WO2005088624A1 - 対物光学素子及び光ピックアップ装置 - Google Patents
対物光学素子及び光ピックアップ装置 Download PDFInfo
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- WO2005088624A1 WO2005088624A1 PCT/JP2005/003715 JP2005003715W WO2005088624A1 WO 2005088624 A1 WO2005088624 A1 WO 2005088624A1 JP 2005003715 W JP2005003715 W JP 2005003715W WO 2005088624 A1 WO2005088624 A1 WO 2005088624A1
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- optical element
- wavelength
- optical
- path difference
- objective optical
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Classifications
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
- G11B7/1353—Diffractive elements, e.g. holograms or gratings
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B13/00—Optical objectives specially designed for the purposes specified below
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/18—Diffraction gratings
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
- G11B7/1365—Separate or integrated refractive elements, e.g. wave plates
- G11B7/1367—Stepped phase plates
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
- G11B7/1372—Lenses
- G11B7/1374—Objective lenses
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
- G11B7/1392—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
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B2007/0003—Recording, reproducing or erasing systems characterised by the structure or type of the carrier
- G11B2007/0006—Recording, reproducing or erasing systems characterised by the structure or type of the carrier adapted for scanning different types of carrier, e.g. CD & DVD
Definitions
- the present invention relates to an optical pickup device, and more particularly, to information recording and Z recording on three or more different optical information recording media using light beams emitted from three light sources having different light source wavelengths. Or, it relates to an optical pickup device capable of reproducing.
- an optical disk having a diameter of 12 cm can be used to transfer 15 to 20 GB of information. Recording becomes possible, and when the NA of the objective lens is increased to 0.85, it becomes possible to record 23 to 25 GB of information on an optical disc with a diameter of 12 cm.
- NA numerical aperture
- an optical disk and a magneto-optical disk using a blue-violet laser light source are collectively referred to as a “high-density optical disk” t.
- the optical pickup device mounted on the optical disk player Z recorder for the high-density optical disk is applicable to any of the three types of optical disks, the high-density optical disk, the DVD and the CD. It is also desirable to have the capability to properly record and reproduce information while maintaining compatibility.
- One aspect of aberration correction is to change the degree of divergence of a light beam incident on the objective optical element.
- off-axis characteristics are deteriorated in accordance with the degree of divergence of the light beam incident on the objective optical element (the greater the degree of divergence, the greater the coma when the lens is shifted during tracking).
- Another aspect of aberration correction is to provide a diffraction structure that gives a diffractive effect on the optical surface of the objective optical element (for example, see Patent Document 1).
- Patent Document 1 Japanese Patent Application Laid-Open No. 2002-298422
- the present invention has been made in view of the problems of the related art, and provides an objective optical element that can perform satisfactory spherical aberration correction even when light beams having three different wavelengths are incident. With the goal.
- the objective optical element and the optical pickup device use the first optical path difference providing structure to give an optical path difference in advance so that the phase changes only with respect to the light beam of the third wavelength to obtain a wavelength ⁇ 3
- Correction of the spherical aberration or wavefront aberration of the light beams of the wavelengths ⁇ 1 and ⁇ 2 by using the second optical path difference providing structure to mainly provide an optical path difference to the light beams of the wavelengths ⁇ 1 and ⁇ 2.
- FIG. 1 is a schematic cross-sectional view of an optical pickup device according to the present embodiment.
- FIG. 2 is a schematic sectional view of an objective optical element OBJ.
- FIG. 3 (a) is a schematic cross-sectional view showing a modification of the objective optical element OBJ.
- FIG. 3 (b) is a schematic sectional view showing another modification of the objective optical element OBJ.
- FIG. 4 (a) is a longitudinal spherical aberration diagram of a light beam (HD) having a wavelength of ⁇ 1 in Example 1.
- FIG. 4 (b) is a longitudinal spherical aberration diagram of a light beam (DVD) of wavelength 2 in Example 1.
- FIG. 4 (c) is a longitudinal spherical aberration diagram of a light beam (CD) having a wavelength of 3 in Example 1.
- FIG. 5 is a diagram showing a wavefront aberration characteristic at the time of wavelength fluctuation in Example 1.
- FIG. 6 (a) is a longitudinal spherical aberration diagram of a light beam (HD) having a wavelength ⁇ 1 in a comparative example.
- FIG. 6 (b) is a longitudinal spherical aberration diagram of a light beam (DVD) having a wavelength ⁇ 2 in a comparative example.
- FIG. 6 (c) is a longitudinal spherical aberration diagram of the light beam (CD) having the wavelength ⁇ 3 in the comparative example.
- FIG. 7 is a diagram showing a wavefront aberration characteristic when a wavelength fluctuates in a comparative example.
- the objective optical element described in item 1 comprises a first light source having a wavelength of ⁇ 1, a second light source having a wavelength of 2 ( ⁇ 1 ⁇ 2), and a wavelength of 3 ( ⁇ 2 ⁇ 3) a third light source, and an objective optical element of an optical pickup device having a condensing optical system including an objective optical element, wherein the light beam from the first light source is passed through the objective optical element,
- a condensing optical system including an objective optical element including an objective optical element
- the light flux of the second light source power is condensed on the information recording surface of the second optical information recording medium via the protective layer having a thickness t2 (tl ⁇ t2), thereby recording and Z or reproducing information.
- the light flux from the third light source is passed through the objective optical element via a protective layer having a thickness t3 (t2 ⁇ t3). Then, by condensing the information on the information recording surface of the third optical information recording medium, it is possible to perform information recording and Z or reproduction,
- the objective optical element gives a substantial phase change to the light beam of the wavelength ⁇ 3, and provides a first optical path difference that gives no substantial change in phase to the light beam of the wavelength ⁇ 1 and the wavelength 2.
- An optical path difference providing structure, the light beam of the wavelength ⁇ 1, the light beam of the wavelength ⁇ 2, and the light beam of the wavelength ⁇ 3 And a second optical path difference providing structure for giving an optical path difference to the light flux.
- spherical aberration or wavefront aberration is corrected by using the first optical path difference providing structure and giving an optical path difference in advance such that the phase changes only for the light beam of the wavelength ⁇ 3.
- the second optical path difference providing structure spherical aberration or wavefront aberration is corrected by mainly giving an optical path difference to the luminous fluxes of the wavelengths ⁇ 1 and ⁇ 2, thereby reducing the burden and reducing the total load.
- the objective optical element according to item 2 in the configuration according to item 1, information is reproduced from the first optical information recording medium, the second optical information recording medium, and the third optical information recording medium. And / or When recording is performed, the objective optical element is configured to have substantially the same imaging magnification.
- the “substantially the same imaging magnification” means that a difference between the imaging magnification of the light beam of the other wavelength and the imaging magnification of the light beam of the second wavelength is within ⁇ 0.008.
- the imaging magnification is 0.
- a parallel light beam is incident on the objective optical element at all wavelengths, off-axis characteristics of the objective optical element are improved. For example, even when the objective optical element is shifted in the track direction, coma and astigmatism are increased. Can be suppressed.
- a light source in which a plurality of light sources are packaged in one package can be used, and the number of components of the optical pickup device can be reduced, and the size and the cost can be reduced.
- the first optical path difference providing structure may be a diffractive structure such as a force NPS (Non-Periodic Surface). good.
- the first optical path difference providing structure includes a predetermined number of discontinuous portions having a groove force centered on an optical axis.
- the grooves are formed by forming them concentrically and periodically, and the depth of the grooves does not substantially change the phase of the light beams of the wavelengths ⁇ 1 and ⁇ 2 passing through the discontinuous portion. And is substantially set for the light beam of the wavelength ⁇ 3 passing through the discontinuous portion. Since it is set so that there is a significant phase change, it is possible to correct the difference by giving a strong phase change. By setting the size and the number of steps of the staircase shape to predetermined steps, it is possible to have a diffractive action for a specific wavelength.
- substantially no change in phase does not mean only a case where there is no phase change at all, but any change in phase within ⁇ 0.2 ⁇ (preferably within 0.1 ⁇ ). Shall be included. Further, “substantial phase change” includes a phase change exceeding ⁇ 0.2 ⁇ .
- the refractive index with respect to the wavelength ⁇ 1 of the objective optical element in which the first optical path difference providing structure is formed is nl
- the number of discontinuous portions is ml (integer)
- d ⁇ 1 / (nl-1)
- the second optical path difference providing structure has a saw-tooth structure
- the second optical path difference providing structure has a structure with respect to the first optical information recording medium.
- a condensed spot is formed by a light beam of M (M is an integer) order diffracted light generated by the 2 optical path difference providing structure, and the Nth order diffraction generated by the second optical path difference providing structure with respect to the third optical information recording medium. It is configured such that a converged spot is formed by a light beam.
- both the light beams of the wavelengths 1 and ⁇ 3 passing through the second optical path difference providing structure have high diffraction efficiencies
- a wavelength difference that is not an integral multiple is given only to the light flux of wavelength 3 (an integer multiple of wavelength difference is given to the other two light fluxes).
- the L-order diffracted light having the wavelength ⁇ 1 and the wavelength ⁇ that pass through the second optical path difference providing structure Assuming that the diffraction efficiencies of the second-order diffracted light of 2 and the second-order diffracted light of the wavelength ⁇ 3 are ⁇ 1, 7-2 and 7-3, respectively, 7-1> 80%, 7-2> 70% And 7? 3> 80%.
- r? L and 7? 2 are luminous fluxes having as high a diffraction efficiency as possible so that SZN can be further improved.
- the incident light transmitted through the objective optical element is reflected on the information recording surface, and the diffraction efficiency when transmitted again through the objective optical element is 50% or more.
- the first optical path difference providing structure is expected to reduce the efficiency of the ⁇ 3rd order diffracted light of ⁇ 3 when a diffraction action is generated, the light flux should have the highest possible diffraction efficiency. No.
- the objective optical element according to item 14 is the configuration according to any one of items 1 to 13, wherein the objective optical element is a first optical element arranged on a light source side and an optical information recording medium side. It is composed of two elements, the second optical element to be arranged.
- the objective optical element is By configuring the optical element power, the degree of freedom of the correction function is increased, which is advantageous in design and performance.
- the objective element may be formed of a single element.
- the first optical element has the first optical path difference providing structure
- the second optical element has the second optical path difference providing structure. Be prepared.
- the objective optical element according to item 16 wherein in the configuration according to item 14, the first optical path difference providing structure is provided on one surface of the first optical element, and the second optical path difference providing structure is provided on the other surface.
- the first optical path difference providing structure is provided on one surface of the first optical element
- the second optical path difference providing structure is provided on the other surface.
- the first optical path difference providing structure is provided on an optical surface on a light source side of the first optical element.
- the groove-shaped optical path difference providing structure has a larger step amount in the optical axis direction than the sawtooth optical path difference providing structure, and vignetting of light rays occurs due to oblique incidence. This causes a reduction in diffraction efficiency.
- the focal length of the first optical element with respect to the wavelength ⁇ 1 is fl1
- the focal length of the first optical element is in front of the second optical element.
- At least one surface of the first optical element has a substantially infinite paraxial radius of curvature.
- radius of curvature on the optical axis is 200 mm or more. It refers to that.
- a more preferable radius of curvature is 500 mm or more, and more preferably a flat surface.
- the objective optical element according to item 20 wherein in the configuration according to any one of items 1 to 19, the objective optical element includes a third optical path difference providing structure, and the third optical path difference providing structure includes:
- the cross-sectional shape in the optical axis direction is a saw-tooth shape and is composed of a plurality of annular zones centered on the optical axis.
- P times and Q times do not indicate only the value, but include those within a range of ⁇ 0.12 from the value.
- the third optical path difference providing structure is provided in order to reduce the occurrence of aberration due to a wavelength change of several nm which can be caused by the first and second optical path difference providing structures.
- the refraction of the light of wavelength 1 and ⁇ 2 passing through the diffractive structure is represented by the difference of the following equations (6) and (7).
- nl, n2 wavelength respectively
- the first optical path difference providing structure is formed by using a first optical path difference function ⁇ (h).
- the objective optical element described in Item 24 is characterized in that, in the configuration according to any one of Items 1 to 23, the reproduction of information and the recording or Z or recording on the third optical information recording medium are performed as described above. Note that the focal position of the Nth-order diffracted light beam and the focal position of the (N ⁇ l) th-order light beam are separated by at least 0.1 Olmm in the optical axis direction.
- At least one of the optical surfaces of the objective optical element has an aperture limiting function according to a wavelength.
- the aperture limiting function is a function of a dichroic filter that transmits only a specific wavelength.
- the objective lens according to item 25 wherein Noh is a function of flaring a light beam of a predetermined wavelength by a diffraction structure.
- At least one optical surface of the objective optical element has a concentric central region including an optical axis and centered on the optical axis; At least two peripheral regions are located around the central region and have a diffraction structure that flares the light beam of the predetermined wavelength, and the luminous flux of the wavelength ⁇ 3 that has passed through the peripheral region is flared.
- a concentric outer peripheral region centered on the optical axis and located around the peripheral region is provided, and passes through the outer peripheral region. Either the light beam of the wavelength ⁇ 1 or the light beam of the wavelength ⁇ 2 flares
- the term "flare component (flare light)” refers to a predetermined aperture which has an effect of not contributing to spot formation necessary for recording or reproduction on a predetermined information recording surface. It is a luminous flux of a number or more.
- the numerical aperture necessary for recording or reproducing the CD corresponds to a numerical aperture higher than 0-0.43 or 0.45. This refers to a light beam that has an aberration of 0.07 rms or more (in this case, ⁇ is the CD operating wavelength) for the incident light beam.
- ⁇ is the CD operating wavelength
- the term “flare” refers to a property of irradiating an incident light beam onto the information recording surface as a light beam causing such aberration.
- the central region has the first optical path difference providing structure.
- the optical pickup device described in the item 31 is an optical pickup device using the objective optical element according to any one of the items 110 to 130.
- the objective optical element is arranged in a narrow sense in a state where the optical information recording medium is loaded in the optical pickup device, at the position closest to the optical information recording medium, and opposed to the optical information recording medium.
- it refers to an optical element that can be actuated by an actuator at least in the optical axis direction.
- the first optical information recording medium refers to, for example, information recording / reproducing with an objective optical element of NAO. 65 to 0.67, and a protective layer having a thickness of about 0.6 mm.
- NAO.85 objective optical elements record and play back Z information and have a protective layer with a thickness of about 0.1 mm (eg, Blu-ray disc).
- Disc, BD Blu-ray disc
- the second optical information recording medium includes not only DVD-ROM and DVD-Video used exclusively for playback, but also various DVD-type optical discs such as DVD-RAM, DVD-R and DVD-RW which also play / record. It is a thing.
- the third optical information recording medium refers to a CD-type optical disk such as a CD-R or a CD-RW. Note that, in this specification, the thickness of the protective layer includes the thickness Omm.
- FIG. 1 shows a first optical pickup device PU that can appropriately record and reproduce information and reproduce Z from high-density optical disks HD (first optical disk), DVD (second optical disk), and CD (third optical disk).
- FIG. 2 is a diagram schematically showing the configuration of FIG.
- the optical pickup device PU is a blue-violet semiconductor laser L D1 (first light source) that emits a 408-nm laser light beam (first light beam) when performing information recording and Z reproduction on a high-density optical disk HD.
- a red semiconductor laser (second light source) that emits a 658 nm laser beam (second light beam) that is emitted when performing information recording and Z reproduction on DVDs, and performs information recording and Z reproduction on CDs
- the laser unit 2L1P which contains an infrared semiconductor laser (third light source) that emits light and emits a 785 nm laser light beam (third light beam) in a single knockout, reflection from the information recording surface RL1 of the high-density optical disk HD
- the first photodetector PD1 that receives the light beam
- the second photodetector PD2 that receives the reflected light beam from the information recording surface RL2 of DVD and the information recording surface RL3 of CD
- the blue-violet semiconductor laser LD1 when performing Z recording of information on the high-density optical disk HD, the blue-violet semiconductor laser LD1 is used as shown by the solid line in FIG. Flash.
- the divergent light beam emitted from the blue-violet semiconductor laser LD1 is converted into a parallel light beam by the first collimating lens COL1, then passes through the first polarizing beam splitter BS1, and passes through the second polarizing beam splitter BS2.
- the beam diameter is regulated by the stop STO, and the spot is formed on the information recording surface RL1 by the objective optical element OBJ via the first protective layer PL1.
- the effect of the objective optical element OBJ on the light beam of wavelength ⁇ 1 will be described later.
- the objective optical element OBJ performs focusing / tracking by a two-axis actuator AC 1 arranged around the objective optical element OBJ.
- the reflected light beam modulated by the information pits on the information recording surface RL1 passes through the objective optical element OBJ and the second polarizing beam splitter BS2 again, is reflected by the first polarizing beam splitter BS1, and is reflected by the sensor lens.
- the astigmatism is given by SEN1, converted into a convergent light beam by the third collimating lens COL3, and converged on the light receiving surface of the first photodetector PD1.
- the information recorded on the high-density optical disk HD can be read using the output signal of the first photodetector PD1.
- the second light source of the laser unit 2L1P is caused to emit light.
- the divergent light beam emitted from the laser unit 2L1P passes through the third polarizing beam splitter and the fourth polarizing beam splitter as indicated by the dotted line in FIG. 1 and is collimated by the second collimating lens COL2.
- the light is reflected by the second polarizing beam splitter BS2, and becomes a spot formed on the information recording surface RL2 by the objective optical element OBJ via the second protective layer PL2.
- the effect of the objective optical element OBJ on the light beam of wavelength 2 will be described later.
- the objective optical element OBJ performs focusing / tracking by a two-axis actuator AC1 disposed around the objective optical element OBJ.
- the reflected light flux modulated by the information pits on the information recording surface RL2 passes through the objective optical element OBJ again, is reflected by the second polarizing beam splitter BS2, is converted by the second collimating lens COL2 into a convergent light flux, and The light is reflected by the polarizing beam splitter BS4, is given astigmatism by the second sensor lens SEN2, and converges on the light receiving surface of the second photodetector PD2. And Thus, information recorded on the DVD can be read using the output signal of the second photodetector PD2.
- the third light source of the laser unit 2L1P is caused to emit light.
- the divergent light beam emitted from the laser unit 2L1P passes through the third polarizing beam splitter and the fourth polarizing beam splitter, and is converted into a parallel light beam by the second collimator lens COL2.
- the light is reflected by the polarizing beam splitter BS2 and becomes a spot formed on the information recording surface RL3 by the objective optical element OBJ via the third protective layer PL3.
- the effect of the objective optical element OBJ on the light beam of wavelength 3 will be described later.
- the objective optical element OBJ performs focusing / tracking by a two-axis actuator AC1 arranged around the objective optical element OBJ.
- the reflected light beam modulated by the information pits on the information recording surface RL3 passes through the objective optical element OBJ again, is reflected by the second polarizing beam splitter BS2, is converted by the second collimating lens COL2 into a convergent light beam, and The light is reflected by the polarization beam splitter BS4, is given astigmatism by the second sensor lens SEN2, and converges on the light receiving surface of the second photodetector PD2. Then, the information recorded on the CD can be read using the output signal of the second photodetector PD2.
- FIG. 2 is a schematic sectional view of the objective optical element OBJ, and the optical surface shape is exaggerated.
- the objective optical element OBJ is composed of an error correction element L1 and a light condensing element L2.
- a flange unit integrally formed with the optical function unit is provided around each optical function unit (the area of the aberration correction element L1 and the light condensing element L2 through which the first light beam passes).
- the flanges are integrated by joining a part of the flanges.
- the optical surface S 1 (incident surface) of the aberration correction element L 1 on the side of the semiconductor laser light source is concentric with the optical axis L corresponding to the region inside NA 3 as the center. It is divided into a first region (center region) A1 containing L and a concentric second region (peripheral region) A2 formed in a region outside the first region A1. Further, a first diffraction structure 10 as a first optical path difference providing structure is formed in the first region A1.
- the first diffraction structure 10 has a plurality of concentric grooves (discontinuous grooves) centered on the optical axis having the same depth dl. 11), and the second diffraction structure 20 periodically forms a concentric annular zone 23 centered on the optical axis L having a stepped structure having a predetermined number of step portions 21 and discontinuous portions 22 therein.
- the formed structural force is a plurality of concentric grooves (discontinuous grooves) centered on the optical axis having the same depth dl. 11), and the second diffraction structure 20 periodically forms a concentric annular zone 23 centered on the optical axis L having a stepped structure having a predetermined number of step portions 21 and discontinuous portions 22 therein.
- the first diffraction structure 10 may have a stepped configuration as schematically shown in FIGS. 3 (a) and 3 (b), for example, in addition to the configuration shown in FIG. .
- the first diffraction structure 10 substantially gives a phase difference only to the light beam of wavelength 3 out of the light beams of wavelength 1, wavelength 2, and wavelength 3 passing through the groove 11, and
- the luminous flux of ⁇ 1 and ⁇ 2 is set so as not to give a substantial phase difference. Since the luminous flux of wavelength 3 is substantially subjected to a diffracting action by being given a phase difference, the diffracted light having the highest diffraction efficiency among the diffracted light of wavelength 3 generated by this is used for recording information on CD and ⁇ ⁇ . Or it can be used for playback.
- the refractive index of the aberration correction element L 1 on which the first diffraction structure 10 is formed with respect to the light beam of wavelength ⁇ 1 is nl
- the step amount of the groove 11 in the first diffraction structure 10 in the optical axis direction Is dl
- the number of discontinuous parts is ml (integer)
- d ⁇ 1 / (nl-1)
- the step dl of the first diffraction structure 10 is set to a depth that is almost an integral multiple of the wavelength ⁇ 1.
- a light beam of wavelength ⁇ 1 is incident on the groove structure in which the depth of the step dl is set as described above, an optical path difference of almost an integral multiple of ⁇ 1 is generated between adjacent steps. Since substantially no phase difference is given to the light beam having the wavelength ⁇ 1, the incident light beam having the wavelength ⁇ 1 is transmitted through the first diffraction structure 10 without being diffracted. Further, when a light beam having a wavelength of 2 is incident on this diffraction structure, substantially no phase difference is given, and the light beam is transmitted as it is.
- a phase difference corresponding to the depth of the groove and the number of discontinuous portions is generated for the incident light beam having the wavelength ⁇ 3.
- this diffraction light it is possible to record and reproduce information on CDs, as well as to correct chromatic aberration of CDs and spherical aberration due to temperature changes.
- recording / reproducing information on / from the CD only the light beam having passed through the first area A1 of the light beam having the wavelength ⁇ 3 is used, so that the light beam having the wavelength ⁇ 3 which has passed through the second area ⁇ 2 is used. It becomes unnecessary light.
- the diffractive structure formed in the second area A2 so that the light flux of the wavelength 3 passing through the second area ⁇ 2 is not condensed on the information recording surface RL3 of the CD, and is generated by this. It is also possible to flare the diffracted light with relatively high diffraction efficiency (for example, 30% or more) of the different order diffracted light.
- the objective optical element OBJ can be provided with an aperture limiting function for NA3, and a powerful diffraction structure discontinuously reduces the longitudinal spherical aberration of the light beam of wavelength ⁇ 3 from the first area A1 to the second area A2.
- the detection accuracy of the reflected light of the light beam of wavelength 3 in the second photodetector PD2 can be improved.
- a plurality of diffracted lights of wavelength 3 may have almost the same diffraction efficiency (for example, about 40%). In such a case, Higher diffraction efficiency All of the multiple diffracted light or the diffracted light that may be condensed on the information recording surface RL3 of the CD will be flared.
- a third optical path difference providing structure 40 is formed on the optical surface S2 (output surface) of the aberration correction element L1 on the optical disk side.
- the third optical path difference providing structure 40 is composed of a plurality of orbicular zones 17 in which the direction of the step 16 is the same within the effective diameter, and the cross-sectional shape including the optical axis L is a step shape.
- the phase difference is not substantially given to the incident light beams of the wavelengths ⁇ 1 and ⁇ 2.
- the third optical path difference providing structure 40 provides an optical path difference of ⁇ times the wavelength ⁇ 1 when the incident light beam of the wavelength ⁇ 1 passes through each of the orbicular zones 17, and 2 is set to give an optical path difference of Q times the wavelength ⁇ 2 when passing through each of the annular zones, and using an optical path difference function ⁇ (h),
- Wavelength, hmax is the height from the optical axis L that is the numerical aperture NA1 of the high-density optical disc HD [0075]
- the first diffraction structure 10 is obtained by using the first optical path difference function ⁇ (h)
- the wavelength ⁇ 1 and ⁇ 2 are perpendicularly incident on the optical surface on which the second optical path difference providing structure 40 is formed (the emission surface S 2 in the present embodiment), the wavelength ⁇ 1
- the difference in the incident angle of light due to the diffracting structure of the light beam of and 2 is expressed by the following formulas (6) and (7).
- nl, n2 Refractive index of aberration correction element LI at wavelength 1 and ⁇ 2
- the influence on the refractive power of an optical element is greater attributable to a change in the wavelength than that attributable to a change in the refractive index of the optical element itself.
- the bending (emission angle) by the third optical path difference providing structure 40 depends on the wavelength change of the wavelength 1 and the wavelength ⁇ 2.
- the third optical path difference providing structure so that ⁇ (hmax)> 0, when the light flux of wavelength ⁇ 1 and 2 has a wavelength variation of about several nm,
- the aberration generated by the second diffraction structure 50 and the first diffraction structure 10, which are the second optical path difference providing structures, is reduced by the second optical path difference. It can be reduced by the application structure 40.
- a second diffraction structure 50 is formed on the optical surface S 1 (incident surface) of the light-collecting element L2 on the semiconductor laser light source side.
- the second diffraction structure 50 includes a plurality of orbicular zones 15, and has a sawtooth cross section including the optical axis L.
- the light beams of wavelengths ⁇ 1, e 2 and e 3 that have passed through the aberration correction element L 1 are diffracted by the second diffraction structure 50, and the L-order diffracted light (L is (Even number) forms a condensed spot on the information recording surface RL1 of the high-density optical disc HD after undergoing refraction at the exit surface S2 of the condensing element L2, and generates a second-order diffracted light ( ⁇ Is an integer) forms a converging spot on the information recording surface RL2 of the DVD after undergoing refraction at the exit surface of the condensing element L2, and the ⁇ th order diffracted light ( ⁇ is an integer) of the light beam of wavelength ⁇ 3 is After being subjected to a refraction effect on the exit surface of the light-collecting element L2, a light-converged spot is formed on the information recording surface RL3 of the CD.
- L is (Even number) forms a condensed spot on the information recording surface
- the second diffraction structure 50 performs aberration correction so that the L-order diffracted light of the light beam of the wavelength ⁇ 1 forms a good condensed spot on the information recording surface RL 1 of the high-density optical disc HD!
- the aberration correction is performed to form a good condensed spot on the information recording surface RL2 of the DVD by the phase difference given when the second-order diffracted light of the light beam of wavelength ⁇ 2 passes through the first diffraction structure 10.
- the third order diffracted light of the light beam of wavelength ⁇ 3 is designed to perform aberration correction so as to form a good condensing spot on the information recording surface RL3 of the CD.
- the objective optical element OBJ has a two-group configuration including the aberration correction element L1 and the condenser L2.
- the diffraction power and the refraction power can be shared between the two optical elements, and there is an advantage that the degree of freedom in design is improved.
- the present invention is not limited to this, and the objective optical element OBJ can be replaced by a single lens.
- the optical path difference providing structure and the diffractive structure may be provided on the entrance surface and the exit surface of the lens.
- the condenser element L2 can be a glass lens. Occurrence can be suppressed.
- the first diffraction structure 10 at the incidence S1 of the aberration correction element L1. If the first diffractive structure 10 is formed from a stepped portion orthogonal to the optical axis, the step amount in the optical axis L direction becomes larger than that of the saw-toothed structure, and vignetting occurs due to oblique incidence of the light beam, thereby lowering the diffraction efficiency. This is because the first diffraction structure 10 is desirably provided on a surface on which each light beam that is to be prevented as a parallel light is incident as parallel light.
- the focal length of the aberration correction element L1 is fl1
- the focal length of the light-collecting element L2 is fl2
- the focal position of the Nth-order diffracted light and the focal position of the (N ⁇ l) th-order diffracted light are shifted by 0.1 Olmm in the optical axis L direction. It is preferable to separate them.
- the objective optical element may have an aperture limiting function.
- the aperture limiting function may be a function of flaring a light beam having a predetermined wavelength by a diffraction structure. For example, on at least one optical surface of the objective optical element OBJ, a concentric central region including the optical axis and centered on the optical axis, and a central region around the central region.
- the optical pickup device PU described in the above embodiment, a rotation drive device for rotatably holding the optical disk, and a control device for controlling the driving of these various devices are mounted, so that the optical disk for the optical disk is mounted.
- An optical information recording / reproducing apparatus capable of performing at least one of recording information and reproducing information recorded on an optical disk can be obtained.
- the objective optical element OBJ is composed of two groups, an aberration correction element L1 and a condensing element L2, and the entrance surface S1 (third surface) of the aberration correction element L1 is
- the emission surface S2 (fourth surface) is an aspheric surface
- the entrance surface S1 (fourth surface) and the emission surface S2 (fifth surface) of the light-collecting element L2 are aspheric surfaces.
- the first diffraction structure 10 (first phase difference structure) is formed on the entrance surface S1 of the aberration correction element L1, and the third optical path difference providing structure is provided on the exit surface S2 of the aberration correction element L1.
- a second diffraction structure 50 (second phase difference structure) having a sawtooth cross section including the optical axis is formed on the incident surface S1 of the light-collecting element L2.
- Table 1 shows the lens data.
- Ri is the radius of curvature
- di is the i-th surface force
- ni is the refractive index of each surface.
- an exponent of 10 for example, 2. 5 X 10- 3
- E e.g., 2. 5 XE-3
- di represents the displacement from the i-th surface to the (i + 1) -th surface.
- 1 is an optical path difference for 5 wavelengths
- 2 is an optical path difference for 3 wavelengths, and does not diffract because there is almost no phase difference.3rd surface Aspherical surface coefficient
- the incident surface (fourth surface) and the outgoing surface (fifth surface) of the light-collecting element are respectively defined around the optical axis, which are defined by equations obtained by substituting the coefficients shown in Table 1 into Equation 1 below. It is formed on an axisymmetric aspheric surface.
- X (h) is an axis in the optical axis direction (the traveling direction of light is assumed to be positive)
- ⁇ is a conic coefficient
- A is
- h is the height of optical axis force.
- optical path length given to the light flux of each wavelength by the first diffraction structure is defined by a mathematical expression obtained by substituting the coefficients shown in Table 1 into the optical path difference function of Expression 2.
- B is a coefficient of the optical path difference function.
- FIG. 4 (a)-Fig. 4 (c) show the vertical direction of the luminous flux (HD) of wavelength ⁇ 1, the luminous flux of wavelength 2 (DVD) and the luminous flux (CD) of wavelength ⁇ 3 in Example 1.
- FIG. 3 is a spherical aberration diagram, in which the vertical axis represents NA when the DVD aperture diameter is set to 1, and the horizontal axis represents SA (mm), and the dotted line represents a required aperture diameter for each optical disc.
- FIG. 5 is a diagram illustrating a wavefront aberration characteristic at the time of wavelength fluctuation in the first embodiment.
- This comparative example is an example in which a single diffraction structure is provided for one objective lens to perform spherical aberration.
- Table 2 shows the lens data.
- Ri indicates the radius of curvature
- di indicates the position in the optical axis direction up to the (i + 1) th surface force
- ni indicates the refractive index of each surface.
- 6 (a) to 6 (c) show longitudinal spherical aberration diagrams of the comparative example
- FIG. 7 shows a wavefront aberration characteristic of the comparative example when the wavelength changes.
- NA1 0.65
- NA2 0.65
- NA3 0.51
- the vertical length is within the required numerical aperture.
- the spherical aberration of the CD of the comparative example is continuous, and the spherical aberration of the CD of the embodiment is not. It is continuous, indicating that aperture restriction is required.
- An optical surface or the like for correcting spherical aberration generated by a wavelength change of several nm to several tens of nm caused by the diffraction structure can be provided as necessary.
- an objective optical element that can perform favorable spherical aberration correction even when light beams having three different wavelengths are incident.
Abstract
Description
Claims
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CN2005800022442A CN1910670B (zh) | 2004-03-15 | 2005-03-04 | 对物光学元件以及光拾取装置 |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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JP2004073024 | 2004-03-15 | ||
JP2004-073024 | 2004-03-15 |
Publications (1)
Publication Number | Publication Date |
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WO2005088624A1 true WO2005088624A1 (ja) | 2005-09-22 |
Family
ID=34918646
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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PCT/JP2005/003715 WO2005088624A1 (ja) | 2004-03-15 | 2005-03-04 | 対物光学素子及び光ピックアップ装置 |
Country Status (4)
Country | Link |
---|---|
US (1) | US7525879B2 (ja) |
KR (1) | KR20070012785A (ja) |
CN (1) | CN1910670B (ja) |
WO (1) | WO2005088624A1 (ja) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7545573B2 (en) | 2007-01-10 | 2009-06-09 | Nikon Corporation | Projector optical system, projector, and method for forming real image in use of projector optical system |
Families Citing this family (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2004032127A2 (en) * | 2002-09-30 | 2004-04-15 | Konica Minolta Holdings, Inc. | Optical element, objective optical element and optical pickup device |
CN1877716B (zh) * | 2005-05-23 | 2011-11-16 | Hoya株式会社 | 物镜和光学信息读取/写入装置 |
US7738345B2 (en) * | 2005-07-12 | 2010-06-15 | Hoya Corporation | Optical disc drive and objective lens for the same |
JP2009252309A (ja) * | 2008-04-08 | 2009-10-29 | Hoya Corp | 光情報記録再生装置用対物レンズ、および光情報記録再生装置 |
JP7091053B2 (ja) * | 2017-10-27 | 2022-06-27 | キヤノン株式会社 | 撮像装置および焦点検出方法 |
Citations (3)
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JP2001060336A (ja) * | 1998-10-28 | 2001-03-06 | Matsushita Electric Ind Co Ltd | 光学ヘッド |
JP2002056560A (ja) * | 2000-08-08 | 2002-02-22 | Samsung Electronics Co Ltd | 収差補正素子及びこれを採り入れた光ピックアップ装置 |
WO2003075267A1 (fr) * | 2002-03-06 | 2003-09-12 | Matsushita Electric Industrial Co., Ltd. | Mecanisme de tete optique et dispositif de lecture d'informations optiques utilisant un tel mecanisme, lecteur de disque optique, systeme de navigation automobile, enregistreur de disque optique et serveur de disque optique utilisant ce dispositif de lecture d'informations optiques |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN1248209C (zh) * | 2001-04-05 | 2006-03-29 | 皇家菲利浦电子有限公司 | 光学扫描装置 |
US7206276B2 (en) * | 2001-10-12 | 2007-04-17 | Konica Corporation | Objective lens, optical element, optical pick-up apparatus and optical information recording and/or reproducing apparatus equipped therewith |
EP1313095B1 (en) * | 2001-11-15 | 2008-10-15 | Samsung Electronics Co. Ltd. | Compatible optical pickup |
JP4254469B2 (ja) * | 2003-05-23 | 2009-04-15 | 日本ビクター株式会社 | 光ピックアップ装置及び光記録媒体駆動装置 |
WO2005043523A1 (ja) * | 2003-11-04 | 2005-05-12 | Konica Minolta Opto, Inc. | 光ピックアップ装置及び発散角変換素子 |
-
2005
- 2005-03-04 CN CN2005800022442A patent/CN1910670B/zh not_active Expired - Fee Related
- 2005-03-04 KR KR1020067013892A patent/KR20070012785A/ko not_active Application Discontinuation
- 2005-03-04 WO PCT/JP2005/003715 patent/WO2005088624A1/ja active Application Filing
- 2005-03-10 US US11/076,232 patent/US7525879B2/en not_active Expired - Fee Related
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2001060336A (ja) * | 1998-10-28 | 2001-03-06 | Matsushita Electric Ind Co Ltd | 光学ヘッド |
JP2002056560A (ja) * | 2000-08-08 | 2002-02-22 | Samsung Electronics Co Ltd | 収差補正素子及びこれを採り入れた光ピックアップ装置 |
WO2003075267A1 (fr) * | 2002-03-06 | 2003-09-12 | Matsushita Electric Industrial Co., Ltd. | Mecanisme de tete optique et dispositif de lecture d'informations optiques utilisant un tel mecanisme, lecteur de disque optique, systeme de navigation automobile, enregistreur de disque optique et serveur de disque optique utilisant ce dispositif de lecture d'informations optiques |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7545573B2 (en) | 2007-01-10 | 2009-06-09 | Nikon Corporation | Projector optical system, projector, and method for forming real image in use of projector optical system |
Also Published As
Publication number | Publication date |
---|---|
US7525879B2 (en) | 2009-04-28 |
CN1910670B (zh) | 2010-08-04 |
US20050201250A1 (en) | 2005-09-15 |
KR20070012785A (ko) | 2007-01-29 |
CN1910670A (zh) | 2007-02-07 |
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