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WO2011040225A1 - Elément de diffraction et dispositif de capture optique - Google Patents

Elément de diffraction et dispositif de capture optique Download PDF

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Publication number
WO2011040225A1
WO2011040225A1 PCT/JP2010/065797 JP2010065797W WO2011040225A1 WO 2011040225 A1 WO2011040225 A1 WO 2011040225A1 JP 2010065797 W JP2010065797 W JP 2010065797W WO 2011040225 A1 WO2011040225 A1 WO 2011040225A1
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WO
WIPO (PCT)
Prior art keywords
light
step surface
length
optical
wavelength
Prior art date
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Ceased
Application number
PCT/JP2010/065797
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English (en)
Japanese (ja)
Inventor
徹 木村
健太郎 中村
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Konica Minolta Opto Inc
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Konica Minolta Opto Inc
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Priority to JP2011534179A priority Critical patent/JPWO2011040225A1/ja
Publication of WO2011040225A1 publication Critical patent/WO2011040225A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—Lenses
    • G11B7/1374—Objective lenses
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1353—Diffractive elements, e.g. holograms or gratings
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1365—Separate or integrated refractive elements, e.g. wave plates
    • G11B7/1367—Stepped phase plates
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • 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 a diffraction element for an optical pickup device that records and / or reproduces information (also referred to as recording / reproduction in the present specification) interchangeably with respect to different types of optical disks, and uses the same.
  • the present invention relates to an optical pickup device.
  • a high-density optical disk system capable of recording and / or reproducing information (hereinafter, “recording and / or reproduction” is referred to as “recording / reproduction”) using a blue-violet semiconductor laser having a wavelength of about 400 nm.
  • an optical disc for recording / reproducing information with specifications of NA 0.85 and light source wavelength 405 nm, so-called Blu-ray Disc (hereinafter referred to as BD), DVD (NA 0.6, light source wavelength 650 nm, storage capacity 4. It is possible to record 25 GB of information per layer on an optical disk having a diameter of 12 cm, which is the same size as 7 GB).
  • optical disks that use blue-violet laser light sources are collectively referred to as “high-density optical disks”.
  • the value as a product of an optical disc player / recorder cannot be said to be sufficient simply by saying that information can be appropriately recorded / reproduced on such a high-density optical disc.
  • DVDs and CDs compact discs
  • making it possible to appropriately record / reproduce information on DVDs and CDs leads to an increase in commercial value as an optical disc player / recorder for high-density optical discs.
  • an optical pickup device mounted on an optical disc player / recorder for high density optical discs can appropriately receive information while maintaining compatibility with both high density optical discs, DVDs, and even CDs. It is desired to have a performance capable of recording / reproducing.
  • a condensing optical system for high-density optical discs and a DVD or CD It is possible to selectively switch the light collecting optical system according to the recording density of the optical disk for recording / reproducing information.
  • a plurality of light collecting optical systems are required, which is disadvantageous for downsizing. Cost increases.
  • a condensing optical system for high-density optical discs and a condensing optical system for DVDs and CDs It is preferable to reduce the number of optical components constituting the optical pickup device as much as possible.
  • a diffractive element having a diffractive structure having a wavelength dependency of spherical aberration is disposed in the condensing optical system.
  • Patent Document 1 describes an objective optical system that has a diffractive structure and can be used in common with, for example, high-density optical discs and conventional DVDs and CDs, and an optical pickup device equipped with the objective optical system. .
  • Patent Document 1 the first diffraction surface that does not diffract the light beam having the first wavelength ⁇ 1 and the light beam having the third wavelength ⁇ 3 but diffracts the light beam having the second wavelength ⁇ 2, and the first Three different types using a diffractive optical element having a second diffractive surface that does not diffract the light beam having the wavelength ⁇ 1 and the light beam having the second wavelength ⁇ 2 and diffracts the light beam having the third wavelength ⁇ 3.
  • Information is recorded / reproduced so as to be compatible with an optical disc of the above type.
  • information is recorded / reproduced to be compatible with three different types of optical disks by using a diffraction structure that generates three different orders of diffracted light when light beams of three different wavelengths are incident.
  • Technology is also being developed. As an example, as shown in Table 1 and FIG. 1, when a blue-violet laser beam is incident, ⁇ 1st order diffracted light is generated, and when a red laser beam is incident, + 2nd order diffracted light is generated. When an infrared laser beam is incident, a diffractive structure that generates + third-order diffracted light is formed, thereby forming an appropriate focused spot on the information recording surface of a high-density optical disc, DVD, or CD.
  • This aspect is a preferable aspect that is easy to manufacture because it is not necessary to form a plurality of types of diffraction structures for compatibility.
  • the information recording surface of the BD is only one layer, no significant problem occurs even if unnecessary light having a diffraction order different from that of the main light is generated.
  • a two-layer type BD having a two-layer information recording surface has also been developed and already on the market, and it has been found that problems arise when such a two-layer type BD is used. More specifically, since the distance between the information recording surfaces of the two-layer type BD is relatively close to 25 ⁇ m, the first-order diffracted light is converted into the first diffracted light using the objective lens OBJ having the diffractive structure described above. When the light is condensed on the information recording surface L1 of the layer, the ⁇ 2nd order diffracted light is just condensed on the information recording surface L2 of the second layer, which may cause an error signal.
  • the present invention has been made in view of the problems of the prior art, and includes a BD having a plurality of information recording surfaces stacked in the thickness direction and / or a plurality of information recording surfaces stacked in the thickness direction.
  • An object of the present invention is to provide a diffractive element for an optical pickup device and an optical pickup device using the same that can increase the light use efficiency when using a CD while suppressing the generation of an error signal when the DVD is used. .
  • the diffractive element according to claim 1 includes a first light source that emits a first light flux having a wavelength ⁇ 1, a second light source that emits a second light flux having a wavelength ⁇ 2 ( ⁇ 1 ⁇ 2), and a wavelength ⁇ 3 ( ⁇ 2 ⁇ 3).
  • a third light source that emits a third light beam, an objective optical system, a light detector, and an optical path between the light source and the light detector, are disposed in the first light beam, the second light beam, and the first light beam.
  • a diffraction element through which three light beams pass in common, and the light beam from the first light source is condensed on the information recording surface of the first optical disk by the diffraction element and the objective optical system.
  • a diffraction element used in an optical pickup device for recording and / or reproducing information on an optical disc The first optical disc and / or the second optical disc has a plurality of information recording surfaces stacked in a thickness direction,
  • the diffractive element has a diffractive structure for correcting spherical aberration generated due to the thickness of a protective layer of the first optical disc, the second optical disc, and the third optical disc,
  • the diffractive structure has seven step surfaces extending substantially parallel to the optical axis of the diffractive element and seven terrace surfaces intersecting the step surface, and the adjacent terrace surface is light of the diffractive element.
  • the present inventor made the fourth to seventh or fifth to seventh terrace surfaces counted from the end of the step unit in the direction of the optical axis based on a seven-step staircase structure having a ring shape.
  • shifting it is possible to reduce the diffraction efficiency of the ⁇ 2nd order diffracted light, which is unnecessary light generated when a light beam with wavelength ⁇ 1 is incident, so the first information recording surface and the second information recording surface of the first optical disc
  • the information recording surface of the third optical disc can be appropriately recorded / reproduced, and the diffraction efficiency of the + third-order diffracted light, which is the main light when the light beam having the wavelength ⁇ 3 is incident, can be increased. It was also found that information can be recorded / reproduced appropriately.
  • the “fourth to seventh or fifth to seventh terrace surfaces” means the optical axis of the objective lens that is the most in one step unit in which seven adjacent terrace surfaces are gradually shifted in the optical axis direction. May be counted from a terrace surface that is closest to the optical axis of the objective lens, or may be counted from a terrace surface other than the end of one step unit.
  • the diffractive element according to a second aspect is the same as the diffractive element according to the first aspect, in the step periodic structure, along the optical axis direction by a predetermined amount of the fourth to seventh or fifth to seventh terrace surfaces.
  • ⁇ is an optical path difference of wavelength ⁇ 1 ( ⁇ m) generated by the shift amount ⁇ .
  • ⁇ ⁇ ( ⁇ / ⁇ 1) ⁇ (n1-1) n1: The refractive index of the diffraction element at the wavelength ⁇ 1.
  • the diffractive element according to claim 3 includes a first light source that emits a first light flux having a wavelength ⁇ 1, a second light source that emits a second light flux having a wavelength ⁇ 2 ( ⁇ 1 ⁇ 2), and a wavelength ⁇ 3 ( ⁇ 2 ⁇ 3).
  • a third light source that emits the third light beam, an objective optical system, a photodetector, and a light path between the light source and the light detector, the first light beam, the second light beam, and the A diffraction element through which the third light beam passes in common, and the light beam from the first light source is condensed on the information recording surface of the first optical disk by the diffraction element and the objective optical system.
  • Information is recorded and / or reproduced on the first optical disk based on a signal from the photodetector that forms a spot and receives the reflected light, and a light beam from the second light source is diffracted.
  • the light is condensed on the information recording surface of the second optical disk by the element and the objective optical system.
  • information is recorded and / or reproduced on the second optical disk, and the light beam from the third light source is reflected.
  • a spot is formed by condensing the diffraction element and the objective optical system on an information recording surface of the third optical disk, and the reflected light is received on the basis of a signal from the photodetector.
  • a diffraction element used in an optical pickup device for recording and / or reproducing information with respect to an optical disc The first optical disc and / or the second optical disc has a plurality of information recording surfaces stacked in a thickness direction
  • the diffractive element has a diffractive structure for correcting spherical aberration generated due to the thickness of a protective layer of the first optical disc, the second optical disc, and the third optical disc
  • the diffractive structure has seven step surfaces extending substantially parallel to the optical axis of the diffractive element and seven terrace surfaces intersecting the step surface, and the adjacent terrace surface is light of the diffractive element.
  • a step periodic structure in which a plurality of stepped structures sequentially shifted in the axial direction are arranged along a direction intersecting the optical axis of the diffraction element, Of the diffracted light generated when the first light beam is incident on the diffractive structure, the -1st order diffracted light has the largest amount of diffracted light, and the diffracted light generated when the second light beam is incident on the diffractive structure + 2nd order diffracted light has the maximum amount of diffracted light, and among the diffracted light generated when the third light beam is incident on the diffractive structure, + 3rd order diffracted light has the maximum amount of diffracted light,
  • the step surfaces present in the step periodic structure are classified into three types: a step surface L having a maximum length, a step surface S having a minimum length, and a step surface M having an intermediate length. There are two or three step surfaces S having the minimum length between the step surface L having the maximum length and the step surface M having the intermediate length.
  • the present inventor has found that in a step periodic structure in which a plurality of 7-step staircase structures are arranged, the step surface existing in the step periodic structure has a step surface L having the maximum length and a length of the step surface.
  • the length is classified into three types, that is, the minimum step surface S and the intermediate step surface M, and the length is between the maximum step surface L and the intermediate step surface M. 2 or 3 can reduce the diffraction efficiency of the ⁇ 2nd order diffracted light, which is unnecessary light generated when a light beam having the wavelength ⁇ 1 is incident.
  • Information can be appropriately recorded / reproduced on both the first information recording surface and the second information recording surface of the optical disc, and the diffraction efficiency of the + third-order diffracted light, which is the main light when a light beam with wavelength ⁇ 3 is incident, is increased.
  • Information recording on the third optical disc It was found that information can be recorded / reproduced appropriately on the recording surface.
  • the length of the step surface refers to the length in the optical axis direction.
  • the diffraction element according to claim 4 is the invention according to any one of claims 1 to 3, wherein the step surface existing in the step periodic structure has a step surface L having a maximum length and a minimum length.
  • the stepped surface S and the stepped surface M having an intermediate length are classified into three types, and the three types of stepped surfaces and the wavelength ⁇ 1 satisfy the following expressions.
  • ⁇ L is the phase difference of the wavelength ⁇ 1 generated by the step surface L having the maximum length
  • ⁇ S is the phase difference of the wavelength ⁇ 1 generated by the step surface S having the minimum length
  • ⁇ M is the long Is the phase difference of the wavelength ⁇ 1 generated by the intermediate stepped surface M.
  • ⁇ S ⁇ S -ROUND ( ⁇ S )
  • ⁇ S (d S / ⁇ 1) ⁇ (n1-1)
  • ⁇ M ⁇ M -ROUND ( ⁇ M )
  • ⁇ M (d M / ⁇ 1) ⁇ (n1-1) Refractive index of the diffraction element at the wavelength ⁇ 1 ( ⁇ m): n1
  • the step surface existing in the step periodic structure has a step surface L having a maximum length and a minimum length.
  • the refractive index n1 of the diffractive element at the wavelength ⁇ 1 and the three types of stepped surfaces are classified into the following formulas: 6.00 ⁇
  • the diffractive element according to claim 6 is the invention according to any one of claims 1 to 3, wherein the step surface existing in the step periodic structure has a step surface L having a maximum length and a minimum length.
  • the refractive index n1 of the diffractive element at the wavelength ⁇ 1 and the three types of stepped surfaces are classified into the following formulas: 6.40 ⁇
  • the diffractive element according to claim 7 is the diffractive element according to any one of claims 1 to 6, wherein the step surface existing in the step periodic structure has a step surface L having a maximum length and a minimum length.
  • the step surface S and the step surface M having an intermediate length the number of the step surfaces L having the maximum length, the number of the step surfaces S having the minimum length, and the length
  • the ratio of the number of intermediate step surfaces M is approximately 1: 5: 1.
  • the diffractive element according to an eighth aspect is the invention according to any one of the first to seventh aspects, wherein the step surface existing in the step periodic structure has a step surface L having a maximum length and a minimum length.
  • the step surface S and the step surface M having an intermediate length are classified into three types, and the step surface S having the smallest length and the step surface M having the intermediate length have the same sign of length.
  • the step surface L having the maximum length and the step surface S having the minimum length are characterized by having different length signs. Note that “the signs of the lengths are different from each other” means that one of the step surfaces to be compared faces the optical axis and the other faces the opposite of the optical axis.
  • a diffraction element is characterized in that, in the invention according to any one of the first to eighth aspects, the following expression is satisfied.
  • 1
  • 2
  • 3
  • a diffractive element according to claim 10 is characterized in that, in the invention according to any one of claims 1 to 9, the diffractive element is integrated with the objective optical system. “Integrated” means when the diffractive element and the objective optical system are integrated via another member such as a lens frame, or when the diffractive structure is formed on a single objective optical system (objective lens) Including.
  • An optical pickup device includes the diffractive element according to any one of the first to tenth aspects.
  • the optical pickup device includes at least a first light source, a second light source, and a third light source. Furthermore, the optical pickup device of the present invention condenses the first light flux on the information recording surface of the first optical disc, condenses the second light flux on the information recording surface of the second optical disc, and causes the third light flux to be third. It has a condensing optical system for condensing on the information recording surface of the optical disc.
  • the optical pickup device of the present invention includes a light receiving element that receives reflected light from the information recording surfaces of the first optical disc, the second optical disc, and the third optical disc.
  • the first optical disc has a protective substrate having a thickness of t1 and a first information recording surface, and preferably the protective substrate having a thickness of t1 ′ (t1 ⁇ t1 ′) and the second information recording surface are arranged in the thickness direction. And laminated.
  • the second optical disc has a protective substrate having a thickness of t2 (t1, t1 ′ ⁇ t2) and an information recording surface, and preferably has a thickness of t2 ′ (t1, t1 ′ ⁇ t2 ′ ⁇ t2).
  • a substrate and a second information recording surface are stacked in the thickness direction.
  • the third optical disc has a protective substrate having a thickness t3 (t2 ⁇ t3) and an information recording surface.
  • the first optical disk is preferably a high density optical disk
  • the second optical disk is a DVD
  • the third optical disk is preferably a CD, but is not limited thereto.
  • the first optical disc, the second optical disc, or the third optical disc may be a multi-layer optical disc having a plurality of information recording surfaces.
  • BD means that information is recorded / reproduced by a light beam having a wavelength of about 390 to 415 nm and an objective lens having an NA of about 0.8 to 0.9, and the thickness of the protective substrate is 0.05 to 0.00 mm.
  • BD series optical disc of about 125 mm, and includes a BD having only a single information recording layer, a BD having two or more information recording layers, and the like.
  • a DVD is a DVD series optical disc in which information is recorded / reproduced by an objective optical system having an NA of about 0.60 to 0.67, and a protective substrate has a thickness of about 0.6 mm.
  • a CD is a CD series optical disc in which information is recorded / reproduced by an objective optical system having an NA of about 0.45 to 0.51 and a protective substrate has a thickness of about 1.2 mm. It is a generic term and includes CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW and the like. As for the recording density, the recording density of BD is the highest, followed by the order of DVD and CD.
  • the present invention is not limited to this.
  • the first light source, the second light source, and the third light source are preferably laser light sources.
  • the laser light source a semiconductor laser, a silicon laser, or the like can be preferably used.
  • the wavelength ⁇ 3 ( ⁇ 3> ⁇ 2) is defined by the following conditional expressions (5), (6), 1.5 ⁇ ⁇ 1 ⁇ 2 ⁇ 1.7 ⁇ ⁇ 1 (5) 1.9 ⁇ ⁇ 1 ⁇ 3 ⁇ 2.1 ⁇ ⁇ 1 (6) It is preferable to satisfy.
  • the first wavelength ⁇ 1 of the first light source is 390 nm or more and 420 nm or less.
  • the second wavelength ⁇ 2 of the second light source is preferably 570 nm or more and 680 nm or less, more preferably 630 nm or more and 670 nm or less, and the third wavelength ⁇ 3 of the third light source is preferably 750 nm or more and 880 nm or less, and more Preferably, it is 760 nm or more and 820 nm or less.
  • the first light source, the second light source, and the third light source may be unitized.
  • the unitization means that the first light source and the second light source are fixedly housed in one package, for example. However, the unitization is not limited to this, and the two light sources are fixed so that the aberration cannot be corrected. Is widely included.
  • a light receiving element to be described later may be packaged.
  • a photodetector such as a photodiode is preferably used.
  • Light reflected on the information recording surface of the optical disc enters the light receiving element, and a read signal of information recorded on each optical disc is obtained using the output signal.
  • it detects the change in the light amount due to the change in the shape and position of the spot on the light receiving element, performs focus detection and track detection, and moves the objective optical system for focusing and tracking based on this detection I can do it.
  • the light receiving element may comprise a plurality of photodetectors.
  • the light receiving element may have a main photodetector and a sub photodetector.
  • two sub photodetectors are provided on both sides of a photodetector that receives main light used for recording and reproducing information, and the sub light for tracking adjustment is received by the two sub photodetectors. It is good also as a simple light receiving element.
  • the light receiving element may have a plurality of light receiving elements corresponding to the respective light sources.
  • the optical pickup device has a monitoring means for monitoring the intensity of the light beam before the light beam emitted from the light source enters the objective optical system.
  • a monitor means can detect the intensity of the light beam emitted from the light source, but does not detect the intensity of the light beam after passing through the objective optical system. It cannot be detected. Therefore, the effect of the present invention becomes more remarkable in the optical pickup device having such a monitoring means.
  • the condensing optical system of the optical pickup device includes an objective optical system.
  • the condensing optical system may include only the objective optical system, but may include a coupling lens such as a collimator lens in addition to the objective optical system.
  • the coupling lens is a single lens or a lens group that is disposed between the objective optical system and the light source and changes the divergence angle of the light beam.
  • the collimating lens is a kind of coupling lens, and is a lens that emits light incident on the collimating lens as parallel light.
  • the condensing optical system has an optical element such as a diffractive optical element that divides the light beam emitted from the light source into a main light beam used for recording and reproducing information and two sub light beams used for tracking and the like.
  • the objective optical system refers to an optical system that is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing the light beam emitted from the light source onto the information recording surface of the optical disk.
  • the objective optical system is an optical system which is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing a light beam emitted from the light source on the information recording surface of the optical disk, and further includes an actuator
  • An optical system that can be integrally displaced at least in the optical axis direction.
  • the objective optical system may be composed of two or more plural lenses or may be a single lens, but is preferably a single lens.
  • the objective optical system When the objective optical system has a plurality of lenses, it may be a combination of a flat optical element having a diffractive structure and an aspheric lens (which may or may not have a diffractive structure).
  • the refractive surface is preferably an aspherical surface.
  • the base surface on which the diffractive structure is provided is preferably an aspherical surface.
  • the objective optical system is preferably a plastic lens.
  • the resin material it is preferable to use a cyclic olefin-based resin material, and among the cyclic olefin-based materials, the refractive index at a temperature of 25 ° C. with respect to a wavelength of 405 nm is in the range of 1.53 to 1.60, The refractive index change rate dN / dT (° C. ⁇ 1 ) with respect to a wavelength of 405 nm accompanying a temperature change within a temperature range of 5 ° C. to 70 ° C.
  • the coupling lens is preferably a plastic lens.
  • a resin material are Apel manufactured by Mitsui Chemicals, Inc. and ZEONEX manufactured by ZEON Corporation, which are preferable because they are excellent in resistance to light in the wavelength region near 405 nm.
  • At least one optical surface of the objective optical system has a central region and a peripheral region around the central region. More preferably, at least one optical surface of the objective optical system has an outermost peripheral region around the peripheral region. By providing the outermost peripheral region, it becomes possible to perform recording and / or reproduction with respect to the high-density optical disc more appropriately.
  • the central region is preferably a region including the optical axis of the objective optical system, but may be a region not including the optical axis. It is preferable that the central region, the peripheral region, and the most peripheral region are provided on the same optical surface.
  • the central region, the peripheral region, and the most peripheral region are preferably provided concentrically around the optical axis on the same optical surface.
  • a diffractive structure is provided in the central region and the peripheral region of the objective optical system.
  • the outermost peripheral region may be a refractive surface, or a diffractive structure may be provided in the outermost peripheral region.
  • the central region, the peripheral region, and the outermost peripheral region are preferably adjacent to each other, but there may be a slight gap between them.
  • the diffractive structure referred to in this specification is a general term for structures that add an optical path difference and / or a phase difference to an incident light beam.
  • the diffractive structure has a step, preferably a plurality of steps. This step adds an optical path difference and / or phase difference to the incident light flux.
  • the optical path difference added by the diffractive structure 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.
  • the steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis.
  • the diffractive structure can have various cross-sectional shapes (cross-sectional shapes on the plane including the optical axis), and the cross-sectional shape including the optical axis is roughly classified into a blazed structure and a staircase structure.
  • the blazed structure is a sawtooth-shaped cross section including the optical axis of the objective optical system having a diffraction groove.
  • the optical pickup device includes a plurality of step surfaces ST extending along a substantially optical axis direction (vertical direction in the drawing) of the optical pickup device, and a slope CP connecting adjacent step surfaces.
  • the upper side is the light source side and the lower side is the photodetector side, and a diffraction groove is formed on a parallel plate.
  • the length of one blazed unit in the direction perpendicular to the optical axis is referred to as a pitch P (see FIGS. 2A and 2B).
  • the length in the optical axis direction of the step surface parallel to the optical axis of the blaze is referred to as a step amount B (or sometimes referred to as a blaze height h) (see FIG. 2A).
  • the staircase structure is a structure in which the cross-sectional shape including the optical axis of an optical element having a diffraction groove is a small step (referred to as a step unit). More specifically, it has a plurality of step surfaces ST extending substantially along the optical axis direction of the optical pickup device, and a plurality of terrace surfaces TR intersecting with the step surfaces.
  • the stepped structure shown in FIG. 2C has three or more (seven in the figure) step surfaces ST and three or more (seven in the figure) terrace surfaces TR, and adjacent terrace surfaces TR.
  • the step periodic structure is formed by arranging a plurality of step units, which are sequentially shifted in the optical axis direction of the optical pickup device, along the direction intersecting the optical axis of the optical pickup device (left-right direction in the figure). It will be. That is, in particular, the staircase structure with three or more terrace surfaces TR has a small step surface ST and a large step surface LST. In this specification, when there are three terrace surfaces, it is referred to as a three-step structure, and when there are seven terrace surfaces, it is referred to as a seven-step structure.
  • the diffractive structure shown in FIG. 2D is a configuration in which the terrace surfaces TR sandwiched between the end portions of adjacent step surfaces ST and ST extending substantially in the optical axis direction are connected to each other.
  • the terrace surfaces TR and TR are parallel to each other and shifted in the optical axis direction.
  • a structure in which one or more terraces TR are shifted in the direction of lowering by an equal amount from the highest side is also a staircase structure.
  • the length of one staircase unit in the direction perpendicular to the optical axis is referred to as pitch P (see FIGS. 2C and 2D).
  • the lengths of the step surfaces LST and ST along the optical axis direction are referred to as step amounts B1 and B2.
  • a large step amount B1 (kth step amount) and a small step amount B2 exist (see FIG. 2C). At least one of the quantities B2 is changed.
  • B1 B2.
  • the diffractive structure is preferably a structure in which a certain unit shape is periodically repeated.
  • unit shape is periodically repeated” naturally includes shapes in which the same shape is repeated in the same cycle.
  • the unit shape that is one unit of the cycle has regularity, and the shape in which the cycle gradually increases or decreases gradually is also included in the “unit shape is periodically repeated”.
  • the sawtooth shape as a unit shape is repeated. As shown in FIG. 2 (a), the same sawtooth shape may be repeated.
  • the diffractive structure has a stepped structure
  • the diffractive structure preferably has a plurality of concentric annular zones around the optical axis. Each annular zone is preferably separated by a step. Further, the diffractive structure is preferably a type of structure in which a step-like pattern having a cross-sectional shape including the optical axis is repeated. A plurality of diffraction structures may be superimposed on the same region. “Superimposition” means literally overlapping. In this specification, when a diffractive structure and another diffractive structure are provided on different optical surfaces, or even if a diffractive structure and another diffractive structure are on the same optical surface, different regions are used. In the case where there is no overlapping region, it is not superposition in this specification.
  • At least a first diffractive structure is provided in the central region of the objective optical system. Further, it is preferable that at least the second diffractive structure is provided in the peripheral region of the objective optical system.
  • the diffraction order of the diffracted light having the maximum diffracted light quantity is M
  • the first diffraction Of the diffracted light generated when the second light flux of wavelength ⁇ 2 from the second light source is incident on the structure is N
  • the first diffractive structure is Of the diffracted light generated when the third light flux of wavelength ⁇ 3 is incident, when the diffraction order of the diffracted light having the maximum diffracted light amount is O, at least one of M, N, and O is positive, And at least one of M, N, and O is negative.
  • the first diffractive structure is preferably a compatible structure for different optical disks.
  • Examples of preferable combinations of M, N, and O include the following.
  • the first diffractive structure is the diffractive structure according to the present invention.
  • the diffraction order of the diffracted light having the maximum diffracted light quantity is P
  • the second diffraction Of the diffracted light generated when the second light flux of wavelength ⁇ 2 from the second light source is incident on the structure it is preferable that P ⁇ Q, where Q is the diffraction order of the diffracted light having the maximum diffracted light quantity.
  • This second optical path difference providing structure is also preferably a structure for compatibility with different optical disks.
  • the objective optical system has a diffractive structure for temperature characteristic correction that corrects an aberration caused by a temperature change of the objective optical system.
  • the “diffractive structure for correcting temperature characteristics” refers to a diffractive structure that corrects aberrations that occur when a temperature change occurs. For example, the temperature of the first light source, the second light source, and the third light source increases when the temperature rises. This is a diffractive structure having a function of making the spherical aberration in the direction of insufficient correction when is extended.
  • this diffractive structure for temperature characteristic correction is provided so as to overlap with the first diffractive structure in the central region, it is preferable that this is the third diffractive structure.
  • the diffractive structure for temperature characteristic correction is provided so as to overlap the second diffractive structure in the peripheral region, it is preferable that this is the fourth diffractive structure.
  • the objective optical system has a most peripheral region as described later and a diffractive structure for temperature characteristic correction is provided in the most peripheral region, this is preferably the fifth diffractive structure.
  • the diffraction order of the diffracted light having the maximum diffracted light amount is R, and the second light beam is incident on the third diffractive structure.
  • the diffraction order of the diffracted light having the maximum diffracted light amount is S, and the diffracted light having the maximum diffracted light amount among the diffracted light generated when the third light beam enters the third diffractive structure is diffracted.
  • the diffraction order of the diffracted light having the maximum diffracted light quantity is V
  • the second light flux is incident on the fourth diffractive structure.
  • the diffraction order of the diffracted light having the maximum amount of diffracted light is denoted by W.
  • (V, W) (+ 10, +6), (+5, +3) or (+2, +1).
  • the diffractive structure provided in the central region of the objective optical system and the diffractive structure provided in the peripheral region of the objective optical system may be provided on different optical surfaces of the objective optical system. It is preferable to be provided on the surface. Providing them on the same optical surface is preferable because it makes it possible to reduce eccentricity errors during manufacturing.
  • the diffractive structure is preferably provided on the light source side surface of the objective optical system rather than the surface of the objective optical system on the optical disc side.
  • the objective optical system may further include a diffractive structure for flare out of the third light flux in the peripheral region.
  • the diffractive structure for flare out the diffraction order of the diffracted light having the maximum diffracted light amount among the diffracted light generated when the first light beam with the wavelength ⁇ 1 from the first light source is incident on the diffractive structure is denoted by A.
  • the diffraction order of the diffracted light having the maximum diffracted light amount is B, and the wavelength ⁇ 3 from the third light source is applied to the diffractive structure.
  • the third light flux that has passed through the flaring diffraction structure does not converge on the information recording surface of the third optical disk.
  • the objective optical system condenses the first light beam, the second light beam, and the third light beam that pass through the central region of the objective optical system so as to form a condensing spot. Further, when the thicknesses t1 and t1 ′ of the protective substrate of the first optical disc are different from the thickness t2 of the protective substrate of the second optical disc, the first diffractive structure has the first light flux and the second light flux that have passed through the first diffractive structure. On the other hand, due to the spherical aberration generated due to the difference between the thickness t1, t1 ′ of the protective substrate of the first optical disc and the thickness t2 of the protective substrate of the second optical disc, and / or the difference between the wavelengths of the first light flux and the second light flux.
  • the first diffractive structure has a thickness t1, t1 ′ of the protective substrate of the first optical disc and a thickness t3 of the protective substrate of the third optical disc with respect to the first light flux and the third light flux that have passed through the first diffractive structure. It is preferable to correct spherical aberration caused by the difference between the first and third light fluxes and / or spherical aberration caused by the difference between the first light flux and the third light flux.
  • the objective optical system condenses the first light flux and the second light flux that pass through the peripheral area of the objective optical system so as to form a condensed spot.
  • the second diffractive structure has the first light flux and the second light flux that have passed through the second diffractive structure.
  • the spherical aberration generated due to the difference between the thickness t1, t1 ′ of the protective substrate of the first optical disc and the thickness t2 of the protective substrate of the second optical disc and / or the difference between the wavelengths of the first light flux and the second light flux. It is preferable to correct the generated spherical aberration.
  • the third light flux that has passed through the peripheral region having the diffractive structure for flare out is not used for recording and / or reproduction of the third optical disc. It is preferable that the third light flux that has passed through the peripheral region does not contribute to the formation of a focused spot on the information recording surface of the third optical disc. That is, the third light flux that passes through the peripheral area of the objective lens preferably forms a flare on the information recording surface of the third optical disc. In the spot formed on the information recording surface of the third optical disc by the third light flux that has passed through the objective lens, the spot center portion having a high light amount density and the light amount density in order from the optical axis side (or the spot center portion) to the outside.
  • the spot middle part lower than the spot center part and a spot peripheral part whose light intensity is higher than the spot middle part and lower than the spot center part.
  • the center portion of the spot is used for recording and / or reproducing information on the optical disc, and the spot intermediate portion and the spot peripheral portion are not used for recording and / or reproducing information on the optical disc.
  • this spot peripheral part is called flare. That is, the third light flux that has passed through the peripheral area of the objective optical system forms a spot peripheral portion on the information recording surface of the third optical disc.
  • the spot formed on the information recording surface of the second optical disc has a spot central portion, a spot intermediate portion, and a spot peripheral portion.
  • a third diffractive structure for correcting an aberration caused by a temperature change of the objective diffractive structure is superimposed on the first diffractive structure, and the objective optic is applied to the second diffractive structure.
  • a diffractive structure may be provided so that the third light flux that has passed through the peripheral region does not form a flare on the information recording surface of the third optical disc.
  • the objective optical system When the objective optical system has the outermost peripheral area, the objective optical system can record and / or reproduce information on the information recording surface of the first optical disc by using the first light flux passing through the outermost peripheral area of the objective optical system. Condensed to Further, it is preferable that the spherical aberration of the first light flux that has passed through the most peripheral area is corrected during recording and / or reproduction of the first optical disk.
  • the second light flux that has passed through the outermost peripheral area is not used for recording and / or reproduction of the second optical disk, and the third light flux that has passed through the outermost peripheral area is recorded and / or recorded on the third optical disk.
  • An embodiment that is not used for reproduction is included. It is preferable that the second light flux and the third light flux that have passed through the outermost peripheral region do not contribute to the formation of a condensed spot on the information recording surfaces of the second optical disc and the third optical disc, respectively. That is, when the objective optical system has the outermost peripheral region, it is preferable that the third light flux passing through the outermost peripheral region of the objective optical system forms a flare on the information recording surface of the third optical disc.
  • the third light flux that has passed through the outermost peripheral region of the objective optical system forms a spot peripheral portion on the information recording surface of the third optical disc.
  • the second light flux that passes through the most peripheral area of the objective optical system preferably forms a flare on the information recording surface of the second optical disc.
  • the second light flux that has passed through the outermost peripheral region of the objective optical system preferably forms a spot peripheral portion on the information recording surface of the second optical disc.
  • the second light flux and the third light flux that have passed through the most peripheral area may not form flare on the information recording surfaces of the second optical disk and the third optical disk.
  • an annular zone with a small pitch width may occur.
  • the pitch width refers to the width in the direction orthogonal to the optical axis of the optical element having an annular structure and an optical path difference providing structure.
  • this ring width is less than 5 ⁇ m, even if this ring zone is cut or filled, the optical performance is not greatly affected.
  • the ring zone width is less than 5 ⁇ m, even if the ring zone with this small ring zone width is cut, the optical performance is not greatly affected.
  • the pitch width of the step is not too small. Therefore, when an annular zone having a pitch width of less than 5 ⁇ m is generated when the diffractive structure is designed, it is preferable to obtain a final diffractive structure by removing the annular zone having a zone width of less than 5 ⁇ m. . If the ring zone with a ring width less than 5 ⁇ m is convex, it can be removed by cutting the ring zone. If the ring zone with a ring width less than 5 ⁇ m is concave, fill the ring zone. Just remove it.
  • the ring width of the optical system is 5 ⁇ m or more.
  • the value of (step amount / ring zone width) is 1 or less in all ring zones of the diffractive structure. It is 8 or less. More preferably, the value of (level difference / ring zone width) is preferably 1 or less, and more preferably 0.8 or less, in all the annular zones of all diffractive structures.
  • An objective lens necessary for reproducing and / or recording information on the second optical disk is set to NA1 on the image side numerical aperture of the objective optical system necessary for reproducing and / or recording information on the first optical disk.
  • Is NA2 (NA1 ⁇ NA2), and the image side numerical aperture of the objective optical system necessary for reproducing and / or recording information on the third optical disk is NA3 (NA2> NA3).
  • NA1 is preferably 0.8 or more and 0.9 or less, or preferably 0.55 or more and 0.7 or less.
  • NA1 is preferably 0.85.
  • NA2 is preferably 0.55 or more and 0.7 or less.
  • NA2 is preferably 0.60.
  • NA3 is preferably 0.4 or more and 0.55 or less.
  • NA3 is preferably 0.45 or 0.53.
  • the boundary between the central region and the peripheral region of the objective optical system is 0.9 ⁇ NA 3 or more and 1.2 ⁇ NA 3 or less (more preferably 0.95 ⁇ NA 3 or more, 1.15 ⁇ It is preferably formed in a portion corresponding to the range of NA3 or less. More preferably, the boundary between the central region and the peripheral region of the objective lens is formed in a portion corresponding to NA3. Further, the boundary between the peripheral area and the most peripheral area of the objective optical system is 0.9 ⁇ NA 2 or more and 1.2 ⁇ NA 2 or less (more preferably 0.95 ⁇ NA 2 or more, 1) when the second light flux is used. .15 ⁇ NA2 or less) is preferable.
  • the boundary between the peripheral region and the most peripheral region of the objective lens is formed in a portion corresponding to NA2.
  • the outer boundary of the outermost peripheral region of the objective optical system is 0.9 ⁇ NA1 or more and 1.2NA1 or less (more preferably 0.95 ⁇ NA1 or more and 1.15 ⁇ NA1 or less) when the first light beam is used. ) Is preferably formed in a portion corresponding to the range. More preferably, the outer boundary of the outermost peripheral region of the objective optical system is formed in a portion corresponding to NA1.
  • the spherical aberration has at least one discontinuous portion.
  • the discontinuous portion has a range of 0.9 ⁇ NA 3 or more and 1.2 ⁇ NA 3 or less (more preferably 0.95 ⁇ NA 3 or more and 1.15 ⁇ NA 3 or less) when the third light flux is used. It is preferable that it exists in.
  • the spherical aberration has at least one discontinuous portion.
  • the discontinuous portion is in a range of 0.9 ⁇ NA 2 or more and 1.2 ⁇ NA 2 or less (more preferably 0.95 ⁇ NA 2 or more and 1.1 ⁇ NA 2 or less) when the second light flux is used. It is preferable that it exists in.
  • NA2 it is preferable that the absolute value of the longitudinal spherical aberration is 0.03 ⁇ m or more, and in NA3, the absolute value of the longitudinal spherical aberration is 0.02 ⁇ m or less. More preferably, in NA2, the absolute value of longitudinal spherical aberration is 0.08 ⁇ m or more, and in NA3, the absolute value of longitudinal spherical aberration is 0.01 ⁇ m or less.
  • NA1 when the second light flux that has passed through the objective lens is condensed on the information recording surface of the second optical disc, NA1 has an absolute value of longitudinal spherical aberration of 0.03 ⁇ m or more, and NA2 exhibits longitudinal spherical aberration.
  • the absolute value is preferably 0.005 ⁇ m or less.
  • An optical disk drive device having the above-described optical pickup device can be incorporated in the optical information recording / reproducing device.
  • the optical disk drive apparatus can hold an optical disk mounted from the optical information recording / reproducing apparatus main body containing the optical pickup apparatus or the like. There are a system in which only the tray is taken out and a system in which the optical disk drive apparatus main body in which the optical pickup device or the like is stored is taken out.
  • the optical information recording / reproducing apparatus using each method described above is generally equipped with the following components, but is not limited thereto.
  • An optical pickup device housed in a housing or the like, a drive source of an optical pickup device such as a seek motor that moves the optical pickup device together with the housing toward the inner periphery or outer periphery of the optical disc, and the optical pickup device housing the inner periphery or outer periphery of the optical disc include a transfer means of an optical pickup device having a guide rail or the like that guides toward the head, a spindle motor that rotates the optical disk, and the like.
  • the former method is provided with a tray that can be held in a state in which an optical disk is mounted and a loading mechanism for sliding the tray, and the latter method has no tray and loading mechanism. It is preferable that each component is provided in a drawer corresponding to a chassis that can be pulled out to the outside.
  • generation of an error signal is suppressed when using a BD having a plurality of information recording surfaces stacked in the thickness direction and / or when using a DVD having a plurality of information recording surfaces stacked in the thickness direction.
  • an objective lens for an optical pickup device capable of increasing the light utilization efficiency when using a CD, and an optical pickup device using the objective lens.
  • FIG. 1 is a cross-sectional view showing a stepped structure of Example 1.
  • FIG. 1 shows the state of the wave front when the light beam of wavelength (lambda) 1 is entered into the objective optical system of Example 1.
  • FIG. It is a figure which shows the state of the wave front when the light beam of wavelength (lambda) 2 is entered into the objective optical system of Example 1.
  • FIG. It is sectional drawing which shows the step type structure of Example 2.
  • FIG. 3 schematically shows a configuration of the optical pickup apparatus PU1 of the present embodiment that can appropriately record and / or reproduce information on a two-layer type BD, DVD, and CD, which are different optical disks.
  • FIG. 3 Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device.
  • the first optical disc is a BD
  • the second optical disc is a DVD
  • the third optical disc is a CD.
  • the present invention is not limited to the present embodiment.
  • the optical pickup device PU1 emits a laser beam (first beam) of 405 nm that is emitted when recording / reproducing information with respect to the objective optical system OBJ, aperture ST, collimator lens CL, dichroic prism PPS, and BD.
  • 1 semiconductor laser LD1 (1st light source), 1st light receiving element PD1 which receives the reflected light beam from the information recording surface RL1 of BD, laser module LM, etc.
  • the laser module LM also emits a 658 nm laser beam (second beam) when recording / reproducing information on a DVD and emits a 658 nm laser beam (second beam), and a CD.
  • a third semiconductor laser EP2 (third light source) that emits a 785 nm laser beam (third beam) when recording / reproducing information and a second beam that receives a reflected beam from the information recording surface RL2 of the DVD.
  • the objective optical system OBJ of the present embodiment is a single lens made of polyolefin plastic, and according to the type of light beam passing therethrough, as shown in FIG. 4, a central region CN including the optical axis and its surroundings Can be divided into a peripheral region MD of the second peripheral region MD and a peripheral region OT around the peripheral region MD.
  • a first diffractive structure is formed in the central region of the optical surface on the light source side (or on the optical disc side).
  • the first diffractive structure has seven step surfaces extending substantially parallel to the optical axis of the objective optical system OBJ and seven terrace surfaces intersecting the step surface, and adjacent terrace surfaces of the objective lens OBJ.
  • a predetermined amount of light is emitted from the fourth to seventh or fifth to seventh terrace surfaces counted from the terrace surface closest to the center of the objective optical system OBJ. It includes a step periodic structure in which a plurality of step units shifted to the center side of the objective optical system OBJ along the axial direction are arranged along the direction intersecting the optical axis of the objective lens OBJ.
  • the diffraction order of the diffracted light having the maximum diffracted light amount is M
  • the first Of the diffracted light generated when the second light beam having the wavelength ⁇ 2 from the laser module LM is incident on the optical path difference providing structure the diffraction order of the diffracted light having the maximum diffracted light quantity is N
  • the first optical path difference providing structure is provided.
  • the second diffraction structure and the fourth diffraction structure are superimposed.
  • the diffraction order of the diffracted light having the maximum diffracted light amount is P
  • the second light flux having the wavelength ⁇ 2 is input to the second diffractive structure.
  • the diffraction order of the diffracted light having the maximum diffracted light amount is V
  • the fourth diffractive structure has the second wavelength ⁇ 2.
  • W is the diffraction order of the diffracted light having the maximum amount of diffracted light.
  • the diffraction order of the diffracted light having the maximum diffracted light amount is set to 0.
  • the diffracted light generated when the second light flux having the wavelength ⁇ 2 from the laser module LM is incident on the diffractive structure is set to 0.
  • the diffraction order of the diffracted light having the maximum diffracted light quantity is set to 0.
  • the diffracted light generated when the third light flux having the wavelength ⁇ 3 is incident is ⁇ 1.
  • the divergent light beam passes through the dichroic prism PPS and is made into a weak finite convergent light beam or a parallel light beam by the collimating lens CL, and then the diameter of the light beam is regulated by the stop ST, and the objective optical system OBJ has a thickness of 0.05 mm. It becomes a spot formed on the information recording surface RL1 of the BD via the substrate PL1.
  • the reflected light beam modulated by the information pits on the information recording surface RL1 is transmitted again through the objective optical system OBJ and the aperture stop ST, then converged by the collimating lens CL, transmitted through the dichroic prism PPS, and then the first light receiving light. It converges on the light receiving surface of the element PD1. Then, using the output signal of the first light receiving element PD1, the information recorded on the BD can be read by causing the objective optical system OBJ to be focused or tracked by the biaxial actuator AC.
  • the collimating lens CL When recording / reproducing information on the second information recording surface RL1 ′ of the BD, the collimating lens CL is displaced to a second optical axis direction position different from the first optical axis direction position, and the blue-violet semiconductor laser LD1
  • the reflected light beam modulated by the information pits on the information recording surface RL1 ′ is again transmitted through the objective optical system OBJ and the aperture stop ST, then is converged by the collimating lens CL, and is transmitted through the dichroic prism PPS. It converges on the light receiving surface of the light receiving element PD1. Then, using the output signal of the first light receiving element PD1, the information recorded on the BD can be read by causing the objective optical system OBJ to be focused or tracked by the biaxial actuator AC.
  • the collimating lens CL When recording / reproducing information on the information recording surface RL2 of the DVD, the collimating lens CL is displaced to the first optical axis direction position or the second optical axis direction position, and the second light beam emitted from the red semiconductor laser EP1.
  • the light beam condensed by the central region and the peripheral region of the objective optical system OBJ (the light beam that has passed through the most peripheral region is flared and forms a spot peripheral part) is a protective substrate PL2 having a thickness of 0.6 mm.
  • the reflected light beam modulated by the information pits on the information recording surface RL2 is transmitted again through the objective optical system OBJ and the aperture stop ST, then converged by the collimating lens CL, reflected by the dichroic prism PPS, and then the prism. After being reflected twice in the PS, it converges on the second light receiving element DS1.
  • the information recorded on the DVD can be read using the output signal of the second light receiving element DS1.
  • the collimating lens CL When recording / reproducing information on the information recording surface RL3 of the CD, the collimating lens CL is displaced to the first optical axis direction position or the second optical axis direction position, and the third laser beam emitted from the infrared semiconductor laser EP2 is used.
  • the light beam collected by the central region of the objective optical system OBJ becomes a spot formed on the information recording surface RL3 of the CD via the protective substrate PL3 having a thickness of 1.2 mm.
  • the light beam outside the central region is shielded by a dichroic filter (not shown) arranged in front of the objective optical system OBJ and does not enter the peripheral region and the most peripheral region of the objective lens OBJ.
  • the reflected light beam modulated by the information pits on the information recording surface RL3 again passes through the objective optical system OBJ and the aperture stop ST, then becomes a convergent light beam by the collimating lens CL, is reflected by the dichroic prism PPS, and then is reflected by the prism. And then converges to the third light receiving element DS2.
  • the information recorded on the CD can be read using the output signal of the third light receiving element DS2.
  • the objective optical system described here is an example in which the diffraction element of the present invention and the objective optical system are integrated. Note that, in the cross-sectional views of the comparative example and the example, the sign of the diffraction order is defined as “+” when the light beam incident along the horizontal optical axis approaches the optical axis, and “ ⁇ ” when separated from the optical axis.
  • the step amount di is defined as + in the direction toward the right side (side away from the center of the objective optical system) from the terrace surface adjacent to the upper side (the optical axis direction outer side),
  • the direction toward the left side (side closer to the center of the objective optical system) from the upper adjacent terrace surface is defined as ⁇ .
  • the sign of the blaze height h is + for the direction toward the right side from the upper adjacent slope, and ⁇ for the direction toward the left side from the upper adjacent slope.
  • the reference numerals described after the numerical values of the step amount di and the blaze height h represent the step amount di and the sign of the blaze height h as described above.
  • the step-like structures of the following comparative examples and examples are shown as being formed on a parallel plate for easy understanding, but when formed on a single objective optical system, the aspheric shape is used. Accordingly, the terrace surface is shifted in the optical axis direction.
  • the comparative example is an objective optical system having an annular diffraction groove in the center region, which is formed by periodically repeating a seven-step stepped structure having seven terrace surfaces as one step unit.
  • FIG. 5 is a sectional view in the optical axis direction of the objective optical system of the comparative example.
  • the length of the first to sixth step surfaces 0.839 ⁇ m
  • the length of the seventh step surface ⁇ 5.032 ⁇ m.
  • the diffraction efficiency of the ⁇ 1st order diffracted light that is the main light of the first light flux is 89.2%
  • the diffraction efficiency of the ⁇ 2nd order diffracted light that is unnecessary light is 1.4%
  • the + 2nd order diffracted light of the second light flux is The diffraction efficiency is 67.3%
  • the diffraction efficiency of the + 3rd order diffracted light of the third light beam is 52.4%. Therefore, the light intensity of unnecessary light is relatively high, and an error signal may be generated when information is recorded / reproduced on the first information recording surface of the BD.
  • Example 1 Similar to the comparative example, Example 1 is based on a seven-step staircase structure with seven terrace surfaces, and the fourth to seventh terrace surfaces counted from the terrace surface TRO closest to the center of the objective optical system.
  • Table 2 shows the shape data of the objective optical system provided in the central region.
  • FIG. 6 is a cross-sectional view of the objective lens of Example 1 in the optical axis direction.
  • the length of the first and second step surfaces is 0.832 ⁇ m
  • the length of the third step surface is ⁇ 6.399 ⁇ m
  • the fourth to sixth steps The length of the step surface is 0.832 ⁇ m
  • the length of the seventh step surface is 2.241 ⁇ m.
  • there are two step surfaces (long) between the step surface d 3 having the maximum length among the step surfaces between adjacent terrace surfaces and the step surface d 7 having the second largest length. D 1 , d 2 ) are arranged.
  • the step periodic structure of the first embodiment (same as the second embodiment described later) also has a step cycle that is periodically repeated with a seven-step staircase structure extending over adjacent step units as one unit. It can also be called a structure.
  • step Since the wavefronts of the light beams that have passed through the first terrace surface in the unit and the first terrace surface in the adjacent step unit are shifted by ⁇ 1 ⁇ ⁇ 1 wavelength ( ⁇ 1j ⁇ 1)
  • the diffraction order of the first light beam that has passed through the staircase structure is ⁇ 1.
  • the order is + 2nd order.
  • step surfaces existing in the step periodic structure are classified into three types, that is, the step surface L having the maximum length, the step surface S having the minimum length, and the step surface M having the intermediate length.
  • the three types of step surfaces and the wavelength ⁇ 1 satisfy the following expression.
  • ⁇ L is the phase difference of the wavelength ⁇ 1 generated by the step surface L having the maximum length
  • ⁇ S is the phase difference of the wavelength ⁇ 1 generated by the step surface S having the minimum length
  • ⁇ M is the long Is the phase difference of the wavelength ⁇ 1 generated by the intermediate stepped surface M.
  • ⁇ S ⁇ S -ROUND ( ⁇ S )
  • ⁇ S (d S / ⁇ 1) ⁇ (n1-1)
  • ⁇ M ⁇ M -ROUND ( ⁇ M )
  • ⁇ M (d M / ⁇ 1) ⁇ (n1-1) Refractive index of the diffraction element at the wavelength ⁇ 1 ( ⁇ m): n1
  • the shift amount ⁇ ⁇ 7.230 ⁇ m
  • the step surface L having the maximum step amount between the third terrace surface and the fourth terrace surface is 1
  • the second terrace surface is a step surface M having an intermediate step amount
  • the other step surface S has the smallest step amount
  • d L ⁇ 6.399 ⁇ m
  • d S 0.832 ⁇ m
  • d M 2.241 ⁇ m
  • n1 1.56,
  • a 10
  • the ratio of the number of the step surfaces L having the maximum length, the number of the step surfaces S having the minimum length, and the number of the step surfaces M having the intermediate length is 1: 5: 1.
  • the step surface S having the smallest length and the step surface M having the middle length have the same sign (+ and +), and the step surface L having the largest length and the smallest length.
  • the step surfaces S have different length signs (-and +).
  • Example 1 the diffraction efficiency of the ⁇ 1st order diffracted light that is the main light of the first light flux is 92.7%, the diffraction efficiency of the ⁇ 2nd order diffracted light that is unnecessary light is 0.2%, and the + 2nd order diffracted light of the second light flux. Has a diffraction efficiency of 71.6%, and the diffraction efficiency of the + 3rd-order diffracted light of the third light beam is 51.5%.
  • the light intensity of the unnecessary light of the first light flux is reduced, it is possible to suppress the generation of an error signal when recording / reproducing information on the first information recording surface of the BD.
  • the light intensity of the second light beam used when recording / reproducing information on / from the information recording surface of the DVD can be increased.
  • the light intensity of the third light beam used when recording / reproducing information on / from the information recording surface of the CD hardly changes.
  • the fifth to seventh terraces are counted from the terrace surface TRO closest to the center of the objective optical surface based on a seven-step staircase structure having seven terrace surfaces.
  • This is an objective optical system having a groove in the central region, and its shape data is shown in Table 3.
  • FIG. 9 is a sectional view in the optical axis direction of the objective optical system according to the second embodiment.
  • the length of the first to third step surfaces 0.832 ⁇ m
  • the length of the fourth step surface ⁇ 6.399 ⁇ m
  • the length of the step surface is 0.832 ⁇ m
  • the length of the seventh step surface is 2.241 ⁇ m.
  • Example 2 the diffraction efficiency of the ⁇ 1st order diffracted light that is the main light of the first light beam is 92.7%, the diffraction efficiency of the ⁇ 2nd order diffracted light that is unnecessary light is 0.2%, and the second light beam is +2 next time.
  • the diffraction efficiency of the folded light is 71.6%, and the diffraction efficiency of the + 3rd order diffracted light of the third light beam is 51.5%.
  • step surfaces existing in the step periodic structure are classified into three types, that is, the step surface L having the maximum length, the step surface S having the minimum length, and the step surface M having the intermediate length.
  • the three types of step surfaces and the wavelength ⁇ 1 satisfy the following expression.
  • ⁇ L is the phase difference of the wavelength ⁇ 1 generated by the step surface L having the maximum length
  • ⁇ S is the phase difference of the wavelength ⁇ 1 generated by the step surface S having the minimum length
  • ⁇ M is the long Is the phase difference of the wavelength ⁇ 1 generated by the intermediate stepped surface M.
  • ⁇ S ⁇ S -ROUND ( ⁇ S )
  • ⁇ S (d S / ⁇ 1) ⁇ (n1-1)
  • ⁇ M ⁇ M -ROUND ( ⁇ M )
  • ⁇ M (d M / ⁇ 1) ⁇ (n1-1) Refractive index of the diffraction element at the wavelength ⁇ 1 ( ⁇ m): n1
  • the shift amount ⁇ ⁇ 7.230 ⁇ m
  • the step surface L having the maximum step amount between the fourth terrace surface and the fifth terrace surface is 1
  • the other step surface S has the smallest step amount
  • d L ⁇ 6.399 ⁇ m
  • d S 0.832 ⁇ m
  • d M 2.241 ⁇ m
  • n1 1.56,
  • a 10
  • the ratio of the number of the step surfaces L having the maximum length, the number of the step surfaces S having the minimum length, and the number of the step surfaces M having the intermediate length is 1: 5: 1.
  • the step surface S having the smallest length and the step surface M having the middle length have the same sign (+ and +), and the step surface L having the largest length and the smallest length.
  • the step surfaces S have different length signs (-and +).

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

Abstract

L'invention porte sur un élément de diffraction destiné à un dispositif de capture optique et capable d'augmenter le rendement d'utilisation de la lumière lors de l'utilisation d'un CD tout en supprimant l'occurrence d'un signal d'erreur lors de l'utilisation d'un décodeur binaire, possédant une pluralité de surfaces d'enregistrement d'informations empilées dans la direction de l'épaisseur et/ou d'un DVD possédant une pluralité de surfaces d'enregistrement d'informations empilées dans la direction de l'épaisseur, et porte également sur un dispositif de capture optique. Sur la base d'une structure à étages en forme de zone orbiculaire ayant sept étages, les 4ème à 7ème ou les 5ème à 7ème surfaces de dessus comptées à partir d'une extrémité d'une unité à étages étant décalées dans la direction de l'axe optique. Ceci permet de réduire le rendement de diffraction de la lumière de diffraction inférieure au second ordre qui est une lumière inutile se produisant lorsqu'un flux lumineux de longueur d'onde ?1 est incident, permettant ainsi d'enregistrer et/ou de reproduire de manière appropriée les informations soit à partir de la première, soit à partir de la seconde surface d'enregistrement d'informations de premier disque optique. En outre, ceci permet d'augmenter le rendement de diffraction de la lumière de diffraction supérieure au troisième ordre qui est une lumière principale lorsqu'un flux lumineux ayant au moins une longueur d'onde de ?3 est incident, permettant ainsi également d'enregistrer et/ou de reproduire de manière appropriée les informations à partir d'une surface d'enregistrement d'informations d'un troisième disque optique.
PCT/JP2010/065797 2009-09-29 2010-09-14 Elément de diffraction et dispositif de capture optique Ceased WO2011040225A1 (fr)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPWO2013099201A1 (ja) * 2011-12-28 2015-04-30 パナソニックＩｐマネジメント株式会社 光学素子およびこれを備える光ヘッド装置

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2004071134A (ja) * 2002-06-10 2004-03-04 Matsushita Electric Ind Co Ltd 複合対物レンズ、光ヘッド装置、光情報装置、コンピュータ、光ディスクプレーヤー、カーナビゲーションシステム、光ディスクレコーダー、光ディスクサーバー
JP2005515579A (ja) * 2002-01-17 2005-05-26 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 光走査デバイス
JP2010040136A (ja) * 2008-08-07 2010-02-18 Panasonic Corp 複合対物レンズ及び光ヘッド装置及び光情報装置と光ディスクシステム

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2005515579A (ja) * 2002-01-17 2005-05-26 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 光走査デバイス
JP2004071134A (ja) * 2002-06-10 2004-03-04 Matsushita Electric Ind Co Ltd 複合対物レンズ、光ヘッド装置、光情報装置、コンピュータ、光ディスクプレーヤー、カーナビゲーションシステム、光ディスクレコーダー、光ディスクサーバー
JP2010040136A (ja) * 2008-08-07 2010-02-18 Panasonic Corp 複合対物レンズ及び光ヘッド装置及び光情報装置と光ディスクシステム

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPWO2013099201A1 (ja) * 2011-12-28 2015-04-30 パナソニックＩｐマネジメント株式会社 光学素子およびこれを備える光ヘッド装置

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