JPH1186319A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the recording/reproducing of plural optical information recording media varying in thicknesses with one condenser optical system by making the magnification viewed from the optical information recording medium side of an objective lens at the time of the recording or reproducing of the information of the second optical information recording medium smaller than the magnification viewed from the optical information recording medium side of the objective lens at the time of recording or reproduction of the first optical information recording medium. SOLUTION: The magnification viewed from the second optical disk 20' side of the objective lens 16 at the time of the recording/reproducing of the second optical disk 20' is made smaller than the magnification viewed from the first optical disk 20 side of the objective lens 16 at the time of the recording/reproducing of the first optical disk 20. Namely, the dispersion degree of the incident luminous flux on the objective lens 16 is varied at the time of the recording/reproducing of the first optical disk 20 and at the time of the recording/reproducing of the second optical disk 20' so as to deal with a trend toward higher NA. The second light source 12 of a semiconductor laser is brought near to a coupling lens 13 without changing the position of the coupling lens 13 at the time of the recording/reproducing of the first optical disk 20 and at the time of the recording/reproducing of the second optical disk 20'.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device capable of recording and / or reproducing (recording / reproducing) a plurality of optical information recording media having different thicknesses of a transparent substrate with one condensing optical system. About.

[0002]

2. Description of the Related Art In recent years, with the practical use of a short-wavelength red semiconductor laser, a high-density optical disk having the same size and large capacity as a CD (compact disk), which is a conventional optical information recording medium (also referred to as an optical disk), has been developed. The development of DVDs (also referred to as digital video discs or digital versatite discs) as optical information recording media has been progressing. This D
In VD, the numerical aperture NA of the objective lens on the optical disk side when using a short-wavelength semiconductor laser of 635 nm is 0.6.
And DVD has a track pitch of 0.74.
μm, the shortest pit length is 0.4 μm, and the density is reduced to less than half of the CD track pitch of 1.6 μm and the shortest pit length of 0.83 μm. Also, the CD mentioned above,
In addition to DVD, optical disks of various standards, for example, CD
-R (write-once compact disc), LD (laser disc), MD (mini disc), MO (magneto-optical disc), and the like have also been commercialized and spread. Table 1 shows the thicknesses of the transparent substrates of the various optical disks and the required numerical apertures.

[0003]

[Table 1]

[0004] For CD-R, the light source wavelength λ = 7
It must be 80 (nm), but in other optical discs, a light source having a wavelength other than the light source wavelength described in Table 1 can be used. In this case, the required numerical aperture depends on the used light source wavelength λ. NA changes. For example, in the case of a CD, the required numerical aperture is approximated by NA = λ (μm) /1.73, and in the case of a DVD, the required numerical aperture is approximated by NA = λ (μm) /1.06.

[0005] As described above, the era has come to the market where various optical disks having various sizes, substrate thicknesses, recording densities, wavelengths to be used, etc. exist, and optical pickup devices capable of supporting various optical disks have been proposed. .

As one of them, there has been proposed an optical pickup device having a focusing optical system corresponding to each of different optical disks and switching the focusing optical system depending on the optical disk to be reproduced. However, in this optical pickup device, a plurality of condensing optical systems are required, which not only causes an increase in cost, but also requires a drive mechanism for switching the condensing optical systems, complicates the device, and requires a switching accuracy thereof,
Not preferred.

[0007] Therefore, various optical pickup devices for reproducing a plurality of optical disks by using one condensing optical system have been proposed.

One of them is disclosed in Japanese Patent Application Laid-Open No. 9-184975.
Japanese Patent Application Laid-Open Publication No. H11-163873 proposes an optical pickup device in which an objective lens is provided with a slight step concentric with the optical axis. In this pickup device, a light beam emitted from a light source is divided into two regions, a first region on the optical axis side of the step and a third region on the outer side. The recording / reproducing is performed by a light beam passing through the first area and the third area, thereby trying to record / reproduce two optical disks, DVD and CD, using one condensing optical system. The condensing optical system is called a two-region converging optical system, and when applied to an objective lens, this objective lens is called a two-region objective lens).

Also, “International s”
ymposium on optical memory
y and optical data storage
e1996 ", a lecture number OFA3-1 proposes an optical pickup device in which an objective lens is provided with a shielding ring concentric with the optical axis. In this pickup device, the light beam emitted from the light source is divided into three areas: a first area on the optical axis side of the shield ring, a shield area by the shield ring, and a third area outside the shield ring, and records a CD. /
The first area near the optical axis is used for reproduction, and the recording / reproduction of the DVD is performed using a light beam passing through the first area and the third area.
This optical disk is intended to record / reproduce data (hereinafter, this light-collecting optical system is called a shield light-collecting optical system, and when applied to an objective lens, this objective lens is called a light-shielding objective lens).

An optical pickup device equipped with the two-area light condensing optical system and the shield light condensing optical system makes the wavefront aberration (spherical aberration) discontinuous due to a step or a shield ring so that a DVD can be recorded / reproduced during CD recording / reproduction. The purpose of the present invention is to reduce the influence of flare caused by spherical aberration caused by the difference between the thickness of the transparent substrate and the thickness of the transparent substrate of a CD.

[0011]

In these optical pickup devices, since one light source having a short wavelength (λ = 635 nm) is used, the required numerical aperture for reproducing a CD is as small as about NA = 0.370. Since the numerical aperture is sufficient, the diffraction limit performance can be satisfied, and DVD and CD can be reproduced. Here, if it is attempted to use two light sources for CD-R instead of CD, the necessary numerical aperture NA = 0.45 at the time of reproducing CD-R is required, which is the same as that for LD. In addition, a higher NA is required.

However, in the two-region focusing optical system, it is necessary to increase the design substrate thickness and move the position of the step to the high NA region in order to cope with the high NA. When reproducing a DVD, the spot shape deteriorates, and the DVD cannot be reproduced. Also,
In the shielded condensing optical system, the numerical aperture NA = 0.368 barely satisfies the diffraction limit performance. Therefore, if the position of the shield ring is moved to a higher NA region any more, the diffraction limit performance cannot be satisfied. Cannot play.

Accordingly, the present invention provides an optical pickup device capable of recording / reproducing a plurality of optical information recording media having different thicknesses of a transparent substrate with one condensing optical system and capable of coping with a high NA. The task is to

In view of the above, the present inventors have proposed in Japanese Patent Application No. 9-197076 an optical pickup device in which an objective lens is provided with at least two steps concentric with the optical axis. ing. In this pickup device, the light beam emitted from the light source is transmitted to the first light source near the optical axis.
Area, a second area outside the first area, and a third area outside the second area. For recording / reproduction of the second optical disc, the first area and the second area near the optical axis are used. Area
The recording / reproducing of the first optical disc is performed by a light beam passing through the first area and the third area, so that a plurality of optical discs are recorded / reproduced using one condensing optical system (hereinafter, this condensing optical system). Is referred to as a three-region focusing optical system, and when applied to an objective lens, this objective lens is referred to as a three-region objective lens). However, in such an optical pickup device, when trying to correspond to the second optical disk having a high NA, there has been a problem that a loss of light amount at the time of recording / reproducing of the first optical disk becomes large.

Therefore, it is a further object of the present invention to perform the recording / reproducing of the first optical disc satisfactorily even if the second optical disc has a high NA.

[0016]

[Means for Solving the Problems]

(1) The thickness of the transparent substrate is reduced to t1 by providing a condensing optical system including an objective lens with a function of dividing a light beam emitted from a light source into at least two regions in a direction perpendicular to the optical axis. A light beam emitted from a first light source (wavelength λ1 (nm)) is condensed on an information recording surface via a transparent substrate by the condensing optical system with respect to the first optical information recording medium,
While recording or reproducing information on the first optical information recording medium, a second light source (wavelength λ2 (nm)) is applied to a second optical information recording medium having a transparent substrate with a thickness of t2 (t2> t1). In the optical pickup device, the emitted light beam is condensed on the information recording surface via the transparent substrate by the condensing optical system, and information is recorded or reproduced on the second optical information recording medium. Magnification m1 of the objective lens viewed from the optical information recording medium side when recording or reproducing information on the recording medium
The magnification m of the objective lens as viewed from the optical information recording medium side when recording or reproducing information on the second optical information recording medium.
An optical pickup device characterized in that 2 is smaller.

(2) The condensing optical system has a wavefront aberration discontinuous and divides a light beam emitted from the light source into at least two regions in a direction perpendicular to the optical axis. At least one concentric lens surface dividing unit is provided, and at the time of recording or reproducing information on the first optical information recording medium, of the regions divided by the lens surface dividing unit, on the optical axis side of the lens surface dividing unit. The beam spot formed on the information recording surface of the first optical information recording medium has a wavefront aberration of 0.05λ1 (rms) or less due to the light flux passing through the first region and the third region outside the lens surface dividing portion. And when recording or reproducing information on the second optical information recording medium, the second light beam is transmitted by the light flux passing through the first area.
The optical pickup device according to (1), wherein the wave spot aberration of the beam spot formed on the information recording surface of the optical information recording medium is 0.07λ2 (rms) or less.

(3) A light beam from a light source is condensed on an information recording surface via a transparent substrate of an optical information recording medium by a light condensing optical system including an objective lens, and information is recorded or recorded on the optical information recording medium. In an optical pickup device configured to perform reproduction, and recording or reproducing information of at least two types of optical information recording media having different thicknesses and recording densities of transparent substrates, the focusing optical system may include a wavefront. In order to make the aberration discontinuous, at least one lens surface dividing portion substantially concentric with the optical axis of the lens is provided, and the thickness of the transparent substrate is set to t1.
When information is recorded or reproduced on the first optical information recording medium, the information is formed on the information recording surface by a light beam passing through the first region on the optical axis side of the lens division portion and the third region outside the lens surface division portion. When the wavefront aberration of the beam spot is
05λ1 (rms) (where λ1 is the wavelength (n) of the first light source used for recording or reproducing information on the first optical information recording medium.
m)) The light flux from the first light source is condensed and the recording density is lower than that of the first optical information recording medium and the transparent density is lower than that of the first optical information recording medium, where m1 is the magnification of the objective lens viewed from the optical information recording medium side, as described below. When recording or reproducing information on the second optical information recording medium having a substrate thickness of t2 (t2> t1), the wavefront of the beam spot formed on the information recording surface by the light flux passing through the first area is zero. .07λ2 (rms) (where λ2 is not more than the wavelength (nm) of the second light source used for recording or reproducing information on the second optical information recording medium) or less from the optical information recording medium side of the objective lens. An optical pickup device, wherein the magnification seen is m2, and a light beam from the second light source is collected.

(4) The light-collecting optical system is provided with two lens surface dividing portions, and when recording or reproducing on the second optical information recording medium, a second region between the first area and the two lens surface dividing portions is provided.
A light beam passing through the area is condensed to form a beam spot on the information recording surface (2).
Or the optical pickup device according to (3).

(5) The condensing optical system is provided with two lens surface divisions, and a second region between the two lens surface divisions is provided with a shielding structure (2) or The optical pickup device according to (3).

(6) The magnification m2 is a direction for correcting spherical aberration caused by a difference between the thickness t1 of the transparent substrate of the first optical information recording medium and the thickness t2 of the transparent substrate of the second optical information recording medium. The optical pickup device according to any one of (1) to (5), wherein the optical pickup device is a magnification.

(7) The condensing optical system has a divergence changing optical element for changing the divergence of the light beam from the first light source and the second light source, and the divergence changing optical element and the second (1) to (6), wherein the first light source and the second light source are arranged such that a distance from the light source is shorter than a distance between the divergence changing optical element and the first light source. The optical pickup device according to any one of the above.

(8) The first light source also serves as the second light source, any one of (1) to (6).
An optical pickup device according to any one of the above.

(9) The condensing optical system has a divergence changing optical element for changing the divergence of the light beam from the first light source, and the divergence changing optical element is used for recording or reproducing information on the first optical information recording medium. The distance between the divergence changing optical element and the first light source at the time of recording or reproducing information on the second optical information recording medium may be shorter than the distance between the divergence changing optical element and the first light source. The optical pickup device according to (8), which is characterized in that:

(10) The optical pickup device according to (9), wherein the first light source or the divergence changing optical element is moved in an optical axis direction.

(11) The magnification m1 and the magnification m2
Satisfies -0.05 <m2-m1 <-0.005, the optical pickup device according to any one of (1) to (10), wherein

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the embodiments, an optical information recording medium (hereinafter, an optical disk) will be described with reference to FIG. The optical pickup device 10 includes an optical information recording medium (hereinafter, also referred to as an optical disk) 20,
As 0 ', information is recorded on the information recording surfaces 22, 22' of a plurality of optical disks 20, 20 'having different thicknesses of the transparent substrates 21, 21' or information is reproduced on the information recording surfaces 22, 22 '(optical disk 20). , 20 ′, or recording / reproducing of the optical discs 20, 20 ′). The plurality of optical disks 20, 20 '
The first optical disc 20 having a thickness t1 of the transparent substrate 21
And a second optical disc 20 'having a thickness t2 different from the thickness t1 of the transparent substrate 21 of the first optical disc. Further, the necessary numerical aperture on the optical disk side of a condensing optical system (described later) required for recording / reproducing the first optical disk 20 is set to NA1, and the condensing light required for recording / reproducing the second optical disk 20 'is set. The required numerical aperture on the optical disk side of the optical system is N
A2 (in the following description, the first optical disc 20 is
NA1> NA2 because the information recording medium has a higher density than the second optical disc 20 ').

In the following description, DVD (including DVD)
-RAM) refers to the first optical disk 20, in which case the thickness t1 of the transparent substrate is 0.6 mm (DVD
Has a single-sided type and a double-sided type. In both cases, since a transparent substrate having a thickness of t1 is attached to both sides of the information recording surface, the DVD itself has a thickness of 1.2 mm.)
(Includes CD-R, but may be LD, MD, MO, etc.) refers to the second optical disc 20 ', and in this case, t2 = 1.2 mm (however, in the case of LD, t2 = 1.2 mm).
5 mm), and t1 <t2.

First, the outline of the optical pickup device 10 will be described. FIG. 1 is a schematic configuration diagram of the optical pickup device 10. In FIG. 1, a DVD is shown as the first optical disc 20 above the optical axis and a CD as the second optical disc 20 'below the optical axis. Further, in the optical pickup device 10, the optical disks 20, 20 '
Is placed on a tray (not shown) such that the transparent substrate 21 exists between the objective lens 16 (to be described in detail later) and the information recording surfaces 22 and 22 '.

In the optical pickup device 10 of the present embodiment, the first semiconductor laser 11 as the first light source is used as the light source.
(Wavelength λ1 = 635 nm) and a second semiconductor laser 12 (wavelength λ2 = 780 nm) as a second light source.
The first semiconductor laser 11 has a wavelength of 610 nm to 67 nm.
A laser having an emission wavelength between 0 nm and the second semiconductor laser 12 having an emission wavelength between 740 nm and 870 nm can be used. This first semiconductor laser 1
Reference numeral 1 denotes a light source used for recording / reproducing on the first optical disc 20, and a second semiconductor laser 12 is a light source used for recording / reproducing on the second optical disc 20 '. The first semiconductor laser 11 and the second semiconductor laser 12
Will be described in detail later. FIG.
In (2), the outermost light beam of the light beam emitted from the first semiconductor laser 11 that is stopped by the stop 17 (described later) is represented by a two-dot chain line, and the outermost light beam of the light beam that is emitted from the second semiconductor laser 12 is stopped by the stop 17. External rays are indicated by dashed lines.

The dichroic prism 19 as a synthesizing means is a means capable of synthesizing a light beam emitted from the first semiconductor laser 11 and a light beam emitted from the second semiconductor laser 12. This dichroic prism 1
Reference numeral 9 denotes a light beam emitted from the first semiconductor laser 11 or a light beam emitted from the second semiconductor laser 12 via one condensing optical system to be described later, the first optical disk 20 or the second optical disk 20, respectively. In this case, the light path on the optical axis is made the same (almost the same) in order to converge the light on the optical axis. Also, this dichroic prism 19
Is the first optical disc 2 emitted from the first semiconductor laser 11
A light beam reflected from the information recording surface of the optical disc 0 and a light beam emitted from the second semiconductor laser 12 and reflected from the information recording surface of the second optical disc 20 'are respectively referred to as first light detecting means 31 and second light detecting means. It is also a means for leading to the means 32. In this embodiment, in order to exclusively record / reproduce the first optical disk 20 and the second optical disk 20 ', the light beam emitted from the first semiconductor laser 11 by the dichroic prism 19 and the second semiconductor laser The light beam emitted from the light source 12 is not actually synthesized.

The condensing optical system includes a light source (the first semiconductor laser 1).
A light beam emitted from the first or second semiconductor laser 12) is condensed on the information recording surfaces 22, 22 'via the transparent substrates 21, 21' of the optical disks 20, 20 'to form spots. is there. This condensing optical system has a coupling lens 13 which is a divergence changing optical element for changing the divergence of a light beam emitted from the first semiconductor laser 11 and the second semiconductor laser 12, and the divergence is controlled by the coupling lens 13. An objective lens 1 serving as an objective optical element for condensing the changed light beam on the information recording surface 22 of the optical disc 20
6. More specifically, in the present embodiment,
The first semiconductor laser 1 is used as the coupling lens 13.
A collimator lens for converting the light beam emitted from 1 into parallel light (which may be substantially parallel) is used.

In this embodiment, recording / reproducing of a plurality of optical discs is performed by using one condensing optical system, so that the optical pickup device 10 can be realized with a low-cost and simple structure. it can.

In the present embodiment, a so-called infinite system using a coupling lens 13 (collimator lens) and an objective lens 16 as a condensing optical system for the light beam emitted from the first semiconductor laser 11 is used. However, only the objective lens 16 for directly condensing the divergent light from the light source without the coupling lens 13 may be a so-called finite condensing optical system. Further, as a condensing optical system, the divergence of the divergent light emitted from the first semiconductor laser 11 is reduced instead of converting the divergence of the light emitted from the first semiconductor laser 11 into parallel light by the coupling lens 13. A so-called quasi-finite condensing optical system including a coupling lens or a coupling lens for changing a light beam from the first semiconductor laser 11 into convergent light, and an objective lens for condensing the light beam via the coupling lens. It may be.

In the focusing optical system, the light flux is set to a numerical aperture N.
An aperture 17 for limiting the numerical aperture to A1 is provided. In the present embodiment, the aperture 17 has a fixed numerical aperture so as to limit the light beam emitted from the first semiconductor laser 11 to a numerical aperture corresponding to the numerical aperture NA1. That is,
Even when recording / reproducing the second optical disc 20 ', the stop 1
The numerical aperture limited by 7 is a numerical aperture corresponding to NA1, and therefore, no extra mechanism for changing the numerical aperture of the diaphragm 17 is required, and cost reduction can be realized. However, when recording / reproducing the second optical disc 20 ', the second
The numerical aperture of the stop 17 may be variable so that the light beam emitted from the semiconductor laser 12 is limited to the numerical aperture corresponding to the numerical aperture NA2.

Beam splitters 25 and 2 serving as changing means
Reference numeral 6 denotes a light source (first semiconductor laser 11 and second semiconductor laser 1, respectively) for transmitting an optical path of a light beam reflected from the information recording surface.
This is a means for changing to an optical path different from the optical path of the light beam emitted from 2). That is, the beam splitters 25 and 26
Is a light source (first semiconductor laser 11, second semiconductor laser 1) between the beam splitters 25 and 26 and the optical disc.
This is means for making the optical path of the light beam emitted from 2) the same as the optical path of the light beam reflected from the information recording surface of the optical disk. The beam splitter 25 changes the optical path of the light beam emitted from the first semiconductor laser 11 without changing the optical path of the first optical disc 2.
The optical path of the light beam reflected from the information recording surface 22 of No. 0 is changed so as to be guided to the light detecting means 31 described later. Also,
The beam splitter 26 is formed of a plane-parallel plate (half mirror), and the optical path of the light beam emitted from the second semiconductor laser 12 is changed so as to be guided to the second optical disk 20 ', and the information recording surface 22' of the second optical disk 20 '. The light beam reflected from above is guided to the light detecting means 32 described later without changing the optical path. In the beam splitters 25 and 26, one of the optical paths to be changed may not be changed as in the present embodiment, and either one or both may be changed.

The light detecting means 31 and 32 are respectively connected to the optical discs 20 and 2 via beam splitters 25 and 26, respectively.
This is a means for detecting a light beam reflected from the 0 'information recording surface 22, 22'. By the light detecting means 31 and 32,
A change in the light amount distribution of the light beam reflected from the information recording surfaces 22, 22 'is detected, and a focus error signal, a tracking error signal, and a reproduction signal (information) are read by an arithmetic circuit (not shown).

In this embodiment, since the focus error signal is obtained by using the astigmatism method, the light detecting means 3
Before 1 and 32, an astigmatism generation element (in the present embodiment, the astigmatism generation element 27 is formed of a cylindrical lens, and the beam splitter 26 also serves as the astigmatism generation element) Although it is arranged, the focus error signal is not an astigmatism method but various known methods such as a knife edge method (including Foucault method), a phase difference detection (DPD) method, and a spot size detection (SSD) method. It can be detected by the method. As for the detection of the tracking error signal, the three-beam method and the phase difference detection (DP
It can be detected by various known methods such as D) method, push bull method and wobbling method.

The two-dimensional actuator 15 is means for moving the objective lens 16, and based on the focus error signal obtained by the above-mentioned arithmetic circuit, the two-dimensional actuator 15
For focusing control for moving the lens to a predetermined position (focusing and tracking) and for the objective lens 1 based on a track error signal.
6 for tracking control for moving the track 6 to a predetermined position (track following).

Next, such an optical pickup device 1 will be described.
0, the recording / reproducing of the first optical disc 20 will be briefly described.

A light beam (indicated by a two-dot chain line in FIG. 1) emitted from the first semiconductor laser 11 passes through a beam splitter 25, and its optical path is bent by a dichroic prism 19 toward a condensing optical system, and condensed. Light enters the optical system. The divergence of the light beam emitted from the first semiconductor laser 11 and incident on the condensing optical system is changed by the coupling lens 13, that is, the light beam is changed to a parallel light beam in the present embodiment. The luminous flux whose divergence has been changed in parallel by the coupling lens 13 is stopped down by the stop 17,
The light is focused on the information recording surface 22 via the transparent substrate 21 of the first optical disc 20 by the objective lens 16. And
In the case of recording on the first optical disc 20, recording is performed by this focused beam spot.

The light beam reflected by the information recording surface 22 passes through the condensing optical system (the objective lens 16 and the coupling lens 13) again, and passes through the dichroic prism 19,
The optical path is changed by the beam splitter 25, astigmatism is imparted by the cylindrical lens 27, and the light enters the light detection unit 31. Then, when reproducing the first optical disk 20, a reproduction signal of information recorded on the first optical disk 20 is obtained by using a signal output from the light detection unit 31. Further, a change in the light amount distribution due to a change in the spot shape on the light detecting means 31 is detected, and a focus error signal,
Obtain a tracking error signal. First semiconductor laser 11
The light beam emitted from the first optical disk 20 has an information recording surface 2
The objective lens 16 is moved by a two-dimensional actuator (for focusing control) 15 based on the obtained focus error signal so that an image is formed on the object 2. The two-dimensional actuator (for tracking control) 15 uses the objective lens 16 based on the obtained tracking error signal so that the light beam emitted from the first semiconductor laser 11 forms an image on a predetermined track of the first optical disc 20. To move.

As described above, information is recorded on the information recording surface 22 of the first optical disk 20 or information is reproduced on the information recording surface 22 of the first optical disk 20.

Similarly, when recording / reproducing on / from the second optical disc 20 ', the light beam (indicated by the dashed line in FIG. 1) emitted from the second semiconductor laser 12 is bent by the parallel plane plate 26, Dichroic prism 19,
The light passes through the coupling lens 13 (stopped by the stop 17) and the objective lens 16, and passes through the second optical disc 2.
The light is focused on the information recording surface 22 'via the 0' transparent substrate 21 '. Then, the light beam reflected by the information recording surface 22 'passes through the condensing optical system (the objective lens 16 and the coupling lens 13) and the dichroic prism 19 again.
The astigmatism is imparted by the parallel plane plate 26, and the light enters the light detection unit 32. Then, using the signal output from the light detection means 32, a reproduction signal, a focus error signal,
Obtain a tracking error signal. Second semiconductor laser 12
The objective lens 16 is moved by a two-dimensional actuator (for focusing control) 15 based on the obtained focus error signal so that the light beam emitted from the optical disc 20 'forms an image on the information recording surface 22' of the second optical disc 20 '. .
Further, based on the obtained tracking error signal, the two-dimensional actuator (for tracking control) 15 uses the objective lens 1 so that the light beam emitted from the second semiconductor laser 12 forms an image on a predetermined track of the second optical disc.
Move 6.

In this manner, information is recorded on the information recording surface 22 'of the second optical disc 20' or the second optical disc 2
The information on the 0 'information recording surface 22' is reproduced. In the drawing, the refracting surface S of the objective lens 16 on the optical disk side is shown.
The distance between the optical disk 2 and the optical disk surface (so-called working distance) is determined by the first optical disk 20 and the second optical disk 20 '.
Although both are described as the same distance, as will be apparent from the embodiment described later, the distance is different between the first optical disk 20 and the second optical disk 20 ′, and this distance is moved by the two-dimensional actuator (for focusing control) 15. Let me do. Therefore, as the two-dimensional actuator (for focusing control) 15, an actuator having a working distance capable of focusing both optical disks is used.

Next, the condensing optical system will be described. The condensing optical system is configured to divide a light beam emitted from the light sources 11 and 12 into at least two regions in a direction perpendicular to the optical axis (described later in detail with a specific example). For this purpose, a lens surface dividing portion that is substantially concentric with the optical axis is provided in the condensing optical system, thereby making the wavefront aberration discontinuous (not only separated but also bent). Thus, by providing the wavefront aberration discontinuously, an aperture limiting effect (aperture effect) can be obtained, and the recording / reproducing of the first optical disc 20 and the recording / reproducing of the second optical disc 20 'can be performed at the same time.
There is no need to change the numerical aperture limited by the stop 17, and cost reduction can be realized.

In the following description, in the case where one lens surface dividing portion is provided (two-region focusing optical system), the first area is on the optical axis side of the lens surface dividing portion, and the third region is outside the lens surface dividing portion.
The numerical aperture on the optical disk side of the light-converging optical system corresponding to the lens surface dividing portion is NA3. In the case where two lens surface dividing portions are provided, the first region is on the optical axis side of the lens surface dividing portion on the optical axis side, the second region is between the two lens surface dividing portions, and the outer lens surface dividing portion is provided. The area outside the portion is defined as a third area, and the numerical aperture on the optical disk side of the condensing optical system corresponding to the lens division on the optical axis side of the two lens surface divisions is defined as NA3. The numerical aperture on the optical disk side of the corresponding light collecting optical system is NA4. In the case where two lens surface division parts are provided, the second
The region may have a shielding structure (a structure in which light from a light source is absorbed, scattered, reflected, or the like to be shielded (essentially, a light beam corresponding to this portion is prevented from reaching the photodetector 32)). This is a shielded condensing optical system, and a three-region condensing optical system is used when a shielding structure is not used.)

Such a condensing optical system utilizes the luminous fluxes of the first and third areas when recording / reproducing on the first optical disc 20 and uses the first beam when recording / reproducing on the second optical disc 20 '.
The luminous flux in the area (and the luminous flux in the second area in the three-area focusing optical system) is used. Therefore, the luminous flux in the first area on the optical axis side of the lens surface dividing portion is used not only for recording / reproducing on the first optical disc 20 but also for recording / reproducing on the second optical disc 20 '.

However, such a two-region focusing optical system and a shielding focusing optical system in which the wavefront aberration (spherical aberration) is discontinuous cannot be adapted to the second optical disk which requires a high NA. This corresponds to the recording / recording of the first optical disc 20.
When an image is formed on the information recording surface 22 'of the second optical disc 20' with the magnification m1 of the objective lens 16 viewed from the first optical disc side during reproduction, the thicknesses t1, t of the transparent substrate
The difference between the two causes large spherical aberration. for that reason,
The upper limit of the light flux in the first area used when recording / reproducing the second optical disc 20 ', that is, the numerical aperture NA3 must be reduced. Therefore, when the two-region focusing optical system and the shield focusing optical system are used, it is not possible to cope with the second optical disk having a high NA. Also, when the three-area light condensing optical system is adapted to the second optical disk having a high NA, the light amount at the time of recording / reproducing on the first optical disk is greatly reduced.

Therefore, in the present embodiment, the magnification m1 of the objective lens 16 as viewed from the first optical disk 20 side during recording / reproducing of the first optical disk 20 (m1 = 0 in this embodiment because it is an infinite system). From the second optical disk 2
At the time of recording / reproduction of 0 ', the magnification m2 of the objective lens 16 as viewed from the second optical disk 20' side is made smaller. That is, the divergence of the light beam incident on the objective lens 16 is determined when recording / reproducing the first optical disc 20 and when comparing the second optical disc 2
By changing between 0 'and recording / reproducing, the spherical aberration component of wavefront aberration, which is important in the light condensing characteristics, is changed to cope with a higher NA. More specifically, the magnification m2 is determined by the thickness t1 of the transparent substrate 21 of the first optical disc 20 and the second optical disc 2
The direction is set so as to correct (over) spherical aberration caused by the difference between 0 'and the thickness t2 of the transparent substrate 21' (spherical aberration caused when passing through the transparent substrate 21 'having a thickness t2 at a magnification m1). (In other words, it causes negative spherical aberration).

As a result, the spherical aberration that occurs during recording / reproducing of the second optical disc 20 'is corrected, and the upper limit of the first light flux to be condensed when recording / reproducing the second optical disc 20', ie, the numerical aperture The NA3 can be increased, and it is possible to cope with a higher NA.

More specifically, in this embodiment, the position of the coupling lens 13 does not change between recording / reproducing on the first optical disc 20 and recording / reproducing on the second optical disc 20 '. The second semiconductor laser 12 is arranged so that the position of the second semiconductor laser 12 approaches the coupling lens 13. As described above, in the present embodiment, the second semiconductor laser 12 is more coupled to the coupling lens 1 than the first semiconductor laser 11.
3, the magnification m2 can be made smaller than the magnification m1, and it is possible to cope with a higher NA.

In this embodiment, the first and second semiconductor lasers 11 and 12 can be fixedly arranged by making the positions of the first and second semiconductor lasers 11 and 12 different from each other. Cost can be reduced,
At the time of recording / reproduction of the first optical disc 20 and the second optical disc 2
The position of the coupling lens 13 may be changed between the recording / reproducing of 0 '(in this case, the recording / reproducing of the second optical disk is moved closer to the light source). The distance between the second semiconductor laser 12 and the coupling lens 13 in the optical axis direction may be shorter than the distance between the laser 11 and the coupling lens 13 in the optical axis direction.

Here, it is preferable that m2-m1, which is the difference between the magnification m1 and the magnification m2, satisfies -0.05 <m2-m1 <-0.005, and -0.04 <m2-m1 It is more preferable to satisfy <-0.01.

If the lower limit is exceeded, that is, the magnification m1
When the difference between the magnification and the magnification m2 is large, the sine condition is greatly changed, so that the off-axis characteristics are deteriorated and high precision is required when assembling the optical pickup device. If the upper limit is exceeded, that is, if the difference between the magnification m1 and the magnification m2 is small, it is difficult to cope with an increase in NA.

By the way, in the condensing optical system thus configured, when recording / reproducing the first optical disc 20, the wavefront aberration of the beam spot formed on the information recording surface 22 by the luminous fluxes of the first area and the third area. Is 0.05λ1
By setting (rms) or less, recording / reproducing of the first optical disc 20 can be favorably performed. Further, when recording / reproducing the second optical disc 20 ', the first
By setting the wavefront aberration of the beam spot formed on the information recording surface 22 'by the light beam in the area to be 0.07λ2 (rms) or less, it is possible to perform good recording / reproduction on the second optical disc 20'. it can.

Further, in the present embodiment, the wavefront aberration is skipped (discontinuous) at the lens surface dividing portion to provide an aperture limiting effect. Therefore, in order to make use of this effect, the magnification m2 is set. In doing so, the spherical aberration is not completely corrected, but the spherical aberration is left. Therefore, the second
At the time of recording / reproducing of the optical disc 20 ', it is preferable that the wave spot aberration of the beam spot formed on the information recording surface 22' by the light flux of the first area is 0.025λ2 (rms) or more.

Next, a specific example of the condensing optical system will be described with reference to a three-region condensing optical system, a shield condensing optical system, and a two-region condensing optical system. The condensing optical system includes a coupling lens 13 and an objective lens 16, and the coupling lens 13 functions as a collimator lens at the time of recording / reproducing on the first optical disc 20, but is not limited to this.
Of the two refracting surfaces S1 and S2 of the objective lens 16, the lens surface dividing portion is provided on the refracting surface S1 on the light source side. However, the present invention is not limited to this, and the refracting surface S2 may be provided. 13 or a separate optical element. Further, in the present example, the second division surface Sd2 is provided in a ring (circle) shape concentric with the optical axis. However, the present invention is not limited to this, and the second division surface Sd2 may be provided in a concentric elliptical shape or an interrupted ring shape.

In each of the condensing optical systems, the first
The region may be divided into a plurality. Further, in the shield light condensing optical system and the three-area light condensing optical system, the second area is divided into a plurality of parts, and a part of the A surface used for recording / reproduction of one optical disk may be provided.

(Three-area focusing optical system) A description will be given with reference to FIG. 2 which is a schematic diagram and a spherical aberration diagram when recording / reproducing an optical disk by the three-area focusing optical system. FIG. 2A shows the objective lens 1 when recording / reproducing the first optical disc 20.
FIG. 2B is a diagram schematically showing a state in which a light beam passing through the optical disk 6 forms an image on the first optical disk 20, and FIG. 2B is a diagram showing spherical aberration on the information recording surface 22 of the first optical disk 20; (C) shows a light beam passing through the objective lens 16 when recording / reproducing on the second optical disc 20 '.
FIG. 2 is a diagram schematically showing an image formed at 0 '.
(D) is a diagram of spherical aberration on the information recording surface 22 'of the second optical disc 20'. The spherical aberration indicated by the broken line in FIG. 2D is the spherical aberration when the image is formed on the information recording surface 22 'of the second optical disk 20' at the magnification m1 during recording / reproduction of the first optical disk 20. It represents aberration.

In this embodiment, the objective lens 16 is a convex lens having a positive refractive power, in which both the refracting surface S1 on the light source side and the refracting surface S2 (final refracting surface) on the optical disk side have an aspherical shape. The refracting surface S1 of the objective lens 16 is divided into three first divided surfaces Sd1 to third divided surfaces Sd3 substantially concentrically with the optical axis.
(Corresponding to the first to third regions in the above description), and the boundaries between the divided surfaces Sd1 to Sd3 are provided with steps. This step is a lens surface dividing portion, and has a numerical aperture NA3,
It is provided at a position corresponding to NA4, at which wavefront aberration is discontinuous.

As shown in FIGS. 2A and 2B, when recording / reproducing the first optical disc 20, the objective lens 16 has a magnification m1 = 0, so that the parallel light beam is
6 is incident. Then, the first light beam and the third light beam passing through the first division surface Sd1 and the third division surface Sd3 form an image on the information recording surface 22 of the first optical disk. At this time, the first
The wave spot aberration of the beam spot formed on the information recording surface 22 by the light beam and the third light beam is 0.05λ1 (rms).
It is as follows. On the other hand, the second light flux (the light flux indicated by the broken line) passing through the second division surface Sd2 forms an image below the information recording surface 22 of the first optical disc 20 below. Therefore, at the time of recording / reproducing on the first optical disk, the first light beam and the third light beam are converged on the information recording surface 22 of the first optical disk, and the recording / reproducing of the first optical disk 20 is performed.

The objective lens 16 is connected to the first optical disc 2
0 at the recording / reproducing magnification m1 of the second optical disc 20 '.
When an image is formed on the information recording surface 22 ', a large spherical aberration is generated due to the difference between the thicknesses t1 and t2 of the transparent substrate as shown by the broken line in FIG. In the present embodiment,
The magnification m2 at the time of recording / reproduction of the second optical disc 20 'is represented by m
By setting it to be smaller than 1, the large spherical aberration is corrected as shown by the solid line in FIG. 2D.

Therefore, when recording / reproducing the second optical disk 20 '(see FIGS. 2C and 2D), the magnification m
Since 2 <m1, the divergent light beam enters the objective lens 16. Then, the first light flux (indicated by oblique lines rising to the right) and the second light flux (indicated by oblique lines descending to the right) form an image substantially on the information recording surface 22 'of the second optical disc 20'. At this time, the wave spot aberration of the beam spot formed on the information recording surface 22 'by the first light beam is 0.07λ2 (rms) or less. On the other hand, a third light flux (shown partly by a broken line)
Occurs as a flare. Therefore, the second optical disc 2
On the information recording surface 22 'of 0', a nucleus is mainly formed by the first and second light beams, and a beam spot shape is formed around the nucleus by the third light beam. / Reproduction is performed.

As described above, the three-region objective lens 16 can use the area between the numerical apertures NA3 and NA4 (that is, the second division surface Sd2) for recording / reproducing the second optical disc 20 '. Therefore, by optimizing the wavefront aberration of this portion, it is possible to keep the wavefront aberration of the first light beam small while recording / reproducing the second optical disc 20 'while maintaining a high N
A.

It is preferable that the three-region objective lens 16 satisfies the condition 0.7NA2 <NA3 <1.05NA2. If the lower limit is exceeded, the recording / reproducing of the first optical disc 20 will be insufficient in light quantity, depending on the numerical aperture NA2. If the upper limit is exceeded, the spot diameter will be narrowed more than necessary, and the difference between the magnification m1 and the magnification m2 will increase and the sine condition will change significantly. Assembly accuracy of the pickup device 10 is required.

[0067] Further, it is preferable to satisfy ^{0.04 <(NA4 2 -NA3 2)} / NA1 2 <0.4 conditions. If the lower limit is exceeded, the second optical disk 20 'will not be able to read / write the second optical disk 20'.
The effect of increasing the NA by the light beam is reduced. In other words, this is a three-region focusing optical system that can cope with a higher NA than other focusing optical systems (a two-region focusing optical system and a shielding focusing optical system described in detail later). If the lower limit is exceeded, the shape of the stepped portion (working of the mold) causes drooping, so that there is no difference from the two-region objective lens 16 (condensing optical system) described later. If the upper limit is exceeded, a shortage of light quantity occurs during recording / reproduction of the first optical disc.

Further, in the three-region objective lens 16,
Numerical aperture N during recording / reproduction of second optical disc 20 '
The spherical aberration SA3 (1) generated in the light beam passing through the first division surface Sd1 at the position of A3 and the spherical aberration amount S3 generated in the light beam passing through the third division surface Sd3 at the position of the numerical aperture NA4.
Assuming that the difference δ is A4 (3) (see FIG. 2D), it is preferable that the condition of 0.002 mm <δ <0.020 mm is satisfied. Beyond this lower limit,
At the time of recording / reproducing of the second optical disc 20 ', the side lobe of the spot increases, and a problem such as asymmetry of the focus error signal occurs. Also, if you exceed the upper limit,
At the time of recording / reproduction of the first optical disc 20 and the second optical disc 2
It is not possible to balance between 0 'recording / reproduction and
It cannot be performed well. Even if the lower limit is exceeded, the asymmetry of the focus error signal can be improved if the aperture limit that moves together with the objective lens 16 during tracking during recording / reproduction of the second optical disc 20 'is performed. Therefore, there is no need to set this lower limit.

The difference δ is different from the second optical disc 20 ′
Since it is based on the distance between the nucleus of the spot and the flare generated during recording / reproducing of the light, attention is paid to the boundary between individual regions (each light flux), and the micrometer is changed while observing interference fringes and changing the defocus. Measure with

In this example, the first divided surface Sd1 to the third divided surface Sd1
Although a step is provided at each of the boundaries of the division surface Sd3, a step may be provided at only one of the boundaries.
The connection may be made on a surface having a predetermined radius of curvature. In short, it is sufficient that the wavefront aberration is discontinuous (bending or the like is preferable, but separating (flying) is preferable) in the lens surface dividing portion.

Further, in the present embodiment, the second divided surface Sd2 of the objective lens 16 has an aspherical shape, but may be constituted by a hologram (or Fresnel). Note that the second division surface Sd
When the hologram 2 is formed, one of the 0th-order light and the 1st-order light flux is used for recording / reproduction of the first optical disk, and the other is used for recording / reproduction of the second optical disk. At this time, it is preferable that the light amount of the light beam used for recording / reproducing on the second optical disk is larger than the light amount of the light beam used for recording / reproducing on the first optical disk.

In the present embodiment, the second divided surface Sd2
Instead of or in addition to this, a phase difference is provided, that is, the phase of the light beam passing through the second division surface Sd2 is changed to the first division surface Sd1.
And the phase of the light beam passing through the third division surface Sd3 may be shifted.

In the present embodiment, the first division surface Sd1
And the third division surface Sd3 are formed in the same aspherical shape, but a phase difference is provided between the first division surface Sd1 and the third division surface Sd3 so that the spot in the recording / reproducing of the first optical disc 20 can be formed. May be controlled.

(Shielding and Condensing Optical System) A description will be given with reference to FIG. 3 which is a schematic diagram and a spherical aberration diagram when recording / reproducing an optical disk by the shielding and condensing optical system. FIG. 3A is a diagram schematically showing a state in which a light beam passing through the objective lens 16 forms an image on the first optical disc 20 during recording / reproduction on the first optical disc 20, and FIG. 1 optical disk 20
FIG. 3 is a spherical aberration diagram on the information recording surface 22 of FIG.
FIG. 3C shows that the light beam passing through the objective lens 16 at the time of recording / reproducing on the second optical disc 20 'is changed to the second optical disc 20'.
FIG. 3D is a diagram schematically showing a state in which an image is formed on the information recording surface 22 ′ of the second optical disc 20 ′. The spherical aberration indicated by a broken line in FIG. 3D is the spherical aberration when an image is formed on the information recording surface 22 'of the second optical disk 20' at the magnification m1 during recording / reproduction of the first optical disk 20. It represents aberration.

In this embodiment, the objective lens 16 is a convex lens having a positive refractive power, in which both the refraction surface S1 on the light source side and the refraction surface S2 (final refraction surface) on the optical disk side have an aspherical shape. A shielding structure SH is provided on the refraction surface S1 of the objective lens 16 by vapor-depositing a substance that absorbs light from a light source substantially concentrically with the optical axis. By providing this shielding structure SH, the refraction surface S1 of the objective lens 16 can be divided into a first division surface Sd1, a third division surface Sd3 that transmits light from the light source, and a second division surface Sd2 that shields light from the light source. It is composed of three divided surfaces (corresponding to the above-described first region, third region, and second region, respectively). The boundary between the divided surfaces Sd1 to Sd3 is a lens surface divided portion, which is provided at a position corresponding to the numerical apertures NA3 and NA4.
Wavefront aberration jumps between and becomes discontinuous.

As shown in FIGS. 3A and 3B, when recording / reproducing the first optical disc 20, the objective lens 16 has a magnification of m1 = 0, so that the parallel light beam is
6 is incident. Then, the first light beam and the third light beam passing through the first division surface Sd1 and the third division surface Sd3 form an image on the information recording surface 22 of the first optical disk. At this time, the first
The wave spot aberration of the beam spot formed on the information recording surface 22 by the light beam and the third light beam is 0.05λ1 (rms).
It is as follows. On the other hand, the light beam that reaches the second division surface Sd2, that is, the second light beam is absorbed by the shielding structure SH without transmitting. Therefore, at the time of recording / reproducing on the first optical disk, the first light beam and the third light beam are converged on the information recording surface 22 of the first optical disk, and the recording / reproducing of the first optical disk 20 is performed.

The objective lens 16 is connected to the first optical disc 2
0 at the recording / reproducing magnification m1 of the second optical disc 20 '.
When the image is formed on the information recording surface 22 ', a large spherical aberration occurs due to the difference between the thicknesses t1 and t2 of the transparent substrate as shown by the broken line in FIG. In the present embodiment,
The magnification m2 at the time of recording / reproduction of the second optical disc 20 'is represented by m
By making the value smaller than 1, the large spherical aberration is corrected as shown by the solid line in FIG. 3D.

Therefore, when recording / reproducing the second optical disc 20 '(see FIGS. 3 (c) and 3 (d)), the magnification m
Since 2 <m1, the divergent light beam enters the objective lens 16. Then, the first light flux (indicated by oblique lines) forms an image substantially on the information recording surface 22 'of the second optical disc 20'. At this time, the wave spot aberration of the beam spot formed on the information recording surface 22 'by the first light beam is 0.07λ2 (rms) or less. On the other hand, a third light flux (shown partly by a broken line)
Is generated as a flare and reaches the second division surface Sd2, that is, the second light beam is absorbed by the shielding structure SH without transmitting. Therefore, on the information recording surface 22 'of the second optical disk 20', a nucleus is formed by the first light beam, and a beam spot is formed around the nucleus by a flare caused by the third light beam.
Recording / reproduction of 0 'is performed.

As described above, the shielding objective lens 16 is provided with the shielding structure SH between the numerical apertures NA3 and NA4 (ie, the second division surface Sd2), so that the recording / reproducing of the second optical disc 20 'is performed. In this case, the spherical aberration (wavefront aberration) of this portion (second region) jumps, becomes discontinuous, and the influence of flare can be reduced. Further, since m2 <m1, spherical aberration caused by the difference between the thicknesses t1 and t2 of the transparent substrate during recording / reproduction of the second optical disc 20 'can be reduced, and a high NA can be achieved.

In the shielding objective lens 16, the boundary between the positions of the numerical aperture NA3 serves as an aperture limit, and preferably satisfies the condition of 0.9NA2 <NA3 <1.2NA2. If the lower limit is exceeded, the spot diameter cannot be reduced during recording / reproduction of the second optical disc 20 '. If the upper limit is exceeded, the spot diameter will be narrowed more than necessary, and the difference between the magnification m1 and the magnification m2 will increase and the sine condition will change significantly. Pickup device 10
Assembly accuracy is required.

Further, in the shielding objective lens 16, the numerical aperture NA when recording / reproducing the second optical disc 20 'is set.
The amount of spherical aberration SA3 (1) generated in the light beam passing through the first division surface Sd1 at the position of No. 3 and the third aberration at the position of the numerical aperture NA4
Spherical aberration SA generated in a ray passing through division surface Sd3
4 (3) and the difference δ (see FIG. 3D), it is preferable that the condition of 0.002 mm <δ <0.020 mm is satisfied. Beyond this lower limit,
At the time of recording / reproducing of the second optical disc 20 ', the side lobe of the spot increases, and a problem such as asymmetry of the focus error signal occurs. Also, if you exceed the upper limit,
At the time of recording / reproduction of the first optical disc 20 and the second optical disc 2
It is not possible to balance between 0 'recording / reproduction and
It cannot be performed well. Even if the lower limit is exceeded, the asymmetry of the focus error signal can be improved if the aperture limit that moves together with the objective lens 16 during tracking during recording / reproduction of the second optical disc 20 'is performed. Therefore, there is no need to set this lower limit. In addition,
The measurement of the difference δ is the same as that of the above-described three-area light condensing optical system, and will not be described.

(Two-area focusing optical system) A description will be given with reference to FIG. 4 which is a schematic diagram and a spherical aberration diagram when recording / reproducing an optical disk by the two-area focusing optical system. FIG. 4A shows the objective lens 1 when recording / reproducing the first optical disc 20.
FIG. 4B is a diagram schematically showing a state in which a light beam passing through the optical disk 6 forms an image on the first optical disk 20, and FIG. 4B is a diagram of spherical aberration on the information recording surface 22 of the first optical disk 20; (C) shows a light beam passing through the objective lens 16 when recording / reproducing on the second optical disc 20 '.
FIG. 4 is a view schematically showing an image formed at 0 '.
(D) is a diagram of spherical aberration on the information recording surface 22 'of the second optical disc 20'. The spherical aberration indicated by a broken line in FIG. 4D is the spherical aberration when an image is formed on the information recording surface 22 'of the second optical disc 20' at the magnification m1 during recording / reproduction of the first optical disc 20. It represents aberration.

In this embodiment, the objective lens 16 is a convex lens having a positive refractive power, in which both the refracting surface S1 on the light source side and the refracting surface S2 (final refracting surface) on the optical disk side have an aspherical shape. The refraction surface S1 of the objective lens 16 is constituted by two first division surfaces Sd1 and third division surfaces Sd3 substantially concentrically with the optical axis (corresponding to the above-described first and third regions), and each division surface Sd1 , Sd3 have a step. This step is a lens surface dividing portion, which is provided at a position corresponding to the numerical aperture NA3, at which wavefront aberration becomes discontinuous.

As shown in FIGS. 4A and 4B, when recording / reproducing the first optical disc 20, the objective lens 16 has a magnification of m1 = 0 so that the parallel light beam is
6 is incident. Then, the first light beam and the third light beam passing through the first division surface Sd1 and the third division surface Sd3 are substantially image-formed on the information recording surface 22 of the first optical disk. At this time,
The wavefront aberration of the beam spot formed on the information recording surface 22 by the first light beam and the third light beam is 0.05λ1 (rm
s) Therefore, recording / writing on the first optical disc
At the time of reproduction, the first light beam and the third light beam are focused on the information recording surface 22 of the first optical disk, and recording / reproduction of the first optical disk 20 is performed.

The objective lens 16 is connected to the first optical disc 2
0 at the recording / reproducing magnification m1 of the second optical disc 20 '.
When an image is formed on the information recording surface 22 ', a large spherical aberration occurs due to the difference between the thicknesses t1 and t2 of the transparent substrate as shown by the broken line in FIG. In the present embodiment,
The magnification m2 at the time of recording / reproduction of the second optical disc 20 'is represented by m
By setting it to be smaller than 1, the large spherical aberration is corrected as shown by the solid line in FIG. 4D.

Therefore, when recording / reproducing the second optical disk 20 '(see FIGS. 4C and 4D), the magnification m
Since 2 <m1, the divergent light beam enters the objective lens 16. Then, the first light flux (indicated by oblique lines) forms an image substantially on the information recording surface 22 'of the second optical disc 20'. At this time, the wave spot aberration of the beam spot formed on the information recording surface 22 'by the first light beam is 0.07λ2 (rms) or less. On the other hand, a third light flux (shown partly by a broken line)
Occurs as a flare. Therefore, the second optical disc 2
On the information recording surface 22 'of the optical disk 0', a nucleus is formed by the first light beam, and a beam spot is formed around the nucleus by a flare caused by the third light beam. Will be

As described above, since the two-region objective lens 16 has a step at the position of the numerical aperture NA3, when recording / reproducing the second optical disc 20 ', spherical aberration (wavefront aberration) of this portion is reduced. Jumps and discontinuities reduce the effects of flare. Since m2 <m1, the second
The thickness t1 of the transparent substrate when recording / reproducing the optical disc 20 '
And t2 can be reduced, and the NA can be increased.

In the two-region objective lens 16, the step at the position of the numerical aperture NA3 plays a role of limiting the aperture, and preferably satisfies the condition of 0.9NA2 <NA3 <1.2NA2. If the lower limit is exceeded, the spot diameter cannot be reduced during recording / reproduction of the second optical disc 20 '. If the upper limit is exceeded, the spot diameter will be narrowed more than necessary, and the difference between the magnification m1 and the magnification m2 will increase and the sine condition will change significantly. Pickup device 10
Assembly accuracy is required.

Further, in the two-region objective lens 16,
Numerical aperture N during recording / reproduction of second optical disc 20 '
The spherical aberration SA3 (1) generated in the light beam passing through the first division surface Sd1 at the position of A3 and the spherical aberration amount S3 generated in the light beam passing through the third division surface Sd3 at the position of the numerical aperture NA3.
Assuming that the difference δ is A3 (3) (see FIG. 4D), it is preferable that the condition of 0.002 mm <δ <0.010 mm is satisfied. Beyond this lower limit,
At the time of recording / reproducing of the second optical disc 20 ', the side lobe of the spot increases, and a problem such as asymmetry of the focus error signal occurs. Also, if you exceed the upper limit,
At the time of recording / reproduction of the first optical disc 20 and the second optical disc 2
It is not possible to balance between 0 'recording / reproduction and
It cannot be performed well. Even if the lower limit is exceeded, the asymmetry of the focus error signal can be improved if the aperture limit that moves together with the objective lens 16 during tracking during recording / reproduction of the second optical disc 20 'is performed. Therefore, there is no need to set this lower limit. In addition,
The measurement of the difference δ is the same as that of the above-described three-area light condensing optical system, and will not be described.

In this example, the first divided surface Sd1 and the third divided surface Sd1
Although the step is provided at the boundary with the division surface Sd3, the connection may be made not at the step but at a surface having a predetermined radius of curvature.

Further, in this example, unlike the above-mentioned shielded objective lens, the objective lens 16 can control the phase jump (δ) in the boundary region, and can control the recording / reproducing of the first optical disc 20 with respect to the peak intensity. It is possible to balance between reproduction and recording / reproduction of the second optical disc 20 '.

In the embodiment described above, the first semiconductor laser 11 used for recording / reproducing on the first optical disc 20 and the recording / reproducing on the second optical disc 20 'are used as light sources.
The optical pickup device 10 uses a second semiconductor laser 12 used for reproduction. As shown in FIG. 5, only the first semiconductor laser 11, that is, the first semiconductor laser 11 is used.
Also serves as the second semiconductor laser 12 and the second optical disc 2
It may be used for recording / reproduction of 0 '.

This optical pickup device will be described briefly. Note that the same functions, functions, and members as those of the above-described embodiment are given the same reference numerals, and description thereof may be omitted.

In this optical pickup device, the first semiconductor laser 11, which is the first light source, the light detecting means 31, the parallel plane plate 25 serving also as the changing means 25 and the astigmatism generating element 27 in the above-described embodiment. , 27 are integrated as a unit 41. And this unit 4
1 is provided movably by the moving means 40. Also, the first optical disc, the second optical disc, and the second
Since recording / reproducing is performed on an optical disk, the second semiconductor laser 12, the synthesizing means 19, and the plane-parallel plate 2
6. The light detection means 32 is omitted.

When recording / reproducing the first optical disk, the light beam emitted from the first semiconductor laser 11 (2 in FIG. 5)
(Indicated by a dashed-dotted line) is bent by the beam splitters 25 and 27, turned into a parallel light beam by the coupling lens 13 (in this case, the magnification is m1 = 0), is stopped down by the stop 17, and is stopped by the objective lens 16. The light is focused on the information recording surface via the transparent substrate of the first optical disc. Then, the light beam reflected by the information recording surface is condensed again by the condensing optical system (the objective lens 16, the coupling lens 1).
After passing through 3), astigmatism is given by the beam splitters 25 and 27, and the light enters the light detecting means 31. Then, a reproduction signal, a focus error signal, and a tracking error signal are obtained using the signal output from the light detection means 31.

When recording / reproducing the second optical disk with this optical pickup device, the unit 41 is moved by the moving means 40 so as to have the magnification m2 as described in the above-described embodiment (the broken line in FIG. 5). Position). Then, recording / reproducing of the second optical disk is performed in the same manner as described above. In FIG. 5, the dashed line indicates the outermost light beam of the light beam emitted from the first semiconductor laser 11 when recording / reproducing the second optical disk, which is stopped down by the stop 17 (described later).

As described above, this optical pickup device can be composed of one light source and one photodetector, and can be a compact optical pickup device. Instead of moving the light source as in the optical pickup device, the magnifications m1 and m2 may be changed by moving the coupling lens 13.

In the above description, since the thickness t1 of the transparent substrate of the first optical disc having a high recording density is smaller than the thickness t2 of the transparent substrate of the second optical disc having a lower recording density than the first optical disc, m1 However, when the recording density is high and the thickness t1 of the transparent substrate of the first optical disc is higher than the transparent substrate thickness t2 of the second optical disc whose recording density is lower than the first optical disc, m1 <m2. do it.

[0099]

Embodiments of the present invention will be described below. In each of the following embodiments, the coupling lens 13
Optimizing the design, assuming that a lens capable of entering an aberration-free parallel light to the objective lens 16 for focusing on the information recording surface 22 of the first optical disc 20 is used.
The configuration after the stop 17 arranged on the light source side of the objective lens 16 is shown. Therefore, in the table showing paraxial optical data, the stop 17 is set as the first surface, the i-th position is set in this order according to the traveling direction of light, and the information recording surface of the optical disk is shown. Also, r is the radius of curvature of the surface intersecting the optical axis, d is the distance between the i-th surface and the (i + 1) -th surface, and n is the refractive index at the wavelength of the luminous flux of the semiconductor laser to be used. Represents. Incidentally, the sign indicates that the traveling direction of light is positive.

In the tables showing the aspherical surface data in each of the following examples,

[0101]

(Equation 1)

It is assumed that the above equation is based on the aspherical surface equation. Where X is the axis in the optical axis direction, H is the axis perpendicular to the optical axis, and the light traveling direction is positive, K is the conic coefficient, Aj is the aspherical coefficient,
Pj is the power of the aspheric surface.

The wavefront aberration diagrams in each of the following embodiments are shown when viewed at a position where the best wavefront aberration is obtained in a defocused state.

(Embodiment 1) The embodiment 1 is an optical pickup device shown in FIG. 1 equipped with a three-region objective lens 16, wherein a DVD is used as a first optical disc and a CD (CD-R is reproduced as a second optical disc). ).

Table 2 shows paraxial optical data.

[0106]

[Table 2]

Table 3 shows aspherical surface data.

[0108]

[Table 3]

Note that “d2 = 2.
"1995" represents the interval on the optical axis from the intersection with the optical axis when the shape of the second aspherical surface (second divided surface) is extended to the optical axis according to the aspherical surface equation. I have.

FIG. 6A shows a spherical aberration diagram when reproducing a DVD, and FIG. 6B shows a spherical aberration diagram when reproducing a CD.
FIG. 6C shows a wavefront aberration diagram at the time of DVD reproduction, and FIG.
The wavefront aberration diagram at the time of D reproduction is shown. FIG. 7A shows the DV.
FIG. 7B shows a relative intensity distribution diagram of the converged spot when the best spot shape during D reproduction is obtained, and FIG. 7B shows a relative intensity distribution of the converged spot when the best spot shape during CD reproduction is obtained. The distribution map is shown. In this embodiment, the spherical aberration SA3 generated in the light beam passing through the first division surface Sd1 at the position of the numerical aperture NA3 at the time of recording / reproducing a CD.
The difference δ between (1) and the spherical aberration SA4 (3) generated in the light beam passing through the third division surface Sd3 at the position of the numerical aperture NA4.
Is δ = 0.040 mm.

As can be seen from the above, in the present embodiment, DVDs and CDs (CD-R) can be reproduced favorably.

(Embodiment 2) Embodiment 2 is an optical pickup device shown in FIG. 1 on which a three-region objective lens 16 is mounted, wherein a DVD is used as a first optical disk and a CD (CD-R is reproduced as a second optical disk). ). Note that this three-region objective lens has the first divided surface Sd1 and the third divided surface Sd1.
This is provided with a phase difference of 2π from the division surface Sd3. Note that in this case, the rms value of the wavefront aberration is calculated (measured) using the phase difference 2nπ as a parameter and n that minimizes the rms value.

Table 4 shows paraxial optical data.

[0114]

[Table 4]

Table 5 shows aspherical surface data.

[0116]

[Table 5]

Note that “d2 = 2.
“19975” represents the distance on the optical axis from the intersection with the optical axis when the shape of the second aspherical surface (second divided surface) is extended to the optical axis in accordance with the aspherical surface equation. I have. Further, “d3 = 2.22014” of the third aspheric surface in Table 5 is the optical axis when the shape of the third aspheric surface (third divided surface) is extended to the optical axis in accordance with the formula of the aspheric surface shape. Represents the interval on the optical axis from the intersection of to the next surface.

FIG. 8A shows a spherical aberration diagram at the time of reproducing a DVD, and FIG. 8B shows a spherical aberration diagram at the time of reproducing a CD.
FIG. 8C shows a wavefront aberration diagram at the time of reproducing the DVD, and FIG.
The wavefront aberration diagram at the time of D reproduction is shown. FIG. 9A shows the DV.
FIG. 9B shows a relative intensity distribution diagram of the converged spot when the best spot shape at the time of D reproduction is obtained. FIG. 9B shows a relative intensity distribution of the condensed spot at the time of obtaining the best spot shape at the time of CD reproduction. The distribution map is shown. In this embodiment, the spherical aberration SA3 generated in the light beam passing through the first division surface Sd1 at the position of the numerical aperture NA3 at the time of recording / reproducing a CD.
The difference δ between (1) and the spherical aberration SA4 (3) generated in the light beam passing through the third division surface Sd3 at the position of the numerical aperture NA4.
Is δ = 0.0033 mm.

As can be seen from the above, in this embodiment, DVDs and CDs (CD-Rs) can be reproduced favorably.

(Embodiment 3) Embodiment 3 is an optical pickup device shown in FIG. 1 equipped with a three-region objective lens 16, using a DVD as a first optical disk and an LD as a second optical disk. .

Table 6 shows paraxial optical data.

[0122]

[Table 6]

Table 7 shows the aspherical surface data.

[0124]

[Table 7]

Note that “d2 = 2.
"1996" represents the interval on the optical axis from the intersection with the optical axis when the shape of the second aspherical surface (second divided surface) is extended to the optical axis according to the aspherical surface equation. I have.

FIG. 10A shows a spherical aberration diagram at the time of reproducing the DVD, and FIG. 10B shows a spherical aberration diagram at the time of reproducing the LD.
FIG. 10C shows a wavefront aberration diagram during DVD reproduction, and FIG. 10D shows a wavefront aberration diagram during LD reproduction. Further, FIG. 11A shows a relative intensity distribution diagram of the condensed spot when the best spot shape at the time of DVD reproduction is obtained, and FIG. 11B shows the best spot shape at the time of LD reproduction. The relative intensity distribution diagram of the focused spot at the time is shown. In this embodiment,
First position of numerical aperture NA3 during recording / reproduction of LD
Spherical aberration SA generated in a light beam passing through division surface Sd1
3 (1) and the amount of spherical aberration SA4 (3) generated in the light beam passing through the third divided surface Sd3 at the position of the numerical aperture NA4, and the difference δ
Is δ = 0.0066 mm.

As can be seen from the above, in the present embodiment, DVD and LD can be reproduced well.

(Embodiment 4) Embodiment 4 is an optical pickup device shown in FIG. 5 on which a three-region objective lens 16 is mounted, in which a DVD is used as a first optical disk and an MO is used as a second optical disk. .

Table 8 shows paraxial optical data.

[0130]

[Table 8]

Table 9 shows the aspherical surface data.

[0132]

[Table 9]

Note that “d2 = 2.
“1997” represents a distance on the optical axis from the intersection with the optical axis when the shape of the second aspherical surface (second divided surface) is extended to the optical axis according to the formula of the aspherical shape. I have.

FIG. 12A is a spherical aberration diagram during DVD reproduction, and FIG. 12B is a spherical aberration diagram during MO reproduction.
(C) A wavefront aberration diagram at the time of DVD reproduction is shown in FIG.
The wavefront aberration diagram at the time of O reproduction is shown. Further, FIG.
FIG. 13B shows a relative intensity distribution chart of the converged spot when the best spot shape is obtained during VD reproduction. FIG. 13B shows a relative intensity distribution of the condensed spot when the best spot shape is obtained during MO reproduction. The distribution map is shown. In this embodiment, M
The amount of spherical aberration SA3 generated in the light beam passing through the first division surface Sd1 at the position of the numerical aperture NA3 at the time of recording / reproducing O
The difference δ between (1) and the spherical aberration SA4 (3) generated in the light beam passing through the third division surface Sd3 at the position of the numerical aperture NA4.
Is δ = 0.0086 mm.

As can be seen from the above, in this embodiment, two optical disks, DVD and MO, can be favorably reproduced.

(Embodiment 5) Embodiment 5 is the optical pickup device shown in FIG. 1 equipped with a two-region objective lens 16, using a DVD as the first optical disk and a CD as the second optical disk. .

Table 10 shows paraxial optical data.

[0138]

[Table 10]

Table 11 shows aspherical surface data.

[0140]

[Table 11]

Note that “d2 =
2.20 ”means the distance on the optical axis from the intersection with the optical axis when the shape of the second aspherical surface (second division surface) is extended to the optical axis according to the aspherical surface equation. Is represented.

FIG. 14A is a spherical aberration diagram at the time of reproducing a DVD, and FIG. 14B is a spherical aberration diagram at the time of reproducing a CD.
FIG. 14C shows a wavefront aberration diagram at the time of reproducing the DVD, and FIG. 14D shows a wavefront aberration diagram at the time of reproducing the CD. FIG. 15A shows a relative intensity distribution diagram of the converging spot when the best spot shape at the time of reproducing a DVD is obtained, and FIG. 15B shows a spot shape at the time of reproducing a CD. The relative intensity distribution diagram of the focused spot at the time is shown. In this embodiment,
First position of numerical aperture NA3 during recording / reproducing of CD
Spherical aberration SA generated in a light beam passing through division surface Sd1
3 (1) and the amount of spherical aberration SA3 (3) generated in the light beam passing through the third division surface Sd3 at the position of the numerical aperture NA3, and the difference δ
Is δ = 0.0012 mm.

As can be seen from the above, in this embodiment, DVDs and CDs can be reproduced favorably.

(Embodiment 6) Embodiment 6 is the optical pickup device shown in FIG. 1 on which the shielding objective lens 16 is mounted, using a DVD as the first optical disk and a CD as the second optical disk.

Table 12 shows paraxial optical data.

[0146]

[Table 12]

Table 13 shows the aspherical surface data.

[0148]

[Table 13]

FIG. 16A shows a spherical aberration diagram at the time of reproducing a DVD, and FIG. 16B shows a spherical aberration diagram at the time of reproducing a CD.
FIG. 16C shows a wavefront aberration diagram when reproducing a DVD, and FIG. 16D shows a wavefront aberration diagram when reproducing a CD. Further, FIG. 17A shows a relative intensity distribution diagram of the converging spot when the best spot shape at the time of reproducing the DVD is obtained, and FIG. 17B shows the best spot shape at the time of reproducing the CD. The relative intensity distribution diagram of the focused spot at the time is shown. In this embodiment,
First position of numerical aperture NA3 during recording / reproducing of CD
Spherical aberration SA generated in a light beam passing through division surface Sd1
3 (1) and the amount of spherical aberration SA4 (3) generated in the light beam passing through the third divided surface Sd3 at the position of the numerical aperture NA4, and the difference δ
Is δ = 0.0034 mm.

As can be seen from the above, in this embodiment, DVDs and CDs can be reproduced favorably.

[0151]

As described in detail above, according to the present invention,
A single light condensing optical system can record / reproduce a plurality of optical information recording media having different thicknesses of the transparent substrate, can cope with a high NA, and can cope with a high NA second optical disc. In addition, recording / reproducing of the first optical disk can be performed well.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical pickup device.

FIG. 2 is a schematic diagram and a spherical aberration diagram when recording / reproducing an optical disc by a three-area light condensing optical system.

3A and 3B are a schematic diagram and a spherical aberration diagram, respectively, during recording / reproducing of an optical disk by a shielded condensing optical system.

4A and 4B are a schematic diagram and a spherical aberration diagram, respectively, during recording / reproducing of an optical disk by a two-area focusing optical system.

FIG. 5 is a schematic configuration diagram of an optical pickup device.

FIG. 6 shows a spherical aberration diagram and a wavefront aberration diagram of Example 1.

FIG. 7 is a diagram illustrating a relative intensity distribution of a condensed spot according to the first embodiment.

FIG. 8 shows a spherical aberration diagram and a wavefront aberration diagram of Example 2.

FIG. 9 is a diagram showing a relative intensity distribution of a condensed spot according to the second embodiment.

FIG. 10 shows a spherical aberration diagram and a wavefront aberration diagram of Example 3.

FIG. 11 is a diagram showing a relative intensity distribution of a condensed spot according to the third embodiment.

FIG. 12 shows a spherical aberration diagram and a wavefront aberration diagram of Example 4.

FIG. 13 is a diagram showing a relative intensity distribution of a condensed spot according to the fourth embodiment.

14A and 14B are a spherical aberration diagram and a wavefront aberration diagram of Example 5.

FIG. 15 is a diagram showing a relative intensity distribution of a condensed spot according to the fifth embodiment.

16A and 16B are a spherical aberration diagram and a wavefront aberration diagram of Example 6.

FIG. 17 is a diagram showing a relative intensity distribution of a condensed spot according to the sixth embodiment.

[Explanation of symbols]

 Reference Signs List 10 optical pickup device 11 first light source 12 second light source 13 coupling lens 15 two-dimensional actuator 16 objective lens 17 aperture 19 dichroic prism 20 first optical disk 20 'second optical disk 21, 21' transparent substrate 22, 22 'information recording surface 25, 26 beam splitters 31, 32 light detecting means 40 moving means

Claims (11)

[Claims] The thickness of a transparent substrate is increased by providing a condensing optical system including an objective lens with a function of dividing a light beam emitted from a light source into at least two regions in a direction perpendicular to an optical axis. For the first optical information recording medium at t1,
A light beam emitted from a first light source (wavelength λ1 (nm)) is condensed on an information recording surface via a transparent substrate by the condensing optical system to record or reproduce information on the first optical information recording medium. A light beam emitted from a second light source (wavelength λ2 (nm)) is transmitted to the second optical information recording medium having a transparent substrate thickness t2 (t2> t1) through the transparent substrate by the condensing optical system. An optical pickup device for recording or reproducing information on the second optical information recording medium by condensing the information on the information recording surface by using the light of the objective lens when recording or reproducing the information on the first optical information recording medium. From the magnification m1 viewed from the information recording medium side, the magnification m2 of the objective lens viewed from the optical information recording medium side when recording or reproducing information on the second optical information recording medium.
An optical pickup device characterized in that it is smaller. 2. An optical system according to claim 1, wherein the converging optical system has a wavefront aberration discontinuous and divides a light beam emitted from the light source into at least two regions in a direction perpendicular to the optical axis. At least one lens surface dividing portion is provided, and when recording or reproducing information on the first optical information recording medium,
Of the regions divided by the lens surface division unit, a light beam passing through a first region on the optical axis side of the lens surface division unit and a third region outside the lens surface division unit,
The wave spot aberration of the beam spot formed on the information recording surface of the first optical information recording medium is 0.05λ1 (rms) or less, and when recording or reproducing information on the second optical information recording medium,
The wavefront aberration of a beam spot formed on an information recording surface of a second optical information recording medium by a light beam passing through the first area is 0.07λ2 (rms) or less. Optical pickup device. 3. A light beam from a light source is condensed on an information recording surface via a transparent substrate of an optical information recording medium by a condensing optical system including an objective lens, and recording or reproduction of information on the optical information recording medium is performed. And an optical pickup device for recording or reproducing information on at least two types of optical information recording media having different thicknesses and recording densities of transparent substrates, wherein the focusing optical system has a wavefront aberration. Is provided, at least one lens surface dividing portion substantially concentric with the optical axis of the lens is provided, and when recording or reproducing information on the first optical information recording medium having a thickness of t1 of the transparent substrate, First on the optical axis side of the lens division
The wavefront aberration of the beam spot formed on the information recording surface by the light beam passing through the region and the third region outside the lens surface dividing portion is 0.05λ1 (rms) (where λ1
Is the wavelength (nm) of the first light source used for recording or reproducing information on the first optical information recording medium) or less, and the magnification of the objective lens viewed from the optical information recording medium side is m1,
At the time of recording or reproducing information on a second optical information recording medium having a recording density lower than that of the first optical information recording medium and a thickness of a transparent substrate of t2 (t2> t1), The wavefront aberration of the beam spot formed on the information recording surface by the light beam passing through the first area is 0.07λ2 (rms) (where λ2 is the second optical information recording medium used for recording or reproducing information). The light from the second light source is condensed with the magnification of the objective lens viewed from the optical information recording medium side being m2 so as to be equal to or less than the wavelength (nm) of the two light sources. Pickup device. 4. A converging optical system, comprising: a lens surface dividing portion;
During recording or reproduction of the second optical information recording medium, a light beam passing through the first area and the second area between the two lens surface dividing portions is condensed to form a beam spot on the information recording surface. The optical pickup device according to claim 2, wherein the optical pickup device is configured to perform the operation. 5. A converging optical system comprising: a lens surface dividing unit;
4. The optical pickup device according to claim 2, wherein a second region between the two lens surface divided portions has a shielding structure. 5. 6. The magnification m2 is a magnification in a direction for correcting spherical aberration caused by a difference between the thickness t1 of the transparent substrate of the first optical information recording medium and the thickness t2 of the transparent substrate of the second optical information recording medium. The method according to any one of claims 1 to 5, wherein
An optical pickup device according to any one of the above. 7. The light-converging optical system includes a divergence changing optical element that changes the divergence of light beams from the first light source and the second light source, and the divergence changing optical element and the second light source. The first light source and the second light source are arranged such that a distance between the first light source and the second light source is shorter than a distance between the divergence changing optical element and the first light source. An optical pickup device according to any one of the above. 8. The optical pickup device according to claim 1, wherein the first light source also serves as the second light source. 9. The convergence optical system has a divergence changing optical element for changing a divergence of a light beam from the first light source, and the divergence at the time of recording or reproducing information on the first optical information recording medium. The distance between the divergence changing optical element and the first light source at the time of recording or reproducing information on the second optical information recording medium is shorter than the distance between the degree changing optical element and the first light source. The optical pickup device according to claim 8, wherein 10. The apparatus according to claim 9, wherein the first light source or the divergence changing optical element is moved in an optical axis direction.
An optical pickup device according to item 1. 11. The optical pickup according to claim 1, wherein the magnification m1 and the magnification m2 satisfy −0.05 <m2−m1 <−0.005. apparatus.