JPWO2008120594A1 - Lens unit for optical pickup device and optical pickup device - Google Patents

Abstract

The present invention relates to a lens for an optical pickup device capable of sharing a photodetector and a collimator while maintaining optical characteristics in order to perform information recording and / or reproduction on different optical information recording media. A unit and an optical pickup device are provided. The lens unit and the optical pickup device for the optical pickup device include the distance (WD1) from the surface vertex on the optical disc side to the surface of the DVD in the first objective lens portion OL1, and the optical information recording in the second objective lens portion OL2. By making the distance (WD2) from the surface apex on the medium side to the CD approximately equal, it is possible to suppress the burden on the actuator that drives the lens unit OE, and it is possible to realize highly accurate driving by suppressing resonance and the like.

Description

  The present invention relates to a lens unit for an optical pickup device capable of recording and / or reproducing information on different types of optical information recording media (also referred to as optical discs), and an optical pickup device using the lens unit.

  In recent years, research and development of high-density optical disc systems that can record and / or reproduce information (hereinafter, “recording and / or reproduction” is referred to as “recording / reproduction”) using a blue-violet semiconductor laser having a wavelength of about 400 nm. Development is progressing rapidly. As an example, in an optical disc for recording / reproducing information with specifications of NA 0.85 and light source wavelength 405 nm, so-called Blu-ray Disc (hereinafter referred to as BD), DVD (NA 0.6, light source wavelength 650 nm, storage capacity 4, 7 GB) Can record information of about 25 GB per layer on an optical disc having a diameter of 12 cm, which is the same size as the above, and an optical disc for recording / reproducing information with specifications of NA 0.65 and light source wavelength 405 nm, so-called HD In a DVD (hereinafter referred to as HD), information of about 15 GB per layer can be recorded on an optical disk having a diameter of 12 cm. In the BD, since coma aberration generated due to the tilt (skew) of the optical disk increases, the protective layer is designed to be thinner than in the DVD (0.1 mm with respect to 0.6 mm of the DVD) The amount of coma due to skew is reduced. Hereinafter, in this specification, such an optical disc is referred to as a “high-density optical disc”.

  In addition, based on the reality that DVDs (digital versatile discs) and CDs (compact discs) on which a wide variety of information is recorded are currently being sold, various types of optical discs can be used with a single player. It is desired to appropriately record / reproduce information. Furthermore, considering that the optical pickup device is mounted on a notebook personal computer or the like, it is not only necessary to have compatibility with a plurality of types of optical discs, but it is important to further promote downsizing.

  Here, in the optical pickup device, it is preferable to realize compactness if it is possible to use different optical disks interchangeably using a single objective lens. However, considering the specifications of the high-density optical disc, it can be said that it is technically difficult to share the objective lens. For example, BD and HD use light beams having the same wavelength even though the protective substrate thickness is different, so that aberration correction cannot be performed using a diffractive structure, and it is difficult to share an objective lens. There is.

  Also, although DVD / CD compatible lenses have already been put into practical use, the outer diameter of compatible lenses tends to increase in order to ensure a certain degree of CD WD (working distance). Eventually, there arises a problem that the lens diameter cannot be increased to a desired size as the lens diameter increases. On the other hand, if dedicated lenses are used for DVD and CD, respectively, the DVD lens can be made small regardless of the limitation on the CD-side WD, and the thickness can be reduced particularly in the thickness direction of the pickup device. .

As described above, in the optical pickup device, in order to achieve both “compatibility” and “compact” for different optical discs and to obtain more preferable optical performance, a composite optical element in which lenses are arranged in parallel and integrally formed is used. Can be considered. Such a composite optical element has a merit that the interval between the lenses can be narrowed since the flange portion can be made common as compared with the case where two lenses molded individually are used. There is also an advantage that assembly adjustment can be simplified and cost can be reduced. Examples of such composite optical elements include:
There exists what was described in patent document 1. FIG.
JP-A-9-115170

  By the way, in order to reduce the cost of the optical pickup device, it is conceivable to share a photodetector that detects reflected light from different types of optical disks. In such a case, in order to perform appropriate detection, it is desired to make the rim (periphery) intensity of any reflected light as equal as possible. Similarly, in order to reduce the cost of the optical pickup device, it is desirable to use a common collimator that allows the light beam to enter the objective lens. In such a case, it can be said that it is effective to bring the effective diameters of the two lenses closer. However, there is a problem that sufficient optical characteristics cannot be obtained simply by matching the effective diameters of the lenses.

  The present invention has been made in view of the problems of the prior art, and in order to perform information recording and / or reproduction on different optical information recording media, while maintaining optical characteristics, It is an object of the present invention to provide a lens unit for an optical pickup device and an optical pickup device that can share a collimator.

  In this specification, an optical disk (also referred to as an optical information recording medium) that uses a blue-violet semiconductor laser or a blue-violet SHG laser as a light source for recording / reproducing information is generally referred to as a “high-density optical disk”, and NA0 In addition to a standard optical disc (for example, BD: Blu-ray Disc) in which information is recorded / reproduced by an objective optical system of .85 and the thickness of the protective layer is about 0.1 mm, NA 0.65 to 0.67 Information is recorded / reproduced by the objective optical system, and includes a standard optical disc (for example, HD DVD: also simply referred to as HD) having a protective layer thickness of about 0.6 mm. In addition to an optical disc having such a protective layer on its information recording surface, an optical disc having a protective film with a thickness of several to several tens of nanometers on the information recording surface, the thickness of the protective layer or protective film It also includes an optical disc with 0. In this specification, the high-density optical disk includes a magneto-optical disk that uses a blue-violet semiconductor laser or a blue-violet SHG laser as a light source for recording / reproducing information.

  Furthermore, in this specification, DVD is a generic term for DVD series optical disks such as DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like. Is a general term for CD-series optical disks such as CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW and the like. The recording density is highest for BD, and then decreases in the order of HD, DVD, and CD.

A lens unit for an optical pickup device according to claim 1 includes a single or a plurality of light sources, a lens unit in which a first objective lens unit and a second objective lens unit are integrally formed, and a photodetector. And condensing the light beam from the light source on the information recording surface of the first optical information recording medium via the first objective lens unit, and detecting the reflected light by the photodetector. Information can be recorded and / or reproduced on the information recording surface, and the light beam from the light source is applied to the information recording surface of the second optical information recording medium via the second objective lens unit. A lens unit for an optical pickup device capable of recording and / or reproducing information on the information recording surface by collecting light and detecting the reflected light with the photodetector,
The required numerical aperture of the first optical information recording medium is larger than the required numerical aperture of the second optical information recording medium, or the wavelength λ1 of the light beam incident on the first objective lens unit is the second optical information recording medium. When the wavelength is shorter than the wavelength λ2 of the light beam incident on the objective lens unit, the following expression is satisfied.

1.0 ≤ φ1 (mm) ≤ 4.1 (1)
1.0 ≤ φ2 (mm) ≤ 4.1 (2)
0.7 · φ1 ≤ φ2 (mm) ≤ 1.3 · φ1 (3)
0.60 ≦ (f2 · WD1) / (f1 · WD2) ≦ 1.90 (4)
Where φ1: effective diameter of the first objective lens portion φ2: effective diameter of the second objective lens portion WD1: focused spot for recording and / or reproducing information on the first optical information recording medium The distance (mm) from the surface vertex on the first optical information recording medium side to the surface of the first optical information recording medium in the first objective lens section
WD2: From the surface apex on the second optical information recording medium side in the second objective lens portion when a condensing spot is formed to perform information recording and / or reproduction on the second optical information recording medium Distance to the surface of the second optical information recording medium (mm)
f1: Focal length (mm) of the first objective lens unit with a light beam having a wavelength λ1
f2: Focal length (mm) of the second objective lens unit with a light beam with wavelength λ2
According to the present invention, the effective diameters φ1 and φ2 are made substantially equal by defining the working distance and the focal length of the first objective lens and the second objective lens so as to satisfy the expression (4). As a result, the photodetector can be easily shared, and the cost of the optical pickup device can be reduced. In addition, a collimator that allows the light beam from the light source to enter the first objective lens unit and the second objective lens unit can be shared. Note that making the effective diameters φ1 and φ2 substantially equal means that the expression (3) is satisfied. For practical use in an optical pickup device, it is preferable that the effective diameter of the objective lens portion satisfies the expressions (1) and (2).

  It is more preferable to satisfy the following formula (3 ′), and it is more preferable to satisfy the following formula (3 ″).

0.9 · φ1 ≤ φ2 (mm) ≤ 1.1 · φ1 (3 ')
φ1 = φ2 (3 ″)
The first objective lens unit has a first optical surface and a second optical surface that face each other, and the curvature of the first optical surface is larger than that of the second optical surface. It is preferable that the first optical surface is on the light source side and the second optical surface is on the optical information recording medium side. Similarly, the second objective lens also has a first optical surface and a second optical surface that face each other, and the first optical surface has a larger curvature than the second optical surface.

  In this specification, “working distance (WD1, WD2)” means from the surface apex of the second optical surface of the objective lens unit when information is recorded / reproduced to / from the optical information recording medium. The distance in the optical axis direction to the optical information recording medium. More specifically, the distances are shown as WD1 and WD2 in FIG. However, if it is difficult to determine the position of the surface vertex of the objective lens unit from the actual optical element, when the optical element is attached to the bobbin of the optical pickup device, the reference surface of the flange part of the optical element that contacts the bobbin The location of the second optical surface of the first objective lens portion furthest away from the (surface in contact with the bobbin) in the optical axis direction is the surface vertex, and the distance from the surface vertex to the first optical information recording medium is Similarly, the position of the second optical surface of the second objective lens portion farthest in the optical axis direction from the reference surface is defined as WD1, and the distance from the surface vertex to the second optical information recording medium is defined as WD2. It is good.

  The “optical element in which the first objective lens portion and the second objective lens portion are integrally formed” according to the present invention refers to a case where the first objective lens portion and the second objective lens portion are fused ( For example, not only when an optical element having a first objective lens part and a second objective lens part is obtained by injection molding or the like, but also, an optical element having a first objective lens part and a second objective The optical element may be an integrated optical element by separately molding an optical element having a lens portion and then fitting, adhering or engaging.

  In the present invention, the required numerical aperture NA1 of the first optical information recording medium is larger than the required numerical aperture NA2 of the second optical information recording medium, or the wavelength λ1 of the light beam incident on the first objective lens unit. Is shorter than the wavelength λ2 of the light beam incident on the second objective lens portion. Accordingly, combinations of the first optical information recording medium and the second optical information recording medium to which the present invention is applied include DVD and CD, BD and DVD, BD and CD, HD and CD (NA1> NA2, λ1> λ2), BD and HD (λ1 = λ2, but NA1> NA2), HD and DVD (NA1 = NA2, but λ1> λ2), and the like. The preferable values of NA and λ in each optical information recording medium are as follows.

BD: NA = 0.8 to 0.9, λ = 380 to 420 nm
(Particularly preferably, NA = 0.85, λ = 405 nm)
HD: NA = 0.5 to 0.7, λ = 380 to 420 nm
(Particularly preferably, NA = 0.65, λ = 405 nm)
DVD: NA = 0.5 to 0.7, λ = 640 to 680 nm
(Particularly preferably, NA = 0.6, λ = 655 nm)
CD: NA = 0.4-0.55, λ = 750-820 nm
(Particularly preferably, NA = 0.45 or 0.51, λ = 780 nm)
The light source of the optical pickup device will be described below. For example, when the first optical information recording medium is a BD and the second optical information recording medium is an HD, an optical pickup device may have a single light source with a wavelength of 380 to 420 nm. On the other hand, when the first optical information recording medium is a DVD and the second optical information recording medium is a CD, the optical pickup device has a first light source having a wavelength of 640 to 680 nm and a second light source having a wavelength of 740 to 820 nm. Need to be. As described above, the light source may be a single light source or a plurality of light sources depending on the type of optical information recording medium to be used.

  The lens unit for an optical pickup device described in claim 2 is characterized in that, in the invention described in claim 1, the following expression is satisfied.

0 (mm) ≦ | d1-d2 | ≦ 0.2 (mm) (5)
Where d1: axial thickness of the first objective lens portion d2: axial thickness of the second objective lens portion The axial thickness of the objective lens portion is the thickness of the objective lens portion on the optical axis. Say. More specifically, for example, it refers to d1 and d2 shown in FIG.

  The lens unit for an optical pickup device described in claim 3 is characterized in that, in the invention described in claim 1 or 2, the following expression is satisfied.

1.0 ≤ φ1 (mm) ≤ 2.1 (1 ')
1.0 ≤ φ2 (mm) ≤ 2.1 (2 ')
Satisfying the above conditional expression is preferable because the lens unit can be made more compact and the value of the working distance can be made closer between the first objective lens portion and the second objective lens portion. More preferably, the following conditional expression is satisfied from the viewpoint of working distance and compactification.

1.0 ≤ φ1 (mm) ≤ 1.5 (1 '')
1.0 ≤ φ2 (mm) ≤ 1.5 (2 '')
The lens unit for an optical pickup device described in claim 4 satisfies the following expression in the invention described in any one of claims 1 to 3.

0.7 · WD1 ≤ WD2 ≤ 1.5 · WD1 (6)
According to the present invention, the distance (WD1) from the surface vertex on the first optical information recording medium side to the surface of the first optical information recording medium in the first objective lens unit during information recording and / or reproduction, By reducing the distance (WD2) from the surface vertex on the second optical information recording medium side to the surface of the second optical information recording medium in the objective lens unit 2, the burden on the actuator that drives the lens unit can be suppressed. In addition, high-accuracy driving can be realized by suppressing resonance and the like.

  The lens unit for an optical pickup device according to claim 5 is the lens unit according to any one of claims 1 to 4, wherein the first optical information recording medium is a DVD, and the second optical information recording medium. Is CD and satisfies the following expression.

0.80 ≦ (f2 · WD1) / (f1 · WD2) ≦ 1.79 (4 ′)
Preferably, the following is satisfied.

0.80 ≦ (f2 · WD1) / (f1 · WD2) ≦ 1.77
In the following, a particularly preferable numerical range is defined for each type of optical information recording medium. First, in Claim 5 and Claim 6 below, a particularly preferable numerical range is defined when the first optical information recording medium is a DVD and the second optical information recording medium is a CD. . In order to form a focused spot on the information recording surface of DVD and CD while making the effective diameters substantially the same, it is preferable to satisfy the conditional expressions (1), (2), (3) and (4 ′).

    The lens unit for an optical pickup device described in claim 6 is characterized in that, in the invention described in claim 5, the following expression is satisfied.

0 (mm) ≦ | d1-d2 | ≦ 0.2 (mm) (5)
1.0 ≤ φ1 (mm) ≤ 2.1 (1 ')
1.0 ≤ φ2 (mm) ≤ 2.1 (2 ')
0.7 · WD1 ≤ WD2 ≤ 1.5 · WD1 (6)
0.99 ≦ (f2 · WD1) / (f1 · WD2) ≦ 1.79 (4 ′)
However, d1: Axial thickness of the first objective lens part d2: Axial thickness of the second objective lens part The lens unit for the optical pickup device according to claim 7, wherein 4. The invention according to claim 4, wherein the first optical information recording medium is a BD, and the second optical information recording medium is an HD, which satisfies the following expression.

0.60 ≦ (f2 · WD1) / (f1 · WD2) ≦ 1.25 (4 ″)
Preferably, the following is satisfied.

0.60 ≦ (f2 · WD1) / (f1 · WD2) ≦ 1.21
Next, in the above-mentioned Claim 7 and Claim 8 below, a particularly preferable numerical range is defined when the first optical information recording medium is BD and the second optical information recording medium is HD. Yes. In order to form a focused spot on the BD and HD information recording surfaces while making the effective diameters substantially the same, it is preferable to satisfy the conditional expressions (1), (2), (3) and (4 ″). .

  The lens unit for an optical pickup device described in claim 8 satisfies the following expression in the invention described in claim 7.

0 (mm) ≦ | d1-d2 | ≦ 0.2 (mm) (5)
1.0 ≤ φ1 (mm) ≤ 2.1 (1 ')
1.0 ≤ φ2 (mm) ≤ 2.1 (2 ')
0.7 · WD1 ≤ WD2 ≤ 1.5 · WD1 (6)
1.00 ≦ (f2 · WD1) / (f1 · WD2) ≦ 1.25 (4 ′ ″)
Where d1: axial thickness of the first objective lens portion d2: axial thickness of the second objective lens portion The first optical information recording medium is a BD, and the second optical information recording medium is a DVD. When it is, it is preferable to satisfy the following formulas and formulas (1), (2), and (3).
1.16 ≦ (f2 · WD1) / (f1 · WD2) ≦ 1.31 (4 ″ ″)
Further, when the first optical information recording medium is HD and the second optical information recording medium is DVD, it is preferable to satisfy the following equations and equations (1), (2), and (3).
1.00 ≦ (f2 · WD1) / (f1 · WD2) ≦ 1.08 (4 ′ ″ ″)
It is more preferable to satisfy the following.
1.01 ≦ (f2 · WD1) / (f1 · WD2) ≦ 1.07
Further, when the first optical information recording medium is HD and the second optical information recording medium is CD, it is preferable to satisfy the following formulas and formulas (1), (2), and (3).
0.81 ≦ (f2 · WD1) / (f1 · WD2) ≦ 1.92 (4 ″ ″ ″)
It is more preferable to satisfy the following.
0.81 ≦ (f2 · WD1) / (f1 · WD2) ≦ 1.89
The lens unit for an optical pickup device according to claim 9 is characterized in that, in the invention according to any one of claims 1 to 8, the following expression is satisfied.
−0.02 <m1 <0.02 (9)
−0.02 <m2 <0.02 (10)
However, m1: magnification of a light beam emitted from the light source and incident on the first objective lens unit m2: magnification of a light beam emitted from the light source and incident on the second objective lens unit. It is preferable because a substantially parallel light beam can be incident on the first and second objective lens portions. In particular, it is preferable that a parallel light beam (m1, m2 = 0) is incident on the first and second objective lens portions. However, the present invention is not limited to a mode in which a parallel light beam is incident on the objective lens unit, and can also be applied to a mode in which a divergent light beam or a convergent light beam is incident on the objective lens unit.

  The lens unit for an optical pickup device according to claim 10 is the invention according to any one of claims 1 to 9, wherein at least one of the first objective lens portion and the second objective lens is: It has only an optical surface of an aspherical refracting surface.

  The lens unit for an optical pickup device according to claim 11 is the lens unit according to claim 9, wherein both the first objective lens portion and the second objective lens portion are aspherical refractive surfaces. It has only an optical surface.

  In the lens unit of the present invention, the first objective lens unit and the second objective lens unit are both dedicated lenses (object lenses corresponding to only one kind of optical information recording medium using a certain wavelength in one objective lens unit). It may be a compatible lens (an objective lens corresponding to a plurality of types of optical information recording media using different wavelengths in one objective lens unit), or a combination of a compatible lens and a dedicated lens. May be. Particularly preferably, when both the first objective lens portion and the second objective lens portion are dedicated lenses, the effect that can be achieved by satisfying the conditional expression of the present invention becomes more remarkable. When the first objective lens unit or the second objective lens unit is a dedicated lens, it is preferable that both the first optical surface and the second optical surface are aspherical refractive surfaces. An optical path difference providing structure that reduces aberrations that occur when the wavelength is changed may be provided within the effective diameter, or an optical path difference providing structure for flaring a light beam outside the effective diameter may be provided outside the effective diameter. .

  The lens unit for an optical pickup device according to claim 12 is the invention according to any one of claims 1 to 11, wherein the first objective lens portion and the second objective lens portion are integrally molded. It is characterized by being.

  The lens unit for an optical pickup device according to claim 13 is the invention according to any one of claims 1 to 11, wherein the first objective lens portion and the second objective lens portion are engaged with each other. And are integrally formed.

FIG. 7 shows an example of a lens unit in which the first objective lens portion and the second objective lens portion are integrally formed by engagement. A first example is shown in FIG. Plastic second objective lens section OL2 is, forms an opening HL having a stepped portion ST on the rectangular plate-like flange portion FL2, the stepped portion ST of the opening HL, held the flange portion FL 1 In this way, the first objective lens portion OL1 made of glass or plastic is assembled from the optical axis direction and integrated by bonding or the like, so that the first objective lens portion OL1 and the second objective lens portion OL2 are combined. Parallel optical elements (also referred to as lens units) OE are formed.

Another example is shown in FIG. Plastic second objective lens section OL2 is, forms a cutout CT having a stepped portion ST on the rectangular plate-like flange portion FL2, the stepped portion ST of the cutout CT, is held the flange portion FL 1 In this way, the first objective lens portion OL1 made of glass or plastic is assembled from the direction orthogonal to the optical axis and integrated by bonding or the like, and the first objective lens portion OL1 and the second objective lens portion OL2 are assembled. Is formed in parallel.

  As shown in FIG. 7C, the flange portion FL1 of the first objective lens OL1 may be supported on the upper surface of the flange portion FL2 without forming the step ST in the opening HL or the notch CT. . Alternatively, although not shown, the first objective lens portion OL1 made of glass or plastic and the second objective lens portion OL2 made of plastic may be integrated by being assembled to a holding member which is a separate member. good. In any case, it is preferable that the holding member has an opening, and the objective lens unit is fitted therein.

  Note that either the first objective lens unit or the second objective lens unit may be a glass lens and the other may be a plastic lens, or both the first objective lens unit and the second objective lens unit may be plastic lenses or It may be a glass lens.

  A lens unit for an optical pickup device according to a fourteenth aspect is the invention according to any one of the first to thirteenth aspects, wherein the first objective lens portion is opposite to the first optical surface and the second optical surface. And the second objective lens unit has a first optical surface and a second optical surface facing each other, and the second objective lens unit includes a first objective lens unit and a second objective lens unit. The first optical surface has a larger curvature than the second optical surface of the first objective lens unit and the second objective lens unit, and is a surface vertex of the second optical surface of the first objective lens unit. And the height of the surface vertex of the second optical surface of the second objective lens portion in the optical axis direction is equal.

  The optical pickup device described in claim 15 uses the lens unit for an optical pickup device described in any of claims 1 to 14.

  According to the present invention, in order to reduce the burden on the actuator and perform information recording and / or reproduction on different optical information recording media, the optical detector and the collimator are shared while maintaining the optical characteristics. It is possible to provide a lens unit for an optical pickup device and an optical pickup device.

It is a figure which shows schematic structure of optical pick-up apparatus PU1. It is the figure which looked at the lens unit used by this Embodiment in the optical axis orthogonal direction. 2 is a cross-sectional view of an objective lens unit for DVD (a) and an objective lens unit for CD (b) according to Example 1. FIG. FIG. 7 is a cross-sectional view of a DVD objective lens section (a) and a CD objective lens section (b) according to Example 4; FIG. 10 is a cross-sectional view of an objective lens portion for DVD (a) and an objective lens portion for CD (b) according to Example 6; FIG. 10 is a cross-sectional view of an objective lens unit for DVD (a) and an objective lens unit for CD (b) according to Example 8. It is a figure which shows the modification of lens unit OE.

Explanation of symbols

2L1P 2 laser 1 package AC1 2 axis actuator BS beam splitter COL collimator OL1 1st objective lens part OL2 2nd objective lens part PD photodetector PL1 protection board PL2 protection board PU1 optical pickup device QWP λ / 4 wavelength plate RL1 information Recording surface RL2 Information recording surface

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiment, a case where the first optical information recording medium is a DVD and the second optical information recording medium is a CD will be described. The optical pickup device PU1 according to the present embodiment can be incorporated in an optical disk drive device. FIG. 1 is a diagram showing a schematic configuration of the optical pickup device PU1. FIG. 2 is a view of the lens unit of the present embodiment as viewed in the direction perpendicular to the optical axis.

  The optical pickup device PU1 records and reproduces information with respect to a CD and a first light source that emits a laser beam (first beam) of λ1 = 655 nm when recording / reproducing information with respect to a DVD. 2 laser 1 package 2L1P in which a second light source that emits a laser beam (second light beam) of λ2 = 785 nm emitted in the case of performing the above, a reflected light from a DVD, and a reflected light from a CD And a photodetector PD that receives light in common. The collimator COL is commonly used when using a DVD and when using a CD.

  Further, the lens unit OE held by the holding member H has a first objective lens portion OL1 and a second objective lens portion OL2 each having only an aspheric optical surface, and as shown in FIG. The effective diameter φ1 of the first objective lens section OL1 and the effective diameter φ2 of the second objective lens section OL2 are substantially equal. The working distance WD1 of the first objective lens portion OL1 (distance between the optical surface S2 on the optical disc side of the first objective lens portion OL1 and the DVD) is the working distance WD2 (second distance of the second objective lens portion OL2). The distance between the optical surface S2 on the optical disc side of the objective lens section OL2 and the CD) may be used approximately equal. Further, as shown in FIG. 2, in the lens unit OE, the surface vertex P12 of the second optical surface of the first objective lens portion OL1 and the surface vertex P22 of the second optical surface of the second objective lens portion OL2. Are equal in height in the optical axis direction.

  When recording / reproducing information with respect to the DVD in the optical pickup device PU1, the holding member H is moved to the position shown in FIG. 1, and the first objective lens section OL1 is inserted into the optical path, and two lasers are used. The first light source of one package 2L1P is caused to emit light. The divergent light beam emitted from the first light source is converted into a parallel light beam by the collimator COL as shown by the solid line in FIG. 1, and passes through the polarization beam splitter PBS and the λ / 4 wavelength plate QWP. After entering the first objective lens section OL1 in the state of parallel light, it becomes a spot formed on the information recording surface RL1 via the protective substrate PL1 of the DVD. The lens unit OE having the first objective lens portion OL1 is driven together with the holding member H by the biaxial actuator AC1 to perform focusing and tracking.

  The reflected light flux modulated by the information pits on the information recording surface RL1 passes through the first objective lens section OL1 and the λ / 4 wave plate QWP again, is reflected by the polarization beam splitter PBS, and is detected by the sensor lens SN. Is incident on the light receiving surface of the detector PD. And the information recorded on DVD can be read using the output signal of a photodetector.

  In the optical pickup device PU1, when recording / reproducing information with respect to a CD, the holding member H is moved from the position shown in FIG. 1, the second objective lens portion OL2 is inserted into the optical path, and two lasers are used. The second light source of one package 2L1P is caused to emit light. The divergent light beam emitted from the second light source is converted into a parallel light beam by the collimator COL and passes through the polarization beam splitter PBS and the λ / 4 wavelength plate QWP, as shown by the dotted line in FIG. After entering the second objective lens section OL2 in the state of parallel light, it becomes a spot formed on the information recording surface RL2 via the CD protective substrate PL2. The lens unit OE having the second objective lens section OL2 is driven together with the holding member H by the biaxial actuator AC1 to perform focusing and tracking.

The reflected light flux modulated by the information pits on the information recording surface RL2 passes through the second objective lens section OL2 and the λ / 4 wavelength plate QWP again, is reflected by the polarization beam splitter PBS, and is detected by the sensor lens SN. Is incident on the light receiving surface of the detector PD. And the information recorded on CD can be read using the output signal of a photodetector. In addition to this, the objective lens unit capable of forming a focused spot on any of the four types of optical disks of BD, HD, DVD, and CD can be arbitrarily combined in the lens knit.
(Example)
Hereinafter, an example suitable as the above-described lens unit will be described. The following objective lens portions are all dedicated lenses, have an aspherical refracting surface, and do not have an optical path difference providing structure. Table 1 shows lens data of the second objective lens unit for CD and the first objective lens unit for DVD. In this embodiment, all the light beams are incident on the objective lens unit as parallel light beams, and the conditions under which CDs and DVDs can be recorded / reproduced are examined. FIG. 3 shows a cross-sectional view of the objective lens unit (a) for DVD and the objective lens unit (b) for CD according to the first embodiment, and FIG. 4 shows the objective lens unit for DVD according to the fourth embodiment. FIG. 5 is a sectional view of a) and an objective lens portion (b) for CD, and FIG. 5 is a sectional view of an objective lens portion (a) for DVD and an objective lens portion (b) for CD according to Example 6. FIG. 6 is a cross-sectional view of the objective lens unit (a) for DVD and the objective lens unit (b) for CD according to the eighth embodiment.

  According to Table 1, when the effective diameter φ of the objective lens portion for CD and the objective lens portion for DVD are matched and changed within the range of 1.0 to 2.3 (mm), (f2 · WD1) / (F1 · WD2) is 0.819 to 1.375, and | d1-d2 | is 0.2 mm. The difference of the working distance WD is 0 to 0.3809 (mm).

  Table 2 shows lens data of another example of the second objective lens unit for CD and the first objective lens unit for DVD. In this embodiment, the axial thicknesses d1 and d2 of the objective lens portion are changed from the embodiment shown in Table 1 for examination. Also in this embodiment, all the light beams are incident on the objective lens unit as parallel light beams, and the conditions under which CDs and DVDs can be recorded / reproduced are examined. According to Table 2, the effective diameters Φ1 and Φ2 in the first objective lens portion and the second objective lens portion are set to substantially the same value, and the effective diameter Φ is changed in a range of 1.0 to 4.0 (mm). Sometimes (f2 · WD1) / (f1 · WD2) is 0.878 to 1.784, and | d1-d2 | is 0.11 to 0.26 mm. The difference of the working distance WD is 0.04 to 0.69 (mm).

  In the examples of DVD-CD described in Table 1 and Table 2, when Φ1 and Φ2 are 1.0 mm or more and 2.1 mm or less, | d1-d2 | is 0.11 to 0.20 mm. Yes, WD2 is 0.71WD1 to 1.29WD1, and (f2 · WD1) / (f1 · WD2) is 0.998 to 1.784.

  Table 3 shows lens data of the second objective lens unit for HD and the first objective lens unit for BD. Also in this embodiment, all the light beams are incident on the objective lens unit as parallel light beams, and the conditions under which HD and BD can be recorded / reproduced are examined. According to Table 3, the effective diameters Φ1 and Φ2 in the first objective lens portion and the second objective lens portion are set to substantially the same value, and the effective diameter Φ is changed in a range of 1.7 to 4.0 (mm). Sometimes (f2 · WD1) / (f1 · WD2) is 0.604 to 1.209, and | d1-d2 | is 0.12 to 1.46 mm. The difference of the working distance WD is 0.01 to 0.83 (mm).

  In the examples of BD-HD described in Table 3, when Φ1 and Φ2 are 1.0 mm or more and 2.1 mm or less, | d1-d2 | is 0.12 mm, and WD2 is 1. 05WD1, and (f2 · WD1) / (f1 · WD2) is 1.209.

  Next, Table 4 shows lens data of the second objective lens unit for DVD and the first objective lens unit for BD. Also in this embodiment, all the light beams are incident on the objective lens unit as parallel light beams, and the conditions under which DVD / BD can be recorded / reproduced are examined. According to Table 4, the effective diameters Φ1 and Φ2 in the first objective lens portion and the second objective lens portion are set to substantially the same value, and the effective diameter Φ is changed in a range of 1.7 to 4.0 (mm). Sometimes (f2 · WD1) / (f1 · WD2) is 1.163 to 1.308, and | d1-d2 | is 0.06 to 0.16 mm. The difference in the working distance WD is 0.00 to 0.09 (mm).

  Next, Table 5 shows lens data of the second objective lens unit for DVD and the first objective lens unit for HD. Also in this embodiment, all the light beams are incident on the objective lens unit as parallel light beams, and the conditions under which DVD / HD can be recorded / reproduced are examined. According to Table 5, the effective diameters Φ1 and Φ2 in the first objective lens part and the second objective lens part were set to substantially the same value, and the effective diameter Φ was changed in the range of 1.0 to 4.0 (mm). Sometimes (f2 · WD1) / (f1 · WD2) is 1.000 to 1.069 and | d1-d2 | is 0.00 to 0.05 mm. The difference of the working distance WD is 0.00 to 0.03 (mm).

  Table 6 shows lens data of the second objective lens unit for CD and the first objective lens unit for HD. Also in this embodiment, all the light beams are incident on the objective lens unit as a parallel light beam, and the conditions under which CD and HD can be recorded / reproduced are examined. According to Table 6, the effective diameters Φ1 and Φ2 in the first objective lens portion and the second objective lens portion are set to substantially the same value, and the effective diameter Φ is changed in the range of 1.0 to 4.0 (mm). Sometimes (f2 · WD1) / (f1 · WD2) is 0.815 to 1.912 and | d1-d2 | is 0.10 to 0.26 mm. The difference of the working distance WD is 0.03 to 0.67 (mm).

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be appropriately changed or improved.

Claims (15)

A single or a plurality of light sources, a lens unit in which the first objective lens unit and the second objective lens unit are integrally formed, and a photodetector; Information can be recorded and / or reproduced on the information recording surface by focusing on the information recording surface of the first optical information recording medium through the objective lens unit and detecting the reflected light by the photodetector. The light beam from the light source is condensed on the information recording surface of the second optical information recording medium via the second objective lens unit, and the reflected light is detected by the photodetector. A lens unit for an optical pickup device capable of recording and / or reproducing information on the information recording surface,
The required numerical aperture of the first optical information recording medium is larger than the required numerical aperture of the second optical information recording medium, or the wavelength λ1 of the light beam incident on the first objective lens unit is the second optical information recording medium. A lens unit for an optical pickup device satisfying the following expression when the light beam is shorter than the wavelength λ2 of the light beam incident on the objective lens unit.
1.0 ≤ φ1 (mm) ≤ 4.1 (1)
1.0 ≤ φ2 (mm) ≤ 4.1 (2)
0.7 · φ1 ≤ φ2 (mm) ≤ 1.3 · φ1 (3)
0.60 ≦ (f2 · WD1) / (f1 · WD2) ≦ 1.90 (4)
Where φ1: effective diameter of the first objective lens portion φ2: effective diameter of the second objective lens portion WD1: focused spot for recording and / or reproducing information on the first optical information recording medium The distance (mm) from the surface vertex of the first optical information recording medium side to the surface of the first optical information recording medium in the first objective lens unit
WD2: surface apex on the second optical information recording medium side in the second objective lens portion when a condensing spot is formed to perform information recording and / or reproduction on the second optical information recording medium To the surface of the second optical information recording medium (mm)
f1: Focal length (mm) of the first objective lens unit with a light beam having a wavelength λ1
f2: Focal length (mm) of the second objective lens unit with a light beam with wavelength λ2 The lens unit for an optical pickup device according to claim 1, wherein the following expression is satisfied.
0 (mm) ≦ | d1-d2 | ≦ 0.2 (mm) (5)
Where d1: axial thickness of the first objective lens part d2: axial thickness of the second objective lens part The lens unit for an optical pickup device according to claim 1 or 2, wherein the following expression is satisfied.
1.0 ≤ φ1 (mm) ≤ 2.1 (1 ')
1.0 ≤ φ2 (mm) ≤ 2.1 (2 ') The lens unit for an optical pickup device according to any one of claims 1 to 3, wherein the following expression is satisfied.
0.7 · WD1 ≤ WD2 ≤ 1.5 · WD1 (6) The first optical information recording medium is a DVD, and the second optical information recording medium is a CD;
The lens unit for an optical pickup device according to any one of claims 1 to 4, wherein the following expression is satisfied.
0.80 ≦ (f2 · WD1) / (f1 · WD2) ≦ 1.79 (4 ′) The lens unit for an optical pickup device according to claim 5, wherein the following expression is satisfied.
0 (mm) ≦ | d1-d2 | ≦ 0.2 (mm) (5)
1.0 ≤ φ1 (mm) ≤ 2.1 (1 ')
1.0 ≤ φ2 (mm) ≤ 2.1 (2 ')
0.7 · WD1 ≤ WD2 ≤ 1.5 · WD1 (6)
0.99 ≦ (f2 · WD1) / (f1 · WD2) ≦ 1.79 (4 ′)
Where d1: axial thickness of the first objective lens part d2: axial thickness of the second objective lens part The first optical information recording medium is a BD; the second optical information recording medium is an HD;
The lens unit for an optical pickup device according to any one of claims 1 to 4, wherein the following expression is satisfied.
0.60 ≦ (f2 · WD1) / (f1 · WD2) ≦ 1.25 (4 ″) The lens unit for an optical pickup device according to claim 7, wherein the following expression is satisfied.
0 (mm) ≦ | d1-d2 | ≦ 0.2 (mm) (5)
1.0 ≤ φ1 (mm) ≤ 2.1 (1 ')
1.0 ≤ φ2 (mm) ≤ 2.1 (2 ')
0.7 · WD1 ≤ WD2 ≤ 1.5 · WD1 (6)
1.00 ≦ (f2 · WD1) / (f1 · WD2) ≦ 1.25 (4 ′ ″)
Where d1: axial thickness of the first objective lens part d2: axial thickness of the second objective lens part The lens unit for an optical pickup device according to any one of claims 1 to 8, wherein the following expression is satisfied.
−0.02 <m1 <0.02 (7)
−0.02 <m2 <0.02 (8)
Where m1: magnification of the light beam emitted from the light source and incident on the first objective lens unit m2: magnification of the light beam emitted from the light source and incident on the second objective lens unit   10. At least one of the first objective lens portion and the second objective lens portion has only an aspherical refracting optical surface, according to any one of claims 1 to 9. A lens unit for the optical pickup device described.   11. The lens unit for an optical pickup device according to claim 10, wherein both the first objective lens portion and the second objective lens portion have only an aspherical refracting optical surface. .   The lens unit for an optical pickup device according to any one of claims 1 to 11, wherein the first objective lens portion and the second objective lens portion are integrally molded. .   The light according to any one of claims 1 to 11, wherein the first objective lens portion and the second objective lens portion are integrally formed by engaging with each other. Lens unit for pickup device. The first objective lens unit has a first optical surface and a second optical surface facing each other, and the second objective lens unit has a first optical surface and a second optical surface facing each other. The first optical surfaces of the first objective lens unit and the second objective lens unit have a curvature that is greater than the second optical surfaces of the first objective lens unit and the second objective lens unit. big,
The height in the optical axis direction of the surface vertex of the second optical surface of the first objective lens portion and the surface vertex of the second optical surface of the second objective lens portion are equal. A lens unit for an optical pickup device according to any one of claims 1 to 13.   An optical pickup device using the lens unit for an optical pickup device according to any one of claims 1 to 14.