WO2005066947A1 - Optical head device - Google Patents

Optical head device Download PDF

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Publication number
WO2005066947A1
WO2005066947A1 PCT/JP2004/013047 JP2004013047W WO2005066947A1 WO 2005066947 A1 WO2005066947 A1 WO 2005066947A1 JP 2004013047 W JP2004013047 W JP 2004013047W WO 2005066947 A1 WO2005066947 A1 WO 2005066947A1
Authority
WO
WIPO (PCT)
Prior art keywords
light beam
optical
objective lens
head device
parallel
Prior art date
Application number
PCT/JP2004/013047
Other languages
French (fr)
Japanese (ja)
Inventor
Kenya Nakai
Fumihiro Shiroki
Keiji Nakamura
Masahisa Shinoda
Original Assignee
Mitsubishi Denki Kabushiki Kaisha
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Mitsubishi Denki Kabushiki Kaisha filed Critical Mitsubishi Denki Kabushiki Kaisha
Priority to JP2005516793A priority Critical patent/JP4308204B2/en
Priority to TW093132897A priority patent/TWI279792B/en
Publication of WO2005066947A1 publication Critical patent/WO2005066947A1/en

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Classifications

    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1353—Diffractive elements, e.g. holograms or gratings
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/125—Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for controlling the size or intensity of optical spots or optical traces
    • G11B7/127—Lasers; Multiple laser arrays
    • G11B7/1275—Two or more lasers having different wavelengths
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/13—Optical detectors therefor
    • G11B7/131—Arrangement of detectors in a multiple array
    • 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
    • G11B7/1356—Double or multiple prisms, i.e. having two or more prisms in cooperation
    • 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
    • G11B7/1392—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
    • 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
    • G11B7/1395—Beam splitters or combiners
    • 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
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0901—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following only
    • G11B7/0903—Multi-beam tracking systems
    • 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
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0908—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only
    • G11B7/0909—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only by astigmatic methods

Definitions

  • the present invention relates to an optical head device mounted on an optical disk recording / reproducing device, and more particularly, to an optical head device capable of suppressing the influence of wavefront aberration on recording / reproducing characteristics.
  • An optical head device is mounted as a device for reading and writing information in various optical disk recording / reproducing devices such as a CD player, a DVD player, and an MD player. With the miniaturization and price reduction of the optical disk recording / reproducing device itself, the optical head device is also required to have higher density, higher performance, smaller size, thinner, and lower cost.
  • FIGS. The configuration of a conventional optical head device is shown, for example, in FIGS.
  • the collimator lens converts a light beam, which also emits the power of a semiconductor laser as a light source, into a parallel light beam. Then, the parallel light beam enters the objective lens.
  • An optical system using such a parallel light beam is called an infinite optical system.
  • an optical head device of the infinite optical system as described above exists, there is also an optical head device having a simple configuration without the collimator lens in the conventional optical head mounting force.
  • Such an optical head device without a collimator lens adopts a configuration in which a diffused light beam, not a parallel light beam, is incident on an objective lens.
  • Such a configuration in which the diffused light beam enters the objective lens is called a finite optical system.
  • An optical head device of a finite optical system is shown in FIG. 1 of Patent Document 1 below, for example.
  • Patent Document 1 In addition to Patent Document 1 and Non-Patent Document 1, the following documents are cited as prior art documents relating to the present invention.
  • the optical head device of the finite optical system is advantageous in miniaturization, thinning, and cost reduction with a small number of components because a collimator lens is unnecessary.
  • an optical head device of a finite optical system adopts a configuration in which a diffused light beam is incident on an objective lens. For this reason, when the angle of incidence of the light beam on the objective lens changes due to the light source being shifted by the lens optical axis force of the objective lens, wavefront aberration occurs. Then, the quality of the focused light beam deteriorates. Objective This is because the entrance surface of the lens has a spherical or aspherical shape, so that if incident light deviated from the optical axis of the lens passes through the objective lens, it will not be focused.
  • recording marks which are data, are arranged in a circular or spiral shape on a recording surface of an optical disc information recording medium recorded / reproduced by an optical disc recording / reproducing apparatus.
  • the optical disk recording / reproducing device scans the light beam condensed by the objective lens along the track and reads the reflected light power data.
  • the optical disk information recording medium is rotated by a motor or the like about the center of the track as a central axis.
  • the optical disk recording / reproducing apparatus needs to control the focal position of the optical beam so as to follow the track displacement.
  • the optical head device itself can be displaced by a servo mechanism.
  • the position control of the light beam with respect to the track displacement by the servo mechanism for displacing the entire optical head device is not desirable in terms of the precision and the power consumption.
  • the objective lens can be independently displaced minutely in the radial direction of the optical disc information recording medium in the optical head device. ing. Specifically, an objective lens displacement mechanism using an electromagnetic force generated by a coil or the like is provided in the optical head device so that the objective lens can be displaced.
  • the objective lens displacement mechanism controls the position of the objective lens based on positional deviation information between a track and a light beam obtained from reflected light from an optical disk information recording medium. Therefore, the objective lens displacement mechanism causes the objective lens to follow the track movement of the optical disk information recording medium.
  • the objective lens If the objective lens is caused to follow the track movement while applying force, the light source is displaced on the lens optical axis of the objective lens. As a result, wavefront aberration occurs, and the recording / reproducing characteristics deteriorate.
  • the position of the light source can be regarded as being substantially infinite when viewed from the objective lens. Therefore, even if the objective lens is displaced, the optical axis of the light beam does not deviate in the optical axis force of the objective lens (that is, the angle of incidence of the light beam on the objective lens does not change). The generation of wavefront aberration is not a problem.
  • Patent Document 1 Japanese Patent Application Laid-Open No. 2003-208731
  • Non-patent Document 1 Heitaro Nakajima and Hiroshi Ogawa, "Illustration Compact Disk Reader (Revised 3rd Edition;)", Ohmsha Publishing, May 20, 1996, p.208
  • Non-Patent Document 2 Akira Arimoto et al., "Study of Allowable Aberration of Optical System in Optical Video Disc” Optics, Optical Society of Japan (JSPS) Vol. 12, No. 6, p. 494 (1983)
  • Non-Patent Reference 3 Warren J. 3 ⁇ 4mith, “Modern uptical Engineering the design of optical systems” McGraw-Hill, 1966, pp.83—84
  • the present invention has been made in view of the above circumstances, and is intended to reduce the size, thickness, and cost by adopting a configuration in which a diffused light beam that is not a parallel light beam is incident on an objective lens. It is an object of the present invention to provide an optical head device capable of suppressing the influence of the wavefront aberration on the recording and reproduction characteristics.
  • a first aspect of the optical head device has a light source that emits a light beam, and a diffraction surface on which a grooved diffraction grating is formed.
  • a diffractive optical element for generating diffracted light; and an objective lens for condensing the plurality of diffracted lights on an optical disc information recording medium, wherein the diffractive optical element is configured such that the light source is a lens optical axis of the objective lens.
  • the information recording medium is characterized by having astigmatism in a direction to cancel astigmatism generated by moving away in the radial direction of the information recording medium.
  • the light source that not only generates a plurality of diffracted lights is a lens optical axis force of an objective lens. It also has astigmatism in the direction to cancel astigmatism generated by moving away from the body in the radial direction. Therefore, even when the light beam is incident on the objective lens as a diffused light that is not a parallel light beam, the effect of the wavefront aberration on the recording / reproduction characteristics can be suppressed by the diffractive optical element without using a collimator lens. It is.
  • a first light source that emits a light beam
  • a second light source that emits another light beam
  • a first surface that receives the light beam
  • a second surface for receiving the other light beam
  • a transmission / reflection surface for transmitting the light beam received on the first surface and reflecting the other light beam received on the second surface
  • a dichroic prism having a third surface for emitting, in the same direction, the light beam transmitted through the transmission-reflection surface and the other light beam reflected by the transmission-reflection surface, and the dichroic prism on an optical disk information recording medium.
  • the third surface also passes through the transmission / reflection surface.
  • the first surface and the third surface of the dichroic prism are parallel, and the second surface and the third surface also pass through the transmissive / reflective surface.
  • the third surface is equivalently parallel, and the third surface is arranged at a predetermined angle to the direction of the lens optical axis of the radial direction objective lens. Therefore, both the light beam emitted from the first light source and the other light beams emitted from the second light source have an operation equivalent to passing through a parallel plate optical element inclined at a predetermined angle from the radial direction. Will receive it.
  • the dichroic prism has astigmatism in the direction of canceling astigmatism generated by the light source moving away from the objective lens in the radial direction of the optical disc information recording medium. Therefore, even when the light beam and other light beams are incident on the objective lens as diffused light that is not a parallel light flux, the recording / reproducing characteristics due to wavefront aberration can be reduced by the dichroic prism without using a collimator lens. It is possible to suppress the effects.
  • a third aspect according to the present invention provides a first light source that emits a light beam and another light beam that emits another light beam.
  • a second light source a first surface receiving the light beam, a second surface receiving the other light beam, and the light beam received on the second surface while transmitting the light beam received on the first surface.
  • the other light beam reflects a transmission'reflection surface, and a third surface that emits, in the same direction, the light beam transmitted through the transmission'reflection surface and the other light beam reflected by the transmission'reflection surface.
  • a dichroic prism having: a first dichroic prism; and an objective lens for condensing the light beam and the other light beam emitted from the third surface of the dichroic prism onto an optical disk information recording medium,
  • the surface and the third surface are parallel to each other, and the second surface and the third surface pass through the transmission / reflection surface, so that the other light beam reflected by the transmission / reflection surface is reflected.
  • the second surface and the third surface are not
  • the wedge-shaped flat plate optical element functions as a parallel entrance surface and exit surface, and the third surface is arranged at a predetermined angle in the direction of the radial optical force of the objective lens. It is characterized by that.
  • the first surface and the third surface of the dichroic prism are parallel and the dichroic prism is formed.
  • the second and third surfaces of the system pass through the transmission and reflection surfaces, making the second and third surfaces equivalently non-parallel to other light beams reflected by the transmission and reflection surfaces.
  • a wedge-shaped flat plate optical element that functions as a surface and an exit surface is configured, and the third surface is disposed at a predetermined angle from the radial direction to the direction of the lens optical axis of the objective lens.
  • the astigmatism in the direction to cancel the astigmatism generated by the light source moving away from the lens optical axis of the objective lens in the radial direction of the optical disc information recording medium is defined as:
  • the dichroic prism has.
  • the amount of astigmatism generated in the light beam reflected by the transmission / reflection surface can be changed by the angle difference between the second surface and the third surface, and the amount of astigmatism generated in the light beam can be reduced. Gives design freedom.
  • FIG. 1 is a diagram showing a basic configuration of an optical head device according to Embodiment 1 of the present invention.
  • FIG. 2 is a diagram showing a wavefront aberration generated by a relative optical axis shift from a lens optical axis of an objective lens to a light source in the optical head device according to the first embodiment of the present invention.
  • FIG. 3 is a schematic diagram showing a light-collecting position in a radial section and a tangential section when the objective lens is moved in the radial direction in the optical head device according to Embodiment 1 of the present invention.
  • FIG. 4 is a perspective view showing a positional relationship between an optical disc information recording medium and a radial direction, a tangential direction, and the like.
  • FIG. 5 is a perspective view showing a shape of a diffractive optical element used in the optical head device according to Embodiment 1 of the present invention.
  • FIG. 6 is another perspective view showing the shape of the diffractive optical element employed in the optical head device according to Embodiment 1 of the present invention.
  • FIG. 7 is a perspective view showing another shape of the diffractive optical element used in the optical head device according to Embodiment 1 of the present invention.
  • FIG. 8 is another perspective view showing another shape of the diffractive optical element employed in the optical head device according to Embodiment 1 of the present invention.
  • FIG. 9 is a diagram showing a recording surface of a read-only optical disc information recording medium.
  • FIG. 10 is a diagram showing a recording surface of a writable optical disk information recording medium.
  • FIG. 11 is a diagram showing a change in a combined value of off-axis astigmatism generated by radial movement of an objective lens according to astigmatism generated by a diffractive optical element.
  • FIG. 12 is a schematic diagram showing light condensing positions in a radial section and a tangential section in a state where the objective lens is moved in the radial direction in the optical head device according to Embodiment 1 of the present invention.
  • FIG. 13 is a perspective view showing another shape of the diffractive optical element used in the optical head device according to Embodiment 1 of the present invention.
  • FIG. 14 shows another example of the diffractive optical element employed in the optical head device according to Embodiment 1 of the present invention. It is a perspective view which shows a shape.
  • FIG. 15 is a perspective view showing another shape of the diffractive optical element used in the optical head device according to Embodiment 1 of the present invention.
  • FIG. 16 is a perspective view showing another shape of the diffractive optical element used in the optical head device according to Embodiment 1 of the present invention.
  • FIG. 17 is a view showing the direction in which the grooves of the diffraction grating of the diffractive optical element employed in the optical head device according to Embodiment 1 of the present invention extend.
  • FIG. 18 is a diagram showing a basic configuration of an optical head device according to Embodiment 2 of the present invention.
  • FIG. 19 is a diagram showing the shape and arrangement of a parallel plate type diffractive optical element in an optical head device according to Embodiment 2 of the present invention.
  • FIG. 20 is a diagram showing the shape and arrangement of a parallel plate type diffractive optical element in an optical head device according to Embodiment 2 of the present invention.
  • FIG. 21 is a diagram showing another configuration example of the optical head device according to Embodiment 2 of the present invention.
  • FIG. 22 is a diagram showing a basic configuration of an optical head device according to Embodiment 3 of the present invention.
  • FIG. 23 is a diagram showing a specific shape of a dichroic prism in an optical head device according to Embodiment 3 of the present invention.
  • FIG. 24 is a diagram showing a basic configuration of an optical head device according to Embodiment 4 of the present invention.
  • FIG. 25 illustrates movement of the diffraction grating element according to Embodiment 4 of the present invention.
  • FIG. 26 is a diagram showing a position of a light beam on a photodetector according to Embodiment 4 of the present invention.
  • FIG. 27 is a diagram showing a basic configuration of an optical head device according to Embodiment 5 of the present invention.
  • FIG. 28 is a diagram showing a hologram element according to Embodiment 5 of the present invention.
  • FIG. 29 is a diagram showing a focused state of a semi-luminous beam according to Embodiment 5 of the present invention.
  • FIG. 30 is a diagram showing a light receiving area of the photodetector according to Embodiment 5 of the present invention.
  • the diffractive optical element is provided with a function of generating astigmatism as well as a diffractive function, so that the light source moves away from the lens optical axis of the objective lens in the radial direction of the optical disc information recording medium.
  • Optical head device that cancels astigmatism generated by It is a place.
  • FIG. 1 is a diagram showing a basic configuration of an optical head device according to the present embodiment.
  • This optical head device employs a finite optical system having no collimator lens.
  • reference numeral 1 denotes a semiconductor laser as a light source
  • reference numeral 2a denotes a light beam emitted from the semiconductor laser
  • reference numeral 3 denotes a flat glass serving as an exit window of the light beam 2a
  • reference numeral 4 denotes a semiconductor laser 1.
  • a heat dissipating metal package having a function of integrating the semiconductor laser 1 and the flat glass 3 and dissipating heat generated when the semiconductor laser 1 emits light.
  • the integrated structure of the semiconductor laser 1, the flat glass 3, and the heat dissipating metal package 4 is referred to as a light emitting component 5.
  • Reference numeral 6 denotes a diffractive optical element for diffracting the light beam 2a and dispersing it into a plurality of diffracted light beams 2b.
  • Reference numeral 7 deflects the light beam 2b into a light beam 2c by a reflection surface provided inside.
  • Reference numeral 8 denotes an optical disk information recording medium such as a CD, DVD, or MD, and reference numeral 9 denotes an objective lens that focuses the light beam 2c from the deflection prism 7 on the optical disk information recording medium 8 as a light beam 2d. Since no collimator lens is provided in the path of the light beams 2a-2c, the light beams 2a-2c do not become parallel light beams but become diffused light. Therefore, this optical head device is a finite optical system.
  • the light beam 2d reflected by the optical disk information recording medium 8 again enters the objective lens 9, is converted into convergent light having the optical axes Alb and Ale as central axes, and passes through the deflecting prism 7.
  • the light beam 2e transmitted through the deflecting prism 7 passes through the detection optical element 11 to become a light beam 2f and enters the light detector 10.
  • the photodetector 10 is a photodiode provided with a plurality of divided light receiving surfaces according to the optical system.
  • the light detector 10 converts the amount of the light beam 2f incident on each light receiving surface from the objective lens 9 into an electric signal and outputs the electric signal.
  • the detection optical element 11 is an optical element for appropriately causing the light beam 2e reflected by the optical disk information recording medium 8 to enter the divided light receiving surface of the photodetector 10.
  • the detection optical element 11 is formed of, for example, a concave lens and has a lens function and a beam dividing function.
  • optical disc information recording medium 8 On the optical disc information recording medium 8, tracks in which recording marks (pits) as data are arranged in a circle or a spiral are formed, and the arrangement forms the tracks.
  • An optical disk recording / reproducing apparatus on which the optical head device according to the present embodiment is mounted is an objective laser.
  • the light beam 2d converged by the lens 9 is scanned along the track, and data is read from the reflected light.
  • the optical disk information recording medium 8 is rotated by a motor (not shown) around the center of the track as a central axis.
  • the optical disk recording / reproducing apparatus needs to control the radial position of the optical beam 2d so as to follow the track displacement.
  • the optical head device itself can be displaced by a servo mechanism (not shown).
  • a servo mechanism not shown.
  • radial position control of the light beam by a servo mechanism for displacing the entire optical head device is not desirable from the viewpoint of accuracy and power consumption.
  • the objective lens 9 is independently provided in the optical head device in the radial direction of the optical disk information recording medium 8. Can be moved in parallel. Specifically, an objective lens displacement mechanism (not shown) using an electromagnetic force generated by a coil or the like is provided in the optical head device so that the objective lens 9 can be displaced. This objective lens displacement mechanism calculates the amount of displacement between one track and one light beam based on the signal output from the optical detector 10 after receiving the reflected light from the optical disk information recording medium 8 and controlling the position of the objective lens 9. Perform
  • the semiconductor laser 1 as a light source substantially exists on the lens optical axis of the objective lens 9.
  • the position 9 is often set as the initial design position of the objective lens 9 in the objective lens displacement mechanism.
  • the optical axes Ala and Alb determined by the principal point of the objective lens 9 and the position of the light source at the initial design position are referred to as design optical axes.
  • the light beams 2a-2c from the semiconductor laser 1 enter the objective lens 9 as diffused light.
  • the position of the semiconductor laser 1 as a light source is set with respect to the lens optical axis of the objective lens 9. It will be located off-axis. Therefore, the light beam 2c is The transmission through the lens 9 causes a wavefront aberration.
  • FIG. 2 is a diagram showing a typical characteristic example of a wavefront aberration generated by a relative optical axis shift of the light source with respect to the lens optical axis of the objective lens 9.
  • Typical aberration components of wavefront aberration include astigmatism, coma, spherical aberration, and higher-order aberrations. Further, the total aberration represents a composite value of all these aberrations. Astigmatism occupies the largest proportion of these generated aberrations, and is called off-axis astigmatism.
  • FIG. 3 is a diagram schematically showing a cross section of the light beam 2 in the radial direction D1 and the tangential direction D2 orthogonal thereto.
  • FIG. 4 is a perspective view showing a positional relationship between the optical disc information recording medium 8 and the radial direction Dl, the tangential direction D2, and the like.
  • FIG. 3 for the sake of simplicity, it is assumed that the light beam 2 from the semiconductor laser 1 is directly incident on the objective lens 9 without considering the deflection by the deflection prism 7.
  • the y axis is the same direction as the radial direction D1
  • the X axis is the same direction as the tangential direction D2
  • the z axis is the direction orthogonal to both the x and y axes.
  • the front focal line F2 near the optical disc information recording medium 8 has a direction parallel to the radial direction
  • the rear focal line F1 near the objective lens 9 has a direction parallel to the tangential direction.
  • the objective lens 9 When the objective lens 9 is controlled to be displaced in the radial direction and a relative optical axis shift occurs between the semiconductor laser 1 as the light source and the objective lens 9, the condensing position of the light beam 2 d is changed to the optical disk information. Since the light beam 2d moves from the recording medium 8 toward the objective lens 9 in the direction, the spot shape of the light beam 2d on the optical disk information recording medium 8 changes in the radial direction into an elongated and elliptical shape.
  • the spot of the light beam 2d spreads to the track adjacent to the track being read or written, and the crosstalk of the adjacent track force increases.
  • the resolution in the radial direction is deteriorated, and the ability of the light beam 2d to detect the crossing of the track is also reduced.
  • the position of the objective lens 9 is set so that the recording surface of the optical disc information recording medium 8 is located at a substantially intermediate position between the position of the front focal line F2 and the position of the rear focal line F1. Control in the direction Then, the spot shape of the light beam 2d on the recording surface of the optical disc information recording medium 8 can be made substantially circular. It is thought that this can prevent deterioration of the resolution in the radial direction.
  • the spot of the light beam 2d at that time is larger than that in the case where there is no relative optical axis shift due to the existence of the wavefront aberration. Therefore, the resolution in the tangential direction decreases, and the recording / reproducing characteristics deteriorate.
  • the diffractive optical element 6 has the shape shown in FIGS. 5 and 6, or the shape shown in FIGS. 7 and 8.
  • the diffractive optical element 6a shown in FIGS. 5 and 6 has a diffraction surface 102a on which a diffraction grating DF is formed, and a back surface 101a.
  • the diffraction surface 102a is a plane.
  • the curvature in the ⁇ -axis direction which is the short axis direction of the diffractive optical element 6a
  • the curvature in the ⁇ -axis direction which is the long axis direction of the diffractive optical element 6a
  • the back surface 101a is a convex toric surface having a different curvature and a different curvature C
  • the direction of the grooves of the diffraction grating DF formed on the diffraction surface 102a is substantially parallel to the
  • the traveling direction of the light beam 2a is defined as the ⁇ axis.
  • the axes ⁇ , ⁇ are orthogonal to each other.
  • the light beam 2a emitted from the light emitting component 5 is incident on the back surface 101a of the diffractive optical element 6a, and then the diffraction surface 102a
  • the upper diffraction grating DF splits the light into at least two light beams 2bl-2b3.
  • the number of light beams to be dispersed varies depending on the application.For example, here is the case where light beams are dispersed into three light beams (0th-order diffracted light beam 2bl, + 1st-order diffracted light beam 2b2, and 1st-order diffracted light beam 2b3). Is shown.
  • the 0th-order diffracted light beam 2bl is a transmitted light that is not subjected to a diffraction effect, and is used for recording and reproducing on the optical disc information recording medium 8. Further, the + 1st-order diffracted light beam 2b2 and the 1st-order diffracted light beam 2b3 are both diffracted lights that have undergone a diffractive action and have an optical path bent. Both the 0th-order diffracted light beam 2bl, + the 1st-order diffracted light beam 2b2 and the 1st-order diffracted light beam 2b3 are condensed on the optical disk information recording medium 8 by the objective lens 9 and then reflected, and are respectively received by the photodetector 10. Is done.
  • the diffractive optical element 6b shown in FIGS. 7 and 8 has a diffraction surface 102b on which a diffraction grating DF is formed, and a back surface 101b.
  • the diffraction surface 102b is a plane.
  • the curvature of the diffractive optical element 6b in the ⁇ -axis direction, which is the minor axis direction, is, and the curvature of the diffractive optical element 6b in the ⁇ -axis direction, which is the major axis direction, is C ⁇ .
  • the back surface 101b is a concave toric surface having a different curvature and a different curvature C
  • the direction of the grooves of the diffraction grating DF formed on the diffraction surface 102b is substantially parallel to the
  • the light beam 2a emitted from the light emitting component 5 is incident on the back surface 101b of the diffractive optical element 6b and then diffracted on the diffractive surface 102b.
  • the grating DF splits the beam into at least two or more light beams 2b1 and 2b3.
  • the diffraction gratings DF are not provided on the back surfaces 101a and 101b of the diffraction surfaces, but the diffraction gratings DF are formed not only on the diffraction surfaces 102a and 102b but also on the back surfaces 101a and 101b.
  • a grid DF may be provided.
  • a diffraction grating DF may be provided only on the back surfaces 101a and 101b, and this may be used as a diffraction surface.
  • the 0th-order diffracted light beam 2bl, the + 1st-order diffracted light beam 2b2, and the ⁇ 1st-order diffracted light beam 2b3 separated by the diffraction grating DF of the diffractive surface 102a or 102b are placed on the optical disc information recording medium 8 by the objective lens 9 respectively.
  • the light is converged as a second-order diffracted light beam 2dl, a + first-order diffracted light beam 2d2, and a first-order diffracted light beam 2d3.
  • FIG. 9 is a diagram showing a recording surface of a read-only optical disc information recording medium 8 on which information marks are recorded side by side in the tangential direction D2.
  • FIG. 10 is a diagram showing a recording surface of a writable optical disk information recording medium 8 having a guide groove GR along which a recording mark is recorded.
  • the direction of the arrangement of the three diffracted light beams 2dl-2d3 can be adjusted by rotating the diffracted optical element 6a or 6b around the designed optical axis.
  • a three-beam method is often used for an optical disc information recording medium having a structure without a guide groove GR.
  • the angle ⁇ a of the displacement in the arrangement direction of the three diffracted light beams 2dl—2d3 from the tangential direction D2 is determined by the fact that the radial arrangement distance of the diffracted light beams 2d2 and 2d3 is approximately It is adjusted to an angle that is (N + 1Z2) times the period (N is any integer).
  • the angle of deviation in the arrangement direction of the three diffracted light beams 2dl-2d3 varies depending on the difference in the structure of the optical disc information recording medium and the difference in the deviation detection method, and is relatively large. In some cases, it may be set, while in others it may be set relatively small.
  • the ⁇ -axis is rotated in the tangential direction force, for example, the above-mentioned ⁇ a (in the case of Fig. 9; If the j8 axis is adjusted to the direction in which the radial force is also rotated by, for example, the above ⁇ a (in the case of FIG. 9; ⁇ b in the case of FIG. 10), the three diffracted light beams 2dl— Adjustment in the 2d3 array direction is possible.
  • the 0th-order diffracted light beam 2dl, the + 1st-order diffracted light beam 2d2, and the 1st-order diffracted light beam 2d3 are reflected by the optical disc information recording medium 8, respectively. Then, each reflected diffracted light beam is received by the photodetector 10, and each light amount is output as an electric signal.
  • the electric signals corresponding to the + 1st-order diffracted light beam 2d2 and the ⁇ 1st-order diffracted light beam 2d3 are subjected to calculations according to the deviation detection method, and the 0th-order diffracted light beam 2dl and the information mark sequence are , A tracking error signal representing the relative positional deviation in the radial direction is generated. For example
  • the diffractive optical element 6a or 6b when the light beam 2a passes through the toric surface of the back surface 101a or 101b of the diffractive surface, due to the difference between the curvatures C y and C j8 in the ⁇ -axis direction and the j8-axis direction, Astigmatism occurs. Therefore, by providing the diffractive optical element 6a or 6b with a function of generating astigmatism that is not limited to the diffraction function, the semiconductor laser 1 as a light source is used as a light source for the lens 9 of the objective lens 9. What is necessary is just to cancel the astigmatism generated by moving away in the direction.
  • 8 are set so that the diffractive optical element 6a or 6b has astigmatism in a direction to cancel off-axis astigmatism generated by moving the objective lens 9 in the radial direction. decide.
  • FIG. 11 is a diagram showing a change in a combined value Was of off-axis astigmatism generated by radial movement of the objective lens 9 according to astigmatism generated by the diffractive optical element 6a or 6b.
  • the curve (a) corresponds to the graph of astigmatism in FIG.
  • three states are shown as curves (b), (c), and (d) according to the difference in the amount of astigmatism generated in the diffractive optical element 6a or 6b.
  • the amount of astigmatism generated in the diffractive optical element 6a or 6b is defined as AS g (corresponding to the value of the intercept on each curve in FIG. 11).
  • the relationship between the front focal line F2 and the rear focal line F1 is the relationship shown in FIG. In this case, as shown in FIG. 12, the position of the front focal line F2 and the position of the rear focal line F1 of the light beam are in the relationship of being switched in the case of FIG.
  • the astigmatism amount ASg generated by the diffractive optical element 6a or 6b is set so that the characteristic value of the combined value of the off-axis astigmatism, the characteristic force Was, falls between the curve (b) and the curve (d). Do it.
  • the value of the astigmatism amount ASg is set by the values of the curvatures C y and C of the diffractive optical elements 6a and 6b.
  • the diffractive optical element 6 may have a cylindrical surface shape as shown in FIGS. 13 to 16 as in FIGS. 5 to 8. The effect of generating a large astigmatism is obtained.
  • the diffractive optical element 6c shown in FIG. 13 has a convex cylindrical surface having a curvature only in the ⁇ -axis direction on the back surface 101c of the diffraction surface 102c, and a groove substantially parallel to the
  • a diffraction grating DF having the following formula is formed.
  • the diffractive optical element 6d shown in FIG. 14 has a diffractive grating having a convex cylindrical surface having a curvature only in the ⁇ -axis direction on the diffraction surface 102d and a groove substantially parallel to the
  • DF is formed.
  • the back surface lOld of the diffraction surface 102d is a flat surface.
  • the diffractive optical element 6e shown in FIG. 15 has a concave cylindrical surface having a curvature only in the ⁇ -axis direction on the back surface 101e of the diffraction surface 102e, and has a substantially parallel groove in the
  • the diffraction grating DF is formed.
  • the diffractive optical element 6f shown in FIG. 16 has a concave cylindrical surface having a curvature only in the 8-axis direction on the diffraction surface 102f, and a diffractive surface having grooves substantially parallel to the
  • a grid DF is formed.
  • the back surface 101f of the diffraction surface 102f is a flat surface.
  • the diffraction grating DF is not provided on the back surface 101c to 101f of the diffraction surface, but not only the diffraction surfaces 102c to 102f.
  • a diffraction grating DF may be provided on the back surface 101c-101f.
  • a diffraction grating DF may be provided only on the back surface 101c-1 Olf, and this may be used as a diffraction surface.
  • the spherical aberration and the best image surface force of the light beam focused on the optical disk information recording medium 8 are measured.
  • An aberration (referred to as defocus aberration) caused by defocusing caused by the displacement of the lens 9 in the lens optical axis direction occurs.
  • the toric surface shape shown in FIG. 5 to FIG. 8 when the toric surface shape shown in FIG. 5 to FIG. 8 is adopted, by optimizing the curved surfaces in the ⁇ direction and the j8 direction of the toric surface as aspheric surfaces, a spherical surface besides astigmatism can be obtained. Aberration and defocus aberration can be reduced. In addition, the spherical aberration caused by the distance between the objective lens 9 and the light source deviating from the design value of the objective lens 9 and the thickness of the protective transparent substrate formed on the optical disk information recording medium 8 By optimizing the above-mentioned aspherical shape in consideration of the spherical aberration generated by force such as an error, the quality of the light beam can be further improved, and the recording / reproducing characteristics can be improved. On the other hand, when the cylindrical surface shape shown in FIGS. 13 to 16 is adopted, the amount of astigmatism can only be adjusted.
  • the diffractive surface of the diffractive optical element 6 or the back surface of the diffractive surface is a toric surface or a cylindrical surface
  • the curvature (for example) of a certain meridional surface in the toric surface and the other meridian surface perpendicular to it are obtained.
  • the amount of astigmatism of the diffractive optical element 6 can be adjusted by adjusting the curvature (for example, C
  • a certain meridional surface in the toric surface and another meridional surface perpendicular to the toric surface are formed into an aspherical shape, so that a light beam emitted from a light source that is only affected by astigmatism is reduced to an optical disk. It is also possible to adjust the spherical aberration and the amount of defocus aberration generated in the optical system until the light is focused on the information recording medium 8. Therefore, the quality of the light beam used for recording and reproduction can be further improved.
  • the track direction that is, the tangential direction D2, and the arrangement direction of the 0th-order diffracted light beam 2dl, + 1st-order diffracted light beam 2d2, and 1st-order diffracted light beam 2d3
  • the angle ⁇ a or ⁇ b is provided between the above, the diffractive optical element 6 is rotated in the above.
  • the astigmatism of the diffractive optical element 6 also rotates, and the off-axis astigmatism generated in the objective lens 9 may not be able to be canceled efficiently.
  • the toric surface or the toric surface of the diffractive optical element 6 is set so that the amount of astigmatism generated in the diffractive optical element 6 can cancel out the off-axis astigmatism generated in the objective lens 9 most efficiently. While the direction of curvature of the cylindrical surface is parallel to at least one of the tangential direction D2 and the radial direction D1, the direction in which the groove of the diffraction grating DF extends is only ⁇ a or ⁇ b from the 13th axis as shown in Fig. 17. It is desirable to shift.
  • the direction of the groove of the diffraction grating DF is inclined at an angle ⁇ a or ⁇ b from the radial direction (corresponding to the direction of the ⁇ axis) to the direction of the tangential direction of the optical disc information recording medium 8.
  • a plurality of diffracted lights can be arranged on the optical disc information recording medium 8 at an angle of ⁇ a or ⁇ b with respect to the track direction of the optical disc information recording medium 8, and the diffractive optical element can be arranged.
  • the diffractive optical element 6 can be arranged so that the astigmatism of the objective lens 9 can be canceled most efficiently by the radial movement of the objective lens 9.
  • the diffractive optical element 6 uses the semiconductor laser 1 as a light source that merely generates a plurality of diffracted light beams as a light source.
  • the recording medium 8 also has astigmatism in a direction to cancel astigmatism generated by moving away from the recording medium 8 in the radial direction. Therefore, even when the light beam is incident on the objective lens 9 as a diffused light that is not a parallel light beam, the influence of the wavefront aberration on the recording / reproduction characteristics can be suppressed by the diffractive optical element 6 without using a collimator lens. Is possible. As a result, the size and thickness of the optical head device can be reduced and the cost can be reduced.
  • the diffractive optical element 6 by providing the diffractive optical element 6 with a function of generating astigmatism capable of canceling off-axis astigmatism generated when the objective lens 9 shifts the lens and a spectral function of the diffraction grating DF, it is desirable that It becomes possible to give astigmatism ASg in the direction.
  • the required maximum amount of lens shift is about 600 m
  • the off-axis astigmatism generated by the objective lens 9 at that time is 300 m ⁇ ⁇ It is about. Therefore, the astigmatism ASg of the diffractive optical element 6 is desirably about 300 m ⁇ or less in the direction of canceling off-axis astigmatism.
  • the amount of astigmatism takes into account off-axis astigmatism of the objective lens. In the case of an optical configuration in which astigmatism is further added by a light source or other optical components, the above-described astigmatism is used. In some cases, it should be set larger than the astigmatism amount.
  • the optical configuration described above is an example of a typical finite optical system, but the present embodiment is also applicable to a pseudo finite optical system.
  • the quasi-finite optical system means that even if the light beam emitted from the light source becomes a parallel light beam in the optical path, a separate lens or the like is provided in the optical path between the light source and the objective lens.
  • a separate lens or the like is provided in the optical path between the light source and the objective lens.
  • a separate lens or the like is provided in the optical path between the light source and the objective lens.
  • the light beam incident on the objective lens is the same as in the case of the finite optical system, so that the present embodiment can be applied.
  • This embodiment is a modification of the optical head device according to Embodiment 1, and employs a parallel plate type diffractive optical element instead of the diffractive optical element 6 having a toric surface or a cylindrical surface, The surface is also tilted in the direction of the lens optical axis of the objective lens 9 with respect to the radial force so as to generate astigmatism.
  • FIG. 18 is a diagram showing an optical head device according to the present embodiment.
  • the device configuration is the same as that of FIG. 1 except that the diffractive optical element 6 is changed to a parallel plate type diffractive optical element 61. Therefore, the points other than the parallel plate type diffractive optical element 61 are the same as those of the optical head device according to the first embodiment, and the description is omitted.
  • FIG. 19 and FIG. 20 show the shape and arrangement of the parallel-plate diffractive optical element 61 in FIG.
  • FIG. 19 is a view of the parallel-plate diffractive optical element 61 viewed from the tangential direction
  • FIG. 20 is a view of the parallel-plate diffractive optical element 61 viewed from the radial direction.
  • the parallel plate type diffractive optical element 61 is made of a parallel plate type resin or glass crystal material, and has a diffraction grating DF formed on at least one of a surface on which the light beam 2a enters and a surface on which the light beam 2a exits. ( Figures 19 and 20 show the case where the diffraction grating DF is provided only on the exit surface.)
  • the light beam 2a is split into at least two light beams 2bl-2b3 by the diffraction grating DF of the parallel plate type diffractive optical element 61.
  • the parallel-plate diffractive optical element 61 When the parallel-plate diffractive optical element 61 is given an inclination ⁇ ⁇ with respect to the design optical axis in a direction corresponding to the radial direction D1, the radiated light beam 2a causes the parallel-plate diffractive optical element 61 to Passing it causes astigmatism. Therefore, as in the case of the first embodiment, the axis described in the first embodiment that occurs when the objective lens 9 moves in the radial direction D1 due to astigmatism generated in the parallel-plate diffractive optical element 61. Outer astigmatism can be canceled.
  • the parallel plate diffractive optical element 61 has a parallel plate, in which the j8 axis, which is the direction in which the groove of the diffraction grating DF extends, is aligned with the z-axis, and the ⁇ axis, which is the direction in which the groove of the diffraction grating DF is aligned, is aligned with the X axis.
  • the diffractive surface of the diffractive optical element 61 is arranged at a predetermined angle ⁇ from the radial direction D1 to the direction of the lens optical axis Ala of the objective lens 9.
  • the astigmatism amount W22pv generated by the parallel-plate diffractive optical element 61 is obtained by calculating the numerical aperture of the light beam 2a passing through the parallel-plate diffractive optical element 61 by NA and the wavelength of the light beam 2a by:
  • ⁇ ⁇ be the distance (astigmatic difference) between the front focal line F2 and the rear focal line F1 of astigmatism
  • Equation 1 is based on Non-Patent Document 2 described above.
  • the astigmatic difference ⁇ is calculated using the thickness d and the refractive index ⁇ of the parallel-plate diffractive optical element 61 and the angle ⁇ from the radial direction D1 according to Non-Patent Document 3.
  • the amount of astigmatism ASg generated by the parallel-plate diffractive optical element 61 is expressed by the following equation. Can be determined more.
  • the arrangement direction of each of the light beams 2bl-2b3 after spectroscopy also changes the track directional force of the optical disc information recording medium 8 shown in Figs.
  • the arrangement of the parallel-plate diffractive optical element 61 is adjusted so that ⁇ b is formed with the design optical axis as the rotation axis.
  • the parallel-plate diffractive optical element 61 when the parallel-plate diffractive optical element 61 is rotated, the astigmatism of the parallel-plate diffractive optical element 61 is also rotated, and the off-axis astigmatism generated by the objective lens 9 is efficiently removed. Sometimes it can't be countered.
  • the parallel-plate diffractive optical element 61 is designed so that the amount of astigmatism generated by the parallel-plate diffractive optical element 61 can most effectively cancel the off-axis astigmatism generated by the objective lens 9.
  • the direction of the groove of the diffraction grating DF of the element 61 is desirably shifted from the radial direction D1 in the tangential direction D2 by an angle ⁇ a or ⁇ b, as in FIG.
  • the direction of the groove of the diffraction grating DF is inclined at an angle ⁇ a or ⁇ b from the radial direction (corresponding to the direction of the ⁇ axis) to the direction of the tangential direction of the optical disc information recording medium 8.
  • a plurality of diffracted lights can be arranged on the optical disc information recording medium 8 at an angle ⁇ a or ⁇ b with respect to the track direction of the optical disc information recording medium 8, and a parallel plate type
  • the parallel plate type diffractive optical element 61 can be arranged so that the astigmatism of the diffractive optical element 61 can cancel out the astigmatism generated by the radial movement of the objective lens 9 most efficiently.
  • the diffractive surface of parallel-plate diffractive optical element 61 is arranged at a predetermined angle ⁇ ⁇ from radial direction D1. Therefore, by adjusting the thickness d, the refractive index n, and the degree of inclination 0 of the parallel plate type diffractive optical element 61, the amount of astigmatism of the diffractive optical element can be easily adjusted.
  • the flat glass 3 serving as the exit window of the light beam 2a is positioned in the radial direction.
  • the parallel-plate exit window 3a has a function of generating astigmatism similarly to the parallel-plate diffractive optical element 61. However, since it is inclined obliquely from the radial direction, coma aberration is likely to occur.
  • the parallel-plate diffractive optical element 61 is applied to the light-emitting component 5a in FIG. 21, and the diffractive surface of the parallel-plate diffractive optical element 61 is oriented in the opposite direction to the exit surface of the parallel-plate exit window 3a. If it is tilted, a part or all of the coma generated by the parallel-plate exit window 3 a can be canceled by the coma generated by the parallel-plate diffractive optical element 61. Therefore, the quality of the light beam used for recording and reproduction can be further improved.
  • the required maximum amount of lens shift is about 600 m
  • the off-axis astigmatism generated by the objective lens 9 at that time is 300 m ⁇ ⁇ It is about. Therefore, the amount of astigmatism ASg of the parallel-plate diffractive optical element 61 is desirably about 300 m ⁇ or less in the direction of canceling off-axis astigmatism.
  • the amount of astigmatism takes into consideration off-axis astigmatism of the objective lens.
  • the above-described amount of astigmatism is used. In some cases, it should be set larger than the astigmatism amount.
  • This embodiment is also applicable to a pseudo finite optical system.
  • This embodiment is also a modification of the optical head device according to the first embodiment, and has a dual light source configuration, and uses a dual light source that does not allow the diffractive optical element to perform the function of generating astigmatism.
  • a dichroic prism that emits a light beam in the same direction has an astigmatism generation function.
  • FIG. 22 is a diagram showing an optical head device according to the present embodiment.
  • the semiconductor laser 1 as the first light source, the flat glass 3, the heat dissipating metal package 4, the diffractive optical element 62, the deflecting prism 7, the optical disc information recording medium 8, the objective lens 9, the photodetector 10, the detection Regarding the known optical element 11, a parallel plate type diffractive optical element 62 having a diffractive surface not inclined from the radial direction is used instead of the diffractive optical element 6, and It is the same as FIG. 1 except that a dichroic prism 12 is inserted inside. Therefore, the description of the same components as those in FIG. 1 is omitted.
  • Reference numeral 13 in FIG. 22 denotes a semiconductor laser as a second light source, which emits a light beam 14 (for example, blue light) having a wavelength different from the wavelength of the light beam 2a (for example, red light). I do.
  • Reference numeral 15 denotes a hologram element, and reference numeral 16 denotes a light receiving element formed on the same semiconductor substrate as the semiconductor laser 13.
  • the semiconductor substrate on which the semiconductor laser 13 and the light receiving element 16 are formed is mounted on a package 17 having a heat radiation function. Further, a power supply terminal 18 for supplying power to the semiconductor laser 13 and the light receiving element 16 and an output terminal 19 for outputting an electric signal from the light receiving element 16 are mounted on the package 17.
  • the hologram element 15 is integrated with the package 17 by being bonded thereto.
  • the light beam 14 emitted from the semiconductor laser 13 passes through the hologram element 15.
  • Reference numeral 12 denotes a dichroic prism, which has a characteristic of deflecting the light beam 14 in the z direction by an internal reflection surface and transmitting the light beam 2c from the deflecting prism 7 as it is.
  • the objective lens 9 a wavelength compatible type lens capable of condensing the light beams 2 c and 14 having different wavelengths on the optical disc information recording medium 8 is employed.
  • the light beam 2d output from the semiconductor laser 1 and reflected by the optical disk information recording medium 8 is converted into a light beam that is incident on the objective lens 9 again and converges, and is converted into a dichroic prism 12 and a deflecting prism 7. Through. Then, the light reaches the photodetector 10 via the detection optical element 11.
  • the light beam 14 output from the semiconductor laser 13 is reflected by the optical disk information recording medium 8 and reenters the objective lens 9, is deflected by the dichroic prism 12, and is split into the light receiving element 16 by the hologram element 15. And be deflected.
  • two light beams 2a and 14 emitted from two light sources are made incident on one objective lens 9, and the optical disk information recording medium is 8 is characterized by having a dichroic prism 12 capable of giving astigmatism in the radial direction.
  • FIG. 23 shows a specific shape of the dichroic prism 12.
  • the dichroic prism 12 has a structure in which a prism 12a and a prism 12b are attached by a transmission / reflection surface 105.
  • the transmission / reflection surface 105 functions as a reflection surface for the light beam 14 and simply functions as a transmission surface for the light beam 2c. That is, the dichroic prism 12 transmits the first surface 103 receiving the light beam 2c, the second surface 106 receiving the light beam 14, and the light beam 2c received by the first surface 103, while transmitting the light beam 2c on the second surface 106.
  • the received light beam 14 is transmitted through the transmission / reflection surface 105 and the light beam 2c transmitted through the transmission / reflection surface 105 and the light beam 14 reflected by the transmission / reflection surface 105 in the same direction in which the optical axis Aid extends. And a third surface 104 from which light is emitted.
  • the refractive index of the prism 12a and the refractive index of the prism 12b are the same (n2). Note that there is no change in the cross-sectional shape of the dichroic prism 12 in the yz plane in the x-axis direction in FIG.
  • the Z-axis parallel to the z-axis in FIG. 22 and the Y-axis parallel to the y-axis in FIG. 22 correspond to the intersection P7 between the optical axis A2 of the light beam 14 and the second surface 106. It is newly set with the origin as the origin.
  • the light source is caused by the lens optical axis force of the objective lens 9 moving away from the optical disc information recording medium 8 in the radial direction.
  • the dichroic prism 12 generates astigmatism ASg in a direction to cancel the astigmatism.
  • the perpendiculars L4, L5, L6 of the first surface 103, the third surface 104, and the second surface 106 of the dichroic prism 12 are set to the respective optical axes Alb, Aid, A2 of the incident or emitted light beam. Incline by ⁇ 7, ⁇ 7, ⁇ 1 in each direction.
  • angles ⁇ 2 and ⁇ 6 are respectively the optical axes ⁇ 4 and ⁇ 5 of each light beam inside the dichroic prism 12, the perpendicular L6 of the second surface 106, and the perpendicular L4 or L5 of the first surface 103 or the third surface 104. It is the angle between
  • the straight line L1 passing through the first surface 103 and the third surface 104 and the reflection point P6 is parallel (indicated as “parallel” by the symbol ⁇ ), and the second surface 106 and the reflection point
  • the straight line L2 passing through P6 is parallel (the symbol ⁇ / indicates“ parallel ”).
  • the angle formed between the optical axis A2 before the light beam 14 is incident and the optical axis Aid after the light beam 14 is 90 °.
  • the second surface 106 and the second are designed such that their angles are equivalently parallel through the transmission / reflection surface 105, similarly to the case where the first surface 103 and the third surface 104 are parallel. That is, when the light beam 14 passes through the dichroic prism 12, an effect equivalent to passing through the parallel-plate optical element having an inclination of ⁇ 7 is obtained.
  • the angle difference generated in the light beam 14 is also caused by this angle difference. It is possible to change the amount of astigmatism.
  • the degree of astigmatism generated in the light beam 14 and the shape of the dichroic prism 12 can be freely designed. That is, when the light beam 14 passes through the dichroic prism 12, the light receiving surface and the light emitting surface are subjected to an action equivalent to passing through a non-parallel wedge-shaped flat plate optical element.
  • astigmatism can be given in the radial direction of the optical disc information recording medium 8, and astigmatism generated when the objective lens 9 moves in the radial direction can be canceled.
  • the angle ⁇ 1 and the angle ⁇ 7 are made equal, the amount of astigmatism given to the light beam 14 can be obtained by Equation 3 as in the case of the light beam 2c.
  • the sum may be the sum of the distance drl between the second surface 106 and the straight line L2 in FIG. 23 and the distance dr2 between the third surface 104 and the straight line L1 in FIG.
  • the distance dr2 Since the distance dr2 has already been determined in the transmission optical path, optimizing the distance drl allows the desired astigmatism to be generated in the light beam 14 independently of the amount of astigmatism generated in the light beam 2c.
  • the amount of aberration ASg can be obtained.
  • the light beam 14 is refracted on the second surface 106, and is further refracted on the third surface 104 when exiting the dichroic prism 12.
  • the angle ⁇ 1 is equal to the angle ⁇ 7
  • the transmission / reflection surface 105 must be inclined by an angle ⁇ 3 which has a 45 ° angular force from the Y axis.
  • the light beam 14 is reflected at the point P6, the light beam 14 is The angle ⁇ is equal to the angle between the transmission / reflection surface 105 and the reflected optical axis ⁇ 5.
  • the angle 0 between the transmission / reflection surface 105 and the optical axis ⁇ 5 after reflection is less than the angle ⁇ 3.
  • nl is the refractive index of air outside the dichroic prism 12. So the number
  • first surface 103 and third surface 104 of dichroic prism 12 are parallel, and second surface 106 and third surface 104 are also transmissive / reflective surfaces.
  • the third surface 104 is disposed so as to be equivalently parallel to the third surface 104 through the intermediary of the objective lens 9 at a predetermined angle ⁇ 7 in the direction of the lens optical axis of the objective lens 9.
  • the operation is equivalent to passing through a parallel plate optical element inclined by an angle ⁇ 7 from the radial direction.
  • the second surface 106 and the third surface 104 of the dichroic prism 12 pass through the transmission / reflection surface, so that the transmission / reflection surface
  • the light beam 14 reflected by 105 is subjected to an action equivalent to passing the second surface 106 and the third surface 104 through a wedge-shaped flat optical element functioning as a non-parallel entrance plane and exit plane.
  • the amount of astigmatism generated in the light beam 14 reflected on the transmission / reflection surface 105 can also be changed by the angle difference between the second surface 106 and the third surface 104, and the amount of astigmatism generated in the light beam can be changed.
  • the dichroic prism 12 It is possible to give a degree of freedom to the amount of astigmatism and the design of the shape of the dichroic prism. Therefore, the astigmatism in the direction to cancel the astigmatism generated when the light source moves away from the objective lens 9 in the radial direction of the optical disc information recording medium 8 is reduced by the dichroic prism 12. Has. Therefore, even when the light beam 2c and the light beam 14 are made to enter the objective lens 9 as diffused light that is not a parallel light flux, the recording / reproducing characteristics due to wavefront aberration can be obtained by the dichroic prism 12 without using a collimator lens. It is possible to suppress the effects of As a result, the size and thickness of the optical head device can be reduced and the cost can be reduced.
  • the required maximum amount of lens shift is about 600 m
  • the off-axis astigmatism generated by the objective lens 9 at that time is 300 m ⁇ ⁇ It is about. Therefore, the amount of astigmatism ASg of the dichroic prism 12 is desirably about 300 m ⁇ or less in the direction of canceling off-axis astigmatism.
  • the amount of astigmatism takes into consideration the off-axis astigmatism of the objective lens.
  • the above-described amount of astigmatism is used. In some cases, it should be set larger than the astigmatism amount.
  • This embodiment is also applicable to a pseudo finite optical system.
  • This embodiment is a modification of the optical head device shown in FIG. 1 in the first embodiment.
  • the curvature direction of the cylindrical surface of the diffraction grating element 6 is By setting the light beam almost in the tangential direction, the optical beam device on the light receiving surface of the photodetector 10 is displaced due to positional fluctuation in a plane perpendicular to the design optical axis Ala of the diffraction grating element 6. It is intended to minimize the deterioration of the recording / reproducing characteristics.
  • FIG. 24 is a perspective view showing an optical head device according to Embodiment 4, and the basic optical configuration is the same as that of FIG.
  • the configuration and operation of the optical head device will be described with reference to FIG. 24, but there are no special points or changes in the contents described in Embodiment 1 with reference to FIG. A description of the configuration and operation will be omitted.
  • the diffraction grating element 6 has the shape shown in FIG.
  • the light beam 2a emitted from the laser 1 (not shown) is split into a diffracted light beam 2bl-2b3.
  • FIG. 24 only the path of the zero-order diffracted light beam 2bl among the diffracted light beams is indicated by lines, and the ⁇ first-order diffracted light beams 2b2 and 2b3 are not illustrated. Therefore, in FIG. 24, the path of each light beam is indicated by a line substantially the same as the design optical axis.
  • a flat half mirror 120 arranged at an angle to the design optical axis Alb is used to convert the light beam 2bl—2b3 into the + z direction. And is incident on the objective lens 9.
  • the light beam 2d reflected by the optical disc information recording medium 8 re-enters the objective lens 9, is converted into convergent light having the optical axes Alb and Ale as central axes, and passes through the flat half mirror 120. I do.
  • the light beam 2e transmitted through the flat half mirror 120 passes through the detection optical element 121, becomes a light beam 2f, and enters the light detector 122.
  • the photodetector 122 has a light receiving surface pattern having at least a four-divided light receiving area pair having a light receiving area A-D force and light receiving areas E and F arranged on both sides thereof.
  • the light receiving areas A to D are divided into four by a dividing line substantially parallel to the X axis and a dividing line substantially parallel to the y axis.
  • each light receiving area receives the light beam 2f converted by the detecting optical element 121, it has a function of outputting an electric signal of a magnitude corresponding to the light amount.
  • Focus control is performed on the optical disc information recording medium 8 based on the focus error signal FES. This is performed by displacing the objective lens 9 in the z-axis direction so that the light beam 2d can be condensed at the same time. Specifically, the objective lens 9 is displaced in the z direction by an objective lens displacement mechanism (not shown) using an electromagnetic force generated by a coil or the like.
  • the condensing position of the light beam 2f can be set to an arbitrary distance.
  • the detection optical element 121 has an astigmatism generation function by making the entrance surface or the exit surface a curved surface or forming a hologram, and uses the astigmatism focusing method together with the flat type half mirror 120. It may be used to generate astigmatism of a size necessary for error detection. Further, the detection optical element 121 is generated by the flat-type half mirror 120 if the center axes of the entrance surface and the exit surface are relatively shifted or are arranged at an angle with respect to the design optical axis Ale.
  • Coma can be corrected, and can be used to prevent the light intensity distribution on the photodetector 122 from becoming asymmetric.
  • the detection optical element 121 is not an essential component of the optical head device. For example, when such a lens function, an astigmatism generation function, and a coma aberration correction are not performed, in order to reduce the number of components, the optical head device does not have the optical element 121 for detection. It doesn't matter.
  • the light receiving regions E and F are arranged substantially parallel to the tangential direction D 2, and respectively receive the + 1st-order diffracted light beam 2d2 and the 1st-order diffracted light beam 2d3 reflected by the optical disc information recording medium 8. Receive light.
  • the optical head device shown in FIG. 24 has an optical configuration that performs three-beam tracking error detection by using this. By subtracting output signals from the light receiving areas E and F, the three-beam tracking error is detected. A signal is generated, and based on the signal, the position of the light beam 2d in the radial direction is controlled so as to follow the displacement of the track.
  • the optical head device may use another method as long as it is a tracking error detection method similarly performed using the diffracted light beam 2dl-2d3.
  • a tracking error detection method similarly performed using the diffracted light beam 2dl-2d3.
  • the light receiving areas E and F are each formed as a light receiving surface pattern in which each of the light receiving areas E and F is divided at least into two in the y direction, tracking error detection by the differential push-pull method can be performed.
  • the position may be adjusted so as to be a predetermined initial target value instead of the calculated value SO!
  • the photodetector 122 When the photodetector 122 is arranged near the circle of least confusion as described above, the light beam 2f reflected by the optical disc information recording medium 8 and incident on the optical disc information recording medium 8 is affected by the effect of astigmatism. On 122, it is folded in the tangential D2 direction, which is almost 90 degrees, that is, in the y direction. Therefore, in the fourth embodiment, when the objective lens 9 moves in the radial direction D1, the light beam is shifted on the photodetector 122 in the y direction.
  • the light emitting component 5, the diffraction grating element 6, the flat plate half mirror 120, the detection optical element 121, and the light detector 122 are made of a metal such as a resin. Each is fixed to a powerful optical base and integrated.
  • three diffraction grating elements 6 are formed on track TR or guide groove GR on optical disc information recording medium 8 as described in the first embodiment. It is necessary to adjust the rotation of the diffraction grating element 6 so that the light beams 2dl-2d3 are arranged in a predetermined direction. Therefore, for example, a cylindrical diffraction grating element 6 having a cylindrical outer shape, or a cylindrical diffraction grating element holder indirectly holding the diffraction grating element 6 is fitted into a cylindrical hole provided in the optical base. Thus, the diffraction grating element 6 can be rotated about the ⁇ -axis (however, in FIG.
  • the outer shape of the diffraction grating element 6 is shown as a square instead of a cylinder in order to make the cylindrical surface easier to see).
  • the fixing method is not limited to the embodiment using the fitting structure as in the above example, but a structure in which the optical base and the diffraction grating element 6 or the diffraction grating element holder are fixed with an adhesive.
  • another mode such as fixing via a fixing member such as a panel panel or a screw may be used.
  • the structure involves rotation adjustment, in order to facilitate adjustment during rotation adjustment of the diffraction grating element 6, the diffraction grating element 6 and the optical base or the diffraction grating element holder and the optical Some gap is required between the base and the scientific base. Furthermore, since the diffraction grating element 6, the optical base and the holder for the diffraction grating element usually have an outer dimension tolerance of at least several tens of meters, gaps may be widened within this tolerance range.
  • the gap is filled with the adhesive, or the gap is fixed, and the gap is fixed.
  • a fixing member such as a screw-and-panel panel, it is limited.
  • the diffraction grating element 6 is pressed against the optical base and held at the contact point thus set.
  • FIG. 25 is a cross-sectional view of the cylindrical surface of the diffraction grating element 6 along the curvature direction (that is, the y-axis direction) at this time.
  • the light beam Since the angle of incidence on the entrance surface 101c of the central optical axis of 2a changes with respect to the initial incident angle, the central optical axis of the light beam 2b after passing through the diffraction grating element 6 is the designed optical axis Ala. Bla with inclination to.
  • a state where the central axis of the diffraction grating element 6 is located on the design optical axis Ala is represented as an outer shape 6a indicated by a dotted line.
  • the light beam 2f moves on the photodetector 122 accordingly.
  • the movement of the light beam 2f is a force that affects operations such as the focus error detection described above. The influence depends on the direction in which the light beam 2f on the detector 122 shifts.
  • the control operating point changes, and the light beam 2d is defocused on the optical disk information recording medium 8. Then, the recording / reproducing characteristics of the optical head device are deteriorated due to the influence of the defocus.
  • an optical configuration for minimizing the displacement of the light beam in the X direction is desirable.
  • the curvature direction of the cylindrical surface of diffraction grating element 6 is arranged so as to correspond to tangential direction D2, as shown in FIG. Even if is moved, the direction of displacement of the light beam 2f on the photodetector 122 can be limited to the y direction, and the above-described deterioration of the recording / reproducing characteristics of the optical head device can be suppressed.
  • the diffraction grating element 6 may have a shape shown in FIG. Also in this case, the direction of the light beam shift on the photodetector 122 caused by the movement of the position of the diffraction grating element 6 can be limited to the y direction, and the same effect as described above can be obtained.
  • the diffraction grating element 6 may have a shape shown in FIG. 15 or FIG.
  • the cylindrical surface has a curvature in the j8-axis direction, unlike the case of using the shape of FIG. 13 or FIG. 14 having a cylindrical surface curvature in the ⁇ -axis direction, it is caused by the position movement of the diffraction grating element 6.
  • the shift direction of the light beam on the light detector 122 is the X direction.
  • the displacement of the light beam in the X direction causes the deterioration of the recording and reproducing characteristics of the optical head device. Therefore, when the diffraction grating element 6 having the shape shown in FIG. 15 or FIG.
  • the diffraction grating is used, when the light beam is fixed using a fixing member or the like in order to suppress the occurrence of the displacement of the light beam in the X direction, the diffraction grating is used.
  • the element 6 is kept pressurized in the axial direction, that is, press-fitted against the optical base.
  • the position of the diffraction grating element 6 in the direction of curvature of the cylindrical surface of the diffraction grating element 6 that is, in the ⁇ -axis direction, which is usually set to the radial direction D1 due to rotation adjustment and time-dependent change of the diffraction grating element 6 is prevented. Can be suppressed.
  • This embodiment is a modification of the optical head device according to the first embodiment.
  • the curvature direction of the cylindrical surface of the diffraction grating element 6 is substantially radially changed.
  • the light beam on the light-receiving surface of the photodetector 10 shifts due to position fluctuations in a plane perpendicular to the design optical axis Ala of the diffraction grating element 6, and the recording and reproduction characteristics of the optical head device are It is intended to reduce deterioration.
  • FIG. 27 is a perspective view showing an optical head device according to the present embodiment, and the basic optical configuration is the same as FIG.
  • the configuration and operation of the optical head device will be described with reference to FIG. 27, but there are no special points V or changes to the contents described in Embodiment 1 with reference to FIG. The description of the configuration, operation, and the like is omitted.
  • the diffraction grating element 6 has the shape shown in FIG. 15, and splits the light beam 2a emitted from the semiconductor laser 1 (not shown) inside the light emitting component 5 into a diffracted light beam 2bl-2b3. I do.
  • FIG. 27 only the optical path of the 0th-order diffracted light beam 2bl among the diffracted light beams is indicated by lines, and the ⁇ 1st-order diffracted light beams 2b2 and 2b3 are not shown. Therefore, in FIG. 27, the path of each light beam is indicated by a line substantially the same as the design optical axis.
  • the deflecting prism 140 corresponds to the deflecting prism 7 shown in FIG. 1 of the first embodiment, and deflects the light beam 2bl-2b3 to make it incident on the objective lens 9.
  • the light beam 2d reflected by the optical disc information recording medium 8 again enters the objective lens 9, is converted into convergent light having the optical axes Alb and Ale as central axes, and passes through the deflecting prism 140.
  • the hologram element 141 has a function of dividing the light beam 2e transmitted through the deflecting prism 140 into four half light beams 2fl-2f4 in order to detect a spot size method focus error.
  • the condenser function of the condenser lens 142 may be included in the hologram element 141 and integrated.
  • the hologram element 141 has a concentric shape or a curved shape having different centers in two regions bounded by a line BL parallel to the tangential direction D2 of the optical disc information recording medium 8. As shown in FIG.
  • the half-flux beams 2fl and 2f2 diffracted in the holo-holum region 141a and transmitted through the condenser lens 142 converge at different focal lengths FC1 and FC2 (here, FCKFC2 force FC1 may be greater than FC2).
  • FCKFC2 force FC1 may be greater than FC2
  • the half beam beams 2f3 and 2f4 diffracted by the hologram region 141b and transmitted through the condenser lens 142 similarly converge to different focal lengths FC1 and FC2.
  • the focal lengths FC1 and FC2 are determined by the set value of the focus error detection range of the optical head device.
  • the + 1st-order diffracted light beam 2d2 and the 1st-order diffracted light beam 2d3 are similarly split into half-beam beams, and then pass through the condenser lens 142 and enter the photodetector 143.
  • the photodetector 143 includes four pairs of rectangular light-receiving areas divided into three by a dividing line parallel to at least the radial direction D1 (that is, corresponding to the x-axis direction). , Plb, Pic, and Pld, and light receiving areas A2—D2 and A3—D3 for receiving the half light beam generated by splitting the + 1st-order diffracted light beam 2d2 and the 1st-order diffracted light beam 2d3 by the holo-drum element 141, respectively.
  • the photodetector 143 is disposed at an intermediate distance between the focal lengths FC1 and FC2 of the half beam 2fl-2f4 (that is, in the vicinity of (FC1 + FC2) Z2), and as shown in FIG. Since the short-beam beam having a short distance is converged before the photodetector 143 and the power is spread again, the arcs of the outer shape of the half-beam beam are in the directions shown in FIG. 30, respectively.
  • the photodetector 143 shown in FIG. 30 is provided with a light receiving region or a light receiving region pair for each of the half-beam beams.
  • An embodiment having a light receiving surface pattern in which the region pairs are shared may be used.
  • FIG. 27 shows the optical configuration for performing the tracking error detection by the differential push-pull method
  • an embodiment in which the tracking error detection method using the three-beam method may be used.
  • the arrangement direction of the diffracted light beams 2dl-2d3 with respect to the track direction on the optical disc information recording medium 9 Is set to ⁇ a or ⁇ b.
  • the displacement of the light beam generated when the objective lens 9 moves in the radial direction has the least effect on the calculation of the focus error detection.
  • the direction of the dividing line of the pair of strip-shaped light receiving regions is set to the radial direction so as not to give.
  • the light beam in the y direction that is, the direction corresponding to the tangential direction D2 is used. It is desirable to have an optical configuration that minimizes the deviation of the system.
  • the curvature direction of the cylindrical surface of the diffraction grating element 6 is made to correspond to the radial direction D1 as shown in FIG. 27, the displacement of each light beam on the photodetector 143 caused by the position movement of the diffraction grating element 6
  • the direction can be limited to the X direction, and the deterioration of the recording / reproducing characteristics of the optical head device as described above can be suppressed.
  • the diffraction grating element 6 may have the shape shown in FIG. Also in this case, the direction of the light beam shift on the photodetector 143 caused by the movement of the position of the diffraction grating element 6 can be limited to the X direction, and the same effect as described above can be obtained.
  • the hologram element 141 has a function of splitting a half-beam beam at least in parallel to the X-axis direction corresponding to the radial direction D1, and each of the half-beam beams generated by the hologram element 141 is Alternatively, the light may be detected by the photodetector 143 having a light receiving pattern divided into two by a dividing line parallel to the X-axis direction corresponding to the radial direction.
  • the light receiving pattern having a dividing line parallel to the X-axis direction corresponding to the radial direction for each half-beam beam. Therefore, it is desirable to use an optical configuration that has as much likelihood as possible with respect to the displacement of the half-beam in the y direction, that is, the direction corresponding to the tangential direction D2. This can be realized by the method described above in 4.
  • the diffraction grating element 6 has a cylindrical surface curvature in the ⁇ -axis direction as the force diffraction grating element 6 held by the optical base in the same manner as described in the fourth embodiment.
  • the photodetector generated by the displacement of the diffraction grating element 6 is used.
  • the light beam shift direction on 143 is the y direction.
  • the present invention can be used for an apparatus that performs recording and reproduction on an information recording medium using a light beam, for example, a CD (Compact Disc), a DVD (Digital Versatile Disc), and an MD (Mini Disc) It can be applied to an optical disk recording / reproducing device that performs recording / reproduction via an optical disk information recording medium such as.
  • a CD Compact Disc
  • DVD Digital Versatile Disc
  • MD Mini Disc

Abstract

An optical head device having a structure in which a divergent light beam, not a parallel beam, is made incident on an objective lens and the influence of the wave aberration on the recording/reproducing characteristics is suppressed even if the size, thickness, and cost are reduced. A diffraction optical element (6) is given a diffraction function and, for example, even a function of causing astigmatism so as to cancel the astigmatism caused when the light source is moved away from the lens optical axis of the objective lens (9) in a radial direction of an optical disk information-recording medium (8). Specifically, by forming the diffraction surface or the back surface of the diffraction optical element (6) into a toric or cylindrical surface, and by adjusting the curvature, the degree of the astigmatism is controlled.

Description

明 細 書  Specification
光ヘッド装置  Optical head device
技術分野  Technical field
[0001] 本発明は光ディスク記録 '再生装置に搭載される光ヘッド装置に関し、特に、波面 収差による記録'再生特性への影響を抑制可能な光ヘッド装置に関する。  The present invention relates to an optical head device mounted on an optical disk recording / reproducing device, and more particularly, to an optical head device capable of suppressing the influence of wavefront aberration on recording / reproducing characteristics.
背景技術  Background art
[0002] 光ヘッド装置は、 CDプレーヤ、 DVDプレーヤ、 MDプレーヤ等の多様な光デイス ク記録'再生装置にお 、て、情報の読み取り ·書き込み用装置として搭載されて 、る 。光ディスク記録 ·再生装置自身の小型化、低価格化に伴って、光ヘッド装置にも、 高密度化、高性能化、小型化、薄型化、低コストィ匕が求められている。  [0002] An optical head device is mounted as a device for reading and writing information in various optical disk recording / reproducing devices such as a CD player, a DVD player, and an MD player. With the miniaturization and price reduction of the optical disk recording / reproducing device itself, the optical head device is also required to have higher density, higher performance, smaller size, thinner, and lower cost.
[0003] 従来の光ヘッド装置の構成は、例えば下記非特許文献 1の図 7· 19に示されている 。この構成では、光源である半導体レーザ力も放射される光ビームを、コリメータレン ズが平行光束に変換する。そして、その平行光束が対物レンズへと入射する。このよ うな平行光束を用いる光学系は、無限光学系と称される。  [0003] The configuration of a conventional optical head device is shown, for example, in FIGS. In this configuration, the collimator lens converts a light beam, which also emits the power of a semiconductor laser as a light source, into a parallel light beam. Then, the parallel light beam enters the objective lens. An optical system using such a parallel light beam is called an infinite optical system.
[0004] 上記のような無限光学系の光ヘッド装置が存在する一方で、この従来の光ヘッド装 置力もコリメータレンズを無くしてシンプルな構成とした光ヘッド装置も存在する。コリ メータレンズを有しな 、そのような光ヘッド装置は、平行光束ではな 、拡散した光ビ ームを対物レンズに入射させる構成を採る。拡散した光ビームを対物レンズに入射さ せるこのような構成は、有限光学系と称される。有限光学系の光ヘッド装置は、例え ば下記特許文献 1の図 1に示されて 、る。  [0004] While an optical head device of the infinite optical system as described above exists, there is also an optical head device having a simple configuration without the collimator lens in the conventional optical head mounting force. Such an optical head device without a collimator lens adopts a configuration in which a diffused light beam, not a parallel light beam, is incident on an objective lens. Such a configuration in which the diffused light beam enters the objective lens is called a finite optical system. An optical head device of a finite optical system is shown in FIG. 1 of Patent Document 1 below, for example.
[0005] なお、特許文献 1および非特許文献 1以外にも、以下の文献が本願発明に関する 先行技術文献として挙げられる。  [0005] In addition to Patent Document 1 and Non-Patent Document 1, the following documents are cited as prior art documents relating to the present invention.
[0006] 有限光学系の光ヘッド装置では、コリメータレンズが不要なため部品数が少なぐ小 型化、薄型化および低コスト化に有利である。しかしながら、有限光学系の光ヘッド 装置は拡散した光ビームを対物レンズに入射させる構成を採る。このため、光源が対 物レンズのレンズ光軸力 ずれて光ビームの対物レンズへの入射角が変化した場合 には、波面収差が発生する。すると、集光された光ビームの品質は劣化する。対物レ ンズの入射面は、球面または非球面の形状となっているので、レンズ光軸からずれた 入射光が対物レンズを通過すると合焦しないからである。 [0006] The optical head device of the finite optical system is advantageous in miniaturization, thinning, and cost reduction with a small number of components because a collimator lens is unnecessary. However, an optical head device of a finite optical system adopts a configuration in which a diffused light beam is incident on an objective lens. For this reason, when the angle of incidence of the light beam on the objective lens changes due to the light source being shifted by the lens optical axis force of the objective lens, wavefront aberration occurs. Then, the quality of the focused light beam deteriorates. Objective This is because the entrance surface of the lens has a spherical or aspherical shape, so that if incident light deviated from the optical axis of the lens passes through the objective lens, it will not be focused.
[0007] 光ディスク記録'再生装置において、上記の波面収差は以下のように発生する。  [0007] In the optical disk recording / reproducing apparatus, the above-mentioned wavefront aberration occurs as follows.
[0008] まず、光ディスク記録 ·再生装置で記録 ·再生される光ディスク情報記録媒体の記 録面上には、データである記録マーク (ピット）が円状またはスパイラル状に配列され ており、この配列がトラックを形成している。光ディスク記録'再生装置は、対物レンズ で集光される光ビームをトラックに沿うよう走査させ、その反射光力 データを読み出 す。光ディスク情報記録媒体は、トラック中心を中心軸としてモータなどにより回転さ せる。 First, recording marks (pits), which are data, are arranged in a circular or spiral shape on a recording surface of an optical disc information recording medium recorded / reproduced by an optical disc recording / reproducing apparatus. Form a track. The optical disk recording / reproducing device scans the light beam condensed by the objective lens along the track and reads the reflected light power data. The optical disk information recording medium is rotated by a motor or the like about the center of the track as a central axis.
[0009] ここで、光ディスク情報記録媒体の形状に偏心があったり、あるいは、モータの取り 付け位置に誤差があったりすると、回転とともにトラックが光ディスク情報記録媒体の ラジアル方向（半径方向）に変位する。よって、光ディスク記録'再生装置は、光ビー ムの焦点位置をトラックの変位に沿うよう制御する必要がある。  Here, if the shape of the optical disc information recording medium is eccentric or if there is an error in the mounting position of the motor, the track is displaced in the radial direction (radial direction) of the optical disc information recording medium with rotation. . Therefore, the optical disk recording / reproducing apparatus needs to control the focal position of the optical beam so as to follow the track displacement.
[0010] 光ヘッド装置自体はサーボ機構により変位可能である。しかし、上記のようなトラック 変位は微小変位であるため、光ヘッド装置全体を変位させるサーボ機構によるトラッ ク変位に対する光ビームの位置制御は、精度の点力 も消費電力の点力 も望ましく ない。  [0010] The optical head device itself can be displaced by a servo mechanism. However, since the above-described track displacement is a minute displacement, the position control of the light beam with respect to the track displacement by the servo mechanism for displacing the entire optical head device is not desirable in terms of the precision and the power consumption.
[0011] そこで、上記のトラック変位に対して光ビームの位置を精密に追従させるために、光 ヘッド装置内にて、対物レンズが独立して光ディスク情報記録媒体のラジアル方向に 微小変位可能とされている。具体的には、対物レンズを変位可能とするために、コィ ル等で発生する電磁力を利用した対物レンズ変位機構が光ヘッド装置内に設けられ る。この対物レンズ変位機構は、光ディスク情報記録媒体からの反射光より得られるト ラック一光ビーム間の位置ずれ情報に基づいて、対物レンズの位置制御を行なう。従 つて、対物レンズ変位機構が、対物レンズを光ディスク情報記録媒体のトラック移動 に追従させる。  [0011] Therefore, in order to precisely follow the position of the light beam with respect to the track displacement described above, the objective lens can be independently displaced minutely in the radial direction of the optical disc information recording medium in the optical head device. ing. Specifically, an objective lens displacement mechanism using an electromagnetic force generated by a coil or the like is provided in the optical head device so that the objective lens can be displaced. The objective lens displacement mechanism controls the position of the objective lens based on positional deviation information between a track and a light beam obtained from reflected light from an optical disk information recording medium. Therefore, the objective lens displacement mechanism causes the objective lens to follow the track movement of the optical disk information recording medium.
[0012] し力しながら、対物レンズをトラック移動に追従させようとすると、光源が対物レンズ のレンズ光軸上力 ずれてしまう。このために波面収差が発生し、記録'再生特性が 劣化するのである。 [0013] 一方、無限光学系の光ヘッド装置であれば、対物レンズに平行光線が入射される ので、対物レンズから見て光源の位置が実質的に無限遠にあるとみなせる。そのた め、対物レンズを変位させても、光ビームの光軸が対物レンズのレンズ光軸力もずれ ることはなく（すなわち、光ビームの対物レンズへの入射角が変化することがなく）、波 面収差の発生は問題とならな 、。 [0012] If the objective lens is caused to follow the track movement while applying force, the light source is displaced on the lens optical axis of the objective lens. As a result, wavefront aberration occurs, and the recording / reproducing characteristics deteriorate. On the other hand, in the case of an optical head device having an infinite optical system, since a parallel light beam is incident on the objective lens, the position of the light source can be regarded as being substantially infinite when viewed from the objective lens. Therefore, even if the objective lens is displaced, the optical axis of the light beam does not deviate in the optical axis force of the objective lens (that is, the angle of incidence of the light beam on the objective lens does not change). The generation of wavefront aberration is not a problem.
[0014] この点に鑑みれば、短波長の光源を用いて高密度な記録'再生を実現する光へッ ド装置に有限光学系を採用することは困難であり、小型化、薄型化および低コストィ匕 に不利な無限光学系を採用せざるを得なかった。  [0014] In view of this, it is difficult to employ a finite optical system in an optical head device that realizes high-density recording and reproduction using a short-wavelength light source. Inevitably, an infinite optical system, which is disadvantageous for Kosutani, was used.
[0015] 特許文献 1：特開 2003— 208731号公報  Patent Document 1: Japanese Patent Application Laid-Open No. 2003-208731
非特許文献 1 :中島平太郎，小川博司共著、「図解 コンパクトディスク読本 (改訂 3版 ；)」オーム社出版、平成 8年 5月 20日、 p.208  Non-patent Document 1: Heitaro Nakajima and Hiroshi Ogawa, "Illustration Compact Disk Reader (Revised 3rd Edition;)", Ohmsha Publishing, May 20, 1996, p.208
非特許文献 2 :有本昭他著、「光ビデオディスクにおける光学系の許容収差量の検 討」光学、 日本光学会 (応用物理学会分科会）第 12卷第 6号 p.494 (1983) 非特干文献 3 : Warren J.¾mith、「Modern uptical Engineering the design of optical systems] McGraw-Hill, 1966、 pp.83— 84  Non-Patent Document 2: Akira Arimoto et al., "Study of Allowable Aberration of Optical System in Optical Video Disc" Optics, Optical Society of Japan (JSPS) Vol. 12, No. 6, p. 494 (1983) Non-Patent Reference 3: Warren J. ¾mith, “Modern uptical Engineering the design of optical systems” McGraw-Hill, 1966, pp.83—84
発明の開示  Disclosure of the invention
[0016] 本発明は上記の事情に鑑みてなされたもので、平行光束ではない拡散した光ビー ムを対物レンズに入射させる構成を採ることにより小型化、薄型化および低コスト化を 図る場合であっても、波面収差による記録'再生特性への影響を抑制可能な光へッ ド装置を提供することにある。  The present invention has been made in view of the above circumstances, and is intended to reduce the size, thickness, and cost by adopting a configuration in which a diffused light beam that is not a parallel light beam is incident on an objective lens. It is an object of the present invention to provide an optical head device capable of suppressing the influence of the wavefront aberration on the recording and reproduction characteristics.
[0017] 本発明に係る光ヘッド装置の第 1の態様は、光ビームを放射する光源と、溝状の回 折格子が形成された回折面を有し、前記光ビームを回折させて複数の回折光を生成 する回折光学素子と、光ディスク情報記録媒体上に前記複数の回折光を集光させる 対物レンズとを備え、前記回折光学素子は、前記光源が前記対物レンズのレンズ光 軸力 前記光ディスク情報記録媒体のラジアル方向に遠ざ力ることにより発生する非 点収差を打ち消す方向の非点収差を有することを特徴としている。  A first aspect of the optical head device according to the present invention has a light source that emits a light beam, and a diffraction surface on which a grooved diffraction grating is formed. A diffractive optical element for generating diffracted light; and an objective lens for condensing the plurality of diffracted lights on an optical disc information recording medium, wherein the diffractive optical element is configured such that the light source is a lens optical axis of the objective lens. The information recording medium is characterized by having astigmatism in a direction to cancel astigmatism generated by moving away in the radial direction of the information recording medium.
[0018] 本発明に係る光ヘッド装置の第 1の態様によれば、回折光学素子は、複数の回折 光を生成するだけでなぐ光源が対物レンズのレンズ光軸力 光ディスク情報記録媒 体のラジアル方向に遠ざ力ることにより発生する非点収差を打ち消す方向の非点収 差をも有する。よって、光ビームを平行光束ではない拡散光として対物レンズに入射 させる場合であっても、コリメータレンズを用いることなく回折光学素子によって、波面 収差による記録 ·再生特性への影響を抑制することが可能である。 According to the first aspect of the optical head device according to the present invention, in the diffractive optical element, the light source that not only generates a plurality of diffracted lights is a lens optical axis force of an objective lens. It also has astigmatism in the direction to cancel astigmatism generated by moving away from the body in the radial direction. Therefore, even when the light beam is incident on the objective lens as a diffused light that is not a parallel light beam, the effect of the wavefront aberration on the recording / reproduction characteristics can be suppressed by the diffractive optical element without using a collimator lens. It is.
[0019] 本発明に係る光ヘッド装置の第 2の態様によれば、光ビームを放射する第 1光源と 、他の光ビームを放射する第 2光源と、前記光ビームを受ける第 1面、前記他の光ビ ームを受ける第 2面、前記第 1面で受けた前記光ビームは透過させつつ、前記第 2面 で受けた前記他の光ビームは反射させる透過 ·反射面、並びに、前記透過'反射面 を透過した前記光ビームおよび前記透過'反射面で反射した前記他の光ビームを同 方向に射出する第 3面を有するダイクロイツクプリズムと、光ディスク情報記録媒体上 に前記ダイクロイツクプリズムの前記第 3面から射出される前記光ビームおよび前記 他の光ビームを集光させる対物レンズとを備え、前記第 1面および前記第 3面は平行 であって、前記第 2面および前記第 3面も前記透過'反射面を介することにより等価 的に平行であって、前記第 3面は、前記ラジアル方向力 前記対物レンズのレンズ光 軸の向きに所定の角度だけ傾けて配置されることを特徴として 、る。  According to the second aspect of the optical head device of the present invention, a first light source that emits a light beam, a second light source that emits another light beam, a first surface that receives the light beam, A second surface for receiving the other light beam, a transmission / reflection surface for transmitting the light beam received on the first surface and reflecting the other light beam received on the second surface; and A dichroic prism having a third surface for emitting, in the same direction, the light beam transmitted through the transmission-reflection surface and the other light beam reflected by the transmission-reflection surface, and the dichroic prism on an optical disk information recording medium. An objective lens for condensing the light beam and the other light beam emitted from the third surface of the prism, wherein the first surface and the third surface are parallel, and the second surface and the third surface are parallel to each other. The third surface also passes through the transmission / reflection surface. By a equivalently parallel, the third surface as being arranged inclined by a predetermined angle in the direction of the lens optical axis of the radial force the objective lens, Ru.
[0020] 本発明に係る光ヘッド装置の第 2の態様によれば、ダイクロイツクプリズムの第 1面 および第 3面は平行であって、第 2面および第 3面も透過'反射面を介することにより 等価的に平行であって、第 3面は、ラジアル方向力 対物レンズのレンズ光軸の向き に所定の角度だけ傾けて配置されている。よって、第 1光源から放射される光ビーム も、第 2光源力も放射される他の光ビームも、いずれもラジアル方向から所定の角度 だけ傾いた平行平板光学素子を通過するのと等価な作用を受けることとなる。このた め、光源が対物レンズのレンズ光軸力 光ディスク情報記録媒体のラジアル方向に 遠ざ力ることにより発生する非点収差を打ち消す方向の非点収差を、ダイクロイツクプ リズムが有する。よって、光ビームおよび他の光ビームを平行光束ではない拡散光と して対物レンズに入射させる場合であっても、コリメータレンズを用いることなくダイク ロイックプリズムによって、波面収差による記録 ·再生特性への影響を抑制することが 可能である。  According to the second aspect of the optical head device according to the present invention, the first surface and the third surface of the dichroic prism are parallel, and the second surface and the third surface also pass through the transmissive / reflective surface. Thereby, the third surface is equivalently parallel, and the third surface is arranged at a predetermined angle to the direction of the lens optical axis of the radial direction objective lens. Therefore, both the light beam emitted from the first light source and the other light beams emitted from the second light source have an operation equivalent to passing through a parallel plate optical element inclined at a predetermined angle from the radial direction. Will receive it. For this reason, the dichroic prism has astigmatism in the direction of canceling astigmatism generated by the light source moving away from the objective lens in the radial direction of the optical disc information recording medium. Therefore, even when the light beam and other light beams are incident on the objective lens as diffused light that is not a parallel light flux, the recording / reproducing characteristics due to wavefront aberration can be reduced by the dichroic prism without using a collimator lens. It is possible to suppress the effects.
[0021] 本発明に係る第 3の態様は、光ビームを放射する第 1光源と、他の光ビームを放射 する第 2光源と、前記光ビームを受ける第 1面、前記他の光ビームを受ける第 2面、前 記第 1面で受けた前記光ビームは透過させつつ、前記第 2面で受けた前記他の光ビ ームは反射させる透過'反射面、並びに、前記透過'反射面を透過した前記光ビーム および前記透過'反射面で反射した前記他の光ビームを同方向に射出する第 3面を 有するダイクロイツクプリズムと、光ディスク情報記録媒体上に前記ダイクロイツクブリ ズムの前記第 3面から射出される前記光ビームおよび前記他の光ビームを集光させ る対物レンズとを備え、前記第 1面および前記第 3面は平行であって、前記第 2面お よび前記第 3面は前記透過 ·反射面を介することにより、前記透過 ·反射面で反射さ れる前記他の光ビームに対して等価的に前記第 2面および前記第 3面が非平行な入 射面および出射面として機能するくさび形平板光学素子を構成し、前記第 3面は、前 記ラジアル方向力 前記対物レンズのレンズ光軸の向きに所定の角度だけ傾けて配 置されることを特徴とする。 [0021] A third aspect according to the present invention provides a first light source that emits a light beam and another light beam that emits another light beam. A second light source, a first surface receiving the light beam, a second surface receiving the other light beam, and the light beam received on the second surface while transmitting the light beam received on the first surface. The other light beam reflects a transmission'reflection surface, and a third surface that emits, in the same direction, the light beam transmitted through the transmission'reflection surface and the other light beam reflected by the transmission'reflection surface. A dichroic prism having: a first dichroic prism; and an objective lens for condensing the light beam and the other light beam emitted from the third surface of the dichroic prism onto an optical disk information recording medium, The surface and the third surface are parallel to each other, and the second surface and the third surface pass through the transmission / reflection surface, so that the other light beam reflected by the transmission / reflection surface is reflected. Equivalently, the second surface and the third surface are not The wedge-shaped flat plate optical element functions as a parallel entrance surface and exit surface, and the third surface is arranged at a predetermined angle in the direction of the radial optical force of the objective lens. It is characterized by that.
[0022] 本発明に係る光ヘッド装置の第 3の態様によれば、請求項 8に記載の発明によれ ば、ダイクロイツクプリズムの第 1面および第 3面は平行であって、ダイクロイツクプリズ ムの第 2面および第 3面は透過 ·反射面を介することにより、透過 ·反射面にて反射さ れる他の光ビームに対して等価的に第 2面および第 3面が非平行な入射面および出 射面として機能するくさび形平板光学素子を構成し、第 3面は、ラジアル方向から対 物レンズのレンズ光軸の向きに所定の角度だけ傾けて配置されている。よって、請求 項 7の場合と同様に、光源が対物レンズのレンズ光軸カゝら光ディスク情報記録媒体の ラジアル方向に遠ざ力ることにより発生する非点収差を打ち消す方向の非点収差を、 ダイクロイツクプリズムが有する。第 2面および第 3面の角度差によって、透過 ·反射面 にて反射される光ビームに発生させる非点収差の量を変化させることが可能となり、 光ビームに発生させる非点収差の量に設計自由度を与える。（ダイクロイツクプリズム の形状設計の自由度を与えることが可能である。 )よって、光ビームおよび他の光ビ ームを平行光束ではな 、拡散光として対物レンズに入射させる場合であっても、コリ メータレンズを用いることなくダイクロイツクプリズムによって、波面収差による記録 '再 生特性への影響を抑制することが可能である。  According to the third aspect of the optical head device of the present invention, according to the invention of claim 8, the first surface and the third surface of the dichroic prism are parallel and the dichroic prism is formed. The second and third surfaces of the system pass through the transmission and reflection surfaces, making the second and third surfaces equivalently non-parallel to other light beams reflected by the transmission and reflection surfaces. A wedge-shaped flat plate optical element that functions as a surface and an exit surface is configured, and the third surface is disposed at a predetermined angle from the radial direction to the direction of the lens optical axis of the objective lens. Therefore, as in the case of claim 7, the astigmatism in the direction to cancel the astigmatism generated by the light source moving away from the lens optical axis of the objective lens in the radial direction of the optical disc information recording medium is defined as: The dichroic prism has. The amount of astigmatism generated in the light beam reflected by the transmission / reflection surface can be changed by the angle difference between the second surface and the third surface, and the amount of astigmatism generated in the light beam can be reduced. Gives design freedom. (It is possible to provide a degree of freedom in the shape design of the dichroic prism.) Therefore, even when the light beam and other light beams are incident on the objective lens as diffused light, not as parallel light flux, By using a dichroic prism without using a collimator lens, it is possible to suppress the influence of the wavefront aberration on the recording / reproducing characteristics.
[0023] この発明の、目的、特徴、局面、および利点は、以下の詳細な説明と添付図面とに よって、より明白となる。 [0023] Objects, features, aspects, and advantages of the present invention will be set forth in the following detailed description and accompanying drawings. Thus, it becomes more apparent.
図面の簡単な説明 Brief Description of Drawings
[図 1]本発明の実施の形態 1に係る光ヘッド装置の基本構成を示す図である。 FIG. 1 is a diagram showing a basic configuration of an optical head device according to Embodiment 1 of the present invention.
[図 2]本発明の実施の形態 1による光ヘッド装置における対物レンズのレンズ光軸か ら光源までの相対的な光軸ずれにより発生する波面収差を示す図である。  FIG. 2 is a diagram showing a wavefront aberration generated by a relative optical axis shift from a lens optical axis of an objective lens to a light source in the optical head device according to the first embodiment of the present invention.
[図 3]本発明の実施の形態 1に係る光ヘッド装置における対物レンズがラジアル方向 に移動した状態のラジアル方向断面とタンジ ンシャル方向断面の集光位置を表す 模式図である。 FIG. 3 is a schematic diagram showing a light-collecting position in a radial section and a tangential section when the objective lens is moved in the radial direction in the optical head device according to Embodiment 1 of the present invention.
[図 4]ラジアル方向、タンジ ンシャル方向等と光ディスク情報記録媒体との位置関係 を示す斜視図である。  FIG. 4 is a perspective view showing a positional relationship between an optical disc information recording medium and a radial direction, a tangential direction, and the like.
[図 5]本発明の実施の形態 1に係る光ヘッド装置に採用される回折光学素子の形状 を示す斜視図である。  FIG. 5 is a perspective view showing a shape of a diffractive optical element used in the optical head device according to Embodiment 1 of the present invention.
[図 6]本発明の実施の形態 1に係る光ヘッド装置に採用される回折光学素子の形状 を示す他の斜視図である。  FIG. 6 is another perspective view showing the shape of the diffractive optical element employed in the optical head device according to Embodiment 1 of the present invention.
[図 7]本発明の実施の形態 1に係る光ヘッド装置に採用される回折光学素子の他の 形状を示す斜視図である。  FIG. 7 is a perspective view showing another shape of the diffractive optical element used in the optical head device according to Embodiment 1 of the present invention.
[図 8]本発明の実施の形態 1に係る光ヘッド装置に採用される回折光学素子の他の 形状を示す他の斜視図である。  FIG. 8 is another perspective view showing another shape of the diffractive optical element employed in the optical head device according to Embodiment 1 of the present invention.
[図 9]読み出し専用光ディスク情報記録媒体の記録面を示した図である。  FIG. 9 is a diagram showing a recording surface of a read-only optical disc information recording medium.
[図 10]書き込み可能光ディスク情報記録媒体の記録面を示した図である。  FIG. 10 is a diagram showing a recording surface of a writable optical disk information recording medium.
[図 11]回折光学素子で発生させる非点収差に応じた、対物レンズのラジアル方向移 動により発生する軸外非点収差の合成値の変化を示す図である。  FIG. 11 is a diagram showing a change in a combined value of off-axis astigmatism generated by radial movement of an objective lens according to astigmatism generated by a diffractive optical element.
[図 12]本発明の実施の形態 1に係る光ヘッド装置における対物レンズがラジアル方 向に移動した状態のラジアル方向断面とタンジ ンシャル方向断面の集光位置を表 す模式図である。  FIG. 12 is a schematic diagram showing light condensing positions in a radial section and a tangential section in a state where the objective lens is moved in the radial direction in the optical head device according to Embodiment 1 of the present invention.
[図 13]本発明の実施の形態 1に係る光ヘッド装置に採用される回折光学素子の他の 形状を示す斜視図である。  FIG. 13 is a perspective view showing another shape of the diffractive optical element used in the optical head device according to Embodiment 1 of the present invention.
[図 14]本発明の実施の形態 1に係る光ヘッド装置に採用される回折光学素子の他の 形状を示す斜視図である。 FIG. 14 shows another example of the diffractive optical element employed in the optical head device according to Embodiment 1 of the present invention. It is a perspective view which shows a shape.
[図 15]本発明の実施の形態 1に係る光ヘッド装置に採用される回折光学素子の他の 形状を示す斜視図である。  FIG. 15 is a perspective view showing another shape of the diffractive optical element used in the optical head device according to Embodiment 1 of the present invention.
[図 16]本発明の実施の形態 1に係る光ヘッド装置に採用される回折光学素子の他の 形状を示す斜視図である。  FIG. 16 is a perspective view showing another shape of the diffractive optical element used in the optical head device according to Embodiment 1 of the present invention.
[図 17]本発明の実施の形態 1に係る光ヘッド装置に採用される回折光学素子の回折 格子の溝の延びる方向を示す図である。  FIG. 17 is a view showing the direction in which the grooves of the diffraction grating of the diffractive optical element employed in the optical head device according to Embodiment 1 of the present invention extend.
圆 18]本発明の実施の形態 2に係る光ヘッド装置の基本構成を示す図である。 [18] FIG. 18 is a diagram showing a basic configuration of an optical head device according to Embodiment 2 of the present invention.
[図 19]本発明の実施の形態 2に係る光ヘッド装置における平行平板型回折光学素 子の形状と配置を示す図である。 FIG. 19 is a diagram showing the shape and arrangement of a parallel plate type diffractive optical element in an optical head device according to Embodiment 2 of the present invention.
[図 20]本発明の実施の形態 2に係る光ヘッド装置における平行平板型回折光学素 子の形状と配置を示す図である。  FIG. 20 is a diagram showing the shape and arrangement of a parallel plate type diffractive optical element in an optical head device according to Embodiment 2 of the present invention.
圆 21]本発明の実施の形態 2に係る光ヘッド装置の他の構成例を示す図である。 圆 22]本発明の実施の形態 3に係る光ヘッド装置の基本構成を示す図である。 [21] FIG. 21 is a diagram showing another configuration example of the optical head device according to Embodiment 2 of the present invention. [22] FIG. 22 is a diagram showing a basic configuration of an optical head device according to Embodiment 3 of the present invention.
[図 23]本発明の実施の形態 3に係る光ヘッド装置におけるダイクロイツクプリズムの具 体的な形状を示す図である。 FIG. 23 is a diagram showing a specific shape of a dichroic prism in an optical head device according to Embodiment 3 of the present invention.
圆 24]本発明の実施の形態 4に係る光ヘッド装置の基本構成を示す図である。 圆 25]本発明の実施の形態 4に係る回折格子素子の移動を示す図である。 [24] FIG. 24 is a diagram showing a basic configuration of an optical head device according to Embodiment 4 of the present invention. [25] FIG. 25 illustrates movement of the diffraction grating element according to Embodiment 4 of the present invention.
圆 26]本発明の実施の形態 4に係る光検知器上の光ビームの位置を示す図である。 圆 27]本発明の実施の形態 5に係る光ヘッド装置の基本構成を示す図である。 [26] FIG. 26 is a diagram showing a position of a light beam on a photodetector according to Embodiment 4 of the present invention. [27] FIG. 27 is a diagram showing a basic configuration of an optical head device according to Embodiment 5 of the present invention.
[図 28]本発明の実施の形態 5に係るホログラム素子を示す図である。  FIG. 28 is a diagram showing a hologram element according to Embodiment 5 of the present invention.
圆 29]本発明の実施の形態 5に係る半光束ビームの集光状態を示す図である。 圆 30]本発明の実施の形態 5に係る光検知器を受光領域を示す図である。 [29] FIG. 29 is a diagram showing a focused state of a semi-luminous beam according to Embodiment 5 of the present invention. [30] FIG. 30 is a diagram showing a light receiving area of the photodetector according to Embodiment 5 of the present invention.
発明を実施するための最良の形態 BEST MODE FOR CARRYING OUT THE INVENTION
実施の形態 1.  Embodiment 1.
本実施の形態は、回折光学素子に、回折機能だけではなぐ非点収差を発生させ る機能をも持たせて、光源が対物レンズのレンズ光軸から光ディスク情報記録媒体の ラジアル方向に遠ざ力ることにより発生する非点収差を打ち消すようにした光ヘッド装 置である。 In this embodiment, the diffractive optical element is provided with a function of generating astigmatism as well as a diffractive function, so that the light source moves away from the lens optical axis of the objective lens in the radial direction of the optical disc information recording medium. Optical head device that cancels astigmatism generated by It is a place.
[0026] 図 1は、本実施の形態に係る光ヘッド装置の基本構成を示す図である。この光へッ ド装置は、コリメータレンズを有しない有限光学系の構成を採る。  FIG. 1 is a diagram showing a basic configuration of an optical head device according to the present embodiment. This optical head device employs a finite optical system having no collimator lens.
[0027] 図 1において、符号 1は光源である半導体レーザ、符号 2aは半導体レーザ 1から放 射される光ビーム、符号 3は光ビーム 2aの射出窓となる平板ガラス、符号 4は半導体 レーザ 1と平板ガラス 3とを一体ィ匕し、かつ、半導体レーザ 1の発光時に発生する熱を 放熱する機能を有する放熱金属パッケージである。なお、半導体レーザ 1、平板ガラ ス 3、放熱金属パッケージ 4の一体化構造を発光部品 5とする。  In FIG. 1, reference numeral 1 denotes a semiconductor laser as a light source, reference numeral 2a denotes a light beam emitted from the semiconductor laser 1, reference numeral 3 denotes a flat glass serving as an exit window of the light beam 2a, and reference numeral 4 denotes a semiconductor laser 1. A heat dissipating metal package having a function of integrating the semiconductor laser 1 and the flat glass 3 and dissipating heat generated when the semiconductor laser 1 emits light. The integrated structure of the semiconductor laser 1, the flat glass 3, and the heat dissipating metal package 4 is referred to as a light emitting component 5.
[0028] 符号 6は光ビーム 2aを回折させて複数の回折光たる光ビーム 2bに分光するための 回折光学素子、符号 7は内部に設けられた反射面により光ビーム 2bを光ビーム 2cに 偏向する偏向プリズム、符号 8は CD, DVD, MD等の光ディスク情報記録媒体、符 号 9は偏向プリズム 7からの光ビーム 2cを光ビーム 2dとして光ディスク情報記録媒体 8に集光する対物レンズである。なお、光ビーム 2a— 2cの経路中にはコリメータレン ズが設けられないので、光ビーム 2a— 2cは平行光束とはならず拡散光となる。よって 、この光ヘッド装置は有限光学系である。  [0028] Reference numeral 6 denotes a diffractive optical element for diffracting the light beam 2a and dispersing it into a plurality of diffracted light beams 2b. Reference numeral 7 deflects the light beam 2b into a light beam 2c by a reflection surface provided inside. Reference numeral 8 denotes an optical disk information recording medium such as a CD, DVD, or MD, and reference numeral 9 denotes an objective lens that focuses the light beam 2c from the deflection prism 7 on the optical disk information recording medium 8 as a light beam 2d. Since no collimator lens is provided in the path of the light beams 2a-2c, the light beams 2a-2c do not become parallel light beams but become diffused light. Therefore, this optical head device is a finite optical system.
[0029] 光ディスク情報記録媒体 8で反射された光ビーム 2dは、再び対物レンズ 9に入射し て光軸 Alb, Aleを中心軸とする収束光へと変換され、偏向プリズム 7を透過する。 偏向プリズム 7を透過した光ビーム 2eは、検知用光学素子 11を通過して光ビーム 2f となって光検知器 10に入る。  [0029] The light beam 2d reflected by the optical disk information recording medium 8 again enters the objective lens 9, is converted into convergent light having the optical axes Alb and Ale as central axes, and passes through the deflecting prism 7. The light beam 2e transmitted through the deflecting prism 7 passes through the detection optical element 11 to become a light beam 2f and enters the light detector 10.
[0030] 光検知器 10は、光学系に応じて複数の分割受光面が設けられたフォトダイオード である。対物レンズ 9から各受光面に入射する光ビーム 2fの光量を、光検知器 10が 電気信号に変換して出力する。検知用光学素子 11は、光ディスク情報記録媒体 8で 反射された光ビーム 2eを光検知器 10の分割受光面へ適切に入射させるための光学 素子である。検知用光学素子 11は、例えば凹レンズで構成され、レンズ機能やビー ム分割機能を備える。  [0030] The photodetector 10 is a photodiode provided with a plurality of divided light receiving surfaces according to the optical system. The light detector 10 converts the amount of the light beam 2f incident on each light receiving surface from the objective lens 9 into an electric signal and outputs the electric signal. The detection optical element 11 is an optical element for appropriately causing the light beam 2e reflected by the optical disk information recording medium 8 to enter the divided light receiving surface of the photodetector 10. The detection optical element 11 is formed of, for example, a concave lens and has a lens function and a beam dividing function.
[0031] 光ディスク情報記録媒体 8には、データである記録マーク (ピット）が円状またはスパ ィラル状に配列されたトラックが形成されており、この配列がトラックを形成している。 本実施の形態に係る光ヘッド装置が搭載される光ディスク記録 ·再生装置は、対物レ ンズ 9で集光される光ビーム 2dをトラックに沿うよう走査させ、その反射光からデータ を読み出す。光ディスク情報記録媒体 8は、トラック中心を中心軸としてモータ（図示 せず)などにより回転させる。 [0031] On the optical disc information recording medium 8, tracks in which recording marks (pits) as data are arranged in a circle or a spiral are formed, and the arrangement forms the tracks. An optical disk recording / reproducing apparatus on which the optical head device according to the present embodiment is mounted is an objective laser. The light beam 2d converged by the lens 9 is scanned along the track, and data is read from the reflected light. The optical disk information recording medium 8 is rotated by a motor (not shown) around the center of the track as a central axis.
[0032] ここで、光ディスク情報記録媒体 8の形状に偏心があったり、あるいは、モータの取 り付け位置に誤差があったりすると、回転とともにトラックが光ディスク情報記録媒体 8 のラジアル方向（半径方向）に変位する。よって、光ディスク記録'再生装置は、光ビ ーム 2dのラジアル方向位置をトラックの変位に沿うよう制御する必要がある。  Here, if the shape of the optical disc information recording medium 8 is eccentric or if there is an error in the mounting position of the motor, the track is rotated along the rotation in the radial direction (radial direction) of the optical disc information recording medium 8. Is displaced. Therefore, the optical disk recording / reproducing apparatus needs to control the radial position of the optical beam 2d so as to follow the track displacement.
[0033] 光ヘッド装置自体はサーボ機構（図示せず）により変位可能である。しかし、上記の ようなトラック変位は微小変位であるため、光ヘッド装置全体を変位させるサーボ機構 による光ビームのラジアル方向位置制御は、精度の点からも消費電力の点からも望 ましくない。  [0033] The optical head device itself can be displaced by a servo mechanism (not shown). However, since the track displacement described above is a minute displacement, radial position control of the light beam by a servo mechanism for displacing the entire optical head device is not desirable from the viewpoint of accuracy and power consumption.
[0034] そこで、上記のトラック変位に対して光ビーム 2dのラジアル方向位置を精密に追従 させるために、光ヘッド装置内にて、対物レンズ 9が独立して光ディスク情報記録媒 体 8のラジアル方向に平行移動可能とされている。具体的には、対物レンズ 9を変位 可能とするために、コイル等で発生する電磁力を利用した対物レンズ変位機構 (図示 せず)が光ヘッド装置内に設けられる。この対物レンズ変位機構は、光ディスク情報 記録媒体 8からの反射光を光検知器 10が受光して出力する信号に基づいてトラック 一光ビーム間の位置ずれ量を算出し、対物レンズ 9の位置制御を行なう。  In order to precisely follow the position of the light beam 2d in the radial direction with respect to the track displacement, the objective lens 9 is independently provided in the optical head device in the radial direction of the optical disk information recording medium 8. Can be moved in parallel. Specifically, an objective lens displacement mechanism (not shown) using an electromagnetic force generated by a coil or the like is provided in the optical head device so that the objective lens 9 can be displaced. This objective lens displacement mechanism calculates the amount of displacement between one track and one light beam based on the signal output from the optical detector 10 after receiving the reflected light from the optical disk information recording medium 8 and controlling the position of the objective lens 9. Perform
[0035] なお、光源たる半導体レーザ 1が対物レンズ 9のレンズ光軸上に実質的に存在する  Note that the semiconductor laser 1 as a light source substantially exists on the lens optical axis of the objective lens 9.
(「実質的に」とは、偏向プリズム 7での偏向を考慮せずに、半導体レーザ 1からの光 ビームが対物レンズ 9に直接に入射する場合を想定することを意味する）ときの対物 レンズ 9の位置が、対物レンズ変位機構での対物レンズ 9の設計初期位置とされるこ とが多い。ここでは、この設計初期位置において対物レンズ 9の主点と光源の位置と で決まる光軸 Ala, Albを設計光軸と呼ぶ。  ("Substantially" means that it is assumed that the light beam from the semiconductor laser 1 is directly incident on the objective lens 9 without considering the deflection by the deflection prism 7) The position 9 is often set as the initial design position of the objective lens 9 in the objective lens displacement mechanism. Here, the optical axes Ala and Alb determined by the principal point of the objective lens 9 and the position of the light source at the initial design position are referred to as design optical axes.
[0036] 図 1の構成では、半導体レーザ 1からの光ビーム 2a— 2cは、拡散光として対物レン ズ 9に入射する。発明が解決しょうとする課題の項で説明したように、対物レンズ 9が ラジアル方向に追従制御される際には、光源である半導体レーザ 1の位置は対物レ ンズ 9のレンズ光軸に対して軸外に位置することとなる。よって、光ビーム 2cが対物レ ンズ 9を透過することによって波面収差が発生する。 In the configuration of FIG. 1, the light beams 2a-2c from the semiconductor laser 1 enter the objective lens 9 as diffused light. As described in the section of the problem to be solved by the invention, when the objective lens 9 is controlled to follow in the radial direction, the position of the semiconductor laser 1 as a light source is set with respect to the lens optical axis of the objective lens 9. It will be located off-axis. Therefore, the light beam 2c is The transmission through the lens 9 causes a wavefront aberration.
[0037] 図 2は、対物レンズ 9のレンズ光軸に対する光源の相対的な光軸ずれにより発生す る波面収差の典型的な特性例を示す図である。波面収差の代表的な収差成分とし て、非点収差、コマ収差、球面収差、および高次収差がある。また、トータル収差はこ れらすべての収差の合成値を表す。これら発生する収差のうち最も大きな割合を占 めるのは非点収差であり、これを軸外非点収差と呼ぶ。  FIG. 2 is a diagram showing a typical characteristic example of a wavefront aberration generated by a relative optical axis shift of the light source with respect to the lens optical axis of the objective lens 9. Typical aberration components of wavefront aberration include astigmatism, coma, spherical aberration, and higher-order aberrations. Further, the total aberration represents a composite value of all these aberrations. Astigmatism occupies the largest proportion of these generated aberrations, and is called off-axis astigmatism.
[0038] 図 3はラジアル方向 D1とそれに直交するタンジェンシャル方向 D2の光ビーム 2の 断面を模式的に示した図である。また、図 4はラジアル方向 Dl、タンジェンシャル方 向 D2等と光ディスク情報記録媒体 8との位置関係を示す斜視図である。なお、図 3で は説明の簡単のため、偏向プリズム 7での偏向を考慮せずに、半導体レーザ 1からの 光ビーム 2が対物レンズ 9に直接に入射する場合を想定している。また、各図におい て、ラジアル方向 D1と同方向 ¾y軸とし、タンジェンシャル方向 D2と同方向を X軸とし 、 x、 y両軸に直交する方向を z軸としている。  FIG. 3 is a diagram schematically showing a cross section of the light beam 2 in the radial direction D1 and the tangential direction D2 orthogonal thereto. FIG. 4 is a perspective view showing a positional relationship between the optical disc information recording medium 8 and the radial direction Dl, the tangential direction D2, and the like. In FIG. 3, for the sake of simplicity, it is assumed that the light beam 2 from the semiconductor laser 1 is directly incident on the objective lens 9 without considering the deflection by the deflection prism 7. In each of the drawings, the y axis is the same direction as the radial direction D1, the X axis is the same direction as the tangential direction D2, and the z axis is the direction orthogonal to both the x and y axes.
[0039] 上記の相対光軸ずれで発生する軸外非点収差につ!、て着目すると、光ビーム 2d のラジアル方向断面での集光位置 (焦線 F1)とタンジュンシャル方向断面での集光 位置 (焦線 F2)とは異なる。光ディスク情報記録媒体 8に近い前側焦線 F2はラジアル 方向に平行な向きとなり、対物レンズ 9に近 ヽ後側焦線 F1はタンジ ンシャル方向に 平行な向きとなる。  Focusing on off-axis astigmatism caused by the relative optical axis deviation described above, focusing on the light beam 2d in the radial cross section (focal line F1) and the convergence in the tangential cross section. Different from the light position (focal line F2). The front focal line F2 near the optical disc information recording medium 8 has a direction parallel to the radial direction, and the rear focal line F1 near the objective lens 9 has a direction parallel to the tangential direction.
[0040] 対物レンズ 9がラジアル方向に変位するよう制御されて、光源たる半導体レーザ 1と 対物レンズ 9との間に相対光軸ずれが発生すると、光ビーム 2dの集光位置は光ディ スク情報記録媒体 8から対物レンズ 9側に近 、方向に移動するため、光ディスク情報 記録媒体 8上の光ビーム 2dのスポット形状は、ラジアル方向に長 、楕円形へと変化 する。  When the objective lens 9 is controlled to be displaced in the radial direction and a relative optical axis shift occurs between the semiconductor laser 1 as the light source and the objective lens 9, the condensing position of the light beam 2 d is changed to the optical disk information. Since the light beam 2d moves from the recording medium 8 toward the objective lens 9 in the direction, the spot shape of the light beam 2d on the optical disk information recording medium 8 changes in the radial direction into an elongated and elliptical shape.
[0041] その結果、読み出しまたは書き込み中のトラックに隣接するトラックにまで光ビーム 2 dのスポットが広がり、隣接トラック力ものクロストークが増加する。また、ラジアル方向 の分解能が劣化して光ビーム 2dのトラック横断の検出能力も低下してしまう。  As a result, the spot of the light beam 2d spreads to the track adjacent to the track being read or written, and the crosstalk of the adjacent track force increases. In addition, the resolution in the radial direction is deteriorated, and the ability of the light beam 2d to detect the crossing of the track is also reduced.
[0042] また、仮に、前側焦線 F2の位置と後側焦線 F1の位置とのほぼ中間位置に光デイス ク情報記録媒体 8の記録面が位置するよう、対物レンズ 9の位置を z軸方向に制御す れば、光ディスク情報記録媒体 8の記録面上の光ビーム 2dのスポット形状をほぼ円 形にすることは可能となる。これによりラジアル方向の分解能の劣化が防止できるとも 考えられる。し力し、そのときの光ビーム 2dのスポットは、波面収差の存在のために、 相対光軸ずれのない場合に比べると大きくなつている。よって、タンジュンシャル方向 の分解能が低下して、記録'再生特性が劣化する。 [0042] Further, the position of the objective lens 9 is set so that the recording surface of the optical disc information recording medium 8 is located at a substantially intermediate position between the position of the front focal line F2 and the position of the rear focal line F1. Control in the direction Then, the spot shape of the light beam 2d on the recording surface of the optical disc information recording medium 8 can be made substantially circular. It is thought that this can prevent deterioration of the resolution in the radial direction. The spot of the light beam 2d at that time is larger than that in the case where there is no relative optical axis shift due to the existence of the wavefront aberration. Therefore, the resolution in the tangential direction decreases, and the recording / reproducing characteristics deteriorate.
[0043] そこで、本実施の形態においては、回折光学素子 6を図 5および図 6に示す形状、 または、図 7および図 8に示す形状とする。  Therefore, in the present embodiment, the diffractive optical element 6 has the shape shown in FIGS. 5 and 6, or the shape shown in FIGS. 7 and 8.
[0044] まず、図 5および図 6に示す回折光学素子 6aは、回折格子 DFが形成された回折 面 102aと、その裏面 101aとを有する。回折面 102aは平面である。一方、裏面 101a においては、回折光学素子 6aの短軸方向たる γ軸方向の曲率が であり、回折 光学素子 6aの長軸方向たる β軸方向の曲率が C βである。そして、裏面 101aは、 曲率 と曲率 C |8とが異なった凸型のトーリック面である。なお、回折面 102aに形 成された回折格子 DFの溝の方向は |8軸にほぼ平行である。また、光ビーム 2aの進 行方向を α軸とする。 α , , γの各軸は互いに直交する。  First, the diffractive optical element 6a shown in FIGS. 5 and 6 has a diffraction surface 102a on which a diffraction grating DF is formed, and a back surface 101a. The diffraction surface 102a is a plane. On the other hand, on the back surface 101a, the curvature in the γ-axis direction, which is the short axis direction of the diffractive optical element 6a, is, and the curvature in the β-axis direction, which is the long axis direction of the diffractive optical element 6a, is C β. The back surface 101a is a convex toric surface having a different curvature and a different curvature C | 8. The direction of the grooves of the diffraction grating DF formed on the diffraction surface 102a is substantially parallel to the | 8 axis. The traveling direction of the light beam 2a is defined as the α axis. The axes α, γ are orthogonal to each other.
[0045] 回折格子 DFの溝幅および溝間隔を適当な値に設計することにより、発光部品 5より 射出された光ビーム 2aは、回折光学素子 6aの裏面 101aより入射された後、回折面 102a上の回折格子 DFによって、少なくとも 2つ以上の光ビーム 2bl— 2b3に分光さ れる。分光する光ビームの数はその用途によって様々である力 ここでは一例として、 3つの光ビーム（0次回折光ビーム 2bl、 + 1次回折光ビーム 2b2、 一 1次回折光ビー ム 2b3)に分光される場合を示す。  By designing the groove width and the groove interval of the diffraction grating DF to appropriate values, the light beam 2a emitted from the light emitting component 5 is incident on the back surface 101a of the diffractive optical element 6a, and then the diffraction surface 102a The upper diffraction grating DF splits the light into at least two light beams 2bl-2b3. The number of light beams to be dispersed varies depending on the application.For example, here is the case where light beams are dispersed into three light beams (0th-order diffracted light beam 2bl, + 1st-order diffracted light beam 2b2, and 1st-order diffracted light beam 2b3). Is shown.
[0046] 0次回折光ビーム 2blは回折作用を受けない透過光であり、光ディスク情報記録媒 体 8への記録 '再生に用いられる。また、 + 1次回折光ビーム 2b2および 1次回折光 ビーム 2b3はともに回折作用を受けて光路が曲がった回折光である。 0次回折光ビ ーム 2bl、 + 1次回折光ビーム 2b2および 1次回折光ビーム 2b3のいずれも、対物 レンズ 9により光ディスク情報記録媒体 8上に集光された後に反射され、それぞれ光 検知器 10により受光される。  The 0th-order diffracted light beam 2bl is a transmitted light that is not subjected to a diffraction effect, and is used for recording and reproducing on the optical disc information recording medium 8. Further, the + 1st-order diffracted light beam 2b2 and the 1st-order diffracted light beam 2b3 are both diffracted lights that have undergone a diffractive action and have an optical path bent. Both the 0th-order diffracted light beam 2bl, + the 1st-order diffracted light beam 2b2 and the 1st-order diffracted light beam 2b3 are condensed on the optical disk information recording medium 8 by the objective lens 9 and then reflected, and are respectively received by the photodetector 10. Is done.
[0047] また、図 7および図 8に示す回折光学素子 6bは、回折格子 DFが形成された回折面 102bと、その裏面 101bとを有する。回折面 102bは平面である。一方、裏面 101bに おいては、回折光学素子 6bの短軸方向たる γ軸方向の曲率が であり、回折光 学素子 6bの長軸方向たる β軸方向の曲率が C βである。そして、裏面 101bは、曲 率 と曲率 C |8とが異なった凹型のトーリック面である。なお、回折面 102bに形成 された回折格子 DFの溝の方向は |8軸にほぼ平行である。また、光ビーム 2aの進行 方向を α軸とする。 α , , γの各軸は互いに直交する。 The diffractive optical element 6b shown in FIGS. 7 and 8 has a diffraction surface 102b on which a diffraction grating DF is formed, and a back surface 101b. The diffraction surface 102b is a plane. On the other hand, on the back 101b Here, the curvature of the diffractive optical element 6b in the γ-axis direction, which is the minor axis direction, is, and the curvature of the diffractive optical element 6b in the β-axis direction, which is the major axis direction, is C β. The back surface 101b is a concave toric surface having a different curvature and a different curvature C | 8. The direction of the grooves of the diffraction grating DF formed on the diffraction surface 102b is substantially parallel to the | 8 axis. Further, the traveling direction of the light beam 2a is defined as the α axis. The axes α, γ are orthogonal to each other.
[0048] 回折光学素子 6bにおいても回折光学素子 6aの場合と同様、発光部品 5より射出さ れた光ビーム 2aは、回折光学素子 6bの裏面 101bより入射された後、回折面 102b 上の回折格子 DFによって、少なくとも 2つ以上の光ビーム 2b 1一 2b3に分光される。  In the diffractive optical element 6b, as in the case of the diffractive optical element 6a, the light beam 2a emitted from the light emitting component 5 is incident on the back surface 101b of the diffractive optical element 6b and then diffracted on the diffractive surface 102b. The grating DF splits the beam into at least two or more light beams 2b1 and 2b3.
[0049] なお、回折光学素子 6a, 6bのいずれにおいても、回折面の裏面 101a, 101bに回 折格子 DFは設けられていないが、回折面 102a, 102bだけでなく裏面 101a, 101b にも回折格子 DFを設けてもよい。あるいは、裏面 101a, 101bにのみ回折格子 DF を設けて、こちらを回折面としてもよい。  [0049] In each of the diffractive optical elements 6a and 6b, the diffraction gratings DF are not provided on the back surfaces 101a and 101b of the diffraction surfaces, but the diffraction gratings DF are formed not only on the diffraction surfaces 102a and 102b but also on the back surfaces 101a and 101b. A grid DF may be provided. Alternatively, a diffraction grating DF may be provided only on the back surfaces 101a and 101b, and this may be used as a diffraction surface.
[0050] + 1次回折光ビーム 2b2、— 1次回折光ビーム 2b3は、記録'再生に用いる 0次回折 光ビーム 2b 1が光ディスク情報記録媒体 8上のトラック中心からどれだけずれている かを検出するために利用される。このような検出法の代表例として「3ビーム法」と称さ れる方式や「差動プッシュプル法」と称される方式が、広く知られている。以下にそれ らの検出方法について述べる。なお、 3つ以上の数の回折光ビームを生成して検出 に用いてもよい。  [0050] + 1st-order diffracted light beam 2b2,-1st-order diffracted light beam 2b3 detects how much the 0th-order diffracted light beam 2b1 used for recording and reproduction deviates from the track center on optical disc information recording medium 8. Used for As a typical example of such a detection method, a method called “three-beam method” and a method called “differential push-pull method” are widely known. The detection methods are described below. Note that three or more diffracted light beams may be generated and used for detection.
[0051] 回折面 102aまたは 102bの回折格子 DFによって分光された 0次回折光ビーム 2bl 、 + 1次回折光ビーム 2b2および- 1次回折光ビーム 2b3はそれぞれ、対物レンズ 9 により光ディスク情報記録媒体 8上に 0次回折光ビーム 2dl、 + 1次回折光ビーム 2d 2および 1次回折光ビーム 2d3として集光される。  The 0th-order diffracted light beam 2bl, the + 1st-order diffracted light beam 2b2, and the −1st-order diffracted light beam 2b3 separated by the diffraction grating DF of the diffractive surface 102a or 102b are placed on the optical disc information recording medium 8 by the objective lens 9 respectively. The light is converged as a second-order diffracted light beam 2dl, a + first-order diffracted light beam 2d2, and a first-order diffracted light beam 2d3.
[0052] そして、図 9または図 10に示すように、光ディスク情報記録媒体 8上のトラック TR上 に 0次回折光ビーム 2dlが配置されるように調整される。なお、図 9は、タンジェンシャ ル方向 D2に情報マークが並んで記録されている読み出し専用光ディスク情報記録 媒体 8の記録面を示した図である。また、図 10は、案内溝 GRを有し、それに沿って 記録マークが記録される書き込み可能光ディスク情報記録媒体 8の記録面を示した 図である。 [0053] 3つの回折光ビーム 2dl— 2d3の配列の方向は、設計光軸を中心軸として回折光 学素子 6aまたは 6bを回転させることによって調整が可能である。この調整に当たって は、図 9および図 10に示すような各種の光ディスク情報記録媒体の構造の違い、並 びに、トラック TRをずれ検出に用いるのか案内溝 GRをずれ検出に用いるのかのず れ検出方式の違!、を考慮する必要がある。 Then, as shown in FIG. 9 or FIG. 10, the adjustment is performed so that the zero-order diffracted light beam 2dl is arranged on the track TR on the optical disc information recording medium 8. FIG. 9 is a diagram showing a recording surface of a read-only optical disc information recording medium 8 on which information marks are recorded side by side in the tangential direction D2. FIG. 10 is a diagram showing a recording surface of a writable optical disk information recording medium 8 having a guide groove GR along which a recording mark is recorded. [0053] The direction of the arrangement of the three diffracted light beams 2dl-2d3 can be adjusted by rotating the diffracted optical element 6a or 6b around the designed optical axis. In this adjustment, the difference in the structure of the various types of optical disc information recording media as shown in Figs. 9 and 10, and the method of detecting whether the track TR is used for displacement detection or the guide groove GR is used for displacement detection. Difference !, you need to consider.
[0054] 図 9のように案内溝 GRを有しな 、構造の光ディスク情報記録媒体に対しては 3ビー ム法がよく用いられる。そして、ずれを検出するために、タンジュンシャル方向 D2から の 3つの回折光ビーム 2dl— 2d3の配列方向のずれの角度 φ aは、回折光ビーム 2d 2および 2d3のラジアル方向の配置距離がおよそトラック周期の（N+ 1Z2)倍となる 角度に調整される (Nは任意の整数)。  As shown in FIG. 9, a three-beam method is often used for an optical disc information recording medium having a structure without a guide groove GR. In order to detect the displacement, the angle φa of the displacement in the arrangement direction of the three diffracted light beams 2dl—2d3 from the tangential direction D2 is determined by the fact that the radial arrangement distance of the diffracted light beams 2d2 and 2d3 is approximately It is adjusted to an angle that is (N + 1Z2) times the period (N is any integer).
[0055] 一方、図 10のように案内溝 GRを有する構造であって、案内溝 GRをずれ検出に用 いる差動プッシュプル法を採用する場合は、タンジェンシャル方向 D2からの 3つの回 折光ビーム 2dl— 2d3の配列方向のずれの角度 φ bは、回折光ビーム 2d2および 2d 3のラジアル方向の配置距離がおよそトラック周期の（2M+ 1)倍となる角度に調整さ れる（Mは任意の整数)。  [0055] On the other hand, when the differential push-pull method is used to detect the deviation of the guide groove GR in a structure having the guide groove GR as shown in Fig. 10, three diffraction lights from the tangential direction D2 are used. The deviation angle φ b of the beam 2dl—2d3 in the arrangement direction is adjusted to an angle at which the radial arrangement distance of the diffracted light beams 2d2 and 2d3 is approximately (2M + 1) times the track period (M is an arbitrary value. integer).
[0056] 以上のように、 3つの回折光ビーム 2dl— 2d3の配列方向のずれの角度は、光ディ スク情報記録媒体の構造の違いとずれ検出方式の違いとによって様々であり、比較 的大きく設定される場合もあれば、比較的小さく設定されることもある。  As described above, the angle of deviation in the arrangement direction of the three diffracted light beams 2dl-2d3 varies depending on the difference in the structure of the optical disc information recording medium and the difference in the deviation detection method, and is relatively large. In some cases, it may be set, while in others it may be set relatively small.
[0057] 図 5—図 8に示すように、 γ軸をタンジェンシャル方向力 例えば上記の φ a (図 9の 場合。なお図 10の場合ならば <i) b)だけ回転した方向に合わせておき、 j8軸をラジア ル方向力も例えば上記の φ a (図 9の場合。なお図 10の場合ならば φ b)だけ回転し た方向に合わせておけば、上記の 3つの回折光ビーム 2dl— 2d3の配列方向の調 整が可能である。  [0057] As shown in Fig. 5 to Fig. 8, the γ-axis is rotated in the tangential direction force, for example, the above-mentioned φa (in the case of Fig. 9; If the j8 axis is adjusted to the direction in which the radial force is also rotated by, for example, the above φa (in the case of FIG. 9; φb in the case of FIG. 10), the three diffracted light beams 2dl— Adjustment in the 2d3 array direction is possible.
[0058] 0次回折光ビーム 2dl、 + 1次回折光ビーム 2d2および 1次回折光ビーム 2d3は、 光ディスク情報記録媒体 8でそれぞれ反射される。そして、反射した各回折光ビーム は光検知器 10で受光され、各光量がそれぞれ電気信号として出力される。このうち + 1次回折光ビーム 2d2および- 1次回折光ビーム 2d3に対応する電気信号に対し てずれ検出方式に応じた演算が行なわれ、 0次回折光ビーム 2dlと情報マーク列と のラジアル方向の相対位置ずれを表すトラッキング誤差信号が生成される。例えば[0058] The 0th-order diffracted light beam 2dl, the + 1st-order diffracted light beam 2d2, and the 1st-order diffracted light beam 2d3 are reflected by the optical disc information recording medium 8, respectively. Then, each reflected diffracted light beam is received by the photodetector 10, and each light amount is output as an electric signal. Of these, the electric signals corresponding to the + 1st-order diffracted light beam 2d2 and the −1st-order diffracted light beam 2d3 are subjected to calculations according to the deviation detection method, and the 0th-order diffracted light beam 2dl and the information mark sequence are , A tracking error signal representing the relative positional deviation in the radial direction is generated. For example
+ 1次回折光ビーム 2d2および- 1次回折光ビーム 2d3の各反射光の光量が等しけ れば誤差 0とされ、光量に差があればその差に応じたトラッキング誤差信号が生成さ れる。このトラッキング誤差信号に基づいて、対物レンズ 9の位置がラジアル方向に制 御される。以上が 3ビーム法や差動プッシュプル法によるずれ検出方法の説明である If the reflected light amounts of the + 1st-order diffracted light beam 2d2 and the −1st-order diffracted light beam 2d3 are equal, an error is set to 0, and if there is a difference in the light amounts, a tracking error signal corresponding to the difference is generated. Based on this tracking error signal, the position of the objective lens 9 is controlled in the radial direction. The above is the description of the displacement detection method using the three-beam method or the differential push-pull method.
[0059] さて、回折光学素子 6aまたは 6bにおいて、回折面の裏面 101aまたは 101bのトー リック面を光ビーム 2aが通過すると、 γ軸方向と j8軸方向の曲率 C y , C j8の違いに より非点収差が発生する。よって、回折光学素子 6aまたは 6bに、回折機能だけでは なぐ非点収差を発生させる機能をも持たせて、光源たる半導体レーザ 1が対物レン ズ 9のレンズ光軸力 光ディスク情報記録媒体 8のラジアル方向に遠ざ力ることにより 発生する非点収差を打ち消すようにすればよい。すなわち、対物レンズ 9がラジアル 方向に移動することで発生する軸外非点収差を打ち消す方向の非点収差を回折光 学素子 6aまたは 6bが有するように、それぞれの曲率 C γと C |8を決定する。 Now, in the diffractive optical element 6a or 6b, when the light beam 2a passes through the toric surface of the back surface 101a or 101b of the diffractive surface, due to the difference between the curvatures C y and C j8 in the γ-axis direction and the j8-axis direction, Astigmatism occurs. Therefore, by providing the diffractive optical element 6a or 6b with a function of generating astigmatism that is not limited to the diffraction function, the semiconductor laser 1 as a light source is used as a light source for the lens 9 of the objective lens 9. What is necessary is just to cancel the astigmatism generated by moving away in the direction. That is, the respective curvatures C γ and C | 8 are set so that the diffractive optical element 6a or 6b has astigmatism in a direction to cancel off-axis astigmatism generated by moving the objective lens 9 in the radial direction. decide.
[0060] 図 11は、回折光学素子 6aまたは 6bで発生させる非点収差に応じた、対物レンズ 9 のラジアル方向移動により発生する軸外非点収差の合成値 Wasの変化を示す図で ある。図 11では、曲線 (a)が図 2中の非点収差のグラフに相当する。そして、回折光学 素子 6aまたは 6bで発生させる非点収差量の違いに応じて、曲線 (b), (c) ,(d)と 3つの 状態を例示している。なお、回折光学素子 6aまたは 6bで発生する非点収差量を AS g (図 11の各曲線上の切片の値に相当）とする。  FIG. 11 is a diagram showing a change in a combined value Was of off-axis astigmatism generated by radial movement of the objective lens 9 according to astigmatism generated by the diffractive optical element 6a or 6b. In FIG. 11, the curve (a) corresponds to the graph of astigmatism in FIG. Then, three states are shown as curves (b), (c), and (d) according to the difference in the amount of astigmatism generated in the diffractive optical element 6a or 6b. The amount of astigmatism generated in the diffractive optical element 6a or 6b is defined as AS g (corresponding to the value of the intercept on each curve in FIG. 11).
[0061] 軸外非点収差の合成値 Wasの値がプラスである場合は、前側焦線 F2と後側焦線 F 1との関係が図 3で示した関係にあるのに対し、マイナスの場合には、図 12に示すよ うに光ビームの前側焦線 F2の位置と後側焦線 F1の位置とが図 3の場合力 入れ替 わった関係となる。  When the value of the combined value Was of the off-axis astigmatism is positive, the relationship between the front focal line F2 and the rear focal line F1 is the relationship shown in FIG. In this case, as shown in FIG. 12, the position of the front focal line F2 and the position of the rear focal line F1 of the light beam are in the relationship of being switched in the case of FIG.
[0062] 前に述べた、記録'再生特性、光ビームのトラック横断検出の能力、および、低クロ ストークの 、ずれをも維持できる非点収差の許容範囲と、対物レンズ 9の設計光軸か らラジアル方向への必要最大移動量が図 11に示す関係にあるとき、必要最大移動 量と非点収差の許容範囲とで決まる点 P4および点 P5で規定される長方形の領域内 に軸外非点収差の合成値 Wasが収まればよい。すなわち、軸外非点収差の合成値 Wasの特性力 曲線 (b)と曲線 (d)の間に収まればよぐそうなるように回折光学素子 6aまたは 6bで発生する非点収差量 ASgを設定すればょ 、。非点収差量 ASgの値 は、回折光学素子 6a, 6bの曲率 C y , C の値により設定される。 [0062] The recording / reproducing characteristics, the capability of detecting the cross-track of the light beam, the allowable range of astigmatism capable of maintaining low crosstalk and the deviation, and the design optical axis of the objective lens 9 described above. When the required maximum amount of movement in the radial direction is in the relationship shown in Fig. 11, the rectangular area defined by points P4 and P5 determined by the required maximum amount of movement and the allowable range of astigmatism It is sufficient that the combined value Was of the off-axis astigmatism falls within the range. That is, the astigmatism amount ASg generated by the diffractive optical element 6a or 6b is set so that the characteristic value of the combined value of the off-axis astigmatism, the characteristic force Was, falls between the curve (b) and the curve (d). Do it. The value of the astigmatism amount ASg is set by the values of the curvatures C y and C of the diffractive optical elements 6a and 6b.
[0063] なお、曲線 (c)の場合のように、非点収差の許容範囲の最大非点収差 Was(max)と 最小非点収差 Was(min)の平均値 0. 5 X {Was(max)+ Was(min)}を基準としたときに、 対物レンズ移動量ゼロまでの非点収差変化量 Δ AS2と必要最大移動量までの非点 収差変化量 A AS1が同程度になるのが最も望ましい。軸外非点収差の合成値 Was の許容範囲内での上限および下限までの各マージンが最大となる力もである。  As in the case of the curve (c), the average value of the maximum astigmatism Was (max) and the minimum astigmatism Was (min) in the allowable range of astigmatism 0.5 X (Was (max ) + Was (min)}, the astigmatism change ΔAS2 up to the objective lens movement amount of zero and the astigmatism change amount A AS1 up to the required maximum movement amount are almost the same. desirable. It is also the force that maximizes each margin to the upper and lower limits within the allowable range of the combined value of off-axis astigmatism Was.
[0064] なお、図 5—図 8に示したトーリック面形状以外にも、回折光学素子 6を図 13—図 1 6に示すようなシリンドリカル面形状としても、図 5—図 8の場合と同様な非点収差を発 生する効果が得られる。  Note that, in addition to the toric surface shape shown in FIGS. 5 to 8, the diffractive optical element 6 may have a cylindrical surface shape as shown in FIGS. 13 to 16 as in FIGS. 5 to 8. The effect of generating a large astigmatism is obtained.
[0065] 図 13に示す回折光学素子 6cは、回折面 102cの裏面 101cに γ軸方向にのみ曲 率を有する凸型のシリンドリカル面を持ち、回折面 102cにほぼ |8軸方向に平行な溝 を有する回折格子 DFが形成されて 、る。  The diffractive optical element 6c shown in FIG. 13 has a convex cylindrical surface having a curvature only in the γ-axis direction on the back surface 101c of the diffraction surface 102c, and a groove substantially parallel to the | 8-axis direction with respect to the diffraction surface 102c. A diffraction grating DF having the following formula is formed.
[0066] 図 14に示す回折光学素子 6dは、回折面 102dに γ軸方向にのみ曲率を有する凸 型のシリンドリカル面を持ち、回折面 102dにほぼ |8軸方向に平行な溝を有する回折 格子 DFが形成されている。回折面 102dの裏面 lOldは平坦面である。  The diffractive optical element 6d shown in FIG. 14 has a diffractive grating having a convex cylindrical surface having a curvature only in the γ-axis direction on the diffraction surface 102d and a groove substantially parallel to the | 8-axis direction on the diffraction surface 102d. DF is formed. The back surface lOld of the diffraction surface 102d is a flat surface.
[0067] 図 15に示す回折光学素子 6eは、回折面 102eの裏面 101eに β軸方向にのみ曲 率を有する凹型のシリンドリカル面を持ち、回折面 102eにほぼ |8軸方向に平行な溝 を有する回折格子 DFが形成されて 、る。  The diffractive optical element 6e shown in FIG. 15 has a concave cylindrical surface having a curvature only in the β-axis direction on the back surface 101e of the diffraction surface 102e, and has a substantially parallel groove in the | 8-axis direction on the diffraction surface 102e. The diffraction grating DF is formed.
[0068] 図 16に示す回折光学素子 6fは、回折面 102fに |8軸方向にのみ曲率を有する凹 型のシリンドリカル面を持ち、回折面 102fにほぼ |8軸方向に平行な溝を有する回折 格子 DFが形成されている。回折面 102fの裏面 101fは平坦面である。  The diffractive optical element 6f shown in FIG. 16 has a concave cylindrical surface having a curvature only in the 8-axis direction on the diffraction surface 102f, and a diffractive surface having grooves substantially parallel to the | 8-axis direction in the diffraction surface 102f. A grid DF is formed. The back surface 101f of the diffraction surface 102f is a flat surface.
[0069] なお、図 13—図 16に示した回折光学素子 6c— 6fのいずれにおいても、回折面の 裏面 101c— 101fに回折格子 DFは設けられていないが、回折面 102c— 102fだけ でなく裏面 101c— 101fにも回折格子 DFを設けてもよい。あるいは、裏面 101c— 1 Olfにのみ回折格子 DFを設けて、こちらを回折面としてもよい。 [0070] 図 5—図 8に示したトーリック面形状を採用する場合と、図 13—図 16に示したシリン ドリカル面形状を採用する場合とでは、以下の相違がある。 In each of the diffractive optical elements 6c to 6f shown in FIGS. 13 to 16, the diffraction grating DF is not provided on the back surface 101c to 101f of the diffraction surface, but not only the diffraction surfaces 102c to 102f. A diffraction grating DF may be provided on the back surface 101c-101f. Alternatively, a diffraction grating DF may be provided only on the back surface 101c-1 Olf, and this may be used as a diffraction surface. The following differences exist between the case where the toric surface shape shown in FIGS. 5 to 8 is adopted and the case where the cylindrical surface shape shown in FIGS. 13 to 16 are adopted.
[0071] 発散する光ビームが厚みをもつ光学素子を通過すると、非点収差以外にも球面収 差、および、光ディスク情報記録媒体 8上に集光された光ビームの最良像面力 の対 物レンズ 9のレンズ光軸方向へのずれにより生じるデフォーカスカもたらす収差 (デフ オーカス収差と称する）が発生する。  When the diverging light beam passes through an optical element having a thickness, in addition to astigmatism, the spherical aberration and the best image surface force of the light beam focused on the optical disk information recording medium 8 are measured. An aberration (referred to as defocus aberration) caused by defocusing caused by the displacement of the lens 9 in the lens optical axis direction occurs.
[0072] 図 5—図 8に示したトーリック面形状を採用する場合には、トーリック面の γ方向およ び j8方向の曲面を非球面として最適化することにより、非点収差以外にも球面収差 およびデフォーカス収差を低減させることができる。この他にもさらに、対物レンズ 9と 光源との距離が対物レンズ 9の設計値からずれることによって発生する球面収差、お よび、光ディスク情報記録媒体 8上に形成されて ヽる保護透明基板の厚み誤差など 力 発生する球面収差も同時に考慮して上記非球面形状を最適化すれば、さらに光 ビームの品質が向上し、記録 ·再生特性を向上させることができる。一方、図 13—図 16に示したシリンドリカル面形状を採用する場合は、あくまで非点収差量を調節でき るに過ぎない。  When the toric surface shape shown in FIG. 5 to FIG. 8 is adopted, by optimizing the curved surfaces in the γ direction and the j8 direction of the toric surface as aspheric surfaces, a spherical surface besides astigmatism can be obtained. Aberration and defocus aberration can be reduced. In addition, the spherical aberration caused by the distance between the objective lens 9 and the light source deviating from the design value of the objective lens 9 and the thickness of the protective transparent substrate formed on the optical disk information recording medium 8 By optimizing the above-mentioned aspherical shape in consideration of the spherical aberration generated by force such as an error, the quality of the light beam can be further improved, and the recording / reproducing characteristics can be improved. On the other hand, when the cylindrical surface shape shown in FIGS. 13 to 16 is adopted, the amount of astigmatism can only be adjusted.
[0073] すなわち、回折光学素子 6の回折面または回折面の裏面を、トーリック面またはシリ ンドリカル面とすれば、トーリック面内のある子午面の曲率 (例えば )およびそれに 直角な他の子午面の曲率 (例えば C |8 )を、または、シリンドリカル面の曲率を調節す ることにより、回折光学素子 6の有する非点収差の量を調節することが可能である。ま た、トーリック面の場合は、トーリック面内のある子午面およびそれに直角な他の子午 面を非球面形状とすることにより、非点収差の量だけでなぐ光源から放射された光 ビームが光ディスク情報記録媒体 8上に集光されるまでの光学系で発生する球面収 差、および、デフォーカス収差の量も調節することが可能である。よって、記録'再生 に用いられる光ビームの品質をさらに良くすることができる。  That is, if the diffractive surface of the diffractive optical element 6 or the back surface of the diffractive surface is a toric surface or a cylindrical surface, the curvature (for example) of a certain meridional surface in the toric surface and the other meridian surface perpendicular to it are obtained. The amount of astigmatism of the diffractive optical element 6 can be adjusted by adjusting the curvature (for example, C | 8) or the curvature of the cylindrical surface. In the case of a toric surface, a certain meridional surface in the toric surface and another meridional surface perpendicular to the toric surface are formed into an aspherical shape, so that a light beam emitted from a light source that is only affected by astigmatism is reduced to an optical disk. It is also possible to adjust the spherical aberration and the amount of defocus aberration generated in the optical system until the light is focused on the information recording medium 8. Therefore, the quality of the light beam used for recording and reproduction can be further improved.
[0074] なお、図 9および図 10に示したように、トラックの方向、つまりタンジェンシャル方向 D2と、 0次回折光ビーム 2dl、 + 1次回折光ビーム 2d2および 1次回折光ビーム 2d 3の配列方向との間に角度 φ aまたは φ bを設ける場合、上記においては回折光学 素子 6を回転させていた。 [0075] しかし、回折光学素子 6を回転させると、回折光学素子 6の有する非点収差も回転 することとなり、対物レンズ 9で発生する軸外非点収差を効率よく打ち消せないことも ある。 As shown in FIGS. 9 and 10, the track direction, that is, the tangential direction D2, and the arrangement direction of the 0th-order diffracted light beam 2dl, + 1st-order diffracted light beam 2d2, and 1st-order diffracted light beam 2d3 When the angle φ a or φ b is provided between the above, the diffractive optical element 6 is rotated in the above. However, when the diffractive optical element 6 is rotated, the astigmatism of the diffractive optical element 6 also rotates, and the off-axis astigmatism generated in the objective lens 9 may not be able to be canceled efficiently.
[0076] よって、回折光学素子 6で発生する非点収差の量が対物レンズ 9で発生する軸外 非点収差を最も効率よく打ち消すことができるように、回折光学素子 6のトーリック面ま たはシリンドリカル面の曲率を持つ方向はタンジェンシャル方向 D2およびラジアル方 向 D1の少なくとも一方に平行としつつ、回折格子 DFの溝の延びる方向については 図 17に示すように 13軸から φ aまたは φ bだけずらしておくのが望ましい。  Therefore, the toric surface or the toric surface of the diffractive optical element 6 is set so that the amount of astigmatism generated in the diffractive optical element 6 can cancel out the off-axis astigmatism generated in the objective lens 9 most efficiently. While the direction of curvature of the cylindrical surface is parallel to at least one of the tangential direction D2 and the radial direction D1, the direction in which the groove of the diffraction grating DF extends is only φa or φb from the 13th axis as shown in Fig. 17. It is desirable to shift.
[0077] つまり、回折格子 DFの溝の方向を、ラジアル方向（ β軸の方向に相当）から光ディ スク情報記録媒体 8のタンジェンシャル方向の向きに角度 φ aまたは φ bだけ傾けて 配置させておけば、光ディスク情報記録媒体 8のトラックの方向に対して角度 φ aまた は φ bだけ傾けて複数の回折光を光ディスク情報記録媒体 8上に配列可能であるとと もに、回折光学素子 6の有する非点収差が対物レンズ 9のラジアル方向移動で発生 する非点収差を最も効率よく打ち消すように回折光学素子 6を配置することができる。  That is, the direction of the groove of the diffraction grating DF is inclined at an angle φ a or φ b from the radial direction (corresponding to the direction of the β axis) to the direction of the tangential direction of the optical disc information recording medium 8. If so, a plurality of diffracted lights can be arranged on the optical disc information recording medium 8 at an angle of φa or φb with respect to the track direction of the optical disc information recording medium 8, and the diffractive optical element can be arranged. The diffractive optical element 6 can be arranged so that the astigmatism of the objective lens 9 can be canceled most efficiently by the radial movement of the objective lens 9.
[0078] 本実施の形態に係る光ヘッド装置によれば、回折光学素子 6は、複数の回折光を 生成するだけでなぐ光源たる半導体レーザ 1が対物レンズ 9のレンズ光軸力 光デ イスク情報記録媒体 8のラジアル方向に遠ざ力ることにより発生する非点収差を打ち 消す方向の非点収差をも有する。よって、光ビームを平行光束ではない拡散光として 対物レンズ 9に入射させる場合であっても、コリメータレンズを用いることなく回折光学 素子 6によって、波面収差による記録 ·再生特性への影響を抑制することが可能であ る。これにより、光ヘッド装置の小型化、薄型化および低コストィ匕が図れる。  According to the optical head device according to the present embodiment, the diffractive optical element 6 uses the semiconductor laser 1 as a light source that merely generates a plurality of diffracted light beams as a light source. The recording medium 8 also has astigmatism in a direction to cancel astigmatism generated by moving away from the recording medium 8 in the radial direction. Therefore, even when the light beam is incident on the objective lens 9 as a diffused light that is not a parallel light beam, the influence of the wavefront aberration on the recording / reproduction characteristics can be suppressed by the diffractive optical element 6 without using a collimator lens. Is possible. As a result, the size and thickness of the optical head device can be reduced and the cost can be reduced.
[0079] すなわち、対物レンズ 9のレンズシフト時に生じる軸外非点収差を打ち消すことので きる非点収差の発生機能と回折格子 DFによる分光機能とを回折光学素子 6に持た せることで、望ま 、方向に非点収差 ASgを与えることが可能となる。  That is, by providing the diffractive optical element 6 with a function of generating astigmatism capable of canceling off-axis astigmatism generated when the objective lens 9 shifts the lens and a spectral function of the diffraction grating DF, it is desirable that It becomes possible to give astigmatism ASg in the direction.
[0080] 現在実用化されている DVDや CDなどの光ディスク装置では、レンズシフトの必要 最大量は 600 m程度であり、そのときに対物レンズ 9で生じる軸外非点収差が単体 で 300m λ ρν程度である。よって、回折光学素子 6の有する非点収差 ASgは、軸外 非点収差を打ち消す方向に 300m λ ρν程度、またはそれ以下であることが望ましい [0081] ただし、上記非点収差量は、対物レンズの軸外非点収差について考慮したもので あり、光源やその他の光学部品などによってさらに非点収差が付加される光学構成 の場合は、上記非点収差量よりもさらに大きく設定すべき場合もある。 [0080] In optical disk devices such as DVDs and CDs that are currently in practical use, the required maximum amount of lens shift is about 600 m, and the off-axis astigmatism generated by the objective lens 9 at that time is 300 m λ ρν It is about. Therefore, the astigmatism ASg of the diffractive optical element 6 is desirably about 300 mλρν or less in the direction of canceling off-axis astigmatism. However, the amount of astigmatism takes into account off-axis astigmatism of the objective lens. In the case of an optical configuration in which astigmatism is further added by a light source or other optical components, the above-described astigmatism is used. In some cases, it should be set larger than the astigmatism amount.
[0082] なお、上記で説明した光学構成は代表的な有限光学系の例であるが、本実施の形 態は疑似有限光学系にも適用可能である。ここで、疑似有限光学系とは、光源から 放射された光ビームが光路中でたとえ平行光束となる場合であっても、光源と対物レ ンズ間の光路中に別途レンズなどを設けることによって、対物レンズへ入射する前に 光ビームを拡散するように変換する構成を指す。例えば、上記光路中のレンズを光 軸方向へ移動させるなどして、対物レンズへの光ビームの入射条件、または光ビーム の拡散度を変える機能を有する光学構成がこれに当てはまる。  Note that the optical configuration described above is an example of a typical finite optical system, but the present embodiment is also applicable to a pseudo finite optical system. Here, the quasi-finite optical system means that even if the light beam emitted from the light source becomes a parallel light beam in the optical path, a separate lens or the like is provided in the optical path between the light source and the objective lens. Refers to a configuration that converts a light beam so that it is diffused before entering the objective lens. For example, an optical configuration having a function of changing a condition of incidence of a light beam on an objective lens or a degree of diffusion of a light beam by moving a lens in the optical path in an optical axis direction is applicable to this.
[0083] 疑似有限光学系の場合も、対物レンズへ入射する光ビームについては有限光学系 の場合と同様であるので、本実施の形態が適用可能となる。  [0083] Also in the case of the pseudo finite optical system, the light beam incident on the objective lens is the same as in the case of the finite optical system, so that the present embodiment can be applied.
[0084] 実施の形態 2.  Embodiment 2.
本実施の形態は、実施の形態 1に係る光ヘッド装置の変形例であって、トーリック面 またはシリンドリカル面を有する回折光学素子 6に代わって、平行平板型回折光学素 子を採用し、その回折面を、ラジアル方向力も対物レンズ 9のレンズ光軸の向きに傾 けて非点収差を発生させるようにしたものである。  This embodiment is a modification of the optical head device according to Embodiment 1, and employs a parallel plate type diffractive optical element instead of the diffractive optical element 6 having a toric surface or a cylindrical surface, The surface is also tilted in the direction of the lens optical axis of the objective lens 9 with respect to the radial force so as to generate astigmatism.
[0085] 図 18は、本実施の形態に係る光ヘッド装置を示す図である。なお、図 18において は、回折光学素子 6が平行平板型回折光学素子 61に変更されている点以外、装置 構成は図 1と同じである。よって、平行平板型回折光学素子 61以外の点については 、実施の形態 1に係る光ヘッド装置と同様のため、説明を省略する。  FIG. 18 is a diagram showing an optical head device according to the present embodiment. In FIG. 18, the device configuration is the same as that of FIG. 1 except that the diffractive optical element 6 is changed to a parallel plate type diffractive optical element 61. Therefore, the points other than the parallel plate type diffractive optical element 61 are the same as those of the optical head device according to the first embodiment, and the description is omitted.
[0086] 図 18中の平行平板型回折光学素子 61の形状と配置について、図 19および図 20 に示す。なお、図 19はタンジェンシャル方向から平行平板型回折光学素子 61を眺 めた図であり、図 20はラジアル方向から平行平板型回折光学素子 61を眺めた図で ある。  FIG. 19 and FIG. 20 show the shape and arrangement of the parallel-plate diffractive optical element 61 in FIG. FIG. 19 is a view of the parallel-plate diffractive optical element 61 viewed from the tangential direction, and FIG. 20 is a view of the parallel-plate diffractive optical element 61 viewed from the radial direction.
[0087] 平行平板型回折光学素子 61は平行平板型の榭脂またはガラス晶材で構成され、 光ビーム 2aが入射する面および出射する面の少なくとも一方に回折格子 DFが形成 されている（図 19および図 20では出射する面にのみ回折格子 DFを持つ場合を示し ている）。平行平板型回折光学素子 61の回折格子 DFにより、光ビーム 2aは少なくと も 2つの光ビーム 2bl— 2b3に分光される。 The parallel plate type diffractive optical element 61 is made of a parallel plate type resin or glass crystal material, and has a diffraction grating DF formed on at least one of a surface on which the light beam 2a enters and a surface on which the light beam 2a exits. (Figures 19 and 20 show the case where the diffraction grating DF is provided only on the exit surface.) The light beam 2a is split into at least two light beams 2bl-2b3 by the diffraction grating DF of the parallel plate type diffractive optical element 61.
[0088] 平行平板型回折光学素子 61に、設計光軸に対してラジアル方向 D1に対応する方 向にある角度 Θの傾きを与えると、放射する光ビーム 2aが平行平板型回折光学素子 61を通過することで非点収差が発生する。よって、実施の形態 1の場合と同様に、平 行平板型回折光学素子 61で発生する非点収差により、対物レンズ 9がラジアル方向 D1に移動する際に発生する実施の形態 1で述べた軸外非点収差を打ち消すことが できる。  When the parallel-plate diffractive optical element 61 is given an inclination あ る with respect to the design optical axis in a direction corresponding to the radial direction D1, the radiated light beam 2a causes the parallel-plate diffractive optical element 61 to Passing it causes astigmatism. Therefore, as in the case of the first embodiment, the axis described in the first embodiment that occurs when the objective lens 9 moves in the radial direction D1 due to astigmatism generated in the parallel-plate diffractive optical element 61. Outer astigmatism can be canceled.
[0089] つまり、平行平板型回折光学素子 61における回折格子 DFの溝の延びる方向たる j8軸を z軸に合わせ、回折格子 DFの溝の並ぶ方向たる γ軸を X軸に合わせて、平行 平板型回折光学素子 61の回折面を、ラジアル方向 D1から対物レンズ 9のレンズ光 軸 Alaの向きに所定の角度 Θだけ傾けて配置している。  [0089] In other words, the parallel plate diffractive optical element 61 has a parallel plate, in which the j8 axis, which is the direction in which the groove of the diffraction grating DF extends, is aligned with the z-axis, and the γ axis, which is the direction in which the groove of the diffraction grating DF is aligned, is aligned with the X axis. The diffractive surface of the diffractive optical element 61 is arranged at a predetermined angle に from the radial direction D1 to the direction of the lens optical axis Ala of the objective lens 9.
[0090] ここで、平行平板型回折光学素子 61により発生する非点収差量 W22pvは、平行 平板型回折光学素子 61を透過する光ビーム 2aの開口数を NA、光ビーム 2aの波長 をえ、非点収差の前側焦線 F2と後側焦線 F1との距離 (非点隔差)を Δ ζとして  Here, the astigmatism amount W22pv generated by the parallel-plate diffractive optical element 61 is obtained by calculating the numerical aperture of the light beam 2a passing through the parallel-plate diffractive optical element 61 by NA and the wavelength of the light beam 2a by: Let Δ を be the distance (astigmatic difference) between the front focal line F2 and the rear focal line F1 of astigmatism
[0091] [数 1] / _ N A Λ 1 [0091] [number 1] / _ NA Λ 1
VV 2 2 p v— * Δ Z '—  VV 2 2 p v— * Δ Z '—
2 1 2 1
[0092] のように表せる。なお、数 1は上記非特許文献 2に基づく。 [0092] can be expressed as follows. Equation 1 is based on Non-Patent Document 2 described above.
[0093] ここで、非点隔差 Δ ζについては、上記非特許文献 3より平行平板型回折光学素子 61の厚み dと屈折率 η、およびラジアル方向 D1からの角度 Θを用いて [0093] Here, the astigmatic difference Δζ is calculated using the thickness d and the refractive index η of the parallel-plate diffractive optical element 61 and the angle の from the radial direction D1 according to Non-Patent Document 3.
[0094] [数 2] d η · c ο s θ  [0094] [Equation 2] d η · c ο s θ
n 2- s i η ι θ ( π — s i θ ) n 2 -si η ι θ (π — si θ)
[0095] のように表せる。 [0095] can be expressed as follows.
[0096] よって、平行平板型回折光学素子 61で発生させる非点収差の量 ASgは、次式 より決定できる。 [0096] Therefore, the amount of astigmatism ASg generated by the parallel-plate diffractive optical element 61 is expressed by the following equation. Can be determined more.
[0097] [数 3]
Figure imgf000022_0001
[0097] [Number 3]
Figure imgf000022_0001
[0098] なお、分光後の各光ビーム 2bl— 2b3の配列方向が実施の形態 1の場合と同様に 、図 9および図 10に示す光ディスク情報記録媒体 8のトラックの方向力も角度 φ aまた は φ bをなすように、設計光軸を回転軸として平行平板型回折光学素子 61の配置が 調整される。  [0098] Note that, similarly to the case of the first embodiment, the arrangement direction of each of the light beams 2bl-2b3 after spectroscopy also changes the track directional force of the optical disc information recording medium 8 shown in Figs. The arrangement of the parallel-plate diffractive optical element 61 is adjusted so that φb is formed with the design optical axis as the rotation axis.
[0099] しかし、平行平板型回折光学素子 61を回転させると、平行平板型回折光学素子 6 1の有する非点収差も回転することとなり、対物レンズ 9で発生する軸外非点収差を 効率よく打ち消せないこともある。  However, when the parallel-plate diffractive optical element 61 is rotated, the astigmatism of the parallel-plate diffractive optical element 61 is also rotated, and the off-axis astigmatism generated by the objective lens 9 is efficiently removed. Sometimes it can't be countered.
[0100] よって、平行平板型回折光学素子 61で発生する非点収差の量が対物レンズ 9で発 生する軸外非点収差を最も効率よく打ち消すことができるように、平行平板型回折光 学素子 61の回折格子 DFの溝の方向は、図 17と同様にラジアル方向 D1からタンジ ェンシャル方向 D2の向きに角度 φ aまたは φ bだけずらしておくのが望ましい。  [0100] Therefore, the parallel-plate diffractive optical element 61 is designed so that the amount of astigmatism generated by the parallel-plate diffractive optical element 61 can most effectively cancel the off-axis astigmatism generated by the objective lens 9. The direction of the groove of the diffraction grating DF of the element 61 is desirably shifted from the radial direction D1 in the tangential direction D2 by an angle φa or φb, as in FIG.
[0101] つまり、回折格子 DFの溝の方向を、ラジアル方向（ β軸の方向に相当）から光ディ スク情報記録媒体 8のタンジェンシャル方向の向きに角度 φ aまたは φ bだけ傾けて 配置させておけば、光ディスク情報記録媒体 8のトラックの方向に対して角度 φ aまた は φ bだけ傾けて複数の回折光を光ディスク情報記録媒体 8上に配列可能であるとと もに、平行平板型回折光学素子 61の有する非点収差が対物レンズ 9のラジアル方 向移動で発生する非点収差を最も効率よく打ち消すように平行平板型回折光学素 子 61を配置することができる。  [0101] In other words, the direction of the groove of the diffraction grating DF is inclined at an angle φa or φb from the radial direction (corresponding to the direction of the β axis) to the direction of the tangential direction of the optical disc information recording medium 8. In this case, a plurality of diffracted lights can be arranged on the optical disc information recording medium 8 at an angle φa or φb with respect to the track direction of the optical disc information recording medium 8, and a parallel plate type The parallel plate type diffractive optical element 61 can be arranged so that the astigmatism of the diffractive optical element 61 can cancel out the astigmatism generated by the radial movement of the objective lens 9 most efficiently.
[0102] 本実施の形態によれば、平行平板型回折光学素子 61の回折面は、ラジアル方向 D1から所定の角度 Θだけ傾けて配置されている。よって、平行平板型回折光学素 子 61の厚さ d、屈折率 nおよび傾け具合 0を調節することにより、回折光学素子の有 する非点収差の量を容易に調節することが可能である。  According to the present embodiment, the diffractive surface of parallel-plate diffractive optical element 61 is arranged at a predetermined angle か ら from radial direction D1. Therefore, by adjusting the thickness d, the refractive index n, and the degree of inclination 0 of the parallel plate type diffractive optical element 61, the amount of astigmatism of the diffractive optical element can be easily adjusted.
[0103] なお、図 21に示すように、光ビーム 2aの射出窓たる平板ガラス 3が、ラジアル方向 力も対物レンズ 9のレンズ光軸の向きに斜めに傾けられた平行平板射出窓 3aとなつ ている発光部品 5aが存在する。この平行平板射出窓 3aは、平行平板型回折光学素 子 61と同様、非点収差発生機能を担うが、ラジアル方向から斜めに傾けられている ためにコマ収差が発生しやす 、。 As shown in FIG. 21, the flat glass 3 serving as the exit window of the light beam 2a is positioned in the radial direction. There is also a light-emitting component 5a that is a parallel plate exit window 3a that is also obliquely inclined in the direction of the lens optical axis of the objective lens 9. The parallel-plate exit window 3a has a function of generating astigmatism similarly to the parallel-plate diffractive optical element 61. However, since it is inclined obliquely from the radial direction, coma aberration is likely to occur.
[0104] しかし、図 21の発光部品 5aに対して平行平板型回折光学素子 61を適用し、平行 平板型回折光学素子 61の回折面を、平行平板射出窓 3aの射出面とは正反対の向 きに傾ければ、平行平板射出窓 3aにより発生するコマ収差の一部または全部を、平 行平板型回折光学素子 61により発生するコマ収差でキャンセルさせることが可能で ある。よって、記録 '再生に用いられる光ビームの品質をさらに良くすることができる。  However, the parallel-plate diffractive optical element 61 is applied to the light-emitting component 5a in FIG. 21, and the diffractive surface of the parallel-plate diffractive optical element 61 is oriented in the opposite direction to the exit surface of the parallel-plate exit window 3a. If it is tilted, a part or all of the coma generated by the parallel-plate exit window 3 a can be canceled by the coma generated by the parallel-plate diffractive optical element 61. Therefore, the quality of the light beam used for recording and reproduction can be further improved.
[0105] 現在実用化されている DVDや CDなどの光ディスク装置では、レンズシフトの必要 最大量は 600 m程度であり、そのときに対物レンズ 9で生じる軸外非点収差が単体 で 300m λ ρν程度である。よって、平行平板型回折光学素子 61の有する非点収差 ASgの量も、軸外非点収差を打ち消す方向に 300m λ ρν程度、またはそれ以下で あることが望ましい。  In optical disc devices such as DVDs and CDs that are currently in practical use, the required maximum amount of lens shift is about 600 m, and the off-axis astigmatism generated by the objective lens 9 at that time is 300 m λ ρν It is about. Therefore, the amount of astigmatism ASg of the parallel-plate diffractive optical element 61 is desirably about 300 mλρν or less in the direction of canceling off-axis astigmatism.
[0106] ただし、上記非点収差量は、対物レンズの軸外非点収差について考慮したもので あり、光源やその他の光学部品などによってさらに非点収差が付加される光学構成 の場合は、上記非点収差量よりもさらに大きく設定すべき場合もある。また、本実施の 形態は疑似有限光学系にも適用可能である。  However, the amount of astigmatism takes into consideration off-axis astigmatism of the objective lens. In the case of an optical configuration in which astigmatism is further added by a light source or other optical components, the above-described amount of astigmatism is used. In some cases, it should be set larger than the astigmatism amount. This embodiment is also applicable to a pseudo finite optical system.
[0107] 実施の形態 3.  [0107] Embodiment 3.
本実施の形態も、実施の形態 1に係る光ヘッド装置の変形例であって、二光源構 成とし、かつ、回折光学素子に非点収差発生機能を担わせるのではなぐ二光源か らの光ビームを同方向に射出するダイクロイツクプリズムに非点収差発生機能を担わ せるようにしたものである。  This embodiment is also a modification of the optical head device according to the first embodiment, and has a dual light source configuration, and uses a dual light source that does not allow the diffractive optical element to perform the function of generating astigmatism. A dichroic prism that emits a light beam in the same direction has an astigmatism generation function.
[0108] 図 22は、本実施の形態に係る光ヘッド装置を示す図である。なお、図 22において は、第 1の光源たる半導体レーザ 1、平板ガラス 3、放熱金属パッケージ 4、回折光学 素子 62、偏向プリズム 7、光ディスク情報記録媒体 8、対物レンズ 9、光検知器 10、検 知用光学素子 11につ 、ては、ラジアル方向から傾かない回折面を有する平行平板 型回折光学素子 62が回折光学素子 6に代わって採用されている点、および、光路 中にダイクロイツクプリズム 12が挿入されている点以外、図 1と同じである。よって、図 1と同じ構成要素については説明を省略する。 FIG. 22 is a diagram showing an optical head device according to the present embodiment. In FIG. 22, the semiconductor laser 1 as the first light source, the flat glass 3, the heat dissipating metal package 4, the diffractive optical element 62, the deflecting prism 7, the optical disc information recording medium 8, the objective lens 9, the photodetector 10, the detection Regarding the known optical element 11, a parallel plate type diffractive optical element 62 having a diffractive surface not inclined from the radial direction is used instead of the diffractive optical element 6, and It is the same as FIG. 1 except that a dichroic prism 12 is inserted inside. Therefore, the description of the same components as those in FIG. 1 is omitted.
[0109] さて、図 22中の符号 13は第 2の光源である半導体レーザであり、光ビーム 2a (例え ば赤色光）の波長とは異なる波長を有する光ビーム 14 (例えば青色光）を放射する。 符号 15はホログラム素子であり、符号 16は半導体レーザ 13と同一半導体基板上に 形成された受光素子である。  Reference numeral 13 in FIG. 22 denotes a semiconductor laser as a second light source, which emits a light beam 14 (for example, blue light) having a wavelength different from the wavelength of the light beam 2a (for example, red light). I do. Reference numeral 15 denotes a hologram element, and reference numeral 16 denotes a light receiving element formed on the same semiconductor substrate as the semiconductor laser 13.
[0110] 半導体レーザ 13と受光素子 16とが形成された半導体基板は、放熱機能を兼ね備 えたパッケージ 17に取り付けられている。また、半導体レーザ 13および受光素子 16 への給電用端子 18と、受光素子 16からの電気信号を出力する出力用端子 19とが パッケージ 17に取り付けられている。  [0110] The semiconductor substrate on which the semiconductor laser 13 and the light receiving element 16 are formed is mounted on a package 17 having a heat radiation function. Further, a power supply terminal 18 for supplying power to the semiconductor laser 13 and the light receiving element 16 and an output terminal 19 for outputting an electric signal from the light receiving element 16 are mounted on the package 17.
[0111] さらに、ホログラム素子 15はパッケージ 17と接着されることにより一体ィ匕されている 。半導体レーザ 13より放射された光ビーム 14はホログラム素子 15を透過する。  [0111] Further, the hologram element 15 is integrated with the package 17 by being bonded thereto. The light beam 14 emitted from the semiconductor laser 13 passes through the hologram element 15.
[0112] 符号 12はダイクロイツクプリズムであって、内部の反射面で光ビーム 14を z方向に 偏向し、偏向プリズム 7からの光ビーム 2cはそのまま透過させる特性を有する。なお、 対物レンズ 9には、波長の異なる光ビーム 2cおよび光ビーム 14を光ディスク情報記 録媒体 8上に集光できる波長互換タイプのレンズが採用される。  [0112] Reference numeral 12 denotes a dichroic prism, which has a characteristic of deflecting the light beam 14 in the z direction by an internal reflection surface and transmitting the light beam 2c from the deflecting prism 7 as it is. As the objective lens 9, a wavelength compatible type lens capable of condensing the light beams 2 c and 14 having different wavelengths on the optical disc information recording medium 8 is employed.
[0113] 半導体レーザ 1から出力され、光ディスク情報記録媒体 8で反射された光ビーム 2d は、再び対物レンズ 9に入射して収束する光ビームに変換され、ダイクロイツクプリズ ム 12と偏向プリズム 7とを透過する。そして、検知用光学素子 11を介して光検知器 1 0に至る。一方、半導体レーザ 13から出力された光ビーム 14は、光ディスク情報記録 媒体 8で反射されて再び対物レンズ 9に入射した後、ダイクロイツクプリズム 12で偏向 され、ホログラム素子 15により受光素子 16へと分割および偏向される。  [0113] The light beam 2d output from the semiconductor laser 1 and reflected by the optical disk information recording medium 8 is converted into a light beam that is incident on the objective lens 9 again and converges, and is converted into a dichroic prism 12 and a deflecting prism 7. Through. Then, the light reaches the photodetector 10 via the detection optical element 11. On the other hand, the light beam 14 output from the semiconductor laser 13 is reflected by the optical disk information recording medium 8 and reenters the objective lens 9, is deflected by the dichroic prism 12, and is split into the light receiving element 16 by the hologram element 15. And be deflected.
[0114] 本実施の形態では、 2つの光源（半導体レーザ 1および半導体レーザ 13)から発せ られる 2つの光ビーム 2a, 14を 1つの対物レンズ 9へ入射させるとともに、且つ、光デ イスク情報記録媒体 8のラジアル方向への非点収差を与えることができるダイクロイツ クプリズム 12を有することを特徴としている。  In the present embodiment, two light beams 2a and 14 emitted from two light sources (semiconductor laser 1 and semiconductor laser 13) are made incident on one objective lens 9, and the optical disk information recording medium is 8 is characterized by having a dichroic prism 12 capable of giving astigmatism in the radial direction.
[0115] ダイクロイツクプリズム 12の具体的な形状を図 23に示す。ダイクロイツクプリズム 12 は、プリズム 12aとプリズム 12bが透過 ·反射面 105で貼り付けられた構造を有する。 透過 ·反射面 105は、光ビーム 14に対しては反射面として、光ビーム 2cに対しては 単なる透過面として機能する。すなわち、ダイクロイツクプリズム 12は、光ビーム 2cを 受ける第 1面 103と、光ビーム 14を受ける第 2面 106と、第 1面 103で受けた光ビーム 2cは透過させつつ、第 2面 106で受けた光ビーム 14は反射させる透過'反射面 105 と、透過 ·反射面 105を透過した光ビーム 2cおよび透過 ·反射面 105で反射した光ビ ーム 14を、光軸 Aidの延びる同方向に射出する第 3面 104とを有する。また、プリズ ム 12aとプリズム 12bの屈折率は同じ値 (n2)である。なお、図 22における x軸方向に 対しては、ダイクロイツクプリズム 12の y— z平面における断面形状に変化は無い。 FIG. 23 shows a specific shape of the dichroic prism 12. The dichroic prism 12 has a structure in which a prism 12a and a prism 12b are attached by a transmission / reflection surface 105. The transmission / reflection surface 105 functions as a reflection surface for the light beam 14 and simply functions as a transmission surface for the light beam 2c. That is, the dichroic prism 12 transmits the first surface 103 receiving the light beam 2c, the second surface 106 receiving the light beam 14, and the light beam 2c received by the first surface 103, while transmitting the light beam 2c on the second surface 106. The received light beam 14 is transmitted through the transmission / reflection surface 105 and the light beam 2c transmitted through the transmission / reflection surface 105 and the light beam 14 reflected by the transmission / reflection surface 105 in the same direction in which the optical axis Aid extends. And a third surface 104 from which light is emitted. The refractive index of the prism 12a and the refractive index of the prism 12b are the same (n2). Note that there is no change in the cross-sectional shape of the dichroic prism 12 in the yz plane in the x-axis direction in FIG.
[0116] 図 23においては、図 22における z軸に平行な Z軸、および、図 22における y軸に平 行な Y軸を、光ビーム 14の光軸 A2と第 2面 106との交点 P7を原点として、新たに設 定している。 In FIG. 23, the Z-axis parallel to the z-axis in FIG. 22 and the Y-axis parallel to the y-axis in FIG. 22 correspond to the intersection P7 between the optical axis A2 of the light beam 14 and the second surface 106. It is newly set with the origin as the origin.
[0117] 本実施の形態においては、実施の形態 1および 2で述べたような、光源が対物レン ズ 9のレンズ光軸力 光ディスク情報記録媒体 8のラジアル方向に遠ざ力ることにより 発生する非点収差を打ち消す方向の非点収差 ASgを、ダイクロイツクプリズム 12にて 発生させる。そのために、ダイクロイツクプリズム 12の第 1面 103、第 3面 104および第 2面 106の各面の垂線 L4, L5, L6を、入射または出射する光ビームの各光軸 Alb, Aid, A2の各方向に対して Θ 7、 Θ 7、 θ 1の角度だけそれぞれ傾ける。また、角度 Θ 2, Θ 6はそれぞれ、ダイクロイツクプリズム 12内部における各光ビームの光軸 Α4, Α5と、第 2面 106の垂線 L6、第 1面 103または第 3面 104の垂線 L4または L5とがな す角度である。  [0117] In the present embodiment, as described in Embodiments 1 and 2, the light source is caused by the lens optical axis force of the objective lens 9 moving away from the optical disc information recording medium 8 in the radial direction. The dichroic prism 12 generates astigmatism ASg in a direction to cancel the astigmatism. For this purpose, the perpendiculars L4, L5, L6 of the first surface 103, the third surface 104, and the second surface 106 of the dichroic prism 12 are set to the respective optical axes Alb, Aid, A2 of the incident or emitted light beam. Incline by 角度 7, Θ7, θ1 in each direction. The angles Θ2 and Θ6 are respectively the optical axes Α4 and Α5 of each light beam inside the dichroic prism 12, the perpendicular L6 of the second surface 106, and the perpendicular L4 or L5 of the first surface 103 or the third surface 104. It is the angle between
[0118] なお、図 23においては、第 1面 103および第 3面 104および反射点 P6を通る直線 L1とが平行であり（記号〃で「平行」を示す)、第 2面 106および反射点 P6を通る直 線 L2とが平行である（記号〃/で「平行」を示す)。また、光ビーム 14の入射前の光軸 A2と出射後の光軸 Aidとのなす角度は 90° である。  In FIG. 23, the straight line L1 passing through the first surface 103 and the third surface 104 and the reflection point P6 is parallel (indicated as “parallel” by the symbol 〃), and the second surface 106 and the reflection point The straight line L2 passing through P6 is parallel (the symbol 「/ indicates“ parallel ”). The angle formed between the optical axis A2 before the light beam 14 is incident and the optical axis Aid after the light beam 14 is 90 °.
[0119] まず、半導体レーザ 1を光源とする光ビーム 2cの、ダイクロイツクプリズム 12の透過 系光路について述べる。  [0119] First, a transmission optical path of the dichroic prism 12 of the light beam 2c using the semiconductor laser 1 as a light source will be described.
[0120] 光ビーム 2cに対しては、ダイクロイツクプリズム 12は実施の形態 2における平行平 板型回折光学素子 61と同様、ラジアル方向力も対物レンズ 9のレンズ光軸の向きに 斜めに傾いた平行平板型光学素子として作用する。よって、実施の形態 2で述べた 数 3と同じ式を使って、図 11の曲線 (b)から曲線 (d)の間の特性となるような非点収 差 ASgが発生できるように入射面の角度 Θ 7と第 1面 103および第 3面 104間の厚み dを決定する。なお、数 3において、 0 = 0 7と、 n=n2 (プリズム 12aおよびプリズム 1 2bの屈折率）と、それぞれ置き換える。また、 NAはダイクロイツクプリズム 12を透過す る光ビーム 2cの開口数、 λは光ビーム 2cの波長である。 [0120] For the light beam 2c, the dichroic prism 12 has a radial direction force that is in the direction of the lens optical axis of the objective lens 9 similarly to the parallel-plate diffractive optical element 61 in the second embodiment. It functions as a parallel-plate optical element that is inclined obliquely. Therefore, using the same equation as Equation 3 described in the second embodiment, the incident surface is set so as to generate astigmatic error ASg having a characteristic between the curves (b) and (d) in FIG. And the thickness d between the first surface 103 and the third surface 104 are determined. In Equation 3, 0 = 07 and n = n2 (the refractive indexes of the prisms 12a and 12b) are replaced with each other. NA is the numerical aperture of the light beam 2c passing through the dichroic prism 12, and λ is the wavelength of the light beam 2c.
[0121] 次に、半導体レーザ 13を光源とする光ビーム 14の、ダイクロイツクプリズム 12の反 射系光路について述べる。  Next, a reflection optical path of the dichroic prism 12 of the light beam 14 using the semiconductor laser 13 as a light source will be described.
[0122] 本実施の形態においては、入射面たる第 2面 106の角度 θ 1と出射面たる第 3面 1 04の角度 Θ 7とを同じ値に設定することにより、第 2面 106および第 3面 104も、第 1 面 103および第 3面 104が平行であるのと同様に、透過'反射面 105を介することに より等価的に平行となるよう各部の角度を設計する。すなわち、光ビーム 14がダイク ロイックプリズム 12を通過することで、 Θ 7の傾きをもつ平行平板型光学素子を通過し たのと等価な作用を受けるようにする。  In the present embodiment, by setting the angle θ 1 of the second surface 106 as the incident surface and the angle Θ 7 of the third surface 104 as the output surface to the same value, the second surface 106 and the second Similarly to the first surface 103 and the third surface 104, the three surfaces 104 are designed such that their angles are equivalently parallel through the transmission / reflection surface 105, similarly to the case where the first surface 103 and the third surface 104 are parallel. That is, when the light beam 14 passes through the dichroic prism 12, an effect equivalent to passing through the parallel-plate optical element having an inclination of Θ7 is obtained.
[0123] さらに、入射面たる第 2面 106の角度 θ 1と出射面たる第 3面 104の角度 Θ 7とを異 なる値に設定すれば、この角度差によっても光ビーム 14に発生させる非点収差の量 を変化させることが可能である。この場合、光ビーム 14に発生させる非点収差の量、 およびダイクロイツクプリズム 12の形状の設計に自由度を与える。すなわち、光ビー ム 14がダイクロイツクプリズム 12を通過することで、入射面と出射面とが非平行のくさ び形の平板光学素子を通過したのと等価な作用を受けるようにする。  Further, if the angle θ 1 of the second surface 106 as the entrance surface and the angle Θ 7 of the third surface 104 as the exit surface are set to different values, the angle difference generated in the light beam 14 is also caused by this angle difference. It is possible to change the amount of astigmatism. In this case, the degree of astigmatism generated in the light beam 14 and the shape of the dichroic prism 12 can be freely designed. That is, when the light beam 14 passes through the dichroic prism 12, the light receiving surface and the light emitting surface are subjected to an action equivalent to passing through a non-parallel wedge-shaped flat plate optical element.
[0124] そうすれば、光ディスク情報記録媒体 8のラジアル方向に非点収差を与えることが でき、対物レンズ 9がラジアル方向に移動する際に発生する非点収差を打ち消すこと ができる。角度 θ 1と角度 Θ 7とを等しい値にする場合、光ビーム 14に与える非点収 差の量は、光ビーム 2cの場合と同様、数 3により求めることができ、数 3の dを、図 23 中の第 2面 106と直線 L2との距離 drlと、図 23中の第 3面 104と直線 L1との距離 dr 2との和とすればよい。距離 dr2は透過系光路にてすでに決定されているので、距離 drlを最適化することで光ビーム 2cに発生させる非点収差の量とは独立に、光ビーム 14に発生させるべき所望の非点収差 ASgの量を得ることができる。 [0125] また、光ビーム 14は第 2面 106で屈折し、さらにダイクロイツクプリズム 12から出ると きに第 3面 104で再度屈折される力 角度 θ 1と角度 Θ 7とを等しくした場合には、角 度 0 1 (または 0 7)に関係なく透過 ·反射面 105を Y軸に対して 45° ( 0 3 = 0)とす ることで、反射系光路の偏向角度を Y軸に対して 90度にすることができる。 [0124] Then, astigmatism can be given in the radial direction of the optical disc information recording medium 8, and astigmatism generated when the objective lens 9 moves in the radial direction can be canceled. When the angle θ 1 and the angle Θ 7 are made equal, the amount of astigmatism given to the light beam 14 can be obtained by Equation 3 as in the case of the light beam 2c. The sum may be the sum of the distance drl between the second surface 106 and the straight line L2 in FIG. 23 and the distance dr2 between the third surface 104 and the straight line L1 in FIG. Since the distance dr2 has already been determined in the transmission optical path, optimizing the distance drl allows the desired astigmatism to be generated in the light beam 14 independently of the amount of astigmatism generated in the light beam 2c. The amount of aberration ASg can be obtained. The light beam 14 is refracted on the second surface 106, and is further refracted on the third surface 104 when exiting the dichroic prism 12. When the angle θ 1 is equal to the angle Θ7, By setting the transmissive / reflective surface 105 at 45 ° (0 3 = 0) with respect to the Y axis regardless of the angle 0 1 (or 0 7), the deflection angle of the reflective optical path is set with respect to the Y axis. Can be 90 degrees.
[0126] 一方、角度 θ 1と角度 Θ 7とを異なった値にする場合、ダイクロイツクプリズム 12から 出るときに第 3面 104で入射時と異なる屈折条件となるため、ダイクロイツクプリズム 1 2から出た光ビーム 14の出射後の角度を対物レンズ 9の設計光軸と一致させるには、 透過 ·反射面 105を Y軸からの 45° 角力もある角度 Θ 3だけ傾けておく必要がある。 角度 θ 1を角度 Θ 7と異なる値とすることによつても、光ビーム 14に発生させる非点収 差の量を光ビーム 2cに発生させる非点収差の量とは独立に可変とできる。  On the other hand, if the angle θ 1 and the angle Θ 7 are set to different values, the light exiting the dichroic prism 12 will have different refraction conditions from the incident light on the third surface 104, so that the dichroic prism 12 In order to make the angle of the emitted light beam 14 after emission coincide with the design optical axis of the objective lens 9, the transmission / reflection surface 105 must be inclined by an angle Θ3 which has a 45 ° angular force from the Y axis. By setting the angle θ1 to a value different from the angle Θ7, the amount of astigmatism generated in the light beam 14 can be changed independently of the amount of astigmatism generated in the light beam 2c.
[0127] まず、 Z— Y平面内にて Y軸に対して 45° の傾きを有する直線 L3を考える。ここで、 直線 L3と Y軸とのなす角度 0 は、  First, consider a straight line L3 having a 45 ° inclination with respect to the Y axis in the ZY plane. Here, the angle 0 between the straight line L3 and the Y axis is
A  A
[0128] [数 4]  [0128] [Number 4]
Θ k= 5 Θ k = 5
[0129] である。さて、透過 ·反射面 105と Y軸とのなす角度 0 は、透過 ·反射面 105と直線 L [0129] Now, the angle 0 between the transmissive / reflective surface 105 and the Y axis is
B  B
3とのなす角度 0 3を用いて、  Using the angle 0 3 with 3
[0130] [数 5] [0130] [Number 5]
^ g = 4 b 一 Θ s ^ g = 4 b 1 Θ s
[0131] と表せる。 [0131]
[0132] 次に、透過.反射面 105とダイクロイツクプリズム 12内での光ビーム 14の光軸 A4と のなす角度 Θ は、透過'反射面 105と、反射点 P6を通過する Y軸に平行な直線 L7  [0132] Next, the angle Θ between the transmission / reflection surface 105 and the optical axis A4 of the light beam 14 in the dichroic prism 12 is parallel to the transmission / reflection surface 105 and the Y axis passing through the reflection point P6. Straight line L7
C  C
とのなす角度 θ 1 Θ 2を用いて、  Using the angle θ 1 Θ 2 with
[0133] [数 6] [0133] [Number 6]
^ C= ^ 8—（ ，一 2 ) = 4 5° — ^ 3— ( ^ 1— 2 ) ^ C = ^ 8— (, 1 2) = 45 ° — ^ 3— (^ 1— 2)
[0134] と表せる。 [0134]
[0135] ここで、光ビーム 14は点 P6にて反射することから、透過 ·反射面 105と光軸 A4との なす角度 Θ と、透過 ·反射面 105と反射後の光軸 Α5とのなす角度とが等しくなる。よHere, since the light beam 14 is reflected at the point P6, the light beam 14 is The angle す is equal to the angle between the transmission / reflection surface 105 and the reflected optical axis Α5. Yo
C C
つて、透過 ·反射面 105と反射後の光軸 Α5とのなす角度力も角度 Θ 3の分を引いた 角度 0 は、  Therefore, the angle 0 between the transmission / reflection surface 105 and the optical axis Α5 after reflection is less than the angle Θ3.
D  D
[0136] [数 7]  [0136] [Number 7]
[0137] と表せる。 [0137]
[0138] さて、反射点 P6を通過する Z軸に平行な直線 L8と反射後の光軸 A5とのなす角度  [0138] Now, the angle between the straight line L8 passing through the reflection point P6 and parallel to the Z axis and the optical axis A5 after reflection
04は、  04 is
[0139] [数 8] [0139] [Number 8]
Θ 4—45° —θθ—2 ' θ 3+ { θ Λ— Θ 2 ) Θ 4—45 ° —θθ—2 'θ 3+ {θ Λ— Θ 2)
[0140] と表せる。 [0140]
[0141] また、第 3面 104の垂線 L5と反射後の光軸 Α5とのなす角度 Θ 6は、  [0141] The angle Θ6 between the perpendicular L5 of the third surface 104 and the optical axis Α5 after reflection is
[0142] [数 9] [0142] [Number 9]
. . — 1 / Π 1 \ .. — 1 / Π 1 \
Θ Q= s I n · s I n & 7  Θ Q = s I n
n 2 ノ n 2 no
Figure imgf000028_0001
Figure imgf000028_0001
— θ 1 Δ * θ θ ^^Γ θ 2  — Θ 1 Δ * θ θ ^^ Γ θ 2
[0143] と表せる。ここで、 nlはダイクロイツクプリズム 12外の空気の屈折率である。よって、数[0143] Here, nl is the refractive index of air outside the dichroic prism 12. So the number
9を変形すれば、角度 Θ 3は、 By transforming 9, the angle Θ 3 becomes
[0144] [数 10] n 1 \ [0144] [number 10] n 1 \
.'. ^ 3= < θ ι—θ ι + θ 2— Β I η " 1 · s \ η θ Ί \ > ÷2 . '. ^ 3 = <θ ι—θ ι + θ 2— Β I η " 1 · s \ η θ Ί \> ÷ 2
η 2 ノ I  η 2 no I
[0145] と表せる。よって、角度 θ 1と角度 Θ 7とを異なる値にする場合、透過'反射面 105と 直線 L3とがなす角度を数 10で得られる角度 Θ 3に設定することで、光ビーム 14と光 ビーム 2cとが第 3面 104から射出する角度を等しくすることができる。 [0145] Therefore, when the angle θ 1 and the angle Θ 7 are set to different values, by setting the angle formed by the transmission / reflection surface 105 and the straight line L 3 to the angle Θ 3 obtained by Expression 10, the light beam 14 and the light beam The angle at which 2c and 3c exit from third surface 104 can be made equal.
[0146] なお、角度 02が、 [0147] [数 11] [0146] Note that the angle 02 is [0147] [Number 11]
[0148] と表せるので、上述の 0 1 = 0 7の場合、数 10は、 [0148] Therefore, when 0 1 = 07 described above, Equation 10 is
[0149] [数 12]
Figure imgf000029_0001
[0149] [Number 12]
Figure imgf000029_0001
= { θ 2 - θ 2 } ÷ 2 = { θ 2-θ 2} ÷ 2
=〇  = 〇
[0150] となり、 0 3 = 0として透過'反射面 105を Υ軸に対して 45度とすれば、光ビーム 14と 光ビーム 2cとが第 3面 104から射出する角度を等しくすることができる。 [0150] If 0 3 = 0 and the transmission / reflection surface 105 is set at 45 degrees with respect to the Υ axis, the angles at which the light beam 14 and the light beam 2c exit from the third surface 104 can be equalized. .
[0151] 本実施の形態に係る光ヘッド装置によれば、ダイクロイツクプリズム 12の第 1面 103 および第 3面 104は平行であって、第 2面 106および第 3面 104も透過'反射面 105 を介することにより等価的に平行であって、第 3面 104は、ラジアル方向力も対物レン ズ 9のレンズ光軸の向きに所定の角度 Θ 7だけ傾けて配置されている。特に角度 θ 1 と角度 Θ 7とを等しい値にした場合、第 1光源たる半導体レーザ 1から放射される光ビ ーム 2cも、第 2光源たる半導体レーザ 13から放射される光ビーム 14も、いずれもラジ アル方向から角度 Θ 7だけ傾いた平行平板光学素子を通過するのと等価な作用を 受けることとなる。  [0151] According to the optical head device of the present embodiment, first surface 103 and third surface 104 of dichroic prism 12 are parallel, and second surface 106 and third surface 104 are also transmissive / reflective surfaces. The third surface 104 is disposed so as to be equivalently parallel to the third surface 104 through the intermediary of the objective lens 9 at a predetermined angle Θ7 in the direction of the lens optical axis of the objective lens 9. In particular, when the angle θ 1 is equal to the angle Θ7, the light beam 2c emitted from the semiconductor laser 1 as the first light source, the light beam 14 emitted from the semiconductor laser 13 as the second light source, In either case, the operation is equivalent to passing through a parallel plate optical element inclined by an angle Θ7 from the radial direction.
[0152] また、角度 θ 1と角度 Θ 7とを異なる値にした場合には、ダイクロイツクプリズム 12の 第 2面 106および第 3面 104は透過'反射面を介することにより、透過'反射面 105に て反射される光ビーム 14は第 2面 106および第 3面 104が非平行な入射面および出 射面として機能するくさび形平板光学素子を通過したのと等価な作用を受けることと なる。第 2面 106および第 3面 104の角度差によっても、透過'反射面 105にて反射さ れる光ビーム 14に発生させる非点収差の量を変化させることができ、光ビームに発 生させる非点収差の量、およびダイクロイツクプリズムの形状の設計に自由度を与え ることが可能である。 [0153] このため、光源が対物レンズ 9のレンズ光軸力 光ディスク情報記録媒体 8のラジア ル方向に遠ざ力ることにより発生する非点収差を打ち消す方向の非点収差を、ダイク ロイックプリズム 12が有する。よって、光ビーム 2cおよび光ビーム 14を平行光束では ない拡散光として対物レンズ 9に入射させる場合であっても、コリメータレンズを用い ることなくダイクロイツクプリズム 12によって、波面収差による記録'再生特性への影響 を抑制することが可能である。これにより、光ヘッド装置の小型化、薄型化および低コ ストイ匕が図れる。 When the angle θ 1 and the angle Θ 7 are set to different values, the second surface 106 and the third surface 104 of the dichroic prism 12 pass through the transmission / reflection surface, so that the transmission / reflection surface The light beam 14 reflected by 105 is subjected to an action equivalent to passing the second surface 106 and the third surface 104 through a wedge-shaped flat optical element functioning as a non-parallel entrance plane and exit plane. . The amount of astigmatism generated in the light beam 14 reflected on the transmission / reflection surface 105 can also be changed by the angle difference between the second surface 106 and the third surface 104, and the amount of astigmatism generated in the light beam can be changed. It is possible to give a degree of freedom to the amount of astigmatism and the design of the shape of the dichroic prism. Therefore, the astigmatism in the direction to cancel the astigmatism generated when the light source moves away from the objective lens 9 in the radial direction of the optical disc information recording medium 8 is reduced by the dichroic prism 12. Has. Therefore, even when the light beam 2c and the light beam 14 are made to enter the objective lens 9 as diffused light that is not a parallel light flux, the recording / reproducing characteristics due to wavefront aberration can be obtained by the dichroic prism 12 without using a collimator lens. It is possible to suppress the effects of As a result, the size and thickness of the optical head device can be reduced and the cost can be reduced.
[0154] 現在実用化されている DVDや CDなどの光ディスク装置では、レンズシフトの必要 最大量は 600 m程度であり、そのときに対物レンズ 9で生じる軸外非点収差が単体 で 300m λ ρν程度である。よって、ダイクロイツクプリズム 12の有する非点収差 ASg の量も、軸外非点収差を打ち消す方向に 300m λ ρν程度、またはそれ以下であるこ とが望ましい。  [0154] In an optical disk device such as a DVD or a CD that is currently in practical use, the required maximum amount of lens shift is about 600 m, and the off-axis astigmatism generated by the objective lens 9 at that time is 300 m λ ρν It is about. Therefore, the amount of astigmatism ASg of the dichroic prism 12 is desirably about 300 mλρν or less in the direction of canceling off-axis astigmatism.
[0155] ただし、上記非点収差量は、対物レンズの軸外非点収差について考慮したもので あり、光源やその他の光学部品などによってさらに非点収差が付加される光学構成 の場合は、上記非点収差量よりもさらに大きく設定すべき場合もある。また、本実施の 形態は疑似有限光学系にも適用可能である。  [0155] However, the amount of astigmatism takes into consideration the off-axis astigmatism of the objective lens. In the case of an optical configuration in which astigmatism is further added by a light source or other optical components, the above-described amount of astigmatism is used. In some cases, it should be set larger than the astigmatism amount. This embodiment is also applicable to a pseudo finite optical system.
[0156] 実施の形態 4.  [0156] Embodiment 4.
本実施の形態は、実施の形態 1で図 1に示した光ヘッド装置の変形例であって、非 点収差法フォーカスエラー検出を行なう光学系において、回折格子素子 6のシリンド リカル面の曲率方向をほぼタンジェンシャル方向に設定することで、回折格子素子 6 の設計光軸 Alaに垂直な平面内での位置変動で光検知器 10の受光面上の光ビー ムがずれたことによる光ヘッド装置の記録 ·再生特性の劣化を小さくしょうとしたもの である。  This embodiment is a modification of the optical head device shown in FIG. 1 in the first embodiment. In the optical system for performing the astigmatic focus error detection, the curvature direction of the cylindrical surface of the diffraction grating element 6 is By setting the light beam almost in the tangential direction, the optical beam device on the light receiving surface of the photodetector 10 is displaced due to positional fluctuation in a plane perpendicular to the design optical axis Ala of the diffraction grating element 6. It is intended to minimize the deterioration of the recording / reproducing characteristics.
[0157] 図 24は、本実施の形態 4に係る光ヘッド装置を示す斜視図であり、基本的な光学 構成は図 1と同じである。以下、図 24を用いて光ヘッド装置の構成および動作につ いて説明するが、実施の形態 1で図 1を用いて上述した内容に対して、特記すべき点 がない、若しくは変更点がない構成および動作についての説明は省略する。  FIG. 24 is a perspective view showing an optical head device according to Embodiment 4, and the basic optical configuration is the same as that of FIG. Hereinafter, the configuration and operation of the optical head device will be described with reference to FIG. 24, but there are no special points or changes in the contents described in Embodiment 1 with reference to FIG. A description of the configuration and operation will be omitted.
[0158] 回折格子素子 6は、図 13の形状をしたものであり、発光部品 5の内部にある半導体 レーザ 1 (図示せず)から出た光ビーム 2aを回折光ビーム 2bl— 2b3に分光する。図 24では、前記回折光ビームのうち 0次回折光ビーム 2blの経路のみを線で示し、 ± 1 次回折光ビーム 2b2および 2b3は図示しない。よって、図 24では各光ビームの経路 は設計光軸と実質的に同じ線で示される。 [0158] The diffraction grating element 6 has the shape shown in FIG. The light beam 2a emitted from the laser 1 (not shown) is split into a diffracted light beam 2bl-2b3. In FIG. 24, only the path of the zero-order diffracted light beam 2bl among the diffracted light beams is indicated by lines, and the ± first-order diffracted light beams 2b2 and 2b3 are not illustrated. Therefore, in FIG. 24, the path of each light beam is indicated by a line substantially the same as the design optical axis.
[0159] 本実施の形態 4では、実施の形態 1の偏向プリズム 7の代わりに、設計光軸 Albに 対して傾けて配置した平板型ハーフミラー 120を用いて光ビーム 2bl— 2b3を +z方 向へ偏向させ、対物レンズ 9へ入射させている。  In the fourth embodiment, instead of the deflecting prism 7 of the first embodiment, a flat half mirror 120 arranged at an angle to the design optical axis Alb is used to convert the light beam 2bl—2b3 into the + z direction. And is incident on the objective lens 9.
[0160] 光ディスク情報記録媒体 8により反射された光ビーム 2dは、再び対物レンズ 9に入 射して光軸 Alb、 Aleを中心軸とする収束光へと変換され、平板型ハーフミラー 120 を透過する。平板型ハーフミラー 120を透過した光ビーム 2eは、検知用光学素子 12 1を通過して光ビーム 2fとなって光検知器 122に入る。  [0160] The light beam 2d reflected by the optical disc information recording medium 8 re-enters the objective lens 9, is converted into convergent light having the optical axes Alb and Ale as central axes, and passes through the flat half mirror 120. I do. The light beam 2e transmitted through the flat half mirror 120 passes through the detection optical element 121, becomes a light beam 2f, and enters the light detector 122.
[0161] 光検知器 122は、図 24に示すように、少なくとも、受光領域 A— D力も成る 4分割受 光領域対とその両側配置された受光領域 Eおよび Fを有する受光面パターンを有す る。前記受光領域 A— Dは、 X軸にほぼ平行な分割線と y軸にほぼ平行な分割線とに よって 4つに分割されている。各受光領域は、前記検知用光学素子 121により変換さ れた前記光ビーム 2fを受光すると、その光量に応じた大きさの電気信号を出力する 機能を有する。  [0161] As shown in Fig. 24, the photodetector 122 has a light receiving surface pattern having at least a four-divided light receiving area pair having a light receiving area A-D force and light receiving areas E and F arranged on both sides thereof. You. The light receiving areas A to D are divided into four by a dividing line substantially parallel to the X axis and a dividing line substantially parallel to the y axis. When each light receiving area receives the light beam 2f converted by the detecting optical element 121, it has a function of outputting an electric signal of a magnitude corresponding to the light amount.
[0162] 光検知器 122に向力 前記反射光ビーム 2cが、収束しながら、光軸に対して傾け て配置された平板型ハーフミラー 120を透過すると非点収差が発生する。このとき、 平板型ハーフミラー 120の設計光軸 Albに対する傾きを、 X方向および y方向に対し て斜め方向に設定しているため、光検知器 122上に受光される光束の方向は、前記 4分割受光領域対の分割線方向に対して斜め方向となる。各受光領域 A— Dからの 電気信号の出力を A— Dとすると、 FES= (A+C)— (B+D)の演算によりフォーカスェ ラー信号 FESを得て非点収差法フォーカスエラー検出を実現することができる。この とき、平板型ハーフミラー 120を配置する方向を、 X方向および y方向に対しておよそ 45度に設定すれば、検出感度の高い非点収差法フォーカスエラー検出が可能とな る。  [0162] Direction toward the photodetector 122 When the reflected light beam 2c converges and passes through the flat half mirror 120 arranged at an angle to the optical axis, astigmatism occurs. At this time, since the inclination of the flat half mirror 120 with respect to the design optical axis Alb is set oblique to the X direction and the y direction, the direction of the light beam received on the photodetector 122 is The direction is oblique to the direction of the dividing line of the divided light receiving area pair. Assuming that the electric signal output from each light receiving area A-D is A-D, the focus error signal FES is obtained by the calculation of FES = (A + C)-(B + D), and the astigmatic focus error is detected. Can be realized. At this time, if the direction in which the flat half mirror 120 is disposed is set to about 45 degrees with respect to the X direction and the y direction, focus error detection with astigmatism with high detection sensitivity is possible.
[0163] 焦点制御は、フォーカスエラー信号 FESに基づ 、て、光ディスク情報記録媒体 8上 に光ビーム 2dが集光できるように、対物レンズ 9を z軸方向に変位させることにより行う 。具体的には、コイルなどで発生する電磁力を利用した対物レンズ変位機構 (図示せ ず）により、対物レンズ 9を z方向に変位させる。 [0163] Focus control is performed on the optical disc information recording medium 8 based on the focus error signal FES. This is performed by displacing the objective lens 9 in the z-axis direction so that the light beam 2d can be condensed at the same time. Specifically, the objective lens 9 is displaced in the z direction by an objective lens displacement mechanism (not shown) using an electromagnetic force generated by a coil or the like.
[0164] 検知用光学素子 121にレンズ機能を付加しておけば、前記光ビーム 2fの集光位置 を任意の距離に設定できる。また、検知用光学素子 121は、入射面や出射面を曲面 にしたりホログラムを形成するなどして非点収差発生機能を付加し、前記平板型ハー フミラー 120と併用して前記非点収差法フォーカスエラー検出に必要な大きさの非点 収差を発生させるために利用してもよい。さらに、検知用光学素子 121は、その入射 面と出射面の中心軸を相対的にシフトさせたり、または設計光軸 Aleに対して傾けて 配置させるなどすれば、前記平板型ハーフミラー 120で生じるコマ収差を補正するこ とができ、光検知器 122上の光強度分布が非対称となるのを防ぐために利用すること も可能である。ただし、検知用光学素子 121は光ヘッド装置に必須の構成要素では ない。例えば、このようなレンズ機能、非点収差発生機能、およびコマ収差の補正を 行わない場合には、部品点数を削減するため、光ヘッド装置が、検知用光学素子 12 1を有さな 、態様であっても構わな 、。  [0164] If a lens function is added to the detection optical element 121, the condensing position of the light beam 2f can be set to an arbitrary distance. Further, the detection optical element 121 has an astigmatism generation function by making the entrance surface or the exit surface a curved surface or forming a hologram, and uses the astigmatism focusing method together with the flat type half mirror 120. It may be used to generate astigmatism of a size necessary for error detection. Further, the detection optical element 121 is generated by the flat-type half mirror 120 if the center axes of the entrance surface and the exit surface are relatively shifted or are arranged at an angle with respect to the design optical axis Ale. Coma can be corrected, and can be used to prevent the light intensity distribution on the photodetector 122 from becoming asymmetric. However, the detection optical element 121 is not an essential component of the optical head device. For example, when such a lens function, an astigmatism generation function, and a coma aberration correction are not performed, in order to reduce the number of components, the optical head device does not have the optical element 121 for detection. It doesn't matter.
[0165] 受光領域 Eおよび Fは、タンジェンシャル方向 D2にほぼ平行に並んで配置され、そ れぞれ光ディスク情報記録媒体 8で反射される +1次回折光ビーム 2d2および 1次 回折光ビーム 2d3を受光する。図 24に示す光ヘッド装置は、これを利用して 3ビーム 法トラッキングエラー検出を行なう光学構成を有しており、受光領域 Eおよび Fからの 出力信号を差分することによって、 3ビーム法トラッキングエラー信号を生成し、当該 信号に基づ 、てトラックの変位に追従するように光ビーム 2dのラジアル方向位置制 御を行なう。  The light receiving regions E and F are arranged substantially parallel to the tangential direction D 2, and respectively receive the + 1st-order diffracted light beam 2d2 and the 1st-order diffracted light beam 2d3 reflected by the optical disc information recording medium 8. Receive light. The optical head device shown in FIG. 24 has an optical configuration that performs three-beam tracking error detection by using this. By subtracting output signals from the light receiving areas E and F, the three-beam tracking error is detected. A signal is generated, and based on the signal, the position of the light beam 2d in the radial direction is controlled so as to follow the displacement of the track.
[0166] 光ヘッド装置は、同様に回折光ビーム 2dl— 2d3を利用して行なうトラッキングエラ 一検出法であれば、他の方式を利用することもできる。例えば、受光領域 Eおよび F をそれぞれ少なくとも y方向に 2分割とした受光面パターンとすれば、差動プッシュプ ル法トラッキングエラー検出を行なうこともできる。  [0166] The optical head device may use another method as long as it is a tracking error detection method similarly performed using the diffracted light beam 2dl-2d3. For example, if the light receiving areas E and F are each formed as a light receiving surface pattern in which each of the light receiving areas E and F is divided at least into two in the y direction, tracking error detection by the differential push-pull method can be performed.
[0167] 上述したフォーカスエラー検出およびトラッキングエラー検出を最適に行なうために は、光検知器 122を精度良く位置調整する必要がある。具体的には、光検知器 122 の z方向の位置は光ビーム 2fが最小錯乱円となる近傍に、また x方向および y方向へ の位置は (A+D)— (B + C)および (A+ B)— (C + D)の各演算値がほぼ 0となるように 精度よく初期調整する必要がある。ただし、このとき平板型ハーフミラー 120によって 光ビーム 2fにコマ収差が存在する光学構成の場合には、前記コマ収差によって生じ る光検知器 122上での光ビーム 2fの強度分布の非対称性を考慮して、前記演算値 力 SOではなく所定の初期目標値となるように位置調整を行ってもよ!、。 [0167] In order to optimally perform the above-described focus error detection and tracking error detection, it is necessary to accurately adjust the position of the photodetector 122. Specifically, the light detector 122 The position in the z direction is near where the light beam 2f is the circle of least confusion, and the positions in the x and y directions are (A + D) — (B + C) and (A + B) — (C + D) It is necessary to make initial adjustments with high accuracy so that each of the calculated values becomes almost zero. However, in this case, in the case of an optical configuration in which the light beam 2f has a coma due to the flat half mirror 120, the asymmetry of the intensity distribution of the light beam 2f on the photodetector 122 caused by the coma is considered. Then, the position may be adjusted so as to be a predetermined initial target value instead of the calculated value SO!
[0168] 上記のように光検知器 122が最小錯乱円の近傍に配置されると、光ディスク情報記 録媒体 8で反射されて入射する光ビーム 2fは、非点収差の効果によって、光検知器 122上で、ほぼ 90度方向であるタンジュンシャル D2方向、つまり y方向に折り返され る。したがって、本実施の形態 4においては、対物レンズ 9がラジアル方向 D1への移 動する際、光ビームは光検知器 122上において y方向にずれることになる。  [0168] When the photodetector 122 is arranged near the circle of least confusion as described above, the light beam 2f reflected by the optical disc information recording medium 8 and incident on the optical disc information recording medium 8 is affected by the effect of astigmatism. On 122, it is folded in the tangential D2 direction, which is almost 90 degrees, that is, in the y direction. Therefore, in the fourth embodiment, when the objective lens 9 moves in the radial direction D1, the light beam is shifted on the photodetector 122 in the y direction.
[0169] 一方、上記の光学構成を実現するために、前記発光部品 5、回折格子素子 6、平 板型ハーフミラー 120、検知用光学素子 121、および光検知器 122は、榭脂ゃ金属 など力 なる光学ベースにそれぞれ固定され一体ィ匕されている。  On the other hand, in order to realize the above optical configuration, the light emitting component 5, the diffraction grating element 6, the flat plate half mirror 120, the detection optical element 121, and the light detector 122 are made of a metal such as a resin. Each is fixed to a powerful optical base and integrated.
[0170] そして、回折格子素子 6は、前記光学ベースへの固定と同時に、実施の形態 1で上 述したように光ディスク情報記録媒体 8上のトラック TR、または案内溝 GRに対して 3 つの回折光ビーム 2dl— 2d3が所定の方向に配列するように前記回折格子素子 6を 回転調整する必要がある。そのため、例えば、円筒状の外形をした回折格子素子 6、 または回折格子素子 6を間接的に保持した円筒状の回折格子素子用ホルダーを、 前記光学ベースに設けられた円筒状の穴に嵌め込んで、回折格子素子 6を α軸に 回転できる構造となっている（ただし、図 24では、シリンドリカル面を見やすくするため に回折格子素子 6の外形を円筒状とせず四角形として表示している)。ただし、固定 方法については、上記の例のような嵌め合い構造を利用する態様に限らず、前記光 学ベースと、回折格子素子 6または回折格子素子用ホルダーと、を接着剤で固定す る構造や、板パネやネジなどの固定部材を介して固定するなど、他の態様であっても 構わない。  [0170] At the same time as the fixation to the optical base, three diffraction grating elements 6 are formed on track TR or guide groove GR on optical disc information recording medium 8 as described in the first embodiment. It is necessary to adjust the rotation of the diffraction grating element 6 so that the light beams 2dl-2d3 are arranged in a predetermined direction. Therefore, for example, a cylindrical diffraction grating element 6 having a cylindrical outer shape, or a cylindrical diffraction grating element holder indirectly holding the diffraction grating element 6 is fitted into a cylindrical hole provided in the optical base. Thus, the diffraction grating element 6 can be rotated about the α-axis (however, in FIG. 24, the outer shape of the diffraction grating element 6 is shown as a square instead of a cylinder in order to make the cylindrical surface easier to see). However, the fixing method is not limited to the embodiment using the fitting structure as in the above example, but a structure in which the optical base and the diffraction grating element 6 or the diffraction grating element holder are fixed with an adhesive. Alternatively, another mode such as fixing via a fixing member such as a panel panel or a screw may be used.
[0171] 回転調整を伴う構造である以上、回折格子素子 6の回転調整時に調整を行ないや すくするために、回折格子素子 6と光学ベース、または回折格子素子用ホルダーと光 学ベースとの間に、構造上いくらかの隙間を必要とする。さらに、回折格子素子 6、光 学ベース、回折格子素子用ホルダーは通常少なくとも数 10 mの外形寸法公差を 持つので、この公差の範囲で隙間が広がる可能性がある。 [0171] Since the structure involves rotation adjustment, in order to facilitate adjustment during rotation adjustment of the diffraction grating element 6, the diffraction grating element 6 and the optical base or the diffraction grating element holder and the optical Some gap is required between the base and the scientific base. Furthermore, since the diffraction grating element 6, the optical base and the holder for the diffraction grating element usually have an outer dimension tolerance of at least several tens of meters, gaps may be widened within this tolerance range.
[0172] 接着剤で固定する場合には隙間に接着剤が充填されたり、あるいは隙間を残した 状態で固定されることになり、またネジゃ板パネなどの固定部材により固定する場合 には限られた接触点で回折格子素子 6が前記光学ベースに押し当てられて保持され ることになる。 [0172] In the case of fixing with an adhesive, the gap is filled with the adhesive, or the gap is fixed, and the gap is fixed. In the case of fixing with a fixing member such as a screw-and-panel panel, it is limited. The diffraction grating element 6 is pressed against the optical base and held at the contact point thus set.
[0173] このような回折格子素子 6の固定状態の場合、外部からの衝撃や温度衝撃が繰り 返し加わることによって、接着剤や固定部材が膨張収縮するために、回折格子素子 6の光学ベースに対する位置力 固定前の隙間の範囲で経時的に変化する可能性 がある。  [0173] In such a fixed state of the diffraction grating element 6, the adhesive or the fixing member expands and contracts due to repeated impacts from the outside and temperature shocks. Positional force may change over time in the range of the gap before fixing.
[0174] 例えば、前記シリンドリカル面の曲率方向に沿って回折格子素子 6が移動した場合 を考える。図 25は、このときの回折格子素子 6のシリンドリカル面の曲率方向（つまり、 y軸方向）に沿った断面図を示す図であるが、回折格子素子 6が γ方向に移動する と、光ビーム 2aの中心光軸の入射面 101cに入射する角度が、初期の入射角度に対 して変化するので、前記回折格子素子 6を透過した後の光ビーム 2bの中心光軸は、 設計光軸 Alaに対して傾きをもつ Blaとなる。図 25では、回折格子素子 6の中心軸 が設計光軸 Ala上に位置して 、る状態を、点線で示す外形 6aとして表して 、る。  For example, consider a case where the diffraction grating element 6 moves along the direction of curvature of the cylindrical surface. FIG. 25 is a cross-sectional view of the cylindrical surface of the diffraction grating element 6 along the curvature direction (that is, the y-axis direction) at this time. When the diffraction grating element 6 moves in the γ direction, the light beam Since the angle of incidence on the entrance surface 101c of the central optical axis of 2a changes with respect to the initial incident angle, the central optical axis of the light beam 2b after passing through the diffraction grating element 6 is the designed optical axis Ala. Bla with inclination to. In FIG. 25, a state where the central axis of the diffraction grating element 6 is located on the design optical axis Ala is represented as an outer shape 6a indicated by a dotted line.
[0175] このような回折格子素子 6の位置移動によって光ビーム 2bの中心光軸の変化が生 じると、それに応じて光ビーム 2fが光検知器 122上で移動する。光ビーム 2fの移動 は、上述のフォーカスエラー検出等の動作に影響する力 その影響は、検知器 122 上の光ビーム 2fのずれ方向によって異なる。  When the center optical axis of the light beam 2b changes due to such position movement of the diffraction grating element 6, the light beam 2f moves on the photodetector 122 accordingly. The movement of the light beam 2f is a force that affects operations such as the focus error detection described above. The influence depends on the direction in which the light beam 2f on the detector 122 shifts.
[0176] 図 26 (a)は、光ビーム 2fが光検知器 122上で x方向にずれたときの様子を模式的 に示したものである力 この状態でもフォーカスエラー信号の演算値は FES = 0を維 持している。そして、対物レンズ 9がラジアル方向 D1に移動したとすると、図 26 (b)の 点線で示すように光ビームが y方向に移動する。その結果、 4分割受光領域対の中 心付近にあった光ビーム力 分割線に対して斜め方向に移動することになる。この状 態から、 FESを 0に維持するように上述のフォーカスエラー検出による焦点制御を行 うと、初期に調整された光ビーム 2fの最小錯乱円を維持できず制御動作点が変化し て光ディスク情報記録媒体 8上で光ビーム 2dの焦点ずれが生じてしまう。そして、こ の焦点ずれの影響によって、光ヘッド装置の記録'再生特性が劣化することになる。 [0176] Fig. 26 (a) schematically shows the state when the light beam 2f is displaced in the x-direction on the photodetector 122. Force In this state, the calculated value of the focus error signal is FES = 0 is maintained. If the objective lens 9 moves in the radial direction D1, the light beam moves in the y direction as shown by the dotted line in FIG. 26 (b). As a result, the light beam moves in an oblique direction with respect to the light beam force dividing line located near the center of the light receiving region pair. From this state, the focus control by the focus error detection described above is performed so that FES is maintained at 0. In this case, the initially adjusted minimum circle of confusion of the light beam 2f cannot be maintained, the control operating point changes, and the light beam 2d is defocused on the optical disk information recording medium 8. Then, the recording / reproducing characteristics of the optical head device are deteriorated due to the influence of the defocus.
[0177] これに対し、光ビーム 2fが y方向にずれる場合には、これが対物レンズ 9のラジアル 方向 D1への移動によって生じる光ビーム 2fの位置ずれ方向と一致するため、図 26 ( b)のような 4分割受光領域対の分割線に対して斜め方向に光ビーム 2fが移動するこ とはな 、。そのため光ディスク情報記録媒体 8上で光ビーム 2dの焦点ずれは発生し ない。 [0177] On the other hand, when the light beam 2f is shifted in the y-direction, this coincides with the displacement direction of the light beam 2f caused by the movement of the objective lens 9 in the radial direction D1, and therefore, FIG. The light beam 2f does not move obliquely with respect to such a dividing line of the four light receiving area pairs. Therefore, no defocus of the light beam 2d occurs on the optical disc information recording medium 8.
[0178] 即ち、非点収差法フォーカスエラー検出をする光学構成の場合、 X方向への光ビー ムのずれをでき限り抑える光学構成が望ましい。  That is, in the case of an optical configuration for detecting a focus error by the astigmatism method, an optical configuration for minimizing the displacement of the light beam in the X direction is desirable.
[0179] そして、本実施の形態 4では、回折格子素子 6のシリンドリカル面の曲率方向をタン ジェンシャル方向 D2に対応させて配置しているため、図 25で説明したように回折格 子素子 6が位置移動しても光検知器 122上の光ビーム 2fのずれ方向を y方向に限定 でき、上述した光ヘッド装置の記録 ·再生特性の劣化を抑制することができる。  In the fourth embodiment, since the curvature direction of the cylindrical surface of diffraction grating element 6 is arranged so as to correspond to tangential direction D2, as shown in FIG. Even if is moved, the direction of displacement of the light beam 2f on the photodetector 122 can be limited to the y direction, and the above-described deterioration of the recording / reproducing characteristics of the optical head device can be suppressed.
[0180] 尚、回折格子素子 6は、図 14に示す形状のものであっても構わない。この場合でも 、回折格子素子 6の位置移動により生じる光検知器 122上の光ビームずれ方向を y 方向に限定することが可能であり、上述したのと同様の効果を得ることができる。  The diffraction grating element 6 may have a shape shown in FIG. Also in this case, the direction of the light beam shift on the photodetector 122 caused by the movement of the position of the diffraction grating element 6 can be limited to the y direction, and the same effect as described above can be obtained.
[0181] また、回折格子素子 6は、図 15または図 16に示す形状のものであっても構わない。  The diffraction grating element 6 may have a shape shown in FIG. 15 or FIG.
この場合、 j8軸方向にシリンドリカル面の曲率を有するため、 γ軸方向にシリンドリカ ル面の曲率を有する図 13または図 14の形状のものを用いる場合と異なり、回折格子 素子 6の位置移動によって生じる光検知器 122上の光ビームのずれ方向が X方向と なる。上述したように X方向への光ビームのずれは、光ヘッド装置の記録'再生特性 の劣化原因となる。よって、図 15または図 16に示す形状の回折格子素子 6を利用す る場合は、光ビームの X方向へのずれの発生を抑制するため、固定部材等を用いて 固定するときに、回折格子素子 6の 軸方向に与圧が付加された状態、即ち光学べ ースに押し当てられた圧入状態にしておく。これにより、回折格子素子 6の回転調整 や経時変化による回折格子素子 6のシリンドリカル面の曲率方向（すなわち、 β軸方 向であり、通常この方向をラジアル方向 D1に設定する）への位置移動を抑制できる。 そして、その結果、光検知器 122上の X方向への光ビームのずれを抑制することがで きる。尚、このような回折格子素子 6固定時の与圧の付カ卩は、本実施の形態に限らず 、全ての光ヘッド装置において、光ビームのずれを抑制するために有効である。 In this case, since the cylindrical surface has a curvature in the j8-axis direction, unlike the case of using the shape of FIG. 13 or FIG. 14 having a cylindrical surface curvature in the γ-axis direction, it is caused by the position movement of the diffraction grating element 6. The shift direction of the light beam on the light detector 122 is the X direction. As described above, the displacement of the light beam in the X direction causes the deterioration of the recording and reproducing characteristics of the optical head device. Therefore, when the diffraction grating element 6 having the shape shown in FIG. 15 or FIG. 16 is used, when the light beam is fixed using a fixing member or the like in order to suppress the occurrence of the displacement of the light beam in the X direction, the diffraction grating is used. The element 6 is kept pressurized in the axial direction, that is, press-fitted against the optical base. As a result, the position of the diffraction grating element 6 in the direction of curvature of the cylindrical surface of the diffraction grating element 6 (that is, in the β-axis direction, which is usually set to the radial direction D1) due to rotation adjustment and time-dependent change of the diffraction grating element 6 is prevented. Can be suppressed. As a result, the displacement of the light beam in the X direction on the light detector 122 can be suppressed. Note that such pressurized knitting when the diffraction grating element 6 is fixed is effective not only in the present embodiment but also in all optical head devices for suppressing the displacement of the light beam.
[0182] 実施の形態 5.  [0182] Embodiment 5.
本実施の形態は、実施の形態 1に係る光ヘッド装置の変形例であって、スポットサ ィズ法フォーカスエラー検出を行なう光学系において、回折格子素子 6のシリンドリカ ル面の曲率方向をほぼラジアル方向に設定することで、回折格子素子 6の設計光軸 Alaに垂直な平面内の位置変動で光検知器 10の受光面上の光ビームがずれたこと による光ヘッド装置の記録 ·再生特性の劣化を小さくしょうとしたものである。  This embodiment is a modification of the optical head device according to the first embodiment. In the optical system that performs the spot size method focus error detection, the curvature direction of the cylindrical surface of the diffraction grating element 6 is substantially radially changed. By setting the direction, the light beam on the light-receiving surface of the photodetector 10 shifts due to position fluctuations in a plane perpendicular to the design optical axis Ala of the diffraction grating element 6, and the recording and reproduction characteristics of the optical head device are It is intended to reduce deterioration.
[0183] 図 27は、本実施の形態に係る光ヘッド装置を示す斜視図であり、基本的な光学構 成は図 1と同じである。以下、図 27を用いて光ヘッド装置の構成および動作について 説明するが、実施の形態 1で図 1を用いて上述した内容に対して、特記すべき点がな V、、若しくは変更点がな 、構成および動作にっ 、ての説明は省略する。  FIG. 27 is a perspective view showing an optical head device according to the present embodiment, and the basic optical configuration is the same as FIG. Hereinafter, the configuration and operation of the optical head device will be described with reference to FIG. 27, but there are no special points V or changes to the contents described in Embodiment 1 with reference to FIG. The description of the configuration, operation, and the like is omitted.
[0184] 回折格子素子 6は図 15の形状をしたものであり、発光部品 5の内部にある半導体レ 一ザ 1 (図示せず)から出た光ビーム 2aを回折光ビーム 2bl— 2b3に分光する。図 27 では、前記回折光ビームのうち 0次回折光ビーム 2blの光路のみを線で示し、 ± 1次 回折光ビーム 2b2および 2b3は図示しない。よって、図 27では各光ビームの経路は 設計光軸と実質的に同じ線で示される。  The diffraction grating element 6 has the shape shown in FIG. 15, and splits the light beam 2a emitted from the semiconductor laser 1 (not shown) inside the light emitting component 5 into a diffracted light beam 2bl-2b3. I do. In FIG. 27, only the optical path of the 0th-order diffracted light beam 2bl among the diffracted light beams is indicated by lines, and the ± 1st-order diffracted light beams 2b2 and 2b3 are not shown. Therefore, in FIG. 27, the path of each light beam is indicated by a line substantially the same as the design optical axis.
[0185] 偏向プリズム 140は、実施の形態 1の図 1で示した偏向プリズム 7に相当するもので あって、光ビーム 2bl— 2b3を偏向させ対物レンズ 9へ入射させている。  The deflecting prism 140 corresponds to the deflecting prism 7 shown in FIG. 1 of the first embodiment, and deflects the light beam 2bl-2b3 to make it incident on the objective lens 9.
[0186] 光ディスク情報記録媒体 8により反射された光ビーム 2dは、再び対物レンズ 9に入 射して光軸 Alb、 Aleを中心軸とする収束光へと変換され、偏向プリズム 140を透過 する。ホログラム素子 141は、スポットサイズ法フォーカスエラー検出を行なうために、 偏向プリズム 140を透過した光ビーム 2eを 4つの半光束ビーム 2fl— 2f4に分割する 機能を有する。  [0186] The light beam 2d reflected by the optical disc information recording medium 8 again enters the objective lens 9, is converted into convergent light having the optical axes Alb and Ale as central axes, and passes through the deflecting prism 140. The hologram element 141 has a function of dividing the light beam 2e transmitted through the deflecting prism 140 into four half light beams 2fl-2f4 in order to detect a spot size method focus error.
[0187] 集光レンズ 142を透過した前記半光束ビーム 2fl— 2f4は光検知器 143に入る。前 記集光レンズ 142の集光機能はホログラム素子 141に含めて一体ィ匕されていてもよ い。 [0188] 前記ホログラム素子 141は、図 28に示すように、光ディスク情報記録媒体 8のタンジ ェンシャル方向 D2に平行な線 BLを境界とした 2つの領域にそれぞれ異なる中心をも つ同心円状または曲線状のホログラムパターンを有し、図 29に示すように、ホロダラ ム領域 141aで回折され集光レンズ 142を透過した半光束ビーム 2flおよび 2f2は、 それぞれ異なる焦点距離 FC1および FC2に収束する（ここでは、 FCKFC2とする 力 FC1 >FC2であってもよい）。また、ホログラム領域 141bで回折され集光レンズ 1 42を透過した半光束ビーム 2f3および 2f4も、同様に異なる焦点距離 FC1および FC 2に収束する。焦点距離の FC1および FC2は、本光ヘッド装置のフォーカスエラー 検出範囲の設定値によって決定される。また、 + 1次回折光ビーム 2d2および 1次 回折光ビーム 2d3についてもそれぞれ同様に半光束ビームに分割された後、集光レ ンズ 142を透過して光検知器 143に入る。 The half beam 2 fl-2 f 4 transmitted through the condenser lens 142 enters the photodetector 143. The condenser function of the condenser lens 142 may be included in the hologram element 141 and integrated. [0188] As shown in Fig. 28, the hologram element 141 has a concentric shape or a curved shape having different centers in two regions bounded by a line BL parallel to the tangential direction D2 of the optical disc information recording medium 8. As shown in FIG. 29, the half-flux beams 2fl and 2f2 diffracted in the holo-holum region 141a and transmitted through the condenser lens 142 converge at different focal lengths FC1 and FC2 (here, FCKFC2 force FC1 may be greater than FC2). Also, the half beam beams 2f3 and 2f4 diffracted by the hologram region 141b and transmitted through the condenser lens 142 similarly converge to different focal lengths FC1 and FC2. The focal lengths FC1 and FC2 are determined by the set value of the focus error detection range of the optical head device. Similarly, the + 1st-order diffracted light beam 2d2 and the 1st-order diffracted light beam 2d3 are similarly split into half-beam beams, and then pass through the condenser lens 142 and enter the photodetector 143.
[0189] 光検知器 143は、図 30に示すように、少なくともラジアル方向 D1 (つまり x軸方向に 相当する）と平行な分割線で 3つに分割された 4組の短冊形受光領域対 Pla、 Plb、 Picおよび Pldと、 + 1次回折光ビーム 2d2および 1次回折光ビーム 2d3がホロダラ ム素子 141で分割され生成された半光束ビームをそれぞれ受光する受光領域 A2— D2および A3— D3から成る。  [0189] As shown in Fig. 30, the photodetector 143 includes four pairs of rectangular light-receiving areas divided into three by a dividing line parallel to at least the radial direction D1 (that is, corresponding to the x-axis direction). , Plb, Pic, and Pld, and light receiving areas A2—D2 and A3—D3 for receiving the half light beam generated by splitting the + 1st-order diffracted light beam 2d2 and the 1st-order diffracted light beam 2d3 by the holo-drum element 141, respectively.
[0190] 光検知器 143は、半光束ビーム 2fl— 2f4の焦点距離 FC1と FC2のおよそ中間距 離 (つまり（FC1 +FC2) Z2の近傍）に配置されており、図 29に示すように焦点距離 が短い半光束ビームは光検知器 143の手前でー且集光して力も再び広がるので、 半光束ビームの外形の円弧はそれぞれ図 30に示す方向となる。  [0190] The photodetector 143 is disposed at an intermediate distance between the focal lengths FC1 and FC2 of the half beam 2fl-2f4 (that is, in the vicinity of (FC1 + FC2) Z2), and as shown in FIG. Since the short-beam beam having a short distance is converged before the photodetector 143 and the power is spread again, the arcs of the outer shape of the half-beam beam are in the directions shown in FIG. 30, respectively.
[0191] 前記スポットサイズ法フォーカスエラー検出信号 FESは、各受光面からの検出信号 を用いて、 FES= (A1 + C1 +E1)— (B1 + D1 +F1) + (G1 +11 +K1)— (HI +J1 +L1)により生成され、光検知器 143は前記 FESがほぼ 0となるようにその位置が初 期調整されている。  [0191] The spot size method focus error detection signal FES is obtained by using a detection signal from each light receiving surface, FES = (A1 + C1 + E1)-(B1 + D1 + F1) + (G1 + 11 + K1) — Generated by (HI + J1 + L1), and the position of the photodetector 143 is initially adjusted so that the FES becomes almost zero.
[0192] 一方、トラッキングエラー検出信号については、 TES= (A1 + B1 +C1 + D1 +E1  On the other hand, regarding the tracking error detection signal, TES = (A1 + B1 + C1 + D1 + E1
+F1)— (G1 +H1 +I1 +J1 +K1 +L1) +MG X (A2 + B2+A3 + B3— C2— D2— C3— D3)の演算により作動プッシュプル法トラッキングエラー検出信号 TESを得るこ とができる。ここで MGはゲインであり、対物レンズ 9がラジアル方向に位置移動しても TES信号のオフセットが発生しな 、ように最適設定する。 + F1) — (G1 + H1 + I1 + J1 + K1 + L1) + MG X (A2 + B2 + A3 + B3— C2— D2— C3— D3) Operates by the push-pull tracking error detection signal TES Obtainable. Here, MG is a gain, and even if the objective lens 9 moves in the radial direction, The optimal setting is made so that the offset of the TES signal does not occur.
[0193] 尚、図 30に示した光検知器 143には、前記半光束ビームのそれぞれに対して受光 領域または受光領域対が設けられている力 光検知器 143は、前記受光領域または 前記受光領域対を共通化した受光面パターンを有する態様であっても構わない。  The photodetector 143 shown in FIG. 30 is provided with a light receiving region or a light receiving region pair for each of the half-beam beams. An embodiment having a light receiving surface pattern in which the region pairs are shared may be used.
[0194] また、図 27では、差動プッシュプル法トラッキングエラー検出を行なう光学構成を示 しているが、 3ビーム法トラッキングエラー検出法をも利用可能な態様であっても構わ ない。この場合、実施の形態 1で上述したとおり、「3ビーム法」または「差働プッシュプ ル法」を選択することによって、光ディスク情報記録媒体 9上のトラック方向に対する 回折光ビーム 2dl— 2d3の配列方向のずれ角が、 φ a、または φ bに設定される。  Although FIG. 27 shows the optical configuration for performing the tracking error detection by the differential push-pull method, an embodiment in which the tracking error detection method using the three-beam method may be used. In this case, as described above in the first embodiment, by selecting the “three-beam method” or the “differential push-pull method”, the arrangement direction of the diffracted light beams 2dl-2d3 with respect to the track direction on the optical disc information recording medium 9 Is set to φa or φb.
[0195] 上記のような短冊形受光領域対 Pla— Pldを用いて行なうスポットサイズ法フォー カスエラー検出における、半光束ビーム 2fl— 2f4の各短冊形受光領域の分割線に 平行な方向へのずれ、または光強度分布ずれについては、受光される各半光束ビ ームの内側受光領域と外側受光領域の光量比が変わらな 、ため、前記フォーカスェ ラー検出の演算に影響を与えにくい。  [0195] In the spot size method focus error detection performed using the rectangular light receiving area pair Pla-Pld as described above, the displacement of the half light beam 2fl-2f4 in the direction parallel to the dividing line of each rectangular light receiving area, Or, regarding the light intensity distribution deviation, since the light quantity ratio between the inner light receiving area and the outer light receiving area of each received half beam is not changed, it hardly affects the calculation of the focus error detection.
[0196] し力しながら、前記分割線に直交する方向（すなわち、 y軸方向）への前記ずれに ついては前記フォーカスエラー検出の演算に大きく影響を与える。  The displacement in the direction orthogonal to the parting line (ie, the y-axis direction) while applying force greatly affects the calculation of the focus error detection.
[0197] もし、タンジ ンシャル方向 D2へ前記半光束ビームがずれると、短冊型受光領域 対の内側受光領域で受光される光量とその両側にある外側受光領域で受光される 光量和が等しくならず、前記フォーカスエラー信号の演算結果が理想的な演算結果 と異なってしまう。その結果、前記フォーカスエラー検出の演算を 0に維持するように 制御を行なうと動作点が変化して焦点ずれ生じてしまうという問題が発生し、記録'再 生特性が劣化する。  [0197] If the half-beam beam is displaced in the tangential direction D2, the sum of the amounts of light received in the inner light receiving regions of the pair of strip-shaped light receiving regions and the amounts of light received in the outer light receiving regions on both sides thereof do not become equal. Therefore, the calculation result of the focus error signal is different from the ideal calculation result. As a result, if control is performed so that the calculation of the focus error detection is maintained at 0, a problem occurs in that the operating point changes and a focus shift occurs, and the recording / reproducing characteristics deteriorate.
[0198] 以上の理由から、一般に、スポットサイズ法フォーカスエラー検出を行なう光学構成 においては、対物レンズ 9がラジアル方向に移動する際に生じる光ビームのずれが 前記フォーカスエラー検出の演算に極力影響を与えないように前記短冊形受光領域 対の分割線方向をラジアル方向に設定する。  For the reasons described above, in general, in an optical configuration that performs focus error detection by the spot size method, the displacement of the light beam generated when the objective lens 9 moves in the radial direction has the least effect on the calculation of the focus error detection. The direction of the dividing line of the pair of strip-shaped light receiving regions is set to the radial direction so as not to give.
[0199] したがって、本実施の形態のようにビームサイズ法フォーカスエラー検出をする光 学構成の場合、 y方向、つまりタンジェンシャル方向 D2に対応する方向への光ビー ムのずれをできる限り抑える光学構成が望ましい。 [0199] Therefore, in the optical configuration that detects the focus error by the beam size method as in the present embodiment, the light beam in the y direction, that is, the direction corresponding to the tangential direction D2 is used. It is desirable to have an optical configuration that minimizes the deviation of the system.
[0200] 図 27で示したように回折格子素子 6のシリンドリカル面の曲率方向をラジアル方向 D1に対応させれば、回折格子素子 6の位置移動により生じる光検知器 143上の各 光ビームのずれ方向を X方向に限定することが可能となり、上で述べたような光ヘッド 装置の記録 ·再生特性の劣化を抑制することができる。  If the curvature direction of the cylindrical surface of the diffraction grating element 6 is made to correspond to the radial direction D1 as shown in FIG. 27, the displacement of each light beam on the photodetector 143 caused by the position movement of the diffraction grating element 6 The direction can be limited to the X direction, and the deterioration of the recording / reproducing characteristics of the optical head device as described above can be suppressed.
[0201] 尚、回折格子素子 6は、図 16に示す形状のものであっても構わない。この場合でも 、回折格子素子 6の位置移動により生じる光検知器 143上の光ビームずれ方向を X 方向に限定することが可能であり、上述したのと同様の効果を得ることができる。  [0201] The diffraction grating element 6 may have the shape shown in FIG. Also in this case, the direction of the light beam shift on the photodetector 143 caused by the movement of the position of the diffraction grating element 6 can be limited to the X direction, and the same effect as described above can be obtained.
[0202] また、フォーカスエラー検出法としてナイフエッジ法を用いる態様であっても構わな い。この場合、前記ホログラム素子 141が少なくともラジアル方向 D1に対応する X軸 方向に平行に半光束ビームを分割する機能を有するようにし、且つ、前期ホログラム 素子 141によって生成された前記半光束ビームのそれぞれを、ラジアル方向に対応 する X軸方向に平行な分割線で 2分割された受光パターンを有する光検知器 143で 検出するようにすればよい。  [0202] Further, a mode using a knife edge method as a focus error detection method may be used. In this case, the hologram element 141 has a function of splitting a half-beam beam at least in parallel to the X-axis direction corresponding to the radial direction D1, and each of the half-beam beams generated by the hologram element 141 is Alternatively, the light may be detected by the photodetector 143 having a light receiving pattern divided into two by a dividing line parallel to the X-axis direction corresponding to the radial direction.
[0203] 前記ナイフエッジ法フォーカスエラー検出を行う場合も、スポットサイズ法フォーカス エラー検出を行う場合と同様に、各半光束ビームをラジアル方向に対応する X軸方向 に平行な分割線を有する受光パターンで検出することから、前記半光束ビームの y方 向、つまりタンジュンシャル方向 D2に対応する方向へのずれに対してできる限り尤度 を持った光学構成が望ましいが、これについては本実施の形態 4で上述した方法に より実現することが可能である。  [0203] Also in the case of performing the knife edge method focus error detection, similarly to the case of performing the spot size method focus error detection, the light receiving pattern having a dividing line parallel to the X-axis direction corresponding to the radial direction for each half-beam beam. Therefore, it is desirable to use an optical configuration that has as much likelihood as possible with respect to the displacement of the half-beam in the y direction, that is, the direction corresponding to the tangential direction D2. This can be realized by the method described above in 4.
[0204] また、回折格子素子 6は実施の形態 4で説明したのと同様にして光学ベースに保持 される力 回折格子素子 6として γ軸方向にシリンドリカル面の曲率を有する図 13ま たは図 14の形状のものを用いる場合には、 β軸方向にシリンドリカル面の曲率を有 する図 15または図 16の形状のものを用いる場合と異なり、回折格子素子 6の位置移 動によって生じる光検知器 143上の光ビームずれ方向が y方向となる。この場合、実 施の形態 4で上述したのと同様に、固定部材等を用いて固定するときに、回折格子 素子 6の γ軸方向に与圧が付加された状態、即ち光学ベースに押し当てられた圧入 状態にしておく。これにより、回折格子素子 6の回転調整や経時変化による回折格子 素子 6のシリンドリカル面の曲率方向（すなわち、 j8軸方向であり、通常この方向をタ ンジヱンシャル方向 D2に設定する）への位置移動を抑制できる。そして、その結果、 光検知器 143上の y方向への光ビームのずれを抑制することができる。尚、このような 回折格子素子 6固定時の与圧の付カ卩は、本実施の形態に限らず、全ての光ヘッド装 、て、光ビームのずれを抑制するために有効である。 The diffraction grating element 6 has a cylindrical surface curvature in the γ-axis direction as the force diffraction grating element 6 held by the optical base in the same manner as described in the fourth embodiment. In the case of using the shape of FIG. 14, unlike the case of using the shape of FIG. 15 or FIG. 16 having the curvature of the cylindrical surface in the β-axis direction, the photodetector generated by the displacement of the diffraction grating element 6 is used. The light beam shift direction on 143 is the y direction. In this case, as described above in the fourth embodiment, when fixing is performed using a fixing member or the like, a state in which pressurization is applied in the γ-axis direction of the diffraction grating element 6, that is, pressing against the optical base. Press-fitted. This makes it possible to adjust the rotation of the diffraction grating element 6 and change the diffraction grating over time. The position movement of the cylindrical surface of the element 6 in the curvature direction (that is, the j8-axis direction, which is usually set to the tangential direction D2) can be suppressed. As a result, the displacement of the light beam in the y direction on the photodetector 143 can be suppressed. Incidentally, such a pressurized knitting at the time of fixing the diffraction grating element 6 is not limited to the present embodiment, but is effective for suppressing the displacement of the light beam in all the optical head devices.
[0205] この発明は詳細に説明されたが、上記した説明は、すべての局面において、例示 であって、この発明がそれに限定されるものではない。例示されていない無数の変形 例力 この発明の範囲力 外れることなく想定され得るものと解される。 [0205] Although the present invention has been described in detail, the above description is illustrative in all aspects and the present invention is not limited thereto. Innumerable modifications not illustrated Example power It is understood that it can be assumed without departing from the scope of the present invention.
産業上の利用の可能性  Industrial potential
[0206] この発明は、光ビームを利用して情報記録媒体に記録'再生を行う装置に利用可 能であり、例えば、 CD (Compact Disc)、 DVD (Digital Versatile Disc)、 MD (Mini Disc)等の光ディスク情報記録媒体を介した記録 ·再生を行なう光ディスク記録 ·再生 装置に応用できる。 The present invention can be used for an apparatus that performs recording and reproduction on an information recording medium using a light beam, for example, a CD (Compact Disc), a DVD (Digital Versatile Disc), and an MD (Mini Disc) It can be applied to an optical disk recording / reproducing device that performs recording / reproduction via an optical disk information recording medium such as.

Claims

請求の範囲 The scope of the claims
[1] 光ビームを放射する光源（1)と、  [1] a light source (1) that emits a light beam,
溝状の回折格子が形成された回折面を有し、前記光ビームを回折させて複数の回 折光を生成する回折光学素子 (6)と、  A diffractive optical element (6) having a diffraction surface on which a grooved diffraction grating is formed, and diffracting the light beam to generate a plurality of diffraction lights;
光ディスク情報記録媒体 (8)上に前記複数の回折光を集光させる対物レンズ (9)と を備え、  An objective lens (9) for condensing the plurality of diffracted lights on an optical disc information recording medium (8),
前記回折光学素子は、前記光源が前記対物レンズのレンズ光軸から前記光デイス ク情報記録媒体のラジアル方向に遠ざ力ることにより発生する非点収差を打ち消す 方向の非点収差を有する  The diffractive optical element has astigmatism in a direction to cancel astigmatism generated by the light source moving away from the lens optical axis of the objective lens in the radial direction of the optical disc information recording medium.
光ヘッド装置。  Optical head device.
[2] 前記回折光学素子 (6)を光学ベースに回転自在に固定したときに、前記回折光学 素子に与圧が付加された状態にある  [2] When the diffractive optical element (6) is rotatably fixed to the optical base, a pressure is applied to the diffractive optical element.
請求の範囲 1記載の光ヘッド装置。  The optical head device according to claim 1.
[3] 前記回折光学素子 (6)の前記回折面または前記回折面の裏面は、トーリック面また はシリンドリカル面である [3] The diffractive surface or the back surface of the diffractive surface of the diffractive optical element (6) is a toric surface or a cylindrical surface.
請求の範囲 1記載の光ヘッド装置。  The optical head device according to claim 1.
[4] 前記トーリック面または前記シリンドリカル面の曲率を持つ方向は前記光ディスク情報 記録媒体（8)のタンジェンシャル方向およびラジアル方向の少なくとも一方に平行で あって、 [4] A direction having a curvature of the toric surface or the cylindrical surface is parallel to at least one of a tangential direction and a radial direction of the optical disc information recording medium (8),
前記回折格子 (6)の溝の方向は、前記ラジアル方向から前記光ディスク情報記録 媒体のタンジュンシャル方向の向きに所定の角度だけ傾けて配置された  The direction of the grooves of the diffraction grating (6) was arranged at a predetermined angle from the radial direction to the tangential direction of the optical disc information recording medium.
請求の範囲 3記載の光ヘッド装置。  4. The optical head device according to claim 3.
[5] 前記シリンドリカル面の曲率を持つ方向は前記光ディスク情報記録媒体 (8)のタンジ ェンシャル方向に並行であって、 [5] The direction having the curvature of the cylindrical surface is parallel to the tangential direction of the optical disc information recording medium (8),
前記光ディスク情報記録媒体力 の反射光を利用した非点収差法によるフォー力 スエラー検出結果に基づ 、て焦点制御を行う  Focus control is performed based on a force error detection result by an astigmatism method using reflected light of the optical disc information recording medium.
請求の範囲 3記載の光ヘッド装置。  4. The optical head device according to claim 3.
[6] 前記回折光学素子 (6)を光学ベースに回転自在に固定したときに、前記回折光学 素子にラジアル方向に与圧が付加された状態にある [6] When the diffractive optical element (6) is rotatably fixed to an optical base, The element is radially pressurized
請求項 5記載の光ヘッド装置。  The optical head device according to claim 5.
[7] 前記シリンドリカル面の曲率を持つ方向は前記光ディスク情報記録媒体 (8)のラジア ル方向に並行であって、 [7] The direction having the curvature of the cylindrical surface is parallel to the radial direction of the optical disc information recording medium (8),
前記光ディスク情報記録媒体力 の反射光を利用したスポットサイズ法またはナイ フエッジ法によるフォーカスエラー検出結果に基づいて焦点制御を行う  Focus control is performed based on a focus error detection result by a spot size method or a knife edge method using reflected light of the optical disk information recording medium.
請求の範囲 3記載の光ヘッド装置。  4. The optical head device according to claim 3.
[8] 前記回折光学素子 (6)を光学ベースに回転自在に固定したときに、前記回折光学 素子にタンジュンシャル方向に与圧が付加された状態にある [8] When the diffractive optical element (6) is rotatably fixed to an optical base, a pressure is applied to the diffractive optical element in a tangential direction.
請求項 5記載の光ヘッド装置。  The optical head device according to claim 5.
[9] 前記回折光学素子 (6)は平行平板型回折光学素子 (61)であって、 [9] The diffractive optical element (6) is a parallel plate type diffractive optical element (61),
前記平行平板型回折光学素子の前記回折面は、前記ラジアル方向から前記対物 レンズ (9)のレンズ光軸の向きに所定の角度だけ傾けて配置された  The diffractive surface of the parallel-plate diffractive optical element is disposed at a predetermined angle from the radial direction to a direction of a lens optical axis of the objective lens (9).
請求の範囲 1記載の光ヘッド装置。  The optical head device according to claim 1.
[10] 前記光ビームの射出窓たる平行平板射出窓（3a) [10] A parallel-plate emission window (3a) which is an emission window for the light beam.
をさらに備え、  Further comprising
前記平行平板射出窓の射出面は、前記ラジアル方向から前記対物レンズ (9)のレ ンズ光軸の向きに傾けて配置され、  The exit surface of the parallel plate exit window is arranged to be inclined from the radial direction to the direction of the lens optical axis of the objective lens (9),
前記平行平板型回折光学素子 (61)の前記回折面は、前記平行平板射出窓の前 記射出面とは正反対の向きに傾けられている  The diffractive surface of the parallel-plate diffractive optical element (61) is inclined in a direction exactly opposite to the exit surface of the parallel-plate exit window.
請求の範囲 9記載の光ヘッド装置。  The optical head device according to claim 9.
[11] 前記回折格子 (6)の溝の方向は、前記ラジアル方向から前記光ディスク情報記録媒 体（8)のタンジュンシャル方向の向きに他の所定の角度だけ傾けて配置された 請求の範囲 9記載の光ヘッド装置。 [11] The groove direction of the diffraction grating (6) is arranged to be inclined by another predetermined angle from the radial direction to the tangential direction of the optical disc information recording medium (8). The optical head device as described in the above.
[12] 光ビームを放射する第 1光源（1)と、 [12] a first light source (1) that emits a light beam;
他の光ビームを放射する第 2光源（13)と、  A second light source (13) that emits another light beam,
前記光ビームを受ける第 1面（103)、前記他の光ビームを受ける第 2面（106)、前 記第 1面で受けた前記光ビームは透過させつつ、前記第 2面で受けた前記他の光ビ ームは反射させる透過 ·反射面（105)、並びに、前記透過 ·反射面を透過した前記 光ビームおよび前記透過'反射面で反射した前記他の光ビームを同方向に射出する 第 3面（ 104)を有するダイクロイツクプリズム（ 12)と、 A first surface (103) for receiving the light beam, a second surface (106) for receiving the other light beam, and the light beam received on the second surface while transmitting the light beam received on the first surface. Other light The beam is reflected by a transmission / reflection surface (105), and a third surface (the same surface) that emits the light beam transmitted through the transmission / reflection surface and the other light beam reflected by the transmission / reflection surface in the same direction. A dichroic prism (12) having 104);
光ディスク情報記録媒体 (8)上に前記ダイクロイツクプリズムの前記第 3面から射出 される前記光ビームおよび前記他の光ビームを集光させる対物レンズ (9)と を備え、  An objective lens (9) for focusing the light beam and the other light beam emitted from the third surface of the dichroic prism on an optical disk information recording medium (8);
前記第 1面および前記第 3面は平行であって、  The first surface and the third surface are parallel,
前記第 2面および前記第 3面も前記透過 ·反射面を介することにより等価的に平行 であって、  The second surface and the third surface are also equivalently parallel through the transmission / reflection surface,
前記第 3面は、前記ラジアル方向力 前記対物レンズのレンズ光軸の向きに所定の 角度だけ傾けて配置された  The third surface is disposed so as to be inclined by a predetermined angle in a direction of a lens optical axis of the objective lens in the radial direction force.
光ヘッド装置。 Optical head device.
光ビームを放射する第 1光源（1)と、 A first light source (1) for emitting a light beam;
他の光ビームを放射する第 2光源（13)と、  A second light source (13) that emits another light beam,
前記光ビームを受ける第 1面（103)、前記他の光ビームを受ける第 2面（106)、前 記第 1面で受けた前記光ビームは透過させつつ、前記第 2面で受けた前記他の光ビ ームは反射させる透過 ·反射面（105)、並びに、前記透過 ·反射面を透過した前記 光ビームおよび前記透過'反射面で反射した前記他の光ビームを同方向に射出する 第 3面（ 104)を有するダイクロイツクプリズム（ 12)と、  A first surface (103) for receiving the light beam, a second surface (106) for receiving the other light beam, and the light beam received on the second surface while transmitting the light beam received on the first surface. The other light beam reflects the transmission / reflection surface (105), and the same light beam transmitted through the transmission / reflection surface and the other light beam reflected by the transmission / reflection surface in the same direction. A dichroic prism (12) having a third surface (104);
光ディスク情報記録媒体 (8)上に前記ダイクロイツクプリズムの前記第 3面から射出 される前記光ビームおよび前記他の光ビームを集光させる対物レンズ (9)と を備え、  An objective lens (9) for focusing the light beam and the other light beam emitted from the third surface of the dichroic prism on an optical disk information recording medium (8);
前記第 1面および前記第 3面は平行であって、  The first surface and the third surface are parallel,
前記第 2面および前記第 3面は前記透過 ·反射面を介することにより、前記透過 ·反 射面で反射される前記他の光ビームに対して等価的に前記第 2面および前記第 3面 が非平行な入射面および出射面として機能するくさび形平板光学素子を構成し、 前記第 3面は、前記ラジアル方向力 前記対物レンズのレンズ光軸の向きに所定の 角度だけ傾けて配置された 光ヘッド装置。 The second surface and the third surface pass through the transmission / reflection surface, so that the second surface and the third surface are equivalent to the other light beam reflected by the transmission / reflection surface. Constitutes a wedge-shaped flat plate optical element functioning as a non-parallel incident surface and an outgoing surface, and the third surface is arranged at a predetermined angle in the direction of the radial direction force with respect to the lens optical axis of the objective lens. Optical head device.
PCT/JP2004/013047 2004-01-09 2004-09-08 Optical head device WO2005066947A1 (en)

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