WO2005117002A1 - Système optique à objectif, dispositif de prélèvement optique et dispositif de lecteur de disque optique - Google Patents

Système optique à objectif, dispositif de prélèvement optique et dispositif de lecteur de disque optique Download PDF

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Publication number
WO2005117002A1
WO2005117002A1 PCT/JP2005/008983 JP2005008983W WO2005117002A1 WO 2005117002 A1 WO2005117002 A1 WO 2005117002A1 JP 2005008983 W JP2005008983 W JP 2005008983W WO 2005117002 A1 WO2005117002 A1 WO 2005117002A1
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WO
WIPO (PCT)
Prior art keywords
phase structure
optical system
wavelength
aberration correction
light beam
Prior art date
Application number
PCT/JP2005/008983
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English (en)
Japanese (ja)
Inventor
Tohru Kimura
Yuichi Atarashi
Original Assignee
Konica Minolta Opto, Inc.
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Application filed by Konica Minolta Opto, Inc. filed Critical Konica Minolta Opto, Inc.
Priority to JP2006513850A priority Critical patent/JP4483864B2/ja
Publication of WO2005117002A1 publication Critical patent/WO2005117002A1/fr

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Classifications

    • 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
    • G11B7/1365—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
    • G11B7/1392—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 objective optical system, an optical pickup device, and an optical disk drive device.
  • Patent Document 1 JP 2004-079146 A
  • Patent Document 2 Japanese Patent Application Laid-Open No. 2002-298422
  • Patent Document 3 JP 2003-207714 A
  • Patent Literature 1 discloses a numerical example 7 in which a blue-violet laser beam generates second-order diffracted light and a red laser beam and an infrared laser beam generate first-order diffracted light on the surface of an objective lens.
  • the structure of this diffraction structure is used to correct the spherical aberration caused by the difference in the thickness of the protective layer between the high-density optical disk and the DVD.
  • the divergent light beam is applied to the objective lens during Z playback.
  • an objective lens that corrects spherical aberration caused by a difference in protective layer thickness between a high-density optical disc and a CD by being incident.
  • the spherical aberration caused by the difference in the protective layer thickness between the high-density optical disk and the DVD and the spherical aberration due to the difference in the protective layer thickness between the high-density optical disk and the CD are corrected by the action of the diffraction structure.
  • the diffraction efficiency of the third-order diffracted light of the blue-violet laser light beam and the diffraction efficiency of the second-order diffracted light of the infrared laser light beam are as low as about 70%, so that the recording / reproducing speed for optical discs can be increased. It is not possible to obtain good recording / reproducing characteristics due to the low S / N ratio of the detection signal from the photodetector, or to shorten the life of the laser light source due to the high voltage applied to the laser light source. There is a problem.
  • the objective lens of Numerical Example 7 of Patent Document 1 which corresponds to a case where both the diffraction efficiency of the diffracted light of the blue-violet laser beam and the diffraction efficiency of the diffracted light of the infrared laser beam are ensured, Since the diffraction angle of the diffracted light of the blue-violet laser beam and the diffraction angle of the diffracted light of the infrared laser beam almost coincide, the diffraction structure corrects the spherical aberration due to the difference in the thickness of the protective layer between the high-density optical disc and the CD. You can't.
  • the present invention has been made in view of the above-mentioned problems, and has a spherical aberration due to a difference in protective layer thickness between a high-density optical disc, a DVD, and a CD due to the action of a phase structure including a diffractive structure.
  • Is capable of satisfactorily correcting spherical aberration due to the difference in wavelength used between high-density optical discs, DVDs, and CDs, as well as a blue-violet wavelength region near 400 nm, a red wavelength region near 650 nm, and a blue wavelength region near 780 nm.
  • An objective optical system capable of obtaining high light use efficiency in any wavelength region including the infrared wavelength region, an optical pickup device using the objective optical system, and an optical disk drive device equipped with the optical pickup device The purpose is to provide.
  • the configuration according to item 1 is characterized in that the thickness t is determined by using the first wavelength emitted from the first light source;
  • An objective optical system used in an optical pickup device that records and / or reproduces information on an optical disc wherein the objective optical system includes a first aberration correction element, a second aberration correction element, (1) An objective lens for converging the first to third light beams passing through the aberration correction element and the second aberration correction element on the information recording surfaces of the first to third optical disks, respectively.
  • the first aberration correction element has a first phase structure made of a material having an Abbe number V1 at d-line that satisfies the following equation (1).
  • the second aberration correction element is made of a material whose Abbe number V 2 at d-line satisfies the following equation (2):
  • a second phase structure formed from the material.
  • the first phase structure and the second phase structure are made of a material having an Abbe number that satisfies the equations (1) and (2), the blue-violet laser light flux and the red laser light flux, which are difficult with the related art, are obtained. While maintaining high transmittance for any wavelength of the infrared laser beam, Mutual compatibility between high-density optical discs and DVDs and CDs can be realized.
  • the transmittance of the first phase structure for the third wavelength ⁇ 3 increases, but the transmittance of the first phase structure for the second wavelength ⁇ 2 increases.
  • the transmittance of the phase structure is reduced.
  • a material whose Abbe number is larger than the upper limit of the equation (1) is not realistic because the production becomes difficult.
  • the transmittance of the second phase structure for the second wavelength ⁇ 2 increases, but the transmittance of the second phase structure for the third wavelength ⁇ 3 increases. This is preferable because the transmittance of the two-phase structure is reduced.
  • the Abbe number is smaller than the lower limit of the equation (2), it is not practical because the material is difficult to manufacture.
  • a 0.85 mm objective lens and a protective layer thickness of 0.1 mm are used for a Blu-ray disc or NA 0.65 to 0.67 objective lens.
  • Optical disks that use a blue-violet laser light source such as HD DVDs with a diameter of 0.6 mm, are collectively called “high-density optical disks” and abbreviated as “HD”.
  • high-density optical disks such as HD DVDs with a diameter of 0.6 mm
  • a magneto-optical disc, an optical disc having a protective film with a thickness of several to several tens nm on the information recording surface, or an optical disc having a protective layer or a protective film of zero thickness Is included in the high-density optical disk are included in the high-density optical disk.
  • a DVD digital versatile disc
  • DVD-RM digital versatile disc
  • DVD-Video DVD-Audio
  • DVD-RAM DVD-R
  • DVD_RW DVD_RW
  • DV D + R DVD +
  • CD compact disc
  • the “objective lens” is a lens disposed at a position facing the optical disk in the optical pickup device, and emits the light flux emitted from the light source to the optical disk.
  • a condenser lens that has the function of collecting light on the information recording surface.
  • the “objective optical system” refers to the above-described condensing lens, a first aberration correction element that performs tracking and focusing by an actuator integrated with the converging lens, and a second condensing lens. Refers to an optical system composed of an aberration correction element.
  • phase structure has a plurality of steps in the optical axis direction
  • This is a general term for a structure that adds an optical path difference (phase difference) to a bundle.
  • the optical path difference added to the incident light beam by this step may be an integral multiple of the wavelength of the incident light beam or a non-integer multiple of the wavelength of the incident light beam.
  • Specific examples of such a phase structure include a diffractive structure in which the steps are arranged at periodic intervals in the direction perpendicular to the optical axis, and a diffraction structure in which the steps are arranged at non-periodic intervals in the direction perpendicular to the optical axis.
  • An optical path difference providing structure (also referred to as a phase difference providing structure) is arranged.
  • the phase structure can have various cross-sectional shapes as schematically shown in FIGS. 7 (a) to 12 (b).
  • FIGS. 7 (a) and 7 (b) show the case where the shape is a sawtooth shape
  • FIGS. 8 (a) and 8 (b) show the case where the steps are all in the same direction
  • FIG. Figures a) and 9 (b) show the case where the direction of the step is stepwise, with the direction of the step being reversed in the middle.
  • FIGS. 10 (a) and 10 (b) show a step-shaped pattern 11 including a plurality of level surfaces 12 arranged concentrically, and a predetermined number of level surfaces (FIGS. 10 (a) and 10 (b)). In each case, the steps are shifted by the height corresponding to the number of levels (four steps in FIGS. 10 (a) and 10 (b)) every 5 levels in (b).
  • Figs. 7 (a) and 7 (b) show the case where the direction of each saw tooth is the same, and Figs. 10 (a) and 10 (b) show that the direction of each pattern having a stepped cross section is Although the same case is shown, as shown in FIGS. 11 (a) and 11 (b) and FIGS. 12 (a) and 12 (b), the phase inversion portion PR and the closer to the optical axis than the phase inversion portion PR There may be a sawtooth whose direction is opposite to the sawtooth on the side or a pattern whose direction is opposite to the pattern closer to the optical axis than the phase inversion portion PR.
  • FIGS. 11 (a) and 11 (b) and FIGS. 12 (a) and 12 (b) show the phase inversion portion PR and the closer to the optical axis than the phase inversion portion PR.
  • each structure is formed on a plane, but each structure may be formed on a spherical surface or an aspherical surface.
  • the force having a predetermined number of level faces is not limited to five.
  • FIG. 1 is a plan view of a principal part showing a configuration of an optical pickup device.
  • FIG. 2 is a side view showing an example of the configuration of the objective lens unit.
  • FIG. 3 is a side view showing an example of the configuration of the objective lens unit.
  • FIG. 4 is a side view showing an example of the configuration of the objective lens unit.
  • FIG. 5 is a side view showing an example of the configuration of the objective lens unit.
  • FIG. 6 is a side view showing an example of the configuration of the objective lens unit.
  • FIG. 7 is cross-sectional views (a) and (b) showing an example of a configuration of a phase structure.
  • FIG. 8 is cross-sectional views (a) and (b) showing an example of the configuration of a phase structure.
  • FIG. 9 is cross-sectional views (a) and (b) showing an example of a configuration of a phase structure.
  • FIG. 10 is cross-sectional views (a) and (b) showing an example of the configuration of a phase structure.
  • FIG. 11 is cross-sectional views (a) and (b) showing an example of the configuration of a phase structure.
  • FIG. 12 is cross-sectional views (a) and (b) showing an example of the configuration of a phase structure.
  • FIG. 13 is a side view showing an example of the configuration of the objective lens unit.
  • Item 2 is the objective optical system according to Item 1, wherein the first phase structure of the first aberration correction element has a refractive index n 1 at d-line represented by the following expression (3): Filling resin d
  • the second phase structure included in the second aberration correction element is formed of a resin whose refractive index n 2 at d-line satisfies the following expression (4).
  • a resin for an optical element has a refractive index n of 1.48 to d at d-line (587.6 nm).
  • both the first phase structure and the second phase structure are made of resin as in the configuration described in Item 2, the first phase structure and the second phase structure are made of a material having n that satisfies the equations (3) and (4). d
  • the configuration according to Item 3 is the objective optical system according to Item 1 or 2, wherein the first phase structure is a spherical aberration caused by a difference between the first and the second wavelengths or the first wavelength ⁇ and the first wavelength ⁇ . 2 wavelength
  • the first phase structure formed of the material satisfying the formula (1) or (3) formed in the first aberration correction element makes the high-density optical disc and DVD compatible with each other. In this way, while maintaining high transmittance for both the blue-violet laser beam and the red laser beam, the spherical aberration due to the difference between t and t, or the first wavelength ⁇ and the second wavelength ⁇ In the difference
  • the first phase structure may be a diffraction structure or an optical path difference providing structure.
  • the configuration described in Item 4 is the objective optical system according to Item 3, wherein the first phase structure does not diffract the first light beam and the third light beam but diffracts the second light beam.
  • the first phase structure is a diffractive structure that selectively diffracts only the second light beam as described in item 4, it is possible to independently control the aberration with respect to the second light beam, and to achieve high density. Good light-collecting characteristics are obtained for both optical disks and DVDs.
  • Item 5 is the objective optical system according to Item 4, wherein the first phase structure is a structure in which a pattern having a stepped cross section including an optical axis is arranged on a concentric circle. Therefore, for each predetermined number A of level surfaces, the level is shifted by a height corresponding to the number of levels corresponding to the number of level surfaces.
  • the optical path difference added by each step constituting each pattern slightly deviates from an integral multiple of the wavelength.
  • the wavefront having the local spherical aberration is interrupted at the position where the steps are shifted by the height corresponding to the number of power level planes at which local spherical aberration occurs, causing local spherical aberration.
  • the macroscopic wavefront becomes flat.
  • a diffraction structure having a property of selectively diffracting one of the first to third light beams is hereinafter referred to as a "wavelength selective diffraction structure”.
  • the number A of the predetermined level surfaces is any one of 4, 5, and 6, and The resulting optical path difference is twice the first wavelength I.
  • the required level Preferably, the number A is 5.
  • the principle of generation of diffracted light will be described for a wavelength-selective diffraction structure (first phase structure) that selectively diffracts the second light beam without diffracting the first light beam and the third light beam.
  • the first wavelength ⁇ is 405 nm, which is the recording / reproducing wavelength of the high-density optical disc HD
  • the second wavelength I is 655 nm, which is the recording / reproducing wavelength of the DVD
  • the third wavelength ⁇ is the recording / reproducing of the CD.
  • ⁇ (Ml) ⁇ ( ⁇ 1)-( ⁇ 1) (11)
  • ⁇ 1 depth in the optical axis direction of each step constituting each pattern of the first phase structure ⁇ : refractive index of the material forming the first phase structure with respect to the first wavelength;
  • ⁇ refractive index of the material forming the first phase structure for the second wavelength ⁇ 2
  • ⁇ third wavelength; refractive index of the material forming the first phase structure for 13
  • A Number of level surfaces formed in each pattern of the first phase structure
  • Ll, Ml, and N1 are optical path differences in wavelength units added to the first light flux, the second light flux, and the third light flux by each step formed in each pattern of the first phase structure.
  • L1 is 2
  • the optical path difference L1 added to the first light beam due to the step ⁇ 1 is twice the first wavelength; I, so that the first The wavefront of the light beam is exactly
  • connection is shifted by two wavelengths. Therefore, the first light beam is transmitted as it is at a transmittance of 100% without being subjected to diffraction by the first phase structure. Further, when the first phase structure is formed from a material whose Abbe number V 1 at the d-line satisfies the above equation (1), the step ⁇ The optical path difference Nl added to the third luminous flux by 1 is very close to one time of the third wavelength; I.
  • the wavefronts of the third luminous flux passing through the level surfaces that are in tangent to each other are connected by being shifted by one wavelength. Therefore, the third light beam is also transmitted as it is with almost 100% transmittance which is not affected by the diffraction effect by the first phase structure.
  • the optical path difference Ml applied to the second luminous flux by the step ⁇ 1 is about 1.2 times the second wavelength; I, so that the adjacent level surfaces
  • the wavefront of the passing second light beam is shifted by 1.2 wavelengths, but the actual wavefront shift is 0.2 wavelength excluding the shift of one wavefront that is optically in phase.
  • the above equation (12) is a conditional equation for increasing the diffraction efficiency of the first-order diffracted light of the second light flux, and the number of level surfaces A formed in each pattern is set so as to satisfy the equation (12). By determining the value, it is possible to sufficiently secure the diffraction efficiency of the first-order diffracted light of the second light flux.
  • the Abbe number V1 at the d-line is the above-mentioned (1)
  • the diffraction efficiency of the diffracted light of the second light beam depends only on the Abbe number V 1 at the d-line of the material from which the wavelength-selective diffraction structure is formed.
  • the refractive index n 1 has a relatively high degree of freedom.
  • the configuration according to Item 7 is the objective optical system according to Item 3, wherein the first phase structure generates first-order diffracted light when the first light beam enters, and When two light beams are incident, a / 3 1 (1 ⁇ 1) order diffracted light is generated.When the third light beam is incident, a ⁇ 1 ( ⁇ 1 ⁇ ⁇ 1) order diffracted light is generated. Diffraction structure.
  • the first phase structure has the diffraction characteristics described in Item 7 Let me good.
  • the diffraction structure having such diffraction characteristics has a saw-tooth shape or a step-like shape in cross section including the optical axis.
  • the cross-sectional shape including the optical axis has a sawtooth shape, the absolute value of the refractive power of the optical surface on which the first phase structure is formed and the absolute value of the diffraction power of the first phase structure are different from each other.
  • the case where the cross-sectional shape includes a step-like shape is a case where the signs of the refractive power of the optical surface on which the first phase structure is formed and the diffraction power of the first phase structure are opposite to each other and the absolute values are the same.
  • the diffraction order ct 1 of the first light beam be an even number.
  • the production wavelength ⁇ of the first phase structure should be longer than 1.
  • the configuration according to Item 9 is the objective optical system according to any one of Items 1 to 8, wherein the second phase structure includes a spherical aberration caused by a difference between t and t, or Wavelength; I and
  • the compatibility between the high-density optical disc and the CD is achieved by the second phase structure formed of the material satisfying the formula (2) or (4) formed on the second aberration correction element.
  • the second phase structure may be a diffraction structure or an optical path difference providing structure.
  • the configuration according to Item 10 is the objective optical system according to Item 9, wherein the second phase structure includes The diffraction structure diffracts the third light beam without diffracting the first light beam and the second light beam.
  • the second phase structure is a diffraction structure that selectively diffracts only the third light beam as described in item 10, it is possible to independently control the aberration of the third light beam, Good light-gathering characteristics are obtained for both high-density optical discs and CDs.
  • the second phase structure is a structure in which a pattern having a stepped cross section including an optical axis is arranged on a concentric circle.
  • the level is shifted by a height corresponding to the number of levels corresponding to the number of level surfaces.
  • the oscillation wavelength of the first light source can be changed in the same manner as the configuration described in Item 5. Tolerances for individual differences can be reduced.
  • the number B of the predetermined level surfaces is any one of 3 and 4, and an optical path difference caused by one step of the stairs is provided. Is seven times the first wavelength.
  • the second phase structure With the diffraction characteristics as described in item 10, and to provide three light beams High transmittance can be secured.
  • the second phase structure In order to ensure the highest transmittance for the three light beams, the second phase structure must be formed from a material whose Abbe number V 2 at d-line satisfies 25 ⁇ v 2 ⁇ 40.
  • the number B of the predetermined level surfaces is 3, and the second phase structure is the Abbe number V 2 at the d-line.
  • the number B of the specified level surface shall be 4 and d
  • the principle of diffracted light generation will be described for a wavelength-selective diffraction structure (second phase structure) that selectively diffracts the third light beam without diffracting the first light beam and the second light beam.
  • the first wavelength ⁇ is 405 nm, which is the recording / reproducing wavelength of the high-density optical disc HD
  • the second wavelength is 655 nm, which is the recording / reproducing wavelength of the DVD
  • the third wavelength ⁇ is the CD recording / reproducing.
  • the raw wavelength is 785 nm.
  • the first phase structure needs to satisfy the following equations (15) to (21).
  • ⁇ 2 ⁇ 2 ( ⁇ '- ⁇ ) / ⁇ (16)
  • ⁇ 2 ⁇ 2 ( ⁇ -1) / ⁇ (17)
  • ⁇ 2 Depth in the optical axis direction of each step constituting each pattern of the second phase structure ⁇ : Refractive index of the material on which the second phase structure is formed with respect to the first wavelength 1
  • ⁇ refractive index of the material on which the second phase structure is formed for the third wavelength 3
  • L2, M2, and N2 are optical path differences in wavelength units added to the first light flux, the second light flux, and the third light flux by each step formed in each pattern of the second phase structure. If L2 is set to 7, the optical path difference L2 added to the first light beam due to the step ⁇ 2 is seven times the first wavelength I, so that the first light beam passing through adjacent level surfaces The wavefront is exactly 7
  • the connection is shifted by the wavelength. Therefore, the first light beam is transmitted as it is at a transmittance of 100% without being subjected to diffraction by the first phase structure.
  • the second phase structure is formed of a material having an Abbe number V 2 at d-line that satisfies the above equation (2), the step ⁇ d
  • the optical path difference M2 added to the second light beam by 2 is very close to four times the second wavelength; I.
  • the wavefronts of the second luminous flux passing through the level surfaces that are in contact with each other are connected by being shifted by four wavelengths. Therefore, the second light flux is also transmitted as it is with almost 100% transmittance, which is not affected by the diffraction effect by the second phase structure.
  • the optical path difference N2 applied to the third luminous flux by the step ⁇ 2 is about 3.3 times the third wavelength, so that the adjacent level surfaces are The wavefront of the third luminous flux passing therethrough is shifted by 3.3 wavelengths, but the actual wavefront shift excluding the wavefront shift of 3 wavelengths that are optically equiphase is 0.3 wavelength. .
  • the third light beam is diffracted in the first order with a high diffraction efficiency of 70-80% (first order diffraction).
  • the above equation (19) is a conditional equation for increasing the diffraction efficiency of the diffracted light of the third light flux, and the number B of the level surfaces formed in each pattern is determined so as to satisfy the equation (19). By making the determination, it is possible to sufficiently secure the diffraction efficiency of the first-order diffracted light of the third light flux.
  • the second phase structure is formed from a material whose Abbe number V 2 at the d-line satisfies 25 ⁇ v 2 ⁇ 40, the value of equation (12) is used.
  • the diffraction efficiency of the first-order diffracted light of the third light beam depends only on the Abbe number V 2 at the d-line of the material on which the wavelength-selective diffraction structure is formed, and dd
  • Depth in the optical axis direction of each step increases as the value of the refractive index n2 decreases.
  • Item 13 is the objective optical system according to Item 9, wherein the second phase structure generates second-order diffracted light when the first light beam enters, and When two light beams are incident, a diffracted light of order / 32 (2 ⁇ hi2) is generated, and when the third light beam is incident, a diffracted light of order ⁇ 2 ( ⁇ 2 ⁇ 2 ) is generated. Diffraction structure.
  • the second phase structure has the diffraction characteristics described in Item 13 You can do it.
  • the diffraction structure having such diffraction characteristics has a saw-tooth shape or a step-like shape in cross section including the optical axis.
  • the configuration described in Item 14 is the objective optical system according to Item 13, wherein the diffraction order ⁇ 2 is odd. Is a number.
  • the diffraction order 2 of the first light beam be an odd number.
  • magnification of the objective optical system for recording / reproducing information on the third optical disc is in the range of 0.2 to 0, the spherical aberration caused by the difference between t and t will be better.
  • the ability to rectify s can.
  • Patent Document 2 which corresponds to a case where the diffraction angle of the blue-violet laser beam and the diffraction angle of the infrared laser beam are made different by setting the diffraction order of the purple laser beam (first light beam) to an odd number.
  • the objective lens of Numerical Example 3 uses a relatively low-dispersion material having an Abbe number of about 55 at the d-line, so that the diffraction efficiency of both wavelengths is low.
  • a material having high dispersibility that satisfies the expression (2) is used as the material of the second phase structure. Therefore, even if the diffraction order of the violet laser light beam (first light beam) is an odd number, High diffraction efficiency for both wavelengths can be ensured.
  • the configuration described in Item 15 is the objective optical system according to any one of Items 1 to 14, wherein the first aberration correction element and the second aberration correction element are joined to each other.
  • the configuration described in Item 16 is the objective optical system according to any one of Items 1 to 14, wherein the first aberration correction element and the second aberration correction element are separated from each other.
  • the configuration according to Item 17 is the object optical system according to any one of Items 1 to 16, wherein at least one of the first aberration correction element and the second aberration correction element is the second aberration correction element. It has a three-phase structure.
  • the third phase structure As described in Item 17, by forming the third phase structure on one of the optical surfaces of the first aberration correction element and the second aberration correction element, light is condensed for each light beam of the objective optical system. The characteristics can be made better.
  • This third phase structure is a diffractive structure. Or an optical path difference providing structure.
  • the aberration corrected by the third phase structure may be, for example, chromatic aberration caused by a minute change in the first wavelength ⁇ 1, or spherical aberration caused by a change in the refractive index of the objective lens caused by a change in temperature. May be.
  • the detection of the focus signal and the tracking signal by the photodetector may be unstable due to the influence of the reflected light from the objective optical system.
  • any one of the first to third phase structures is formed on the optical surface closest to the laser light source. It ’s been a good thing,
  • the light reflected by the optical surface closest to the laser light source is diffracted, so that it is diffracted in a direction having a predetermined angle with respect to the optical axis.
  • reflected light can be prevented from entering the light receiving surface of the photodetector, and stable detection characteristics can be obtained.
  • the third phase structure includes a near-field generated in the objective optical system when the first wavelength ⁇ changes within ⁇ 5 nm.
  • switching from reproduction to recording is performed by providing the third phase structure with a function of suppressing the movement of the paraxial image point position in the wavelength region of the first wavelength ⁇ ⁇ 5 nm.
  • the focused spot does not become large and it is possible to always maintain a good focused state .
  • the configuration according to Item 19 is the objective optical system according to Item 17 or 18, wherein the third phase structure is used when the first wavelength ⁇ changes within ⁇ 5 nm. It has the function of suppressing the change in generated spherical aberration.
  • the oscillation wavelength of the first light source can be reduced.
  • the tolerance for individual differences can be relaxed, and the selection of the first light source is not required, so that the cost of the optical pickup device can be reduced.
  • the configuration of Item 20 is the objective optical system according to any one of Items 17 to 19, wherein the third phase structure suppresses a change in spherical aberration caused by a change in the refractive index of the objective optical system.
  • the increase in spherical aberration due to a change in the refractive index increases in proportion to the fourth power of the NA of the objective lens. Therefore, when the objective lens is made of a resin that has a large change in the refractive index due to a temperature change. It is necessary to take measures against the increase of strong spherical aberration.
  • the increase in spherical aberration due to temperature change may not be negligible. According to the configuration described in Item 20, it is possible to provide an objective optical system having a wide usable temperature range by correcting an increase in spherical aberration due to a strong temperature change by the third phase structure.
  • the configuration according to Item 21 is the objective optical system according to any one of Items 17 to 20, wherein the third phase structure is one of the first aberration correction element and the second aberration correction element. It is formed on either one.
  • the third phase structure is formed in the first aberration correction element, and the first wavelength ⁇ Of 10
  • the third phase structure is formed in the first aberration correction element, and the optical path difference added to the first light beam by the third phase structure is equal to the first wavelength. Designed to be 10 times
  • the optical path difference added to the second light flux is approximately six times the second wavelength ⁇
  • Item 23 is the objective optical system according to any one of Items 1 to 22, wherein the first phase structure and the second phase structure are both formed of resin.
  • any optical glass or optical resin can be applied as a material of the aberration correction element.
  • a material having a low viscosity in a molten state that is, Resins are suitable.
  • resin is lower cost and lighter than glass.
  • the driving force for performing the focus and tracking control of the optical pickup device during recording / reproducing of the optical disk may be reduced.
  • the first phase structure may be made of Zeonex (registered trademark) manufactured by Zeon Corporation or Abel (registered trademark) manufactured by Mitsui Chemicals, Inc.
  • the second phase structure that is preferably formed from a cyclic oleolefin-based resin represented by a mark) or the like is a fluorene-based polyester represented by an ultraviolet curable resin or a thermosetting resin, or OKP4 manufactured by Osaka Gas Chemical Company, etc.
  • a resin is used.
  • Item 24 is the objective optical system according to any one of items 1 to 23, wherein one of the first phase structure and the second phase structure is an ultraviolet curable resin. Or formed from a thermosetting resin.
  • the material thereof is described in Item 24.
  • Such an ultraviolet curable resin or a thermosetting resin is suitable for production.
  • a method of manufacturing the aberration correction element formed on the surface of the phase structure a method of forming the phase structure directly on a resin substrate or a glass substrate by repeating a process of photolithography and etching is used.
  • a mold (die) with a phase structure is manufactured, and an aberration correction element with a phase structure formed on the surface is obtained as a replica of the mold. So-called molding is suitable for mass production. ing.
  • a method of manufacturing a mold having a phase structure formed thereon a method of repeating a process of photolithography and etching to form a diffraction structure or a method of machining a diffraction structure with a precision lathe may be used.
  • Item 25 is the objective optical system according to Item 24, wherein the phase formed from an ultraviolet curable resin or a thermosetting resin among the first phase structure and the second phase structure.
  • the structure is the second phase structure.
  • a second phase structure having a small tolerance of several v is formed from an ultraviolet-curing resin or a thermosetting resin.
  • the configuration according to Item 26 is the objective optical system according to Item 24 or 25, wherein the first phase structure and the second phase structure are formed of an ultraviolet curable resin or a thermosetting resin.
  • the phase structure is formed on a glass substrate.
  • An ultraviolet curable resin or a thermosetting resin has relatively excellent adhesion to a glass substrate. Accordingly, the mold and the phase structure are separated from each other by forming the phase structure formed of the ultraviolet curable resin or the thermosetting resin on the glass substrate among the first phase structure and the second phase structure. Deformation of the phase structure during molding can be suppressed, and the occurrence of aberrations and a decrease in diffraction efficiency due to shape errors are reduced.
  • the structure according to Item 27 is the objective optical system according to any one of Items 1 to 26, wherein the objective lens corrects spherical aberration for a combination of the t and the first wavelength ⁇ . Is optimized.
  • the aspherical shape of the objective lens is determined so that spherical aberration correction is minimized with respect to the first wavelength ⁇ and the thickness tl of the protective layer of the first optical disc.
  • the focusing performance of the first wavelength ⁇ is determined by the objective lens. Therefore, as described in Item 27, the objective is set so that spherical aberration correction is minimized with respect to the first wavelength and the thickness tl of the first protective layer.
  • the objective lens has been optimized for spherical aberration correction with respect to the combination of the tl and the first wavelength” means that the objective lens and the first optical disc are protected by the first optical disc through the protective layer. It means that the wavefront aberration when the light beam is collected is 0.05 ⁇ RMS or less.
  • Item 29 is the objective optical system according to any one of Items 4 to 6, wherein the first phase structure has an action of diverging the second light flux.
  • the second phase structure has an action of diverging the third light flux.
  • the configuration according to Item 31 is the objective optical system according to Item 7 or 8, wherein the first phase structure is used in the objective optical system when the first wavelength ⁇ 1 changes in wavelength within ⁇ 5 nm. It has a function of suppressing the movement of the paraxial image point position that occurs.
  • Item 32 is the objective optical system according to any one of Items 1 to 31, wherein at least one of the first aberration correction element and the second aberration correction element is the first wavelength. It has a negative paraxial power with respect to ⁇ .
  • paraxial power (combined power of diffraction power and refraction power) for at least one of the first aberration correction element and the second aberration correction element with respect to the first wavelength ⁇ .
  • the design magnification of the objective lens is negative. Furthermore, spherical aberration correction is minimized with respect to the first wavelength and the thickness ti of the protective layer of the first optical disc.
  • the aspherical shape is determined.
  • the first to third light beams are all the first aberration correction element and the second aberration light.
  • the light enters the correction element in the form of a parallel light beam.
  • the first aberration correction element has an Abbe number V1 at d-line satisfying Expression (1) and a first phase structure.
  • the aberration correction element has the Abbe number V 2 at the d-line satisfying the expression (2) and the second phase structure d
  • the first aberration correction element has a refractive index n1 at d-line satisfying Expression (3) and a first phase structure.
  • the aberration correction element has a refractive index n 2 at d-line that satisfies equation (4) and a second phase structure
  • the configuration according to Item 36 is the objective optical system according to any one of Items 1 to 35, wherein the first aberration correction element has a positive paraxial power with respect to the first wavelength ⁇ .
  • the second error correction element has a negative paraxial power with respect to the first wavelength ⁇ .
  • the difference in dispersion between the first aberration correction element that is a positive lens and the second aberration correction element that is a negative lens is used.
  • the movement of the paraxial image point position can be suppressed, so even if a mode hop occurs due to a change in the output of the first light source when switching from playback to recording, the focused spot does not increase, and It is possible to maintain a good light-collecting state.
  • Item 37 is the objective optical system according to Item 36, wherein the first aberration correction element and the second aberration correction element are joined to each other, and the first aberration correction element and the second aberration It is characterized in that the joint surface of the correction element has a convex shape on the side of the second aberration correction element.
  • first aberration correction element and the second aberration correction element are joined to each other as described in Item 37.
  • Item 38 is the objective optical system according to Item 24, wherein the phase structure formed of an ultraviolet curable resin or a thermosetting resin among the first phase structure and the second phase structure.
  • a non-heat-reflection anti-reflection coat is formed on the surface of.
  • the heat resistance is relatively low, and the antireflection coat can be formed on the surface of the phase structure formed of the ultraviolet curable resin or the thermosetting resin.
  • the transmittance of the first aberration correction element and the second aberration correction element can be improved.
  • the configuration according to Item 39 is the objective optical system according to Item 23, wherein the first phase structure is formed of a cyclic oleolefin resin, and the second phase structure is formed of a fluorene-based polyester resin. ing.
  • the configuration according to Item 40 is the object optical system according to any one of Items 4 to 6, wherein the optical surface on which the first phase structure is formed has a first central region including an optical axis. And a first peripheral region surrounding the first central region, wherein the first phase structure is formed in the first central region.
  • the objective optical system according to the present invention has an aperture control corresponding to the light beam of the second wavelength ⁇ .
  • the configuration according to Item 41 is the objective optical system according to Item 40, wherein the first peripheral region has a small size. At least in part, a fourth phase structure for controlling the condensing position of the second light beam passing through this portion is formed, and the fourth phase structure converts the first light beam and the third light beam. This is a diffraction structure that diffracts the second light beam without diffraction.
  • the diffraction power for the second wavelength ⁇ of the first phase structure formed in the first central region and the second wavelength ⁇ of the fourth phase structure formed in the first peripheral region are provided.
  • the fourth phase structure By making the diffraction powers different from each other, it is possible to arbitrarily control the position at which the second light beam passing through the fourth phase structure is collected and the amount of spherical aberration. At this time, by designing the fourth phase structure so that the detection characteristic of the focus error signal of the second light beam by the photodetector is the best, the focusing characteristic of the objective optical system at the time of recording / reproducing information on / from the second optical disc is achieved. Can be improved.
  • the fourth phase structure is not necessarily formed in the second peripheral region. It is only necessary to control the condensing position of the second light beam and the amount of spherical aberration only in a portion that adversely affects the detection characteristic of the focus error signal. Therefore, it is not always necessary to form the fourth phase structure over the entire first peripheral region.This prevents the range in which the fourth phase structure is formed from being unnecessarily widened. 3 It is possible to improve the transmittance of the light beam.
  • the configuration according to Item 42 is the objective optical system according to any one of Items 10 to 12, wherein the optical surface on which the second phase structure is formed includes: a second central region including an optical axis; Divided into a second peripheral region surrounding the second central region, the second phase structure is formed in the second central region.
  • the second central area is an area corresponding to a numerical aperture ( ⁇ ) necessary for recording / reproducing information on / from the third optical disc, the difference between t and t
  • the spherical aberration caused by 3 13 is corrected only within the NA (second central area), and the area outside the NA (second
  • the luminous flux of the third wavelength ⁇ passing through the area outside the NA does not contribute to spot formation.
  • the configuration described in Item 43 is the objective optical system according to Item 42, wherein the second peripheral region has a small size. At least in part, a fifth phase structure for controlling the condensing position of the third light beam passing through this portion is formed, and the fifth phase structure converts the first light beam and the second light beam. It is a diffraction structure that diffracts the third light beam without diffraction.
  • the configuration described in Item 44 is characterized in that, in the objective optical system according to any one of Items 1 to 43, the back focus fB for the first wavelength and the back focus fB for the second wavelength ⁇ .
  • the difference from the back focus fB with respect to 2 1 1 3 is 0.2 mm or less.
  • the “back focus fB with respect to the i-th wavelength ⁇ ” is defined as the position on the optical axis of the objective optical system and the i-th optical disc when the i-th light beam is focused on the information recording surface of the i-th optical disc. Refers to the interval.
  • the configuration according to Item 45 is characterized in that, in the objective optical system according to Item 11 or 12, the ratio ⁇ / ⁇ power S25 of the minimum width ⁇ of the pattern of the second phase structure to the first wavelength ⁇ is equal to or more than S25.
  • the configuration according to Item 46 is the objective optical system according to any one of Items 1 to 45, wherein the first phase structure is formed on a surface of the first aberration correction element, and The phase structure is
  • both the first phase structure and the second phase structure are formed on a plane.
  • both the first phase structure and the second phase structure are formed on a plane.
  • the configuration according to Item 49 is the object optical system according to any one of Items 1 to 48, wherein the first aberration correction element and the second aberration correction element are relative to the objective lens. It is held by the holding member so that the general positional relationship is universal.
  • the configuration according to item 50 is characterized in that a first light source that emits a first light beam of a first wavelength ⁇ for recording and / or reproducing information on the first optical disc, and a second light source Writing information
  • a second light source that emits a second light beam of a second wavelength ⁇ (> ⁇ ) for recording and recording or reproduction
  • a third light source that emits a third light beam of (3 ⁇ ), and the objective optical according to any one of claims 1 to 49.
  • the first optical disk is used to record and Z or reproduce information on a first optical disk having a protective layer having a thickness of t, and has a protective layer having a thickness of t ( ⁇ t) using the second optical beam.
  • Item 50 an optical pickup device having the same effects as in any one of Items 1 to 49 can be obtained.
  • Item 51 is the optical disk drive device equipped with the optical pickup device according to item 50 and a moving device that moves the optical pickup device in a radial direction of the optical information recording medium.
  • an optical disk drive having the same effect as the item 50 can be obtained.
  • FIG. 1 is a diagram schematically showing a configuration of an optical pickup device PU capable of appropriately recording / reproducing information on any of a high-density optical disk HD, a DVD, and a CD.
  • the combination of the layer thickness and the numerical aperture is not limited to this.
  • the optical pickup device PU emits information when recording / reproducing information to / from the HD, emits a blue-violet laser beam (first light beam) of 405 nm, and emits information to the blue-violet semiconductor laser LD1 and DVD.
  • the first emission point EP1 which emits a 655 nm red laser beam (second beam) and emits light when recording / reproducing data, and emits 785 nm light when recording / reproducing information on CDs
  • Objective lens unit ⁇ U (objective optical system) composed of an objective lens OL with aspheric surfaces on both sides, 2-axis Actuator AC1, single-axis actuator AC2, first lens EXP1 with negative paraxial refractive power, second lens EXP2 with positive paraxial refractive power, and expander lens EXP, first polarized lens One splitter BS1, 2nd polarizing beam splitter BS2, 1st collimating lens C ⁇ L1, 2nd It is composed of a collimating lens C ⁇ L2, a third collimating lens C ⁇ L3, and a sensor lens SEN for adding astigmatism to the reflected light beams from the information recording surfaces RL1, RL2 and RL3.
  • a blue-violet SHG laser may be used in addition to the above-mentioned blue-violet
  • the optical pickup device PU when performing Z recording and reproducing of information for HD, as shown in Fig. 1, the light path is drawn by a solid line, and first, the blue-violet semiconductor laser LD1 is used. To emit light. The divergent light beam emitted from the blue-violet semiconductor laser LD1 is converted into a parallel light beam by the first collimator lens COL1, then reflected by the first polarizing beam splitter BS1, passes through the second polarizing beam splitter BS2, and After passing through the 1 lens EXP1 and the 2nd lens EXP2, the beam diameter is regulated by the aperture STO (not shown), and the luminous flux diameter is regulated by the objective lens unit OU on the information recording surface RL1 via the HD protective layer PL1. It is a spot that is formed. The objective lens unit OU performs focusing and tracking by a two-axis actuator AC1 arranged around it.
  • the reflected light flux modulated by the information pits on the information recording surface RL1 has passed through the objective lens unit OU, the second lens EXP2, the first lens EXP1, the second polarizing beam splitter BS2, and the first polarizing beam splitter BS1 again. Later, when the light passes through the third collimating lens COL3, it becomes a convergent light beam, and astigmatism is added by the sensor lens SEN, and converges on the light receiving surface of the photodetector PD. Then, it is possible to read information recorded in the HD using the output signal of the photodetector PD.
  • the light emitting point EP1 emits light.
  • the divergent light beam emitted from the light emitting point EP1 is converted into a parallel light beam by the second collimating lens COL2 and then reflected by the second polarizing beam splitter BS2, as indicated by the broken line in FIG.
  • the diameter is increased by passing through the first lens EXP1 and the second lens EXP2, and becomes a spot formed on the information recording surface RL2 by the objective lens unit OU via the DVD protective layer PL2.
  • the objective lens unit OU performs focusing and tracking by a two-axis actuator AC1 arranged around it.
  • the reflected luminous flux modulated by the information pits on the information recording surface RL2 is returned to the objective lens unit.
  • G OU, the second lens EXP2, the first lens EXP1, the second polarizing beam splitter BS2, and after passing through the first polarizing beam splitter BS1, pass through the third collimating lens COL3 to become a convergent light flux, which is not reflected by the sensor lens SEN.
  • Astigmatism is added and converges on the light receiving surface of the photodetector PD. Then, it is possible to read the information recorded on the DVD using the output signal of the photodetector PD.
  • the interval between the first lens EXP1 and the second lens EXP2 becomes narrower than when recording / reproducing information on the HD.
  • the first lens EXP1 is driven in the optical axis direction by the uniaxial actuator AC2
  • the light emitting point EP2 emits light.
  • the divergent luminous flux emitted from the light emitting point EP2 is converted into a loose divergent luminous flux by the second collimating lens COL2 as shown by the dashed line in FIG. 1, and then reflected by the second polarizing beam splitter BS2.
  • the spot formed on the information recording surface RL3 by the objective lens unit OU via the protective layer PL3 of the CD through the first lens EXP1 and the second lens EXP2 is expanded in diameter and converted into a divergent light beam by the objective lens unit OU.
  • the objective lens unit OU performs focusing and tracking by a two-axis actuator AC1 arranged around it.
  • the reflected light flux modulated by the information pits on the information recording surface RL2 again passes through the objective lens unit OU, the second lens EXP2, the first lens EXP1, the second polarization beam splitter BS2, and the first polarization beam splitter BS1. Later, when the light passes through the third collimating lens COL3, it becomes a convergent light beam, and astigmatism is added by the sensor lens SEN, and converges on the light receiving surface of the photodetector PD. Then, it is possible to read information recorded on the CD using the output signal of the photodetector PD.
  • the objective lens unit OU in the present embodiment has a first phase structure PS1 made of resin and a second phase structure PS2 made of resin, and is joined to each other. And the aspheric shape so that spherical aberration is minimized with respect to the first wavelength ⁇ and the thickness t of the HD protective layer PL1.
  • the glass objective lens ⁇ L is coaxially integrated through a lens frame B.
  • the first aberration correction element L1 and the second aberration correction element L2 are joined and fixed to one end of the cylindrical lens frame B while the objective lens OL is fitted and fixed to the other end. ,these It is configured to be coaxially integrated along the optical axis X.
  • the first aberration correction element L1 and the second aberration correction element L2 are manufactured by molding, and thereafter, the respective aberration correction elements are corrected.
  • a method of joining the elements may be used, or an ultraviolet curable resin is applied on one of the aberration correction elements manufactured by molding, and a phase structure is formed on the surface of the ultraviolet curable resin.
  • a method in which a phase structure is transferred by pressing a molded mold and irradiating ultraviolet rays is acceptable.
  • a thermosetting resin may be used instead of the ultraviolet curable resin.
  • both first phase structure PS1 and second phase structure PS2 are made of resin, but one of the aberration correction elements may be made of glass and the other may be made of resin.
  • the method of manufacturing the aberration correction element having a glass phase structure may be molding or a method of forming a diffraction structure by repeating photolithography and etching processes.
  • an aberration correcting element having a phase structure made of glass is manufactured by molding, in order to extend the life of the mold and improve the transferability of the diffractive structure, the viscosity in the molten state is small and the glass is made of glass. It is preferable to use a glass having a transition point Tg of 450 ° C. or less.
  • Examples of such a glass include “K-PG325” and “K-PG375” manufactured by Sumita Optical Glass Co., Ltd.
  • an aberration correction element having a resin phase structure is manufactured by molding, and thereafter, Alternatively, a method of bonding with an aberration correcting element having a glass phase structure may be used, or an ultraviolet curable resin may be applied on the aberration correcting element having a glass phase structure, and the ultraviolet curable resin may be bonded to the glass.
  • a method of transferring the phase structure by pressing a mold having a phase structure formed on the surface and irradiating the mold with ultraviolet light may be used.
  • a thermosetting resin may be used in place of the ultraviolet curable resin.
  • the objective lens OL is made of glass.
  • the present invention is not limited to this, and the objective lens OL may be made of resin.
  • the resin used for the objective lens ⁇ L is preferably a oleolefin resin.
  • a resin having an average particle diameter of 3 It is acceptable to use a material in which inorganic particles of Onm or less are dispersed.
  • inorganic particles with a refractive index change rate opposite to the sign of the refractive index change rate due to the temperature change of the base resin By mixing inorganic particles with a refractive index change rate opposite to the sign of the refractive index change rate due to the temperature change of the base resin, refraction due to temperature change is achieved while maintaining the moldability of the resin. Since a material having a small absolute value of the rate of change can be obtained, a change in spherical aberration due to a change in temperature of the objective lens ⁇ L can be reduced.
  • the refractive index n 2 is 1.638000.
  • a first phase structure PS1 is formed on the optical surface of the first aberration correction element L1 on the light source side, and a second phase structure PS2 is formed on the optical surface of the second aberration correction element L2 on the optical disk side. It is formed.
  • the first phase structure PS1 does not diffract the first light beam and the third light beam but diffracts the second light beam.
  • a pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle. In this structure, for every predetermined number of level surfaces (five level surfaces in this embodiment), the level is shifted by the height corresponding to the number of level surfaces (in this embodiment, Is shifted four steps).
  • optical path difference N1 added to the third light beam by the step ⁇ 1 is 1X ⁇ (in the present embodiment,
  • the third light beam is also not affected by the first phase structure PS1 at all.
  • the optical path difference Ml added to the second light beam by the step ⁇ 1 is 1.20 X ⁇ (this embodiment
  • the first phase structure PS1 selectively corrects the second light flux to correct spherical aberration caused by a difference between the thickness of the protective layer of D and the thickness of the protective layer of DVD.
  • the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the first light beam generated by the first phase structure PS1 is 100%
  • the diffraction efficiency of the first-order diffracted light of the second light beam is 87.5%
  • the diffraction efficiency of the zero-order diffracted light (transmitted light) of the light beam is 100%
  • high diffraction efficiency is obtained for any light beam.
  • the second phase structure PS2 does not diffract the first light beam and the second light beam but diffracts the third light beam.
  • a pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle.
  • the number of levels is shifted by the number of levels corresponding to the number of level planes for each predetermined number of level planes (four level planes in this embodiment). Is shifted three steps).
  • n is the refractive index of the second aberration correction element at the wavelength.
  • the second light beam is also transmitted through the second phase structure PS2 with almost no effect.
  • the second phase structure PS2 selectively diffracts only the third luminous flux, thereby correcting spherical aberration caused by the difference between the thickness of the protective layer of ⁇ D and the thickness of the protective layer of CD.
  • the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the first light flux generated by the second phase structure PS1 is 100%, and the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the second light flux is 94.8. %, and The diffraction efficiency of the first-order diffracted light of the third light beam is 78.2%, and high diffraction efficiency is obtained for any light beam.
  • the first aberration correction element L1 is made of a material that satisfies the expression (1) or (3), and the HD and the DVD are mutually compatible by the first phase structure PS1.
  • the second aberration correction element L2 can be expressed by the equation (2) or (4).
  • the second phase structure PS2 ensures high transmissivity for both blue-violet laser light and infrared laser light by making the HD and CD compatible with each other. Become possible
  • the first phase structure PS1 is formed only within the numerical aperture NA2 of the DVD, the light flux passing through the area outside of NA2 becomes a flare component on the information recording surface RL2 of the DVD, Is automatically restricted.
  • the second phase structure PS2 is formed only within the numerical aperture NA3 of the CD, the luminous flux passing through the area outside NA3 becomes a flare component on the information recording surface RL3 of the CD, Is automatically restricted.
  • the spherical aberration of the spot formed on the HD information recording surface RL1 can be corrected.
  • the causes of spherical aberration that are corrected by adjusting the position of the negative lens EXP1 include, for example, wavelength variations due to manufacturing errors of the first light source LD1, changes in the refractive index and refractive index distribution of the objective lens system due to temperature changes, double-layer disks, This includes focus jumps between the information recording layers of a multi-layer disc such as a four-layer disc, and variations in thickness and thickness distribution due to manufacturing errors of the protective layer of a high-density optical disc.
  • a DVD / CD laser light source unit LU in which the first light emitting point EP1 and the second light emitting point EP2 are formed on one chip is used.
  • a laser light source unit for HD / DVDZCD in which the emission point for emitting a laser beam of wavelength 408 nm for HD is formed on the same chip.
  • a laser light source unit for HD / DVDZCD housed in one housing may be used.
  • the light source and the photodetector PD are arranged separately, but the present invention is not limited to this, and a laser light source module in which the light source and the photodetector are integrated is used. May be.
  • a force obtained by integrating the first aberration correction element L1 and the second aberration correction element L2 joined to each other and the objective lens ⁇ L via the lens frame B is joined to each other.
  • the first aberration correction element L1 and the second aberration correction element L2 and the objective lens ⁇ L are integrated, the first aberration correction element L1 and the second aberration correction element L2, and the object lens OL
  • the first aberration correction element L1 and the second aberration correction element bonded to each other may be used in addition to the method using the lens frame B as described above, as long as the relative positional relationship between them is kept unchanged. This is a method of fitting and fixing the respective flange portions of L2 and the objective lens OL.
  • phase control using a liquid crystal As a method for correcting the spherical aberration of the spot formed on the HD information recording surface RL1, in addition to the method of driving the lens in the optical axis direction as described above, a phase control using a liquid crystal is performed. An element may be used. Since a method for correcting spherical aberration by using such a phase control element is known, a detailed description thereof is omitted here.
  • the objective lens unit OU and the phase control element are integrated.
  • the first aberration correction element L1 and the second aberration correction element L2, which are joined to each other, and the objective lens OL are held so that the relative positional relationship between them does not change. Accordingly, it is possible to suppress the occurrence of aberration at the time of focusing / tracking, and to obtain good focusing characteristics or tracking characteristics.
  • the present embodiment is characterized in that in the objective lens unit OU, the first aberration correction element L1 and the second aberration correction element L2 are separated from each other.
  • the objective lens unit OU in the present embodiment is made of resin as schematically shown in FIG.
  • the first aberration correction element LI having the first phase structure PS1 of the first
  • the second aberration correction element L2 having the second phase structure PS2 made of resin
  • the first wavelength ⁇ the first wavelength
  • It has a configuration in which it is coaxially integrated via a glass objective lens OL lens frame B whose aspherical shape is designed so as to minimize spherical aberration.
  • the first aberration correction element L1 and the second aberration correction element L2 are fitted and fixed to one end of the cylindrical lens frame B with the first aberration correction element L1 and the second aberration correction element L2 separated from each other, and the objective lens OL is fitted and fixed to the other end.
  • they are coaxially integrated along the optical axis X.
  • Refractive index n 2 1.607000.
  • a first phase structure PS1 is formed on the optical surface on the light source side of the first aberration correction element L1, and a second phase structure PS2 is formed on the optical surface on the optical disk side of the second aberration correction element L2. It is formed.
  • the first phase structure PS1 does not diffract the first light beam and the third light beam, but diffracts the second light beam.
  • a pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle.
  • n is the wavelength ⁇ (in the present embodiment,
  • This is the refractive index of the first aberration correction element L1 at (fly 405 nm).
  • the optical path difference L1 added to the first light beam by the first phase structure PS1 is 2X ⁇ , the first light beam is transmitted through the first phase structure PS1 without any action.
  • the first phase structure PS 1 selectively corrects the second light flux to correct spherical aberration caused by a difference between the thickness of the protective layer of D and the thickness of the protective layer of DVD.
  • the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the first light beam generated by the first phase structure PS1 is 100%
  • the diffraction efficiency of the first-order diffracted light of the second light beam is 87.3%
  • the diffraction efficiency of the zero-order diffracted light (transmitted light) of the light beam is 99.2%
  • a high diffraction efficiency is obtained for any light beam.
  • the second phase structure PS2 diffracts the first to third light beams, and has a stepped cross section including the optical axis.
  • ⁇ is the wavelength (e.g., 400 nm in this embodiment).
  • the seventh-order diffracted light of the first light beam has the maximum diffraction efficiency.
  • the optical path difference added to the second light beam when passing through the second phase structure PS2 is 3.94 ⁇ ⁇
  • the fourth-order diffracted light of the second light flux has the maximum diffraction efficiency.
  • optical path difference added to the third light beam when passing through the second phase structure PS2 is 3.25 ⁇ ⁇
  • the third-order diffracted light of the third light beam has the maximum diffraction efficiency.
  • the diffraction efficiency of the 7th-order diffracted light of the first light beam generated by the second phase structure PS2 is 96.0%
  • the diffraction efficiency of the 4th-order diffracted light of the second light beam is 99.0%
  • the diffraction efficiency of the third light beam is 39.0%.
  • the diffraction efficiency of the second-order diffracted light is 81.2%, and high diffraction efficiency is obtained for any light flux.
  • the paraxial diffraction power for the first wavelength of the second phase structure PS2 and the paraxial refraction power for the first wavelength of the optical surface on the light source side of the second aberration correction element L2 have opposite signs, and By making the values the same, the first aberration passing through the optical surface on the light source side of the second aberration correction element L2 The beam diameter of the light beam does not change.
  • the first aberration correction element L1 and the second aberration correction element L2 are separated from each other, and the third phase structure PS3 is connected to the first aberration correction element. It is characterized in that it is provided on the optical surface of L1 on the optical disk side.
  • the objective lens unit OU in the present embodiment includes a first aberration correction element L1 having a first phase structure PS1 made of resin, and a second phase structure PS2 made of resin. With respect to the second aberration correction element L2 and the first wavelength ⁇ and the thickness t of the HD protective layer PL1.
  • a glass objective lens whose aspherical shape is designed to minimize spherical aberration.
  • the first aberration correction element L1 and the second aberration correction element L2 are joined and fixed at one end of a cylindrical lens frame B, and the objective lens OL is fitted and fixed at the other end. Therefore, they are coaxially integrated along the optical axis X.
  • Refractive index n 2 1.607000.
  • a first phase structure PS1 is formed on the optical surface of the first aberration correction element L1 on the light source side, and a second phase structure PS2 is formed on the optical surface of the second aberration correction element L2 on the optical disk side.
  • the third phase structure PS3 is formed on the optical surface of the first aberration correction element L1 on the optical disk side.
  • the first phase structure PS1 does not diffract the first light beam and the third light beam, but diffracts the second light beam.
  • a pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle. In this structure, for every predetermined number of level surfaces (five level surfaces in this embodiment), the level is shifted by the height corresponding to the number of level surfaces (in this embodiment, Is shifted four steps).
  • the first phase structure PS1 does not diffract the first and third light beams, but diffracts the second light beam.
  • n is the wavelength ⁇ (in the present embodiment,
  • This is the refractive index of the first aberration correction element L1 at (fly 405 nm).
  • the optical path difference L1 added to the first light beam by the first phase structure PS1 is 2X ⁇ , the first light beam is transmitted through the first phase structure PS1 without any effect.
  • the first phase structure PS1 selectively corrects the second light flux to correct spherical aberration due to a difference between the thickness of the protective layer of D and the thickness of the protective layer of DVD.
  • the diffraction efficiency of the first-order diffracted light (transmitted light) of the first light beam generated by the first phase structure PS1 is 100%
  • the diffraction efficiency of the first-order diffracted light of the second light beam is 87.3%
  • the diffraction efficiency of the third light beam is
  • the diffraction efficiency of the zero-order diffracted light (transmitted light) is 99.2%, and a high diffraction efficiency is obtained for any light flux.
  • the second phase structure PS2 does not diffract the first light beam and the second light beam but diffracts the third light beam.
  • a pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle.
  • the level is shifted by a height corresponding to the number of levels corresponding to the number of the level surfaces (in this embodiment, Is a two-stage shifted structure).
  • n is the refractive index of the second aberration correction element at the wavelength.
  • the second light beam is also transmitted through the second phase structure PS2 with almost no effect.
  • phase difference obtained by subtracting an integral multiple of 2 ⁇ , which is the phase, is 2 ⁇ ⁇ 0.33.
  • the phase difference of the third light beam is exactly 3 ⁇ 2 ⁇ ⁇ 0.33 for one sawtooth.
  • the second phase structure PS2 selectively diffracts only the third light beam
  • the spherical aberration caused by the difference between the protective layer thickness of D and the protective layer thickness of CD is corrected.
  • the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the first light beam generated by the second phase structure PS1 is 1
  • the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the second light flux is 99.8%, and the diffraction efficiency of the first-order diffracted light of the third light flux is 66.6%, which is high for any light flux. Diffraction efficiency is obtained.
  • the third phase structure PS3 diffracts the first to third light beams, and has a stepped cross section including the optical axis. This third phase structure PS3 is used in response to small changes in the first wavelength.
  • the optical path difference added to the first light beam when passing through the third phase structure PS3 is 10.0 X ⁇ .
  • the 10th-order diffracted light of the first light beam has the highest diffraction efficiency.
  • optical path difference added to the second light beam when passing through the third phase structure PS3 is 5.97 ⁇ ⁇
  • the sixth-order diffracted light of the second light beam has the maximum diffraction efficiency.
  • optical path difference added to the third light beam when passing through the third phase structure PS3 is 4.95 ⁇ ⁇
  • the fifth-order diffracted light of the third light beam has the maximum diffraction efficiency.
  • the diffraction efficiency of the 10th-order diffracted light of the first light beam generated by the third phase structure PS3 is 100%
  • the diffraction efficiency of the 6th-order diffracted light of the second light beam is 99.7%
  • the fifth-order diffracted light of the third light beam is generated.
  • the paraxial diffraction power for the first wavelength of the third phase structure PS3 and the paraxial refraction power for the first wavelength of the optical surface of the first aberration correction element L1 on the optical disk side have opposite signs, and their absolute values are the same. By making the values the same, the light beam diameter of the first light beam passing through the optical surface of the first aberration correction element L1 on the optical disk side does not change.
  • the first aberration correction element L1 and the second aberration correction element L2 are configured to be separated from each other, and the second lens made of an ultraviolet curable resin is formed on the glass substrate GL. It is characterized in that the second aberration correcting element L2 is formed by forming the phase structure PS2, and the paraxial power of the first aberration correcting element L1 with respect to the first wavelength is negative.
  • the objective lens unit OU in the present embodiment includes a first aberration correction element L1 having a first phase structure PS1 made of resin, and a first aberration correction element L1 made of resin on a glass substrate GL.
  • the second aspherical correction element L2 having a configuration in which the two-phase structure PS2 is formed, and the aspheric shape thereof is minimized with respect to the first wavelength and the thickness t of the HD protective layer PL1 so that spherical aberration is minimized.
  • the designed glass objective lens ⁇ L is coaxially integrated via a lens frame B.
  • the first aberration correction element L1 and the second aberration correction element L2 are joined and fixed to one end of the cylindrical lens frame B, and the objective lens ⁇ L is fitted and fixed to the other end.
  • these are coaxially integrated along the optical axis X.
  • Refractive index n 2 1.60000.
  • the first phase structure PS1 does not diffract the first light beam and the third light beam, but diffracts the second light beam.
  • a pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle.
  • the number of predetermined level planes (5 level planes in this embodiment) It has a structure in which the steps are shifted by a height corresponding to the number of steps corresponding to the number of faces (in this embodiment, a structure shifted by four steps).
  • the first phase structure PS1 does not diffract the first light beam and the third light beam but diffracts the second light beam, and a pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle.
  • n is the wavelength ⁇ (in the present embodiment,
  • This is the refractive index of the first aberration correction element L1 at (fly 408 nm).
  • the optical path difference L1 added to the first light beam by the first phase structure PS1 is 2 X ⁇ , the first light beam is transmitted through the first phase structure PS1 without any action.
  • optical path difference N1 added to the third light flux by the step ⁇ 1 is 1 X ⁇ (in the present embodiment,
  • the third light beam is also not affected by the first phase structure PS1 at all.
  • the optical path difference Ml added to the second light beam by the step ⁇ 1 is 1.20 X
  • the first phase structure PS1 selectively corrects the second light flux to correct spherical aberration due to a difference between the thickness of the protective layer of D and the thickness of the protective layer of DVD.
  • the diffraction efficiency of the first-order diffracted light (transmitted light) of the first light beam generated by the first phase structure PS1 is 100%
  • the diffraction efficiency of the first-order diffracted light of the second light beam is 87.5%
  • the diffraction efficiency of the zero-order diffracted light (transmitted light) of the light beam is 100%
  • high diffraction efficiency is obtained for any light beam.
  • the second phase structure PS2 does not diffract the first light beam and the second light beam but diffracts the third light beam.
  • a pattern having a stepped cross section including the optical axis is arranged on a concentric circle.
  • the level is shifted by a height corresponding to the number of levels corresponding to the number of the level surfaces (in this embodiment, Is 2 (Shifted structure).
  • n is the refractive index of the second aberration correction element at wavelength
  • the second light beam is also transmitted through the second phase structure PS2 with almost no effect.
  • the second phase structure PS2 corrects spherical aberration due to the difference between the thickness of the protective layer of D and the thickness of the protective layer of CD by selectively diffracting only the third light beam.
  • the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the first light flux generated by the second phase structure PS1 is 100%, and the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the second light flux is 95.8. %, and The diffraction efficiency of the first-order diffracted light of the third light beam is 77.5%, and high diffraction efficiency is obtained for any light beam.
  • the objective optical system OU of the present embodiment is arranged such that the first wavelength of the first aberration correction element L1;
  • the thickness t of the protective layer PL1 is 0.6 mm and the numerical aperture NA is 0.67.
  • the objective lens unit OU is characterized by the fact that the first aberration compensating element L1 and the second aberration compensating element L2 are joined together and the first phase structure PS1 is a diffraction structure with a saw-tooth cross section. Have.
  • the objective lens units OU in this embodiment are joined to each other, each having a first phase structure PS1 made of resin and a second phase structure SP2 made of resin.
  • the first aberration correction element L1 and the second aberration correction element L2 and the resin objective lens OL are coaxially integrated by fitting and fixing respective flange portions FL1 and FL2.
  • the first phase structure PS1 diffracts the first to third light beams, and has a sawtooth cross section including the optical axis.
  • the first phase structure PS1 has the first wavelength and the second wavelength ⁇ .
  • an eighth-order diffracted light of the first light flux, a fifth-order diffracted light of the second light flux, and a fourth-order diffracted light of the third light flux are generated.
  • the optical path difference added to the first light flux when passing through the first phase structure PS1 is 8.0 X ⁇ .
  • the fourth-order diffracted light of the third light beam has the maximum diffraction efficiency.
  • the diffraction efficiency of the 8th-order diffracted light of the first light beam generated by the first phase structure PS1 is 100%
  • the diffraction efficiency of the 5th-order diffracted light of the second light beam is 89.1%
  • the fourth-order diffracted light of the third light beam is generated.
  • the second phase structure PS2 diffracts the third light beam without diffracting the first light beam and the second light beam, and a pattern in which the cross section including the optical axis is stepped is arranged on a concentric circle.
  • the number of predetermined level planes (four level planes in this embodiment)
  • the structure is such that the steps are shifted by a height corresponding to the number of steps corresponding to the number of surfaces (in the present embodiment, a structure shifted three steps).
  • n is the refractive index of the second aberration correction element at wavelength
  • the second light beam is also transmitted through the second phase structure PS2 with almost no effect.
  • phase difference obtained by subtracting an integral multiple of 2 ⁇ , which is the phase is 2 ⁇ 0.25.
  • the phase difference of the third light beam is exactly 4 X 2 ⁇ ⁇ 0.25 for one sawtooth.
  • the second phase structure PS2 selectively diffracts only the third light beam
  • the spherical aberration caused by the difference between the protective layer thickness of D and the protective layer thickness of CD is corrected.
  • the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the second light flux is 97.5%
  • the diffraction efficiency of the first-order diffracted light of the third light flux is 79.6%, which is high for any light flux. Diffraction efficiency is obtained.
  • the first aberration correction element L1 and the second aberration correction element L2 are joined, and the joint surface is convex toward the second aberration correction element L2. It is characterized in that a fifth phase structure PS5 is formed in a peripheral area PA (second peripheral area) of the optical surface on the light source side of the second aberration correction element L2.
  • the objective lens unit OU in the present embodiment has a first aberration correction element L1 having a first phase structure PS1 made of resin and a second phase structure made of resin.
  • a glass objective lens OL the aspherical shape of which is designed to minimize the surface aberration, is coaxially integrated via a lens frame B.
  • the first aberration correction element L1 and the second aberration correction element L2 are joined and fixed to one end of a cylindrical lens frame B, and the objective lens ⁇ L is fitted and fixed to the other end. Therefore, they are coaxially integrated along the optical axis X.
  • Refractive index n 2 1.630000.
  • a first phase structure PS1 is formed on the optical surface of the first aberration correction element L1 on the optical disk side, and a central area CA (second center area) of the optical surface of the second aberration correction element L2 on the light source side is provided.
  • the second phase structure PS2 is formed in the region (region), and the fifth phase structure PS5 is formed in the peripheral region PA (second peripheral region) surrounding the central region CA.
  • the first phase structure PS1 does not diffract the first light beam and the third light beam but diffracts the second light beam.
  • a pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle. In this structure, for every predetermined number of level surfaces (five level surfaces in this embodiment), the level is shifted by the height corresponding to the number of level surfaces (in this embodiment, Is shifted four steps).
  • the first phase structure PS1 does not diffract the first light beam and the third light beam but diffracts the second light beam.
  • a pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle.
  • the optical path difference L1 added to the first light beam by the first phase structure PS1 is 2 ⁇ ⁇ , the first light beam is transmitted through the first phase structure PS1 without any action.
  • the first phase structure PS1 selectively corrects the second light flux to correct spherical aberration caused by a difference between the thickness of the protective layer of D and the thickness of the protective layer of DVD.
  • the diffraction efficiency of the first-order diffracted light (transmitted light) of the first light beam generated by the first phase structure PS1 is 100%
  • the diffraction efficiency of the first-order diffracted light of the second light beam is 87.3%
  • the diffraction efficiency of the zero-order diffracted light (transmitted light) of the light beam is 99.1%
  • a high diffraction efficiency is obtained for any light beam.
  • the second phase structure PS2 diffracts the third light beam without diffracting the first light beam and the second light beam, and a pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle.
  • the number of levels is shifted by the number of levels corresponding to the number of level planes for each predetermined number of level planes (four level planes in this embodiment). Is shifted three steps).
  • n is the refractive index of the second aberration correction element at wavelength
  • the second light beam is also transmitted through the second phase structure PS2 with almost no effect.
  • the optical path difference ⁇ 2 added to the third light beam by the step ⁇ 2 is 3.25 X ⁇
  • the second phase structure PS2 selectively corrects the third light flux to correct spherical aberration caused by a difference between the thickness of the protective layer of HD and the thickness of the protective layer of CD.
  • the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the first light flux generated by the second phase structure PS1 is 100%, and the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the second light flux is 88.8. %,
  • the diffraction efficiency of the first-order diffracted light of the third light beam is 81.0%, and high diffraction efficiency is obtained for any light beam.
  • the central area CA of the optical surface on the light source side of the second aberration correction element L2 is an area corresponding to the inside of the numerical aperture NA3, and the peripheral area PA is an area corresponding to the outside of the numerical aperture NA3.
  • a fifth phase structure PS5 which is a structure for controlling the condensing position of the third light beam passing through this area, is formed.
  • Fifth phase structure PS5 diffracts the third light beam without diffracting the first light beam and the second light beam, and has a concentric circle-shaped pattern with a stepped cross section including the optical axis.
  • the principle of diffracted light generation by the fifth-phase structure PS5 is the same as that of the second-phase structure PS2, and a detailed description is omitted here.
  • the third light beam passing through the peripheral area PA becomes a flare component having large spherical aberration, and this flare component is formed by the second phase structure PS2. Since the light is condensed so as to overlap on the condensing spot, there is a possibility that the focusing operation for the third light beam may be adversely affected.
  • the fourth phase structure PS4 has a function of converting the third light beam passing through the peripheral area PA into a flare component that is condensed on the under side (in a direction in which the condensing position approaches the objective lens unit ⁇ U). Good focus pull-in operation characteristics can be obtained for the third light flux.
  • the first wavelength in the wavelength region of I ⁇ 5 nm.
  • the focus spot does not increase even if a mode hop occurs due to a change in the output of the first light source when switching from playback to recording. It becomes possible.
  • Example 1 a specific numerical example (Example 1) of the objective lens unit ⁇ U shown in FIG. 2 will be described.
  • the first aberration correction element L1 having the first resin phase structure PS1 and the second aberration correction element L2 having the second resin phase structure have a configuration in which they are joined to each other, and the objective lens OL is a glass lens (HOYA LAC130) whose aspheric shape is designed to minimize spherical aberration with respect to the first wavelength and the thickness t of the HD protective layer PL1.
  • a good resin lens is a glass lens (HOYA LAC130) whose aspheric shape is designed to minimize spherical aberration with respect to the first wavelength and the thickness t of the HD protective layer PL1.
  • Table 1 1 1 2 shows the lens data of this example.
  • the optical path difference added to the incident light beam by the first phase structure PS1 and the second phase structure PS2 is represented by an optical path difference function.
  • the numerical aperture NA of HD is 0.85, and the numerical aperture NA of DVD in Examples 2 to 4, Example 7, and Example 8 described below, including this example. Is 0 ⁇ 65 and of the CD
  • the numerical aperture NA is 0.51.
  • the paraxial refraction power of the first aberration correction element L1 is set to be negative, and a divergent light beam is incident on the objective lens OL, so that DVDs and CDs having a thick protective layer can be used.
  • the working distance to this is sufficiently secured.
  • the objective optical system having the negative / positive configuration as in the present embodiment is advantageous in that the working distance for DVDs and CDs is ensured even when the focal length is reduced. Therefore, the objective optical system of this embodiment is most suitable for a slim type optical pickup device.
  • M is the diffraction order of the diffracted light used for recording / reproducing to HD, DVD
  • exponent of 10 (for example, 2. 5 X 10- 3), shall be expressed by using E (for example, 2. 5E- 3).
  • the optical surface on the light source side (first surface) of the first aberration correction element L1, the optical surface on the light source side (fourth surface) of the objective lens ⁇ L, and the optical surface on the optical disk side (fifth surface) are each non-uniform.
  • the aspheric surface is represented by an equation obtained by substituting the coefficients in the table into the following aspherical form equation. [Aspheric expression]
  • z Aspherical shape (distance along the optical axis from the plane tangent to the apex of the aspheric surface)
  • y Distance from the optical axis
  • first phase structure PS1 and the second phase structure PS2 are represented by an optical path difference added to the incident light beam by each phase structure.
  • Such an optical path difference is represented by an optical path difference function ⁇ (mm) obtained by substituting the coefficients in the table into an equation representing the following optical path difference function.
  • ⁇ wavelength of the light beam incident on the diffraction structure
  • the paraxial power of the diffractive structure diffracted in a direction away from the optical axis is negative (a light beam incident as a parallel light beam on the first phase structure PS1 and the second phase structure PS2 diverges).
  • Direction a light beam incident as a parallel light beam on the first phase structure PS1 and the second phase structure PS2 diverges.
  • the paraxial power of the diffractive structure that diffracts in the direction approaching the optical axis is positive (the light beam entering the first phase structure PS1 and the second phase structure PS2 as a parallel light beam converges).
  • the first aberration correction element LI having the first resin phase structure PS1 and the second aberration correction element L2 having the second resin phase structure have a configuration in which they are spaced apart from each other.
  • ⁇ L is a glass lens (HOYA BACD5) whose aspheric shape is designed to minimize spherical aberration with respect to the first wavelength; I and the thickness t of the HD protective layer PL1.
  • r (mm) is the radius of curvature
  • d (mm) is the lens spacing
  • v is the Abbe number of the d-line lens, M, M,
  • M is the diffraction order of the diffracted light used for recording / reproducing to HD, DVD
  • the optical surface on the light source side (third surface) of the second aberration correction element L2, the optical surface on the light source side (fifth surface) of the objective lens ⁇ L, and the optical surface on the optical disk side (sixth surface) are each non-uniform.
  • the aspheric surface is represented by a mathematical expression obtained by substituting the coefficients in the table into the aspherical surface expression.
  • first phase structure PS1 and the second phase structure PS2 are represented by an optical path difference added to the incident light beam by each phase structure.
  • Such an optical path difference is represented by an optical path difference function ⁇ (mm) obtained by substituting the coefficients in Tables 2-1 and 2-2 into the expression representing the optical path difference function.
  • Example 3 a specific numerical example (Example 3) of the objective lens unit OU shown in FIG. 4 will be described.
  • the first aberration correction element L1 having the first resin phase structure PS1 and the second aberration correction element L2 having the second resin phase structure have a configuration in which they are spaced apart from each other.
  • the lens OL has the smallest spherical aberration with respect to the first wavelength 1 and the thickness t of the HD protective layer PL1.
  • the glass lens (HOYA BACD5) whose aspherical shape is designed, but may be a resin lens.
  • Lens data of the present example are shown in Tables 3-1 and 3-2. [0296] [sf £ _Table. 3-1]
  • M is the diffraction order of the diffracted light used for recording / reproducing to HD, DVD
  • the optical surface (second surface) of the first aberration correction element LI on the optical disk side, the optical surface of the objective lens OL on the light source side (fifth surface), and the optical surface of the optical disk side (sixth surface) are each aspherical.
  • This aspherical surface is represented by a mathematical expression obtained by substituting the coefficients in the table into the aspherical shape expression.
  • the first to third phase structures PS1 to PS3 are represented by optical path differences added to the incident light beam by the respective phase structures.
  • Such an optical path difference is represented by an optical path difference function ⁇ (mm) obtained by substituting the coefficients in Tables 3-1 and 3_2 into the equation representing the optical path difference function.
  • Example 4 a specific numerical example (Example 4) of the objective lens unit ⁇ U shown in FIG. 5 will be described.
  • the first aberration correction element L1 having the first resin phase structure PS1 and the second aberration correction element L2 having the second resin phase structure have a configuration in which they are spaced apart from each other.
  • the lens OL has the smallest spherical aberration with respect to the first wavelength and the thickness t of the HD protective layer PL1.
  • the glass lens (HOYA BACD5) whose aspherical shape is designed, but may be a resin lens.
  • the paraxial refraction power of the first aberration correction element L1 is set to be negative, and a divergent light beam is incident on the objective lens OL.
  • the working distance to this is sufficiently secured.
  • the objective optical system having the negative / positive configuration as in the present embodiment is advantageous in that the working distance for DVDs and CDs is ensured even when the focal length is reduced. Therefore, the objective optical system of this embodiment is most suitable for a slim type optical pickup device.
  • r (mm) is the radius of curvature
  • d (mm) is the lens spacing
  • the optical surface on the light source side (the fourth surface) of the first aberration correction element LI, the optical surface on the light source side (the sixth surface) of the objective lens ⁇ L, and the optical surface (the seventh surface) on the optical disk side are each non-uniform.
  • the aspheric surface is represented by a mathematical expression obtained by substituting the coefficients in the table into the aspherical surface expression.
  • the first phase structure PS1 and the second phase structure PS2 are represented by optical path differences added to the incident light beam by the respective phase structures.
  • Such an optical path difference is represented by an optical path difference function ⁇ (mm) obtained by substituting the coefficients in Table 4-1 2 into the equation representing the optical path difference function.
  • Example 5 a specific numerical example (Example 5) of the objective lens unit ⁇ U shown in FIG. 6 will be described.
  • the first aberration correction element L1 having the first resin phase structure PS1 and the second aberration correction element L2 having the second resin phase structure PS2 have a configuration in which they are joined to each other. Is a resin lens.
  • the numerical aperture NA of HD is 0.67
  • the numerical aperture NA of DVD is 0.65
  • the numerical aperture NA of CD is 0.51. It is.
  • r (mm) is the radius of curvature
  • d (mm) is the lens spacing
  • M is the diffraction order of the diffracted light used for recording / reproducing to HD, DVD
  • optical surface (fourth surface) on the light source side and the optical surface (fifth surface) on the optical disk side of the objective lens OL are aspherical, respectively. It is expressed by a formula with the coefficients inside substituted.
  • the first phase structure PS1 and the second phase structure PS2 are represented by optical path differences added to the incident light beam by the respective phase structures.
  • Such an optical path difference is represented by an optical path difference function ⁇ (mm) obtained by substituting the coefficients in Table 5-15_2 into the expression representing the optical path difference function.
  • the objective lens unit OU of the present embodiment has the diffraction order of the diffracted light of each wavelength generated by the first phase structure PS1 of the objective lens unit ⁇ U shown in FIG. It is characterized in that the first-order diffracted light is the second-order diffracted light, the first-order diffracted light is the second light, and the first-order diffracted light is the third light.
  • the first aberration correction element L1 having the first resin phase structure PS1 and the second aberration correction element L2 having the second resin phase structure have a configuration in which they are joined to each other. It is a resin lens.
  • 111111) is the radius of curvature
  • (1 (111111) is the lens interval
  • 11 n is the lens interval
  • M is the diffraction order of the diffracted light used for recording / reproducing to HD, DVD
  • the optical surface (fourth surface) on the light source side and the optical surface (fifth surface) on the optical disk side of the objective lens ⁇ L are aspherical, respectively. It is represented by an equation with the coefficients in the table substituted.
  • first phase structure PS1 and the second phase structure PS2 are represented by the optical path difference added to the incident light beam by each phase structure.
  • Such an optical path difference is represented by an optical path difference function ⁇ (mm) obtained by substituting the coefficients in Tables 6-1 and 6_2 into the expression representing the optical path difference function.
  • the objective lens unit OU of the present embodiment is different from the objective lens unit OU shown in FIG. 3 in that the light flux incident surface and the light flux exit surface of the second aberration correction element L2 are replaced with each other. It has a configuration in which the correction element L2 is joined. Further, by passing through the second phase structure PS2, the fifth-order diffracted light of the first light beam, the third-order diffracted light of the second light beam, and the second-order diffracted light of the third light beam are generated.
  • Both the first phase structure PS1 and the second phase structure PS2 are made of resin, and the objective lens OL has a minimum spherical aberration with respect to the first wavelength and the thickness t of the HD protective layer PL1. So that non
  • HOYA BACD5 glass lens
  • Tables 7-1 and 7-2 show the lens data of this example.
  • r (mm) is the radius of curvature
  • d (mm) is the lens spacing
  • M is the diffraction order of the diffracted light used for recording / reproducing to HD, DVD This is the diffraction order of the diffracted light used for recording / reproducing, and the diffraction order of the diffracted light used for recording / reproducing for CD.
  • optical surface of the second aberration correction element L2 on the optical disk side (third surface), the optical surface of the objective lens OL on the light source side (fourth surface), and the optical surface of the optical disk side (fifth surface) are each aspherical.
  • This aspherical surface is represented by a mathematical expression obtained by substituting the coefficients in the table into the aspherical shape expression.
  • first phase structure PS1 and the second phase structure PS2 are represented by the optical path difference added to the incident light beam by each phase structure.
  • optical path difference is expressed by the above equation representing the optical path difference function as shown in Table 7-
  • Example 8 a specific numerical example (Example 8) of the objective lens unit OU shown in FIG. 13 will be described.
  • the first aberration correction element L1 having the first resin phase structure PS1 and the second aberration correction element L2 having the second resin phase structure have a configuration in which they are joined to each other. And the first wavelength and the thickness t of the HD protective layer PL1 so that spherical aberration is minimized.
  • the glass lens (HOYA LAC130) is designed with the aspherical shape, it is also good as a resin lens.
  • Lens data of the present example are shown in Tables 8-1 and 8-2.
  • r (mm) is the radius of curvature
  • d (mm) is the lens interval
  • M is the diffraction order of the diffracted light used for recording / reproducing to HD, DVD
  • optical surface (fourth surface) on the light source side and the optical surface (fifth surface) on the optical disk side of the objective lens ⁇ L are aspherical, respectively. It is represented by an equation with the coefficients in the table substituted.
  • the first phase structure PS1, the second phase structure PS2, and the fourth phase structure PS4 are each a phase structure. It is represented by the optical path difference added to the incident light beam by the structure. Such an optical path difference is represented by an optical path difference function ⁇ (mm) obtained by substituting the coefficients shown in Table 7 into the equation representing the optical path difference function.
  • the central area CA (the area where the second phase structure PS2 is formed) is an area within ⁇ 2.33 mm
  • the peripheral area PA (the area where the fifth phase structure PS5 is formed) is an area outside ⁇ 2.33 mm.
  • Table 9 shows a list of numerical data in each of the above Examples. ⁇ in the table is HD, D
  • VD CD design wavelength (nm)
  • f is the focal length of the whole objective lens unit system of HD, DVD, CD (mm)
  • NA is the numerical aperture of HD
  • DVD CD
  • STO is the entrance pupil diameter of HD (mm) ).
  • a high-density optical disc and a DV The spherical aberration due to the difference in the protective layer thickness between D and CD, or the spherical aberration due to the difference in the wavelength used between the high-density optical disk and the DVD and CD can be corrected well, and the blue-violet wavelength region around 400 nm can be corrected.
  • An objective optical system capable of obtaining high light use efficiency in any of a red wavelength region near 650 nm and an infrared wavelength region near 780 nm, an optical pickup device using this objective optical system, and Thus, an optical disk drive device equipped with this optical pickup device can be obtained.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Head (AREA)
  • Lenses (AREA)

Abstract

Un système optique à objectif est utilisé dans un dispositif de prélèvement optique pour enregistrer et/ou reproduire des informations en utilisant un premier flux de lumière émis par une première source lumineuse et un deuxième flux de lumière émis par une deuxième source lumineuse et un troisième flux de lumière émis par une troisième source lumineuse. Le système optique à objectif comprend un premier et un deuxième élément de correction d’aberration et une lentille d’objectif pour focaliser du premier au troisième flux lumineux qui sont passés au travers du premier et du deuxième élément de correction d’aberration sur la surface d’enregistrement d’information du premier au troisième disque optique. Le premier élément de correction d’aberration possède une première structure de phase formée par un matériau ayant l’Abbe constant νd1 sur la ligne d satisfaisant 40 ≤ νd1 ≤ 80 alors que le deuxième élément de correction d’aberration possède une deuxième structure de phase formée par un matériau ayant l’Abbe constant νd2 sur la ligne d satisfaisant 20 ≤ νd2 < 40.
PCT/JP2005/008983 2004-05-27 2005-05-17 Système optique à objectif, dispositif de prélèvement optique et dispositif de lecteur de disque optique WO2005117002A1 (fr)

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008041234A (ja) * 2006-07-10 2008-02-21 Ricoh Co Ltd 光ピックアップおよび光情報処理装置
JP2008527593A (ja) * 2005-01-11 2008-07-24 コーニンクレッカ フィリップス エレクトロニクス エヌ ヴィ 光学スキャニング装置
WO2008146675A1 (fr) * 2007-05-31 2008-12-04 Konica Minolta Opto, Inc. Elément optique d'objectif pour un dispositif optique et dispositif de capteur optique
JP2008293629A (ja) * 2007-04-26 2008-12-04 Ricoh Co Ltd 光ピックアップおよび光情報処理装置
JP2009070547A (ja) * 2007-08-21 2009-04-02 Hoya Corp 光情報記録再生装置用対物光学系および光情報記録再生装置
JP2010008809A (ja) * 2008-06-27 2010-01-14 Canon Inc 光学系及びそれを用いた光学機器
JP4745442B2 (ja) * 2007-08-02 2011-08-10 パナソニック株式会社 複合対物レンズ、回折素子、光ヘッド装置、光情報装置、対物レンズ駆動方法および制御装置

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Publication number Priority date Publication date Assignee Title
JP2001209966A (ja) * 2000-01-26 2001-08-03 Pioneer Electronic Corp 光ピックアップ
JP2004079146A (ja) * 2001-10-12 2004-03-11 Konica Minolta Holdings Inc 光ピックアップ装置、対物レンズ、回折光学素子、光学素子及び記録・再生装置
JP2004138895A (ja) * 2002-10-18 2004-05-13 Asahi Glass Co Ltd 光ヘッド装置

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2001209966A (ja) * 2000-01-26 2001-08-03 Pioneer Electronic Corp 光ピックアップ
JP2004079146A (ja) * 2001-10-12 2004-03-11 Konica Minolta Holdings Inc 光ピックアップ装置、対物レンズ、回折光学素子、光学素子及び記録・再生装置
JP2004138895A (ja) * 2002-10-18 2004-05-13 Asahi Glass Co Ltd 光ヘッド装置

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008527593A (ja) * 2005-01-11 2008-07-24 コーニンクレッカ フィリップス エレクトロニクス エヌ ヴィ 光学スキャニング装置
JP2008041234A (ja) * 2006-07-10 2008-02-21 Ricoh Co Ltd 光ピックアップおよび光情報処理装置
JP2008293629A (ja) * 2007-04-26 2008-12-04 Ricoh Co Ltd 光ピックアップおよび光情報処理装置
WO2008146675A1 (fr) * 2007-05-31 2008-12-04 Konica Minolta Opto, Inc. Elément optique d'objectif pour un dispositif optique et dispositif de capteur optique
JPWO2008146675A1 (ja) * 2007-05-31 2010-08-19 コニカミノルタオプト株式会社 光ピックアップ装置用の対物光学素子及び光ピックアップ装置
CN101681645B (zh) * 2007-05-31 2011-11-23 柯尼卡美能达精密光学株式会社 光拾取装置用物镜光学元件及光拾取装置
JP4745442B2 (ja) * 2007-08-02 2011-08-10 パナソニック株式会社 複合対物レンズ、回折素子、光ヘッド装置、光情報装置、対物レンズ駆動方法および制御装置
JP2009070547A (ja) * 2007-08-21 2009-04-02 Hoya Corp 光情報記録再生装置用対物光学系および光情報記録再生装置
JP2010008809A (ja) * 2008-06-27 2010-01-14 Canon Inc 光学系及びそれを用いた光学機器

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