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WO2009122896A1 - Élément formant objectif optique pour un dispositif de lecture optique, et dispositif de lecture optique - Google Patents

Élément formant objectif optique pour un dispositif de lecture optique, et dispositif de lecture optique Download PDF

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Publication number
WO2009122896A1
WO2009122896A1 PCT/JP2009/055133 JP2009055133W WO2009122896A1 WO 2009122896 A1 WO2009122896 A1 WO 2009122896A1 JP 2009055133 W JP2009055133 W JP 2009055133W WO 2009122896 A1 WO2009122896 A1 WO 2009122896A1
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WIPO (PCT)
Prior art keywords
diffraction efficiency
optical
optical element
order diffraction
temperature characteristic
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PCT/JP2009/055133
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English (en)
Japanese (ja)
Inventor
徹 木村
英司 野村
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 JP2010505550A priority Critical patent/JPWO2009122896A1/ja
Publication of WO2009122896A1 publication Critical patent/WO2009122896A1/fr
Anticipated expiration legal-status Critical
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1353—Diffractive elements, e.g. holograms or gratings
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—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
    • 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 element and an optical pickup device for an optical pickup device, and more particularly to an objective optical element and an optical pickup device for an optical pickup device capable of recording and / or reproducing information on different types of optical disks.
  • HD high density optical disc
  • an optical system for a high-density optical disc and an optical system for a DVD can be selectively switched according to the recording density of the optical disk for recording / reproducing information, but a plurality of optical systems are required, which is disadvantageous for miniaturization and increases the cost.
  • Patent Document 1 discloses an optical pickup device that can realize compatible use of optical disks having different protective substrate thicknesses using a diffraction structure. JP 2005-158217 A
  • Patent Document 1 it is possible to provide an optical pickup device that can be used interchangeably with a high-density optical disk and other optical disks.
  • an objective optical element unit a spherical surface caused by the thickness of the protective substrate of the optical disk. Since a plastic parallel plate on which a diffractive structure for correcting aberration (an optical path difference providing structure for compatibility) is formed and a glass lens are used, there is a problem that the cost is increased. On the other hand, in order to reduce the cost, it is conceivable that the lens is made of plastic, but the characteristic of the plastic becomes a problem.
  • a lens made of plastic may generate a relatively large spherical aberration due to a change in temperature. Such a problem is remarkable particularly in a high-density optical disk used at a high NA.
  • an optical path difference providing structure for correcting the temperature change can be provided separately.
  • different optical disks can be shared.
  • the compatibility performance is degraded or the compatibility is disabled.
  • the configuration of the optical path difference providing structure is as follows. There is a risk that the manufacturing process of the mold that molds the objective lens becomes complicated, and the manufacturing cost of the objective lens is increased, the manufacturing error of the objective lens is promoted, and the optical characteristics are deteriorated. In particular, it is considered that the light utilization efficiency may be reduced due to an increase in the influence of sagging during manufacturing accompanying an increase in the number of steps.
  • the present invention has been made in view of the above-mentioned problems found by the present inventors. Even when a plastic optical element is used, information recording / reproduction is appropriately performed on three different types of optical disks. It is an object of the present invention to provide an objective optical element and an optical pickup apparatus for an optical pickup apparatus that can perform the above-described processing and that can be easily manufactured without complicating the structure of the optical element.
  • the objective optical element for an optical pickup device emits a first light source that emits a first light flux having a wavelength ⁇ 1 (nm) and a second light flux that has a wavelength ⁇ 2 (nm) ( ⁇ 1 ⁇ 2).
  • the objective optical element has at least one plastic lens;
  • the optical surface of the objective optical element includes at least three regions: a central region including an optical axis, an intermediate region disposed around the central region, and a peripheral region disposed around the intermediate region, The objective optical element focuses the first light flux that has passed through the central region, the intermediate region, and the peripheral region on the information recording surface of the first optical disc through a protective substrate having a thickness t1.
  • Information can be recorded / reproduced, and the second light flux that has passed through the central area and the intermediate area is secondly passed through a protective substrate having a thickness t2 (t1 ⁇ t2).
  • Information can be recorded / reproduced by condensing it on the information recording surface of the optical disc, and the third light flux that has passed through the central region has a thickness of t3 (t2 ⁇ t3).
  • the central region does not have a temperature characteristic correction structure
  • the intermediate region has a first temperature characteristic correction structure having a plurality of concentric annular zone steps
  • the peripheral region has a second temperature characteristic correction structure having a plurality of concentric annular zone steps
  • the first temperature characteristic correction structure increases the u-th order diffraction efficiency of the first light flux that has passed through the first temperature characteristic correction structure to be higher than any other order diffraction efficiency.
  • the present inventors have found that, in the objective optical element, there is a difference in spherical aberration generated due to a change in environmental temperature between the vicinity of the optical axis and the vicinity away from the optical axis. That is, there is little change in the thickness of the objective lens in the optical axis direction in the vicinity of the optical axis, but the thickness change in the optical axis direction of the objective lens becomes larger toward the periphery.
  • the aberration is that the periphery tends to be larger than the vicinity of the optical axis.
  • the optical surface in the central region is used to collect light beams having three different wavelengths as described above, in order to reduce as much as possible the loss of light quantity due to manufacturing errors caused by a complicated structure.
  • the intermediate surface is relatively easily affected by the temperature change by simplifying the optical surface by not providing the temperature characteristic correction structure.
  • the first temperature characteristic correction structure and the second temperature characteristic correction structure are provided so as to suppress the spherical aberration caused by the temperature change. This simplifies the optical path difference providing structure, facilitates processing of the mold for molding the objective optical element, reduces the manufacturing cost of the objective optical element, improves the manufacturing accuracy of the objective optical element, and achieves desired optical characteristics. Can be demonstrated.
  • the peripheral region is a dedicated region for the first wavelength, and therefore does not need to have a compatibility function. As long as the light use efficiency can be maintained high and the mold can be easily manufactured, any one of them can be used. You may make it correspond to an order (however, an integer).
  • the objective optical element for an optical pickup device described in claim 2 is characterized in that, in the invention described in claim 1, at least the central region has a compatible optical path difference providing structure.
  • the objective optical element for an optical pickup device is the invention according to claim 2, wherein the interchangeable optical path difference providing structure is formed by superimposing a first basic structure and a second basic structure.
  • the second-order diffraction efficiency of the first light flux that has passed through the first basic structure is made larger than any other order diffraction efficiency, and the second light-efficiency of the second light flux that has passed through the first basic structure is 1
  • the 0th-order diffraction efficiency of the first light beam that has passed through the second basic structure is made larger than the diffraction efficiency of any other order, and the 0th-order diffraction efficiency of the second light beam that has passed through the second basic structure.
  • the compatible optical path difference providing structure is configured as described above, the shape of the compatible optical path difference providing structure becomes complicated, and therefore, when the temperature characteristic correction structure is further superimposed on the compatible optical path difference providing structure.
  • the shape becomes very complicated, the number of steps in the central region is greatly increased, and the decrease in light utilization efficiency due to manufacturing errors becomes more remarkable. Therefore, the compatibility optical path difference providing structure as in the claims is preferable because the effect of the present invention becomes more remarkable.
  • the objective optical element for an optical pickup device is the invention according to claim 2, wherein the compatible optical path difference providing structure is the first light flux that has passed through the compatible optical path difference providing structure.
  • the diffraction efficiency of the second order of the second light flux that has passed through the first basic structure is larger than the diffraction efficiency of any other order.
  • the ⁇ -order diffraction efficiency of the third light flux that has passed through the first basic structure is made larger than the diffraction efficiency of any other order, and the following equation is satisfied.
  • the objective optical element for an optical pickup device described in claim 5 is characterized in that, in the invention described in claim 4, the following expression is satisfied. (
  • ) (1, 1, 2) or (1, 2, 3)
  • the shape of the compatible optical path difference providing structure is a stepped structure having a fine pitch, and therefore the temperature characteristic correcting structure is further added to the compatible optical path difference providing structure. If superposed, the shape becomes very complicated, the number of steps in the central region is greatly increased, and the reduction in light utilization efficiency due to manufacturing errors becomes more remarkable. Therefore, the compatibility optical path difference providing structure as in the claims is preferable because the effect of the present invention becomes more remarkable.
  • the objective optical element for an optical pickup device is the optical beam difference providing structure according to claim 2, wherein the compatible optical path difference providing structure is the first light flux that has passed through the compatible optical path difference providing structure.
  • the first-order diffraction efficiency of the second light flux that has passed through the compatible optical path difference providing structure is made higher than any other order diffraction efficiency.
  • the first-order diffraction efficiency of the third light flux that has passed through the compatible optical path difference providing structure is larger than any other order diffraction efficiency.
  • the objective optical element for an optical pickup device is the invention according to claim 2, wherein the compatible optical path difference providing structure is the first light flux that has passed through the compatible optical path difference providing structure. Is larger than any other order diffraction efficiency, and the ⁇ -th order diffraction efficiency of the second light flux that has passed through the compatible optical path difference providing structure is higher than any other order diffraction efficiency.
  • the ⁇ -order diffraction efficiency of the third light flux that has passed through the compatible optical path difference providing structure is made larger than any other order diffraction efficiency, and the following equation is satisfied.
  • the objective optical element for an optical pickup device described in claim 8 satisfies the following expression in the invention described in claim 7. ( ⁇ ,
  • ) (0, 1, 2) or (0, 1, 3)
  • the objective optical element for an optical pickup device is the invention according to any one of claims 1 to 9, wherein the first temperature characteristic correction structure and the second temperature characteristic correction structure are combined.
  • the structure is characterized in that it becomes deeper in the optical axis direction as the height from the optical axis becomes higher, or becomes shallower in the optical axis direction as the height from the optical axis becomes higher.
  • the objective optical element for an optical pickup device is the invention according to any one of claims 1 to 10, wherein the first temperature characteristic correction structure and the second temperature characteristic correction structure are combined.
  • the structure is such that the stepped surface extending along the optical axis faces the outside in the optical axis orthogonal direction at a predetermined height from the optical axis, and extends along the optical axis after exceeding the predetermined height.
  • the step surface has a shape facing the inner side in the optical axis orthogonal direction.
  • the objective optical element for an optical pickup device is the invention according to any one of claims 1 to 11, wherein the plastic forming the objective optical element has a temperature of -5 ° C to 70 ° C.
  • the refractive index change rate dN / dT (° C. ⁇ 1 ) with respect to the wavelength of 405 nm accompanying the temperature change within the range is in the range of ⁇ 20 ⁇ 10 ⁇ 5 to ⁇ 5 ⁇ 10 ⁇ 5 .
  • the objective optical element for an optical pickup device is the invention according to any one of claims 1 to 12, wherein the objective optical element is a flat optical element and a lens having an aspherical surface. It is characterized by having.
  • the objective optical element for an optical pickup device is the invention according to claim 13, wherein the plate-like optical element includes the first temperature characteristic correction structure and the second temperature characteristic correction structure. It is characterized by having.
  • An objective optical element for an optical pickup device is the invention according to the thirteenth aspect, wherein the lens has the first temperature characteristic correction structure and the second temperature characteristic correction structure. It is characterized by.
  • the objective optical element for an optical pickup device is the invention according to any one of claims 1 to 12, wherein the objective optical element comprises only a single lens made of plastic.
  • the objective optical element for an optical pickup device is the invention according to any one of claims 1 to 16, wherein the compatible optical path difference providing structure having a plurality of concentric annular zone steps is provided. It has a structure superimposed on the first temperature characteristic correction structure or the second temperature characteristic correction structure.
  • An optical pickup device has the objective optical element according to any one of claims 1 to 17.
  • the optical pickup device of the present invention can have a first light source, a second light source, and a third light source.
  • the first light beam from the first light source is condensed on the information recording surface of the first optical disk (also referred to as an optical information recording medium, hereinafter the same), and the second light from the second light source is collected.
  • a condensing optical system including an objective optical element for condensing the light beam on the information recording surface of the second optical disk and condensing the third light beam from the third light source on the information recording surface of the third optical disk; ing.
  • the optical pickup device of the present invention may include a light receiving element that receives a reflected light beam from the information recording surface 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 t1 and an information recording surface.
  • the second optical disc has a protective substrate having a thickness t2 (t1 ⁇ t2) and an information recording surface.
  • the third optical disc has a protective substrate having a thickness t3 (t2 ⁇ t3) and an information recording surface.
  • the first optical disc is preferably a high-density optical disc, the second optical disc is preferably a DVD, and the third optical disc is preferably a CD, but is not limited thereto.
  • t1 ⁇ t2 for example, when the first optical disk is BD and the second optical disk is DVD
  • 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.
  • a high-density optical disc a standard optical disc (for example, a BD) in which information is recorded / reproduced by an objective optical element having a NA of 0.85 and a protective substrate has a thickness of about 0.1 mm.
  • Blu-ray Disc As another example of a high-density optical disk, information is recorded / reproduced by an objective optical element having an NA of 0.65 to 0.67, and a protective optical disk having a protective substrate thickness of about 0.6 mm (for example, HD DVD: also simply referred to as HD).
  • an optical disk having a protective film with a thickness of several to several tens of nanometers is not used for the high-density optical disk.
  • An optical disk is also included.
  • the high-density optical disk includes a magneto-optical disk in which a blue-violet semiconductor laser or a blue-violet SHG laser is used as a light source for recording / reproducing information.
  • a DVD is a DVD series optical disc in which information is recorded / reproduced by an objective optical element 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 element 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 the high-density optical disk is the highest, and then decreases in the order of DVD and CD.
  • the thicknesses t1, t2, and t3 of the protective substrate it is preferable to satisfy the following conditional expressions (1), (2), and (3), but is not limited thereto.
  • NA1 The numerical aperture of the objective optical element necessary for recording / reproducing information on the first optical disk
  • NA2 NA1 ⁇ NA2
  • 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
  • NA2 is preferably 0.55 or more and 0.7 or less
  • NA3 is preferably 0.4 or more and 0.55 or less.
  • the first light source emits a first light flux having a wavelength ⁇ 1.
  • the second light source emits a second light flux having a wavelength ⁇ 2 ( ⁇ 1 ⁇ 2).
  • the third light source emits a third light flux having a wavelength ⁇ 3 ( ⁇ 2 ⁇ 3).
  • the first light source and the second light source are preferably laser light sources.
  • a laser light source may be used when a third light source is used.
  • the laser light source a semiconductor laser, silicon laser, SHG laser, or the like can be preferably used. Note that ⁇ 1, ⁇ 2, and ⁇ 3 preferably satisfy the following conditional expressions (4) and (5).
  • the first wavelength ⁇ 1 of the first light source is preferably 350 nm or more and 440 nm or less, more preferably 380 nm or more and 415 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.
  • the third wavelength ⁇ 3 of the third light source is preferably 750 nm or more and 880 nm or less, more preferably 760 nm or more and 820 nm or less.
  • first light source and the second light source may be unitized, and in addition to these, 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.
  • a light receiving element to be described later may be packaged.
  • a photodetector such as a photodiode is preferably used.
  • Light reflected on the information recording surface of the optical disc enters the light receiving element, and a read signal of information recorded on each optical disc is obtained using the output signal. Furthermore, it detects the change in the amount of light 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 element 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.
  • a light receiving element may be used (so-called three beam method).
  • the light receiving element may have a plurality of light receiving portions corresponding to the respective light sources.
  • the condensing optical system (or an objective optical element to be described later) records / reproduces information by condensing the first light flux on the information recording surface of the first optical disc via a protective substrate having a thickness t1. It is possible to record / reproduce information by condensing the second light flux on the information recording surface of the second optical disc via the protective substrate having a thickness t2. Further, the condensing optical system makes it possible to record / reproduce information by condensing the third light flux on the information recording surface of the third optical disc via the protective substrate having a thickness t3.
  • the condensing optical system has an objective optical element.
  • the condensing optical system may include only the objective optical element, but may include a coupling lens such as a collimator lens in addition to the objective optical element.
  • the coupling lens is a single lens or a lens group that is disposed between the objective optical element and the light source and changes the divergence angle of the light beam.
  • the collimating lens is a lens that emits an incident light beam as a parallel light beam.
  • 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. May be.
  • the objective optical element is disposed at a position facing the optical disk in a state where the optical disk is loaded in the optical pickup device, and has a function of condensing the light beam emitted from the light source on the information recording surface of the optical disk.
  • the objective optical element of the present invention there is an objective optical element having a single flat optical element and a lens. It is preferable that the flat optical elements and the lenses are arranged in the optical axis direction and their positions are relatively fixed. At least one of the flat optical element and the lens has a portion extending in the optical axis direction, the extending portion is in contact with the other, the flat optical element and the lens are bonded to each other, and the objective It is preferable to form an optical element.
  • the objective optical element may be formed by fixing a flat optical element and a lens to a separate frame. Normally, when the objective optical element is disposed in the optical pickup device, the flat optical element is on the light source side, and the lens is on the optical disk side.
  • the objective optical element can be constituted by only a single lens.
  • the objective optical element of the present invention is made of plastic. More specifically, when the objective optical element is composed of a plate-like optical element and a lens, when only the plate-like optical element is made of plastic, when only the lens is made of plastic, the plate-like optical element And the lens may be made of plastic. On the other hand, when the objective optical element is a single lens, it is made of plastic.
  • the plastic may be any plastic that is generally used for optical materials, but is preferably a cyclic olefin resin material.
  • the refractive index change rate with respect to the wavelength of 405 nm is in the range of 1.54 to 1.60, and the refractive index change rate with respect to the wavelength of 405 nm accompanying a temperature change within a temperature range of ⁇ 5 ° C. to 70 ° C.
  • the coupling lens is also preferably a plastic lens.
  • the frame is preferably made of plastic.
  • At least one optical surface of the objective optical element has a central region, an intermediate region around the central region, and a peripheral region around the intermediate region.
  • the central region is preferably a region including the optical axis of the objective optical element, but may be a region not including the optical axis.
  • the central region, the intermediate region, and the peripheral region are preferably provided on the same optical surface. Taking a single lens as an example, as shown in FIG. 11, the central region CN, the intermediate region MD, and the peripheral region OT are provided on the same optical surface in a concentric manner with the optical axis as the center. Preferably it is.
  • the temperature characteristic correction structure is not provided in the central area of the objective optical element, the first temperature characteristic correction structure is provided in the intermediate area, and the second temperature characteristic correction structure is provided in the peripheral area.
  • the central region, the intermediate region, and the peripheral region are preferably adjacent to each other, but there may be a slight gap between them.
  • the first temperature characteristic correction structure is preferably provided in a region that is 70% or more of the area of the intermediate region of the objective optical element, and more preferably 90% or more. More preferably, the first temperature characteristic correction structure is provided on the entire surface of the intermediate region.
  • the second temperature characteristic correction structure is preferably provided in a region of 70% or more of the area of the peripheral region of the objective optical element, and more preferably 90% or more. More preferably, the second temperature characteristic correction structure is provided on the entire surface of the peripheral region.
  • the optical path difference providing structure is a general term for structures that add an optical path difference to an incident light beam.
  • the optical path difference providing structure includes a phase difference providing structure for providing a phase difference.
  • the phase difference providing structure includes a diffractive structure.
  • the optical path difference providing structure is preferably a diffractive structure.
  • the optical path difference providing structure has a step, preferably a plurality of steps. This step adds an optical path difference and / or phase difference to the incident light flux.
  • a structure called an NPS structure can also be regarded as a kind of optical path difference providing structure, and can also be regarded as a kind of diffraction structure.
  • a plurality of unit shapes are arranged around the optical axis (also referred to as an annular structure), a light beam enters each unit shape, and a wavefront of transmitted light is generated for each adjacent annular zone.
  • a structure in which the light is condensed by approximately an integer wavelength or an integer wavelength and a new wavefront is formed.
  • the temperature characteristic correction structure is a structure that corrects a spherical aberration that occurs with a change in environmental temperature with respect to a passing light beam. It is preferable that the structure corrects the spherical aberration caused by the change when the wavelength of the light beam passing through the change in the environmental temperature or when the refractive index of the optical element changes.
  • An example of a preferable structure is a so-called NPS structure.
  • NPS structure so-called NPS structure.
  • the temperature characteristic correcting structure does not change the power with respect to the light beam when the wavelength of the light beam is the design wavelength, and changes the power with respect to the light beam when the wavelength deviates from the design wavelength.
  • a structure is preferred. Since the temperature characteristic correction structure has such a function, it is possible to correct spherical aberration that occurs with a change in temperature.
  • “the wavelength deviates from the design wavelength” is preferably within ⁇ 10 nm.
  • the temperature characteristic correction structure can take various cross-sectional shapes as schematically shown in FIGS. (Note that the examples shown in FIGS. 1 to 4 are cases where the objective optical element has a flat optical element.)
  • FIG. 1 is a sawtooth shape
  • FIG. 2 shows all steps in the same direction. This is a case of a staircase shape.
  • FIG. 3 shows a step shape in which the direction of the step is opposite in the middle, that is, the cross-sectional shape including the optical axis is a predetermined height from the optical axis, the optical path length becomes longer as the distance from the optical axis increases.
  • FIG. 4 shows a pattern in which the cross-sectional shape including the optical axis is stepped, arranged concentrically, for each predetermined number of level surfaces (in the example shown in FIG. 4, the number of level surfaces is 5), respectively.
  • a case is shown in which the steps are shifted by the height corresponding to the level plane (four steps in the example shown in FIG. 4).
  • the steps of the temperature characteristic correction structure may be arranged with an aperiodic interval in the direction perpendicular to the optical axis.
  • the temperature characteristic correction structure formed in the intermediate region is a first temperature correction structure
  • the temperature characteristic correction structure formed in the peripheral region is a second temperature correction structure.
  • the first or second temperature characteristic correction structure is also a ring-shaped step structure separated by concentric steps.
  • the objective optical element is composed of a flat optical element and a lens
  • the first and second temperature characteristic correction structures are formed only on the flat optical element, and the first and second only on the lens.
  • a temperature characteristic correction structure may be formed.
  • first to second temperature characteristic correction structures are formed on the optical surface.
  • the optical surface on which the temperature characteristic correction structure is provided is a plane
  • the cross-sectional shape including the optical axis of the objective optical element is from the optical axis to a predetermined height (NA3) as shown in FIG.
  • NA3 predetermined height
  • the second temperature characteristic correction structure is a sawtooth optical path difference providing structure on the peripheral side from the predetermined height (NA2) from the optical axis.
  • NA2 predetermined height
  • the structure gradually becomes shallower or thicker in the optical axis direction as the height from the optical axis increases.
  • the optical surface on which the composite structure including the first temperature characteristic correction structure and the second temperature characteristic correction structure is provided is a plane
  • the cross-sectional shape including the optical axis of the objective optical element is as shown in FIG.
  • the plane from the optical axis to the predetermined height (NA3) is a plane orthogonal to the optical axis
  • the peripheral side from the predetermined height (NA3) from the optical axis is the first temperature characteristic correction structure.
  • the staircase structure is such that the optical path length decreases as the distance from the optical axis increases.
  • a staircase structure in which the optical path length becomes longer as the distance from the optical axis is within the range of the second temperature characteristic correction structure.
  • the depth increases in the optical axis direction.
  • it can be said to be a structure that becomes thinner and becomes shallower or thicker in the direction of the optical axis when it exceeds a predetermined height.
  • the position where the depth of the step changes may be in the first temperature characteristic correction structure or in the second temperature characteristic correction structure, It may be a boundary between the first temperature characteristic correction structure and the second temperature characteristic correction structure. In this case, it is preferable that the depth in the optical axis direction of the composite structure returns before the height from the optical axis reaches the second temperature characteristic correction structure.
  • a step surface in a substantially parallel cylindrical shape extending along the optical axis ( It can be said that ⁇ ′, ⁇ ′, and ⁇ ′) preferably have a shape facing the inner side in the optical axis orthogonal direction.
  • the preferable first temperature characteristic correction structure makes the u-order diffraction efficiency of the first light beam that has passed through the first temperature characteristic correction structure larger than the diffraction efficiency of any other order, and v-order diffraction of the second light beam.
  • (u, v) (10, 6), (5, 3) or (2, 1). It is a structure.
  • the second temperature characteristic correction structure only needs to make the diffraction efficiency of an arbitrary integer of the first light flux that has passed through the second temperature characteristic correction structure larger than the diffraction efficiency of any other order.
  • the diffraction order of the diffracted light with the maximum light amount is 5th or less. Further, it is preferable that the diffraction order is 5 or less because it is possible to suppress the fluctuation of the diffraction efficiency when the wavelength fluctuates.
  • the line (A) in FIG. 6 represents the state of the wavefront when the temperature rises from the design reference temperature of an example single lens having two optical surfaces that are made of plastic and are aspherical.
  • the horizontal axis represents the effective radius of the optical surface, and the vertical axis represents the optical path difference.
  • spherical aberration occurs due to the influence of the refractive index change accompanying the temperature rise, and the wavefront changes as shown by the line (A).
  • the single lens is made of plastic, the amount of spherical aberration is increased because the refractive index change with temperature change is large.
  • a line (B) is an optical path difference added to the transmitted wavefront by the first to second temperature characteristic correction structures
  • a line (C) is the first to the first when the temperature rises from the design reference temperature. It is a figure showing the mode of the wave front which permeate
  • the temperature characteristic is corrected in the central region. No structure is provided.
  • the objective optical element can be provided with a compatible optical path difference providing structure which is an optical path difference providing structure.
  • the optical path difference providing structure for compatibility is a structure that corrects spherical aberration generated according to the thickness of the protective substrate of the optical disk by using the wavelength difference of the light flux.
  • the compatible optical path difference providing structure may be provided in the flat optical element or may be provided in the lens.
  • the first or second temperature characteristic correcting structure may be provided on one optical surface
  • the compatible optical path difference providing structure may be provided on the other optical surface.
  • the first or second temperature characteristic correction structure and the compatible optical path difference providing structure may be superimposed on one optical surface.
  • the lens when the lens is provided with a compatible optical path difference providing structure, it is preferable to superimpose the first or second temperature characteristic correcting structure and the compatible structure on the optical surface on the light source side. May be.
  • the objective optical element is composed of only a single lens, it is preferable to superimpose the first or second temperature characteristic correction structure and the compatible optical path difference providing structure on the optical surface on the light source side, but each on another optical surface. It may be formed.
  • the interchangeable optical path difference providing structure also has a plurality of concentric annular zones around the optical axis.
  • the compatible optical path difference providing structure can take various cross-sectional shapes (cross-sectional shapes in a plane including the optical axis) as shown in FIGS. 1 to 3.
  • a pattern whose cross-sectional shape including the optical axis is stepped is arranged concentrically, for each predetermined number of level surfaces (in the example shown in FIG. 4, the number of level surfaces is 5).
  • a first compatible optical path difference providing structure is provided in the central region of the objective optical element.
  • a preferred example of the first compatible optical path difference providing structure here is a structure in which the first basic structure and the second basic structure are overlapped.
  • the first basic structure makes the second-order diffraction efficiency of the first light beam that has passed through the first basic structure larger than the diffraction efficiency of any other order, and the first-order diffraction efficiency of the second light beam becomes any other order.
  • This is an optical path difference providing structure that is larger than the diffraction efficiency and makes the first-order diffraction efficiency of the third light beam larger than the diffraction efficiency of any other order.
  • a 1st basic structure is an optical path difference providing structure which makes the diffraction angle of the 2nd light beam which passed the 1st basic structure differ from the diffraction angle of a 1st light beam and a 3rd light beam.
  • a preferred example of the shape of the first basic structure is a sawtooth structure as shown in FIG.
  • the second basic structure makes the diffraction efficiency of the 0th order (transmitted light) of the first light flux that has passed through the second basic structure larger than the diffraction efficiency of any other order, and the 0th order (transmitted light) of the second light flux. ) Is made larger than any other order diffraction efficiency, and the ⁇ 1st order diffraction efficiency of the third light flux is made larger than any other order diffraction efficiency.
  • a 2nd basic structure is an optical path difference providing structure which makes the diffraction angle of the 3rd light beam which passed the 2nd basic structure differ from the diffraction angle of a 1st light beam and a 2nd light beam.
  • a preferable example of the shape of the second basic structure is a binary structure as shown as D2 in FIG.
  • the first compatible optical path difference providing structure may not be a structure in which a plurality of basic structures are stacked.
  • the ⁇ -th order diffraction efficiency of the first light beam that has passed through the first compatible optical path difference providing structure is made larger than any other order diffraction efficiency, and the first light beam having passed through the first basic structure.
  • the ⁇ -order diffraction efficiency of the two light beams is made larger than any other order diffraction efficiency
  • the ⁇ -order diffraction efficiency of the third light beam that has passed through the first basic structure is made larger than any other order diffraction efficiency.
  • a structure satisfying the following formula is included.
  • the first-order diffraction efficiency of the first light flux that has passed through the first compatible optical path difference providing structure is made larger than the diffraction efficiency of any other order
  • the first-order diffraction efficiency of the second light beam that has passed through the first compatible optical path difference providing structure is made larger than the diffraction efficiency of any other order
  • 1 of the third light beam that has passed through the first compatible optical path difference providing structure examples include a structure in which the next diffraction efficiency is higher than that of any other order.
  • the ⁇ -order diffraction efficiency of the first light flux that has passed through the first compatible optical path difference providing structure is made larger than any other order diffraction efficiency.
  • the third-order diffraction efficiency of the second light flux that has passed through the first compatible optical path difference providing structure is made larger than the diffraction efficiency of any other order, and the third light beam has passed through the first compatible optical path difference providing structure.
  • ⁇ 0, ⁇ ⁇ ⁇ > 0,
  • the following examples are preferable examples. ( ⁇ ,
  • ) (0, 1, 2) or (0, 1, 3)
  • Another preferred example of the first compatible optical path difference providing structure is a structure in which two sawtooth-shaped basic structures are superimposed.
  • the ⁇ -order diffraction efficiency of the first light beam that has passed through one basic structure is made larger than the diffraction efficiency of any other order, and the ⁇ -order diffraction efficiency of the second light beam that has passed through the basic structure is changed to any other It is larger than the diffraction efficiency of the order, and the ⁇ -order diffraction efficiency of the third light flux that has passed through the basic structure is made larger than the diffraction efficiency of any other order.
  • the x-order diffraction efficiency of the first light beam that has passed through another basic structure is made larger than the diffraction efficiency of any other order
  • the y-order diffraction efficiency of the second light beam that has passed through the basic structure is It is larger than any other order diffraction efficiency
  • the z-th order diffraction efficiency of the third light beam that has passed through the basic structure is made larger than any other order diffraction efficiency.
  • a second compatible optical path difference providing structure is overlapped with the first temperature characteristic correction structure.
  • a preferable example of the second compatible optical path difference providing structure is the same structure as the first compatible optical path difference providing structure.
  • Other preferable examples of the second compatible optical path difference providing structure include, but are not limited to, the first basic structure, the third basic structure, and the fourth basic structure.
  • the 0th-order diffraction efficiency of the first light beam that has passed through the second compatible optical path difference providing structure is set to be higher than the diffraction efficiency of any other order.
  • there is a two-step staircase structure that makes the -1st-order diffraction efficiency of the second light beam that has passed through the interchangeable optical path difference providing structure larger than any other order diffraction efficiency.
  • the third basic structure makes the first-order diffraction efficiency of the first light flux that has passed through the third basic structure larger than the diffraction efficiency of any other order, and the first-order diffraction efficiency of the second light flux becomes any other order.
  • This is an optical path difference providing structure that is larger than the diffraction efficiency and makes the first-order diffraction efficiency of the third light beam larger than the diffraction efficiency of any other order.
  • This is preferably a sawtooth structure.
  • the fourth basic structure makes the third-order diffraction efficiency of the first light beam that has passed through the fourth basic structure larger than the diffraction efficiency of any other order, and the second-order diffraction efficiency of the second light beam becomes any other order.
  • This is an optical path difference providing structure that is larger than the diffraction efficiency and makes the second-order diffraction efficiency of the third light flux larger than any other order diffraction efficiency.
  • This is preferably a sawtooth structure.
  • the peripheral area of the objective optical element preferably has only the second temperature characteristic correction structure and does not have a compatible structure.
  • the flat optical element has a first optical surface and a second optical surface that face each other, the first optical surface being the light source side, and the second optical surface being the optical disc side and the aspherical lens side.
  • Only the first compatible optical path difference providing structure is provided in the central region of the second optical surface of the flat optical element.
  • the first compatible optical path difference providing structure provided in the central region of the second optical surface preferably includes only the second basic structure. It is preferable that neither an optical path difference providing structure for compatibility nor a temperature characteristic correcting optical path difference providing structure is provided in the intermediate region and the peripheral region of the second optical surface of the flat optical element.
  • optical path difference providing structure for the first compatibility is also provided in the central region of the first optical surface of the flat optical element.
  • This first compatible optical path difference providing structure is composed of only the fifth basic structure.
  • the diffraction efficiency of the 0th order (transmitted light) of the first light beam that has passed through the fifth basic structure is made larger than the diffraction efficiency of any other order, and the first order diffraction efficiency of the second light beam is changed to the other.
  • This is an optical path difference providing structure in which the diffraction efficiency of the third light beam is larger than the diffraction efficiency of any other order, and the diffraction efficiency of the third light beam is larger than the diffraction efficiency of any other order.
  • the fifth basic structure is preferably an optical path difference providing structure that makes the diffraction angle of the second light beam that has passed through the fifth basic structure different from the diffraction angles of the first light beam and the third light beam.
  • a pattern in which the cross-sectional shape including the optical axis is stepped is arranged concentrically, for each predetermined number of level surfaces (see FIG. In the example shown in FIG. 4, the number of level surfaces is 5), and the shape is shifted by the height corresponding to each level surface (4 steps in the example shown in FIG. 4).
  • a first temperature characteristic correcting structure and a second compatible optical path difference providing structure are provided in an overlapping manner in an intermediate region of the first optical surface of the flat optical element.
  • the second compatible optical path difference providing structure preferably includes only the fifth basic structure.
  • only the second temperature characteristic correction structure is provided in the peripheral region of the first optical surface of the flat optical element.
  • the temperature characteristic is as follows by having the temperature characteristic correcting structure of the present invention. It is preferable to satisfy the conditional expressions (6) and (7).
  • ⁇ SAT1 represents ⁇ SA3 / ⁇ T of the objective optical element at the time of recording and / or reproduction of the first optical disk at the wavelength used (in this case, there is no wavelength variation accompanying temperature change).
  • the used wavelength refers to the wavelength of a light source used in an optical pickup device having an objective optical element.
  • the wavelength used is a wavelength in the range of 400 nm or more and 415 nm or less, and is a wavelength at which recording and / or reproduction of the first optical disc can be performed via the objective optical element.
  • ⁇ SAT1 of the objective optical element and ⁇ SAT2 and ⁇ SAT3 described later may be obtained using 405 nm as the use wavelength.
  • ⁇ SAT1 indicates the temperature change rate (temperature characteristic) of the third-order spherical aberration of the objective optical element when recording and / or reproducing the first optical disk at the used wavelength (no wavelength variation).
  • WFE indicates that the third-order spherical aberration is expressed by wavefront aberration.
  • ⁇ SA ⁇ represents ⁇ SA3 / ⁇ when recording and / or reproducing the first optical disk at the used wavelength under a condition where the environmental temperature is constant. That is, ⁇ SA ⁇ indicates the wavelength change rate (wavelength characteristic) of the third-order spherical aberration of the objective optical element when recording and / or reproducing the first optical disk at the used wavelength under the condition where the environmental temperature is constant.
  • the ambient temperature is preferably room temperature.
  • the room temperature is 10 ° C. or more and 40 ° C. or less, and preferably 25 ° C.
  • f indicates the focal length of the objective optical element at the used wavelength (preferably 405 nm) of the first light flux.
  • conditional expression (6) ′ is satisfied. + 0.00091 ⁇ ⁇ SAT1 / f (WFE ⁇ rms / (° C./mm)) ⁇ +0.0018 (6) ′
  • conditional expression (7) ′ is satisfied, and more preferably, the following conditional expression (7) ′′ is satisfied.
  • the objective optical element has the wavelength dependency of the spherical aberration so that the change of the spherical aberration due to the refractive index change accompanying the temperature change of the objective optical element is corrected by the wavelength change of the first wavelength accompanying the temperature change.
  • the following conditional expression (8) is satisfied.
  • ⁇ SAT2 is ⁇ SA3 / ⁇ T of the objective optical element at the time of recording and / or reproducing the first optical disc at a use wavelength of 405 nm (wavelength variation with temperature change is 0.05 nm / ° C.) (preferably 405 nm).
  • ⁇ SAT2 is a temperature change rate (temperature characteristic of the third-order spherical aberration of the objective optical element at the time of recording and / or reproduction of the first optical disc at the wavelength used (wavelength variation with temperature change is 0.05 nm / ° C.). ).
  • ⁇ SAT3 is an optical including a coupling lens and an objective optical element when recording and / or reproducing the first optical disk at a wavelength used (wavelength variation with temperature change is 0.05 nm / ° C. (preferably 405 nm)).
  • ⁇ SA3 Represents ⁇ SA3 / ⁇ T of the entire system, that is, ⁇ SAT3 is the third order of the entire optical system when performing recording and / or reproduction of the first optical disc at the wavelength used (wavelength variation accompanying temperature change is 0.05 nm / ° C.).
  • ⁇ SAT3 is the third order of the entire optical system when performing recording and / or reproduction of the first optical disc at the wavelength used (wavelength variation accompanying temperature change is 0.05 nm / ° C.).
  • an optical information recording / reproducing apparatus includes an optical disc drive apparatus having the optical pickup device described above.
  • the optical disk drive apparatus provided in the optical information recording / reproducing apparatus will be described.
  • 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.
  • an objective optical element and an optical pickup device for an optical pickup device that can appropriately record and / or reproduce information on three different types of optical disks at low cost.
  • FIG. 7 shows a configuration of an optical pickup apparatus PU1 that can appropriately record and reproduce information on any of a high-density optical disc BD (first optical disc), DVD (second optical disc), and CD (third optical disc). It is a figure shown roughly.
  • BD high-density optical disc
  • DVD second optical disc
  • CD third optical disc
  • NA3 785 nm
  • the thickness t3 of the protective substrate PL3 1.2 mm
  • NA3 0.45
  • the optical pickup device PU1 includes a blue-violet semiconductor laser LD1 (first light source) that emits a first light beam with a wavelength ⁇ 1 for BD, and a red semiconductor laser LD2 (second light source) for DVD that emits a second light beam with a wavelength ⁇ 2.
  • a blue-violet semiconductor laser LD1 first light source
  • a red semiconductor laser LD2 second light source
  • FIG. 8 is a cross-sectional view of the objective optical element OBU according to the present embodiment.
  • the objective optical element unit OBU has a configuration in which a plastic flat first optical element L1 and a second optical element L2 which is a plastic aspherical lens are connected by a plastic lens frame HL. .
  • the optical axis of the first optical element L1 is inclined by 2.5 degrees with respect to the optical axis of the second optical element L2.
  • the first optical element L1 has a refractive index of 1.56 in the first light flux having the wavelength ⁇ 1, is made of a polyolefin-based plastic having an Abbe number of 50 or more and 60 or less, and the first optical surface S1 on the light source side is: For convenience, it is divided into a region C2 including the optical axis and a surrounding region C3, and the second optical surface S2 on the optical disc side is divided into a region C1 including the optical axis and a surrounding region C4. ing.
  • the central region is a range inside the region C1, the intermediate region is outside the region C1 and inside the region C2, and the peripheral region is outside the region C2 and inside the region C3. is there.
  • the outer edge of the region C1 corresponds to the numerical aperture NA3
  • the outer edge of the region C2 corresponds to the numerical aperture NA2
  • the outer edge of the region C3 corresponds to the numerical aperture NA1.
  • the first compatible optical path difference providing structure provided in the region of NA3 or less and the second compatibility provided in the region of NA3 or more and NA2 or less.
  • An optical path difference providing structure is formed, and a first temperature characteristic correction structure is superimposed on the second compatible optical path difference providing structure.
  • a second temperature characteristic correction structure is formed in the region C3 in the first optical surface S1 of the first optical element L1.
  • FIG. 12A shows the shapes of the first compatible optical path difference providing structure and the second compatible optical path difference providing structure
  • FIG. 12B shows the first temperature characteristic correcting structure and the second temperature characteristic correcting structure.
  • the shape of is shown.
  • the shape in which these are overlapped is shown in FIG. That is, the central region has only the first compatible optical path difference providing structure, the middle region has the second compatible optical path difference providing structure and the first temperature characteristic correcting structure, and the peripheral region has only the second temperature characteristic correcting structure.
  • the shape is shown in FIG.
  • the first temperature characteristic correction structure makes the second-order diffraction efficiency of the first light beam that has passed through larger than the diffraction efficiency of any other order, and makes the first-order diffraction efficiency of the second light beam any other
  • the first and second compatible optical path difference providing structures of the optical surface S1 use the wavelength difference between the wavelength ⁇ 1 of the first light beam and the wavelength ⁇ 2 of the second light beam, and the thickness t1 of the protective substrate of the BD, DVD This structure corrects spherical aberration that occurs based on the difference from the thickness t2 of the protective substrate.
  • the first and second compatible optical path difference providing structures make the zero-order diffraction efficiency of the first light flux that has passed through the first and second compatible optical path difference providing structures larger than the diffraction efficiency of any other order.
  • the optical path difference providing structure that makes the first-order diffraction efficiency of the second light beam larger than any other order diffraction efficiency, and makes the zero-order diffraction efficiency of the third light beam larger than any other order diffraction efficiency.
  • the optical path difference providing structure has power only for the second light flux.
  • the light beam that has passed through the center of the first temperature characteristic correction structure always passes through the center of the second compatibility structure. Therefore, information can be appropriately recorded / reproduced without generating coma due to wavelength change or temperature change.
  • the second temperature characteristic correction structure makes the fifth-order diffraction efficiency of the first light beam that has passed through the second temperature characteristic correction structure larger than any other order diffraction efficiency.
  • the cross-sectional shape including the optical axis moves away from the optical axis at a predetermined height from the optical axis.
  • the depth is deep, and after the predetermined height from the optical axis, a staircase structure is formed in which the depth decreases as the distance from the optical axis increases.
  • first compatible optical path difference providing structure D2 having a binary structure is formed in the region C1 of the second optical surface S2 of the first optical element L1.
  • the first compatible optical path difference providing structure D2 of the optical surface S2 uses the wavelength difference between the wavelength ⁇ 1 of the first light beam and the wavelength ⁇ 3 of the third light beam, and the thickness t1 of the BD protective substrate and the CD protective substrate. In this structure, spherical aberration generated based on the difference in thickness t3 is corrected.
  • the first compatible optical path difference providing structure of the optical surface S2 makes the zero-order diffraction efficiency of the first light flux that has passed through the first compatible optical path difference providing structure larger than the diffraction efficiency of any other order,
  • the 0th-order diffraction efficiency of the two light beams is made larger than any other order diffraction efficiency
  • the ⁇ 1st-order diffraction efficiency of the third light beam is made larger than any other order diffraction efficiency.
  • the second optical element is an aspheric lens made of polyolefin plastic having a refractive index of 1.56.
  • the second optical element is designed to be capable of condensing the first light beam on the information recording surface of the BD without using the first optical element.
  • FIG. 9 is an enlarged sectional view showing a part of the objective optical element unit OBU.
  • the center of the first optical surface on the light source side of the first optical element L1 that is, the optical surface on which the first optical path difference providing structure and the third optical path difference providing structure are provided.
  • a marker M1 is provided at (optical axis position), and a marker M2 is provided at the center (optical axis position) of the second optical element L2.
  • These markers M1 and M2 are used for alignment of the first optical element L1 and the second optical element L2.
  • the marker may be provided by a paint, or may be provided as a concave portion or a convex portion.
  • the laser light LL incident in parallel to the optical axis OA2 of the second optical element L2 from the light source side is used. It is desirable to perform alignment so that the marker M1 that is the center of the first optical element L1 passes through the marker M2 that is the center of the second optical element L2 and travels along the optical axis OA2. As described above, by using the markers M1 and M2 to place the centers of the second optical element L2 and the first optical element L1 on the same optical path in the optical axis OA2 direction, the inclination angle of the first optical element L1. Regardless of the value of ⁇ , coma generated at least as the objective optical element OBU (especially for the first light flux and the second light flux) can be reduced.
  • the first optical path difference providing structure and the third optical path difference providing structure are provided not on the light source side surface of the first optical element but on the surface on the optical disk side, It is preferable that the marker is also provided on the surface on the optical disc side and aligned so that the marker and the marker of the second optical element have the same optical path.
  • the second optical element L2 attached to the lens frame HL is placed on the optical axis OA2 from the left side of the drawing. While observing, the first optical element L1 is arranged on the front side of the second optical element L2, and the first optical element L1 is moved within the lens frame so that both the markers M1 and M2 coincide. Thereby, the state shown in FIG. 9 is achieved, and the imaging characteristics of the objective optical element OBU can be ensured.
  • the blue-violet laser beam (first beam) having the wavelength ⁇ 1 is emitted from the collimator optical system CL in the state of a parallel beam.
  • the blue-violet semiconductor laser LD1 is caused to emit light.
  • the divergent light beam emitted from the blue-violet semiconductor laser LD1 is reflected by the first prism P1 and then sequentially passes through the second prism P2 and the third prism P3, as depicted by the solid line in FIG. Then, it is converted into a parallel light beam by the collimating optical system CL.
  • the light beam diameter is regulated by the stop STO, and becomes a condensed spot formed on the information recording surface RL1 by the objective optical element OBU via the BD protective substrate PL1.
  • the objective optical element OBU performs focusing and tracking by a biaxial actuator AC1 arranged in the periphery thereof.
  • the first light beam passes through the first optical surface S1 of the first optical element L1, passes through the second optical surface S2, and enters the second optical element L2 in the state of a parallel light beam. All the first light fluxes within the range (that is, the region where C2 and C3 are combined or the region where C1 and C4 are combined) are collected on the information recording surface of the BD by the second optical element L2. Further, when the environmental temperature changes, the spherical aberration can be suppressed by the mechanism described above.
  • the reflected light beam modulated by the information pits on the information recording surface RL1 is again transmitted through the objective optical element OBU, then reflected by the rising mirror ML, and becomes a convergent light beam when passing through the collimating optical system CL.
  • astigmatism is added by the sensor optical system SE and converges on the light receiving surface of the light receiving element PD.
  • Information recorded on the BD can be read using the output signal of the light receiving element PD.
  • the red laser beam (second beam) having the wavelength ⁇ 2 is emitted from the collimating optical system CL in the state of a parallel beam.
  • the red semiconductor laser LD2 is caused to emit light.
  • the divergent light beam emitted from the red semiconductor laser LD2 is reflected by the second prism P2 and then transmitted through the third prism P3 and parallel by the collimating optical system CL as shown by the broken line in FIG. Converted into luminous flux.
  • the objective optical element OBU performs focusing and tracking by a biaxial actuator AC1 arranged in the periphery thereof.
  • the second light flux is converted into divergent light in the region C2 of the first optical surface S1 of the first optical element L1, and is transmitted in the region C3.
  • the second light flux that has passed through the region C2 and converted into divergent light passes through the second optical surface S2, enters the second optical element as divergent light, and is collected on the information recording surface of the DVD. .
  • the second light beam transmitted through the region C3 is incident on the second optical element as a parallel light beam, and does not form a condensing spot by the second optical element, and becomes a flare on the information recording surface of the DVD. Therefore, the second light flux in the range within NA2 (namely, the C2 region) is condensed on the information recording surface of the DVD, and the second light flux in the range larger than NA2 (namely, the C3 region) becomes flare.
  • the reflected light beam modulated by the information pits on the information recording surface RL2 is again transmitted through the objective optical element OBU, then reflected by the rising mirror ML, and becomes a convergent light beam when passing through the collimating optical system CL.
  • astigmatism is added by the sensor optical system SE and converges on the light receiving surface of the light receiving element PD.
  • Information recorded on the DVD can be read using the output signal of the light receiving element PD.
  • an infrared laser beam (third beam) having a wavelength ⁇ 3 is emitted in a state of a parallel beam from the collimating optical system CL.
  • the infrared semiconductor laser LD3 is caused to emit light.
  • the divergent light beam emitted from the infrared semiconductor laser LD3 is reflected by the third prism P3 and then converted into a parallel light beam by the collimating optical system CL, as depicted in the dashed line in FIG.
  • the objective optical unit OBU performs focusing and tracking by a biaxial actuator AC1 arranged in the periphery thereof.
  • the third light flux passes through the first optical surface S1 of the first optical element L1.
  • the third light flux is converted into divergent light in the region C1 of the second optical surface S2 of the first optical element L1, and is transmitted through the region C4.
  • the third light beam that has passed through the region C1 and converted into divergent light is incident on the second optical element as divergent light, and is condensed on the information recording surface of the CD.
  • the third light beam transmitted through the region C4 enters the second optical element as a parallel light beam, and does not form a condensing spot by the second optical element, and becomes a flare on the information recording surface of the CD. Accordingly, the third light flux in the range within NA3 (namely, the C1 region) is collected on the information recording surface of the CD, and the third light flux in the range larger than NA3 (namely, the C4 region) is flare.
  • the reflected light beam modulated by the information pits on the information recording surface RL2 is again transmitted through the objective optical unit OBU, then reflected by the rising mirror ML, and becomes a converged light beam when passing through the collimating optical system CL.
  • astigmatism is added by the sensor optical system SE and converges on the light receiving surface of the light receiving element PD.
  • Information recorded on the CD can be read using the output signal of the light receiving element PD.
  • the spherical aberration when using the BD can be corrected by driving the collimating optical system CL in the optical axis direction by the uniaxial actuator AC2.
  • a spherical aberration correction mechanism wavelength variations due to manufacturing errors of the blue-violet semiconductor laser LD1, refractive index change and refractive index distribution of the objective optical system with temperature change, focus jump between information recording eyebrows of multilayer disks, manufacturing of the protective substrate PL1 It is possible to correct spherical aberration due to thickness variation and thickness distribution due to error.
  • the spherical aberration correction mechanism may correct spherical aberration when using a DVD or CD.
  • FIG. 10 is a diagram schematically showing a configuration of an optical pickup device PU2 of another embodiment capable of appropriately recording / reproducing information with respect to BD, DVD and CD which are different optical disks.
  • Such an optical pickup device PU2 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 PU2 emits a laser beam (first beam) of 405 nm that is emitted when information is recorded / reproduced with respect to the objective optical element OBJ, aperture stop ST, collimator lens CL, polarization dichroic prism PPS, and BD. It includes a first semiconductor laser LD1 (first light source), a first light receiving element PD1 that receives a reflected light beam from the information recording surface RL1 of the BD, a laser module LM, and the like.
  • first semiconductor laser LD1 first light source
  • a first light receiving element PD1 that receives a reflected light beam from the information recording surface RL1 of the BD
  • a laser module LM and the like.
  • the laser module LM also emits a 658 nm laser beam (second beam) and emits a laser beam (second beam) of 658 nm when information is recorded / reproduced on a DVD, 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 element OBJ of the present embodiment is a single plastic aspheric lens.
  • a central region CN including the optical axis on the aspheric optical surface on the light source side, an intermediate region MD disposed around the central region CN, and a peripheral region OT disposed further around the central region CN are formed concentrically around the optical axis. Note that the ratios of the area of the central region, the intermediate region, and the peripheral region in FIG.
  • a first compatible optical path difference providing structure that is a ring-shaped step as described above is formed in the central region, and a first temperature characteristic correction structure that is a ring-shaped step as described above and a second structure are formed in the middle region.
  • a structure in which the compatible optical path difference providing structures are superimposed is formed, and a second temperature characteristic correction structure that is a ring-shaped step is formed in the peripheral region OT.
  • the first temperature characteristic correction structure makes the fifth-order diffraction efficiency of the first light beam larger than any other order diffraction efficiency, and makes the third-order diffraction efficiency of the second light beam larger than any other order diffraction efficiency.
  • the second-order diffraction efficiency of the third light beam is made larger than the diffraction efficiency of any other order.
  • the second temperature characteristic correction structure makes the fifth-order diffraction efficiency of the first light beam larger than any other order diffraction efficiency, and makes the third-order diffraction efficiency of the second light beam larger than any other order diffraction efficiency.
  • the second-order diffraction efficiency of the third light beam is made larger than the diffraction efficiency of any other order.
  • the first compatible optical path difference providing structure is a structure in which the first basic structure and the second basic structure are overlapped.
  • the first basic structure makes the second-order diffraction efficiency of the first light beam larger than any other order diffraction efficiency, and makes the first-order diffraction efficiency of the second light beam larger than any other order diffraction efficiency.
  • the first-order diffraction efficiency of the third light flux is made larger than the diffraction efficiency of any other order.
  • the second basic structure makes the zero-order diffraction efficiency of the first light beam larger than any other order diffraction efficiency, and makes the zero-order diffraction efficiency of the second light beam larger than any other order diffraction efficiency.
  • the ⁇ 1st-order diffraction efficiency of the third light flux is made larger than the diffraction efficiency of any other order.
  • the second compatible optical path difference structure includes only the first basic structure.
  • the first compatible optical path difference providing structure makes the first-order diffraction efficiency of the first light beam larger than the diffraction efficiency of any other order without overlapping the basic structure, and the ⁇ 1st-order of the second light beam.
  • the optical path difference providing structure may be such that the diffraction efficiency of the third light beam is larger than any other order diffraction efficiency, and the ⁇ 2nd order diffraction efficiency of the third light flux is larger than any other order diffraction efficiency.
  • the first compatible optical path difference providing structure makes the first-order diffraction efficiency of the first light beam larger than the diffraction efficiency of any other order without overlapping the basic structure, and the second-order of the second light beam.
  • the optical path difference providing structure may be such that the diffraction efficiency of the third light beam is larger than any other order diffraction efficiency, and the third-order diffraction efficiency of the third light beam is larger than any other order diffraction efficiency.
  • the first compatible optical path difference providing structure makes the 0th-order diffraction efficiency of the first light beam larger than any other order diffraction efficiency without overlapping the basic structure, and the ⁇ 1st-order of the second light beam.
  • the optical path difference providing structure may be such that the diffraction efficiency of the third light beam is larger than any other order diffraction efficiency, and the ⁇ 2nd order diffraction efficiency of the third light flux is larger than any other order diffraction efficiency.
  • Polarized light is converted into circularly polarized light, its beam diameter is regulated by the stop ST, and becomes a spot formed on the information recording surface RL1 of the BD via the protective substrate PL1 having a thickness of 0.0875 mm by the objective optical element OBJ. .
  • the reflected light beam modulated by the information pits on the information recording surface RL1 is again transmitted through the objective optical element OBJ and the aperture stop ST, and then converted from circularly polarized light to linearly polarized light by a ⁇ 1 / 4 wavelength plate (not shown), and by the collimating lens CL.
  • a converged light beam is transmitted through the polarization dichroic prism PPS, and then converges on the light receiving surface of the first light receiving element PD1. Then, by using the output signal of the first light receiving element PD1 to focus or track the objective optical element OBJ by the biaxial actuator AC, information recorded on the BD can be read.
  • Polarized light is converted by the ⁇ 1 / 4 wave plate and enters the objective optical element OBJ.
  • the light beam condensed by the central region and the intermediate region of the objective optical element OBJ (the light beam that has passed through the peripheral region is flared and forms a spot peripheral portion) is passed through the protective substrate PL2 having a thickness of 0.6 mm.
  • the spot is formed on the information recording surface RL2 of the DVD, and the center of the spot is formed.
  • the reflected light beam modulated by the information pits on the information recording surface RL2 is again transmitted through the objective optical element OBJ and the aperture stop ST, is then polarized by a ⁇ 1 / 4 wavelength plate (not shown), and is converged by the collimator lens CL, After being reflected by the polarization dichroic prism PPS, then after being reflected twice in the prism, 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. Note that the light utilization efficiency can be increased by performing polarization conversion at ⁇ 1 / 4 in the round-trip path as compared with the case without ⁇ 1 / 4.
  • the polarization is converted by the ⁇ 1 / 4 wavelength plate that is not, and enters the objective optical element OBJ.
  • the light beam condensed by the central region of the objective optical element OBJ (the light beam that has passed through the intermediate region and the peripheral region is flared and forms a spot peripheral part) is passed through the protective substrate PL3 having a thickness of 1.2 mm.
  • the spot is formed on the information recording surface RL3 of the CD.
  • the reflected light beam modulated by the information pits on the information recording surface RL3 is again transmitted through the objective optical element OBJ and the aperture stop ST, is then polarized by a ⁇ 1 / 4 wavelength plate (not shown), and is converged by the collimator lens CL. After being reflected by the polarization dichroic prism PPS, and thereafter reflected twice in the prism, it converges on 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. Note that the light utilization efficiency can be increased by performing polarization conversion at ⁇ 1 / 4 in the round-trip path as compared with the case without ⁇ 1 / 4.
  • the first compatible optical path difference providing structure in the central region When the first light beam emitted from the blue-violet semiconductor laser LD1 enters the objective optical element OBJ as a parallel light beam, the first compatible optical path difference providing structure in the central region, the second compatible optical path difference providing structure in the intermediate region, and In the peripheral area, the spherical aberration of the first light flux is appropriately corrected, and information can be recorded and / or reproduced appropriately with respect to the BD having the thickness t1 of the protective substrate.
  • the second light beam emitted from the red semiconductor laser EP1 enters the objective optical element OBJ as a parallel light beam
  • the first compatible optical path difference providing structure in the central region and the second compatible optical path difference providing structure in the intermediate region are provided.
  • the first compatible optical path difference providing structure in the central region is the thickness of the protective substrate for BD and CD.
  • the spherical aberration of the third light beam generated due to the difference in wavelength between the first light beam and the third light beam are appropriately corrected, and the second compatible optical path difference providing structure in the intermediate region and the peripheral region are the third light beam. Is flared on the information recording surface of the CD, information can be recorded and / or reproduced appropriately for the CD having the thickness t3 of the protective substrate.
  • the first compatible optical path difference providing structure in the central region separates the condensing spot of the necessary light of the third light beam used for recording and reproduction from the condensing spot of the unnecessary light of the third light beam by an appropriate distance, As a result, the tracking characteristics when using a CD are also improved.
  • the second compatible optical path difference providing structure in the peripheral region has a spherochromatism (when the wavelength deviates from the reference wavelength due to a laser manufacturing error or the like with respect to the first light flux and the second light flux. Chromatic spherical aberration) can be corrected.
  • optical path difference function ⁇ / ⁇ B ⁇ dor ⁇ (C 2 y 2 + C 4 y 4 + C 6 y 6 + C 8 y 8 + C 10 y 10 )
  • ⁇ optical path difference function
  • ⁇ wavelength of light beam incident on the diffractive structure
  • ⁇ B manufacturing wavelength dor: diffraction order of diffracted light used for recording / reproducing on optical disc
  • y distance from optical axis
  • C 2 , C 4 , C 6 , C 8 , C 10 Diffraction surface coefficient
  • the optical surface of the objective optical element is a non-symmetrical material around the optical axis, which is defined by the following aspheric expression expression, which is substituted with the coefficient shown in the table.
  • the present embodiment is a single objective lens, in which the first compatible optical path difference providing structure is provided in the central area, and the second compatible optical path difference providing structure and the first temperature characteristic correcting structure are superimposed in the intermediate area.
  • the second temperature characteristic correction structure is provided in the peripheral region.
  • the first compatible optical path difference providing structure is a structure in which the first basic structure and the second basic structure are overlapped. The first basic structure makes the second-order diffraction efficiency of the first light beam larger than any other order diffraction efficiency, and makes the first-order diffraction efficiency of the second light beam larger than any other order diffraction efficiency.
  • the first-order diffraction efficiency of the third light flux is made larger than the diffraction efficiency of any other order.
  • the second basic structure makes the zero-order diffraction efficiency of the first light beam larger than any other order diffraction efficiency, and makes the zero-order diffraction efficiency of the second light beam larger than any other order diffraction efficiency.
  • the ⁇ 1st-order diffraction efficiency of the third light flux is made larger than the diffraction efficiency of any other order.
  • the second compatible optical path difference structure includes only the first basic structure.
  • both the first temperature characteristic correction structure and the second temperature characteristic correction structure make the fifth-order diffraction efficiency of the first light beam higher than the diffraction efficiency of any other order, so that the third light-characteristic correction structure 3
  • the next diffraction efficiency is made larger than any other order diffraction efficiency, and the third and second order diffraction efficiencies of the third light flux are made larger than any other order diffraction efficiency.
  • Tables 1 to 3 show lens data of this example.
  • the wavefront aberration change (with wavelength shift, +0.05 nm / ° C.) when the environmental temperature rises by 30 ° C. in BD is shown in Table 4.
  • the environmental temperature does not change and the wavelength is Table 5 shows the change in aberration when changed by 5 nm. From Table 4, it can be seen that the temperature characteristic correction effect appears due to the effect of the intermediate region temperature characteristic correction structure. In addition, since there is no temperature characteristic correction structure in the central region, the structure can be simplified.
  • the present embodiment is a single objective lens, in which the first compatible optical path difference providing structure is provided in the central area, and the second compatible optical path difference providing structure and the first temperature characteristic correcting structure are superimposed in the intermediate area.
  • the second temperature characteristic correction structure is provided in the peripheral region.
  • the first compatible optical path difference providing structure makes the first-order diffraction efficiency of the first light beam larger than the diffraction efficiency of any other order, and the ⁇ 1st-order diffraction efficiency of the second light beam. Is made larger than any other order diffraction efficiency, and the -2nd order diffraction efficiency of the third light flux is made larger than any other order diffraction efficiency.
  • the second compatible optical path difference structure makes the zero-order diffraction efficiency of the first light beam larger than any other order diffraction efficiency, and makes the first-order diffraction efficiency of the second light beam more than any other order diffraction efficiency.
  • the diffraction efficiency of the third light beam is made larger than that of any other order.
  • both the first temperature characteristic correction structure and the second temperature characteristic correction structure make the fifth-order diffraction efficiency of the first light beam higher than the diffraction efficiency of any other order, so that the third light-characteristic correction structure 3
  • the next diffraction efficiency is made larger than any other order diffraction efficiency, and the third and second order diffraction efficiencies of the third light flux are made larger than any other order diffraction efficiency.
  • Tables 6 to 8 show lens data of this example.
  • the wavefront aberration change (with wavelength shift, +0.05 nm / ° C.) when the environmental temperature rises by 30 ° C. is shown in Table 9.
  • the environmental temperature does not change and the wavelength is Table 10 shows the change in aberrations when changed by 5 nm. From Table 9, it can be seen that the temperature characteristic correction effect appears.
  • the structure can be simplified.
  • the present embodiment is a single objective lens, in which the first compatible optical path difference providing structure is provided in the central area, and the second compatible optical path difference providing structure and the first temperature characteristic correcting structure are superimposed in the intermediate area.
  • the second temperature characteristic correction structure is provided in the peripheral region.
  • the first compatible optical path difference providing structure makes the 0th-order diffraction efficiency of the first light beam larger than the diffraction efficiency of any other order, and the ⁇ 1st-order diffraction efficiency of the second light beam. Is made larger than any other order diffraction efficiency, and the -2nd order diffraction efficiency of the third light flux is made larger than any other order diffraction efficiency.
  • the second compatible optical path difference structure makes the zero-order diffraction efficiency of the first light beam larger than any other order diffraction efficiency, and makes the first-order diffraction efficiency of the second light beam more than any other order diffraction efficiency.
  • the diffraction efficiency of the third light beam is made larger than that of any other order.
  • both the first temperature characteristic correction structure and the second temperature characteristic correction structure make the fifth-order diffraction efficiency of the first light beam higher than the diffraction efficiency of any other order, so that the third light-characteristic correction structure 3
  • the next diffraction efficiency is made larger than any other order diffraction efficiency, and the third and second order diffraction efficiencies of the third light flux are made larger than any other order diffraction efficiency.
  • Tables 11 to 13 show lens data of this example.
  • the wavefront aberration change (with wavelength shift, +0.05 nm / ° C.) when the environmental temperature rises by 30 ° C. in BD is shown in Table 14.
  • the environmental temperature does not change and the wavelength is Table 15 shows the change in aberration when the wavelength changes by 5 nm. From Table 14, it can be seen that the temperature characteristic correction effect appears.
  • the structure can be simplified.

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  • Optics & Photonics (AREA)
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Abstract

La présente invention concerne un élément formant objectif optique pour un dispositif de lecture optique, et un dispositif de lecture optique qui est apte à enregistrer et/ou à lire des informations sur différents supports d'enregistrement optique ou à partir de ceux-ci, d'une façon appropriée et à moindre coût. L'élément formant objectif optique se divise en une région centrale dépourvue de structure de correction de caractéristiques de température, en une région intermédiaire qui comprend une première structure de correction de caractéristiques de température pourvue d'une pluralité de crans coaxiaux de forme annulaire, et en une région périphérique qui comprend une seconde structure de correction de caractéristiques de température pourvue d'une pluralité de crans coaxiaux de forme annulaire. La première structure de correction de caractéristiques de température est une structure d'indication de différence de chemin optique qui amène l'efficacité de diffraction u-dimensionnelle du premier flux lumineux à être supérieure à toute autre efficacité de diffraction dimensionnelle, et qui amène l'efficacité de diffraction v-dimensionnelle du second flux lumineux à être supérieure à toute autre efficacité de diffraction dimensionnelle. La seconde structure de correction de caractéristiques de température est une structure d'indication de différence de chemin optique qui amène l'efficacité de diffraction x-dimensionnelle du premier flux lumineux, qui est passé à travers la seconde structure de correction de caractéristiques de température, à être supérieure à toute autre efficacité de diffraction dimensionnelle, et qui satisfait l'équation suivante : (u, v) = (10, 6), (5, 3) ou (2, 1), x étant un nombre entier arbitraire.
PCT/JP2009/055133 2008-04-01 2009-03-17 Élément formant objectif optique pour un dispositif de lecture optique, et dispositif de lecture optique Ceased WO2009122896A1 (fr)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2002122780A (ja) * 2000-10-12 2002-04-26 Asahi Optical Co Ltd 光ヘッド用対物レンズおよび光ヘッドの光学系
JP2004030725A (ja) * 2002-06-21 2004-01-29 Konica Minolta Holdings Inc 光ピックアップ装置の対物光学素子及び光ピックアップ装置
JP2006092720A (ja) * 2004-08-25 2006-04-06 Konica Minolta Opto Inc 対物光学素子、光ピックアップ装置及び光ディスクドライブ装置
WO2007102315A1 (fr) * 2006-03-07 2007-09-13 Konica Minolta Opto, Inc. Dispositif de lecture optique, element optique a objectif et dispositif d'enregistrement et de lecture de donnees optique
WO2007123112A1 (fr) * 2006-04-21 2007-11-01 Konica Minolta Opto, Inc. Capteur optique, élément optique, dispositif d'enregistrement et de reproduction d'informations optiques ET methode de fabrication d'element optique

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4562645B2 (ja) * 2004-12-01 2010-10-13 Ｈｏｙａ株式会社 光学素子の設計方法および光情報記録再生装置

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2002122780A (ja) * 2000-10-12 2002-04-26 Asahi Optical Co Ltd 光ヘッド用対物レンズおよび光ヘッドの光学系
JP2004030725A (ja) * 2002-06-21 2004-01-29 Konica Minolta Holdings Inc 光ピックアップ装置の対物光学素子及び光ピックアップ装置
JP2006092720A (ja) * 2004-08-25 2006-04-06 Konica Minolta Opto Inc 対物光学素子、光ピックアップ装置及び光ディスクドライブ装置
WO2007102315A1 (fr) * 2006-03-07 2007-09-13 Konica Minolta Opto, Inc. Dispositif de lecture optique, element optique a objectif et dispositif d'enregistrement et de lecture de donnees optique
WO2007123112A1 (fr) * 2006-04-21 2007-11-01 Konica Minolta Opto, Inc. Capteur optique, élément optique, dispositif d'enregistrement et de reproduction d'informations optiques ET methode de fabrication d'element optique

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