JP2008198281A - Lens unit for optical pickup device and optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lens unit for an optical pickup device, which is simple and inexpensive while different kinds of optical disks can be used, and to provide the optical pickup device using the same. <P>SOLUTION: Since a diffraction plate DP emits zero-order diffraction light and first-order diffraction light to an incident luminous flux having a wavelength λ1, a first objective lens OBJ1 can focus the light on an information recording surface of a BD when zero-order diffraction light is made incident and can focus the light on an information recording surface of an HD when first-order diffraction light is made incident. Thereby, a single first light source is used and the BD and the HD can be compatibly used with a simple and inexpensive construction without using a movable mirror and the like. <P>COPYRIGHT: (C)2008,JPO&INPIT

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.

  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 in recent years. 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 23 to 27 GB per layer on an optical disk with a diameter of 12 cm, which is the same size as the above, and an optical disk that records and reproduces information with specifications of NA 0.65 and light source wavelength 405 nm, so-called With HD DVD (hereinafter referred to as HD), information of 15 to 20 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, such an optical disc is referred to as a “high density optical disc” in the present specification.

  Also, given the reality that DVDs and CDs (compact discs) on which a wide variety of information is recorded are currently being sold, information can be appropriately recorded on as many different types of optical discs as possible with a single player. It is desired to enable reproduction. 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 disk, 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.

In this way, in a compatible optical pickup device, in order to achieve both “common” and “compact” objective lenses and to obtain more favorable optical performance, a composite optical element in which lenses are arranged in parallel and integrally molded is used. It is possible to use it. 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. An example of such a composite optical element is described in Patent Document 1.
JP 2005-512253 A

  Here, even if the composite optical element described in Patent Document 1 is used, there is a problem that must be solved in order to realize compatible use of BD and HD. For example, when one objective lens is for BD and the other objective lens is for HD, when using a light beam from a single light source, the optical path is switched so as to enter one of the selected objective lenses. Therefore, a mirror or the like that reflects the light beam from the light source must be moved, and therefore a drive unit such as a mirror must be provided, which causes a problem that the size of the optical pickup device is increased. On the other hand, if two light sources capable of emitting the same blue-violet light beam are provided, there is no need to switch the optical path. However, since a laser emitting a blue-violet light beam is relatively expensive, the cost of the optical pickup device is increased. There is a problem of inviting.

  The present invention has been made in view of the problems of the prior art, and a simple and low-cost lens unit for an optical pickup apparatus and a lens unit thereof can be used despite the fact that different types of optical disks can be used. An object of the present invention is to provide an optical pickup device.

  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 in the high-density optical disc, and then decreases in the order of DVD and CD. The optical disc focused on the information recording surface by the first objective lens may be any of BD, HD, DVD, and CD, and the optical disc focused on the information recording surface by the second objective lens may be BD, HD, Either a DVD or a CD may be used, but at least the first objective lens is preferably used for a high-density optical disk.

The lens unit for an optical pickup device according to claim 1 includes a first light source that emits a light beam having a wavelength λ1, a second light source that emits a light beam having a wavelength λ2 (λ2> λ1), a correction element, A first objective lens and a lens unit including a second objective lens, and the light beam from the first light source is transmitted through the correction element and the first objective lens to a first thickness of the protective substrate t1. By focusing on the information recording surface of the optical information recording medium, it is possible to record and / or reproduce information on the information recording surface, and through the correction element and the second objective lens. By focusing on the information recording surface of the second optical information recording medium having the protective substrate thickness t2 (t2> t1), information can be recorded and / or reproduced on the information recording surface. The light beam from the light source of the second By focusing on the information recording surface of the third optical information recording medium having the protective substrate thickness t3 (t3 ≧ t2) through the object lens, information can be recorded and / or reproduced on the information recording surface. A lens unit for an optical pickup device,
The correction element emits a first phase light beam and a second phase light beam that are provided with an optical path difference with respect to the incident light beam having the wavelength λ1 and have different phase states. When the first phase light beam is incident on the first objective lens, the first objective light is condensed on the information recording surface of the first optical information recording medium, and when the second phase light beam is incident, the second optical information is collected. It is characterized by being focused on the information recording surface of the recording medium.

  According to the present invention, the correction element emits a first phase light beam and a second phase light beam that are different in phase from each other by giving an optical path difference to the incident light beam having the wavelength λ1. Therefore, when the first objective lens enters the first phase light beam, the first objective lens can focus the light on the information recording surface of the first optical information recording medium (for example, BD), and the second objective lens. Can be focused on the information recording surface of the second optical information recording medium (for example, HD), thereby using a single first light source and using a movable mirror or the like. BD and HD compatible use can be realized with a simple and low-cost configuration, and in addition, the second objective lens can be used compatible with DVD or CD as the third optical information recording medium. it can. In such a case, since the existing product can be used as the second objective lens, the cost can be kept low. Note that “different phase states” refers to a state in which the focal positions are different when the first phase light beam and the second phase light beam having different phase states are incident on the first objective lens. And

  A lens unit for an optical pickup device according to a second aspect is characterized in that, in the invention according to the first aspect, the lens unit is made of plastic, and thus can be mass-produced at a low cost.

  A lens unit for an optical pickup device according to a third aspect of the present invention is the lens unit according to the first aspect, wherein the lens unit is made of glass, so that an objective lens having excellent temperature characteristics and the like is provided. it can.

  According to a fourth aspect of the present invention, in the lens unit for the optical pickup device according to the second or third aspect, the first objective lens and the second objective lens are integrally formed. Therefore, it is excellent in assembling and handling.

  The lens unit for an optical pickup device according to claim 5 is the invention according to claim 2 or 3, wherein the first objective lens and the second objective lens are formed separately. Therefore, the degree of freedom of assembly is increased because tilting can be independently performed at the time of assembly, and the distance between the optical axes can be arbitrarily adjusted.

  A lens unit for an optical pickup device according to a sixth aspect is the invention according to any one of the first to fifth aspects, wherein the correction element has an optical path difference providing structure. The optical path difference providing structure refers to a structure that provides an optical path difference, and includes a diffraction structure and NPS.

  A lens unit for an optical pickup device according to a seventh aspect has a third light source that emits a light beam having a wavelength λ3 (λ3> λ2) in the invention according to any one of the first to sixth aspects, The second objective lens has an optical path difference providing structure, and the light beam from the third light source is transmitted through the second objective lens to a fourth optical information recording medium having a protective substrate thickness t4 (t4> t3). Since it is possible to record and / or reproduce information on the information recording surface by focusing on the information recording surface, for example, four types of light such as BD, HD, DVD, and CD are used. An information recording medium can be used interchangeably.

  An optical pickup device according to an eighth aspect includes the lens unit according to any one of the first to seventh aspects.

  In this specification, the objective lens is, in a narrow sense, a light collecting action that is arranged to face the optical information recording medium at the position closest to the optical information recording medium when the optical information recording medium is loaded in the optical pickup device. It shall refer to the lens it has.

  According to the present invention, it is possible to provide a simple and low-cost lens unit for an optical pickup device and an optical pickup device using the same, although different types of optical disks can be used.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 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.

  The optical pickup device PU1 emits a blue-violet laser beam (first beam) having a wavelength λ1 = 407 nm, which is emitted when information is recorded / reproduced with respect to the BD (or HD) that is the first optical information recording medium. A laser beam (second beam) having a wavelength λ2 = 655 nm is emitted when information is recorded / reproduced with respect to the first light emitting point EP1 (first light source) and the DVD that is the third optical information recording medium. The second light emitting point EP2 (second light source), the first light receiving unit DS1 that receives the reflected light beam from the information recording surface RL1 of BD (or HD), and the reflected light beam from the information recording surface RL2 of the DVD. Light is emitted when information is recorded / reproduced with respect to the laser module LM composed of the second light receiving unit DS2 for receiving light and the prism PS, and the CD which is the second optical information recording medium, and has a wavelength of λ3 = 785 nm. Les A third light source for emitting laser light flux (third light flux) has a hologram laser HL is a light-emitting portion and the light-receiving elements integrated light source unit that integrates a photodetector and a lens unit OU. The lens unit OU is directly driven by the actuator AC1.

  In the present embodiment, a lens unit OU is arranged to face the optical disk. FIG. 2 is a cross-sectional view of the lens unit OU. The lens unit OU includes a frame F integrally formed so that a part of the flange portion FL2 of the second objective lens OBJ2 is connected to the cylindrical portion CY, a first objective lens OBJ1, and a correction element. It consists of a certain diffraction plate DP. An opening AP having an axis parallel to the optical axis X2 of the second objective lens OBJ2 is formed in the cylindrical portion CY of the frame F. In the cylindrical portion CY, a step SP1 is formed on the optical disc side (lower side in FIG. 2) of the opening AP, and a step SP2 is formed on the light source side (upper side in FIG. 2) of the opening AP. Further, the end surface on the light source side of the cylindrical portion CY is a tapered surface TP facing outward. In addition, it is preferable to form an antireflection film for light of wavelength λ3, for example, on the entire frame F (including the second objective lens OBJ2).

  In FIG. 2, the flange portion FL1 of the first objective lens OBJ1 is attached to the step portion SP1. A diffraction plate DP, which is an optical element, is attached to a step SP2 that is inclined with respect to a plane orthogonal to the optical axis X1 of the first objective lens OBJ1. Therefore, although the optical axis of the diffraction plate DP is inclined with respect to the optical axis X1, the direction of the inclination is not limited to the example shown in FIG.

The diffractive plate DP is formed with a diffractive structure DOE which is an optical path difference providing structure on one surface, the other surface is a flat surface, and a stepped portion so that the diffractive structure DOE faces the inside of the cylindrical part CY. It is attached to SP2. As shown in FIG. 3, the diffractive structure DOE has a step-like annular zone structure, and when a light beam IL having a wavelength λ1 is incident, the 0th-order diffracted light having a light intensity of 50% with respect to the incident light beam IL ( The first phase light beam OL ₀ and the first-order diffracted light (second phase light beam) OL ₁ having a light intensity of 50% are emitted. The light beam emitted from the diffractive structure DOE is not limited to the above order. Furthermore, a diffractive structure that compensates for wavelength characteristics and temperature characteristics may be provided on the other surface, or may be superimposed on one surface. Conversely, the coma aberration of the second objective lens OBJ2 may be matched with the tilt direction of the diffraction plate DP. Further, the coma aberration of the diffraction plate DP and the coma aberration of the first objective lens OBJ1 may be combined so as to cancel each other. The optical surface of the second objective lens OBJ2 is provided with a diffractive structure (not shown) that corrects spherical aberration caused by the difference in thickness of the protective substrate between the DVD and the CD.

  FIG. 4 is a diagram illustrating an assembly process of the lens unit OU. A first objective lens OBJ2 made of glass (which may be made of plastic) is inserted from below into the opening AP of the cylindrical portion CY with respect to the frame F formed from a mold (not shown), and the diffraction plate DP is The optical element OU can be assembled by inserting from above the opening AP and fixing with an adhesive. The flange portion FL1 of the first objective lens OBJ1 may be brought into contact with the stepped portion SP1 (FIG. 2) of the frame body F, but is held in a state with a slight gap therebetween, and the second objective lens. It is preferable that the OBJ2 is assembled while adjusting the parallelism and shift amount of the optical axes X1 and X2 described above.

  In the present embodiment, the first optical information recording medium BD and the second optical information recording medium HD are condensed using the diffraction plate DP and the first objective lens OBJ1, and the third The second objective lens is used to condense the DVD as the optical information recording medium and the CD as the fourth optical information recording medium.

  In the optical pickup device PU1, when recording / reproducing information with respect to the BD, the frame F is moved to the position shown in FIG. 1, the first objective lens OBJ1 is inserted into the optical path, and the first The light emitting point EP1 is caused to emit light. The divergent light beam emitted from the first light emitting point EP1 is converted into a parallel light beam by the collimator COL as shown by the solid line in FIG. 1, passes through the beam splitter BS, and further in the state of a parallel light beam. After passing through the diffraction plate DP, as shown by the dotted line, the 0th-order diffracted light is incident on the first objective lens OBJ1 in the form of a parallel light beam and then formed on the information recording surface RL1 via the protective substrate PL1 of the BD. Although it becomes a spot, the first-order diffracted light generated from the diffraction plate DP becomes flare light on the information recording surface after passing through the first objective lens OBJ1, so that it does not adversely affect BD information recording / reproduction. The first objective lens OBJ1 is driven by the biaxial actuator AC1 together with the frame body F to perform focusing and tracking.

  The reflected light beam modulated by the information pits on the information recording surface RL1 is again transmitted through the first objective lens OBJ1, the diffraction plate DP, the beam splitter BS, and the collimator COL, and then enters the laser module LM. After being reflected twice, it converges to the first light receiving part DS1. And the information recorded on BD can be read using the output signal of 1st light-receiving part DS1. Spherical aberration caused by temperature changes during BD recording / reproduction and spherical aberration due to the use of a two-layer disc can be corrected by driving the collimator COL.

  In the optical pickup device PU1, when recording / reproducing information with respect to the HD, the frame F is moved to the position shown in FIG. 1, the first objective lens OBJ1 is inserted into the optical path, and the first The light emitting point EP1 is caused to emit light. The divergent light beam emitted from the first light emitting point EP1 is converted into a parallel light beam by the collimator COL as shown by the solid line in FIG. 1, passes through the beam splitter BS, and further in the state of a parallel light beam. After passing through the diffraction plate DP, the first-order diffracted light is incident on the first objective lens OBJ1 in the state of a weak finite divergent beam as shown by the solid line, and then formed on the information recording surface RL1 via the HD protective substrate PL1. However, since the 0th-order diffracted light generated from the diffraction plate DP passes through the first objective lens OBJ1 and becomes flare light on the information recording surface, it does not adversely affect HD information recording / reproduction. The first objective lens OBJ1 is driven by the biaxial actuator AC1 together with the frame body F to perform focusing and tracking.

  The reflected light beam modulated by the information pits on the information recording surface RL1 is again transmitted through the first objective lens OBJ1, the diffraction plate DP, the beam splitter BS, and the collimator COL, and then enters the laser module LM. After being reflected twice, it converges to the first light receiving part DS1. And the information recorded on HD can be read using the output signal of 1st light-receiving part DS1. Spherical aberration caused by temperature change during HD recording / reproduction and spherical aberration caused by using a two-layer disc can be corrected by driving the collimator COL.

  In the optical pickup device PU1, when recording / reproducing information with respect to a DVD, the frame F is moved upward in the drawing from the position shown in FIG. 1, and the second objective lens OBJ2 is inserted into the optical path. Then, the second light emitting point EP2 is caused to emit light. The divergent light beam emitted from the second light emitting point EP2 is converted into a parallel light beam by the collimator COL as shown by the alternate long and short dash line in FIG. 1, passes through the beam splitter BS, and the second objective lens. It is incident on OBJ2 in the state of a parallel light beam. The light beam that has passed through the second objective lens OBJ2 becomes a spot formed on the information recording surface RL2 via the DVD protective substrate PL2. The objective lens OBJ1 is driven together with the frame F by a biaxial actuator AC1 to perform focusing and tracking.

  The reflected light flux modulated by the information pits on the information recording surface RL2 is again transmitted through the second objective lens OBJ2, the beam splitter BS, and the collimator COL, then enters the laser module LM, and then is reflected twice in the prism. After that, it converges on the second light receiving part DS2. Then, information recorded on the DVD can be read using the output signal of the second light receiving unit DS2.

  When recording / reproducing information with respect to the CD in the optical pickup device PU1, the frame F is moved upward from the position shown in FIG. 1, and the second objective lens OBJ2 is inserted into the optical path. Then, the hologram laser HL is caused to emit light. The divergent light beam emitted from the hologram laser HL is reflected by the beam splitter BS and enters the second objective lens OBJ2 in the state of a finite divergent light beam, as depicted by the dotted line in FIG. To a spot formed on the information recording surface RL3 via the CD protective substrate PL3. The second objective lens OBJ2 is driven together with the frame F by the biaxial actuator AC1 to perform focusing and tracking.

  The reflected light beam modulated by the information pits on the information recording surface RL3 is reflected again by the second objective lens OBJ2 and the beam splitter BS, then enters the hologram laser HL, and converges on the light receiving surface of the photodetector. And the information recorded on CD can be read using the output signal of a photodetector. In the above embodiment, the example in which the second objective lens has only a refractive surface has been described. However, the second objective lens is caused by compatibility of a different optical information recording medium, temperature change, and slight wavelength change. A diffractive structure may be provided for the purpose of correcting changes in spherical aberration and the like.

  According to the present embodiment, the diffractive plate DP emits 0th-order diffracted light and 1st-order diffracted light with respect to the incident light beam having the wavelength λ1, so that the first objective lens OBJ1 has 0th-order diffracted light. Is incident on the information recording surface of the BD, and when the first-order diffracted light is incident, the light can be condensed on the information recording surface of the HD. In addition, BD and HD can be used interchangeably with a simple and low-cost configuration without using a movable mirror or the like. In addition, because the second objective lens OBJ2 can be used for compatibility with DVDs and CDs, information can be recorded / reproduced on four different types of optical disks.

  FIG. 5 is a cross-sectional view similar to FIG. 2 of a lens unit according to a modification. In FIG. 5, the first objective lens OBJ1 and the second objective lens OBJ2 are connected by a flange portion FL, and are integrally formed of glass or plastic. The cylindrical body CY is bonded and fixed to the upper surface of the flange portion FL, and the diffraction plate DP is further bonded to the stepped portion SP2. Since other configurations are the same as those in the above-described embodiment, the description thereof is omitted.

  FIG. 6 is a cross-sectional view of a correction element according to a modification. In FIG. 6, the optical surface S1 of the correction element DP includes a first region DPa that is a concave aspheric surface including the optical axis, and a planar second region DPb that is formed around the first region DPa. The optical surface S2 of the correction element DP is a plane. Thus, since a part of the optical surface S1 of the correction element DP is an aspherical refracting surface and the rest is a flat surface, the light beam passing through the first region DPa is weakly finite when the light beam having the wavelength λ1 is incident. A divergent light beam is converged on the HD information recording surface by the first objective lens OBJ1, and a light beam passing through the second region DPb becomes a parallel light beam and is condensed on the BD information recording surface by the first objective lens OBJ1. The Rukoto.

  In FIG. 1, the frame F is configured to move, but it may be a fixed configuration. That is, the two objective lenses may be both arranged on the radial direction or may be perpendicular to the radial direction. In the case of a fixed configuration, two optical paths for guiding the light beam to the objective lens, such as a collimator lens, are required, but a configuration suitable for the first objective lens side and a configuration suitable for the second objective lens side may be taken. There is an advantage that you can. In particular, it is preferable to divide the collimating lens into a blue light source and a DVD / CD because correction suitable for each can be made.

(Example)
Next, examples will be described. This embodiment is of a lens unit suitable for the optical pickup device PU1 shown in FIG. Table 1 shows lens data of the first objective lens according to the example, and Table 2 shows lens data of the second objective lens. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) is represented by using E (for example, 2.5E-3).

  The correction element of the present embodiment has a superposition type diffractive structure. The optical surfaces of the first objective lens and the second objective lens are aspherical surfaces that are axisymmetric about the optical axis and are defined by mathematical formulas obtained by substituting the coefficients shown in Tables 1 and 2 into Formula 1, respectively. Is formed.

Here, X (h) is an axis in the optical axis direction (the light traveling direction is positive), κ is a conical coefficient, A _2i is an aspherical coefficient, and h is a height from the optical axis.

  Further, the optical path length given to the light flux of each wavelength by the diffractive structure is defined by a mathematical formula in which the coefficient shown in Table 1 is substituted into the optical path difference function of Formula 2.

λ is the wavelength of the incident light beam, λB is the manufacturing wavelength (blazed wavelength), dor is the diffraction order, and C _2i is the coefficient of the optical path difference function.

It is a figure which shows schematically the structure of optical pick-up apparatus PU1. It is sectional drawing of the lens unit OU concerning this Embodiment. It is a schematic diagram which expands and shows the cross section of the diffraction structure provided in the correction element. It is a figure which shows the assembly process of lens unit OU. It is sectional drawing of the optical element unit concerning the modification of this Embodiment.

Explanation of symbols

AC1 Biaxial actuator AP Aperture BS Beam splitter COL Collimator CY Cylindrical portion DOE Diffraction structure DP Diffraction plate DS1 First light receiving portion DS2 Second light receiving portion EP1 First light emitting point EP2 Second light emitting point F Frame body FL1 Flange Part FL2 flange part HL hologram laser LM laser module OBJ1 first objective lens OBJ2 second objective lens OU optical element units PL1 to PL4 protective substrate PS prism PT protective member PU1 optical pickup devices RL1 to RL4 information recording surface S1 optical surface S2 Optical surface SP1 Step portion SP2 Step portion TP Tapered surface X1 Optical axis X2 Optical axis

Claims (8)

A lens unit including a first light source that emits a light beam having a wavelength λ1, a second light source that emits a light beam having a wavelength λ2 (λ2> λ1), a correction element, a first objective lens, and a second objective lens And condensing the light beam from the first light source on the information recording surface of the first optical information recording medium having the protective substrate thickness t1 through the correction element and the first objective lens, Information can be recorded and / or reproduced on the information recording surface, and second optical information recording with a protective substrate thickness t2 (t2> t1) is performed via the correction element and the second objective lens. By focusing on the information recording surface of the medium, information can be recorded and / or reproduced on the information recording surface, and the light beam from the second light source is transmitted to the second objective lens. Through the third optical information of the protective substrate thickness t3 (t3 ≧ t2) By focused on the information recording surface of the recording medium, a lens unit for the optical pickup device which is capable of recording and / or reproducing information for the information recording surface,
The correction element emits a first phase light beam and a second phase light beam that are provided with an optical path difference with respect to the incident light beam having the wavelength λ1 and have different phase states. When the first phase light beam is incident on the first objective lens, the first objective light is condensed on the information recording surface of the first optical information recording medium, and when the second phase light beam is incident, the second optical information is collected. A lens unit for an optical pickup device, wherein the lens unit is focused on an information recording surface of a recording medium.   The lens unit for an optical pickup device according to claim 1, wherein the lens unit is made of plastic.   The lens unit for an optical pickup device according to claim 1, wherein the lens unit is made of glass.   The lens unit for an optical pickup device according to claim 2 or 3, wherein the first objective lens and the second objective lens are integrally formed.   The lens unit for an optical pickup device according to claim 2 or 3, wherein the first objective lens and the second objective lens are formed separately.   The lens unit for an optical pickup device according to claim 1, wherein the correction element has an optical path difference providing structure.   A third light source that emits a light beam having a wavelength of λ3 (λ3> λ2), the second objective lens has an optical path difference providing structure, and the light beam from the third light source is By focusing on the information recording surface of the fourth optical information recording medium having the protective substrate thickness t4 (t4> t3) through the lens, information can be recorded and / or reproduced on the information recording surface. The lens unit for an optical pickup device according to claim 1, wherein the lens unit is a lens unit.   An optical pickup device comprising the lens unit according to claim 1.

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