WO2011052469A1 - Dispositif de lecture optique - Google Patents

Dispositif de lecture optique Download PDF

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Publication number
WO2011052469A1
WO2011052469A1 PCT/JP2010/068570 JP2010068570W WO2011052469A1 WO 2011052469 A1 WO2011052469 A1 WO 2011052469A1 JP 2010068570 W JP2010068570 W JP 2010068570W WO 2011052469 A1 WO2011052469 A1 WO 2011052469A1
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WIPO (PCT)
Prior art keywords
lens
objective lens
information recording
information
optical
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PCT/JP2010/068570
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English (en)
Japanese (ja)
Inventor
徹 木村
雄樹 小野
Original Assignee
コニカミノルタオプト株式会社
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Priority to JP2011538378A priority Critical patent/JPWO2011052469A1/ja
Publication of WO2011052469A1 publication Critical patent/WO2011052469A1/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
    • G11B7/1378—Separate aberration correction lenses; Cylindrical lenses to generate astigmatism; Beam expanders
    • 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
    • G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
    • G11B2007/0009—Recording, reproducing or erasing systems characterised by the structure or type of the carrier for carriers having data stored in three dimensions, e.g. volume storage
    • G11B2007/0013—Recording, reproducing or erasing systems characterised by the structure or type of the carrier for carriers having data stored in three dimensions, e.g. volume storage for carriers having multiple discrete layers

Definitions

  • the present invention relates to an optical pickup device capable of recording and / or reproducing information with respect to an optical disc having three or more information recording surfaces in the thickness direction.
  • a high-density optical disk system capable of recording and / or reproducing information (hereinafter, “recording and / or reproduction” is referred to as “recording / reproduction”) using a blue-violet semiconductor laser having a wavelength of about 400 nm.
  • Patent Document 1 discloses a luminous flux in which a magnification is changed by moving a coupling lens arranged between a light source and an objective lens in the optical axis direction, and aberration is suppressed with respect to a selected information recording surface.
  • An optical pickup device capable of condensing light is disclosed.
  • the present invention has been made in consideration of the above-mentioned problems, and provides an optical pickup device capable of recording / reproducing information with respect to an optical disc having a multilayer information recording surface while being compact and low in cost.
  • the purpose is to provide.
  • the optical pickup device is an optical pickup device that selects and records information and / or reproduces information by selecting any information recording surface in an optical disk having three or more information recording surfaces in the thickness direction.
  • a light source that emits a light beam having a wavelength of ⁇ 1 (390 nm ⁇ 1 ⁇ 415 nm)
  • an objective lens that focuses the light beam on an information recording surface of an optical disc
  • a positive light source disposed between the light source and the objective lens.
  • the image side numerical aperture (NA) of the objective lens is 0.8 or more,
  • the objective lens is a single ball, formed from a glass material, Information is recorded and / or reproduced by causing the light beam emitted from the light source to enter the objective lens via the coupling lens and condensing it on the selected information recording surface of the optical disc by the objective lens. Is supposed to do When changing an information recording surface on which information is to be recorded and / or reproduced on the optical disc from one information recording surface to another information recording surface, at least one lens of the positive lens group is moved in the optical axis direction.
  • the objective lens is formed of a glass material that has a smaller refractive index change with respect to a temperature change than, for example, plastic, an increase in spherical aberration can be effectively suppressed even when the environmental temperature changes. Thus, it is not necessary to correct spherical aberration that increases with changes in temperature, whereby the amount of movement of the coupling lens can be kept small.
  • focus jump when performing an operation of changing an information recording surface on which information is to be recorded and / or reproduced from one information recording surface to another information recording surface (hereinafter referred to as “focus jump” in this specification).
  • the power of the lens group moved in the optical axis direction among the lens groups constituting the coupling lens is increased (that is, moved in the optical axis direction). It is conceivable to shorten the focal length of the lens group. This is because the amount of movement of the lens group moved in the optical axis direction decreases as the power of the lens group increases (that is, as the focal length of the lens group decreases).
  • the coupling lens has a group configuration
  • the focal length of the lens group moved in the optical axis direction that is, equal to the focal length of the coupling lens
  • the spot condensed by the objective lens becomes an ellipse.
  • the recording and / or reproduction of information on the BD may be hindered. The reason for this will be described below.
  • the coupling lens has a two-group configuration including a positive lens group and a negative lens group, and at least one lens of the positive lens group moves in the optical axis direction. It was made to make it composition.
  • the system magnification M In order to improve the symmetry of the distribution of the amount of light captured by the coupling lens and make the shape of the spot collected by the objective lens circular, it is optical with respect to the ellipticity of the light beam emitted from the semiconductor laser used as the light source. It is necessary to set the system magnification M to an optimum value. In the BD optical pickup device, the optimum value of the magnification of the condensing optical system is about -0.1.
  • the optimum value of the magnification is maintained at ⁇ 0.1, the coupling lenses are configured in two groups, and at least one lens is moved in the optical axis direction, thereby reducing the amount of movement of the coupling lens required at the time of focus jump. Can be small.
  • the coupling lens is a two-group thin lens system composed of a positive lens and a negative lens, and the positive lens is moved along the optical axis direction during focus jump.
  • the power of the positive lens is P P
  • the focal length of the positive lens is f P
  • the power of the negative lens is P N
  • the focal length of the negative lens is f N
  • the distance between the positive lens and the negative lens is L
  • the coupling lens The system power P C and the focal length f C of the entire coupling lens system are expressed by the following equation (1).
  • the focal length f C of the entire coupling lens system cannot be extremely shortened. Furthermore, when recording and / or reproducing information on the BD, the distance between the objective lens and the BD (also referred to as a working distance) is not too short, and in order to reduce the thickness of the optical pickup device, optimal range of the focal length f O of the lens naturally determined. From the above, based on the condition that the optimum value as described above exists in the value determined by the expression (2), the entire focal length range of the coupling lens for the optical pickup device for BD is a predetermined value. The focal length f C of the entire coupling lens system cannot be reduced excessively considering only the amount of movement of the coupling lens required at the time of focus jump.
  • the focal length f C of the coupling lens system is too short no way to increase the absolute value of the power P N of the negative lens ((see 1)).
  • the optical pickup device As described above, in the optical pickup device according to the present invention, it is possible to reduce both the amount of movement of the positive lens group required at the time of focus jump and the symmetry of the light amount distribution taken in by the coupling lens.
  • the optical pickup device can be downsized.
  • the NA of the entire coupling lens system can be reduced in a state where the focal length of the entire coupling lens system is smaller than the focal length of the coupling lens of only the positive lens group, so that the asymmetry of the light quantity distribution captured by the coupling lens Can be relaxed.
  • the optical path length from the light source to the objective lens is suppressed, and the optical pickup device can be reduced in size and size. Cost can be reduced.
  • a lens that is movable in the optical axis direction may be referred to as a “movable lens”.
  • “movement amount of the coupling lens” is used in the same meaning as “movement amount of the movable lens”.
  • An optical pickup device is the optical pickup device according to the first aspect of the present invention, in a state where a parallel light beam is incident on the objective lens, between 60% and 90% of the effective radius of the objective lens,
  • the coma aberration correction state is set such that the sine condition violation amount of the objective lens has a positive maximum value, and the sine condition violation amount monotonously decreases in the peripheral portion.
  • the sine condition violation amount of the objective lens has a positive maximum value between 60% and 90% of the effective radius of the objective lens, and in the peripheral part
  • the state in which a parallel light beam is incident on the objective lens means that the position of the movable lens of the coupling lens is optimized so that the light beam emitted from the coupling lens and directed to the objective lens becomes a parallel light beam. It is synonymous with that.
  • the third order spherical aberration generated by the objective lens due to the change in the divergence / convergence of the incident light and the third order spherical aberration caused by the change in the higher order spherical aberration are generated. It is preferable to set the positive maximum value of the sine condition so as to be approximately similar to the aberration and the change in higher-order spherical aberration.
  • the amount of coma aberration generated when the optical surfaces of the objective lens are decentered parallel to the direction perpendicular to the optical axis (this In the specification, the amount of coma generated (sometimes referred to as “surface shift sensitivity”) can be reduced, and the spherical aberration generated when the lens thickness on the optical axis deviates from the design value. Since the generation amount (in this specification, the generation amount of such spherical aberration may be referred to as “axial thickness error sensitivity”) can be reduced, an objective lens that is easy to manufacture can be obtained.
  • the sine condition violation amount has a negative maximum value between 10% to 50% of the effective radius of the objective lens, and the sine condition violation amount from negative to positive in the periphery.
  • the off-axis coma aberration correction state so that the sine condition violation amount has a positive maximum value between 60% and 90% of the effective radius, and the sine condition violation amount decreases monotonously at the periphery. Is preferably set.
  • the objective lens used in the optical pickup device of the present invention may be set in the shape of the sine condition violation amount, giving priority to reducing the amount of movement of the coupling lens, and the residual aberration at the time of focus jump.
  • the shape of the sine condition violation amount may be set with priority on keeping it small, or the shape of the sine condition violation amount is set with priority on reducing the surface shift sensitivity and on-axis thickness error sensitivity. It may be.
  • the shape of the sine condition violation amount may be set so as to balance the three points.
  • the optical pickup device in a state where a parallel light beam is incident on the objective lens, between 40% and 80% of the effective radius of the objective lens.
  • the coma aberration correction state is set so that the sine condition violation amount of the objective lens has a negative maximum value, and the sine condition violation amount monotonously decreases in the periphery.
  • the surface shift sensitivity of the objective lens can be kept small, and the on-axis thickness error sensitivity can be reduced, so that an objective lens that is easy to manufacture can be obtained. it can. Accordingly, the occurrence of aberration based on the manufacturing error of the objective lens can be prevented, so that it is possible to suppress the movement distance of the coupling lens from being extended based on the manufacturing error.
  • the optical pickup device wherein the objective lens can be tilted along a radial direction and / or a tangential direction of the optical disc.
  • the absolute value of the ratio of the third-order coma aberration CM (DT) that occurs when the same is tilted by the same amount is 0.4 or more.
  • the “state of recording and / or reproducing information on the information recording surface having the longest distance from the light incident surface of the optical disk” means that the information recording surface having the longest distance from the light incident surface is This is synonymous with optimizing the position of the movable lens of the coupling lens so that the third-order spherical aberration generated when the spot focused by the objective lens is focused is corrected.
  • the amount of lens tilt required to correct the coma generated by the disc tilt will increase.
  • the objective lens collides with the optical disk when the lens is tilted.
  • the coma generated by the lens tilt changes depending on the sine condition violation amount of the objective lens, and the sine condition violation amount of the objective lens in a state where information is recorded and / or reproduced on the optical disc. It varies depending on the magnification. Specifically, in an objective lens in which the sine condition violation amount is corrected when a parallel light beam is incident on the objective lens, the sine condition violation amount is changed to the negative side when a divergent light beam is incident on the objective lens. Therefore, the amount of coma generated by the lens tilt is reduced. The amount of coma aberration decreases as the divergence of the light beam incident on the objective lens increases.
  • the divergence of the light beam incident on the objective lens is maximized when information is recorded and / or reproduced on the information recording surface having the longest distance from the light beam incident surface.
  • the third-order coma aberration generated when the objective lens is tilted in a state where information is recorded and / or reproduced with respect to the information recording surface having the longest distance from the light incident surface Information with the longest distance from the light incident surface so that the absolute value of the ratio of the third-order coma aberration CM (DT) generated when the optical disk is tilted by the same amount with respect to CM (LT) is 0.4 or more.
  • CM third-order coma aberration
  • the absolute value of the ratio of DT to LT is 0.5 or more.
  • One is to set the amount of violation of the sine condition of the objective lens so that the amount of violation of the sine condition of the objective lens is on the plus side when a parallel light beam is incident on the objective lens.
  • Another one occurs when the spot focused by the objective lens is focused on the information recording surface with the shortest distance from the light beam incident surface in a state where a parallel light beam is incident on the objective lens.
  • the absolute value of the spherical aberration generated when the spot focused by the objective lens is focused on the information recording surface having the longest distance from the light incident surface is smaller than the absolute value of the spherical aberration.
  • the correction state of the spherical aberration of the objective lens is set.
  • the position of the movable lens in a state where a parallel light beam is incident on the objective lens is T0, and the position of the movable lens in a state where information is recorded and / or reproduced on the information recording surface having the longest distance from the light beam incident surface.
  • Is T1, and T2 is the position of the movable lens in a state where information is recorded and / or reproduced with respect to the information recording surface with the shortest distance from the light incident surface. It is.
  • the optical pickup device has at least one light source (first light source).
  • first light source a plurality of types of light sources may be provided so as to support a plurality of types of optical disks.
  • the optical pickup device of the present invention has a condensing optical system for condensing at least the first light flux from the first light source on the information recording surface of the first optical disc.
  • the condensing optical system condenses the second light beam on the information recording surface of the second optical disk, and the third light beam on the information recording surface of the third optical disk. You may make it condense.
  • the optical pickup device of the present invention includes a light receiving element that receives at least a reflected light beam from the information recording surface of the first optical disc.
  • the light receiving element receives a reflected light beam from the information recording surface of the second optical disk and receives a reflected light beam from the information recording surface of the third optical disk. Also good.
  • 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 BD
  • the second optical disc is a DVD
  • the third optical disc is preferably a CD, but is not limited thereto.
  • the first optical disc has three or more information recording surfaces stacked in the thickness direction. Of course, you may have four or more information recording surfaces.
  • the second optical disc and the third optical disc may also have a plurality of information recording surfaces.
  • BD means that information is recorded / reproduced by a light beam having a wavelength of about 390 to 415 nm and an objective lens having an NA of about 0.8 to 0.9, and the thickness of the protective substrate is 0.05 to 0.00 mm.
  • the optical pickup device of the present invention has at least three layers. It is preferable to be able to cope with a BD having the above information recording surface.
  • DVD is a general term for DVD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.60 to 0.67 and the thickness of the protective substrate is about 0.6 mm.
  • CD is a general term for CD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.45 to 0.51 and the thickness of the protective substrate is about 1.2 mm.
  • CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW and the like As for the recording density, the recording density of BD is the highest, followed by the order of DVD and CD.
  • the thickness of the protective substrate referred to here is the thickness of the protective substrate provided on the surface of the optical disk. That is, the thickness of the protective substrate from the optical disc surface to the information recording surface closest to the surface.
  • the first light source, the second light source, and the third light source are preferably laser light sources.
  • the laser light source a semiconductor laser, a silicon laser, or the like can be preferably used.
  • the wavelength ⁇ 3 ( ⁇ 3> ⁇ 2) preferably satisfies the following conditional expressions (7) and (8).
  • the first wavelength ⁇ 1 of the first light source is preferably 350 nm or more and 440 nm or less, more preferably 390 nm.
  • the second wavelength ⁇ 2 of the second light source is preferably 570 nm or more and 680 nm or less, more preferably 630 nm or more and 670 nm or less, and the third wavelength ⁇ 3 of the third light source is preferably 415 nm or less. It is 750 nm or more and 880 nm or less, More preferably, it is 760 nm or more and 820 nm or less.
  • the first light source, the second light source, and the third light source may be unitized.
  • the unitization means that the first light source and the second light source are fixedly housed in one package, for example.
  • 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 a coupling lens and an objective lens.
  • the coupling lens is a lens group that is disposed between the objective lens and the light source and changes the divergence angle of the light beam.
  • the coupling lens has a positive lens group and a negative lens group.
  • the positive lens group has at least one positive lens.
  • the positive lens group may include only one positive lens or may include a plurality of lenses.
  • the negative lens group has at least one negative lens.
  • the negative lens group may include only one negative lens or may include a plurality of lenses.
  • An example of a preferable coupling lens is a combination of one positive lens and one negative lens.
  • the arrangement of the positive lens group and the negative lens group may be arranged in the order of the negative lens group and the positive lens group from the light source side, or may be arranged in the order of the positive lens group and the negative lens group from the light source side. good.
  • the light from the light source is incident on the positive lens with the divergence angle enlarged by the negative lens
  • the light from the light source is incident on the negative lens after being condensed by the positive lens.
  • the former increases from the negative lens to the positive lens, and the latter increases when the positive lens is incident and decreases toward the negative lens. Therefore, from the viewpoint of reducing the light diameter in order to reduce the size of the coupling lens, the preferred arrangement is the former.
  • the optimum example of the coupling lens in the optical pickup device of the present invention is a combination of one positive lens and one negative lens, and is arranged in order of the negative lens and the positive lens from the light source side. .
  • At least one lens (preferably positive lens) of the positive lens group is movable in the optical axis direction.
  • the positive lens group of the coupling lens group Spherical aberration that occurs at the time of focus jump to a different information recording surface of the first optical disk by moving at least one lens in the optical axis direction, changing the divergence of the light beam, and changing the magnification of the objective lens Correct.
  • FIG. 1 is a diagram showing the results of studies conducted by the present inventors.
  • an optical disc having a surface
  • the maximum spherical aberration difference A that occurs when an optimum focused spot is formed on each information recording surface that is the maximum distance, and the maximum that occurs when the environmental temperature changes by ⁇ 30 ° C.
  • the maximum spherical aberration C that occurs when the wavelength of the light source changes by ⁇ 5 nm. This is represented by the bar graph of FIG.
  • Such spherical aberration can be corrected by moving the coupling lens in the optical axis direction and changing the magnification of the objective lens.
  • the total amount of spherical aberration is the amount of movement of the coupling lens. It is equivalent to.
  • the amount of spherical aberration is obtained regardless of whether the optical surface is an aspherical refractive surface or a diffractive surface. Is about 410 to 430 m ⁇ , and the amount of movement of the coupling lens is relatively small.
  • the total amount of spherical aberration is 680 m ⁇ in the case of an objective lens having an aspherical refracting surface. The amount of movement is required to be about 1.5 times that required when an optical disc having two information recording surfaces is used. Furthermore, as shown in FIG.
  • the objective lens is made of glass and the optical surface is an aspherical refracting surface
  • the objective lens is made of glass and the optical surface is a diffractive surface that corrects spherical aberration that occurs when the wavelength varies, in addition to spherical aberration B caused by environmental temperature changes, spherical aberration C caused by wavelength fluctuations of the light source due to the function of the diffractive surface.
  • the amount of movement of the coupling lens is smaller (corresponding to the correction amount of the spherical aberration of 500 m ⁇ in FIG. 1C).
  • the amount of movement of the coupling lens when the optical disk having two information recording surfaces is used is smaller than that of the coupling lens when the optical disk having four information recording surfaces is used. Since the amount of movement is still about twice, further ingenuity is required to suppress the amount of movement of the coupling lens. The same applies to the amount of movement of the coupling lens when using an optical disc having three information recording surfaces or five or more information recording surfaces.
  • an optical disc having two information recording surfaces an information recording surface having a smaller distance from the light beam incident surface of the optical disc is RL1, an information recording surface having a larger distance from the light beam incident surface of the optical disc is RL2
  • optical disk having four information recording surfaces (assuming that the information recording surface having the smallest distance from the light beam incident surface of the optical disk is RL1, and the information recording surface having the largest distance from the light beam incident surface of the optical disk is RL4), An optical disk was assumed in which the distance from the light beam incident surface of the optical disk to RL1 was 50 ⁇ m and the distance from the light beam incident surface of the optical disk to RL4 was 100 ⁇ m.
  • FIG. 2 shows a coupling lens CL1 including only a positive lens group (one in the figure) L1, and a coupling lens CL2 including a positive lens group (one in the figure) L2 and a negative lens group (one in the figure) L3.
  • the focal length of the coupling lens CL1 is equal to the combined focal length of the coupling lens CL2, which is f. Therefore, the focal length f2 of the positive lens unit L2 of the coupling lens CL2 is shorter than the focal length f of the positive lens unit L1 of the coupling lens CL1.
  • 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 a light beam emitted from the light source onto the information recording surface of the optical disk.
  • the objective lens is a single glass lens.
  • the objective lens is a single convex lens.
  • the objective lens may be composed of only a refractive surface or may have an optical path difference providing structure.
  • the hybrid lens which provided the optical path difference providing structure with the photocurable resin, UV curable resin, or thermosetting resin etc. on the glass lens may be sufficient.
  • 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, as described with reference to FIG. 1, it is not necessary to move the coupling lens in order to correct the spherical aberration caused by the temperature change. This is preferable because it can be reduced and the optical pickup device can be downsized.
  • 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.
  • a physical property value that is important when molding a glass lens is the linear expansion coefficient ⁇ . Even if a material having a Tg of 400 ° C. or lower is selected, the temperature difference from room temperature is still large compared to the resin material. When lens molding is performed using a glass material having a large linear expansion coefficient ⁇ , cracks are likely to occur when the temperature is lowered.
  • the linear expansion coefficient ⁇ of the glass material is preferably 200 (10E-7 / K) or less, more preferably 120 or less.
  • 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 mass is increased 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.
  • the Abbe number of the material constituting the objective lens is preferably 50 or more.
  • the sine condition is h when a light beam having a height h 1 from the optical axis is incident on the lens parallel to the optical axis, and when the light beam is emitted from the lens at an emission angle U. 1 / sinU satisfies a certain value.
  • U. 1 / sinU a constant value regardless of the height from the height h 1 from the optical axis
  • the sine condition is satisfied and the lateral magnification of each light ray within the effective diameter can be regarded as constant.
  • This sine condition is a calculated value on the axis, but is effective in correcting off-axis lateral magnification error (ie off-axis coma).
  • FIG. 4 is a graph showing the sine condition violation amount in the objective lens on the horizontal axis and the height from the optical axis on the vertical axis.
  • the graph corresponds to the vertical axis, but in the case of an objective lens that does not satisfy the sine condition, the graph moves away from the vertical axis to the positive side and / or the negative side as shown in FIG. It becomes.
  • the sine condition violation amount always has a maximum value.
  • OSCmax the maximum value on the positive side of the sine condition violation amount
  • OSCmin the maximum value on the negative side
  • the sine condition violation amount has one local maximum value OSCmin on the negative side.
  • Examples in which the sine condition violation amount has one negative maximum OSCmin are not only those shown by the solid line in FIG. 4A, but also the sine condition violation amount from the middle as shown by the dotted line.
  • Such an objective lens may be an example.
  • the manufacturing is easy. Further, even when information is recorded and / or reproduced on the information recording surface having the longest distance from the light incident surface, the third-order coma aberration CM (DT) generated when the optical disc is tilted by the same amount is also obtained.
  • DT third-order coma aberration CM
  • the design substrate thickness that minimizes spherical aberration when a parallel light beam is incident is 0.087 mm or less, 0 It is also possible to use an objective lens designed with a thinner design substrate thickness, such as 0.05 mm or more.
  • the coupling lens moves, higher-order spherical aberration increases, and the change in spherical aberration due to the change in magnification is small. Therefore, when the coupling lens is moved to select an information recording surface in an optical disc having three or more layers, there is a possibility that the necessary movement amount increases.
  • the objective lens having the characteristics shown in FIG. 4C has one local maximum value OSCmax whose sine condition violation amount is between 60% and 90% of the effective radius of the objective lens.
  • OSCmax whose sine condition violation amount monotonously decreases in the peripheral portion, but does not have a negative maximum value.
  • the high-order spherical aberration generated with the movement of the coupling lens is reduced, and the change of the spherical aberration due to the change in magnification is large.
  • the coupling lens is moved to select the surface, the necessary movement amount can be reduced.
  • the BD in an objective lens designed with a thin design substrate thickness such that the design substrate thickness that minimizes spherical aberration when a parallel light beam is incident is 0.15 mm or less and 0.0875 mm or more. preferable.
  • the objective lens having the characteristics shown in FIG. 4B has a maximum value OSCmax where the sine condition violation amount is between 60% and 90% of the effective radius of the objective lens and 10% of the effective radius of the objective lens. Between the maximum value OSCmax, the sine condition violation amount decreases monotonously at the periphery, and the sine condition violation amount on the optical axis side from the maximum value OSCmin. This is an example of monotonously decreasing. This example is a balance between the characteristics shown in FIG. 4A and the characteristics shown in FIG. 4C. Therefore, the information recording surface of an optical disk having three or more layers is ensured while ensuring manufacturability. Therefore, when the coupling lens is moved, a necessary movement amount can be reduced.
  • 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
  • NA3 NA2> NA3
  • NA1 is preferably 0.75 or more and 0.9 or less, and more preferably 0.8 or more and 0.9 or less.
  • NA1 is preferably 0.85.
  • NA2 is preferably 0.55 or more and 0.7 or less.
  • NA2 is preferably 0.60 or 0.65.
  • NA3 is preferably 0.4 or more and 0.55 or less.
  • NA3 is preferably 0.45 or 0.53.
  • the objective lens satisfies the following conditional expression (9).
  • d represents the thickness (mm) on the optical axis of the objective lens
  • f represents the focal length of the objective lens in the first light flux. Note that f is preferably 1.0 mm or more and 1.8 mm or less.
  • the working distance of the objective lens when using the first optical disk is preferably 0.15 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 disk drive apparatus can hold an optical disk mounted from the optical information recording / reproducing apparatus main body containing the optical pickup apparatus or the like. There are a system in which only the tray is taken out, and a system in which the optical disc drive apparatus main body in which the optical pickup device is stored is taken out to the outside.
  • the optical information recording / reproducing apparatus using each method described above is generally equipped with the following components, but is not limited thereto.
  • An optical pickup device housed in a housing or the like, a drive source of an optical pickup device such as a seek motor that moves the optical pickup device together with the housing toward the inner periphery or outer periphery of the optical disc, and the optical pickup device housing the inner periphery or outer periphery of the optical disc include a transfer means of an optical pickup device having a guide rail or the like that guides toward the head, a spindle motor that rotates the optical disk, and the like.
  • the former method is provided with a tray that can be held in a state in which an optical disk is mounted and a loading mechanism for sliding the tray, and the latter method has no tray and loading mechanism. It is preferable that each component is provided in a drawer corresponding to a chassis that can be pulled out to the outside.
  • an optical pickup device capable of recording / reproducing information with respect to an optical disc having a multilayer information recording surface while being compact and low in cost.
  • FIG. 5 shows that information is appropriately recorded on a BD that is an optical disc having three information recording surfaces RL1 to RL3 in the thickness direction (referred to as RL1, RL2, and RL3 in order of increasing distance from the light incident surface of the optical disc).
  • FIG. 2 is a diagram schematically showing a configuration of an optical pickup device PU1 of the present embodiment that can perform reproduction. Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device.
  • the present invention is not limited to the present embodiment.
  • the optical pickup device PU1 moves the objective lens OBJ, the objective lens OBJ in the focusing direction and the tracking direction, and tilts in the radial direction and / or tangential direction of the optical disc, the ⁇ / 4 wavelength plate QWP, Coupling CL having a positive lens unit L2 composed of one positive lens having a refractive power and a negative lens unit L3 composed of one negative lens having a negative refractive power, only the positive lens unit L2 in the optical axis direction.
  • the coupling lens CL is disposed between the polarizing prism PBS and the ⁇ / 4 wavelength plate QWP.
  • the objective lens OBJ is a single ball made of glass, but two or more optical elements may be used in combination.
  • the positive lens group L2 of the coupling lens CL is moved to the position of the solid line by the uniaxial actuator AC1.
  • the lens unit L2 After passing through the lens unit L2 to be a weakly convergent light beam, it is converted from linearly polarized light to circularly polarized light by the ⁇ / 4 wave plate QWP, the light beam diameter is regulated by a diaphragm (not shown), and the first thickness is obtained by the objective lens OBJ.
  • the protective substrate PL1 Through the protective substrate PL1, the spot is formed on the first information recording surface RL1 as shown by the solid line.
  • the reflected light beam modulated by the information pits on the first information recording surface RL1 is again transmitted through the objective lens OBJ and the diaphragm, and then converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wavelength plate QWP.
  • the information recorded on the first information recording surface RL1 can be read by focusing or tracking the objective lens OBJ by the triaxial actuator AC2.
  • the positive lens group L2 of the coupling lens CL is moved to the position of the alternate long and short dash line by the uniaxial actuator AC1.
  • the lens unit L2 After passing through the lens unit L2 to be a substantially parallel light beam, it is converted from linearly polarized light to circularly polarized light by the ⁇ / 4 wavelength plate QWP, the light beam diameter is regulated by a diaphragm (not shown), and the objective lens OBJ has the second thickness. This is a spot formed on the second information recording surface RL2 as shown by the alternate long and short dash line through the protective substrate PL2 having a thickness (thicker than the first thickness).
  • the reflected light beam modulated by the information pits on the second information recording surface RL2 is again transmitted through the objective lens OBJ and the aperture, and then converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wavelength plate QWP.
  • the information recorded on the second information recording surface RL2 can be read by focusing or tracking the objective lens OBJ by the triaxial actuator AC2.
  • the positive lens group L2 of the coupling lens CL is moved to the dotted line position by the uniaxial actuator AC1.
  • the lens unit L2 After passing through the lens unit L2 to be a weak divergent light beam, it is converted from linearly polarized light into circularly polarized light by the ⁇ / 4 wave plate QWP, the diameter of the light beam is regulated by a diaphragm (not shown), and the third thickness is obtained by the objective lens OBJ. This is a spot formed on the third information recording surface RL3 as shown by the dotted line through the protective substrate PL3 (thicker than the second thickness).
  • the reflected light beam modulated by the information pits on the third information recording surface RL3 is again transmitted through the objective lens OBJ and the diaphragm, and then converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wavelength plate QWP.
  • the information recorded on the third information recording surface RL3 can be read by focusing or tracking the objective lens OBJ by the triaxial actuator AC2.
  • FIG. 6 shows that information is appropriately recorded on a BD that is an optical disc having three information recording surfaces RL1 to RL3 (referred to as RL1, RL2, and RL3 in order of increasing distance from the light beam incident surface of the optical disc) in the thickness direction.
  • FIG. 6 is a diagram schematically showing a configuration of an optical pickup device PU2 according to a second embodiment capable of performing reproduction. Such an optical pickup device PU2 can be mounted on an optical information recording / reproducing device.
  • the present invention is not limited to the present embodiment.
  • the optical pickup device PU2 differs from the above-described optical pickup device PU1 only in the arrangement of the coupling lens CL. Specifically, the positive lens group L2 of the coupling lens CL is disposed between the polarizing prism PBS and the objective lens OBJ, and the negative lens group L3 is disposed between the blue-violet semiconductor laser LD and the polarizing prism PBS. Yes. About another structure, it is the same as that of optical pick-up apparatus PU1.
  • the positive lens group L2 of the coupling lens CL is moved to the position of the solid line by the uniaxial actuator AC1.
  • the lens unit L2 After passing through the lens unit L2 to be a weakly convergent light beam, it is converted from linearly polarized light to circularly polarized light by the ⁇ / 4 wave plate QWP, the light beam diameter is regulated by a diaphragm (not shown), and the first thickness is obtained by the objective lens OBJ.
  • the protective substrate PL1 Through the protective substrate PL1, the spot is formed on the first information recording surface RL1 as shown by the solid line.
  • the reflected light beam modulated by the information pits on the first information recording surface RL1 is again transmitted through the objective lens OBJ and the diaphragm, and then converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wavelength plate QWP.
  • the information recorded on the first information recording surface RL1 can be read by focusing or tracking the objective lens OBJ by the triaxial actuator AC2.
  • the positive lens group L2 of the coupling lens CL is moved to the position of the alternate long and short dash line by the uniaxial actuator AC1.
  • the lens unit L2 After passing through the lens unit L2 to be a substantially parallel light beam, it is converted from linearly polarized light to circularly polarized light by the ⁇ / 4 wavelength plate QWP, the light beam diameter is regulated by a diaphragm (not shown), and the objective lens OBJ has the second thickness. This is a spot formed on the second information recording surface RL2 as shown by the alternate long and short dash line through the protective substrate PL2 having a thickness (thicker than the first thickness).
  • the reflected light beam modulated by the information pits on the second information recording surface RL2 is again transmitted through the objective lens OBJ and the aperture, and then converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wavelength plate QWP.
  • the information recorded on the second information recording surface RL2 can be read by focusing or tracking the objective lens OBJ by the triaxial actuator AC2.
  • the positive lens group L2 of the coupling lens CL is moved to the dotted line position by the uniaxial actuator AC1.
  • the lens unit L2 After passing through the lens unit L2 to be a weak divergent light beam, it is converted from linearly polarized light into circularly polarized light by the ⁇ / 4 wave plate QWP, the diameter of the light beam is regulated by a diaphragm (not shown), and the third thickness is obtained by the objective lens OBJ. This is a spot formed on the third information recording surface RL3 as shown by the dotted line through the protective substrate PL3 (thicker than the second thickness).
  • the reflected light beam modulated by the information pits on the third information recording surface RL3 is again transmitted through the objective lens OBJ and the aperture, and then converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wavelength plate QWP.
  • the information recorded on the third information recording surface RL3 can be read by focusing or tracking the objective lens OBJ by the triaxial actuator AC2.
  • the negative lens group in the coupling lens may be disposed on the objective lens side, and the positive lens group may be disposed on the light source side.
  • the objective lens OBJ is attached by the triaxial actuator AC2. Tilt along the radial direction and / or tangential direction of the optical disc. As a result, it is possible to stably record and / or reproduce information on the warped optical disc, and to maintain a good spot quality on the information recording surface even when the optical disc is tilted during rotation.
  • the focal length of the objective lens OBJ is preferably in the range of 1.0 mm to 1.8 mm.
  • the focal length of the objective lens of the condensing optical system is 1.41 mm
  • the focal length of the positive lens of the coupling lens is 8 mm
  • the focal length of the entire coupling lens system is 14.1 mm.
  • the magnification of the system is -0.1.
  • the design wavelength of the condensing optical system is 405 nm
  • ri in the table below is the radius of curvature
  • di is the position in the optical axis direction from the i-th surface to the i + 1-th surface
  • ndi is each of the d-line (587.6 nm).
  • the refractive index of the surface, n405i represents the refractive index of each surface at the design wavelength of 405 nm, and ⁇ d represents the Abbe number in the d-line.
  • the objective lens in the example is made of glass and SK5 manufactured by HOYA Corporation is used. In the following (including the lens data in the table), a power of 10 (for example, 2.5 ⁇ 10 ⁇ 3 ) is represented by using E (for example, 2.5 ⁇ E ⁇ 3).
  • the optical surface of the objective lens is formed as an aspherical surface that is axisymmetric about the optical axis, each of which is defined by an equation in which the coefficient shown in Table 1 is substituted into Equation (1).
  • X (h) is an axis in the optical axis direction (the light traveling direction is positive)
  • ⁇ is a conical coefficient
  • a i is an aspherical coefficient
  • h is a height from the optical axis
  • r is a paraxial curvature.
  • Tables 1 and 2 show the lens data of Example 1. This embodiment is composed of a two-group coupling lens having a negative lens and a positive lens, and an objective lens.
  • the objective lens in this example has a spherical aberration and a sine condition violation amount (with a combination of a protective substrate thickness of 0.075 mm and a magnification of zero (corresponding to the parallel light beam entering the objective lens) ( The shape of the optical surface is determined so that (see FIG. 7) is corrected satisfactorily. Further, the sine condition violation amount of the objective lens in this state is shown in FIG.
  • Table 1 shows a state where information is recorded and / or reproduced on the information recording surface (RL1) having a distance of 0.05 mm from the light incident surface in this embodiment.
  • the positive lens is moved toward the objective lens so that the light beam emitted from the positive lens becomes a weak convergent light beam, and from the light beam incident surface to the information recording surface.
  • the third-order spherical aberration associated with the change in the distance is corrected.
  • Table 2 shows a state where information is recorded and / or reproduced on the information recording surface (RL3) having a distance of 0.1 mm from the light incident surface in the present embodiment.
  • the light beam emitted from the positive lens is weak by moving the positive lens to the light source side.
  • a divergent light beam is used to correct third-order spherical aberration associated with a change in the distance from the light beam incident surface to the information recording surface.
  • Tables 3 and 4 show lens data of Example 2. This embodiment is composed of a two-group coupling lens having a negative lens and a positive lens, and an objective lens.
  • the coupling lens in this example is the same as that in Example 1 described above.
  • spherical aberration is satisfactorily corrected by a combination of a protective substrate thickness of 0.075 mm and a magnification of zero (corresponding to a parallel light beam entering the objective lens).
  • the coma aberration correction state is set so that the sine condition violation amount of the objective lens has a positive maximum value between 60% and 90% of the effective radius, and the sine condition violation amount decreases monotonously at the periphery. Has been. Also, the sine condition violation amount of the objective lens in this state is shown in FIG.
  • Table 3 shows a state where information is recorded and / or reproduced on the information recording surface (RL1) whose distance from the light incident surface in the present embodiment is 0.05 mm.
  • the positive lens is moved toward the objective lens so that the light beam emitted from the positive lens becomes a weak convergent light beam, and from the light beam incident surface to the information recording surface.
  • the third-order spherical aberration associated with the change in the distance is corrected.
  • Table 4 shows a state where information is recorded and / or reproduced on the information recording surface (RL3) having a distance of 0.1 mm from the light incident surface in the present embodiment.
  • the light beam emitted from the positive lens is weak by moving the positive lens to the light source side.
  • a divergent light beam is used to correct third-order spherical aberration associated with a change in the distance from the light beam incident surface to the information recording surface.
  • Tables 5 and 6 show the lens data of Example 3. This embodiment is composed of a two-group coupling lens having a negative lens and a positive lens, and an objective lens.
  • the coupling lens in this example is the same as that in Example 1 described above.
  • the objective lens in this example has a spherical aberration and a sine condition violation amount in a combination of a protective substrate thickness of 0.090 mm and a magnification of zero (corresponding to a parallel light beam entering the objective lens).
  • the optical surface shape is determined so that (see FIG. 7) is corrected satisfactorily. Further, the sine condition violation amount of the objective lens in this state is shown in FIG.
  • Table 5 shows a state where information is recorded and / or reproduced on the information recording surface (RL1) having a distance of 0.05 mm from the light incident surface in this comparative example.
  • the positive lens is moved toward the objective lens so that the light beam emitted from the positive lens becomes a weak convergent light beam, and from the light beam incident surface to the information recording surface.
  • the third-order spherical aberration associated with the change in the distance is corrected.
  • Table 6 shows a state where information is recorded and / or reproduced on the information recording surface (RL3) having a distance of 0.1 mm from the light incident surface in this embodiment.
  • the light beam emitted from the positive lens is weak by moving the positive lens to the light source side.
  • a divergent light beam is used to correct third-order spherical aberration associated with a change in the distance from the light beam incident surface to the information recording surface.
  • Table 7 shows the amount of movement of the positive lens when the information is recorded and / or reproduced with respect to RL1 in Example 1, Example 2, and Example 3 (the zero point of the amount of movement is relative to the objective lens).
  • the position of the positive lens when a parallel light beam is incident “+” when the positive lens moves toward the objective lens with respect to the zero point, and “ ⁇ ” when the positive lens moves in the direction closer to the light source
  • the absolute value of the third-order spherical aberration ( ⁇ rms) and fifth-order spherical aberration ( ⁇ rms) with the positive lens position optimized, and a light beam tilted by 0.5 degrees with respect to the objective lens.
  • Table 8 shows the amount of movement of the positive lens when the information is recorded and / or reproduced with respect to the RL 3 in Example 1, Example 2 and Example 3 (the zero point of the amount of movement is the object lens).
  • the position of the positive lens when a parallel light beam is incident is defined as “+” when the positive lens moves toward the objective lens with respect to the zero point, and “+” when the positive lens moves toward the light source.
  • the movement amount of the positive lens in the coupling lens composed of the positive lens and the negative lens is smaller than that in the case where the coupling lens is a single collimator lens.
  • the objective lens of the condensing optical system of Example 2 has an effective radius of 6 in the state in which a parallel light beam is incident on the objective lens. Between 90% and 90%, the coma aberration correction state is set so that the sine condition violation amount of the objective lens has a positive maximum value, and the sine condition violation amount monotonously decreases in the peripheral area. From the condensing optical system of Example 1, it can be seen that the moving amount of the positive lens can be further reduced by about 10%.
  • Example 2 can be further improved in terms of fifth-order spherical aberration.
  • the objective lens of the condensing optical system of Example 3 has a protective substrate thickness of 0.090 mm when a parallel light beam is incident on the objective lens. Since the shape of the optical surface is determined so that the spherical aberration is minimized, the absolute value of the movement amount of the positive lens in the state in which information is recorded and / or reproduced with respect to RL1 is set with respect to RL3. Thus, the absolute value of the movement amount of the positive lens in a state where information is recorded and / or reproduced is reduced.

Abstract

La présente invention concerne un dispositif de lecture optique qui, tout en étant compact et peu coûteux, peut enregistrer/reproduire des informations sur/à partir d'un disque optique comportant une surface d'enregistrement d'informations à couches multiples. Une lentille de focalisation est réalisée en un verre présentant une plus faible variation d'indice de réfraction correspondant à la variation thermique, par exemple, d'une matière plastique, peut supprimer une augmentation d'une aberration sphérique même si la température ambiante varie, et peut par conséquent ramener la quantité de déplacement d'un objectif de couplage à un faible niveau. En outre, parmi un groupe de lentilles positives et un groupe de lentilles négatives qui configurent l'objectif de couplage susmentionné, la surface d'enregistrement d'informations sur le disque optique susmentionné sur lequel/à partir duquel des informations sont enregistrées et/ou reproduites est sélectionnée en déplaçant une ou plusieurs des lentilles du groupe de lentilles positives susmentionné dans la direction de l'axe de la lumière, et ainsi la quantité de déplacement de l'objectif de couplage susmentionné est ramenée à un niveau encore plus faible. En conséquence, la longueur du trajet de lumière de la source de lumière à la lentille de focalisation susmentionnée est supprimée, et il est possible d'obtenir une réduction du coût et de la taille du dispositif de lecture optique.
PCT/JP2010/068570 2009-10-28 2010-10-21 Dispositif de lecture optique WO2011052469A1 (fr)

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Cited By (1)

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Publication number Priority date Publication date Assignee Title
WO2013005672A1 (fr) * 2011-07-07 2013-01-10 コニカミノルタアドバンストレイヤー株式会社 Dispositif de tête optique

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Publication number Priority date Publication date Assignee Title
JP2003085806A (ja) * 2001-09-07 2003-03-20 Pentax Corp 光ヘッド用対物レンズおよびこれを用いた光ヘッド
JP2007133967A (ja) * 2005-11-10 2007-05-31 Canon Inc 光学式情報記録再生装置

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2003085806A (ja) * 2001-09-07 2003-03-20 Pentax Corp 光ヘッド用対物レンズおよびこれを用いた光ヘッド
JP2007133967A (ja) * 2005-11-10 2007-05-31 Canon Inc 光学式情報記録再生装置

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013005672A1 (fr) * 2011-07-07 2013-01-10 コニカミノルタアドバンストレイヤー株式会社 Dispositif de tête optique

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