WO2012133363A1 - Lentille de focalisation pour dispositif de capture optique, dispositif de capture optique et lecteur/enregistreur d'informations optique - Google Patents

Lentille de focalisation pour dispositif de capture optique, dispositif de capture optique et lecteur/enregistreur d'informations optique Download PDF

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WO2012133363A1
WO2012133363A1 PCT/JP2012/057851 JP2012057851W WO2012133363A1 WO 2012133363 A1 WO2012133363 A1 WO 2012133363A1 JP 2012057851 W JP2012057851 W JP 2012057851W WO 2012133363 A1 WO2012133363 A1 WO 2012133363A1
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Prior art keywords
objective lens
light
basic structure
optical
light beam
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PCT/JP2012/057851
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English (en)
Japanese (ja)
Inventor
立山清乃
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コニカミノルタアドバンストレイヤー株式会社
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Priority to JP2013507580A priority Critical patent/JPWO2012133363A1/ja
Publication of WO2012133363A1 publication Critical patent/WO2012133363A1/fr

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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
    • G11B7/125—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
    • 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

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.
  • 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.
  • Patent Document 1 describes an objective lens that can be used in common for three types of optical discs, and an optical pickup device equipped with the objective lens.
  • Patent Document 1 discloses an objective lens for an optical pickup device that can be compatible with three types of optical disks of HD-DVD / DVD / CD, and regards the problem of off-axis characteristics as a problem. Therefore, in Patent Document 1, an attempt is made to solve the off-axis characteristic problem by changing the magnification when each optical disk is used. However, when the magnification is greatly changed for each optical disk, the amount of movement of a coupling lens or the like that changes the magnification for each optical disk increases, and when finite light having a strong divergence enters the objective lens, Aberration occurs. Therefore, it is desirable to solve the problem of off-axis characteristics with a single objective lens without depending on the change in magnification.
  • the protective substrate thickness of BD is generally 0.1 mm, whereas the protective substrate of CD Since the thickness is 1.2 mm, the difference between the thicknesses of the two protective substrates is large. If the sine condition that determines the off-axis characteristics is set so as to satisfy BD, CD is not satisfied, and the off-axis characteristics deteriorate. There is a fear. However, in Patent Document 1, no particular countermeasure is taken against the sine condition for DVD and CD.
  • Patent Document 1 describes HD-DVD / DVD / CD as described above, but as described above, there are three types of BD / DVD / CD, which are more problematic due to the large substrate thickness difference. There is no specific measure for improving off-axis characteristics in an objective lens for an optical pickup device that enables compatibility of optical discs. Further, there is a demand to extend the working distance when using a CD, which is difficult to ensure due to being thicker than an HD-DVD / DVD / CD compatible lens, and to keep unnecessary diffracted light that causes an error signal away from the used diffracted light.
  • the present invention has been made to solve the above-mentioned problems. In spite of a relatively short focal length, the working distance in the CD is ensured, and unnecessary diffracted light that causes an error signal is kept away. Is an optical pickup device equipped with an objective lens that enables compatibility of three types of optical disks of BD / DVD / CD with a common objective lens while improving off-axis characteristics in all BD / DVD / CD, and An object of the present invention is to provide an optical information recording / reproducing apparatus and an objective lens suitable for the apparatus.
  • 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 protective substrate having a thickness of t1 (mm) using the first light beam, and a third light source that emits a third light beam having a third wavelength ⁇ 3 (760 nm ⁇ ⁇ 3 ⁇ 820 nm).
  • An objective lens used in an optical pickup device for recording and / or reproducing information on a CD having a protective substrate having a thickness of t3 (mm) (t2 ⁇ t3) using a third light beam The objective lens is a single ball, 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 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 coma aberration of the objective lens when using BD is 0.07 ⁇ rms or less with respect to an incident light beam with an angle of view of 0.3 degrees, The following formula is satisfied.
  • fB1 WD1 + t1 ⁇ (1-1 / n1)
  • fB3 WD3 + t3 ⁇ (1-1 / n3)
  • ⁇ Abbe number m1 of the material of the objective lens
  • m1 Imaging magnification when the light beam having the first wavelength ⁇ 1 is incident on the objective lens
  • m3 Result when the light beam having the third wavelength ⁇ 3 is incident on the objective lens
  • d On-axis thickness of the objective lens (mm)
  • WD1 Working distance when using the BD (mm)
  • WD3 Working distance when using the CD (mm)
  • n1 Refractive index of the protective substrate of the BD with respect to the light beam with the first wavelength ⁇ 1
  • n3 Refractive index of the protective substrate of the
  • the objective lens used in a slim type optical pickup device satisfying the expression (3) has a field angle of off-axis light flux due to mounting errors. Tends to be large, which makes the coma problem more pronounced. The problem of coma will be specifically described.
  • the sine condition that defines the off-axis characteristics of the objective lens is determined by (a) the thickness of the protective substrate of the optical disc, (b) the magnification, and (c) the paraxial diffraction power. Since the protective substrate thickness of the optical disk is different, if the sine condition is satisfied in one optical disk, the sine condition may not be satisfied in another optical disk. In such a case, when an off-axis light beam enters an optical disk that does not satisfy the sine condition, a relatively large coma aberration is generated. Usually, since the sine condition at the time of BD use with a strict spot standard is often satisfied, in such a case, the sine condition at the time of use of DVD and CD may not be satisfied, and there is a risk of being forced to use.
  • the present inventor has found that the optimum sine condition is obtained by adjusting the paraxial diffraction power under the conditions (1) and (2) where the magnification difference is small and the absolute value of the magnification is small. It was found that it can be secured. More specifically, on the premise that the sine condition at the time of using BD is in a range where there is no problem, by setting the paraxial diffraction power within a certain range that satisfies the equation (4), DVD and DVD are used. Alternatively, the difference in sine conditions when using a CD can be kept small, and the off-axis characteristics can be improved.
  • the first optical path difference providing structure Undesired diffracted light (diffracted light other than the used diffracted light used for recording / reproducing information) may approach the used diffracted light and be detected by the photodetector to generate an error signal, or the CD working distance
  • the risk of the objective lens colliding with the CD is remarkably increased.
  • the value of equation (4) is equal to or greater than the lower limit, the CD sine condition changes to the positive side as shown in [2] in FIG. 15, the off-axis characteristics of CD deteriorate, and the diffraction pitch decreases.
  • Unnecessary light having a 1/1/1 structure can be kept away, erroneous detection that is detected by the photodetector along with the main light can be suppressed, and a working distance in the CD can be sufficiently secured.
  • satisfying the value of equation (4) improves off-axis characteristics when using a CD, secures the working distance of the CD, divergence of unwanted diffracted light from used diffracted light, improves mold workability, and moldability. Is possible.
  • the objective lens described in claim 2 is characterized in that, in the invention described in claim 1, the following expression is satisfied. m2 ⁇ 0 (5) Where m2: imaging magnification when the light beam having the second wavelength ⁇ 2 is incident on the objective lens
  • the objective lens described in claim 3 is characterized in that, in the invention described in claim 1 or 2, the following expression is satisfied.
  • ⁇ 1 Effective diameter when using the BD (mm)
  • the objective lens according to any one of the first to third aspects, wherein the first optical path difference providing structure has a structure in which at least the first basic structure and the second basic structure are overlapped. And the first basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the first basic structure larger than any other order of diffracted light quantity, and the second light flux that has passed through the first basic structure.
  • the first order diffracted light amount is made larger than any other order diffracted light amount
  • the first order diffracted light amount of the third light beam that has passed through the first basic structure is made larger than any other order diffracted light amount (1 / May be referred to as a 1/1 structure)
  • the second basic structure makes the second-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
  • First-order diffracted light of the second light beam that has passed through the second basic structure Is made larger than any other order of the diffracted light quantity
  • the first order diffracted light quantity of the third light beam that has passed through the second basic structure is made larger than any other order of diffracted light quantity (2/1/1 structure and
  • a balanced objective lens can be provided. Further, in the combination of the 1/1/1 structure and the 2/1/1 structure, the axial chromatic aber
  • the first basic structure provided at least in the vicinity of the optical axis of the central region has a step in a direction opposite to the optical axis.
  • the second basic structure provided at least in the vicinity of the optical axis of the central region is characterized in that the step is directed in the direction of the optical axis.
  • the level difference in the optical axis direction can be further reduced, thereby further suppressing the decrease in diffraction efficiency when the wavelength varies. it can.
  • the intermediate region has a second optical path difference providing structure in which at least the third basic structure and the fourth basic structure are overlapped.
  • the third basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the third basic structure larger than any other order of diffracted light quantity, so that 1 of the second light flux that has passed through the third basic structure.
  • Make the next diffracted light quantity larger than any other order diffracted light quantity In the fourth basic structure, the second-order diffracted light amount of the first light beam that has passed through the fourth basic structure is made larger than any other order of diffracted light amount, and 1st of the second light beam that has passed through the fourth basic structure. It is characterized in that the next diffracted light quantity is made larger than any other order diffracted light quantity.
  • the step amount in the optical axis direction can be reduced, thereby reducing the diffraction efficiency at the time of wavelength variation. Can be suppressed.
  • the orders of the diffracted light having the highest light intensity in the first basic structure and the third basic structure are matched, and the orders of the diffracted light having the highest light intensity in the second basic structure and the fourth basic structure are matched. Therefore, the spherical aberration can be made continuous even when the temperature and the wavelength of the light flux passing through the central region and the intermediate region are changed, and the occurrence of higher order aberrations can be suppressed.
  • the pupil transmittance distribution is almost flat between the intermediate region and the peripheral region, and it is possible to effectively suppress the spot thickening that occurs when the amount of light changes greatly at the boundary due to abolishment or the like. It is also possible to ensure the degree of freedom in designing the objective lens.
  • the objective lens according to claim 7 is the objective lens according to claim 6, wherein the third foundation structure and the fourth foundation structure are blazed, and one objective lens closest to the central region in the fourth foundation structure is provided.
  • One to three annular zones of the third basic structure are included on the annular zone.
  • the condensing position of unnecessary light generated by passing through the intermediate region is the information recording layer other than the information recording layer for recording / reproducing information. It can be separated from the information recording device. In addition, the wavelength characteristics when using a DVD can be improved.
  • the third basic structure provided in the vicinity of the boundary with the central region has a step in a direction opposite to the optical axis.
  • the fourth foundation structure provided in the vicinity of the boundary with the central region is characterized in that the step is directed in the direction of the optical axis.
  • the level difference in the optical axis direction can be further reduced, thereby further suppressing the decrease in diffraction efficiency at the time of wavelength fluctuation. it can.
  • the objective lens according to claim 9 is the invention according to any one of claims 6 to 8, wherein the annular zone of the third foundation structure is arranged on one annular zone closest to the peripheral region in the fourth foundation structure. 1 to 5 are included.
  • the objective lens according to claim 10 is the invention according to any one of claims 6 to 9, wherein the intermediate region is provided with only the third foundation structure and the fourth foundation structure, and other foundations. The structure is not provided.
  • An objective lens according to claim 11 is the invention according to any one of claims 6 to 10, wherein the annular zone of the first foundation structure is disposed on one annular zone closest to the intermediate region in the second foundation structure. 1 to 5 are included.
  • the objective lens described in claim 12 is characterized in that, in the invention described in any one of claims 1 to 11, the following expression is satisfied. 160 (mm) ⁇ N ⁇ f ⁇ 210 (mm) (7)
  • the total number of annular zones in the central region is N
  • the focal length of the objective lens in the first light flux is f (mm).
  • the value of the expression (7) above the lower limit, the working distance of the CD can be secured, and the possibility of scratching by interference with the optical disk can be reduced.
  • the value of the expression (7) below the upper limit, it is possible to prevent the pitch from becoming too small, thereby preventing the workability from being lowered and reducing the shape error, and as a result, preventing the diffraction efficiency from being lowered.
  • An optical pickup device has the objective lens according to any one of the first to twelfth aspects.
  • An optical information recording / reproducing apparatus includes the optical pickup apparatus according to a thirteenth aspect.
  • 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 means that information is recorded / reproduced by a light beam having a wavelength of about 390 to 415 nm and an objective lens having an NA of about 0.8 to 0.9, and the thickness of the protective substrate is 0.05 to 0.00 mm.
  • It is a generic term for a BD series optical disc of about 125 mm, and includes a BD having only a single information recording layer, a BD having two or more information recording layers, and the like.
  • DVD is a general term for DVD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.60 to 0.67 and the thickness of the protective substrate is about 0.6 mm.
  • CD is a general term for CD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.45 to 0.51 and the thickness of the protective substrate is about 1.2 mm.
  • 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. 0.01 mm ⁇ t1 ⁇ 0.125 mm (10) 0.5mm ⁇ t2 ⁇ 0.7mm (11) 1.0 mm ⁇ t3 ⁇ 1.3 mm (12)
  • 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 (13) and (14). 1.5 ⁇ ⁇ 1 ⁇ 2 ⁇ 1.7 ⁇ ⁇ 1 (13) 1.8 ⁇ ⁇ 1 ⁇ 3 ⁇ 2.0 ⁇ ⁇ 1 (14)
  • the first wavelength ⁇ 1 of the first light source is preferably 350 nm to 440 nm, more preferably 390 nm to 415 nm
  • the second wavelength ⁇ 2 of the second light source is preferably 570 nm to 680 nm, more preferably.
  • the third wavelength ⁇ 3 of the third light source is preferably 750 nm or more and 880 nm or less, more preferably 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 photodetectors are provided on both sides of a photodetector that receives main light used for recording and reproducing information, and the sub light for tracking adjustment is received by the two sub photodetectors.
  • a light receiving element 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 an optical system 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 onto the information recording surface of the optical disk.
  • the objective lens of the present invention is preferably a single plastic lens, but may be a glass 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.
  • an alicyclic hydrocarbon-based polymer material such as a cyclic olefin-based resin material
  • the resin material has a refractive index within a range of 1.54 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 (1) 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) ).
  • R 1 to R 18 , R a and R b are each independently a hydrogen atom, A halogen atom or a hydrocarbon group, 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 Alternatively, 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 50 or more.
  • the first optical path difference providing structure in which the first basic structure and the second basic structure are superimposed is formed in the central region, and the third basic structure is provided in the intermediate region.
  • An objective lens in which the second optical path difference providing structure on which the fourth basic structure is superimposed will be described as an example.
  • the optical path difference providing structure is not limited to this form.
  • 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 intensity density is lower than that of the spot central portion, and a spot peripheral portion SOT whose light intensity 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 objective lens is a single-lens aspherical convex lens, even if it is an optical path difference providing structure that provides the same optical path difference, generally the distance from the optical axis tends to increase.
  • 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 aspherical convex lens, even if it is a diffractive structure that generates diffracted light of the same diffraction order, generally, the distance from the optical axis tends to increase.
  • the optical path difference providing structure has a plurality of concentric annular zones with the optical axis as the center.
  • 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 shapes including the optical axis are roughly classified into a blazed structure and a staircase structure.
  • 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 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 plane as a mother 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. 3 (a))
  • the staircase structure has a cross-sectional shape including an 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 vertical direction of the optical axis 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. 3C is referred to as a five-level staircase structure
  • the optical path difference providing structure illustrated in FIG. 3D is referred to as a two-level staircase structure (also referred to as a binary structure). .
  • 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. 3 (a), the same sawtooth shape may be repeated, and as shown in FIG. 3 (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. It is also conceivable to provide the first basic structure and the second basic structure on different optical surfaces without overlapping. Similarly, the third basic structure and the fourth basic structure may be provided on different optical surfaces without overlapping.
  • the first optical path difference providing structure is preferably a structure in which at least the first basic structure and the second basic structure are overlapped, but is not limited thereto.
  • 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.
  • the first basic structure is a blaze type structure.
  • the first basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the first basic structure larger than any other order of diffracted light quantity, and the first-order diffracted light quantity that has passed through the first basic structure. Is made larger than any other order of the diffracted light quantity, and the first order diffracted light quantity of the third light flux that has passed through the first basic structure is made larger than any other order of diffracted light quantity. This is called a (1/1/1) structure.
  • the step amount of the first basic structure does not become too large, so that the manufacture is facilitated, and the light quantity loss due to the manufacturing error can be suppressed, and the wavelength It is preferable because the diffraction efficiency fluctuation at the time of fluctuation can be reduced.
  • the first basic structure provided at least in the vicinity of the optical axis in the central region has a step in a direction opposite to the optical axis.
  • the step is directed in the direction opposite to the optical axis means a state as shown in FIG.
  • the first basic structure provided “at least in the vicinity of the optical axis of the central region” refers to a step at least closest to the optical axis among steps of the (1/1/1) structure.
  • at least a (1/1/1) structure step existing between the optical axis and the 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 is the optical axis. Is pointing in the opposite direction.
  • the step may be directed in the direction of the optical axis. That is, as shown in FIG. 5B, the step is directed in the opposite direction to the optical axis when the first foundation structure is near the optical axis, but is switched halfway, and the step of the first foundation structure is near the intermediate region. It is good also as a shape which faces the direction of an optical axis. However, it is preferable that all the steps of the first basic structure provided in the central region are directed in a direction opposite to the optical axis.
  • the direction of the step of the first basic structure in which the diffraction order of the first light beam is the first order is directed in the direction opposite to the optical axis, so that the three types of optical disks of BD / DVD / CD can be used interchangeably. Even with a thick objective lens having a large axial thickness, a sufficient working distance can be secured 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 a negative paraxial power with respect to the luminous flux.
  • “having negative paraxial power” means that C 2 h 2 > 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 blaze type structure.
  • the second-order diffracted light amount of the first light beam that has passed through the second basic structure is made larger than the diffracted light amount of any other order, and the first-order diffraction of the second light beam that has passed through the first basic structure.
  • the light quantity is made larger than any other order of diffracted light quantity, and the first order diffracted light quantity of the third light flux that has passed through the first basic structure is made larger than any other order of diffracted light quantity. This is called a (2/1/1) structure.
  • the step amount of the second basic structure does not become too large, which facilitates manufacturing and suppresses light loss caused by manufacturing errors. This is preferable because it can reduce the diffraction efficiency fluctuation at the time of wavelength fluctuation.
  • the step of the second basic structure provided at least in the vicinity of the optical axis in the central region is directed in the direction of the optical axis.
  • the level difference faces the direction of the optical axis means a state as shown in FIG.
  • the second basic structure provided “at least in the vicinity of the optical axis of the central region” refers to a step at least closest to the optical axis among steps of the (2/1/1) structure.
  • the step may be directed in a direction opposite to the optical axis. That is, as shown in FIG. 5A, the step is directed in the direction of the optical axis when the second foundation structure is near the optical axis, but is switched halfway, and the step of the second foundation structure is located near the optical axis. It is good also as a shape which faces the reverse 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 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 (15) and (16). More preferably, the following conditional expressions (15) and (16) 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 perpendicular to the optical axis from the optical axis to the boundary between the central region and the intermediate region.
  • 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.
  • d11 and d12 of the first optical path difference providing structure are the following conditional expressions (19) and (20 ) Is preferably satisfied. More preferably, the following conditional expressions (19) and (20) are satisfied in all the regions of the central region. 0.6 ⁇ ( ⁇ 1 / (n-1)) ⁇ d11 ⁇ 1.5 ⁇ ( ⁇ 1 / (n-1)) (19) 0.6 ⁇ ( ⁇ 1 / (n-1)) ⁇ d12 ⁇ 1.5 ⁇ ( ⁇ 1 / (n-1)) (20)
  • conditional expressions (19) ′ and (20) ′ are preferably satisfied. More preferably, the following conditional expressions (19) ′ and (20) ′ are satisfied in all the regions of the central region. 0.9 ⁇ ( ⁇ 1 / (n-1)) ⁇ d11 ⁇ 1.5 ⁇ ( ⁇ 1 / (n-1)) (19) ' 0.9 ⁇ ( ⁇ 1 / (n-1)) ⁇ d12 ⁇ 1.5 ⁇ ( ⁇ 1 / (n-1)) (20) '
  • the spherical aberration when the wavelength of the incident light beam is changed to be longer, the spherical aberration is changed in the undercorrection direction (under), and (2 / In the second basic structure having the 1/1) structure, when the wavelength of the incident light beam is changed to be longer, it is preferable that the spherical aberration is changed in the undercorrection direction (under).
  • the refractive index of the objective lens when the refractive index of the objective lens changes due to an increase in the temperature of the optical pickup device, the refractive index of the objective lens is also utilized by utilizing the fact that the wavelength of the light source increases due to the increase in the environmental temperature.
  • the paraxial power of the first foundation structure is larger than that of the second foundation structure. That is, it is preferable that the average pitch of the first foundation structure is smaller than the average pitch of the second foundation structure.
  • 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.
  • the chromatic aberration is reduced, a good light spot is formed even when the light source has a high frequency superposition, and the problem of stray light when the optical disk has a plurality of information recording surfaces is reduced.
  • one ring zone closest to the optical axis of the second basic structure has two or more ring zones of the first basic structure. It is preferable that 6 (particularly preferably 2 to 3) are included.
  • 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. ) Is included.
  • 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 projecting portion is shifted in parallel along the optical axis, and eliminating the projecting portion has no significant effect, so that one annular zone of the second foundation structure can have a plurality of the first foundation structure.
  • the zonal is just like that (see the solid line). Therefore, in the example of FIG. 6 (d), it is assumed that three annular zones of the first foundation structure are on one annular zone of the second 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.
  • 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 N2 of the first foundation structure annular zones superimposed on one annular zone closest to the intermediate region in the second foundation structure is preferably equal to or smaller than N1, for example, 1 to 5 overlapping zones. It should be done.
  • 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 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 (22).
  • 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.
  • f13 [mm] indicates the focal length of the third light flux that passes through the first optical path difference providing structure and forms the first best focus
  • L [mm] indicates the first best focus and the second best focus. Refers to the distance between.
  • conditional expression (22) ′ is satisfied. 0.10 ⁇ L / f13 ⁇ 0.25 (22) ′
  • FIGS. 6 (a), 6 (b), and 6 (c) Some preferred examples of the first optical path difference providing structure described above are shown in FIGS. 6 (a), 6 (b), and 6 (c).
  • FIG. 6 shows the first optical path difference providing structure ODS1 as a flat plate for convenience, it may be 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.
  • the step of the second foundation structure BS2 faces the direction of the optical axis OA
  • the step of the first foundation structure BS1 also faces the direction of 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 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 focal length of the first light flux of the objective lens is f (mm)
  • the focal length of the first light flux of the objective lens is f (mm)
  • 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.
  • first optical path difference providing structure As described above, the preferable structure of the first optical path difference providing structure has been described focusing on the structure in which the blaze type (1/1/1) structure and the blaze type (2/1/1) structure are superimposed. Examples of other first optical path difference providing structures include the following.
  • a first optical path difference providing structure composed only of a blazed (2/1/1) structure or a (1/1/1) structure alone while utilizing the magnification difference of the objective lens.
  • the 1st optical path difference providing structure which becomes becomes.
  • Preferred examples of (B) include a first optical path difference providing structure consisting only of a (1/3/4) structure which is a 7-level staircase structure, and a 7-level staircase structure (1 / -2 / -3) a first optical path difference providing structure consisting only of a structure, a first optical path difference providing structure consisting only of a (1 / -1 / -2) structure which is a six-level stepped structure, and the like.
  • the blaze type (2/1/1) structure and a blaze-type (1/0/0) structure may be mentioned as a first optical path difference providing structure.
  • a first optical path difference providing structure in which a blaze type (2/1/1) structure and a (1/0/0) structure that is a four-level step structure are overlapped.
  • a first optical path difference providing structure in which a blaze type (2/1/1) structure and a (0/0/1) structure that is a two-level stepped structure are superimposed.
  • the second optical path difference providing structure is preferably a structure in which at least two basic structures of the third basic structure and the fourth basic structure are overlapped, but is not limited thereto.
  • both the third basic structure and the fourth basic structure are blazed structures.
  • the third basic structure makes the first-order diffracted light quantity of the first light flux that has passed through the third basic structure larger than any other order of diffracted light quantity, and the first-order diffracted light quantity of the second light flux that has passed through the third basic structure Is preferably larger than any other order of diffracted light.
  • the first-order diffracted light amount of the third light flux that has passed through the third basic structure is larger than any other order diffracted light amount.
  • the fourth foundation structure makes the second-order diffracted light amount of the first light beam that has passed through the fourth foundation structure larger than any other order of diffracted light amount, and the first-order of the second light beam that has passed through the fourth foundation structure. Is preferably larger than any other order of diffracted light. Further, the first-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.
  • the orders of the diffracted light having the highest light intensity in the first basic structure and the third basic structure are matched, and the orders of the diffracted light having the highest light intensity in the second basic structure and the fourth basic structure are matched. Therefore, the spherical aberration can be made continuous even when the temperature and the wavelength change for the light flux passing through the central region and the intermediate region, and as a result, the occurrence of higher order aberrations can be suppressed.
  • the second optical path difference providing structure may be a structure in which the fifth basic structure is overlapped in addition to the third and fourth basic structures. However, in order to simplify the structure and suppress a decrease in light utilization efficiency due to manufacturing errors.
  • the second optical path difference providing structure preferably includes only the third basic structure and the fourth basic structure.
  • the fifth basic structure makes the 0th-order diffracted light quantity of the first light flux that has passed through the fifth basic structure larger than any other order diffracted light quantity, and the second light flux that has passed through the fifth basic structure.
  • the 0th-order diffracted light amount is made larger than any other order diffracted light amount
  • the G-th order diffracted light amount of the third light flux that has passed through the fifth basic structure is made larger than any other order diffracted light amount. It is preferable.
  • G is ⁇ 1.
  • the fifth basic structure is preferably a two-level step structure (also referred to as a binary structure) as shown in FIG.
  • the third-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 second-order diffracted light amount of the second light beam that has passed through the third basic structure is changed to other values.
  • the diffraction light quantity of any order is made larger (also referred to as (3/2) structure)
  • the second-order diffraction light quantity of the first light beam that has passed through the fourth basic structure is made larger than any other order of diffraction light quantity
  • the first-order diffracted light amount of the second light beam that has passed through the four basic structures may be made larger than any other order diffracted light amount (also referred to as a (2/1) structure). With such a configuration, the diffraction efficiency in BD can be further increased.
  • the 3rd foundation structure and the 4th foundation structure are the combination of the (1/1) structure and the (2/1) structure, it is the combination of the (3/2) structure and the (2/1) structure.
  • the third basic structure provided at least in the middle region at the position closest to the central region has the step in the direction opposite to the optical axis, and at least in the middle region at the position closest to the central region.
  • step difference has faced the direction of an optical axis. More preferably, the steps of all the third foundation structures in the intermediate region are directed in the direction opposite to the optical axis, and the steps of all the fourth foundation structures in the intermediate region are directed in the direction of the optical axis. is there.
  • the spherical aberration changes in an undercorrected (under) direction
  • the wavelength of the incident light beam becomes longer. If it changes, the spherical aberration may change in the direction of under-correction (under).
  • 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 -10 m ⁇ rms or more and +10 m ⁇ rms or less. More preferably.
  • 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 two-optical path difference providing structure is composed of only the third and fourth basic structures, flare can be easily produced when using the CD. Accordingly, 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. As a result, the light use efficiency 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 third optical path difference providing structure preferably has a sixth basic structure.
  • the P-order diffracted light amount of the first light beam that has passed through the sixth 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 sixth basic structure.
  • the light quantity is made larger than any other order of diffracted light quantity, and the R-order diffracted light quantity of the third light flux that has passed through the sixth basic structure is made larger than any other order of diffracted light quantity.
  • P is preferably 5 or less in order to suppress fluctuations in diffraction efficiency during wavelength fluctuations.
  • FIG. 7 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.
  • FIG. 7 is a schematic diagram to the last, and is not a drawing showing an accurate length ratio or the like based on the embodiment.
  • a first optical path difference providing structure ODS1 is provided in the central area
  • a second optical path difference providing structure ODS2 is provided in the middle area
  • a third optical path difference providing structure is provided in the peripheral area.
  • the first optical path difference providing structure ODS1 in FIG. 7 has a (2/1/1) blaze structure and a second basic structure BS2 in which a step is directed toward the optical axis, and (1/1/1).
  • 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 four 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.
  • two 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. 7 is a (2/1/1) blazed structure in which a step is directed toward the optical axis and a fourth basic structure BS4 of (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.
  • the fourth foundation structure BS4 has three annular zones, and three annular zones of the third foundation structure BS3 are included on the annular zone closest to the central region in the fourth foundation structure BS4. Further, one ring zone of the third foundation structure BS3 is included in one ring zone closest to the peripheral region in the fourth foundation structure BS4.
  • the third optical path difference providing structure ODS3 in FIG. 7 is composed of only a sixth basic structure BS6 having a blaze structure of (2/1/1) and having a step facing the optical axis.
  • NA1 is preferably 0.75 or more and 0.9 or less, and more 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 objective lens preferably satisfies the following conditional expression (23). 0.8 ⁇ d / f ⁇ 1.5 (23)
  • d represents the thickness (mm) on the optical axis of the objective lens
  • f represents the focal length (mm) of the objective lens in the first light flux.
  • the objective lens is likely to generate astigmatism and is likely to generate decentration coma, but satisfies the conditional expression (18). As a result, it is possible to suppress the occurrence of astigmatism and decentration coma.
  • the objective lens since the objective lens has a thick on-axis thickness, the working distance at the time of CD recording / playback tends to be short, so the upper limit of conditional expression (23) may not be exceeded. preferable.
  • the coma aberration of the objective lens when the BD is used is 0.07 ⁇ rms (marechal limit value) or less with respect to an incident light beam having an angle of view of 0.3 degrees. Moreover, the following formula is satisfied.
  • the first light beam and the third light beam are incident on the objective lens as parallel light or substantially parallel light.
  • the second 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 in the first light beam incident on the objective lens as parallel light or substantially parallel light satisfies the following expression (1). -0.01 ⁇ m1 ⁇ 0.01 (1)
  • the imaging magnification m2 of the objective lens when the second light beam is incident on the objective lens satisfies the following expression (7). Is preferred. -0.01 ⁇ m2 ⁇ 0.01 (7)
  • the imaging magnification m2 of the objective lens when the second light beam is incident on the objective lens satisfy the following formula (5).
  • m2 It is more preferable to satisfy the following (5) ′ from the imaging magnification when the light beam having the second wavelength ⁇ 2 is incident on the objective lens. ⁇ 0.025 ⁇ m2 ⁇ ⁇ 0.01 (5) ′
  • the imaging magnification m3 of the objective lens in the third light beam incident on the objective lens as a parallel light beam or a substantially parallel light beam satisfies the following formula (2). -0.01 ⁇ m3 ⁇ 0.01 (2)
  • the working distance (WD) 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, it is 0.2 mm or more and 0.5 mm or less.
  • the WD 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 WD of the objective optical element when using the first optical disk is preferably 0.25 mm or more and 1.0 mm or less.
  • the coupling lens may have an actuator through which at least the first light beam and the second light beam pass and move 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. It is conceivable to correct the generated spherical aberration by moving the coupling lens in the optical axis direction and changing the magnification of the objective lens. Further, 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 reason is that flare does not occur when using BD, but flare occurs when using DVD.
  • 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 displacement of the coupling lens in the drive.
  • 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 So that the spherical aberration changes in the direction of insufficient correction, and on the other side, the spherical aberration changes in the direction of overcorrection when the wavelength of the incident light beam changes longer.
  • both the temperature characteristic and the wavelength characteristic when using the DVD can be improved, and as a result, when using the DVD, the position of the coupling lens in the optical axis direction is fixed when the second light beam passes.
  • 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 optical information recording / reproducing apparatus including an objective lens that can be performed in the above-described manner, and an objective lens suitable for the optical pickup apparatus.
  • 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.
  • It is a conceptual diagram of a 1st optical path difference providing structure, (a) thru
  • FIG. 8 is a diagram schematically showing a configuration of the optical pickup device 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 that can be mounted on an optical information recording / reproducing device. Some slim types have a raised mirror between the collimating lens and the objective lens and bend the optical path at a right angle.
  • 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 central region CN of the objective lens OL is a structure in which the first basic structure and the second basic structure are overlapped as shown in FIG.
  • the first-order diffracted light amount of the first light beam that has passed through the first basic structure is made larger than any other order of diffracted light amount, and the first-order diffracted light amount of the second light beam that has passed through the first basic structure is set to any other order.
  • the first order diffracted light amount of the third light flux that has passed through the first basic structure is made larger than any other order diffracted light amount, and is provided at least near the optical axis of the central region CN.
  • the step is directed in the direction opposite to the optical axis, and in the second basic structure, the second-order diffracted light quantity of the first light beam that has passed through the second basic structure is greater than the diffracted light quantity of any other order. And the primary of the second light flux that has passed through the second basic structure.
  • the amount of diffracted light is made larger than the amount of diffracted light of any other order
  • the amount of first order diffracted light of the third light beam that has passed through the second basic structure is made larger than the amount of diffracted light of any other order
  • the objective when using BD The coma aberration of the lens is 0.07 ⁇ rms or less with respect to an incident light beam having an angle of view of 0.3 degrees, and satisfies the following expression.
  • fB1 WD1 + t1 ⁇ (1-1 / n1)
  • fB3 WD3 + t3 ⁇ (1-1 / n3)
  • ⁇ Abbe number m1 of the material of the objective lens
  • m1 Imaging magnification when the light beam having the first wavelength ⁇ 1 is incident on the objective lens
  • m3 Imaging magnification when the light beam having the third wavelength ⁇ 3 is incident on the objective lens
  • d Objective Lens axial thickness (mm)
  • WD1 Working distance when using BD (mm)
  • WD3 Working distance when using CD (mm)
  • n1 Refractive index of the BD protective substrate for the light beam having the first wavelength ⁇ 1
  • n3 Refractive index of the CD protective substrate for the light beam having the third wavelength ⁇ 3
  • 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.
  • 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.
  • the 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. Correction can be made by changing the divergence angle or convergence angle of the light beam incident on the objective optical element OL by changing the collimating lens COL as means in the optical axis direction.
  • 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 portion) is recorded on the DVD through the protective substrate PL2. It becomes a spot formed on the surface RL2, and forms the center of the spot.
  • the reflected light flux modulated by the information pits on the information recording surface RL2 is again transmitted through the objective lens OL, converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wave plate QWP, and converted into a parallel light flux by the collimator 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 linearly polarized light is converted into circularly polarized light by the ⁇ / 4 wave plate QWP, and is incident on the objective lens OL.
  • the light beam collected 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 and forms a spot peripheral part) is recorded on the CD through the protective substrate PL3. It becomes a spot formed on the surface RL3.
  • the reflected light beam modulated by the information pits on the information recording surface RL3 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 parallel light beam by the collimator 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 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. .
  • ⁇ 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 i ⁇ h 2i-1 )).
  • Example 1 The objective lens of Example 1 is a plastic single lens. Table 1 shows lens data.
  • a conceptual diagram of the first optical path difference providing structure of the first embodiment is shown in FIG. 6A (FIG. 6A is a conceptual diagram different from the actual shape of the first embodiment).
  • the (1/1/1) blaze is added to the second basic structure BS2 that is a (2/1/1) blaze-type diffraction structure in the entire central region.
  • the first basic structure BS1 which is a diffractive structure of the mold, is an optical path difference providing structure that is overlapped.
  • 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.
  • FIG. 9A is a diagram showing longitudinal spherical aberration SA and sine condition unsatisfied amount SC when BD is used in the objective lens of Example 1
  • FIG. 9B is a diagram showing CD use in the objective lens of Example 1.
  • FIG. 6 is a diagram showing longitudinal spherical aberration SA and sine condition unsatisfactory amount SC, with the vertical axis indicating 1 as the height from the optical axis corresponding to each effective diameter of BD / CD.
  • the sine condition violation amount in the CD is kept small despite the fact that the sine condition is almost satisfied in the BD.
  • Example 2 The objective lens of Example 2 is a plastic single lens. Table 2 shows lens data.
  • the (1/0/0) blaze-type diffraction is added to the basic structure which is the (2/1/1) blaze-type diffraction structure in the entire central region. This is an optical path difference providing structure in which another basic structure is overlapped.
  • a (1/0/0) structure that is a four-level step-type structure may be used.
  • FIG. 10A is a diagram showing longitudinal spherical aberration SA and sine condition dissatisfaction amount SC when BD is used in the objective lens of Example 2
  • FIG. 10B is a diagram showing CD in the objective lens of Example 2. It is a figure which shows the longitudinal spherical aberration SA at the time of use, and sine condition unsatisfactory amount SC, but the height from the optical axis corresponding to each effective diameter of each BD / CD is shown as 1 on the vertical axis. As is apparent from FIG. 10, the sine condition violation amount in the CD is kept small despite the fact that the sine condition is almost satisfied in the BD.
  • Example 3 The objective lens of Example 3 is a plastic single lens.
  • Table 3 shows lens data.
  • the first optical path difference providing structure of Example 3 is a two-level stepped structure (0/0) in the entire structure of the central region, with a basic structure that is a (2/1/1) blazed diffraction structure (0/0). / 1) An optical path difference providing structure in which another basic structure called a structure is overlapped.
  • FIG. 11A is a diagram showing longitudinal spherical aberration SA and sine condition dissatisfaction amount SC when BD is used in the objective lens of Example 3
  • FIG. 11B is a diagram of CD in the objective lens of Example 3. It is a figure which shows the longitudinal spherical aberration SA at the time of use, and sine condition unsatisfactory amount SC, but the height from the optical axis corresponding to each effective diameter of each BD / CD is shown as 1 on the vertical axis. As apparent from FIG. 11, the sine condition violation amount in the CD is kept small even though the sine condition is almost satisfied in the BD.
  • Example 4 The objective lens of Example 4 is a plastic single lens. Table 4 shows the lens data.
  • the first optical path difference providing structure of Example 4 is the same structure as the first optical path difference providing structure of Example 3.
  • the on-axis thickness d 1.69 mm
  • (fB3-fB1) /d 0.089
  • (fB2-fB1 ) /D ⁇ 0.06 mm
  • effective diameter ⁇ 1 2.72 mm.
  • FIG. 12A is a diagram showing longitudinal spherical aberration SA and sine condition dissatisfaction amount SC when BD is used in the objective lens of Example 4, and FIG. 12B is a diagram showing CD in the objective lens of Example 4. It is a figure which shows the longitudinal spherical aberration SA at the time of use, and sine condition unsatisfactory amount SC, but the height from the optical axis corresponding to each effective diameter of each BD / CD is shown as 1 on the vertical axis. As is apparent from FIG. 12, the sine condition violation amount in the CD is kept small despite the fact that the sine condition is almost satisfied in the BD.
  • Example 5 The objective lens of Example 5 is a plastic single lens. Table 5 shows lens data.
  • the first optical path difference providing structure of Example 5 is an optical path difference providing structure including only a (1/3/4) structure that is a seven-level step structure in the entire central region. Further, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS1 faces the direction opposite to the optical axis OA.
  • FIG. 13A is a diagram showing longitudinal spherical aberration SA and sine condition dissatisfaction amount SC when BD is used in the objective lens of Example 5
  • FIG. 13B is a diagram showing CD in the objective lens of Example 5. It is a figure which shows the longitudinal spherical aberration SA at the time of use, and sine condition unsatisfactory amount SC, but the height from the optical axis corresponding to each effective diameter of each BD / CD is shown as 1 on the vertical axis. As is apparent from FIG. 13, the sine condition violation amount in the CD is kept small despite the fact that the sine condition is almost satisfied in the BD.
  • Table 6 summarizes the numerical values of the formulas stipulated in the claims corresponding to the respective examples.
  • the BD wavefront aberration at the field angle of 0.3 ° is 0.025 ⁇ rms at the maximum in all the examples, the BD wavefront aberration at the field angle of 0.3 ° is 0.07 ⁇ rms or less. It can also be seen that the wavefront aberration in a DVD at an angle of view of 0.3 ° is 0.025 ⁇ rms at the maximum and is kept low. Furthermore, it can be seen that the wavefront aberration in CD at an angle of view of 0.3 ° is 0.036 ⁇ rms at the maximum, and is suppressed to a low level. That is, it can be seen that DVD and CD have good off-axis characteristics.
  • the distance in the optical axis direction between the spot position of the necessary light required for recording and reproduction and the position of the spot of the diffracted light with the largest amount of unnecessary light not used for recording and reproduction is plural layers. This is larger than the distance between adjacent layers of a BD having, and unnecessary light does not adversely affect recording and reproduction.

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Abstract

L'invention concerne un dispositif de capture optique doté d'une lentille de focalisation, un lecteur/enregistreur d'informations optique, et une lentille de focalisation optimale pour une utilisation dans les dispositifs de capture optiques et les lecteurs/enregistreurs d'informations optiques. Malgré une distance focale assez courte, ce dispositif, ce lecteur/enregistreur et cette lentille permettent d'obtenir la distance de travail d'un CD, ils ne sont pas affectés par la lumière diffractée inutile susceptible de créer des signaux d'erreur, et en plus de présenter de bonnes caractéristiques hors de l'axe du faisceau principal, ils sont compatibles avec trois types de disques optiques, les Blu-Rays, les DVD et les CD, la lentille de focalisation restant la même. Si la valeur de la formule (5) est supérieure ou égale à la limite la plus basse, la lumière inutile d'une structure 1/1/1 peut être écartée, il ne se produit plus de détections erronées en provenance d'un détecteur optique sur le chemin principal de la lumière, et une distance de travail suffisante qui convient aux CD est assurée. En outre, si la valeur de la formule (5) est inférieure ou égale à la limite la plus haute, la différence entre les conditions des sinus au cours de l'utilisation d'un Blu-Ray et au cours de l'utilisation d'un CD diminue, et les caractéristiques hors de l'axe du faisceau principal lors de l'utilisation d'un CD s'améliorent. De plus, dans les combinaisons de structures 1/1/1 et 2/1/1, le respect des expressions conditionnelles suivantes limite l'aberration chromatique axiale des Blu-Rays. 0,04 ≤ (fB3 - fB1) / d ≤ 0,12 (5), étant entendu que fB1 = WD1 + t1 × (1 - 1 / n1), que fB3 = WD3 + t3 × (1 - 1 / n3), et que d est l'épaisseur sur l'axe de la lentille de focalisation (mm).
PCT/JP2012/057851 2011-03-30 2012-03-27 Lentille de focalisation pour dispositif de capture optique, dispositif de capture optique et lecteur/enregistreur d'informations optique WO2012133363A1 (fr)

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JP2013507580A JPWO2012133363A1 (ja) 2011-03-30 2012-03-27 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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JP2011-074510 2011-03-30
JP2011074510 2011-03-30

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2007328887A (ja) * 2006-06-09 2007-12-20 Konica Minolta Opto Inc 光ピックアップ装置及び光情報記録媒体記録再生装置
JP2009211775A (ja) * 2008-03-05 2009-09-17 Hitachi Maxell Ltd 対物レンズ

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2007328887A (ja) * 2006-06-09 2007-12-20 Konica Minolta Opto Inc 光ピックアップ装置及び光情報記録媒体記録再生装置
JP2009211775A (ja) * 2008-03-05 2009-09-17 Hitachi Maxell Ltd 対物レンズ

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