disk playback device. <P>SOLUTION: A second laser light source is arranged nearer an optical axis than a first laser light source, a second laser beam from the second laser light source is converged on an optical disk by a numerical aperture smaller than that of a first laser beam from the first laser light source, and further astigmatism caused by the shifting of the first laser beams from the optical axis is corrected by an astigmatism correcting means. The astigmatism of the second laser light source is smaller because it is nearer to the optical axis. There is a possibility of an increase in astigmatism because of the passage of the second laser beam through the astigmatism correcting means. However, this astigmatism is not such a big problem because the numerical aperture is smaller than that of the first laser beam. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical pickup and an optical disc reproducing apparatus.

2. Description of the Related Art An optical disc playback apparatus includes a light source that emits light of a plurality of wavelengths in order to enable playback of a plurality of types of optical discs (optical recording media) such as a CD (Compact Disc) and a DVD (Digital Versatile Disc). is there. As this light source, for example, a semiconductor laser in which a plurality of regions emitting light of different wavelengths on a semiconductor chip are formed close to each other can be used.
Thus, when light beams having different wavelengths are emitted from a plurality of locations (a plurality of light sources), a deviation occurs in the optical conditions (sine conditions, etc.) of these light beams. For example, in an objective lens for two wavelengths, a sine condition is almost satisfied with a light source for DVD, and a deviation from the sine condition is usually large with a light source for CD. In this case, when the incident direction of the light beam is tilted with respect to the objective lens, the change from the optimum tilt angle is relatively small for the DVD light source, and the change from the optimum tilt angle is large for the CD light source. A technique for correcting phase aberration such as chromatic aberration at a plurality of wavelengths is disclosed (see Patent Document 1).
JP 2001-236680 A.

However, since the numerical aperture of DVD is larger than the numerical aperture of CD, when the light source for DVD is arranged away from the optical axis, astigmatism increases, and the spot quality of the light flux on the optical disk, and consequently the S / The N ratio may decrease. In particular, when recording on a DVD, since it is necessary to increase the numerical aperture, the S / N ratio of the reproduced signal may be further reduced.
When recording on a DVD, the ratio fc / fo between the focal length fo of the objective lens and the focal length fc of the collimator may be made larger than that of the reproducing optical system in order to increase the light utilization efficiency. . In this case, at the time of recording, the inclination of the light beam with respect to the optical axis becomes larger than at the time of reproduction, astigmatism increases, and there is a possibility that the recording quality deteriorates.
In order to solve this problem, a technique for matching the optical axes at two wavelengths is known. However, it is necessary to add parts for matching the optical axes, which increases the cost and size of the optical disk apparatus. Invite.
In view of the above, an object of the present invention is to provide an optical pickup and an optical disc reproducing apparatus that can easily correct astigmatism for a plurality of light sources.

  A. An optical pickup according to the present invention includes a first laser light source that emits a first laser light, and a first laser light source that is disposed near the optical axis in the vicinity of the first laser light source and emits a second laser light. Two laser light sources and the first and second laser beams emitted from the first and second laser light sources are incident, and the second laser beam is an optical disc with a numerical aperture smaller than that of the first laser beam. The first and second laser beams are incident and the first laser beam is collected on the optical disc. And astigmatism correcting means for correcting astigmatism when illuminated.

The second laser light source is disposed closer to the optical axis than the first laser light source, and the second laser light from the second laser light source is more than the first laser light from the first laser light source. It is focused on the optical disk with a small numerical aperture. Since the first laser light source is off the optical axis, astigmatism occurs in the first laser light. This astigmatism correction means can correct this astigmatism. On the other hand, since the second laser light source is closer to the optical axis, the astigmatism is small. Although the second laser beam may pass through the astigmatism correction means, the astigmatism may increase. However, since the numerical aperture is smaller than that of the first laser beam, this astigmatism is a very large problem. It will not be.
As described above, astigmatism can be set within an appropriate range for the laser light from both the first and second laser light sources.
The first and second light sources may be separated from each other or may be integrally formed. As an example in which the first and second light sources are integrated, a semiconductor laser having a plurality of light emitting points can be given.

(1) The astigmatism correction means may be an anamorphic aspheric lens.
Astigmatism of the first laser light can be canceled by using the lens as an anamorphic aspheric surface and applying astigmatism opposite to the astigmatism inherent in the first laser light.

(2) The astigmatism correction means may be an anamorphic aspherical lens disposed between the first and second laser light sources and the lens.
For example, a coupling lens (including a collimator lens that converts diffused light into parallel light) that adjusts the diffusion state of diffused light emitted from the first and second laser light sources is an anamorphic aspherical surface. By providing astigmatism opposite to the astigmatism inherent to the laser light, the astigmatism of the first laser light can be corrected.

(3) The astigmatism correction unit may be an anamorphic aspheric lens that focuses the first and second laser beams reflected from the optical disc on a photodetecting element.
For example, the detection lens for condensing the first and second laser beams on the light detection element is an anamorphic aspheric surface, and astigmatism opposite to the astigmatism inherent in the first laser beam is given. As a result, the astigmatism of the first laser beam can be corrected.

(4) The astigmatism correction unit may be an optical member having a flat surface that is disposed to be inclined with respect to the optical axis in the divergent light of the first and second laser beams.
Astigmatism occurs when divergent light passes through a slope inclined with respect to the optical path of the divergent light. By making this astigmatism astigmatism opposite to that inherent in the first laser beam, the astigmatism of the first laser beam can be corrected.
As an example of the optical member for this purpose, a light transmitting member having a flat plate shape or a wedge shape can be mentioned.

(5) The astigmatism correction means may be a liquid crystal element.
Since the liquid crystal has an anisotropy of refractive index, astigmatism can be caused by light passing through the liquid crystal layer. By making this astigmatism astigmatism opposite to that inherent in the first laser beam, the astigmatism of the first laser beam can be corrected.

B. An optical disk reproducing apparatus according to the present invention includes the optical pickup according to A.
By correcting the astigmatism of the first laser beam by the astigmatism correction means, it is possible to make the astigmatism within an appropriate range for both the first and second laser beams.

  As described above, according to the present invention, it is possible to provide an optical pickup and an optical disc reproducing apparatus that can easily correct astigmatism for a plurality of light sources.

(First embodiment)
FIG. 1 is a schematic diagram showing an optical disk reproducing apparatus 10 according to the first embodiment of the present invention.
The optical disk reproducing apparatus 10 includes an optical pickup 20 and an optical pickup driving unit 30, and reads information from a plurality of optical disks D (CD (Compact Disc), DVD (Digital Versatile Disc), etc.) having different standards.

The optical pickup 20 includes a laser diode LD, a grating 21, a beam splitter BS, a collimator lens L1, a mirror M, an objective lens L2, an objective lens driving unit 22, an optical axis correction element 23, a detection lens L3, and a photodiode PD. Information is read from the optical disc D.
The optical pickup driving unit 30 is an actuator for moving (seeking or the like) the entire optical pickup 20.

The laser diode LD as the first and second laser light sources emits a first laser beam having a first wavelength (λ1) and a second laser beam having a second wavelength (λ2). Examples of the first and second wavelengths include a wavelength of 650 nm for reproducing a DVD and a wavelength of 780 nm for reproducing a CD. In the laser diode LD, for example, a first region (first light emission point) that emits the first laser light and a second region (second light emission point) that emits the second laser light are close to each other. It is comprised from the formed semiconductor chip.
Here, the second light emitting point is closer to the optical axis of the optical system than the first light emitting point. For this reason, the second laser beam has less astigmatism than the first laser beam. As will be described later, the second laser beam has a smaller numerical aperture (NA) than the first laser beam when focused on the optical disc D.

  The grating 21 is a two-wavelength diffraction grating that diffracts the incident first and second laser beams in different states according to the first and second wavelengths. Each of the first and second laser beams is diffracted by the grating 21 and divided into a main beam and two sub beams, which can be used to generate a tracking error signal (differential push-pull signal: DPP signal). For example, since the track pitch is different between DVD and CD, the optimum angle between the three beams is different. Therefore, the diffraction states at the first and second wavelengths are set so as to correspond to the optimum angle between the beams. This can be done by appropriately setting the lattice spacing (grating pitch) of the grating 21 and the like.

  The beam splitter BS is a polarizing element that passes light having a predetermined polarization direction and reflects light having a polarization direction orthogonal to the polarization direction, and reflects the first and second laser beams incident from the laser diode LD. The first and second laser beams reflected by the optical disc D are set to pass through.

The collimator lens L1 is an optical element that converts the first and second laser beams emitted from the beam splitter BS into parallel beams and converts the first and second laser beams reflected from the optical disc D into convergent beams. is there.
As described above, the first laser beam has astigmatism because the first emission point is off the optical axis of the optical system. In the present embodiment, when the first laser light passes through the collimator lens L1, the opposite astigmatism is given, and the astigmatism of the first laser light is canceled.
FIG. 2 is a top view illustrating an example of the collimator lens L1. The shape of the collimator lens L1 is a so-called anamorphic aspheric surface, and the radius of curvature and the focal length are different in the vertical and horizontal directions.

When the collimator lens L1 is not an anamorphic aspherical surface (for example, a spherical lens), the first laser light has astigmatism, so that the beam spot SP1 of the first laser light on the optical disc D The shape is elliptical. By making the collimator lens L1 an appropriate anamorphic aspherical surface, the shape of the beam spot SP of the first laser beam on the optical disc D can be made circular (elimination of astigmatism).
On the other hand, the second laser light has astigmatism as it passes through the anamorphic aspherical collimator lens L1, and the shape of the beam spot SP2 of the second laser light on the optical disk D changes from an original circle to an ellipse. Become a shape. However, since the numerical aperture of the second laser beam is not so large (that is, the spot diameter of the beam spot SP2 does not have to be so small), the influence of this astigmatism (decrease in the S / N ratio of the reproduction signal) is Not a problem.
As described above, when the first and second laser beams pass through the anamorphic aspherical collimator lens L1, both astigmatisms can be maintained in an appropriate range.

The mirror M is an optical element that changes the directions of the first and second laser beams.
The objective lens L2 is an optical element for condensing the first and second laser beams onto the optical disc D and converting the laser beam reflected from the optical disc D into parallel light.
On the optical disc D, the first and second laser beams form beam spots SP1 and SP2, respectively. At this time, the numerical aperture of the second laser light is smaller than the numerical aperture of the first laser light.
This can be done, for example, by arranging a stop whose aperture is changed by the first and second laser beams immediately before the objective lens L2 (the aperture size of the stop is large for the first laser beam, 2 is small). Such an aperture has a two-wavelength aperture patterned with a wavelength-dependent optical material (transmits light of the first wavelength and does not transmit (reflects or absorbs) the light of the second wavelength). Can be used.

The objective lens drive mechanism 22 is a mechanism for moving the objective lens L2 in the front-rear direction and the radial direction RD of the optical disc D and tilting (tilt angle θ) in the radial direction. The objective lens driving mechanism 22 performs focusing (focusing) of the first and second laser beams, adjustment of the spot position (tracking), and adjustment of the tilt angle.
FIGS. 3A and 3B are a top view and a side view showing details of the objective lens driving mechanism 22.
The objective lens driving mechanism 22 includes a lens holding unit 51, a focus / tracking driving unit 52, a connection unit 53, and a tilt driving unit 54.

The lens holding unit 51 is a holding mechanism for holding the objective lens L2.
The focus / tracking drive unit 52 is a moving mechanism for moving the objective lens L2 in the front-rear direction with respect to the optical disc D and in the radial direction of the optical disc D, and focuses the first and second laser beams on the optical disc D (focusing). ) And the spot positions of the first and second laser beams with respect to the track of the optical disk D (tracking). The focus / tracking drive unit 52 includes, for example, a focus coil and a tracking coil, and focusing and tracking can be performed by adjusting the amount of current flowing through these coils.
The connection unit 53 is a mechanism for dynamically connecting the focus / tracking drive unit 52 and the rotation unit 61.

The tilt driving unit 54 is a tilting mechanism for changing the tilt angle θ of the objective lens L2 in the radial direction RD with respect to the optical disc D (tilt angle in the radial direction RD), and the first and second laser beams with respect to the optical disc D are changed. Adjust the tilt angle.
The tilt drive unit 54 includes a rotating unit 61, an electromagnet 62, a shaft 63, a fixed unit 64, and a magnet unit 65.
The rotating unit 61 is connected to the fixed unit 64 by a shaft 63 and rotates in the tilt direction of the optical disc D with the shaft 63 as a rotation axis.
The electromagnet 62 is a drive mechanism that is connected to the rotating unit 61 and rotates the rotating unit 61 relative to the fixed unit 64. By passing an electric current through the electromagnet 62, an attractive force or a repulsive force is generated between the electromagnet 62 and the rotating portion 61 can be rotated to adjust the inclination angle θ. The rotation direction can be controlled by the direction of current flow, and the absolute value of the rotation angle can be controlled by the amount of current.
The shaft 63 is a connection mechanism that rotatably connects the rotating portion 61 and the fixed portion 64.
The fixing unit 64 is connected to the main body of the optical pickup 20 and is moved together with the main body of the optical pickup 20 by the optical pickup driving unit 30 (seek operation).
The magnet portion 65 is a fixed magnet connected to the fixed portion 64, and the rotating portion 61 is rotated by the attractive / repulsive force between the magnet portion 65 and the electromagnet 62.

The optical axis correction element 23 corrects the optical paths of the first and second wavelength laser beams emitted from the laser diode LD with respect to the optical axis of the optical system of the optical pickup 20, and the first and second laser beams. Is an optical element for condensing light at substantially the same location of the photodiode PD. Since the emission points of the first and second laser beams are misaligned, for example, when the emission point of the first laser beam is aligned with the optical axis, the emission point of the second laser beam is offset from the optical axis. Shift. Accordingly, the first and second laser beams are condensed at different positions on the photodiode PD. For this reason, the optical path of the emitted light is adjusted by the optical axis correction element 23 at each of the first and second wavelengths so that the first and second laser beams are condensed at substantially the same position on the photodiode PD. ing.
(Please explain the specific configuration of the optical axis correction element 23)
Specifically, the optical axis correction element 23 can be configured as follows.

The detection lens L3 is an optical element for condensing the first and second laser beams on the photodiode PD.
The photodiode PD as a light receiving element is an element for detecting the first and second laser beams reflected by the optical disc D and reading information from the optical disc D.
The photodiode PD has a detection area divided so that each of these three beams can be detected independently in response to the laser beam being divided into a main beam and two sub beams by the grating 21. By detecting and calculating each of the three beams, a tracking error signal (differential push-pull signal: DPP signal) is generated by the differential push-pull method (DPP method).

(Operation of optical pickup 20)
The operation of the optical pickup 20 will be described. Here, it is usual that only one of the first and second laser beams is emitted according to the type of the optical disk D, etc., but the first and second lasers are easy to understand. A description will be given in contrast to light.

(1) The first and second laser beams emitted from the laser diode LD are divided into three beams by the grating 21, then reflected by the beam splitter BS, incident on the collimator lens L1, and converted into parallel light. Converted.
Since the first emission point is off the optical axis, the first laser beam has aspherical aberration. This aspherical aberration is eliminated by passing through the collimator lens L1. When the second laser beam passes through the collimator lens L1, the aspherical aberration becomes rather large, but the influence is not so great because the numerical aperture is small.

(2) Thereafter, the first and second laser beams are reflected by the mirror M, enter the objective lens L2, and are condensed on the optical disc D. For example, the first laser beam is focused on the DVD and the second laser beam is focused on the CD to form beam spots SP1 and SP2, respectively.
Since the aspherical aberration of the first laser beam is corrected, the beam spot SP1 of the first laser beam on the optical disc D is substantially circular. On the other hand, since the aspherical aberration of the second laser light is rather increased, the beam spot SP2 of the second laser light on the optical disc D is substantially elliptical, but the numerical aperture of the second laser light is Is somewhat large (it is not necessary that the size of the beam spot SP2 is so small), the influence of the aspherical aberration is not so great.

(3) The first and second laser beams reflected by the optical disk D pass through the objective lens L2, the mirror M, and the collimator lens L1, pass through the beam splitter BS, and the optical path is corrected by the optical axis correction element 23.
(4) The first and second laser beams that have passed through the optical axis correction element 23 enter the photodiode PD through the detection lens L3. The first and second laser beams are condensed at the same position on the photodiode PD by the optical axis correction element 23. Signals corresponding to the three beams are output from the photodiode PD, and a DPP signal is generated by calculating these three outputs, and tracking control of the optical pickup 20 can be performed.

As described above, in the present embodiment, the light emission point of the second laser light is disposed on the optical axis, the light emission point of the first laser light is shifted from the optical axis, and the aspherical surface of the first laser light. The aberration is corrected by the collimator lens L1. As a result, the quality of the beam spot SP of the first and second laser beams on the optical disc D, and thus the recording / reproducing ability of the optical pickup 20 can be made good.
Since the aspherical aberration is corrected by using an anamorphic aspherical surface as the collimator lens L1 that is originally required for the device configuration, the quality of the beam spot of the first laser beam is improved without increasing the number of parts. Therefore, it is possible to provide an optical pickup and an optical disc apparatus that are small, inexpensive, and excellent in recording / reproducing ability.

(Second Embodiment)
FIG. 4 is a schematic diagram showing an optical disk reproducing apparatus 10a according to the second embodiment of the present invention.
The optical disk reproducing device 10a includes an optical pickup 20a and an optical pickup driving unit 30, and reads information from a plurality of optical disks D having different standards.

  The optical pickup 20a includes a laser diode LD, a grating 21, a coupling lens L4, a beam splitter BS, a mirror M, an objective lens L2, an objective lens driving unit 22, an optical axis correction element 23, a detection lens L3, and a photodiode PD. The information is read from the optical disc D.

Compared to the first embodiment, in the optical pickup 20a, a coupling lens L4 is disposed between the grating 21 and the beam splitter BS instead of the collimator lens L1.
The coupling lens L4 adjusts the divergence angle of the incident first and second laser beams. A collimator lens that converts incident diverging light into parallel light may be considered as a kind of coupling lens.

In the present embodiment, the coupling lens L4 is an anamorphic aspheric lens, and has different radii of curvature in the vertical direction and the horizontal direction, and consequently the focal length.
When the coupling lens L4 is not an anamorphic aspherical surface (for example, a spherical lens), the first laser beam has astigmatism, and therefore the beam spot SP1 of the first laser beam on the optical disc D. The shape of becomes an ellipse. By making the coupling lens L4 an appropriate anamorphic aspherical surface, the shape of the beam spot SP of the first laser beam on the optical disc D can be made circular (elimination of astigmatism).

On the other hand, the second laser light is astigmatized by passing through the anamorphic aspheric coupling lens L4, and the shape of the beam spot SP2 of the second laser light on the optical disc D is from the original circular shape. It becomes oval. However, since the numerical aperture of the second laser beam is not so large, the influence of this astigmatism (reduction in the S / N ratio of the reproduction signal) is not a problem.
As described above, the first and second laser beams pass through the anamorphic aspheric coupling lens L4, so that both astigmatisms can be maintained in an appropriate range.
In other respects, the present embodiment is not essentially different from the first embodiment, and thus description thereof is omitted.

As described above, in the present embodiment, the light emission point of the second laser light is disposed on the optical axis, the light emission point of the first laser light is shifted from the optical axis, and the aspherical surface of the first laser light. Aberration is corrected by the coupling lens L4. As a result, the quality of the beam spot SP of the first and second laser beams on the optical disc D, and thus the recording / reproducing ability of the optical pickup 20 can be made good.
In addition, since the aspherical aberration is corrected by making the coupling lens L4 an anamorphic aspherical surface, the quality of the beam spot of the first laser beam can be improved without increasing the number of parts, and it is small and inexpensive. In addition, it is possible to provide an optical pickup and an optical disc apparatus that are excellent in recording / reproducing capability.

(Third embodiment)
FIG. 5 is a schematic diagram showing an optical disc reproducing apparatus 10b according to the second embodiment of the present invention.
The optical disk reproducing device 10b includes an optical pickup 20b and an optical pickup driving unit 30, and reads information from a plurality of optical disks D having different standards.

  The optical pickup 20b includes a laser diode LD, a grating 21, a beam splitter BS, a collimator lens L10, a mirror M, a liquid crystal element 24, an objective lens L2, an objective lens driving unit 22, an optical axis correction element 23, a detection lens L3, and a photodiode PD. And reading information from the optical disc D.

Compared to the first embodiment, in the optical pickup 20b, a collimator lens L10 is disposed instead of the collimator lens L1, and the liquid crystal element 24 is disposed between the mirror M and the objective lens L2.
The collimator lens L10 converts incident diverging light into parallel light in the same manner as in the first embodiment, but is not an anamorphic aspherical lens, but a curvature radius in the vertical and horizontal directions, and hence a focal length. Match. That is, the collimator lens L10 is not used for correcting the aspherical aberration of the first and second laser beams.

The liquid crystal element 24 is an optical element for correcting the aspherical aberration of the first laser beam.
FIG. 6 is a side view showing the liquid crystal element 24. The liquid crystal element 24 is obtained by enclosing a liquid crystal material 73 between a pair of transparent substrates 72 on which a transparent electrode 71 is formed. Various orientations such as parallel orientation can be used for the liquid crystal material 73 sealed between the transparent substrates 72.
The liquid crystal material has a refractive index anisotropy. Therefore, astigmatism can be imparted to the light incident on the liquid crystal element 24 by appropriately setting the alignment state of the liquid crystal and the value of the refractive index anisotropy.
Furthermore, by applying a voltage between the pair of transparent electrodes 71, the orientation of the liquid crystal molecules can be changed, and the magnitude of this astigmatism can be changed.

By passing the first laser beam through the liquid crystal element 24, the astigmatism inherent in the first laser beam can be corrected. At this time, a voltage is applied to the liquid crystal element 24 as necessary.
The second laser beam has astigmatism as it passes through the liquid crystal element 24, but its numerical aperture is not so large, so the effect of this astigmatism (reduction in the S / N ratio of the reproduction signal) is a problem. Not enough. Furthermore, the astigmatism characteristic can be changed by adjusting the voltage applied to the liquid crystal element 24, and the astigmatism of the second laser beam can be kept in an appropriate state without substantially changing before and after the incidence. .

As described above, when the first and second laser beams pass through the liquid crystal element 24, both astigmatisms can be maintained in an appropriate range. Further, by adjusting the applied voltage, it is possible to generate astigmatism in the liquid crystal element 24 only when recording / reproducing the DVD, and the reproduction signal from the CD can be made better. it can.
In other respects, the present embodiment is not essentially different from the first embodiment, and thus description thereof is omitted.

  As described above, in the present embodiment, the light emission point of the second laser light is disposed on the optical axis, the light emission point of the first laser light is shifted from the optical axis, and the aspherical surface of the first laser light. The aberration is corrected by the liquid crystal element 24. As a result, the quality of the beam spot SP of the first and second laser beams on the optical disc D, and thus the recording / reproducing ability of the optical pickup 20 can be made good.

(Fourth embodiment)
FIG. 7 is a schematic diagram showing an optical disc reproducing apparatus 10c according to the second embodiment of the present invention.
The optical disk reproducing device 10c includes an optical pickup 20c and an optical pickup driving unit 30, and reads information from a plurality of optical disks D having different standards.

  The optical pickup 20c includes a laser diode LD, a grating 21, a coupling lens L4, a beam splitter BS1, a collimator lens L10, a mirror M, an objective lens L2, an objective lens driving unit 22, an optical axis correction element 23, a detection lens L3, and a photodiode. It has a PD and reads information from the optical disc D.

  Compared to the first embodiment, in the optical pickup 20c, a coupling lens L4 is added, and the beam splitter BS1 is replaced with the beam splitter BS, and the collimator lens L10 is replaced with the collimator lens L1. . Further, in the optical pickup 20c, the first and second laser beams emitted from the laser diode LD are transmitted through the beam splitter BS1 to the optical disc D, and the first and second laser beams reflected by the optical disc D are Reflected by the beam splitter BS1 and heading toward the photodiode PD (in the first embodiment, the forward is reflected and the return is transmitted).

  The coupling lens L4 adjusts the divergence angle of the incident first and second laser beams. This adjustment is performed to adjust the astigmatism characteristics of the beam splitter BS1. That is, astigmatism at the coupling lens L4 is large if the divergence angle of the first and second laser beams emitted from the coupling lens L4 is large, and astigmatism is small if the divergence angle is small.

  The collimator lens L10 converts incident diverging light into parallel light in the same manner as in the first embodiment, but is not an anamorphic aspherical lens, but a curvature radius in the vertical and horizontal directions, and hence a focal length. Match. As a result, the collimator lens L10 does not correct the aspherical aberration of the first and second laser beams.

The beam splitter BS1 is a polarizing element that passes light having a predetermined polarization direction and reflects light having a polarization direction orthogonal to the polarization direction, and transmits the first and second laser beams incident from the laser diode LD. The first and second laser beams reflected by the optical disc D are set to be reflected. This can be done by forming an appropriate optical film on the reflecting surface of the beam splitter BS1.
The beam splitter BS1 is also an optical element for correcting the aspherical aberration of the first laser beam. For this purpose, the beam splitter BS1 has a plane disposed obliquely with respect to the optical axis in diverging light. Astigmatism can be generated by refracting light and changing its direction by means of a plane arranged obliquely with respect to the optical axis during diverging light. As a result, it is possible to correct astigmatism caused by the first laser beam incident obliquely with respect to the optical axis. As described above, the magnitude of astigmatism can be adjusted by adjusting the divergence angle with the coupling lens L4.
The beam splitter BS1 can be configured, for example, from a flat plate shape or a wedge shape. This plane can also be used as a reflecting surface.
As can be seen from the above, the beam splitter BS1 can be formed by forming an optical film on one surface of a plate-shaped or wedge-shaped translucent material.

The first laser light can pass through the beam splitter BS1 to correct astigmatism.
On the other hand, the second laser beam has astigmatism by passing through the beam splitter BS1, but since the numerical aperture of the laser beam is not so large, the influence of this astigmatism (the S / N ratio of the reproduction signal). Is not a problem.
As described above, both the astigmatism can be maintained in an appropriate range by passing the first and second laser beams through the beam splitter BS1.
In other respects, the present embodiment is not essentially different from the first embodiment, and thus description thereof is omitted.

As described above, in the present embodiment, the light emission point of the second laser light is disposed on the optical axis, the light emission point of the first laser light is shifted from the optical axis, and the aspherical surface of the first laser light. The aberration is corrected by the beam splitter BS1. As a result, the quality of the beam spot SP of the first and second laser beams on the optical disc D, and thus the recording / reproducing ability of the optical pickup 20 can be made good.
In addition, since the aspherical aberration is corrected by forming the beam splitter BS1 from a flat plate or the like, the quality of the beam spot of the first laser beam can be improved without increasing the number of components, and the size, cost, and recording can be improved. It is possible to provide an optical pickup and an optical disc apparatus that are excellent in reproduction capability.

1 is a schematic diagram showing an optical disc reproducing apparatus according to a first embodiment of the present invention. It is a top view showing an example of the collimator lens of the optical disk reproducing device according to the first embodiment. It is the top view and side view showing the detail of the optical disk reproducing | regenerating apparatus objective lens drive mechanism which concern on 1st Embodiment. It is a schematic diagram which shows the optical disk reproducing | regenerating apparatus concerning the 2nd Embodiment of this invention. It is a schematic diagram which shows the optical disk reproducing | regenerating apparatus concerning the 3rd Embodiment of this invention. It is a top view showing an example of the liquid crystal element of the optical disk reproducing | regenerating apparatus concerning 3rd Embodiment. It is a schematic diagram which shows the optical disk reproducing | regenerating apparatus concerning the 4th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical disk reproducing | regenerating apparatus 20 Optical pick-up 21 Grating 22 Objective lens drive mechanism 23 Optical axis correction element 30 Optical pick-up drive part 51 Lens holding part 52 Focus tracking drive part 53 Connection part 54 Tilt drive part 61 Rotation part 62 Electromagnet 63 Shaft 64 Fixation Part 65 Magnet part D Optical disk L1 Collimator lens L2 Objective lens L3 Detection lens LD Laser diode M Mirror PD Photodiode

Claims (8)

A first laser light source that emits a first laser beam;
A second laser light source disposed near the first laser light source and closer to the optical axis and emitting a second laser light;
A lens for entering the first and second laser beams emitted from the first and second laser light sources and condensing the second laser beam on the optical disc with a smaller numerical aperture than the first laser beam; ,
Astigmatism when the first and second laser beams are incident on the first and second laser light sources and the optical disc, and the first laser beam is focused on the optical disc. Astigmatism correction means for correcting the aberration,
An optical pickup comprising: The optical pickup according to claim 1, wherein the astigmatism correction unit is an anamorphic aspheric lens. 2. The optical pickup according to claim 1, wherein the astigmatism correction means is an anamorphic aspherical lens disposed between the first and second laser light sources and the lens. 2. The light according to claim 1, wherein the astigmatism correction unit is an anamorphic aspherical lens that focuses the first and second laser beams reflected from the optical disc on a photodetecting element. pick up. 2. The optical pickup according to claim 1, wherein the astigmatism correction unit is an optical member having a flat surface that is disposed inclined with respect to an optical axis in the divergent light of the first and second laser beams. . The optical pickup according to claim 5, wherein the optical member has a flat plate shape or a wedge shape. The optical pickup according to claim 1, wherein the astigmatism correction means is a liquid crystal element. A first laser light source that emits a first laser beam;
A second laser light source disposed near the first laser light source and closer to the optical axis and emitting a second laser light;
A lens for entering the first and second laser beams emitted from the first and second laser light sources and condensing the second laser beam on the optical disc with a smaller numerical aperture than the first laser beam; ,
Astigmatism when the first and second laser beams are incident on the first and second laser light sources and the optical disc, and the first laser beam is focused on the optical disc. An optical disc reproducing apparatus comprising an optical pickup having astigmatism correcting means for correcting aberration.

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