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WO2013168692A1 - Objectif et dispositif de capture optique - Google Patents

Objectif et dispositif de capture optique Download PDF

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Publication number
WO2013168692A1
WO2013168692A1 PCT/JP2013/062815 JP2013062815W WO2013168692A1 WO 2013168692 A1 WO2013168692 A1 WO 2013168692A1 JP 2013062815 W JP2013062815 W JP 2013062815W WO 2013168692 A1 WO2013168692 A1 WO 2013168692A1
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WIPO (PCT)
Prior art keywords
objective lens
basic structure
light
optical
path difference
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
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PCT/JP2013/062815
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English (en)
Japanese (ja)
Inventor
立山清乃
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Konica Minolta Inc
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Konica Minolta Inc
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Publication date
Application filed by Konica Minolta Inc filed Critical Konica Minolta Inc
Priority to CN201380024707.XA priority Critical patent/CN104335277A/zh
Publication of WO2013168692A1 publication Critical patent/WO2013168692A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1353—Diffractive elements, e.g. holograms or gratings
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1365—Separate or integrated refractive elements, e.g. wave plates
    • G11B7/1367—Stepped phase plates
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—Lenses
    • G11B7/1374—Objective lenses
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1392—Means for controlling the beam wavefront, e.g. for correction of aberration
    • G11B7/13922—Means for controlling the beam wavefront, e.g. for correction of aberration passive
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
    • G11B2007/0006—Recording, reproducing or erasing systems characterised by the structure or type of the carrier adapted for scanning different types of carrier, e.g. CD & DVD
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/125—Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for controlling the size or intensity of optical spots or optical traces
    • G11B7/127—Lasers; Multiple laser arrays
    • G11B7/1275—Two or more lasers having different wavelengths

Definitions

  • the present invention relates to an optical pickup device, an objective lens, and an optical information recording / reproducing apparatus capable of recording and / or reproducing (recording / reproducing) information interchangeably with different types of optical discs.
  • a laser light source used as a light source for reproducing information recorded on an optical disc and recording information on the optical disc has been shortened.
  • a wavelength 390 such as a blue-violet semiconductor laser is used.
  • a laser light source of ⁇ 420 nm has been put into practical use.
  • these blue-violet laser light sources are used, it is possible to record 15 to 20 GB of information on an optical disk having a diameter of 12 cm when an objective lens having the same numerical aperture (NA) as that of a DVD (digital versatile disk) is used.
  • NA of the objective optical element is increased to 0.85, 23 to 25 GB of information can be recorded on an optical disk having a diameter of 12 cm.
  • BD Blu-ray Disc
  • the BD is an example of an optical disc that uses an NA 0.85 objective lens as described above. Since the coma generated due to the tilt (skew) of the optical disk increases, the BD has a thinner protective substrate (0.1 mm with respect to 0.6 mm of DVD) than the case of the DVD cage, and is caused by skew. The amount of coma is reduced.
  • an information system for BD and an optical system for DVD and CD are used.
  • a method of selectively switching according to the recording density of the optical disk for recording / reproducing the image is conceivable, a plurality of optical systems are required, which is disadvantageous for miniaturization and increases the cost.
  • the optical system for BD and the optical system for DVD or CD can be shared. It is preferable to reduce the number of optical components constituting the pickup device as much as possible. And, it is most advantageous to simplify the configuration of the optical pickup device and to reduce the cost to make the objective lens arranged facing the optical disc in common.
  • an optical path difference providing structure such as a diffraction structure having a wavelength dependency of spherical aberration in the objective lens. is there.
  • the objective lens used in common for the three types of optical disks of BD, DVD, and CD needs to be able to cope with the difference in the required numerical aperture of BD, DVD, and CD.
  • a light beam that has passed through almost the entire area of the effective optical surface of the objective lens is condensed on the information recording surface of the BD.
  • the light beam that has passed through the region near the center of the lens is condensed on the information recording surface of the CD, but the light beam that has passed through the outer region of the lens needs to be blown off as a flare so as not to be collected on the information recording surface of the CD. Therefore, as shown in FIG.
  • the objective lens used in common for the three types of optical disks of BD, DVD, and CD collects light beams for concentric three regions (BD, DVD, and CD) as shown in FIG. Center region CN, BD and intermediate region MD for condensing the luminous flux for DVD, and peripheral region OT for condensing the luminous flux for BD), and each region needs to exhibit different optical performance behavior Comes out. Further, in order to show the behavior of different optical performance, a lens having a different structure that generates different diffraction orders for each region has been considered.
  • Patent Document 1 by defining a relational expression of the optical path difference function in the central region and the peripheral region, spherical aberration when using three types of optical discs is corrected well, and at the same time, spot performance deterioration due to unnecessary diffraction order light is reduced.
  • three types of compatible objective lenses for optical discs that can be avoided and have a sufficient working distance, and an optical information recording / reproducing apparatus equipped with the objective lenses.
  • the objective lens described in Patent Document 1 is not easy to manufacture because the number of ring zones in the peripheral region is very large and the pitch (ring zone width in the direction perpendicular to the optical axis) is also small. This problem is particularly noticeable when the objective lens is downsized. It has also been found that there is a problem that the spot diameter increases when BD is used. As a result of intensive research on the increase in the BD spot diameter, the present inventor has found that there are the following three causes.
  • the first cause is that the expected angle of the light source side optical surface is large in the vicinity of the effective diameter of the objective lens when a BD light beam is used.
  • the power balance between the light source side optical surface and the disk side optical surface is uniquely determined, and therefore the light source side optical surface expected angle increases near the effective diameter of the light flux with wavelength ⁇ 1. Therefore, it becomes difficult for the cutting tool for cutting the die to cut the optical path difference providing structure as designed, and the processing accuracy is lowered.
  • the second cause is an increase in reflectivity associated with an increase in the incident angle of light on the optical surface because the expected angle of the objective lens is large.
  • the rim intensity is reduced and the amount of transmitted light to the focused spot is reduced. Therefore, a phenomenon that can be referred to as a reverse apodization effect occurs. And an increase in spot diameter when using BD may occur.
  • FIG. 2 is a diagram illustrating a part of a cross-sectional view of an objective lens provided with a blazed optical path difference providing structure as an example.
  • a serrated annular zone R is formed concentrically along the mother aspherical surface.
  • the light beam LB1 incident on the root side of the sawtooth passes through the annular zone R, exhibits a behavior based on the design, and travels in the objective lens.
  • the light beam LB2 (indicated by hatching) incident on the leading end side of the saw blade is reflected by the inner side surface (step surface) SP after entering the annular zone R, so-called “shadow effect”. Is generated. Due to the effect of the shadow, the light beam LB2 is not condensed on the information recording surface of the optical disc, and the use efficiency of light is reduced accordingly. The effect of the shadow is particularly significant in the high NA region where the light refraction angle is large. In addition, due to mold processing accuracy and transferability problems, a fine shape such as the tip of the serrated ring zone or the vicinity of the root tends to cause a molding error with respect to the design shape, thereby increasing scattered light. Therefore, the use efficiency of light is reduced. That is, when the number of ring zones of the optical path difference providing structure is increased, the light region that does not contribute to light collection increases, and accordingly, the light use efficiency decreases accordingly.
  • the number of annular zones in the peripheral region is very large, and the number of annular zones tends to increase from the optical axis side toward the periphery in the peripheral region.
  • the influence of the shadow effect becomes very large, and the rim strength is reduced.
  • a phenomenon that can be called a reverse apodization effect occurs, and an increase in the spot diameter when BD is used has occurred.
  • the present invention has been made in view of the above-described problems, and has improved the moldability of the objective lens, can cope with downsizing, and is stable by forming an appropriate spot diameter even when using a BD. It is an object of the present invention to provide a compatible single objective lens for three types of optical discs of BD / DVD / CD capable of recording / reproducing information, and an optical pickup device equipped with this objective lens.
  • the objective lens according to claim 1 emits a first light source that emits a first light flux having a first wavelength ⁇ 1 (390 nm ⁇ ⁇ 1 ⁇ 415 nm) and a second light flux that has a second wavelength ⁇ 2 (630 nm ⁇ ⁇ 2 ⁇ 670 nm). And a third light source that emits a third light beam having a third wavelength ⁇ 3 (760 nm ⁇ ⁇ 3 ⁇ 820 nm), and a protective substrate having a thickness t1 using the first light beam.
  • An objective lens used in an optical pickup device for recording and / or reproducing information of a CD having a protective substrate having a thickness of t3 (t2 ⁇ t3) The objective lens is a single lens, The optical surface of the objective lens has at least a central region, an intermediate region around the central region, and a peripheral region around the intermediate region, The central region has a first optical path difference providing structure, The intermediate region has a second optical path difference providing structure, The peripheral region has a third optical path difference providing structure; The objective lens condenses the first light flux that passes through the central region so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux that passes through the central region.
  • the objective lens condenses the first light flux passing through the intermediate area so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passes through the intermediate area. Is recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the intermediate region is recorded and / or recorded on the information recording surface of the CD.
  • the objective lens condenses the first light flux passing through the peripheral area so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passes through the peripheral area. Is recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the peripheral area is recorded on the information recording surface of the CD.
  • the first optical path difference providing structure is a structure in which at least a first basic structure and a second basic structure are overlapped,
  • the first basic structure is a blaze-type structure, and the first-order diffracted light quantity of the first light beam that has passed through the first basic structure is made larger than any other order of diffracted light quantity, and passes through the first basic structure.
  • the first-order diffracted light quantity of the second light flux is made larger than any other order diffracted light quantity, and the first-order diffracted light quantity of the third light flux that has passed through the first basic structure is changed to any other order diffracted light quantity.
  • the second basic structure is a blazed structure, and the second-order diffracted light quantity of the first light beam that has passed through the second basic structure is made larger than any other order of diffracted light quantity, and passes through the second basic structure.
  • the first order diffracted light quantity of the second light flux is made larger than any other order diffracted light quantity, and the first diffracted light quantity of the third light flux that has passed through the second basic structure is changed to any other order diffracted light quantity.
  • the second optical path difference providing structure is a structure in which at least a third basic structure and a fourth basic structure are overlapped,
  • the third basic structure is a blazed structure, and the first-order diffracted light quantity of the first light beam that has passed through the third basic structure is made larger than any other order of diffracted light quantity, and passes through the third basic structure.
  • the first-order diffracted light amount of the second light flux is made larger than any other order diffracted light amount
  • the fourth foundation structure is a blazed structure, and the fifth or seventh-order diffracted light quantity of the first light flux that has passed through the fourth basic structure is made larger than any other order of diffracted light quantity, Making the third or fourth order diffracted light quantity of the second light flux that has passed through the structure larger than any other order diffracted light quantity;
  • the third optical path difference providing structure has at least a fifth basic structure,
  • the fifth basic structure is a blazed structure, and the second-order or fourth-order diffracted light quantity of the first light beam that has passed through the fifth basic structure is made larger than any other order diffracted light quantity. It is said.
  • the three types of optical disks of BD / DVD / CD can be used interchangeably with a common objective lens.
  • the first and second optical path difference providing structures are formed by superimposing two types of blazed basic structures, the degree of design freedom is 2 compared to the case where the optical path difference providing structure is formed with a single structure.
  • the magnification can be freely determined for the three disks while achieving compatibility.
  • the first basic structure existing in the central region has a (1/1/1) structure (the most first-order diffracted light is generated in any of the first light flux, the second light flux, and the third light flux).
  • the basic structure is a (2/1/1) structure (the second-order diffracted light is generated most in the first light beam, and the first-order diffracted light is generated most in the second light beam and the third light beam).
  • the amount of step of the diffractive structure in the central region does not become too large, it is possible to suppress light loss due to manufacturing errors, to suppress the shadow effect, to ensure high light utilization efficiency, and to maintain the wavelength and temperature. Variations in diffraction efficiency during the change can also be reduced.
  • the third basic structure existing in the intermediate region is a (1/1) structure (most first-order diffracted light is generated in the first and second light beams), and the fourth basic structure is a (5/3) structure ( The 5th-order diffracted light is generated most in the first light beam, the 3rd-order diffracted light is generated most in the second light beam, or the fourth basic structure is the (7/4) structure (the 7th-order diffracted light is most generated in the first light beam).
  • the second light flux most of the fourth-order diffracted light is generated), so that it is possible to appropriately control the variation of spherical aberration at the time of temperature change when using BD or DVD. Also, high diffraction efficiency can be obtained when using BD and DVD.
  • the pitch is set as compared with the first-order case. Since the number of ring zones can be reduced, manufacturing can be facilitated and errors can be reduced in both mold processing and resin molding. In the peripheral area, the number of annular zones tends to increase from the optical axis side toward the periphery, and the angle of view of the objective lens increases near the outer diameter in the peripheral area. Decrease, increase in reflectance, etc., especially when the pitch is small, this problem becomes significant and the rim strength decreases, but the pitch of the fifth foundation structure in the peripheral region can be increased.
  • the objective lens according to claim 2 is the invention according to claim 1, wherein the ratio of pupil transmittance in the vicinity of the peripheral area of the intermediate area to the vicinity of the optical axis center of the objective lens in the second light flux.
  • r2 is r2 ⁇ 0.9 (1)
  • the effective diameter of the objective lens in the second light flux is h2
  • the imaging magnification in the second light flux is m2
  • the focal length in the first light flux is f1, 0.66 ⁇ h2 / (2 ⁇ f1 ⁇ (1-m2)) ⁇ 0.75 (2) It is characterized by satisfying.
  • the objective lens of the present invention overlaps two basic structures in the intermediate region, and further, in a certain region, the number of annular zones tends to increase toward the periphery from the optical axis. In the vicinity of the region, the light utilization efficiency is deteriorated.
  • the ratio r2 of the pupil transmittance in the vicinity of the peripheral region of the intermediate region with respect to the vicinity of the optical axis center of the objective lens in the second light flux is within the range of the expression (1), and a phenomenon that can be called a reverse apodization effect occurs.
  • the spot diameter may increase.
  • the term “near” in the vicinity of the optical axis center refers to a range of 10% of the effective radius when using a DVD from the optical axis to the direction perpendicular to the optical axis.
  • the vicinity of the peripheral area of the intermediate area refers to a range of 10% of the effective radius when using the DVD with respect to the intermediate area direction from the boundary between the intermediate area and the peripheral area.
  • the objective lens of the present invention is a BD / DVD / CD compatible objective lens.
  • the sine condition cannot be satisfied for all optical disks, and BD, DVD, Since the sine condition is set so that the balance is improved to some extent in all the CDs, there is a possibility that the spot diameter is further increased when the BD is used.
  • the effective diameter of the second light flux when the objective lens is used in DVD is increased, that is, the NA is increased. Since the spot diameter when the DVD is used is narrowed down, the reverse apodization effect when using the DVD can be suppressed.
  • an intermediate region having a relatively small amount of transmitted light as compared with the vicinity of the optical axis is widened, so that an apodization effect is produced and the spot diameter of the BD can be reduced. This can be preferably used particularly for a compatible lens for reproduction of three types of optical disks of BD / DVD / CD.
  • the spot diameter when using the DVD is not reduced more than necessary. Also, on the DVD side, the error sensitivity of wavefront aberration can be kept small, and stable recording / reproducing characteristics can be obtained.
  • the objective lens described in claim 3 is the invention described in claim 1 or 2 and is characterized by satisfying the following expression. 1.0 ⁇ f1 ⁇ 2.2 (3)
  • the focal length f1 when using the BD is within the range of the expression (3), the objective lens becomes relatively small, and therefore the pitch in the vicinity of the outer diameter in the peripheral region becomes even finer, and the problem of the present invention is large.
  • such a large problem can be solved by making the second-order or fourth-order diffracted light quantity of the first light flux that has passed through the fifth basic structure larger than any other order diffracted light quantity.
  • the focal length f1 is within the range of the expression (3), the number of ring zones in the central region is increased in order to secure a working distance when using the CD, that is, in order to increase the paraxial power of diffraction.
  • the working distance refers to the distance in the optical axis direction from the surface of the optical disk to the position closest to the optical disk of the objective lens.
  • the focal length is within the range of the expression (3), the distance from the objective lens to the disk can be reduced, and it can be suitably mounted on a slim type optical pickup device.
  • the objective lens according to claim 4 is the invention according to any one of claims 1 to 3, wherein when an effective diameter of the objective lens in the first light flux is h1, the following expression is obtained: It is characterized by satisfying. 1.9 ⁇ h1 ⁇ 3.0 (4)
  • the pitch in the vicinity of the outer diameter in the peripheral region becomes even finer, and the problem of the present invention becomes large.
  • This can be solved by making the second-order or fourth-order diffracted light quantity of the first light flux that has passed through the fifth basic structure larger than any other order diffracted light quantity.
  • the pitch in the vicinity of the intermediate region, particularly the peripheral region of the intermediate region is also small, there is a possibility that the spot diameter increases when using DVD or BD. In this case, satisfying the equation (2) solves the problem. it can.
  • the fourth-order and sixth-order optical path difference function coefficients are secondary in the optical path difference function (i is a natural number) of the i-th substructure.
  • the fourth-order and sixth-order optical path difference function coefficients Mi is the diffraction order in the optical path difference function of the i-th basic structure that maximizes the diffraction order of the incident light beam, and ⁇ (unit: mm) is the use of the incident light beam.
  • ⁇ B i (unit: mm) represents a manufacturing wavelength in the i-th basic structure, respectively)
  • the focal length of the first basic structure is expressed as fD 1
  • fD 1 ⁇ B 1 / (2 ⁇ C 12 ⁇ M1 ⁇ ⁇ )
  • M1 the value of M1 is 1.
  • the effective diameter (diameter) of the second light beam is defined as h2 (unit: mm)
  • the effective diameter (diameter) of the third light beam is defined as h3 (unit: mm)
  • the following conditional expression (6) ⁇ 0.025 ⁇ ( ⁇ 5 (h3 / 2) ⁇ 5 (h2 / 2)) / (M5 ⁇ f1) ⁇ 0.025 (6)
  • M5 ⁇ f1 the value of M5 is 2 or 4.
  • the chromatic aberration at the time of using the BD does not become too large while ensuring the working distance at the time of using the CD. If the lower limit of Expression (5) is exceeded, the pitch is widened, so that the workability is improved, and the amount of chromatic aberration generated when the first optical disk is used can be suppressed to a level that allows recording and reproduction. Moreover, it is preferable to fall below the upper limit of the formula (5) because a working distance when using a CD can be sufficiently secured.
  • the effective diameter (diameter) of the second light beam is defined as h2 (unit: mm) and the effective diameter (diameter) of the third light beam is defined as h3 (unit: mm)
  • the following condition (6) ⁇ 0.025 ⁇ ( ⁇ 5 (h3 / 2) ⁇ 5 (h2 / 2)) / (M5 ⁇ f1) ⁇ 0.025 (6) (However, the value of M5 is 2 or 4.)
  • An objective lens according to a sixth aspect is the invention according to any one of the first to fifth aspects, wherein the objective lens satisfies the following expression. 0.68 ⁇ h2 / (2 ⁇ f1 ⁇ (1-m2)) ⁇ 0.74 (2) ′
  • the pitch in the vicinity of the intermediate region, particularly the peripheral region of the intermediate region is also small, there is a possibility that the spot diameter will increase when using the DVD, but it is preferable because it can be solved by satisfying the equation (2) ′.
  • An objective lens according to a seventh aspect is the invention according to any one of the first to sixth aspects, wherein when the thickness of the objective lens on the optical axis is d (mm), It is characterized by satisfying the formula. 1.0 ⁇ d / f1 ⁇ 1.5 (7)
  • the objective lens When dealing with a short-wavelength, high-NA optical disk such as BD, the objective lens is likely to generate astigmatism and decent coma, but the above configuration causes astigmatism and It is possible to suppress the occurrence of decentration coma.
  • An objective lens according to an eighth aspect of the present invention is the invention according to any one of the first to seventh aspects, wherein the first basic structure provided at least in the vicinity of the optical axis of the central region has a light level difference. Facing the opposite direction of the axis, The second basic structure provided at least near the optical axis of the central region is characterized in that the step is directed in the direction of the optical axis.
  • the step amount in the optical axis direction can be further reduced, thereby suppressing the shadow effect and the diffraction efficiency at the time of wavelength variation. It is possible to further suppress the decrease in the above.
  • the objective lens according to claim 9 is the invention according to any one of claims 1 to 8, wherein the following expression is satisfied when the total number of annular zones in the peripheral region is N3: It is a feature. 5 (mm) ⁇ N3 ⁇ f1 ⁇ 100 (mm) (8)
  • An optical pickup device has the objective lens according to any one of the first to ninth aspects.
  • An optical pickup device is the optical pickup device according to the tenth aspect, in which at least the coupling lens through which the first light flux and the second light flux pass, and the coupling lens in the optical axis direction.
  • the position of the coupling lens in the optical axis direction is fixed.
  • the coupling lens is displaced in the optical axis direction so as to correspond to recording / reproduction on each information recording layer.
  • the function of displacing the coupling lens in the optical axis direction is indispensable.
  • the coupling lens may be fixed without being displaced in the optical axis direction. is there. The reason is that flare does not occur when using BD, but flare occurs when using DVD. By changing the coupling lens, the flare aberration changes, and as a result, the flare is recorded / reproduced.
  • the objective lens of the present invention is used to suppress aberrations caused by changes in temperature and wavelength when using a DVD.
  • a coupling lens is used when the second light beam passes when using a DVD. Can be recorded / reproduced with respect to the information recording surface of the DVD even when the position in the optical axis direction is fixed (that is, when spherical aberration correction is not performed by the coupling lens).
  • the optical pickup device has at least three light sources: a first light source, a second light source, and a third light source. Furthermore, the optical pickup device of the present invention condenses the first light beam on the information recording surface of the BD, condenses the second light beam on the information recording surface of the DVD, and focuses the third light beam on the information recording surface of the CD.
  • the optical pickup device of the present invention includes a light receiving element that receives a reflected light beam from an information recording surface of a BD, DVD, or CD.
  • the BD has a protective substrate having a thickness t1 and an information recording surface.
  • the DVD has a protective substrate having a thickness t2 (t1 ⁇ t2) and an information recording surface.
  • the CD has a protective substrate having a thickness of t3 (t2 ⁇ t3) and an information recording surface.
  • the BD, DVD, or CD may be a multi-layer optical disc having a plurality of information recording surfaces.
  • BD is information recording / reproduction by a light beam having a wavelength of 390 to 415 nm, an objective lens having a designed NA of 0.80 to 0.90, and the thickness of the protective substrate is 0.02
  • a DVD means a light beam having a wavelength of 630 to 670 nm, and information is recorded / reproduced by an objective lens having a designed NA of 0.550 to 0.70.
  • DVD series optical discs of about 0.6 mm, including DVD-ROM, DVD-Video, DVD- Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like.
  • the CD is a light beam having a wavelength of 760 to 820 nm
  • information is recorded / reproduced by an objective lens having a designed NA of 0.40 to 0.55
  • the thickness of the protective substrate is A general term for CD series optical discs of about 1.2 mm, including CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW and the like.
  • the recording density the recording density of BD is the highest, followed by the order of DVD and CD.
  • the thickness of the protective substrate referred to here is the thickness of the protective substrate provided on the surface of the optical disk. That is, the thickness of the protective substrate from the optical disc surface to the information recording surface closest to the surface. 0.050 mm ⁇ t1 ⁇ 0.125 mm (9) 0.5mm ⁇ t2 ⁇ 0.7mm (10) 1.0 mm ⁇ t3 ⁇ 1.3 mm (11)
  • the first light source, the second light source, and the third light source are preferably laser light sources.
  • the laser light source a semiconductor laser, a silicon laser, or the like can be preferably used.
  • the wavelength ⁇ 3 ( ⁇ 3> ⁇ 2) preferably satisfies the following conditional expressions (12) and (13). 1.5 ⁇ ⁇ 1 ⁇ 2 ⁇ 1.7 ⁇ ⁇ 1 (12) 1.8 ⁇ ⁇ 1 ⁇ 3 ⁇ 2.0 ⁇ ⁇ 1 (13)
  • the first wavelength ⁇ 1 of the first light source is 390 nm or more and 415 nm or less
  • the second wavelength ⁇ 2 of the second light source is 630 nm or more and 670 nm or less
  • the third wavelength ⁇ 3 of the third light source is 760 nm or more and 820 nm or less.
  • first light source the second light source
  • third light source may be unitized.
  • the unitization means that the first light source and the second light source are fixedly housed in one package, for example.
  • first light source, the second light source, and the third light source may all be fixedly housed in one package.
  • a light receiving element to be described later may be packaged.
  • a photodetector such as a photodiode is preferably used.
  • Light reflected on the information recording surface of the optical disc enters the light receiving element, and a read signal of information recorded on each optical disc is obtained using the output signal. Furthermore, it detects the change in the light amount due to the spot shape change and position change on the light receiving element, performs focus detection and track detection, and based on this detection, the objective lens can be moved for focusing and tracking I can do it.
  • the light receiving element may comprise a plurality of photodetectors.
  • the light receiving element may have a main photodetector and a sub photodetector.
  • two sub photo detectors are provided on both sides of a photo detector that receives main light used for recording and / or reproducing information, and sub light for tracking adjustment is provided by the two sub photo detectors.
  • a light receiving element that receives light may be used.
  • the light receiving element may have a plurality of light receiving elements corresponding to the respective light sources.
  • the condensing optical system has an objective lens.
  • the condensing optical system preferably has a coupling lens such as a collimator in addition to the objective lens.
  • the coupling lens is a single lens or a lens group that is disposed between the objective lens and the light source and changes the divergence angle of the light beam.
  • the collimator is a type of coupling lens, and is a lens that emits light incident on the collimator as parallel light.
  • the objective lens refers to a single lens that is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing the light beam emitted from the light source on the information recording / reproducing surface of the optical disk. .
  • the single objective lens of the present invention is preferably a plastic lens.
  • a convex lens is preferable.
  • the objective lens preferably has a refractive surface that is aspheric.
  • the base surface on which the optical path difference providing structure is provided is preferably an aspherical surface.
  • the resin material has a refractive index in the range of 1.50 to 1.60 at a temperature of 25 ° C. with respect to a wavelength of 405 nm, and a wavelength of 405 nm associated with a temperature change within a temperature range of ⁇ 5 ° C. to 70 ° C.
  • the refractive index change rate dN / dT (° C.
  • the coupling lens is also a plastic lens.
  • a first preferred example includes a polymer block [A] containing a repeating unit [1] represented by the following formula (I), a repeating unit [1] represented by the following formula (I) and the following formula ( II) and / or polymer block [B] containing a repeating unit [3] represented by the following formula (III), and repeating in the block [A] From the block copolymer in which the relationship between the molar fraction a (mol%) of the unit [1] and the molar fraction b (mol%) of the repeating unit [1] in the block [B] is a> b. It is the resin composition which becomes.
  • R 1 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms
  • R 2 to R 12 each independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, a carbon number of 1 ⁇ 20 alkoxy groups or halogen groups.
  • R 13 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.
  • R 14 and R 15 each independently represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.
  • a second preferred example is obtained by addition polymerization of a monomer composition comprising at least an ⁇ -olefin having 2 to 20 carbon atoms and a cyclic olefin represented by the following general formula (IV).
  • Polymer (B) obtained by addition polymerization of polymer (A) and a monomer composition comprising an ⁇ -olefin having 2 to 20 carbon atoms and a cyclic olefin represented by the following general formula (V) ).
  • n is 0 or 1
  • m is 0 or an integer of 1 or more
  • q is 0 or 1
  • R 1 to R 18 , Ra and Rb each independently represent a hydrogen atom or a halogen atom.
  • R 15 to R 18 may be bonded to each other to form a monocycle or polycycle, and the monocycle or polycycle in parentheses may have a double bond, R 15 and R 16 , or R 17 and R 18 may form an alkylidene group.
  • R 19 to R 26 each independently represents a hydrogen atom, a halogen atom or a hydrocarbon group.
  • the following additives may be added.
  • Stabilizer It is preferable to add at least one stabilizer selected from a phenol stabilizer, a hindered amine stabilizer, a phosphorus stabilizer, and a sulfur stabilizer. By suitably selecting and adding these stabilizers, for example, it is possible to more highly suppress the white turbidity and the optical characteristic fluctuations such as the refractive index fluctuations when continuously irradiated with light having a short wavelength of 405 nm. .
  • phenol-based stabilizer conventionally known ones can be used.
  • 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate
  • 2 4-di-t-amyl-6- (1- (3,5-di-t-amyl-2-hydroxyphenyl) ethyl) phenyl acrylate and the like
  • JP-A Nos. 63-179953 and 1-168643 JP-A Nos. 63-179953 and 1-168643.
  • Preferred hindered amine stabilizers include bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (2,2,6,6-tetramethyl-4-piperidyl) succinate, bis ( 1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, bis (N-octoxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (N-benzyloxy-2, 2,6,6-tetramethyl-4-piperidyl) sebacate, bis (N-cyclohexyloxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (1,2,2,6,6) -Pentamethyl-4-piperidyl) 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-butylmalonate, bis (1-acryloyl-2,2, , 6-Tetramethyl-4-piperidyl) 2,2-bis (3,5-di-t-but
  • the preferable phosphorus stabilizer is not particularly limited as long as it is a substance usually used in the general resin industry.
  • triphenyl phosphite diphenylisodecyl phosphite, phenyl diisodecyl phosphite, tris (nonyl).
  • Phenyl) phosphite tris (dinonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite, 10- (3,5-di-t-butyl-4-hydroxybenzyl) -9 Monophosphite compounds such as 1,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; 4,4′-butylidene-bis (3-methyl-6-tert-butylphenyl-di-tridecyl) Phosphite), 4,4 'isopropylidene-bis (phenyl-di-alkyl (C12-C15)) Fight) and the like diphosphite compounds such as.
  • monophosphite compounds are preferable, and tris (nonylphenyl) phosphite, tris (dinonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite and the like are particularly preferable.
  • Preferred sulfur stabilizers include, for example, dilauryl 3,3-thiodipropionate, dimyristyl 3,3′-thiodipropionate, distearyl 3,3-thiodipropionate, lauryl stearyl 3,3- Thiodipropionate, pentaerythritol-tetrakis- ( ⁇ -lauryl-thio) -propionate, 3,9-bis (2-dodecylthioethyl) -2,4,8,10-tetraoxaspiro [5,5] undecane Etc.
  • each of these stabilizers is appropriately selected within a range not to impair the purpose of the present invention, but is usually 0.01 to 2 parts by mass with respect to 100 parts by mass of the alicyclic hydrocarbon-based copolymer, The amount is preferably 0.01 to 1 part by mass.
  • a surfactant is a compound having a hydrophilic group and a hydrophobic group in the same molecule.
  • the surfactant can prevent white turbidity of the resin composition by adjusting the rate of moisture adhesion to the resin surface and the rate of moisture evaporation from the surface.
  • hydrophilic group of the surfactant examples include a hydroxy group, a hydroxyalkyl group having 1 or more carbon atoms, a hydroxyl group, a carbonyl group, an ester group, an amino group, an amide group, an ammonium salt, a thiol, a sulfonate, A phosphate, a polyalkylene glycol group, etc. are mentioned.
  • the amino group may be primary, secondary, or tertiary.
  • the hydrophobic group of the surfactant include an alkyl group having 6 or more carbon atoms, a silyl group having an alkyl group having 6 or more carbon atoms, and a fluoroalkyl group having 6 or more carbon atoms.
  • the alkyl group having 6 or more carbon atoms may have an aromatic ring as a substituent.
  • Specific examples of the alkyl group include hexyl, heptyl, octyl, nonyl, decyl, undecenyl, dodecyl, tridecyl, tetradecyl, myristyl, stearyl, lauryl, palmityl, cyclohexyl and the like.
  • the aromatic ring include a phenyl group.
  • the surfactant only needs to have at least one hydrophilic group and hydrophobic group as described above in the same molecule, and may have two or more groups.
  • examples of such a surfactant include myristyl diethanolamine, 2-hydroxyethyl-2-hydroxydodecylamine, 2-hydroxyethyl-2-hydroxytridecylamine, 2-hydroxyethyl-2- Hydroxytetradecylamine, pentaerythritol monostearate, pentaerythritol distearate, pentaerythritol tristearate, di-2-hydroxyethyl-2-hydroxydodecylamine, alkyl (8-18 carbon atoms) benzyldimethylammonium chloride, ethylene
  • examples thereof include bisalkyl (carbon number 8 to 18) amide, stearyl diethanolamide, lauryl diethanolamide, myristyl diethanolamide, palmityl diethanolamide, and the like.
  • amine compounds or amide compounds having a hydroxyalkyl group are preferably used. In the present invention, two or more of these compounds may be used in combination.
  • the surfactant is added to 100 parts by mass of the alicyclic hydrocarbon-based polymer.
  • the addition amount of the surfactant is more preferably 0.05 to 5 parts by mass, still more preferably 0.3 to 3 parts by mass with respect to 100 parts by mass of the alicyclic hydrocarbon-based polymer.
  • Plasticizer The plasticizer is added as necessary to adjust the melt index of the copolymer.
  • Plasticizers include bis (2-ethylhexyl) adipate, bis (2-butoxyethyl) adipate, bis (2-ethylhexyl) azelate, dipropylene glycol dibenzoate, tri-n-butyl citrate, tricitrate citrate -N-butylacetyl, epoxidized soybean oil, 2-ethylhexyl epoxidized tall oil, chlorinated paraffin, tri-2-ethylhexyl phosphate, tricresyl phosphate, t-butylphenyl phosphate, tri-2-ethylhexyl phosphate Diphenyl, dibutyl phthalate, diisohexyl phthalate, diheptyl phthalate, dinonyl phthalate, diundecyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate, diisode
  • cycloolefin resins are preferably used.
  • ZEONEX manufactured by Nippon Zeon Co., Ltd. APEL manufactured by Mitsui Chemicals, Inc.
  • TOPAS® ADVANCED® POLYMERS manufactured by TOPAS and JSR manufactured by ARTON are preferable. Take as an example.
  • the Abbe number of the material constituting the objective lens is preferably 35 or more and 80 or less, more preferably 50 or more and 80 or less.
  • the objective lens is described below.
  • the objective lens of the present invention is a single lens, and at least one optical surface of the objective lens has at least a central region, an intermediate region around the central region, and a peripheral region around the intermediate region.
  • the central region is preferably a region including the optical axis of the objective lens, but a minute region including the optical axis is used as an unused region or a special purpose region, and the surroundings are defined as a central region (also referred to as a central region). Also good.
  • the central region, the intermediate region, and the peripheral region are preferably provided on the same optical surface. As shown in FIG. 1, the central region CN, the intermediate region MD, and the peripheral region OT are preferably provided concentrically around the optical axis on the same optical surface.
  • a first optical path difference providing structure is provided in the central area of the objective lens
  • a second optical path difference providing structure is provided in the intermediate area
  • a third optical path difference providing structure is provided in the peripheral area.
  • the central region, the intermediate region, and the peripheral region are preferably adjacent to each other, but there may be a slight gap between them.
  • the central area of the objective lens can be said to be a BD / DVD / CD shared area used for recording / reproducing BD, DVD and CD. That is, the objective lens condenses the first light flux passing through the central area so that information can be recorded / reproduced on the information recording surface of the BD, and the second light flux passing through the central area is recorded as information recording on the DVD. The light is condensed so that information can be recorded and / or reproduced on the surface, and the third light flux passing through the central region is condensed so that information can be recorded / reproduced on the information recording surface of the CD.
  • the first optical path difference providing structure provided in the central region has the BD protective substrate thickness t1 and the DVD protective substrate thickness with respect to the first and second light fluxes passing through the first optical path difference providing structure. It is preferable to correct spherical aberration generated due to the difference in thickness t2 / spherical aberration generated due to the difference in wavelength between the first light beam and the second light beam. Further, the first optical path difference providing structure is different from the thickness t1 of the BD protective substrate and the thickness t3 of the CD protective substrate with respect to the first and third light fluxes that have passed through the first optical path difference providing structure. It is preferable to correct the spherical aberration caused by the difference in the wavelength of the first light beam and the third light beam.
  • the intermediate area of the objective lens is used for BD / DVD recording / reproduction and can be said to be a BD / DVD shared area not used for CD recording / reproduction. That is, the objective lens condenses the first light flux passing through the intermediate area so that information can be recorded / reproduced on the information recording surface of the BD, and the second light flux passing through the intermediate area is recorded as information recording on the DVD. Light is collected so that information can be recorded / reproduced on the surface.
  • the third light flux passing through the intermediate region is not condensed so that information can be recorded / reproduced on the information recording surface of the CD.
  • the third light flux passing through the intermediate region of the objective lens preferably forms a flare on the information recording surface of the CD. As shown in FIG.
  • the spot center having a high light amount density in the order from the optical axis side (or the spot center) to the outside. It is preferable to have a portion SCN, a spot intermediate portion SMD whose light density is lower than that of the spot central portion, and a spot peripheral portion SOT whose light amount density is higher than that of the spot intermediate portion and lower than that of the spot central portion.
  • the center portion of the spot is used for recording / reproducing information on the optical disc, and the middle portion of the spot and the peripheral portion of the spot are not used for recording / reproducing information on the optical disc. In the above, this spot peripheral part is called flare.
  • the spot peripheral part may be called a flare.
  • the third light flux that has passed through the intermediate region of the objective lens preferably forms a spot peripheral portion on the information recording surface of the CD.
  • the peripheral region of the objective lens is used for BD recording / reproduction, and can be said to be a BD-dedicated region that is not used for DVD / CD recording / reproduction. That is, the objective lens condenses the first light flux passing through the peripheral region so that information can be recorded / reproduced on the information recording surface of the BD.
  • the second light flux that passes through the peripheral area is not condensed so that information can be recorded / reproduced on the information recording surface of the DVD, and the third light flux that passes through the peripheral area does not converge. Do not collect light so that information can be recorded / reproduced on top.
  • the second light flux and the third light flux that pass through the peripheral area of the objective lens preferably form a flare on the information recording surface of DVD and CD. That is, it is preferable that the second light flux and the third light flux that have passed through the peripheral area of the objective lens form a spot peripheral portion on the information recording surface of DVD and CD.
  • the first optical path difference providing structure is preferably provided in a region of 70% or more of the area of the central region of the objective lens, and more preferably 90% or more. More preferably, the first optical path difference providing structure is provided on the entire surface of the central region.
  • the second optical path difference providing structure is preferably provided in a region of 70% or more of the area of the intermediate region of the objective lens, and more preferably 90% or more. More preferably, the second optical path difference providing structure is provided on the entire surface of the intermediate region.
  • the third optical path difference providing structure is preferably provided in a region of 70% or more of the area of the peripheral region of the objective lens, and more preferably 90% or more. More preferably, the third optical path difference providing structure is provided on the entire surface of the peripheral region.
  • optical path difference providing structure referred to in this specification is a general term for structures that add an optical path difference to an incident light beam.
  • the optical path difference providing structure also includes a phase difference providing structure for providing a phase difference.
  • the phase difference providing structure includes a diffractive structure.
  • the optical path difference providing structure of the present invention is preferably a diffractive structure.
  • the optical path difference providing structure has a step, preferably a plurality of steps. This step adds an optical path difference and / or phase difference to the incident light flux.
  • the optical path difference added by the optical path difference providing structure may be an integer multiple of the wavelength of the incident light beam or a non-integer multiple of the wavelength of the incident light beam.
  • the steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis.
  • the objective lens provided with the optical path difference providing structure is a single aspherical lens
  • the incident angle of the light flux to the objective lens differs depending on the height from the optical axis.
  • Each will be slightly different.
  • the step amount increases as the distance from the optical axis increases even with the optical path difference providing structure that provides the same optical path difference.
  • the diffractive structure referred to in this specification is a general term for structures that have a step and have a function of converging or diverging a light beam by diffraction.
  • a plurality of unit shapes are arranged around the optical axis, and a light beam is incident on each unit shape, and the wavefront of the transmitted light is shifted between adjacent annular zones, resulting in new It includes a structure that converges or diverges light by forming a simple wavefront.
  • the diffractive structure preferably has a plurality of steps, and the steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis.
  • the objective lens provided with the diffractive structure is a single aspherical lens
  • the incident angle of the light beam to the objective lens differs depending on the height from the optical axis, so the step amount of the diffractive structure is slightly different for each annular zone. It will be.
  • the objective lens is a single lens aspherical convex lens, even if the diffractive structure generates diffracted light of the same diffraction order, the step amount increases as the distance from the optical axis increases.
  • the optical path difference providing structure has a plurality of concentric annular zones with the optical axis as the center.
  • the basic structure of the optical path difference providing structure can generally have various cross-sectional shapes (cross-sectional shapes on the plane including the optical axis), and the cross-sectional shape including the optical axis is roughly divided into a blazed structure and a staircase structure. Is done.
  • the blaze-type structure means that the cross-sectional shape including the optical axis of the optical element having the optical path difference providing structure is a sawtooth shape.
  • the expression is a sawtooth shape, a shape in which the apex portion of the sawtooth is rounded is also included in the sawtooth shape.
  • the upper side is the light source side and the lower side is the optical disc side, and the optical path difference providing structure is formed on a flat surface as an aspherical surface.
  • the length in the direction perpendicular to the optical axis of one blaze unit is called a pitch P.
  • the length of the step in the direction parallel to the optical axis of the blaze is referred to as a step amount B. (See Fig. 4 (a))
  • the staircase structure has a small staircase shape in cross section including the optical axis of an optical element having an optical path difference providing structure (referred to as a staircase unit). ).
  • V level means a ring-shaped surface (hereinafter also referred to as a terrace surface) corresponding to (or facing) the optical axis vertical direction in one step unit of the step structure. In other words, it is divided by V steps and divided into V ring zones.
  • a three-level or higher staircase structure has a small step and a large step.
  • the optical path difference providing structure illustrated in FIG. 4C is referred to as a five-level step structure
  • a two-level staircase structure will be described.
  • a plurality of annular zones including a plurality of concentric annular zones around the optical axis, and a plurality of annular zones including the optical axis of the objective lens have a plurality of stepped surfaces Pa and Pb extending in parallel to the optical axis,
  • the light source side terrace surface Pc for connecting the light source side ends of the adjacent step surfaces Pa and Pb and the optical disk side terrace surface Pd for connecting the optical disk side ends of the adjacent step surfaces Pa and Pb are formed.
  • the surface Pc and the optical disc side terrace surface Pd are alternately arranged along the direction intersecting the optical axis.
  • the length of one step unit in the direction perpendicular to the optical axis is referred to as a pitch P (see FIGS. 4C and 4D).
  • the length of the step in the direction parallel to the optical axis of the staircase is referred to as step amounts B1 and B2.
  • a large step amount B1 and a small step amount B2 exist (see FIG. 4C).
  • the optical path difference providing structure is preferably a structure in which a certain unit shape is periodically repeated.
  • the unit shape is periodically repeated here naturally includes shapes in which the same shape is repeated in the same cycle.
  • the unit shape that is one unit of the cycle has regularity, and the shape in which the cycle gradually increases or decreases gradually is also included in the “unit shape is periodically repeated”.
  • the sawtooth shape as a unit shape is repeated. As shown in FIG. 4 (a), the same sawtooth shape may be repeated, and as shown in FIG. 4 (b), the shape of the sawtooth shape gradually increases as it moves away from the optical axis. A shape in which the pitch becomes longer or a shape in which the pitch becomes shorter may be used.
  • the blazed structure has a step opposite to the optical axis (center) side, and in other areas, the blazed structure has a step toward the optical axis (center).
  • the first optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure may be provided on different optical surfaces of the objective lens, but are preferably provided on the same optical surface. Providing them on the same optical surface is preferable because it makes it possible to reduce eccentricity errors during manufacturing.
  • the first optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure are preferably provided on the light source side surface of the objective lens rather than the optical disk side surface of the objective lens.
  • the first optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure are preferably provided on the optical surface having the smaller absolute value of the radius of curvature of the objective lens.
  • the minimum annular zone width of the basic structure can be designed wider, and there is an advantage that light amount loss due to a step portion of the annular zone can be suppressed.
  • the annular structure does not wear when the objective lens is rubbed with a lens cleaner. It is also conceivable to provide the first basic structure and the second basic structure on different optical surfaces without overlapping. Similarly, the third basic structure and the fourth basic structure may be provided on different optical surfaces without overlapping.
  • the first optical path difference providing structure is a structure in which at least the first basic structure and the second basic structure are overlapped.
  • the first optical path difference providing structure is preferably a structure in which only the first basic structure and the second basic structure are overlapped. Since the optical path difference providing structure is made by superimposing two types of blazed basic structures, the design flexibility is doubled and compatibility is achieved compared to the case where the optical path difference providing structure is formed with a single structure. However, the magnification can be freely determined for the three disks.
  • the first basic structure is a blaze type structure.
  • the first basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the first basic structure larger than any other order of diffracted light quantity, and the first-order diffracted light quantity that has passed through the first basic structure. Is made larger than any other order of the diffracted light quantity, and the first order diffracted light quantity of the third light flux that has passed through the first basic structure is made larger than any other order of diffracted light quantity. This is called a (1/1/1) structure.
  • the diffraction order that maximizes the amount of diffracted light of the first light beam is an odd first order
  • different paraxial powers can be applied to BD and CD, and correction of relative spherical aberration that occurs between BD and CD is good. Can be done.
  • the first-order diffracted light which is a lower order, is generated when the first light beam is used, the step amount of the first basic structure does not become too large, making the manufacture easy, and suppressing the light amount loss caused by the manufacturing error. This is preferable because it can reduce the diffraction efficiency fluctuation at the time of wavelength fluctuation.
  • the first basic structure provided at least in the vicinity of the optical axis in the central region has a step in a direction opposite to the optical axis.
  • the step is directed in the direction opposite to the optical axis means a state as shown in FIG.
  • the first basic structure provided “at least in the vicinity of the optical axis of the central region” refers to a step at least closest to the optical axis among steps of the (1/1/1) structure.
  • at least 50% or more are directed in the direction opposite to the optical axis, more preferably 70% or more, and even more preferably 90% or more. Is in the opposite direction to the optical axis.
  • the step of the first basic structure provided near the middle region of the center region may face the direction of the optical axis. That is, as shown in FIG. 6 (b), when the first foundation structure is in the vicinity of the optical axis, the step is opposite to the optical axis. It is good also as a shape which faces the direction. However, it is preferable that all the steps of the first basic structure provided in the central region are directed in a direction opposite to the optical axis.
  • the direction of the step of the first basic structure in which the diffraction order of the first light beam is the first order is directed in the direction opposite to the optical axis, so that the three types of optical disks of BD / DVD / CD can be used interchangeably. Even with a thick objective lens having a large axial thickness, a working distance can be further ensured when the CD is used.
  • the first basic structure is the first basic structure from the viewpoint of securing a sufficient working distance when using a CD even in a thick objective lens having a thick on-axis thickness, which is used for compatibility with three types of optical disks of BD / DVD / CD. It is preferable to have paraxial power with respect to the light beam.
  • “having paraxial power” means that C 2 h 2 is not 0 when the optical path difference function of the first basic structure is expressed by the following equation ( 2 ).
  • the focal length of the first basic structure is defined as fD 1 (unit: mm)
  • fD 1 unit: mm
  • fD 1 ⁇ B 1 / (2 ⁇ C 12 ⁇ M1 ⁇ ⁇ )
  • M1 the diffraction order of the first basic structure
  • the “manufacturing wavelength” is the wavelength of the luminous flux that gives the highest Mi-order diffraction efficiency when passing through the i-th basic structure.
  • chromatic aberration when using a BD does not become too large while ensuring a working distance when using a CD. If the lower limit of the formula (5) is exceeded, the amount of chromatic aberration generated when the first optical disk is used is sufficiently suppressed, and if it is less than the upper limit of the formula (5), a working distance when using the CD can be secured sufficiently.
  • the second basic structure is also a blazed structure. Further, the second basic structure makes the second-order diffracted light quantity of the first light beam that has passed through the second basic structure larger than any other order of diffracted light quantity, and the first-order of the second light beam that has passed through the second basic structure. Is made larger than any other order of the diffracted light quantity, and the first order diffracted light quantity of the third light flux that has passed through the second basic structure is made larger than any other order of diffracted light quantity. This is called a (2/1/1) structure. Since the diffraction order that maximizes the amount of diffracted light of the first light beam is an even second order, high diffraction efficiency can be obtained for all of the first to third light beams.
  • the step amount of the second basic structure does not become too large, making the manufacture easy, and suppressing the light quantity loss caused by the manufacturing error. This is preferable because it can reduce the diffraction efficiency fluctuation at the time of wavelength fluctuation.
  • the step of the second basic structure provided at least in the vicinity of the optical axis in the central region is directed in the direction of the optical axis.
  • the step is directed in the direction of the optical axis means a state as shown in FIG.
  • the second basic structure provided “at least in the vicinity of the optical axis of the central region” refers to a step at least closest to the optical axis among steps of the (2/1/1) structure. It is preferable that at least 50% or more of all the steps of the second basic structure existing in the central region face the direction of the optical axis, more preferably 70% or more, more preferably 90% or more. It is facing the direction of.
  • the step may be directed in a direction opposite to the optical axis. That is, as shown in FIG. 6A, the step is directed toward the optical axis when the second foundation structure is near the optical axis, but the step of the second foundation structure is opposite to the optical axis near the intermediate region. It is good also as a shape which faces a direction.
  • the second basic structure provided in the central region is that all the steps are directed in the direction of the optical axis.
  • the first optical path difference providing structure is a (1/1/1) structure and the second basic structure (2/1/1) are overlapped, the height of the step is Very low. Therefore, it is possible to further reduce manufacturing errors, further reduce the light amount loss, and further suppress the change in diffraction efficiency when the wavelength changes.
  • the step is directed toward the optical axis.
  • the height of the step after superposition is higher than when superimposing the steps so that the steps of the first and second foundation structures are the same. Accordingly, it is possible to further suppress the shadow effect, to further suppress the light amount loss due to the manufacturing error, and to further suppress the fluctuation of the diffraction efficiency at the time of the wavelength fluctuation.
  • the three types of optical discs of BD / DVD / CD be compatible, but also the light usage efficiency that can maintain high light usage efficiency for any of the three types of optical discs of BD / DVD / CD.
  • an objective lens that has a diffraction efficiency of 80% or more for the wavelength ⁇ 1, a diffraction efficiency of 70% or more for the wavelength ⁇ 2, and a diffraction efficiency of 60% or more for the wavelength ⁇ 3.
  • a diffraction efficiency of 80% or more for the wavelength ⁇ 1 a diffraction efficiency of 70% or more for the wavelength ⁇ 2, and a diffraction efficiency of 60% or more for the wavelength ⁇ 3.
  • the first optical path difference providing structure in which the first basic structure having the (1/1/1) structure and the second basic structure having the (2/1/1) structure are overlapped is expressed as follows. be able to.
  • the first optical path difference providing structure provided at least in the vicinity of the optical axis of the central region has both a step facing in the opposite direction to the optical axis and a step facing in the direction of the optical axis.
  • the step amount d11 of the step facing the direction opposite to the axis and the step amount d12 of the step facing the direction of the optical axis satisfy the following conditional expressions (14) and (15). More preferably, the following conditional expressions (14) and (15) are satisfied in all the regions of the central region. If the objective lens provided with the optical path difference providing structure is a single aspherical convex lens, the incident angle of the light flux to the objective lens differs depending on the height from the optical axis, so that the optical path difference providing structure that gives the same optical path difference Even so, in general, as the distance from the optical axis increases, the step amount tends to increase.
  • n the refractive index of the objective lens at the first wavelength ⁇ 1.
  • the first optical path difference providing structure provided “at least in the vicinity of the optical axis of the central region” includes at least a step facing in a direction opposite to the optical axis closest to the optical axis and an optical axis closest to the optical axis.
  • An optical path difference providing structure having both of the steps facing the direction of.
  • the optical path difference providing structure has a step existing between at least a half position in the direction orthogonal to the optical axis from the optical axis to the boundary between the central region and the intermediate region.
  • conditional expression can be expressed as follows.
  • the shape of the foundation structure is finely adjusted so that the positions of all the steps of the second foundation structure and the positions of the steps of the first foundation structure are matched.
  • conditional expressions (14) ′, ( 15) ′ are the following conditional expressions (14) ′, ( 15) ′ is preferably satisfied. More preferably, the following conditional expressions (14) ′ and (15) ′ are satisfied in all regions of the central region. 0.6 ⁇ ( ⁇ 1 / (n-1)) ⁇ d11 ⁇ 1.5 ⁇ ( ⁇ 1 / (n-1)) (14) ' 0.6 ⁇ ( ⁇ 1 / (n-1)) ⁇ d12 ⁇ 1.5 ⁇ ( ⁇ 1 / (n-1)) (15) '
  • conditional expressions (14) ′′ and (15) ′′ are preferably satisfied. More preferably, the following conditional expressions (14) ′′ and (15) ′′ are satisfied in all the regions of the central region. 0.9 ⁇ ( ⁇ 1 / (n-1)) ⁇ d11 ⁇ 1.5 ⁇ ( ⁇ 1 / (n-1)) (14) '' 0.9 ⁇ ( ⁇ 1 / (n-1)) ⁇ d12 ⁇ 1.5 ⁇ ( ⁇ 1 / (n-1)) (15) '''
  • the spherical aberration when the wavelength of the incident light beam is changed to be longer, the spherical aberration is changed in the undercorrection direction (under), and (2 / In the second basic structure having the 1/1) structure, when the wavelength of the incident light beam is changed to be longer, it is preferable that the spherical aberration is changed in the undercorrection direction (under).
  • the refractive index of the objective lens when the refractive index of the objective lens changes due to an increase in the temperature of the optical pickup device, the refractive index of the objective lens is also utilized by utilizing the fact that the wavelength of the light source increases due to the increase in the environmental temperature.
  • the paraxial power of the first foundation structure is larger than that of the second foundation structure. That is, it is preferable that the average pitch of the first foundation structure is smaller than the average pitch of the second foundation structure. Thereby, a working distance in the CD can be secured even in an objective lens having a large axial thickness, which is a BD / DVD / CD compatible objective lens.
  • ring zones of the first foundation structure are included in one ring zone closest to the optical axis of the second foundation structure.
  • the “ring zone” closest to the optical axis of the second foundation structure is described, but in practice, it is usually a “circle” including the optical axis. Accordingly, the “annular zone closest to the optical axis” mentioned here includes a circular shape.
  • 1 to 5 ring zones of the first foundation structure are included in one ring zone of the second foundation structure.
  • the ratio of the total number of ring zones of the first foundation structure to the second foundation structure in the central region is preferably 1.0 or more and 5.0 or less, more preferably 2.0 or more and 3.0 or less. is there.
  • a part when the first basic structure and the second basic structure are directly overlapped, a part may protrude as shown by a dotted line, but the width of the protruding part is 5 ⁇ m or less. If it is narrow, the protruding portion is shifted in parallel along the optical axis, and eliminating the protruding portion has no significant effect, so that one annular zone of the second foundation structure can have a plurality of first foundation structures.
  • the zonal zone is exactly as shown (see solid line). Therefore, in the example of FIG.7 (d), it handles as the ring zone of three 1st foundation structures on one ring zone of a 2nd foundation structure.
  • a dent may be eliminated in the same manner even when a dent having a width of 5 ⁇ m or less is generated.
  • ⁇ 1 (nm) is the change amount of the first wavelength
  • ⁇ WD ( ⁇ m) is the chromatic aberration of the objective lens caused by the change ⁇ of the first wavelength
  • one annular zone closest to the optical axis of the second basic structure includes two to two annular zones of the first basic structure. It is preferable to include 5 (particularly preferably 2 to 3).
  • the optical disc has a plurality of information recording surfaces while ensuring a working distance in the CD even in an objective lens having a large axial thickness, which is a BD / DVD / CD compatible objective lens. This is preferable because the problem of stray light can be reduced and the temperature and wavelength characteristics can be improved when using a DVD.
  • the number of the first foundation structure annular zones superimposed on one annular zone closest to the intermediate region in the second foundation structure is 1 to 5 overlaps for one annular zone of the second foundation structure. It is preferable that Furthermore, the ratio of the total number of ring zones of the first foundation structure to the second foundation structure in the central region is preferably 1.0 or more and 5.0 or less, more preferably 2.0 or more and 3.0 or less. That is.
  • the first basic structure preferably has a negative paraxial diffraction power, so that a working distance when using a CD can be secured even for an objective lens having a large axial thickness such as an objective lens for BD / DVD / CD.
  • the second basic structure preferably has a positive paraxial diffraction power. As described above, since both the first basic structure and the second basic structure have paraxial diffraction power, when using an optical disk having a plurality of information recording surfaces, unnecessary light reflected by the information recording surface that is not a target for recording / reproducing is used. This is preferable because it can be further away from the necessary light.
  • the minimum pitch of the first optical path difference providing structure is preferably 15 ⁇ m or less.
  • the ratio p / f1 between the minimum pitch p of the first optical path difference providing structure and the focal length f1 at the first wavelength ⁇ 1 is preferably 0.004 or less. More preferably, it is 10 ⁇ m or less.
  • the average pitch of the first optical path difference providing structure is 30 ⁇ m or less. More preferably, it is 20 ⁇ m or less.
  • the best focus position of the necessary light used for recording / reproducing information can be separated from the best focus position of unnecessary light not used for recording / reproducing information on the third optical disc, and erroneous detection can be reduced.
  • the average pitch is a value obtained by adding all pitches of the first optical path difference providing structure in the central region and dividing the sum by the number of steps of the first optical path difference providing structure in the central region.
  • the objective lens of the present invention preferably has an axial chromatic aberration of 0.9 ⁇ m / nm or less. More preferably, the longitudinal chromatic aberration is 0.8 ⁇ m / nm or less. If the pitch of the first basic structure is made too small, the longitudinal chromatic aberration may be deteriorated. Therefore, design is made with care so that the pitch is not larger than 0.9 ⁇ m / nm. It is preferable. From this viewpoint, it is preferable that the ratio p / f1 between the minimum pitch p of the first optical path difference providing structure and the focal length f1 at the first wavelength ⁇ 1 is 0.002 or more. On the other hand, in order to ensure a sufficient working distance in CD, it is preferable that the longitudinal chromatic aberration is 0.4 ⁇ m / nm or more.
  • the first best focus position where the light intensity of the spot formed by the third light flux is the strongest by the third light flux passing through the first optical path difference providing structure, and the second strongest light intensity of the spot formed by the third light flux. It is preferable that the best focus position satisfies the following conditional expression (19).
  • the best focus position refers to a position where the beam waist becomes a minimum within a certain defocus range.
  • the first best focus position is the best focus position of the necessary light used for CD recording / reproduction
  • the second best focus position is the best of the luminous flux having the largest light quantity among the unnecessary light that is not used for CD recording / reproduction.
  • the focus position 0.35 ⁇ L / f1 ⁇ 0.7 (19)
  • L [mm] indicates the distance between the first best focus and the second best focus.
  • FIGS. 7A, 7B, and 7C Several preferable examples of the first optical path difference providing structure described above are shown in FIGS. 7A, 7B, and 7C.
  • the first optical path difference providing structure ODS1 is shown as being provided in a flat plate shape, but it is usually provided on a single aspherical convex lens.
  • the first basic structure BS1 which is a (1/1/1) diffraction structure is overlapped with the second basic structure BS2 which is a (2/1/1) diffraction structure.
  • the step of the second foundation structure BS2 faces the direction of the optical axis OA
  • the step of the first foundation structure BS1 faces the direction opposite to the optical axis OA.
  • the positions of all the steps of the second foundation structure BS2 are aligned with the positions of the steps of the first foundation structure BS1.
  • step difference of 2nd foundation structure BS2 has faced the direction of optical axis OA
  • step difference of 1st foundation structure BS1 has also faced the direction of optical axis OA.
  • the positions of all the steps of the second foundation structure BS2 are aligned with the positions of the steps of the first foundation structure BS1.
  • step difference of 1st foundation structure BS1 has faced the direction opposite to optical axis OA
  • step difference of 2nd foundation structure BS2 has also faced the direction opposite to optical axis OA.
  • the positions of all the steps of the second foundation structure BS2 are aligned with the positions of the steps of the first foundation structure BS1.
  • the total number of ring zones in the central region is N1
  • the following expression is satisfied.
  • the number of steps substantially parallel to the optical axis in the central region may be regarded as the total number of annular zones in the central region.
  • the second optical path difference providing structure is preferably a structure in which at least two basic structures of a third basic structure and a fourth basic structure are overlapped. More preferably, it is a structure in which only the third basic structure and the fourth basic structure are overlapped. Since the optical path difference providing structure is formed by superimposing two types of blazed basic structures, it is possible to secure a greater degree of design freedom than when the optical path difference providing structure is formed with a single structure. This is advantageous in an objective lens having a small diameter.
  • the third basic structure is a blaze type structure. Further, the first-order diffracted light amount of the first light beam that has passed through the third basic structure is made larger than any other order of diffracted light amount, and the first-order diffracted light amount of the second light beam that has passed through the third basic structure is changed to other values. It is made larger than the diffracted light quantity of any order.
  • the fourth basic structure is also a blazed structure. The fifth-order or seventh-order diffracted light quantity of the first light beam that has passed through the fourth basic structure is made larger than any other order diffracted light quantity, and the third-order or fourth-order diffraction of the second light beam that has passed through the fourth basic structure. Make the light intensity larger than any other order of diffracted light.
  • the diffraction order of the first light flux that has passed through the third basic structure is the first order that is an odd number, the diffraction power that is different between BD and DVD can be imparted, and relative spherical aberration that occurs with DVD Can be corrected satisfactorily.
  • the step amount of the third basic structure does not become too large, the manufacturing becomes easy, the light quantity loss caused by the manufacturing error can be suppressed, and the wavelength change It is preferable because fluctuations in diffraction efficiency can be reduced.
  • the BD accompanying the temperature change or the like without affecting the spherical aberration correction of the third basic structure.
  • ⁇ i (h) (C i2 ⁇ h 2 + C i4 ⁇ h 4 + C i6 ⁇ h 6 + C i8 ⁇ h 8 + C i10 ⁇ h 10 ) Mi ⁇ / ⁇ B i (Where h (unit: mm) is the height from the optical axis, C i2 , C i4 , C i6 ...
  • the fourth-order and sixth-order optical path difference function coefficients are secondary in the optical path difference function (i is a natural number) of the i-th substructure.
  • the fourth-order and sixth-order optical path difference function coefficients Mi is the diffraction order in the optical path difference function of the i-th basic structure that maximizes the diffraction order of the incident light beam
  • ⁇ (unit: mm) is the use of the incident light beam.
  • ⁇ B i (unit: mm) represents the manufacturing wavelength of the i-th basic structure, respectively.
  • the effective diameter (diameter) of the second light flux is h2 (mm)
  • the effective diameter (diameter) of the first light flux When h1 (mm), the following formula may be satisfied.
  • the diffraction order in the optical path difference function of the i-th basic structure that maximizes the diffraction order of the incident light beam is, for example, the first order when the basic structure is (1/1/1), (2/1/1). 1) indicates the second order, (7/4) indicates the seventh order, and (5/3) indicates the fifth order.
  • the third and fourth orders of the third light flux that have passed through the intermediate region are within the above formula. It is possible to suppress the unnecessary diffraction order light having the next high diffraction efficiency from being collected in the vicinity of the spot when the CD is used, and the spherical aberration with respect to the temperature change when using the DVD is also well corrected.
  • the focal length of the fourth basic structure is set to fD 4 (mm)
  • the same effect as the above formula can be obtained even if the following two formulas are satisfied at the same time. it can.
  • the magnification of the objective lens is 0 in any of BD, DVD, and CD.
  • high diffraction efficiency can be obtained at all three wavelengths while setting the value to almost zero.
  • the pitch is already sufficiently fine in the second optical path difference providing structure composed of the third basic structure and the fourth basic structure, and the annular zone Since the number is sufficiently large, if another foundation structure is stacked in addition to the third foundation structure and the fourth foundation structure, the pitch will become finer and the number of zones will increase, resulting in manufacturing errors. Problems such as lowering of the diffraction efficiency due to, and lowering of the diffraction efficiency due to the effect of the shadow of the annular zone will increase.
  • the second optical path difference providing structure a structure in which only the third basic structure and the fourth basic structure are overlapped is preferable because the light use efficiency can be increased.
  • the second optical path difference providing structure in the intermediate region has a step in which the third basic structure faces in the direction opposite to the optical axis, and the fourth basic structure has a step in which the optical axis direction faces. It is preferable. Therefore, it is preferable that the second optical path difference providing structure has a step that faces in a direction opposite to the optical axis and a step that faces in the direction of the optical axis.
  • all the steps of the first foundation structure are directed in the direction opposite to the optical axis
  • all the steps of the second foundation structure are directed to the direction of the optical axis
  • all the steps of the third foundation structure are If the direction is opposite to the optical axis, and all the steps of the fourth basic structure are oriented in the direction of the optical axis, the working distance when using the CD becomes longer, and the axial chromatic aberration of the BD is further increased. It becomes easy to take.
  • the spherical aberration changes in the undercorrection (under) direction, and the (7/4) structure (the first) 7th order diffracted light is generated most in one light beam, and 4th order diffracted light is generated most in the second light beam, or (5/3) structure (5th order diffracted light is generated most in the first light beam, and the second light beam is generated.
  • the spherical aberration is undercorrected (under) or overcorrected (over) when the wavelength of the incident light beam is changed to be longer. It is preferable to change in the direction.
  • the overcorrection (over) direction and the undercorrection (under) direction referred to here represent spherical aberration in the intermediate region, and the state in which the condensing position shifts to the over side as NA increases in the intermediate region is overcorrected (
  • the over-correction (under) direction is defined as the converging position shifts to the under side as NA increases. It is not the direction of the condensing position with respect to the paraxial condensing position.
  • the wavelength of the light source also increases due to the increase in the environmental temperature. Is used to correct the deterioration of the spherical aberration due to the change in the refractive index of the objective lens, so that a more appropriate condensing spot can be formed on the information recording surface of each optical disc when the environmental temperature changes.
  • the second optical path difference providing structure is composed of the third basic structure and the fourth basic structure, in addition to compatibility with BD and DVD, the remaining degree of freedom can be used for CD flare out. Therefore, since the aperture limitation at the time of using the CD can be performed by the second optical path difference providing structure having a simple shape, it is possible to suppress a decrease in light use efficiency due to the shadow effect as compared with the case of adding another basic structure. Further, it is possible to suppress a decrease in light utilization efficiency due to a manufacturing error, and as a result, it is possible to improve the light utilization efficiency. In addition, when the DVD is used, both the temperature characteristic and wavelength characteristic of the DVD can be improved.
  • the ring zones of the third basic structure are 3 to 11 in one ring zone closest to the central region of the fourth basic structure. It is preferable that they are included.
  • the objective lens of the present invention has two basic structures superimposed in the intermediate region, and further, in a certain region, the number of annular zones tends to increase as it goes from the optical axis toward the periphery. In the vicinity of the peripheral area, the light utilization efficiency is deteriorated.
  • the ratio r2 of the pupil transmittance in the vicinity of the peripheral region of the intermediate region with respect to the vicinity of the optical axis center of the objective lens in the second light flux is expressed by the following equation: r2 ⁇ 0.9 (1) Therefore, a phenomenon that can be called a reverse apodization effect occurs, and the spot diameter may increase when the DVD is used.
  • the term “near” in the vicinity of the center of the optical axis refers to a range of 10% of the effective diameter when using a DVD from the optical axis to the direction perpendicular to the optical axis.
  • the vicinity of the peripheral area of the intermediate area refers to a range of 10% of the effective diameter when using the DVD with respect to the intermediate area direction from the boundary between the intermediate area and the peripheral area. The range of 10% of the effective diameter when using a DVD from the outer diameter to the intermediate area direction.
  • the objective lens of the present invention is a BD / DVD / CD compatible objective lens.
  • the sine condition cannot be satisfied for all optical discs, and the most required specification is required. Is set so that the sine condition is satisfied with a severe BD, there is a possibility that the spot diameter will be further increased when the DVD is used.
  • the outer diameter of the intermediate region is h2
  • the focal length of the first light beam of the objective lens is f1
  • the imaging magnification of the second light beam of the objective lens is m2.
  • r2 is 0.3 or more and 0.9 or less because the degree of the enlargement of the spot diameter due to the decrease in the rim strength does not become too large, and the effect of the expression (2) becomes more remarkable. More preferably, r2 is 0.4 or more and 0.8 or less, and further preferably r2 is 0.5 or more and 0.75 or less.
  • the following expression (2) ′ is satisfied. 0.68 ⁇ h2 / (2 ⁇ f1 ⁇ (1-m2)) ⁇ 0.74 (2) ′
  • the pitch in the vicinity of the intermediate region, particularly the peripheral region of the intermediate region is also small, there is a possibility that the spot diameter will increase when using the DVD.
  • the objective lens of this invention satisfy
  • the focal length f1 when using the BD is within the range of the expression (3), the objective lens becomes relatively small, and therefore the pitch in the vicinity of the outer diameter in the peripheral region becomes even finer, and the problem of the present invention is large.
  • such a large problem can be solved by making the second-order or fourth-order diffracted light quantity of the first light flux that has passed through the fifth basic structure larger than any other order diffracted light quantity.
  • the focal length f1 is within the range of the expression (3), the number of ring zones in the central region is increased in order to secure a working distance when using the CD, that is, in order to increase the paraxial power of diffraction.
  • the working distance is a distance in the optical axis direction from the surface of the optical disk to the position closest to the optical disk of the objective lens.
  • the focal length is within the range of the expression (3), the distance from the objective lens to the disk can be reduced, and it can be suitably mounted on a slim type optical pickup device. Further, when f1 satisfies the following expression (3) ′, the effect of the present invention becomes more remarkable. 1.0 ⁇ f1 ⁇ 2.0 (3) ′
  • the objective lens may be designed to satisfy the following formula (11) when the focal length of the second light flux of the objective lens is f2. 0.61 ⁇ h2 / (2 ⁇ f2 ⁇ (1-m2)) ⁇ 0.65 (21)
  • formula (11) the effective diameter when using a DVD can be increased, which is preferable.
  • the third optical path difference providing structure has at least a fifth basic structure. Although another foundation structure may be superimposed, it is preferably only the fifth foundation structure.
  • the fifth basic structure is a blaze type structure.
  • the second-order or fourth-order diffracted light amount of the first light flux that has passed through the fifth basic structure is made larger than any other order diffracted light amount.
  • the pitch can be made larger than in the first case, that is, the number of ring zones is reduced, so that the manufacturing can be facilitated and the error can be reduced both in the mold processing and the resin molding.
  • the number of annular zones tends to increase from the optical axis side toward the periphery, and the angle of view of the objective lens increases near the outer diameter in the peripheral area.
  • the fourth-order and sixth-order optical path difference function coefficients are secondary in the optical path difference function (i is a natural number) of the i-th substructure.
  • the fourth-order and sixth-order optical path difference function coefficients Mi is the diffraction order in the optical path difference function of the i-th basic structure that maximizes the diffraction order of the incident light beam
  • ⁇ unit: mm
  • the wavelength ⁇ B i indicates the production wavelength in the i-th basic structure.
  • the second and second unwanted light of the third and third beams transmitted through the peripheral region are transmitted through the central region while satisfactorily correcting the spherical aberration generated when the environment is changed when using the BD. Since it is possible to avoid convergence of the third light flux in the vicinity of the imaging position, it is preferable because deterioration of spot performance can be suppressed. Further, it is preferable that the number of steps is not excessively increased by setting the value within the range of the formula (6), which makes it possible to obtain a good spot that is easy to manufacture and suppresses a decrease in light utilization efficiency. By falling below the upper limit, the spherical aberration at the time of temperature change does not become too large.
  • the fifth basic structure may face the direction of the optical axis, or may face the direction opposite to the optical axis. In particular, it is preferable that the fifth basic structure is directed toward the optical axis because spherical aberration at the time of temperature change is corrected well.
  • FIG. 8 shows a schematic diagram of a preferable objective lens. It is the figure which showed the upper half from the optical axis among the cross sections of the objective lens containing optical axis OA. Note that FIG. 8 is a schematic diagram to the last, and is not a drawing showing an accurate length ratio or the like based on the embodiment.
  • the 8 has a central region CN, an intermediate region MD, and a peripheral region OT.
  • the central region is provided with the first optical path difference providing structure ODS1
  • the intermediate region is provided with the second optical path difference providing structure ODS2
  • the peripheral region is provided with the third optical path difference providing structure ODS3. .
  • the first optical path difference providing structure ODS1 in FIG. 8 is a (2/1/1) blazed structure in which a step is directed toward the optical axis and a (1/1/1) second basic structure BS2.
  • the blazed structure is a structure in which a first basic structure BS1 whose level difference is opposite to the optical axis is superimposed.
  • the second foundation structure BS2 has three annular zones, and two annular zones of the first foundation structure BS1 are included on the annular zone (circular shape) closest to the optical axis in the second foundation structure BS2. ing.
  • three annular zones of the first foundation structure BS1 are included in one annular zone closest to the intermediate region in the second foundation structure BS2.
  • the second optical path difference providing structure ODS2 in FIG. 8 is a (7/4) or (5/3) blazed structure, and a fourth basic structure BS4 in which the step is directed toward the optical axis (1/1). ) And a third base structure BS3 in which the level difference faces the direction opposite to the optical axis.
  • 4th foundation structure BS4 is a 3 ring zone
  • 3 ring zones of 3rd foundation structure BS3 are contained on the ring zone nearest to the center area
  • four ring zones of the third foundation structure BS3 are included in one ring zone closest to the peripheral region in the fourth foundation structure BS4. That is, since the annular density of the annular zone closest to the peripheral region of the intermediate region is high, the shadow effect and the influence of the shaping error are large, and the pupil transmittance is small compared to the vicinity of the optical axis.
  • the third optical path difference providing structure ODS3 in FIG. 8 is a blazed structure in which the second-order or fourth-order diffracted light quantity is maximized when the first light beam passes, and the sixth base has a step toward the optical axis. It consists only of the structure BS5. Compared to the primary case, the pitch can be widened, so that the moldability of the objective lens can be improved, the size can be reduced, and the rim strength is increased. The diameter can be formed.
  • NA1 is preferably 0.8 or more and 0.9 or less.
  • NA1 is preferably 0.85.
  • NA2 is preferably 0.55 or more and 0.7 or less.
  • NA2 is preferably 0.60 or 0.65.
  • NA3 is preferably 0.4 or more and 0.55 or less.
  • NA3 is preferably 0.45 or 0.53.
  • the boundary between the central region and the intermediate region of the objective lens is 0.9 ⁇ NA 3 or more and 1.2 ⁇ NA 3 or less (more preferably 0.95 ⁇ NA 3 or more, 1.15 ⁇ NA 3) when the third light beam is used. It is preferably formed in a portion corresponding to the following range. More preferably, the boundary between the central region and the intermediate region of the objective lens is formed in a portion corresponding to NA3. Further, the boundary between the intermediate region and the peripheral region of the objective lens is 0.9 ⁇ NA 2 or more and 1.2 ⁇ NA 2 or less (more preferably 0.95 ⁇ NA 2 or more, 1.15) when the second light flux is used. -It is preferably formed in a portion corresponding to the range of NA2 or less. More preferably, the boundary between the intermediate region and the peripheral region of the objective lens is formed in a portion corresponding to NA2.
  • the spherical aberration has at least one discontinuous portion.
  • the discontinuous portion has a range of 0.9 ⁇ NA 3 or more and 1.2 ⁇ NA 3 or less (more preferably 0.95 ⁇ NA 3 or more and 1.15 ⁇ NA 3 or less) when the third light flux is used. It is preferable that it exists in.
  • h1 (mm) is 1.9 or more and 4.0 or less about the effective diameter with respect to the 1st light beam of an objective lens, More preferably, it is satisfy
  • the pitch in the vicinity of the outer diameter in the peripheral region becomes even finer, and the problem of the present invention becomes large.
  • This can be solved by making the second-order or fourth-order diffracted light quantity of the first light flux that has passed through the fifth basic structure larger than any other order diffracted light quantity.
  • the pitch in the vicinity of the intermediate region, particularly the peripheral region of the intermediate region is also small, there is a possibility that the spot diameter increases when using DVD or BD. In this case, satisfying the equation (2) solves the problem. it can.
  • the pitch of the optical path difference providing structure is reduced, and the number of annular zones is reduced.
  • the reverse phenomenon of apodization may occur even more strongly when using a DVD.
  • the spot diameter when using the DVD can be reduced by satisfying a value equal to or higher than the lower limit of the above-described formula (2).
  • the total number N all of the annular zones formed on the objective lens is preferably 100 or more and 250 or less.
  • the total number of ring zones in the peripheral region is N3, it is preferable to satisfy the following expression. 5 (mm) ⁇ N3 ⁇ f1 ⁇ 100 (mm) (8)
  • the value is set to be equal to or higher than the lower limit of the formula (8), the spherical aberration generated with respect to the temperature change when using the BD is not excessively increased.
  • the value of equation (8) below the upper limit, it is possible to prevent the pitch from becoming too small, so that the effect of shadows can be suppressed, and the shape error can be reduced by preventing deterioration of workability. Decrease in diffraction efficiency can be prevented.
  • the range in (8) chromatic aberration can also be reduced. Note that the number of steps substantially parallel to the optical axis in the peripheral region may be regarded as the total number of ring zones in the peripheral region.
  • the objective lens preferably satisfies the following conditional expression (7).
  • d represents the thickness (mm) on the optical axis of the objective lens
  • f represents the focal length of the objective lens in the first light flux.
  • the objective lens tends to be a thick objective lens with a thick on-axis thickness, and the working distance at the time of CD recording / reproduction tends to be shortened. Therefore, the upper limit value of conditional expression (7) may not be exceeded. preferable.
  • the working distance (WD3) of the objective optical element when using the third optical disk is preferably 0.15 mm or more and 1.5 mm or less. Preferably, they are 0.25 mm or more and 0.5 mm or less.
  • the working distance (WD2) of the objective optical element when using the second optical disc is preferably 0.2 mm or more and 1.3 mm or less.
  • the working distance (WD1) of the objective optical element when using the first optical disc is 0.25 mm or more and 1.0 mm or less.
  • the first light beam, the second light beam, and the third light beam may be incident on the objective lens as parallel light, or may be incident on the objective lens as divergent light or convergent light. Even during tracking, in order to prevent coma from occurring, it is preferable that all of the first light beam, the second light beam, and the third light beam be incident on the objective lens as parallel light or substantially parallel light.
  • all of the first light beam, the second light beam, and the third light beam can be incident on the objective lens as parallel light or substantially parallel light. The effect becomes more remarkable.
  • the imaging magnification m1 of the objective lens when the first light flux is incident on the objective lens satisfy the following formula (22). -0.01 ⁇ m1 ⁇ 0.01 (22)
  • the imaging magnification m2 of the objective lens when the second light beam is incident on the objective lens satisfies the following expression (23). Is preferred. -0.01 ⁇ m2 ⁇ 0.01 (23)
  • the imaging magnification m2 of the objective lens when the second light beam is incident on the objective lens preferably satisfies the following expression (23) ′. . ⁇ 0.025 ⁇ m2 ⁇ ⁇ 0.01 (23) ′
  • the imaging magnification m3 of the objective lens when the third light beam enters the objective lens satisfies the following expression (24). Is preferred. -0.01 ⁇ m3 ⁇ 0.01 (24)
  • the imaging magnification m3 of the objective lens when the third light beam is incident on the objective lens preferably satisfies the following expression (24) ′. . ⁇ 0.025 ⁇ m3 ⁇ ⁇ 0.01 (24) ′
  • the coma generated during tracking falls within a recordable / reproducible range.
  • the optical pickup device may include a coupling lens through which at least the first light beam and the second light beam pass, and may include an actuator that moves the coupling lens in the optical axis direction.
  • the BD has a plurality of information recording surfaces such as two layers or three layers or more
  • the difference in the thickness of the transparent substrate is required. Therefore, spherical aberration generated due to the difference in thickness must be corrected.
  • spherical aberration that occurs when the temperature or wavelength changes can be corrected by moving the coupling lens in the optical axis direction and changing the magnification of the objective lens.
  • the position of the coupling lens in the optical axis direction is fixed when using DVD. It is preferable.
  • the wavelength of the incident light beam in one of the third basic structure and the fourth basic structure constituting the second optical path difference providing structure of the objective lens In order to fix the position of the coupling lens in the optical axis direction when using a DVD, the wavelength of the incident light beam in one of the third basic structure and the fourth basic structure constituting the second optical path difference providing structure of the objective lens.
  • the spherical aberration changes in the direction of undercorrection when it changes to become longer, while the spherical aberration changes in the overcorrection direction when the wavelength of the incident light beam becomes longer in the other direction.
  • the spherical aberration accompanying the temperature change and wavelength change when using the DVD can be recorded and reproduced.
  • the coupling lens is moved in the optical axis direction when the second light beam passes. Even when the position is fixed, information can be recorded / reproduced on the information recording surface of the DVD.
  • An optical information recording / reproducing apparatus includes an optical disc drive apparatus having the above-described optical pickup apparatus.
  • the optical disk drive apparatus can hold an optical disk mounted from the optical information recording / reproducing apparatus main body containing the optical pickup apparatus or the like. There are a system in which only the tray is taken out, and a system in which the optical disc drive apparatus main body in which the optical pickup device is stored is taken out to the outside.
  • the optical information recording / reproducing apparatus using each method described above is generally equipped with the following components, but is not limited thereto.
  • An optical pickup device housed in a housing or the like, a drive source of an optical pickup device such as a seek motor that moves the optical pickup device together with the housing toward the inner periphery or outer periphery of the optical disc, and the optical pickup device housing the inner periphery or outer periphery of the optical disc include a transfer means of an optical pickup device having a guide rail or the like that guides toward the head, a spindle motor that rotates the optical disk, and the like.
  • the former method is provided with a tray that can be held in a state in which an optical disk is mounted and a loading mechanism for sliding the tray, and the latter method has no tray and loading mechanism. It is preferable that each component is provided in a drawer corresponding to a chassis that can be pulled out to the outside.
  • an objective lens suitable for such an optical pickup device and an optical pickup device equipped with this objective lens can be provided.
  • FIG. 4 is a diagram showing a shape in which a step is directed in the opposite direction to the optical axis in the vicinity of the axis, but is switched in the middle, and the step is directed toward the optical axis in the vicinity of the intermediate region.
  • FIG. 1 It is a conceptual diagram of a 1st optical path difference providing structure, (a), (b), (c) shows the example of a preferable 1st optical path difference providing structure, (d) is a 1st foundation structure and a 2nd foundation structure, An example in which is superimposed is shown.
  • Example 3 It is a figure showing the spherical aberration and sine condition in Example 3 and 4, (a) is BD, (b) is DVD, (c) is the case of CD. It is a figure showing the spherical aberration and sine condition in Example 5 and 6, (a) is BD, (b) is DVD, (c) is the case of CD. It is a figure showing the spherical aberration and sine condition in Example 7 and 8, (a) is BD, (b) is DVD, (c) is the case of CD.
  • FIG. 9 is a diagram schematically showing a configuration of the optical pickup apparatus PU1 of the present embodiment that can appropriately record and / or reproduce information on BD, DVD, and CD, which are different optical disks.
  • the optical pickup device PU1 is a slim type and can be mounted on a thin optical information recording / reproducing device.
  • the first optical disc is a BD
  • the second optical disc is a DVD
  • the third optical disc is a CD. Note that the present invention is not limited to this embodiment.
  • a central region CN including the optical axis on the aspherical optical surface on the light source side, an intermediate region MD arranged around the center region CN, and A peripheral region OT disposed around the periphery is formed concentrically with the optical axis as the center.
  • the first optical path difference providing structure already described in detail is formed in the center region CN
  • the second optical path difference providing structure already described in detail is formed in the intermediate region MD.
  • a third optical path difference providing structure is formed in the peripheral region OT.
  • the third optical path difference providing structure is a blazed diffractive structure.
  • the objective lens of this embodiment is a plastic lens.
  • the first optical path difference providing structure formed in the center region CN of the objective lens OL is a structure in which the first basic structure and the second basic structure are overlapped, and the first basic structure has passed through the first basic structure.
  • the first order diffracted light amount of the first light beam is made larger than any other order diffracted light amount
  • the first order diffracted light amount of the second light beam that has passed through the first basic structure is made larger than any other order diffracted light amount.
  • the first-order diffracted light quantity of the third light beam that has passed through the first basic structure is made larger than any other order of diffracted light quantity
  • the second basic structure has a second-order diffracted light quantity that has passed through the second basic structure.
  • the second optical path difference providing structure formed in the intermediate region MD of the objective lens OL is a structure in which the third basic structure and the fourth basic structure are overlapped, and the third basic structure has passed through the third basic structure.
  • the first order diffracted light amount of the first light beam is made larger than any other order diffracted light amount
  • the first order diffracted light amount of the second light beam that has passed through the third basic structure is made larger than any other order diffracted light amount.
  • the first-order diffracted light amount of the third light beam that has passed through the third basic structure is made larger than any other order of diffracted light amount
  • the fourth basic structure is the fifth-order or first-order light beam that has passed through the fourth basic structure.
  • the seventh-order diffracted light amount is made larger than any other order diffracted light amount
  • the third-order or fourth-order diffracted light amount of the second light flux that has passed through the fourth basic structure is made larger than any other order diffracted light amount.
  • the third optical path difference providing structure formed in the peripheral region OT of the objective lens OL has a fifth basic structure, and the fifth basic structure is the second or fourth order of the first light flux that has passed through the fifth basic structure. Make the amount of diffracted light greater than the amount of diffracted light of any other order.
  • the light beam condensed by the central region, the intermediate region, and the peripheral region of the objective lens OL becomes a spot formed on the information recording surface RL1 of the BD through the protective substrate PL1 having a thickness of 0.1 mm. .
  • the reflected light beam modulated by the information pits on the information recording surface RL1 is again transmitted through the objective lens OL and a diaphragm (not shown), and then converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wavelength plate QWP, and by the collimating lens COL.
  • a converged light beam is reflected by the polarization beam splitter BS, and converges on the light receiving surface of the light receiving element PD via the sensor lens SEN.
  • the information recorded on the BD can be read by using the output signal of the light receiving element PD to focus or track the objective lens OL by the biaxial actuator AC1.
  • the spherical aberration generated due to the wavelength fluctuation or different information recording layers is changed in magnification.
  • the collimating lens COL as a means is changed in the optical axis direction by the uniaxial actuator AC2, and can be corrected by changing the divergence angle or convergence angle of the light beam incident on the objective optical element OL.
  • the ⁇ / 4 wavelength plate QWP converts the linearly polarized light into circularly polarized light and enters the objective lens OL.
  • the light beam condensed by the central region and the intermediate region of the objective lens OL (the light beam that has passed through the peripheral region is flared and forms a spot peripheral part) is passed through the protective substrate PL2 having a thickness of 0.6 mm.
  • the spot is formed on the information recording surface RL2 of the DVD and forms the center of the spot.
  • the reflected light beam modulated by the information pits on the information recording surface RL2 is transmitted again through the objective lens OL, converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wave plate QWP, and converted into a convergent light beam by the collimating lens COL.
  • the light is reflected by the polarization beam splitter BS and converges on the light receiving surface of the light receiving element PD via the sensor lens SEN.
  • the information recorded on DVD can be read using the output signal of light receiving element PD.
  • the control system of the optical pickup device is simplified.
  • the linearly polarized light is converted into circularly polarized light by the ⁇ / 4 wavelength plate QWP, and is incident on the objective lens OL.
  • the light beam condensed by the central region of the objective lens OL (the light beam that has passed through the intermediate region and the peripheral region is flared to form a spot peripheral portion) is passed through the protective substrate PL3 having a thickness of 1.2 mm.
  • the spot is formed on the information recording surface RL3 of the CD.
  • the reflected light beam modulated by the information pits on the information recording surface RL3 passes through the objective lens OL again, is converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wave plate QWP, and is converged by the collimating lens COL, The light is reflected by the polarization beam splitter BS and converges on the light receiving surface of the light receiving element PD via the sensor lens SEN. And the information recorded on CD can be read using the output signal of light receiving element PD.
  • a power of 10 for example, 2.5 ⁇ 10 ⁇ 3
  • E for example, 2.5 ⁇ E ⁇ 3
  • the optical surface of the objective lens is formed as an aspherical surface that is symmetric about the optical axis and is defined by a mathematical formula in which the coefficients shown in Table 1 are substituted into Formula 1.
  • X (h) is an axis in the optical axis direction (with the light traveling direction being positive), ⁇ is a conical coefficient, Ai is an aspherical coefficient, h is a height from the optical axis, and r is a paraxial radius of curvature. It is.
  • the optical path difference given to the light flux of each wavelength by the diffractive structure is defined by an equation in which the coefficient shown in the table is substituted into the optical path difference function of Formula 2. .
  • ⁇ (h) ⁇ (C 2i h 2i ⁇ ⁇ ⁇ m / ⁇ B)
  • ⁇ wavelength used
  • m diffraction order
  • ⁇ B manufacturing wavelength
  • h distance in the direction perpendicular to the optical axis from the optical axis.
  • the “manufacturing wavelength” is the wavelength of the luminous flux that gives the highest Mi-order diffraction efficiency when passing through the i-th basic structure.
  • the pitch P (h) ⁇ B / ( ⁇ (2i ⁇ C 2i ⁇ h 2i-1 )).
  • Example 1 shows lens data of Example 1.
  • the objective lens of Example 1 is a plastic single lens, and the steps of the first basic structure and the third basic structure are opposite to the optical axis, and the second basic structure, the fourth basic structure, and the fifth basic structure.
  • the level difference of the structure faces the direction of the optical axis.
  • the first optical path difference providing structure of Example 1 has (1/1/1) of the second basic structure which is a blazed diffraction structure of (2/1/1) in the entire central region. It is an optical path difference providing structure in which the first basic structure which is a blazed diffraction structure is overlapped.
  • the second optical path difference providing structure is the fourth basic structure, which is a blazed diffraction structure of (5/3), and the third basic structure, which is a blazed diffraction structure of (1/1), in the entire intermediate region. It is an optical path difference providing structure in which the structures are overlapped.
  • the third optical path difference providing structure has a fifth basic structure that makes the second-order diffracted light amount of the first light beam larger than any other order diffracted light amount in the entire peripheral region.
  • FIG. 10 shows a diagram of the spherical aberration SA and the sine condition SC in Example 1.
  • (a) is a graph when BD is used
  • (b) is when DVD is used
  • (c) is a graph when CD is used
  • the vertical axis of (a) is the effective luminous flux when BD is used.
  • the vertical axis of (b) is the half value (h2 / 2) of the effective diameter (diameter) of the luminous flux when using the DVD.
  • the vertical axis of (c) in the case of 1.0 is the distance from the optical axis when the half value (h3 / 2) of the effective diameter (diameter) of the light beam when using the CD is 1.0. Represents.
  • Example 2 shows lens data of Example 2.
  • the objective lens of Example 2 is a plastic single lens, and the steps of the first basic structure and the third basic structure are opposite to the optical axis, and the second basic structure, the fourth basic structure, and the fifth basic structure.
  • the level difference of the structure faces the direction of the optical axis.
  • the first optical path difference providing structure of Example 2 has (1/1/1) of the second basic structure which is a blazed diffraction structure of (2/1/1) in the entire central region. It is an optical path difference providing structure in which the first basic structure which is a blazed diffraction structure is overlapped.
  • the second optical path difference providing structure is the fourth basic structure, which is a blazed diffraction structure of (5/3), and the third basic structure, which is a blazed diffraction structure of (1/1), in the entire intermediate region. It is an optical path difference providing structure in which the structures are overlapped.
  • the third optical path difference providing structure has a fifth basic structure that makes the fourth-order diffracted light amount of the first light flux larger than any other order diffracted light amount in the entire peripheral region.
  • Example 2 is different from Example 1 only in the fifth basic structure.
  • FIG. 10A of Example 1 the flare light of DVD and CD that has passed through the peripheral region is omitted.
  • the spherical aberration SA and sine condition SC in the second embodiment are the same as those in FIG. 10 in the first embodiment.
  • Example 3 shows lens data of Example 3.
  • the objective lens of Example 3 is a plastic single lens, and the steps of the first basic structure and the third basic structure are opposite to the optical axis, and the second basic structure, the fourth basic structure, and the fifth basic structure.
  • the level difference of the structure faces the direction of the optical axis.
  • the first optical path difference providing structure of Example 3 has (1/1/1) of the (2/1/1) blazed diffraction structure of the second basic structure in the entire central region. It is an optical path difference providing structure in which the first basic structure which is a blazed diffraction structure is overlapped.
  • the second optical path difference providing structure has a (7/4) blazed diffractive structure as a fourth basic structure (7/1) blazed diffractive structure as a third basic structure in the entire intermediate region. It is an optical path difference providing structure in which the structures are overlapped.
  • the third optical path difference providing structure has a fifth basic structure that makes the second-order diffracted light amount of the first light beam larger than any other order diffracted light amount in the entire peripheral region.
  • FIG. 11 shows a diagram of spherical aberration SA and sine condition SC in Example 3.
  • (a) is a graph when BD is used
  • (b) is a graph when DVD is used
  • (c) is a graph when CD is used
  • the vertical axis of (a) is the effective luminous flux when BD is used.
  • the vertical axis of (b) is when the half value (h2 / 2) of the effective diameter of the luminous flux when using the DVD is 1.0
  • the vertical axis of (c) represents the distance from the optical axis when the half value (h3 / 2) of the effective diameter of the light beam when using the CD is 1.0.
  • Example 4 shows lens data of Example 4.
  • the objective lens of Example 4 is a plastic single lens, and the steps of the first basic structure and the third basic structure are opposite to the optical axis, and the second basic structure, the fourth basic structure, and the fifth basic structure.
  • the level difference of the structure faces the direction of the optical axis.
  • the first optical path difference providing structure of Example 4 has (1/1/1) of the second basic structure which is a (2/1/1) blazed diffraction structure in the entire central region. It is an optical path difference providing structure in which the first basic structure which is a blazed diffraction structure is overlapped.
  • the second optical path difference providing structure has a (7/4) blazed diffractive structure as a fourth basic structure (7/1) blazed diffractive structure as a third basic structure in the entire intermediate region. It is an optical path difference providing structure in which the structures are overlapped.
  • the third optical path difference providing structure has a fifth basic structure that makes the fourth-order diffracted light amount of the first light flux larger than any other order diffracted light amount in the entire peripheral region.
  • Example 4 is different from Example 3 only in the fifth basic structure.
  • FIG. 11A of Example 3 omits the flare light of the DVD and CD that have passed through the peripheral region.
  • the diagram of the spherical aberration SA and the sine condition SC in the fourth embodiment is the same as FIG. 11 in the third embodiment.
  • Example 5 shows lens data of Example 5.
  • the objective lens of Example 5 is a plastic single lens, and the steps of the first basic structure, the third basic structure, and the fifth basic structure are opposite to the optical axis, and the second basic structure and the fourth basic structure.
  • the level difference of the structure faces the direction of the optical axis.
  • the first optical path difference providing structure of Example 5 has (1/1/1) of the second basic structure which is a blazed diffraction structure of (2/1/1) in the entire central region. It is an optical path difference providing structure in which the first basic structure which is a blazed diffraction structure is overlapped.
  • the second optical path difference providing structure is the fourth basic structure, which is a blazed diffraction structure of (5/3), and the third basic structure, which is a blazed diffraction structure of (1/1), in the entire intermediate region. It is an optical path difference providing structure in which the structures are overlapped.
  • the third optical path difference providing structure has a fifth basic structure that makes the second-order diffracted light amount of the first light beam larger than any other order diffracted light amount in the entire peripheral region.
  • FIG. 12 shows a diagram of spherical aberration SA and sine condition SC in Example 5.
  • (a) is a graph when BD is used
  • (b) is when DVD is used
  • (c) is a graph when CD is used
  • the vertical axis of (a) is the effective luminous flux when BD is used.
  • the vertical axis of (b) is when the half value (h2 / 2) of the effective diameter of the luminous flux when using the DVD is 1.0
  • the vertical axis of (c) represents the distance from the optical axis when the half value (h3 / 2) of the effective diameter of the light beam when using the CD is 1.0.
  • Example 6 shows lens data of Example 6.
  • the objective lens of Example 6 is a plastic single lens, and the steps of the first basic structure, the third basic structure, and the fifth basic structure are opposite to the optical axis, and the second basic structure and the fourth basic structure.
  • the level difference of the structure faces the direction of the optical axis.
  • the first optical path difference providing structure of Example 6 has (1/1/1) of the second basic structure which is a (2/1/1) blazed diffraction structure in the entire central region. It is an optical path difference providing structure in which the first basic structure which is a blazed diffraction structure is overlapped.
  • the second optical path difference providing structure is the fourth basic structure, which is a blazed diffraction structure of (5/3), and the third basic structure, which is a blazed diffraction structure of (1/1), in the entire intermediate region. It is an optical path difference providing structure in which the structures are overlapped.
  • the third optical path difference providing structure has a fifth basic structure that makes the fourth-order diffracted light amount of the first light flux larger than any other order diffracted light amount in the entire peripheral region.
  • Example 6 is different from Example 5 only in the fifth basic structure.
  • the flare light of the DVD and CD that has passed through the peripheral region is omitted.
  • the spherical aberration SA and the sine condition SC in Example 6 are the same as those in Example 5 shown in FIG.
  • Example 7 shows lens data of Example 7.
  • the objective lens of Example 7 is a plastic single lens, and the steps of the first basic structure, the third basic structure, and the fifth basic structure are opposite to the optical axis, and the second basic structure and the fourth basic structure.
  • the level difference of the structure faces the direction of the optical axis.
  • the first optical path difference providing structure of Example 7 has (1/1/1) of the (2/1/1) blazed diffractive structure (2/1/1) in the entire central region. It is an optical path difference providing structure in which the first basic structure which is a blazed diffraction structure is overlapped.
  • the second optical path difference providing structure has a (7/4) blazed diffractive structure as a fourth basic structure (7/1) blazed diffractive structure as a third basic structure in the entire intermediate region. It is an optical path difference providing structure in which the structures are overlapped.
  • the third optical path difference providing structure has a fifth basic structure that makes the second-order diffracted light amount of the first light beam larger than any other order diffracted light amount in the entire peripheral region.
  • FIG. 13 shows a diagram of spherical aberration SA and sine condition SC in Example 3.
  • (a) is a graph when BD is used
  • (b) is when DVD is used
  • (c) is a graph when CD is used
  • the vertical axis of (a) is the effective luminous flux when BD is used.
  • the vertical axis of (b) is when the half value (h2 / 2) of the effective diameter of the luminous flux when using the DVD is 1.0
  • the vertical axis of (c) represents the distance from the optical axis when the half value (h3 / 2) of the effective diameter of the light beam when using the CD is 1.0.
  • Example 8 shows lens data of Example 8.
  • the objective lens of Example 8 is a plastic single lens, and the steps of the first basic structure, the third basic structure, and the fifth basic structure are opposite to the optical axis, and the second basic structure and the fourth basic structure.
  • the level difference of the structure faces the direction of the optical axis.
  • the first optical path difference providing structure of Example 8 has (1/1/1) of the second basic structure which is a (2/1/1) blazed diffraction structure in the entire central region. It is an optical path difference providing structure in which the first basic structure which is a blazed diffraction structure is overlapped.
  • the second optical path difference providing structure has a (7/4) blazed diffractive structure as a fourth basic structure (7/1) blazed diffractive structure as a third basic structure in the entire intermediate region. It is an optical path difference providing structure in which the structures are overlapped.
  • the third optical path difference providing structure has a fifth basic structure that makes the fourth-order diffracted light amount of the first light flux larger than any other order diffracted light amount in the entire peripheral region.
  • Example 8 is different from Example 7 only in the fifth basic structure.
  • the flare light of the DVD and CD that has passed through the peripheral region is omitted.
  • the spherical aberration SA and sine condition SC in Example 8 are the same as those in FIG. 13 in Example 7.
  • AC1 Biaxial actuator B Step amount BS Polarizing beam splitter CN Central region COL Collimating lens DP Dichroic prism LD1 First semiconductor laser or blue-violet semiconductor laser LD2 Second semiconductor laser LD3 Third semiconductor laser LDP Laser unit MD Intermediate region OA Optical axis ODS Optical path difference providing structure OL Objective lens OT Peripheral region P Pitch PD Light receiving element PL1 Protective substrate PL2 Protective substrate PL3 Protective substrate PU1 Optical pickup device QWP ⁇ / 4 wavelength plate RL1 Information recording surface RL2 Information recording surface RL3 Information recording surface SEN Sensor lens

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PCT/JP2013/062815 2012-05-11 2013-05-07 Objectif et dispositif de capture optique Ceased WO2013168692A1 (fr)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2011216176A (ja) * 2010-03-19 2011-10-27 Hoya Corp 光情報記録再生装置用対物光学系、及び光情報記録再生装置
JP2011233183A (ja) * 2010-04-23 2011-11-17 Konica Minolta Opto Inc 光ピックアップ装置用の対物レンズ、光ピックアップ装置及び光情報記録再生装置
WO2012043506A1 (fr) * 2010-09-29 2012-04-05 コニカミノルタオプト株式会社 Lentille de focalisation pour tête optique, et tête optique

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2011216176A (ja) * 2010-03-19 2011-10-27 Hoya Corp 光情報記録再生装置用対物光学系、及び光情報記録再生装置
JP2011233183A (ja) * 2010-04-23 2011-11-17 Konica Minolta Opto Inc 光ピックアップ装置用の対物レンズ、光ピックアップ装置及び光情報記録再生装置
WO2012043506A1 (fr) * 2010-09-29 2012-04-05 コニカミノルタオプト株式会社 Lentille de focalisation pour tête optique, et tête optique

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