WO2013146267A1 - 対物レンズ及び光ピックアップ装置 - Google Patents

対物レンズ及び光ピックアップ装置 Download PDF

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Publication number
WO2013146267A1
WO2013146267A1 PCT/JP2013/056999 JP2013056999W WO2013146267A1 WO 2013146267 A1 WO2013146267 A1 WO 2013146267A1 JP 2013056999 W JP2013056999 W JP 2013056999W WO 2013146267 A1 WO2013146267 A1 WO 2013146267A1
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Prior art keywords
objective lens
basic structure
light
optical
optical axis
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PCT/JP2013/056999
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English (en)
French (fr)
Japanese (ja)
Inventor
立山清乃
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コニカミノルタ株式会社
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Application filed by コニカミノルタ株式会社 filed Critical コニカミノルタ株式会社
Priority to CN201380013567.6A priority Critical patent/CN104335276B/zh
Priority to JP2014507648A priority patent/JP6065347B2/ja
Publication of WO2013146267A1 publication Critical patent/WO2013146267A1/ja

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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 has an optical path difference providing structure formed by superimposing two basic structures that are diffractive structures, and an objective lens that can be used in common for three types of optical discs, and light mounted with the objective lens A pickup device is described.
  • the focal length f1 when using the BD is designed to be 2.2 mm.
  • the focal length is relatively short at 2.2 mm, the working distance when using a CD is shortened, and if the rotating optical disk is warped, there is a risk of causing a collision with the objective lens.
  • the paraxial power of diffraction is increased by reducing the pitch (width in the direction perpendicular to the optical axis) of the optical path difference providing structure in the central region, in other words, by increasing the number of annular zones. I can see that it avoids the problem.
  • the ring zone structure is a blaze structure, the increase in the number of ring pairs is remarkable.
  • 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 area diameter on the optical surface focused on the DVD is made equal to that of the DVD dedicated lens. It was found that the spot diameter when the light beam having the wavelength ⁇ 2 is condensed on the information recording surface of the DVD becomes large, and there is a possibility that information cannot be recorded and / or reproduced appropriately.
  • the present inventor conducted extensive research on the above problems, and ascertained the following two causes.
  • the first cause is a decrease in rim strength.
  • the pitch of the optical path difference providing structure in the central area in order to ensure a working distance when using a CD
  • the focal length of the luminous flux when using a DVD that passes through the central area is also increased.
  • the number of ring zones in a certain region Will increase.
  • the number of ring zones in the vicinity of the intermediate area is very large, and the light transmittance in the vicinity of the intermediate area near the maximum effective diameter of the luminous flux when using a DVD is higher than the transmittance in the vicinity of the optical axis. Becomes smaller and the rim strength is lowered, so that the spot diameter when using the DVD is enlarged.
  • the second cause is a sine condition problem. While it is a BD / DVD / CD compatible objective lens, since there are only two optical surfaces, the sine condition cannot be satisfied for all optical disks. Since the sine condition at the time of using BD that requires stricter accuracy has to be satisfied with priority, the sine condition at the time of using DVD collapses to the positive side, and as a result, the spot diameter at the time of using DVD increases.
  • the rim strength is reduced, and the amount of transmitted light to the condensing spot is reduced. It has been found that the spot diameter may increase even when the BD is used.
  • the object of the present invention is to solve the above-mentioned three problems that the spot diameter becomes large at the time of using DVD and BD at once. Compatibility of three types of optical disks of BD / DVD / CD can be achieved with a common objective lens. In addition, it is possible to perform stable recording / reproduction of information by ensuring a working distance even when using a CD with a thick substrate and forming an appropriate spot diameter when using a BD or DVD. It is an object of the present invention to provide an objective lens suitable for a compact optical pickup device and an optical pickup device equipped with the 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 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. And / or do not collect light for playback
  • 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; The second basic structure is a blazed structure.
  • 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;
  • the fourth basic structure is a blazed structure.
  • the focal length of the objective lens in the first light flux f1 is 1.0 ⁇ f1 ⁇ 2.2 (1)
  • the outer diameter of the intermediate region is ⁇ 2 and the imaging magnification of the objective lens in the second light flux is m2, 0.66 ⁇ ⁇ 2 /(2 ⁇ f1 ⁇ (1-m2)) ⁇ 0.75 (3) It is characterized by satisfying.
  • 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 focal length is within the range of the formula (1), it can be suitably mounted on a thin optical pickup device.
  • the focal length satisfies the relatively short formula (1), the number of ring zones of the optical path difference providing structure in the central region increases in order to ensure the working distance.
  • the focal length of the light flux when using the DVD passing through the central area becomes long. Therefore, by increasing the number of ring zones of the optical path difference providing structure in the intermediate area, the light flux when using the DVD passing through the intermediate area is increased. The focal length must also be increased. As a result, the number of ring zones of the optical path difference providing structure in the intermediate region becomes very large in the vicinity of the peripheral region of the intermediate region, the influence of the shadow effect described later and the molding error increase, and the intermediate region with respect to the vicinity of the optical axis center.
  • the pupil transmittance ratio r2 in the vicinity of the peripheral region of the region falls within the range of Expression (2) in the second light flux.
  • 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 BD from the optical axis to the direction perpendicular to the optical axis. Further, the vicinity of the peripheral area of the intermediate area refers to a range of 10% of the effective diameter when using the BD with respect to the peripheral area direction from the boundary between the intermediate area and the peripheral area.
  • 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 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 becomes particularly significant when the objective lens has a high NA. In addition, due to molding technology problems, the shape near the tip or root of the serrated ring zone is likely to cause molding errors with respect to the design shape, which increases the amount of scattered light. Cause a decline.
  • the objective lens of the present invention at least two basic structures are overlapped in the central region and the intermediate region, and the number of annular zones is particularly large in the vicinity of the peripheral region of the intermediate region due to satisfying the expression (1). Become more. That is, the effect of the shadow and the influence of the molding error are large, and the transmitted light amount in the vicinity of the intermediate region is smaller than the transmitted light amount in the vicinity of the optical axis. As a result, the reverse phenomenon of apodization occurs when using the DVD, and the spot diameter when using the DVD is enlarged.
  • the sine condition when using the DVD is positively lost due to the relationship between the sine conditions, and as a result, the spot diameter when using the DVD is further enlarged.
  • the effective diameter of the second light flux when the objective lens is used in DVD is increased, that is, the NA is increased, and the spot diameter is reduced when using the DVD.
  • it can be preferably used for compatible lenses for reproduction of three types of optical discs of BD / DVD / CD.
  • the spot diameter when using the DVD is not reduced too much than necessary.
  • the objective lens of the present invention satisfies the value equal to or higher than the lower limit of the expression (3), so that the BD When in use, 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 is reduced.
  • An objective lens according to a second aspect is the invention according to the first aspect, wherein the first basic structure determines any X-order diffracted light amount of the first light flux that has passed through the first basic structure.
  • the Y-order diffracted light amount of the second light flux that has passed through the first basic structure is made larger than any other order diffracted light amount, and the first diffracted light amount passed through the first basic structure.
  • the second basic structure makes the L-order diffracted light quantity of the first light flux that has passed through the second basic structure larger than any other order of diffracted light quantity, and the second light flux that has passed through the second basic structure.
  • the Mth order diffracted light quantity is larger than any other order diffracted light quantity
  • the Nth order diffracted light quantity of the third light flux that has passed through the second basic structure is made larger than any other order diffracted light quantity
  • the third basic structure makes the A-order diffracted light quantity of the first light flux that has passed through the third basic structure larger than any other order diffracted light quantity, and the second light flux that has passed through the third basic structure.
  • the B order diffracted light quantity of the other than any other order diffracted light quantity In the fourth basic structure, the D-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 second light flux that has passed through the fourth basic structure.
  • the E-order diffracted light amount of the light is larger than any other order diffracted light amount,
  • the X, Y, Z, L, M, N, A, B, D, and E are integers and satisfy the following formula.
  • X A (4)
  • Y B (5)
  • L D (6)
  • M E (7)
  • the order of the diffracted light having the highest light intensity in the first foundation structure and the third foundation structure is matched, and the light intensity in the second foundation structure and the fourth foundation structure is the highest. Since the orders of high diffracted light are matched, the optical path difference function is almost continuous at the boundary between the central region and the intermediate region not only in the reference state but also at the time of temperature and wavelength change, thereby suppressing the occurrence of high-order aberrations. it can. That is, by satisfying the equations (4) to (7), it is possible to suppress the occurrence of higher order aberrations against environmental fluctuations. Further, by satisfying the expressions (4) to (7), the number of ring zones increases in the intermediate region, particularly in the vicinity of the peripheral region of the intermediate region, as compared with the central region. However, such a big problem can be solved by satisfying Expression (3).
  • the objective lens according to claim 3 is the invention according to claim 1 or 2, wherein the X and A are odd numbers, and the L and D are even numbers.
  • X and A are odd numbers, the diffraction power imparted to the first light flux having the wavelength ⁇ 1 by the first basic structure and the diffraction power imparted to the third light flux having the wavelength ⁇ 3 that is approximately twice the wavelength ⁇ 1 are obtained.
  • the relative spherical aberration generated between the BD and the CD can be corrected satisfactorily.
  • L and D are even numbers, it is possible to satisfactorily correct the relative spherical aberration that occurs between the BD and the DVD remaining by the second basic structure.
  • high diffraction efficiency can be obtained for all of the first to third light beams.
  • X, A, L, and D are preferably low-order from the viewpoints of suppression of the shadow effect, suppression of variation in diffraction efficiency during wavelength variation, ease of manufacture, and the like.
  • the objective lens according to a fourth aspect is the invention according to the third aspect, wherein the X, Y, Z, L, M, N, A, B, D, and E are
  • 1
  • 1
  • 1
  • 2
  • 1
  • 1 It is characterized by satisfying.
  • the steps of the first to fourth foundation structures do not become too large.
  • it is easy to manufacture even in resin molding it is possible to suppress light loss due to manufacturing errors, suppress shadow effects, ensure high light utilization efficiency, and reduce diffraction efficiency fluctuations when wavelength and temperature change can do.
  • a (1/1/1) structure (the first-order diffracted light is generated most in any of the first light beam, the second light beam, and the third light beam) is used.
  • An objective lens according to a fifth aspect is the invention according to any one of the first to fourth aspects, wherein the objective lens satisfies the following expression. 1.0 ⁇ f1 ⁇ 2.0 (1) ′
  • the objective lens according to claim 6 is the invention according to any one of claims 1 to 5, wherein the working when recording and / or reproducing the information of the CD using the third light flux is performed.
  • the distance is WD3 (mm)
  • the following formula is satisfied.
  • An objective lens according to a seventh aspect is the invention according to any one of the first to sixth aspects, wherein the objective lens satisfies the following expression. 0.68 ⁇ ⁇ 2 /(2 ⁇ f1 ⁇ (1-m2)) ⁇ 0.73 (9)
  • the spot diameter suitable for recording / reproducing BD / DVD is also in such an objective lens. Can be obtained.
  • the objective lens according to claim 8 is the invention according to any one of claims 1 to 7, 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 (10)
  • 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.
  • the objective lens according to claim 9 is the invention according to any one of claims 1 to 8, wherein at least the step of the first basic structure provided near the optical axis of the central region is a light step. 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 10 is the invention according to any one of claims 1 to 9, wherein when the focal length of the second light flux of the objective lens is f2. 0.61 ⁇ ⁇ 2 /(2 ⁇ f2 ⁇ (1-m2)) ⁇ 0.65 (11) It is characterized by satisfying.
  • the objective lens according to claim 11 is the invention according to any one of claims 1 to 10, wherein in the first basic structure, all the steps are directed in the same direction, In the second basic structure, all steps are directed in the same direction, In the third basic structure, all the steps are directed in the same direction,
  • the fourth basic structure is characterized in that all the steps are directed in the same direction.
  • first to fourth foundation structures are independently oriented in the same direction, the working distance when using a CD becomes easier.
  • An objective lens according to a twelfth aspect is the invention according to any one of the first to eleventh aspects, wherein the following expression is satisfied when the total number of annular zones in the intermediate region is N2. It is a feature. 110 (mm) ⁇ N2 ⁇ f1 ⁇ 300 (mm) (12)
  • the value By setting the value to be equal to or more than the lower limit of the equation (12), the working distance of the CD can be secured, and the possibility of scratching by interference with the optical disc can be reduced.
  • the value of the expression (12) below the upper limit, it is possible to prevent the pitch from becoming too small, so that it is possible to suppress the effect of shadows, to prevent deterioration of workability and to reduce the shape error, and as a result Decrease in diffraction efficiency can be prevented.
  • An optical pickup device includes the objective lens according to any one of the first to twelfth aspects.
  • An optical pickup device is the optical pickup device according to the thirteenth aspect, wherein 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 reason is that there is a possibility of adversely affecting the driving force, and the reason why it is desired to simplify the control of the coupling lens displacement by the drive.
  • the objective lens of the present invention to improve both the temperature characteristic and the wavelength characteristic when using the DVD, as a result, the coupling occurs when the second light beam passes when using the DVD. Even in a state where the position of the lens in the optical axis direction is fixed, information can be recorded / reproduced with respect to the information recording surface of the DVD, and the above-mentioned problems can be solved.
  • 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 (13) 0.5mm ⁇ t2 ⁇ 0.7mm (14) 1.0 mm ⁇ t3 ⁇ 1.3 mm (15)
  • 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 (16) and (17). 1.5 ⁇ ⁇ 1 ⁇ 2 ⁇ 1.7 ⁇ ⁇ 1 (16) 1.8 ⁇ ⁇ 1 ⁇ 3 ⁇ 2.0 ⁇ ⁇ 1 (17)
  • 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, and a second optical path difference providing structure is provided in the intermediate area.
  • the peripheral region may be a refracting surface, or a third optical path difference providing structure may be provided in the peripheral region.
  • 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 and the second optical path difference providing structure may be provided on different optical surfaces of the objective lens, respectively, but are preferably provided on the same optical surface. Furthermore, also when providing a 3rd optical path difference providing structure, it is preferable to provide in the same optical surface as a 1st optical path difference providing structure and a 2nd optical path difference providing structure. 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 surface of the objective lens on the optical disk side.
  • 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 optical path difference providing structure is provided on a surface having a large effective diameter, for example, the minimum annular zone width of the basic structure can be designed wider, and there is an advantage that the light amount loss due to the step portion of the annular zone can be suppressed.
  • there is a merit that the annular structure does not wear when the objective lens is rubbed with a lens cleaner.
  • the first basic structure and the second basic structure on different optical surfaces without overlapping.
  • 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 X-order diffracted light amount of the first light beam that has passed through the first basic structure larger than any other order of diffracted light amount, and the Y-order of the second light beam that has passed through the first basic structure. Is made larger than any other order of the diffracted light amount, and the Z-order diffracted light amount of the third light flux that has passed through the first basic structure is made larger than any other order of diffracted light amount.
  • This is called an (X / Y / Z) structure.
  • X, Y, and Z are integers.
  • X is preferably an odd number.
  • X is an odd number
  • different paraxial powers can be applied to BD and CD, so that the relative spherical aberration generated between BD and CD can be corrected satisfactorily.
  • a more preferable value of X is that the absolute value is an odd number of 5 or less, and most preferable that the absolute value is 1. If the first-order diffracted light that is low-order is generated, the step amount of the first basic structure does not become too large, which facilitates manufacturing, can suppress the light quantity loss caused by manufacturing errors, and also when the wavelength varies. This is preferable because the fluctuation in diffraction efficiency can be reduced.
  • the absolute value is 1.
  • 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 in the central region” refers to a step at least closest to the optical axis among steps in the (X / Y / Z) 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 flux is Xth 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 in the case of a thick objective lens having a large on-axis 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 second basic structure is also a blazed structure. Further, the second foundation structure makes the L-order diffracted light quantity of the first light beam that has passed through the second foundation structure larger than any other order of diffracted light quantity, and the M-order of the second light flux that has passed through the second foundation structure. Is made larger than any other order of diffracted light, and the Nth order diffracted light of the third light beam that has passed through the second basic structure is made larger than any other order of diffracted light.
  • This is called an (L / M / N) structure.
  • L, M, and N are integers.
  • L is preferably an even number. When L is an even number, high diffraction efficiency can be obtained for all of the first to third light beams.
  • a more preferable value of L is that the absolute value is an even number of 4 or less, and most preferably, the absolute value is 2. If the second-order diffracted light, which is a low order, is generated, the step amount of the second basic structure does not become too large, which facilitates manufacturing, can suppress the light amount loss due to manufacturing errors, and at the time of wavelength variation. This is preferable because the fluctuation in diffraction efficiency can be reduced.
  • a preferable value of M and N is that the absolute value is 1.
  • 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 (L / M / N) 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 formed by superimposing the first basic structure having the (1/1/1) structure and the second basic structure having the (2/1/1) structure, the height of the step is extremely high. Can be lowered. 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 (18) and (19). More preferably, the following conditional expressions (18) and (19) 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 (18) ′, ( 19) ′ are the following conditional expressions (18) ′, ( 19) ′ is preferably satisfied. More preferably, the following conditional expressions (18) ′ and (19) ′ are satisfied in all the regions of the central region. 0.6 ⁇ ( ⁇ 1 / (n ⁇ 1)) ⁇ d11 ⁇ 1.5 ⁇ ( ⁇ 1 / (n ⁇ 1)) (18) ′ 0.6 ⁇ ( ⁇ 1 / (n ⁇ 1)) ⁇ d12 ⁇ 1.5 ⁇ ( ⁇ 1 / (n ⁇ 1)) (19) ′
  • conditional expressions (18) ′′ and (19) ′′ are satisfied. More preferably, the following conditional expressions (18) ′′ and (19) ′′ are satisfied in all the regions of the central region. 0.9 ⁇ ( ⁇ 1 / (n ⁇ 1)) ⁇ d11 ⁇ 1.5 ⁇ ( ⁇ 1 / (n ⁇ 1)) (18) ′′ 0.9 ⁇ ( ⁇ 1 / (n-1)) ⁇ d12 ⁇ 1.5 ⁇ ( ⁇ 1 / (n-1)) (19) '''
  • 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 (L /
  • the second basic structure having the (M / N) structure when the wavelength of the incident light beam is changed to be longer, it is preferable that the spherical aberration is changed in an undercorrected direction (under).
  • 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 positive diffractive 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 negative diffraction power. As described above, since both the first basic structure and the second basic structure have diffraction power, when using an optical disk having a plurality of information recording surfaces, unnecessary light reflected by the information recording surface which is not a recording / reproducing object is required light. It is preferable because it can be further away from the center.
  • 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 (23).
  • 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 (23)
  • 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 A-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 B-order diffracted light amount of the second light beam that has passed through the third basic structure is changed to other values. The amount of diffracted light is greater than any order, and the amount of C-order diffracted light of the third light beam that has passed through the third basic structure is greater than the amount of diffracted light of any other order.
  • the fourth basic structure is also a blazed structure.
  • the D-order diffracted light quantity of the first light beam passing through the fourth basic structure is made larger than any other order diffracted light quantity
  • the E-order diffracted light quantity of the second light beam passing through the fourth basic structure is set to any other order.
  • the F-order diffracted light amount of the third light flux that has passed through the fourth basic structure is made larger than any other order diffracted light amount.
  • A, B, C, D, E, and F are integers.
  • A is preferably an odd number. Since A is an odd number, a paraxial power different between BD and CD can be applied, so that the relative spherical aberration generated between BD and CD can be corrected well.
  • a more preferable value of A is that the absolute value is an odd number of 5 or less, and most preferably, the absolute value is 1. If the first-order diffracted light that is low order is generated, the step amount of the third basic structure does not become too large, which facilitates the manufacture, can suppress the light amount loss caused by the manufacturing error, and at the time of wavelength variation. This is preferable because the fluctuation in diffraction efficiency can be reduced.
  • a preferable value of B and C is that the absolute value is 1.
  • D is preferably an even number, and when D is an even number, high diffraction efficiency can be obtained for all of the first to third light beams.
  • a more preferable value of D is that the absolute value is an even number of 4 or less, and most preferably, the absolute value is 2.
  • the step amount of the fourth basic structure does not become excessively large, which facilitates manufacturing, can suppress light loss due to manufacturing errors, and can change the wavelength. This is preferable because the fluctuation in diffraction efficiency can be reduced. Moreover, as a preferable value of E and F, the absolute value is 1.
  • the first optical path difference providing structure and the second optical path difference providing structure preferably satisfy the following expressions (4) to (7).
  • the optical path difference function becomes almost continuous at the boundary between the central region and the intermediate region not only in the reference state but also at the time of temperature or wavelength change, and the occurrence of higher order aberrations can be suppressed.
  • X A (4)
  • Y B (5)
  • L D (6)
  • M E (7)
  • X, Y, Z, L, M, N, A, B, D, and E are respectively
  • 1
  • 1
  • 1
  • 2
  • 1
  • 1 Since the values of X, Y, Z, L, M, N, A, B, D, and E are all low-order, the steps of the first to fourth foundation structures do not become too large, and manufacturing The amount of light loss caused by manufacturing errors can be suppressed, and the amount of steps is small, so the effect of shadows can be suppressed and high light utilization efficiency can be secured, and fluctuations in diffraction efficiency when the wavelength and temperature change are also reduced. be able to.
  • the (1/1/1) structure (the first-order diffracted light is generated most in any of the first light beam, the second light beam, and the third light beam) is the first and third bases.
  • (2/1/1) structure (the second-order diffracted light is most generated in the first light flux, and the first-order diffracted light is most generated in the second light flux and the third light flux). Because of the basic structure, high diffraction efficiency can be obtained at all three wavelengths while the magnification of the objective lens is 0 or almost 0 in any of BD, DVD, and CD.
  • 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.
  • the spherical aberration changes in an undercorrected (under) direction
  • the fourth basic structure which is a structure, when the wavelength of the incident light beam is changed to be longer, it is preferable that the spherical aberration is changed in an undercorrected (under) direction.
  • 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 spherical aberration changes in the undercorrection (under) direction, and the incident light is incident on the other side.
  • the spherical aberration may be changed in the overcorrection (over) direction.
  • the spherical aberration when the wavelength of the incident light beam is changed so as to become longer, the spherical aberration changes in the undercorrection (under) direction. If the spherical aberration is changed in the overcorrection direction when the wavelength is changed to be longer, when the first light beam is condensed on the information recording surface of the BD as the entire objective lens, the first aberration is changed.
  • the amount of change of the third-order spherical aberration when the wavelength of one light beam changes by +5 nm can be set to ⁇ 30 m ⁇ rms to +50 m ⁇ rms, which is preferable.
  • the amount of change in the third-order spherical aberration when the wavelength of the first light beam changes by +5 nm is set to be ⁇ 10 m ⁇ rms or more and +10 m ⁇ rms or less.
  • the amount of change in the fifth-order spherical aberration when the wavelength of the first light beam changes by +5 nm is -20 m ⁇ rms or more and 20 m ⁇ rms or less. It is preferable that More preferably, it is ⁇ 10 m ⁇ rms or more and +10 m ⁇ rms or less.
  • the spherical aberration when the wavelength of the incident light beam is changed to become longer, the spherical aberration changes in the undercorrection (under) direction, and in the other direction, the incident light beam If the spherical aberration is changed in the overcorrection direction when the wavelength is changed to be longer, the wavelength of the incident light beam is increased in either one of the third basic structure and the fourth basic structure. When the length is changed, the spherical aberration changes in the overcorrection direction. Therefore, even when the second optical path difference providing structure is composed of only the third basic structure and the fourth basic structure, flare is produced when the CD is used. It can be done easily.
  • flare out when using a CD can be performed with a simple second optical path difference providing structure, so that a decrease in light utilization efficiency due to a shadow effect is suppressed, and a decrease in light utilization efficiency due to manufacturing errors is also suppressed.
  • the light utilization efficiency can be improved. This reduces the effect of correcting the temperature characteristics when using BD in the intermediate area, but the temperature characteristics are too poor because both the first basic structure and the second basic structure in the central area are insufficiently corrected at long wavelengths. This can be prevented, and the wavelength characteristic correction effect when using the BD can be increased.
  • both the temperature characteristic and wavelength characteristic of the DVD can be improved.
  • the spherical aberration is changed in an undercorrected (under) direction, and the wavelength of the incident light beam is longer in the third basic structure.
  • the spherical aberration changes in the overcorrected (over) direction because the flare can be easily moved farther when the CD is used.
  • the ring zone of the third basic structure is 1 to 3 in one ring zone closest to the central region of the fourth basic structure. It is preferable that the number (particularly preferably 2 to 3) is included. More preferably, in the second optical path difference providing structure, 1 to 5 (particularly preferably 2 to 3) ring zones of the third foundation structure are provided for one ring zone closest to the peripheral region of the fourth foundation structure. It is included.
  • the ratio of the total number of ring zones of the third foundation structure to the total number of ring zones of the fourth foundation structure in the intermediate region is preferably 1.0 or more and 5.0 or less, more preferably 2.0 or more and 3.0 or less. It is the following.
  • the step amount d21 of the step facing the direction opposite to the optical axis and the step amount d22 of the step facing the direction of the optical axis are expressed by the following conditional expressions (21), (22 ) Is preferably satisfied.
  • n represents the refractive index of the objective lens at ⁇ 1.
  • the objective lens of the present invention satisfies the formula (1) when the focal length of the first light flux of the objective lens is f1. 1.0 ⁇ f1 ⁇ 2.2 (1) Since the focal length is within the range of the formula (1), it can be suitably mounted on an optical pickup device having a small thickness. On the other hand, since the focal length satisfies the relatively short formula (1), the number of ring zones of the optical path difference providing structure in the central region increases in order to secure the working distance. As a result, the focal length of the light flux when using the DVD that passes through the central area becomes long. Therefore, by increasing the number of ring zones of the optical path difference providing structure in the intermediate area, the light flux when using the DVD that passes through the intermediate area is increased.
  • the focal length must also be increased.
  • the number of ring zones of the optical path difference providing structure in the intermediate region becomes very large in the vicinity of the peripheral region of the intermediate region, the influence of the shadow effect and the molding error increase, and the intermediate region with respect to the vicinity of the optical axis center increases.
  • the pupil transmittance ratio r2 in the vicinity of the peripheral region falls within the range of the expression (2) when the second light flux is used. r2 ⁇ 0.9 (2)
  • 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 BD from the optical axis to the direction perpendicular to the optical axis.
  • the vicinity of the peripheral region of the intermediate region means a range of 10% of the effective diameter when using the BD with respect to the peripheral region direction from the boundary between the intermediate region and the peripheral region.
  • r2 falls within the range of the formula (2), the reverse phenomenon of apodization occurs when using a DVD, and the spot diameter when using a DVD increases.
  • the sine condition when using the DVD is positively lost due to the relationship between the sine conditions, and as a result, the spot diameter when using the DVD is further enlarged.
  • the objective lens of the present invention solves the above two problems at once by satisfying the expression (3) described in detail below.
  • r2 is 0.4 or more and 0.9 or less because the degree of the enlargement of the spot diameter due to the reverse phenomenon of apodization does not become too large, and the effect of the present invention becomes more remarkable.
  • r2 is 0.5 or more and 0.8 or less, and further preferably r2 is 0.6 or more and 0.75 or less. Further, when f1 satisfies the following expression (1) ′, the effect of the present invention becomes more remarkable. 1.0 ⁇ f1 ⁇ 2.0 (1) ′
  • 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
  • the processing angle decreases due to the increase in the expected angle of the objective lens in the vicinity of the effective diameter of the objective lens when the wavelength ⁇ 1 is used, and the light on the optical surface is reduced. As the incident angle increases, the reflectance is improved. As a result, the rim strength is reduced, and the spot diameter is enlarged even when BD is used. However, by satisfying the value equal to or higher than the lower limit of the expression (3), the rim strength is smaller than that near the optical axis when BD is used.
  • the intermediate area with a relatively small amount of transmitted light is widened, apodization is generated, the spot diameter of the BD is narrowed, and the problem of increasing the spot diameter of the BD is solved.
  • This can be preferably used particularly for a compatible lens for reproduction of three types of optical disks of BD / DVD / CD. Furthermore, by satisfying a value equal to or lower than the upper limit of Expression (3), the spot diameter when using the DVD is not reduced too much.
  • 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 ⁇ ⁇ 2 /(2 ⁇ f2 ⁇ (1-m2)) ⁇ 0.65 (11)
  • formula (11) the effective diameter when using a DVD can be increased, which is preferable.
  • the third optical path difference providing structure preferably has a fifth basic structure.
  • the P-order diffracted light amount of the first light beam that has passed through the fifth basic structure is made larger than any other order diffracted light amount, and the Q-order diffraction of the second light beam that has passed through the fifth basic structure.
  • the light quantity is made larger than any other order diffracted light quantity, and the R-order diffracted light quantity of the third light flux that has passed through the fifth basic structure is made larger than any other order diffracted light quantity.
  • P is preferably 5 or less in order to suppress fluctuations in diffraction efficiency during wavelength fluctuations. More preferably, P is 2 or less.
  • 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 has a (2/1/1) blazed structure and a fourth basic structure BS4 whose level difference faces the optical axis, and (1/1/1).
  • the blazed structure has a structure in which a third base structure BS3 whose level difference is opposite to the optical axis is superimposed.
  • 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 composed of only a sixth basic structure BS5 having a blaze structure of (2/1/1) and having a step facing the optical axis.
  • 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.
  • the first effective diameter for the light flux phi 1 (mm) of the objective lens is preferably 1.9 to 4.0, more preferably 2.0 to 3.0.
  • the spot diameter when using the DVD can be reduced by satisfying the value equal to or higher than the lower limit of the above-described formula (3), stable information recording and / or reproduction is possible. It is possible to obtain an objective lens that is compatible with three types of optical disks.
  • the number N all of the annular zones formed on the objective lens is preferably 150 or more and 250 or less.
  • the total number of annular zones in the intermediate region is N2
  • the number of steps substantially parallel to the optical axis in the intermediate region may be regarded as the total number of annular zones in the intermediate region. 110 (mm) ⁇ N2 ⁇ f1 ⁇ 300 (mm) (12)
  • an objective lens satisfy
  • 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 during CD recording / playback tends to be short, so the upper limit of conditional expression (10) 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 beam is incident on the objective lens satisfy the following formula (26). -0.01 ⁇ m1 ⁇ 0.01 (26)
  • the imaging magnification m2 of the objective lens when the second light beam is incident on the objective lens satisfies the following expression (27). Is preferred. -0.01 ⁇ m2 ⁇ 0.01 (27)
  • the imaging magnification m2 of the objective lens when the second light beam is incident on the objective lens preferably satisfies the following expression (27) ′. . ⁇ 0.025 ⁇ m2 ⁇ ⁇ 0.01 (27) ′
  • the imaging magnification m3 of the objective lens when the third light beam is incident on the objective lens satisfies the following expression (28). Is preferred. -0.01 ⁇ m3 ⁇ 0.01 (28)
  • the imaging magnification m3 of the objective lens when the third light beam is incident on the objective lens preferably satisfies the following expression (28) ′. . ⁇ 0.025 ⁇ m3 ⁇ ⁇ 0.01 (28) ′
  • 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 a compact optical pickup device capable of recording / reproducing stable information by forming an appropriate spot diameter, and an optical pickup device equipped with the 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.
  • 6 is a diagram illustrating a ratio of pupil transmittance to a ratio of distance from the optical axis in Example 1.
  • 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.
  • the present invention is not limited to the present embodiment.
  • 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 the present 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 quantity of the first light beam is made larger than any other order diffracted light quantity
  • the first order diffracted light quantity of the second light beam that has passed through the third basic structure is made larger than any other order diffracted light quantity.
  • 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 second-order diffracted light beam that has passed through the fourth basic structure.
  • 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 coupling lens COL is fixed, information can be recorded / reproduced on the DVD, so that 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. .
  • Equation 2 ⁇ (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 pitch P (h) ⁇ B / ( ⁇ (2i ⁇ C 2i ⁇ h 2i-1 )).
  • Example 1 Tables 1A and 1B show lens data of Example 1.
  • the objective lens of Example 1 is a plastic single lens, and the steps of the first and third foundation structures are opposite to the optical axis, and the steps of the second and fourth foundation structures are light. The direction of the 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 a (1/1/1) blazed diffractive structure in (4/1/1) blazed diffractive structure in the entire intermediate region.
  • Example 1 It is an optical path difference providing structure in which a certain third basic structure is overlapped.
  • the value of the expression (3) is 0.70
  • the value of the pupil transmittance ratio r2 is 0.70
  • the value of the number N2 of the intermediate zone is 68
  • the value of the expression (11) is 0. .621
  • the value of the expression (12) is 119.68.
  • FIG. 10 is a graph showing the ratio of the pupil transmittance and the ratio of the distance from the optical axis when the second light beam is used in the first embodiment.
  • the vertical axis represents the pupil transmittance value when the pupil transmittance in the vicinity of the optical axis is 1
  • the horizontal axis represents half the effective diameter of the DVD (1 in the first embodiment).
  • .23 mm represents the distance from the optical axis.
  • a boundary BN between the central region and the intermediate region is illustrated by a dotted line. From FIG. 10, the ratio r2 of the pupil transmittance in the vicinity of the peripheral region in the intermediate region with respect to the vicinity of the optical axis center of the objective lens in the second light flux in Example 1 is 0.7.
  • Example 2 Tables 2A and 2B show lens data of Example 2.
  • the objective lens of Example 2 is a plastic single lens, and the steps of the first and third foundation structures are opposite to the optical axis, and the steps of the second and fourth foundation structures are light. The direction of the 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 a (1/1/1) blazed diffractive structure in (4/1/1) blazed diffractive structure in the entire intermediate region.
  • Example 2 It is an optical path difference providing structure in which a certain third basic structure is overlapped.
  • the value of the expression (3) is 0.70
  • the value of the pupil transmittance ratio r2 is 0.62
  • the value of the number of annular zones N2 is 142
  • the value of the expression (11) is 0. .620
  • the value of the expression (12) is 251.34.
  • Example 3 Tables 3A and 3B show lens data of Example 3.
  • the objective lens of Example 3 is a plastic single lens, and the steps of the first foundation structure and the third foundation structure are opposite to the optical axis, and the steps of the second foundation structure and the fourth foundation structure are light. The direction of the 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 is a (1/1/1) blazed diffractive structure in (4/1/1) blazed diffractive structure in the entire intermediate region.
  • Example 3 It is an optical path difference providing structure in which a certain third basic structure is overlapped.
  • the value of the expression (3) is 0.69
  • the value of the pupil transmittance ratio r2 is 0.72
  • the value of the number of annular zones N2 is 58
  • the value of the expression (11) is 0. .631
  • the value of the expression (12) is 127.6.
  • 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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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

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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

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