WO2011148832A1 - Objectif pour tête optique, tête optique et dispositif de lecture et d'écriture d'informations optiques - Google Patents

Objectif pour tête optique, tête optique et dispositif de lecture et d'écriture d'informations optiques Download PDF

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Publication number
WO2011148832A1
WO2011148832A1 PCT/JP2011/061366 JP2011061366W WO2011148832A1 WO 2011148832 A1 WO2011148832 A1 WO 2011148832A1 JP 2011061366 W JP2011061366 W JP 2011061366W WO 2011148832 A1 WO2011148832 A1 WO 2011148832A1
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WIPO (PCT)
Prior art keywords
objective lens
optical
path difference
optical path
difference providing
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PCT/JP2011/061366
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English (en)
Japanese (ja)
Inventor
井上寿志
中村健太郎
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コニカミノルタオプト株式会社
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Priority to JP2012517225A priority Critical patent/JPWO2011148832A1/ja
Priority to CN201180025822XA priority patent/CN102906815A/zh
Publication of WO2011148832A1 publication Critical patent/WO2011148832A1/fr

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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—Lenses
    • G11B7/1374—Objective lenses
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1365—Separate or integrated refractive elements, e.g. wave plates
    • G11B7/1367—Stepped phase plates
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1392—Means for controlling the beam wavefront, e.g. for correction of aberration
    • G11B7/13922—Means for controlling the beam wavefront, e.g. for correction of aberration passive
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
    • G11B2007/0006—Recording, reproducing or erasing systems characterised by the structure or type of the carrier adapted for scanning different types of carrier, e.g. CD & DVD
    • 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
    • G11B7/1376—Collimator lenses
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1392—Means for controlling the beam wavefront, e.g. for correction of aberration
    • G11B7/13925—Means for controlling the beam wavefront, e.g. for correction of aberration active, e.g. controlled by electrical or mechanical means

Definitions

  • the present invention relates to an optical pickup device, an objective lens, and an optical information recording / reproducing apparatus capable of recording and / or reproducing (recording / reproducing) information interchangeably with different types of optical discs.
  • a laser light source used as a light source for reproducing information recorded on an optical disc and recording information on the optical disc has been shortened.
  • a wavelength 390 such as a blue-violet semiconductor laser is used.
  • a laser light source of ⁇ 420 nm has been put into practical use.
  • these blue-violet laser light sources are used, it is possible to record 15 to 20 GB of information on an optical disk having a diameter of 12 cm when an objective lens having the same numerical aperture (NA) as that of a DVD (digital versatile disk) is used.
  • NA of the objective optical element is increased to 0.85, 23 to 25 GB of information can be recorded on an optical disk having a diameter of 12 cm.
  • BD Blu-ray Disc
  • the BD is an example of an optical disc that uses an NA 0.85 objective lens as described above. Since the coma generated due to the tilt (skew) of the optical disk increases, the BD has a thinner protective substrate (0.1 mm with respect to 0.6 mm of DVD) than the case of the DVD cage, and is caused by skew. The amount of coma is reduced.
  • the recording density of an optical disc that records / reproduces information between the optical system for BD and the optical system for DVD Although a method of selectively switching according to the above is conceivable, a plurality of optical systems are required, which is disadvantageous for miniaturization and increases the cost.
  • the optical pickup device can be used by sharing the optical system for BD and the optical system for DVD in a compatible optical pickup device. It is preferable to reduce the number of optical components constituting the lens as much as possible. And, it is most advantageous to simplify the configuration of the optical pickup device and to reduce the cost to make the objective lens arranged facing the optical disc in common. In order to obtain a common objective lens for a plurality of types of optical disks having different recording / reproducing wavelengths, it is desirable to form a diffractive structure having a wavelength dependency of spherical aberration in the objective lens.
  • Patent Document 1 information can be recorded / reproduced to be compatible with BD and DVD using an objective lens in which a phase structure is formed in the central region and the peripheral region is aspherical.
  • An optical pickup device is described.
  • a notebook type PC is used instead of a relatively thick type called a so-called half-height mounted on a stationary recorder or the like that has been conventionally used.
  • a relatively thin optical pickup device called a so-called slim type that is mounted on the back of a thin TV or the like has been developed.
  • the slim type optical pickup device it is necessary to reduce the effective diameter and focal length of the objective lens to be compact as compared with the conventional half-height type.
  • the effective diameter of the objective lens is 3 mm
  • the working distance when using the DVD is 0.284 mm to 0.330 mm.
  • ⁇ 3 mm is an objective lens of a size often used in the above-described half-height type.
  • the effective diameter is simply reduced so that the objective lens of Patent Document 1 can be mounted on a slim type optical pickup device, the working distance when using a DVD is correspondingly shortened, and the rotating optical disc has warpage, etc. There is a risk of causing interference with the objective lens.
  • the objective lens on which the phase structure disclosed in Patent Document 1 is superimposed has a complicated optical surface shape, and there is a problem that it is difficult to manufacture particularly for a small-diameter objective lens.
  • the objective lens in which the superposition of the phase structure is stopped and only the single structure shown in Patent Document 1 is used when the objective lens is a plastic lens, the spherical aberration is good when a temperature change occurs. There is a problem that it cannot be corrected.
  • the present invention is intended to solve the above-mentioned problems, and in the case where two different optical disks, BD and DVD, are used interchangeably, a sufficient working distance can be ensured particularly for a DVD while having a small diameter.
  • the objective lens according to claim 1 includes a first light source that emits a first light beam having a first wavelength ⁇ 1 (nm) (390 ⁇ ⁇ 1 ⁇ 415), and a second wavelength ⁇ 2 (nm) (630 ⁇ ⁇ 2 ⁇ 670).
  • a second light source that emits the second light flux, and records and / or reproduces information of a BD having a protective substrate with a thickness of t1 using the first light flux, and uses the second light flux.
  • An objective lens used in an optical pickup device for recording and / or reproducing information of a DVD having a protective substrate having a thickness t2 (t1 ⁇ t2) The objective lens is a single ball,
  • the optical surface of the objective lens has a central region and a peripheral region around the central region,
  • the central region has a first optical path difference providing structure,
  • the objective lens condenses the first light flux that passes through the central region so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux that passes through the central region.
  • the objective lens condenses the first light flux passing through the peripheral area so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passes through the peripheral area.
  • the first optical path difference providing structure makes the Nth-order diffracted light quantity of the first light beam that has passed through the first optical path difference providing structure larger than any other order diffracted light quantity, and passes through the first optical path difference providing structure.
  • the Nth-order diffracted light amount of the second light flux is larger than any other order diffracted light amount, The following formula is satisfied.
  • ⁇ 1 Effective diameter of the objective lens when using the BD (mm)
  • WD2 Working distance of the objective lens when using the DVD (mm)
  • f Focal length (mm) of the objective lens in the first light flux
  • the inventor has the diffraction order of the diffracted light of the first light flux most frequently generated in the first optical path difference providing structure, even when the effective diameter is small enough to satisfy the formula (1), By making the diffraction order of the diffracted light of the second light beam the same order, it becomes possible to give a negative paraxial power. As a result, while achieving compatibility between BD and DVD, and even when using DVD And found that working distance can be increased.
  • the working distance of the objective lens of the present invention satisfies the formula (2), and is suitable for a so-called slim type optical pickup device.
  • the first optical path difference providing structure does not have to be a structure in which a plurality of optical path difference providing structures are superimposed, that is, the objective lens can be easily manufactured with a relatively simple optical surface shape.
  • the same-order diffracted light generated in the one-optical path difference providing structure spherical aberration when the wavelength is changed to a long wavelength can be made under, and the environmental temperature is changed even if the objective lens is made of plastic. It was found that the spherical aberration that sometimes occurs can be maintained well. Further, the present inventor has also found out that the wavelength characteristic is not greatly deteriorated while the temperature characteristic is improved as described above.
  • the objective lens is suitable for a so-called slim type optical pickup device, while the value of the expression (1) is more than the lower limit.
  • the value of the expression (2) is not more than the upper limit, the pitch of the first optical path difference providing structure does not become too small, so that the objective lens can be easily manufactured, and the axial chromatic aberration can be prevented from becoming too large.
  • the value of the expression (2) is equal to or greater than the lower limit, the working distance when using the second optical disk can be secured, so that the possibility of interference between the optical disk and the objective lens can be reduced.
  • the objective lens according to claim 2 is characterized in that, in the invention according to claim 1, the first optical path difference providing structure is not a structure in which a plurality of optical path difference providing structures are superimposed. According to the present invention, it is possible to obtain an objective lens having a simple shape that is easy to manufacture.
  • the objective lens according to the second aspect wherein the first optical path difference providing structure comprises only a blaze type structure.
  • the objective lens according to claim 4 is characterized in that
  • 1 in the invention according to any one of claims 1 to 3. According to the present invention, since the height of the step of the first optical path difference providing structure can be reduced, an objective lens that is easy to manufacture can be obtained, and fluctuations in diffraction efficiency during wavelength fluctuations can be suppressed to a low level.
  • the first-order diffracted light amount of the first light beam that has passed through the first optical path difference providing structure is made larger than any other order of diffracted light amount, and the first-order diffraction of the second light beam that has passed through the first optical path difference providing structure. This is because the highest diffraction efficiency can be obtained when the amount of light is larger than any other order of the amount of diffracted light.
  • the first-order diffracted light quantity of the first light beam that has passed through the first optical path difference providing structure is made larger than any other order diffracted light quantity and passed through the first optical path difference providing structure.
  • the diffraction efficiency of the first-order diffracted light beam of the first light beam is 89.54%, and the first-order diffracted light beam of the second light beam The diffraction efficiency of the diffracted light was 78.17%.
  • the second-order diffracted light amount of the first light beam that has passed through the first optical path difference providing structure is made larger than any other order of diffracted light amount, and the second-order secondary light beam that has passed through the first optical path difference providing structure.
  • the diffraction efficiency of the second-order diffracted light of the first light flux is 76.17%.
  • the diffraction efficiency of the second-order diffracted light was 47.21%. It can be seen that the diffraction efficiency decreases as the diffraction order increases.
  • the objective lens described in claim 6 is characterized in that, in the invention described in any one of claims 1 to 5, the following expression is satisfied. 0.9 ⁇ ⁇ 1 / (n-1) ⁇ d ⁇ 2.2 ⁇ ⁇ 1 / (n-1) (3) However, d: Level difference in the optical axis direction of the first optical path difference providing structure (nm) n: Refractive index of the objective lens at the first wavelength ⁇ 1 According to the present invention, since the height of the step of the first optical path difference providing structure can be reduced, an objective lens that is easy to manufacture can be obtained and diffraction at the time of wavelength variation Variations in efficiency can be kept low.
  • the step closest to the optical axis of the first optical path difference providing structure faces a direction opposite to the optical axis. It is characterized by. According to the present invention, since the value of the paraxial power can be made negative, the working distance can be extended even when the DVD is used while achieving the two compatibility of BD and DVD.
  • An objective lens according to an eighth aspect is characterized in that, in the invention according to any one of the first to seventh aspects, the value of the paraxial power at the second wavelength ⁇ 2 of the first optical path difference providing structure is negative.
  • the objective lens described in claim 9 is characterized in that, in the invention described in claim 8, the following expression is satisfied. ⁇ 0.44 ⁇ P 0 * f ⁇ ⁇ 0.06 (4) However, P 0 : Paraxial power at the second wavelength ⁇ 2 of the first optical path difference providing structure
  • the value of the expression (4) is less than the upper limit, the pitch of the first optical path difference providing structure does not become too small, so that the objective lens can be easily manufactured, and the axial chromatic aberration can be prevented from becoming too large.
  • the value of the expression (4) is equal to or greater than the lower limit, the working distance when using the second optical disk can be secured, so that the possibility of interference between the optical disk and the objective lens can be reduced.
  • the objective lens described in claim 10 is characterized in that, in the invention described in any one of claims 1 to 9, the following expression is satisfied. 0.75 ⁇ dx / f ⁇ 1.70 (5) However, dx: axial thickness of the objective lens
  • the value of the expression (5) is less than or equal to the upper limit, spherical aberration deterioration with respect to environmental temperature changes can be suppressed, the pitch of the optical path difference providing structure does not become too small, and the objective lens is easy to manufacture. A working distance when using an optical disc can be secured.
  • the value of the expression (5) is equal to or more than the lower limit, the light source side optical surface and the optical disc side optical surface of the objective lens caused by manufacturing errors even when using a short wavelength, high NA optical disc such as BD.
  • the objective lens according to claim 11 is the objective lens according to any one of claims 1 to 10, wherein the peripheral region has a second optical path difference providing structure, and the second optical path difference providing structure is the second optical path difference structure.
  • the fifth-order diffracted light amount of the first light beam that has passed through the optical path difference providing structure is made larger than any other order of diffracted light amount, and the third-order diffracted light amount of the second light beam that has passed through the second optical path difference providing structure is changed.
  • the diffracted light quantity of any order is made larger.
  • the present inventor When the first optical path difference providing structure of the present invention is used, the present inventor generates the fifth-order diffracted light of the first light beam and the third-order diffracted light of the second light beam in the second optical path difference-providing structure, thereby generating a DVD.
  • the present inventors have found that the flare state can be improved and an aperture stop effect can be provided.
  • the objective lens according to a twelfth aspect is the invention according to any one of the first to eleventh aspects, wherein the second light flux passing through the central region and the second light flux passing through the peripheral region.
  • the distance ⁇ in the optical axis direction with respect to the light condensing position is 0.005 mm or more.
  • the optical axis direction from the condensing position of the second light beam BM1 that has passed through the central region to the closest condensing position of the second light beam BM2 that has passed through the peripheral region If ⁇ is 0.005 mm or more, the two do not cover each other, and the aperture limiting function can be effectively provided.
  • the objective lens according to claim 13 is characterized in that, in the invention according to any one of claims 1 to 12, the second optical path difference providing structure comprises only a blaze structure. Thereby, the diffraction efficiency in a reference wavelength can be maintained high.
  • An optical pickup device includes the objective lens according to any one of the first to thirteenth aspects.
  • An optical pickup device is the invention according to the fourteenth aspect, which is a slim type.
  • An optical information recording / reproducing apparatus includes the optical pickup apparatus according to the fourteenth or fifteenth aspect.
  • the optical pickup device has a first light source and a second light source. Furthermore, the optical pickup device of the present invention has a condensing optical system for condensing the first light beam on the information recording surface of the BD and condensing the second light beam on the information recording surface of the DVD.
  • the optical pickup device of the present invention includes a light receiving element that receives a reflected light beam from an information recording surface of a BD or DVD.
  • BD means that information is recorded / reproduced by a light beam having a wavelength of about 390 to 415 nm and an objective lens having an NA of about 0.8 to 0.9, and the thickness (t1) of the protective substrate is 0.05.
  • DVD means that information is recorded / reproduced by a light beam having a wavelength of about 630 to 670 nm and an objective lens having an NA of about 0.60 to 0.67, and the thickness of the protective substrate is 0.5.
  • DVD series optical discs of about 0.7 mm and includes DVD-ROM, DVD-Video, DVD- Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like.
  • the recording density the recording density of BD is the highest, and then the order of DVD is lower.
  • the first light source and the second light source are preferably laser light sources.
  • the laser light source a semiconductor laser, a silicon laser, or the like can be preferably used.
  • the first wavelength ⁇ 1 of the first light flux emitted from the first light source, and the second wavelength ⁇ 2 ( ⁇ 2> ⁇ 1) of the second light flux emitted from the second light source, ⁇ 1 is 390 nm or more and 415 nm or less, ⁇ 2 is not less than 630 nm and not more than 670 nm.
  • first light source and the second 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 light amount due to the spot shape change and position change on the light receiving element, performs focus detection and track detection, and based on this detection, the objective lens can be moved for focusing and tracking I can do it.
  • the light receiving element may comprise a plurality of photodetectors.
  • the light receiving element may have a main photodetector and a sub photodetector.
  • two sub photodetectors are provided on both sides of a photodetector that receives main light used for recording and reproducing information, and the sub light for tracking adjustment is received by the two sub photodetectors. It is good also as a simple light receiving element.
  • the light receiving element may have a plurality of light receiving elements corresponding to the respective light sources.
  • the condensing optical system has an objective lens.
  • the condensing optical system preferably has a coupling lens such as a collimator in addition to the objective lens.
  • the coupling lens is a single lens or a lens group that is disposed between the objective lens and the light source and changes the divergence angle of the light beam.
  • the collimator is a type of coupling lens, and is a lens that emits light incident on the collimator as parallel light.
  • the objective lens refers to an optical system that is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing the light beam emitted from the light source onto the information recording surface of the optical disk.
  • the objective lens is preferably an objective lens composed of a single convex lens.
  • the objective lens may be a glass lens or a plastic lens, or an optical path difference providing structure is provided on the glass lens with a photo-curing resin, a UV-curing resin, or a thermosetting resin.
  • a hybrid lens may also be used.
  • the objective lens has a plurality of lenses, a glass lens and a plastic lens may be mixed and used.
  • the objective lens preferably has a refractive surface that is aspheric.
  • the base surface on which the optical path difference providing structure is provided is preferably an aspherical surface.
  • the objective lens is a glass lens
  • a glass material having a glass transition point Tg of 500 ° C. or lower more preferably 400 ° C. or lower.
  • a glass material having a glass transition point Tg of 500 ° C. or lower molding at a relatively low temperature is possible, so that the life of the mold can be extended.
  • Examples of such a glass material having a low glass transition point Tg include K-PG325 and K-PG375 (both product names) manufactured by Sumita Optical Glass Co., Ltd.
  • the specific gravity of the glass lens is generally larger than that of the resin lens, if the objective lens is a glass lens, the weight increases and a load is imposed on the actuator that drives the objective lens. Therefore, when the objective lens is a glass lens, it is preferable to use a glass material having a small specific gravity.
  • the specific gravity is preferably 4.0 or less, more preferably the specific gravity is 3.0 or less.
  • one of the important physical properties when molding a glass lens is the linear expansion coefficient a. Even if a material having a Tg of 400 ° C. or lower is selected, the temperature difference from room temperature is still larger than that of a plastic material. When lens molding is performed using a glass material having a large linear expansion coefficient a, cracks are likely to occur when the temperature is lowered.
  • the linear expansion coefficient a of the glass material is preferably 200 (10E-7 / K) or less, and more preferably 120 or less.
  • cycloolefin resin is preferably used, and specifically, ZEONEX manufactured by Nippon Zeon Co., Ltd., APEL manufactured by Mitsui Chemicals, TOPAS® ADVANCED® POLYMERS manufactured by TOPAS, JSR manufactured by ARTON, etc. are preferable examples. Can be mentioned.
  • the Abbe number of the material constituting the objective lens is preferably 50 or more.
  • At least one optical surface of the objective lens has a central region and a peripheral region around the central region.
  • the central region is preferably a region including the optical axis of the objective lens, but a minute region including the optical axis is used as an unused region or a special purpose region, and the surroundings are defined as a central region (also referred to as a central region). Also good.
  • the central region and the peripheral region are preferably provided on the same optical surface. As shown in FIG. 2, the central region CN and the peripheral region OT are preferably provided concentrically around the optical axis on the same optical surface.
  • the central region and the peripheral region are preferably adjacent to each other, but there may be a slight gap between them.
  • a first optical path difference providing structure is provided in the central region. It is preferable that a second optical path difference providing structure is provided in the peripheral region.
  • the central area of the objective lens can be said to be a shared area used for recording / reproducing BD and DVD. That is, the objective lens condenses the first light flux passing through the central area so that information can be recorded / reproduced on the information recording surface of the BD, and the second light flux passing through the central area is recorded as information recording on the DVD. Light is collected so that information can be recorded and / or reproduced on the surface.
  • the first optical path difference providing structure provided in the central region has the BD protective substrate thickness t1 and the DVD protective substrate thickness with respect to the first and second light fluxes passing through the first optical path difference providing structure. It is preferable to correct spherical aberration generated due to the difference in thickness t2 / spherical aberration generated due to the difference in wavelength between the first light beam and the second light beam.
  • the peripheral area of the objective lens is used for BD recording / reproduction and can be said to be a BD-dedicated area that is not used for DVD recording / reproduction. That is, the objective lens condenses the first light flux passing through the peripheral region so that information can be recorded / reproduced on the information recording surface of the BD.
  • the second light flux passing through the peripheral region is not condensed so that information can be recorded / reproduced on the information recording surface of the DVD.
  • the second light flux passing through the peripheral area of the objective lens preferably forms a flare on the information recording surface of the DVD.
  • the spot central portion having a high light amount density, and the light amount density is the spot center. It is preferable to have a spot middle part lower than the spot part and a spot peripheral part whose light intensity is higher than the spot middle part and lower than the spot center part.
  • the center portion of the spot is used for recording / reproducing information on the optical disc, and the middle portion of the spot and the peripheral portion of the spot are not used for recording / reproducing information on the optical disc.
  • this spot peripheral part is called flare.
  • the spot peripheral part may be called a flare.
  • the second light flux that has passed through the peripheral region of the objective lens preferably forms a spot peripheral portion on the information recording surface of the DVD.
  • the first optical path difference providing structure is preferably provided in a region of 70% or more of the area of the central region of the objective lens, and more preferably 90% or more. More preferably, the first optical path difference providing structure is provided on the entire surface of the central region.
  • the second optical path difference providing structure is preferably provided in a region of 70% or more of the area of the peripheral region of the objective lens, and more preferably 90% or more. More preferably, the second optical path difference providing structure is provided on the entire surface of the peripheral region.
  • optical path difference providing structure referred to in this specification is a general term for structures that add an optical path difference to an incident light beam.
  • the optical path difference providing structure also includes a phase difference providing structure for providing a phase difference.
  • the phase difference providing structure includes a diffractive structure.
  • the optical path difference providing structure of the present invention is preferably a diffractive structure.
  • the optical path difference providing structure has a step, preferably a plurality of steps. This step adds an optical path difference and / or phase difference to the incident light flux.
  • the optical path difference added by the optical path difference providing structure may be an integer multiple of the wavelength of the incident light beam or a non-integer multiple of the wavelength of the incident light beam.
  • the steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis.
  • the objective lens provided with the optical path difference providing structure is a single aspherical lens
  • the incident angle of the light flux to the objective lens differs depending on the height from the optical axis.
  • Each will be slightly different.
  • the objective lens is a single-lens aspherical convex lens, even if it is an optical path difference providing structure that provides the same optical path difference, generally the distance from the optical axis tends to increase.
  • the diffractive structure referred to in this specification is a general term for structures that have a step and have a function of converging or diverging a light beam by diffraction.
  • a plurality of unit shapes are arranged around the optical axis, and a light beam is incident on each unit shape, and the wavefront of the transmitted light is shifted between adjacent annular zones, resulting in new It includes a structure that converges or diverges light by forming a simple wavefront.
  • the diffractive structure preferably has a plurality of steps, and the steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis.
  • the exit angle from the diffractive structure and the optical path length to enter the lens differ depending on the height from the optical axis.
  • the amount will vary slightly for each zone.
  • the objective lens is a single aspherical convex lens, even if it is a diffractive structure that generates diffracted light of the same diffraction order, generally, the distance from the optical axis tends to increase.
  • the optical path difference providing structure has a plurality of concentric annular zones with the optical axis as the center.
  • the optical path difference providing structure can generally have various cross-sectional shapes (cross-sectional shapes on the plane including the optical axis), and the cross-sectional shapes including the optical axis are roughly classified into a blazed structure and a staircase structure.
  • the blaze-type structure means that the cross-sectional shape including the optical axis of the optical element having the optical path difference providing structure is a sawtooth shape.
  • the upper side is the light source side and the lower side is the optical disc side, and the optical path difference providing structure is formed on a plane as a mother aspherical surface.
  • the length in the direction perpendicular to the optical axis of one blaze unit is called a pitch P.
  • the length of the step in the direction parallel to the optical axis of the blaze is referred to as a step amount d. (See Fig. 3 (a))
  • the staircase structure has a cross-sectional shape including an optical axis of an optical element having an optical path difference providing structure (referred to as a staircase unit).
  • V level means a ring-shaped surface (hereinafter also referred to as a terrace surface) corresponding to (or facing) the vertical direction of the optical axis in one step unit of the step structure. In other words, it is divided by V steps and divided into V ring zones.
  • a three-level or higher staircase structure has a small step and a large step.
  • the optical path difference providing structure illustrated in FIG. 3C is referred to as a five-level staircase structure
  • the optical path difference providing structure illustrated in FIG. 3D is referred to as a two-level staircase structure (also referred to as a binary structure).
  • a two-level staircase structure is described below.
  • a plurality of annular zones including a plurality of concentric annular zones around the optical axis, and a plurality of annular zones including the optical axis of the objective lens have a plurality of stepped surfaces Pa and Pb extending in parallel to the optical axis,
  • the light source side terrace surface Pc for connecting the light source side ends of the adjacent step surfaces Pa and Pb and the optical disk side terrace surface Pd for connecting the optical disk side ends of the adjacent step surfaces Pa and Pb are formed.
  • the surface Pc and the optical disc side terrace surface Pd are alternately arranged along the direction intersecting the optical axis.
  • the length of one staircase unit in the direction perpendicular to the optical axis is called a pitch P.
  • the length of the step in the direction parallel to the optical axis of the staircase is referred to as step amounts B1 and B2.
  • a large step amount B1 and a small step amount B2 exist.
  • the optical path difference providing structure is preferably a structure in which a certain unit shape is periodically repeated.
  • the unit shape is periodically repeated here includes a shape in which the same shape is repeated in the same cycle.
  • the unit shape that is one unit of the cycle has regularity, and the shape in which the cycle gradually increases or decreases gradually is also included in the “unit shape is periodically repeated”.
  • the sawtooth shape as a unit shape is repeated. As shown in FIG. 3 (a), the same sawtooth shape may be repeated, and as shown in FIG. 3 (b), the shape of the sawtooth shape gradually increases as it moves away from the optical axis. A shape in which the pitch becomes longer or a shape in which the pitch becomes shorter may be used.
  • the blazed structure has a step opposite to the optical axis (center) side, and in other areas, the blazed structure has a step toward the optical axis (center).
  • the optical path difference providing structure has a staircase structure
  • the first optical path difference providing structure and the second optical path difference providing structure may be provided on different optical surfaces of the objective lens, respectively, but are preferably provided on the same optical surface. Providing them on the same optical surface is preferable because it makes it possible to reduce eccentricity errors during manufacturing. Moreover, it is preferable that the first optical path difference providing structure and the second optical path difference providing structure are provided on the surface on the light source side of the objective lens rather than the surface on the optical disc side of the objective lens. In other words, the first optical path difference providing structure and the second optical path difference providing structure are preferably provided on the optical surface having the smaller absolute value of the radius of curvature of the objective lens.
  • the first optical path difference providing structure is preferably a blazed structure. Moreover, it is preferable that the first optical path difference providing structure is composed of only one type of blaze type structure and other structures are not superimposed. In addition, the first optical path difference providing structure makes the Nth-order diffracted light amount of the first light flux that has passed through the first optical path difference providing structure larger than any other order diffracted light amount, and passed through the first optical path difference providing structure. The Nth-order diffracted light quantity of the second light beam is made larger than any other order diffracted light quantity.
  • the order of the diffracted light generated most in the first light flux that has passed through the first optical path difference providing structure is equal to the order of the diffracted light generated most in the second light flux that has passed through the first optical path difference providing structure.
  • the absolute value of N is preferably 1 from the viewpoints of high diffraction efficiency, ease of manufacture, small diffraction efficiency fluctuation at the time of wavelength fluctuation, and the like. Further, N is more preferably +1.
  • the step amount of the first optical path difference providing structure satisfies the following conditional expression. 0.9 ⁇ ⁇ 1 / (n-1) ⁇ d ⁇ 2.2 ⁇ ⁇ 1 / (n-1) (3)
  • d is the step amount (nm) in the optical axis direction of the first optical path difference providing structure
  • n represents the refractive index of the objective lens at the first wavelength ⁇ 1.
  • the objective lens provided with the optical path difference providing structure is a single aspherical convex lens, the incident angle of the light flux to the objective lens differs depending on the height from the optical axis, so that the optical path difference providing structure that gives the same optical path difference Even so, in general, as the distance from the optical axis increases, the step amount tends to increase.
  • the reason why the upper limit is multiplied by 2.2 in the conditional expression (3) is because the increase in the level difference is taken into account. It is preferable that the conditional expression (3) is satisfied in all the steps of the first optical path difference providing structure.
  • the blazed wavelength ⁇ B of the first optical path difference providing structure (theoretically, the wavelength at which the diffraction efficiency is 100% in the first optical path difference providing structure) is preferably larger than ⁇ 1 and smaller than ⁇ 2. More preferably, it is 470 nm or more and 550 nm or less. More preferably, they are 480 nm or more and 530 nm or less.
  • the second optical path difference providing structure is preferably a blazed structure. Moreover, it is preferable that the second optical path difference providing structure is composed of only one type of blaze type structure and other structures are not superimposed. In addition, the second optical path difference providing structure makes the fifth-order diffracted light quantity of the first light flux that has passed through the second optical path difference providing structure larger than any other order diffracted light quantity, and passed through the second optical path difference providing structure. It is preferable that the third-order diffracted light quantity of the second light beam is larger than any other order diffracted light quantity. In particular, when
  • the distance ⁇ in the optical axis direction between the condensing position of the second light beam that has passed through the central region and the condensing position of the second light beam that has passed through the peripheral region is It is preferable that it is 0.005 mm or more.
  • the first optical path difference providing structure preferably has a negative paraxial power at the second wavelength ⁇ 2. Particularly preferably, the following formula is satisfied. ⁇ 0.44 ⁇ P 0 * f ⁇ ⁇ 0.06 (4) However, P 0 : Power of the first optical path difference providing structure f: Focal length of the objective lens It is more preferable that the following expression is satisfied. ⁇ 0.44 ⁇ P 0 * f ⁇ ⁇ 0.14 (4 ′)
  • the first optical path difference providing structure has a negative paraxial power (also referred to as power in this specification) with respect to the second light flux.
  • a negative paraxial power also referred to as power in this specification
  • having paraxial power means that C 1 h 2 is not 0 when the optical path difference function of the first optical path difference providing structure is expressed by the following equation ( 2 ).
  • the paraxial power P in the diffractive structure can be generally expressed by the following equation. “Having negative paraxial power” means that this value is negative.
  • C 1 is the optical path difference function coefficient
  • m is the diffraction order
  • ⁇ 2 is the wavelength of the second light source used in the optical pickup device
  • ⁇ B is the blazed wavelength of the first optical path difference providing structure (its diffraction structure)
  • P ⁇ 2 ⁇ m ⁇ ( ⁇ 2 / ⁇ B ) ⁇ C 1 (8)
  • the step closest to the optical axis of the first optical path difference providing structure is directed in a direction opposite to the optical axis.
  • the step is directed in the direction opposite to the optical axis” means a state as shown in FIG. FIG. 23A shows a state in which the step is directed in the direction of the optical axis.
  • at least a half step in the direction perpendicular to the optical axis from the optical axis to the boundary between the central region and the peripheral region and the step existing between the optical axes are directed in the opposite direction to the optical axis. It is.
  • the first optical path difference providing structure when the first optical path difference providing structure is near the optical axis, the step is opposite to the optical axis, but is switched halfway, and near the peripheral region, the first optical path difference providing structure has a step on the optical axis.
  • the shape may be suitable. However, preferably, all the steps of the first optical path difference providing structure provided in the central region are directed in a direction opposite to the optical axis.
  • NA1 The numerical aperture on the image side of the objective lens necessary for reproducing / recording information on the first optical disc is NA1, and the numerical aperture on the image side of the objective lens necessary for reproducing / recording information on the second optical disc.
  • NA2 NA1> NA2
  • NA1 is preferably 0.75 or more and 0.9 or less, and more preferably 0.8 or more and 0.9 or less.
  • NA1 is preferably 0.85.
  • NA2 is preferably 0.55 or more and 0.7 or less.
  • NA2 is preferably 0.60 or 0.65.
  • the boundary between the central region and the peripheral region of the objective lens is 0.9 ⁇ NA 2 or more and 1.2 ⁇ NA 2 or less (more preferably 0.95 ⁇ NA 2 or more, 1.15 ⁇ NA 2) when the second light flux is used. It is preferably formed in a portion corresponding to the following range. More preferably, the boundary between the central region and the peripheral region of the objective lens is formed in a portion corresponding to NA2.
  • the objective lens preferably satisfies the following conditional expression (4). 0.75 ⁇ dx / f ⁇ 1.70 (5)
  • dx represents the thickness (mm) on the optical axis of the objective lens
  • f represents the focal length (mm) of the objective lens in the first light flux.
  • the value of the expression (5) is less than or equal to the upper limit, spherical aberration deterioration with respect to environmental temperature changes can be suppressed, the pitch of the optical path difference providing structure does not become too small, and the objective lens is easy to manufacture. A working distance of the optical disc can be secured.
  • the value of the expression (5) is equal to or greater than the lower limit, the deterioration of the optical characteristics due to the optical axis decentering of the light source side optical surface and the optical disc side optical surface of the objective lens caused by the manufacturing error does not become excessive. Since the edge thickness of the optical surface of the objective lens does not become too thin, the material can be smoothly flowed in injection molding or the like, and molding becomes easy. It is more preferable to satisfy the following formula. 0.90 ⁇ dx / f ⁇ 1.41 (5 ′)
  • the objective lens is likely to generate astigmatism and decentered coma, but the conditional expression (5) occurs. By satisfying the above, it is possible to suppress the generation of astigmatism and decentration coma.
  • conditional expression (5) results in a thick objective lens with a thick on-axis objective lens, so that the working distance during DVD recording / playback tends to be short.
  • the objective lens of the present invention satisfies the following conditional expressions (1) and (2).
  • ⁇ 1 represents the effective diameter (mm) of the objective lens when using BD
  • WD2 represents the working distance (mm) of the objective lens when using DVD
  • f is the focal length of the objective lens in the first light flux.
  • Mm magn ⁇ ⁇ 2.4
  • 1.7 ⁇ ⁇ 1 ⁇ 2.4 (1 ′) 0.10 ⁇ WD2 / f ⁇ 0.32 (2 ′)
  • the first light beam and the second light beam may be incident on the objective lens as parallel light, or may be incident on the objective lens as divergent light or convergent light. Even during tracking, in order to prevent coma from occurring, it is preferable that all of the first light flux and the second light flux be incident on the objective lens as parallel light or substantially parallel light.
  • all of the first light beam and the second light beam can be incident on the objective lens as parallel light or substantially parallel light, and thus the effect of the present invention is more remarkable. It becomes.
  • the imaging magnification m1 of the objective lens when the first light beam is incident on the objective lens satisfy the following formula (9). -0.01 ⁇ m1 ⁇ 0.01 (9)
  • the imaging magnification m2 of the objective lens when the second light beam is incident on the objective lens satisfies the following formula (10). Is preferred. -0.01 ⁇ m2 ⁇ 0.01 (10)
  • the imaging magnification m2 of the objective lens when the second light beam is incident on the objective lens preferably satisfies the following expression (10) ′. . ⁇ 0.025 ⁇ m2 ⁇ ⁇ 0.01 (10) ′
  • the WD of the objective optical element when using the second optical disc is preferably 0.2 mm or more and 0.55 mm or less. Furthermore, the WD of the objective optical element when using the first optical disk is preferably 0.25 mm or more and 1.0 mm or less.
  • An optical information recording / reproducing apparatus includes an optical disc drive apparatus having the above-described optical pickup apparatus.
  • the optical pickup device is preferably a slim type.
  • the optical disk drive apparatus can hold an optical disk mounted from the optical information recording / reproducing apparatus main body containing the optical pickup apparatus or the like. There are a system in which only the tray is taken out, and a system in which the optical disc drive apparatus main body in which the optical pickup device is stored is taken out to the outside.
  • the optical information recording / reproducing apparatus using each method described above is generally equipped with the following components, but is not limited thereto.
  • An optical pickup device housed in a housing or the like, a drive source of an optical pickup device such as a seek motor that moves the optical pickup device together with the housing toward the inner periphery or outer periphery of the optical disc, and the optical pickup device housing the inner periphery or outer periphery of the optical disc include a transfer means of an optical pickup device having a guide rail or the like that guides toward the head, a spindle motor that rotates the optical disk, and the like.
  • the former method is provided with a tray that can be held in a state in which an optical disk is mounted and a loading mechanism for sliding the tray, and the latter method has no tray and loading mechanism. It is preferable that each component is provided in a drawer corresponding to a chassis that can be pulled out to the outside.
  • an objective lens for an optical pickup device, an optical pickup device, and an optical information recording / reproducing device that can suppress the occurrence of an error signal or the like when three different optical disks are used interchangeably.
  • FIG. 4 is a longitudinal spherical aberration diagram when the BD of Example 1 is used.
  • FIG. 4 is a longitudinal spherical aberration diagram when the DVD of Example 1 is used.
  • FIG. 6 is a longitudinal spherical aberration diagram when the BD of Example 2 is used.
  • FIG. 6 is a longitudinal spherical aberration diagram when the DVD of Example 2 is used.
  • FIG. 5 is a longitudinal spherical aberration diagram when the BD of Example 3 is used.
  • FIG. 6 is a longitudinal spherical aberration diagram when the DVD of Example 3 is used.
  • FIG. 6 is a longitudinal spherical aberration diagram when the BD of Example 4 is used.
  • FIG. 6 is a longitudinal spherical aberration diagram when the DVD of Example 4 is used.
  • FIG. 6 is a longitudinal spherical aberration diagram when the DVD of Example 4 is used.
  • FIG. 6 is a longitudinal spherical aberration diagram when the BD of Example 5 is used.
  • FIG. 6 is a longitudinal spherical aberration diagram when using the DVD of Example 5.
  • FIG. 12 is a longitudinal spherical aberration diagram when the BD of Example 6 is used.
  • FIG. 12 is a longitudinal spherical aberration diagram when the DVD of Example 6 is used.
  • FIG. 12 is a longitudinal spherical aberration diagram when the BD of Example 7 is used.
  • FIG. 10 is a longitudinal spherical aberration diagram when the DVD of Example 7 is used.
  • FIG. 12 is a longitudinal spherical aberration diagram when the BD of Example 8 is used.
  • FIG. 10 is a longitudinal spherical aberration diagram when using the DVD of Example 8.
  • FIG. 12 is a longitudinal spherical aberration diagram when the BD of Example 9 is used.
  • FIG. 12 is a longitudinal spherical aberration diagram when the BD of Example 10 is used. It is a figure for demonstrating the direction of an optical path difference providing structure, and the state (a) in which the level
  • FIG. 4 is a diagram schematically showing a configuration of the optical pickup apparatus PU1 of the present embodiment that can appropriately record and / or reproduce information on BD and DVD, which are different optical disks.
  • the optical pickup device PU1 is a slim type and can be mounted on an optical information recording / reproducing device.
  • the first optical disc is a BD
  • the second optical disc is a DVD
  • the third optical disc is a CD.
  • the present invention is not limited to the present embodiment.
  • the optical pickup device PU1 emits light when recording / reproducing information with respect to the objective lens OL, the ⁇ / 4 wavelength plate QWP, the rising mirror M, the collimating lens COL, the polarization beam splitter BS, and the dichroic prisms DP and BD.
  • a first semiconductor laser LD1 first light source
  • a second semiconductor laser LD2 second light source
  • emitting a second light beam a second light beam
  • a sensor lens SEN a light receiving element PD as a photodetector, and the like.
  • the first optical path difference providing structure formed in the central region of the single objective lens OL is not a superposition structure, and the first-order diffracted light amount of the first light beam that has passed through the first optical path difference providing structure is of any other order.
  • the first order diffracted light amount of the second light flux that has passed through the first optical path difference providing structure is made larger than the diffracted light amount of any other order.
  • the second optical path difference providing structure formed in the peripheral region of the objective lens OL makes the fifth-order diffracted light quantity of the first light beam that has passed through the second optical path difference providing structure larger than any other order diffracted light quantity.
  • the third-order diffracted light quantity of the second light flux that has passed through the second optical path difference providing structure is made larger than any other order diffracted light quantity, but is not limited to this combination of diffraction orders. Furthermore, the following expression is satisfied. 1.7 ⁇ ⁇ 1 ⁇ 2.9 (1) 0.10 ⁇ WD2 / f ⁇ 0.40 (2) However, ⁇ 1: Effective diameter when using BD (mm) WD2: Working distance when using DVD (mm) f: Focal length (mm) of the objective lens OL in the first light flux
  • the light beam condensed by the central region, the intermediate region, and the peripheral region of the objective lens OL becomes a spot formed on the information recording surface RL1 of the BD through the protective substrate PL1 having a thickness of 0.1 mm. .
  • the reflected light beam modulated by the information pits on the information recording surface RL1 is transmitted again through the objective lens OL and a diaphragm (not shown), and then converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wavelength plate QWP. , Reflected by the collimating lens COL, reflected by the polarization beam splitter BS, and converged on the light receiving surface of the light receiving element PD via the sensor lens SEN.
  • the information recorded on the BD can be read by using the output signal of the light receiving element PD to focus or track the objective lens OL by the biaxial actuator AC1.
  • the spherical aberration generated due to the wavelength fluctuation or different information recording layers is changed in magnification. Correction can be made by changing the divergence angle or convergence angle of the light beam incident on the objective optical element OL by changing the collimating lens COL as means in the optical axis direction.
  • the light is reflected, converted from linearly polarized light to circularly polarized light by the ⁇ / 4 wavelength plate QWP, and enters the objective lens OL.
  • the light beam condensed by the central region and the intermediate region of the objective lens OL (the light beam that has passed through the peripheral region is flared and forms a spot peripheral part) is passed through the protective substrate PL2 having a thickness of 0.6 mm.
  • the spot is formed on the information recording surface RL2 of the DVD and forms the center of the spot.
  • the reflected light beam modulated by the information pits on the information recording surface RL2 is again transmitted through the objective lens OL, converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wave plate QWP, reflected by the rising mirror M, and collimated.
  • the light beam is converged by the lens COL, reflected by the polarization beam splitter BS, and converged on the light receiving surface of the light receiving element PD via the sensor lens SEN.
  • the information recorded on DVD can be read using the output signal of light receiving element PD.
  • a power of 10 for example, 2.5 ⁇ 10 ⁇ 3
  • E for example, 2.5 ⁇ E ⁇ 3
  • the optical surface of the objective lens is formed as an aspherical surface that is symmetric about the optical axis and is defined by a mathematical formula in which the coefficients shown in Table 1 are substituted into Formula 1.
  • X (h) is an axis in the optical axis direction (the light traveling direction is positive)
  • ⁇ is a conical coefficient
  • Ai is an aspherical coefficient
  • h is a height from the optical axis
  • r is a paraxial radius of curvature. It is.
  • the optical path difference given to the light flux of each wavelength by the diffractive structure is defined by an equation in which the coefficient shown in the table is substituted into the optical path difference function of Formula 2. .
  • ⁇ is the wavelength of the incident light beam (also referred to as the used wavelength)
  • ⁇ B is the design wavelength (called a blazed wavelength in the case of a blazed diffraction structure)
  • dor is the diffraction order
  • C i is a coefficient of the optical path difference function.
  • Example 1 shows lens data of the objective lens of Example 1.
  • FIG. 5 shows a spherical aberration diagram of the objective lens of Example 1 when using the BD. As shown in FIG. 5, the spherical aberration is good in the BD. The spherical aberration is good even when the environmental temperature change of + 30 ° C. occurs, and the spherical aberration is not greatly deteriorated even when the light source wavelength fluctuation of +5 nm occurs.
  • the paraxial power when the second light flux passes through the first optical path difference providing structure is ⁇ 0.41.
  • FIG. 6 is a longitudinal spherical aberration diagram of the objective lens of Example 1 when using a DVD.
  • the horizontal axis is positive in the direction away from the objective lens.
  • the second optical path difference providing structure in the peripheral region having a numerical aperture NA of 0.6 or more makes the fifth-order diffracted light quantity of the first light beam that has passed through the second optical path difference providing structure larger than any other order diffracted light quantity.
  • This is a structure in which the third-order diffracted light quantity of the second light beam that has passed through the two-optical path difference providing structure is larger than any other order diffracted light quantity (hereinafter referred to as a (5/3) structure).
  • the vertical axis of the graph represents the radius of the optical surface of the objective lens as 1, and m represents the diffraction order. Further, the graph shows a diffraction order of 0 order or higher and a diffraction efficiency of 1% or higher.
  • the second optical path difference providing structure is a (5/3) structure, as shown in FIG. 6, the first-order diffracted light of the second light beam that has passed through the central region has a diffraction efficiency of 99. It can be seen that a good flare is formed because the third-order diffracted light of 49% is separated from the condensing position in the optical axis direction, and diffracted light of other orders is hardly generated.
  • FIG. 7 shows a spherical aberration diagram of the objective lens of Example 2 when using the BD.
  • spherical aberration is good in BD.
  • the spherical aberration is good even when the environmental temperature change of + 30 ° C. occurs, and the spherical aberration is not greatly deteriorated even when the light source wavelength fluctuation of +5 nm occurs.
  • the paraxial power when the second light flux passes through the first optical path difference providing structure is ⁇ 0.39.
  • FIG. 8 is a longitudinal spherical aberration diagram of the objective lens of Example 2 when using a DVD.
  • the second optical path difference providing structure in the peripheral region having a numerical aperture NA of 0.6 or more is a (5/3) structure.
  • the vertical axis of the graph represents the radius of the optical surface of the objective lens as 1, and m represents the diffraction order. Further, the graph shows a diffraction order of 0 order or higher and a diffraction efficiency of 1% or higher.
  • the second optical path difference providing structure is a (5/3) structure, as shown in FIG. 8, the first-order diffracted light of the second light beam that has passed through the central region has a diffraction efficiency of 99. It can be seen that a good flare is formed because the third-order diffracted light of 49% is separated from the condensing position in the optical axis direction, and diffracted light of other orders is hardly generated.
  • FIG. 9 shows a spherical aberration diagram of the objective lens of Example 3 when using the BD.
  • spherical aberration is good in BD.
  • the spherical aberration is good even when the environmental temperature change of + 30 ° C. occurs, and the spherical aberration is not greatly deteriorated even when the light source wavelength fluctuation of +5 nm occurs.
  • the paraxial power when the second light flux passes through the first optical path difference providing structure is ⁇ 0.25.
  • FIG. 10 is a longitudinal spherical aberration diagram of the objective lens of Example 3 when using a DVD.
  • the second optical path difference providing structure in the peripheral region having a numerical aperture NA of 0.6 or more is a (5/3) structure.
  • the vertical axis of the graph represents the radius of the optical surface of the objective lens as 1, and m represents the diffraction order. Further, the graph shows a diffraction order of 0 order or higher and a diffraction efficiency of 1% or higher.
  • the second optical path difference providing structure is a (5/3) structure, as shown in FIG. 10, the first-order diffracted light of the second light beam that has passed through the central region has a diffraction efficiency of 99. It can be seen that a good flare is formed because the third-order diffracted light of 49% is separated from the condensing position in the optical axis direction, and diffracted light of other orders is hardly generated.
  • Example 4 shows lens data of the objective lens of Example 4.
  • FIG. 11 shows a spherical aberration diagram of the objective lens of Example 4 when using the BD.
  • spherical aberration is good in BD.
  • the spherical aberration is good even when the environmental temperature change of + 30 ° C. occurs, and the spherical aberration is not greatly deteriorated even when the light source wavelength fluctuation of +5 nm occurs.
  • the paraxial power when the second light flux passes through the first optical path difference providing structure is ⁇ 0.23.
  • FIG. 12 is a longitudinal spherical aberration diagram of the objective lens of Example 4 when using a DVD.
  • the second optical path difference providing structure in the peripheral region having a numerical aperture NA of 0.6 or more is a (5/3) structure.
  • the vertical axis of the graph represents the radius of the optical surface of the objective lens as 1, and m represents the diffraction order. Further, the graph shows a diffraction order of 0 order or higher and a diffraction efficiency of 1% or higher.
  • the second optical path difference providing structure is a (5/3) structure, as shown in FIG. 12, the first-order diffracted light of the second light beam that has passed through the central region has a diffraction efficiency 99 of the second light beam that has passed through the peripheral region. It can be seen that a good flare is formed because the third-order diffracted light of .49% is separated from the condensing position in the optical axis direction, and diffracted light of other orders is hardly generated.
  • Table 5 shows lens data of the objective lens of Example 5.
  • FIG. 13 shows a spherical aberration diagram of the objective lens of Example 5 when using the BD. As shown in FIG. 13, spherical aberration is good in BD. The spherical aberration is good even when the environmental temperature change of + 30 ° C. occurs, and the spherical aberration is not greatly deteriorated even when the light source wavelength fluctuation of +5 nm occurs.
  • the paraxial power when the second light flux passes through the first optical path difference providing structure is ⁇ 0.17.
  • FIG. 14 is a longitudinal spherical aberration diagram of the objective lens of Example 5 when using a DVD.
  • the second optical path difference providing structure in the peripheral region having a numerical aperture NA of 0.6 or more is a (5/3) structure.
  • the vertical axis of the graph represents the radius of the optical surface of the objective lens as 1, and m represents the diffraction order. Further, the graph shows a diffraction order of 0 order or higher and a diffraction efficiency of 1% or higher.
  • the second optical path difference providing structure is a (5/3) structure
  • the first-order diffracted light of the second light beam that has passed through the central region has a diffraction efficiency of 99. It can be seen that a good flare is formed because the third-order diffracted light of 49% is separated from the condensing position in the optical axis direction, and diffracted light of other orders is hardly generated.
  • FIG. 15 shows a spherical aberration diagram of the objective lens of Example 6 when using the BD.
  • the spherical aberration is good in the BD.
  • the spherical aberration is good even when the environmental temperature change of + 30 ° C. occurs, and the spherical aberration is not greatly deteriorated even when the light source wavelength fluctuation of +5 nm occurs.
  • the paraxial power when the second light flux passes through the first optical path difference providing structure is ⁇ 0.18.
  • FIG. 16 is a longitudinal spherical aberration diagram of the objective lens of Example 6 when using a DVD.
  • the second optical path difference providing structure in the peripheral region having a numerical aperture NA of 0.6 or more is a (5/3) structure.
  • the vertical axis of the graph represents the radius of the optical surface of the objective lens as 1, and m represents the diffraction order. Further, the graph shows a diffraction order of 0 order or higher and a diffraction efficiency of 1% or higher.
  • the second optical path difference providing structure is a (5/3) structure, as shown in FIG. 16, the first-order diffracted light of the second light beam that has passed through the central region has a diffraction efficiency 99. It can be seen that a good flare is formed because the third-order diffracted light of 49% is separated from the condensing position in the optical axis direction, and diffracted light of other orders is hardly generated.
  • Table 7 shows lens data of the objective lens of Example 7.
  • FIG. 17 shows a spherical aberration diagram of the objective lens of Example 7 when using the BD.
  • spherical aberration is good in BD.
  • the spherical aberration is good even when the environmental temperature change of + 30 ° C. occurs, and the spherical aberration is not greatly deteriorated even when the light source wavelength fluctuation of +5 nm occurs.
  • the paraxial power when the second light flux passes through the first optical path difference providing structure is ⁇ 0.12.
  • FIG. 18 is a longitudinal spherical aberration diagram of the objective lens of Example 7 when using a DVD.
  • the second optical path difference providing structure in the peripheral region having a numerical aperture NA of 0.6 or more is a (5/3) structure.
  • the vertical axis of the graph represents the radius of the optical surface of the objective lens as 1, and m represents the diffraction order. Further, the graph shows a diffraction order of 0 order or higher and a diffraction efficiency of 1% or higher.
  • the second optical path difference providing structure is a (5/3) structure, as shown in FIG. 18, the first-order diffracted light of the second light beam that has passed through the central region has a diffraction efficiency of 99. It can be seen that a good flare is formed because the third-order diffracted light of 49% is separated from the condensing position in the optical axis direction, and diffracted light of other orders is hardly generated.
  • Table 8 shows lens data of the objective lens of Example 8.
  • FIG. 19 shows a spherical aberration diagram of the objective lens of Example 8 when using the BD.
  • spherical aberration is good in BD.
  • the spherical aberration is good even when the environmental temperature change of + 30 ° C. occurs, and the spherical aberration is not greatly deteriorated even when the light source wavelength fluctuation of +5 nm occurs.
  • the paraxial power when the second light flux passes through the first optical path difference providing structure is ⁇ 0.11.
  • FIG. 20 is a longitudinal spherical aberration diagram of the objective lens of Example 8 when using a DVD.
  • the second optical path difference providing structure in the peripheral region having a numerical aperture NA of 0.6 or more is a (5/3) structure.
  • the vertical axis of the graph represents the radius of the optical surface of the objective lens as 1, and m represents the diffraction order. Further, the graph shows a diffraction order of 0 order or higher and a diffraction efficiency of 1% or higher.
  • the second optical path difference providing structure is a (5/3) structure, as shown in FIG. 20, the first-order diffracted light of the second light beam that has passed through the central region has a diffraction efficiency of 99. It can be seen that a good flare is formed because the third-order diffracted light of 49% is separated from the condensing position in the optical axis direction, and diffracted light of other orders is hardly generated.
  • Example 9 shows lens data of the objective lens of Example 9.
  • FIG. 21 shows a spherical aberration diagram of the objective lens of Example 9 when using the BD. As shown in FIG. 21, spherical aberration is good in BD.
  • the paraxial power when the second light flux passes through the first optical path difference providing structure is ⁇ 0.05.
  • Table 10 shows lens data of the objective lens of Example 10.
  • FIG. 22 shows a spherical aberration diagram of the objective lens of Example 10 when using the BD. As shown in FIG. 22, spherical aberration is good in BD.
  • the paraxial power when the second light flux passes through the first optical path difference providing structure is ⁇ 0.05.
  • Table 11 summarizes the numerical values that are characteristic of Examples 1 to 10. Incidentally, regarding the expression (3), in this embodiment, 0.892 ⁇ m ⁇ d ⁇ 1.508 ⁇ m is satisfied.

Abstract

L'invention concerne un objectif approprié pour des têtes optiques minces assurant une comptabilité entre deux types de disques optiques. L'objectif présente un diamètre réduit, un diamètre effectif φ1 (mm) qui satisfait à l'équation (1) ci-après lorsqu'un premier disque optique est utilisé, et une longueur focale égale à f(mm). L'objectif peut être adapté au prolongement d'une distance de fonctionnement WD2 (mm) permettant une utilisation avec un second disque optique afin de satisfaire à l'équation (2) ci-dessous en créant une puissance de diffraction paraxiale négative à l'aide de faisceaux lumineux ayant le même ordre de diffraction et produits dans une première structure créant une différence de chemin optique. De plus, une structure de diffraction n'est pas superposée aux première et seconde structures créant une différence de chemin optique, cela permettant de les simplifier du point de vue de la forme des plans optiques afin d'en faciliter la fabrication. De plus, le fait d'utiliser des faisceaux lumineux ayant le même ordre de diffraction et produits dans la première structure créant une différence de chemin optique permet de maintenir un état d'aberration sphérique préféré, cette aberration pouvant être provoquée par des variations de longueur d'onde d'une source lumineuse ou par des variations de la température ambiante. 1,7≤φ1≤2,9 (1) 0,10≤WD2/f≤0,42 (2)
PCT/JP2011/061366 2010-05-24 2011-05-18 Objectif pour tête optique, tête optique et dispositif de lecture et d'écriture d'informations optiques WO2011148832A1 (fr)

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JP2012517225A JPWO2011148832A1 (ja) 2010-05-24 2011-05-18 光ピックアップ装置用の対物レンズ、光ピックアップ装置及び光情報記録再生装置
CN201180025822XA CN102906815A (zh) 2010-05-24 2011-05-18 光拾取装置用物镜、光拾取装置及光信息记录再生装置

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JP2005149626A (ja) * 2003-11-17 2005-06-09 Fujinon Corp 光記録媒体用対物レンズおよびこれを用いた光ピックアップ装置
JP2006012393A (ja) * 2004-05-27 2006-01-12 Konica Minolta Opto Inc 対物光学系、光ピックアップ装置、及び光ディスクドライブ装置
WO2006085452A1 (fr) * 2005-02-10 2006-08-17 Konica Minolta Opto, Inc. Lentille de focalisation, dispositif d'enregistrement optique et dispositif d’enregistrement/reproduction d’informations optiques
JP2009193665A (ja) * 1999-01-22 2009-08-27 Konica Minolta Holdings Inc 光ピックアップ装置
JP2009266290A (ja) * 2008-04-24 2009-11-12 Konica Minolta Opto Inc 対物レンズ及び光ピックアップ装置
JP2010092586A (ja) * 2007-10-11 2010-04-22 Konica Minolta Opto Inc 光ピックアップ装置用の対物レンズ及び光ピックアップ装置

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7245407B2 (en) * 2002-06-10 2007-07-17 Matsushita Electric Industrial Co., Ltd. Complex objective lens compatible with information media of different thicknesses

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2009193665A (ja) * 1999-01-22 2009-08-27 Konica Minolta Holdings Inc 光ピックアップ装置
JP2005149626A (ja) * 2003-11-17 2005-06-09 Fujinon Corp 光記録媒体用対物レンズおよびこれを用いた光ピックアップ装置
JP2006012393A (ja) * 2004-05-27 2006-01-12 Konica Minolta Opto Inc 対物光学系、光ピックアップ装置、及び光ディスクドライブ装置
WO2006085452A1 (fr) * 2005-02-10 2006-08-17 Konica Minolta Opto, Inc. Lentille de focalisation, dispositif d'enregistrement optique et dispositif d’enregistrement/reproduction d’informations optiques
JP2010092586A (ja) * 2007-10-11 2010-04-22 Konica Minolta Opto Inc 光ピックアップ装置用の対物レンズ及び光ピックアップ装置
JP2009266290A (ja) * 2008-04-24 2009-11-12 Konica Minolta Opto Inc 対物レンズ及び光ピックアップ装置

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