# US 7,411,883 B2 · Optical pickup device, optical information recording and reproducing apparatus, expander lens, coupling lens and chromatic aberration correcting optical element > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,411,883 B2 - Document ID: US7411883B2 - Status: Granted - Kind: B2 - Application number: 10/826,524 - Filed: 2004-04-19 - Published: 2004-10-28 - Granted: 2008-08-12 - Earliest claimed: 2003-04-22 - Assignees: Konica Minolta Opto, Inc. - Inventors: Tohru Kimura; Nobuyoshi Mori - Web page: https://patentgrep.com/patent/US7411883B2 ## CPC - G11B 7/1275: Two or more lasers having different wavelengths - G11B 7/1353: Diffractive elements, e.g. holograms or gratings {(diffraction gratings per se G02B5/18; holograms per se G02B5/32; grating systems G02B27/44)} - G11B 7/1369: Active plates, e.g. liquid crystal panels or electrostrictive elements - G11B 7/1378: Separate aberration correction lenses; Cylindrical lenses to generate astigmatism; Beam expanders - G11B 7/13922: {passive} - G11B 7/13927: {during transducing, e.g. to correct for variation of the spherical aberration due to disc tilt or irregularities in the cover layer thickness} - G11B 2007/0006: {adapted for scanning different types of carrier, e.g. CD & DVD} - G11B 2007/0013: {for carriers having multiple discrete layers} - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) ## Abstract An optical pickup apparatus includes first and second light sources; an objective lens; a spherical aberration correcting optical unit; and a chromatic aberration correcting optical element which includes a diffractive surface on at least one optical surface of the chromatic aberration correcting optical element such that a diffractive structure which is constructed by a plurality of ring-shaped zones separated by fine steps is formed on the diffractive surface, wherein the depth of steps along an optical axis is designed so that n2, which is a diffraction order of a diffracted ray having a largest diffraction efficiency among diffracted rays caused when the second light flux enters into the diffractive structure, is a lower order than n1, which is a diffraction order of a diffracted ray having a largest diffraction efficiency among diffracted light rays caused when the second first light flux enters into the diffractive structure. ## Claims ### Claim 1 An optical pickup apparatus comprising: a first light source for emitting a first light flux with a first wavelength λ1 of 450 nm or less; a second light source for emitting a second light flux with a second wavelength λ2 which is in the range of 600 nm-700 nm; a third light source for emitting a third wavelength λ3 which is in the range of 730 nm-830 nm; an objective lens unit to converge the first light flux emitted by the first light source onto a first information recording surface of a first optical disk, to converge the second light flux emitted by the second light source onto a second information recording surface of a second optical disk with a different recording density from that of the first optical disk, and to converge the third light flux emitted by the third light source onto a third information recording surface of a third optical disk with a different recording density from those of the first and the second optical disks; a spherical aberration correcting optical unit which is arranged between both of the first light source and the second light source and the objective lens unit and is arranged in a common optical path of the first light flux and the second light flux; and a chromatic aberration correcting optical element which is arranged in the common optical path of the first light flux, the second light flux and the third light flux and includes a diffractive surface on at least one optical surface of the chromatic aberration correcting optical element such that a diffractive structure which is constructed by a plurality of ring-shaped zones separated by fine steps is formed on the diffractive surface, wherein the depth of steps along an optical axis is designed so that n2, which is a diffraction order of a diffracted ray having a largest diffraction efficiency among diffracted rays caused when the second light flux enters into the diffractive structure, is a lower order than n1, which is a diffraction order of a diffracted ray having a largest diffraction efficiency among diffracted light rays caused when the first light flux enters into the diffractive structure, and wherein the chromatic aberration correcting optical element satisfies one of the following combinations: (n1, n2, n3,)=(2, 1, 1), (4, 2, 2), (6, 4, 3), (8, 5, 4), (10, 6, 5) where n1, n2, and n3 are diffraction orders of diffracted rays with the largest diffraction efficiencies in the diffracted rays when the first, second and third light fluxes enter into the chromatic aberration correcting optical element, respectively. ### Claim 2 (depends on 1) The optical pickup apparatus of claim 1, wherein the spherical aberration correcting optical unit changes a slope angle of a marginal ray in an incident light flux to the objective lens unit by variably adjusting an interval between at least one lens group among lens groups composing the spherical aberration correcting optical unit and the objective lens unit. ### Claim 3 (depends on 1) The optical pickup apparatus of claim 1, wherein the chromatic aberration correcting optical element is arranged between both of the first light source and the second light source and the objective lens unit. ### Claim 4 (depends on 3) The optical pickup apparatus of claim 3, wherein the spherical aberration correcting optical unit comprises the chromatic aberration correcting optical element. ### Claim 5 (depends on 1) The optical pickup apparatus of claim 1, wherein the objective lens unit comprises the chromatic aberration correcting optical element. ### Claim 6 (depends on 1) The optical pickup apparatus of claim 1, wherein the optical pickup apparatus further comprises at least a coupling lens for converting a divergence angle of a light flux emitted by the first light source and introducing the converted light flux into the objective lens unit, and the spherical aberration correcting optical unit comprises the coupling lens and an expander lens including a positive lens group and a negative lens group and arranged in an optical path between the coupling lens and the objective lens unit. ### Claim 7 (depends on 1) The optical pickup apparatus of claim 1, wherein the spherical aberration correcting optical unit is a coupling lens for converting a divergence angle of a light flux emitted by the first light source and the second light source and introducing the converted light flux into the objective lens unit. ### Claim 8 (depends on 1) The optical pickup apparatus of claim 1, wherein the spherical aberration correcting optical unit includes a structure in which electrodes and a liquid crystal molecule layer are laminated alternately so that a refractive index distribution of the liquid crystal molecule layer is changed by applying a pre-defined voltage to the electrodes. ### Claim 9 (depends on 8) The optical pickup apparatus of claim 8, wherein the objective lens unit is united with the spherical aberration correcting optical unit into one body that performs a tracking operation. ### Claim 10 (depends on 1) The optical pickup apparatus of claim 1, wherein the spherical aberration correcting optical unit corrects a spherical aberration caused in the objective lens unit due to a wavelength difference between the first wavelength λ1 and the second wavelength λ2. ### Claim 11 (depends on 1) The optical pickup apparatus of claim 1, wherein the spherical aberration correcting optical unit corrects a spherical aberration caused by a variation of the first wavelength λ1 when the first wavelength λ1 varies in the range of ±10 nm. ### Claim 12 (depends on 1) The optical pickup apparatus of claim 1, wherein a recording density of the first optical disk is larger than that of the second optical disk, the first optical disk includes a first protective layer on a first information recording surface thereof, and the spherical aberration correcting optical unit corrects a spherical aberration caused by a thickness error of the first protective layer. ### Claim 13 (depends on 1) The optical pickup apparatus of claim 1, wherein: a recording density of the first optical disk is larger than that of the second optical disk, the first optical disk includes a multi-layer structure in which optically transparent layers and information recording surfaces are alternately laminated in this order from the light source side, and the spherical aberration correcting optical unit corrects a spherical aberration which is caused when the objective lens unit makes a focus jump from an i-th information recording surface to a j-th information recording surface, where i is an arbitrary integer satisfying 1≦i≦n, j is an arbitrary integer satisfying 1≦j≦n, j is different from i, and respective information recording surfaces in the multi-layer structure are arranged from a first information recording surface, to a second information recording surface, to an n-th information recording surface in this order from an information recording surface nearest to the light sources. ### Claim 14 (depends on 1) The optical pickup apparatus of claim 1, wherein a recording density of the first optical disk is larger than that of the second optical disk, the first optical disk includes a first protective layer with a thickness of t1 on a first information recording surface, the second optical disk includes a second protective layer with a thickness of t2 (t1>t2) on a second information recording surface, the spherical aberration correcting optical unit corrects a spherical aberration caused by a thickness difference between a thickness of the first layer and that of the second layer. ### Claim 15 (depends on 1) The optical pickup apparatus of claim 1, wherein the objective lens unit includes at least one plastic lens, the spherical aberration correcting optical unit corrects a refractive index variation resulting from an environmental temperature variation in the plastic lens included in the objective lens unit and/or a spherical aberration resulting from a refractive index distribution caused by a temperature distribution in the plastic lens. ### Claim 16 (depends on 1) The optical pickup apparatus of claim 1, wherein: a recording density of the first optical disk is larger than that of the second optical disk, the first optical disk includes a first protective layer on a first information recording surface thereof, a first magnification and a second magnification are different from each other, and where the first magnification is a magnification of the objective lens unit when information recording and/or reproducing is conducted on the first optical disk, and the second magnification is a magnification of the objective lens unit when information recording and/or reproducing is conducted on the second optical disk, and the spherical aberration correcting optical unit changes an objective point position of the objective lens unit corresponding to a difference of the first magnification and the second magnification. ### Claim 17 (depends on 1) The optical pickup apparatus of claim 1, wherein the optical pickup apparatus includes a coupling lens for converting divergence angles of the first light flux emitted by the first light source and the second light flux emitted by the second light source and introducing the light fluxes into the objective lens unit, and the coupling lens includes the chromatic aberration correcting optical element. ### Claim 18 (depends on 17) The optical pickup apparatus of claim 17, wherein the coupling lens comprises at least one plastic lens or a diffractive surface of the chromatic aberration correcting optical element, and the coupling lens functions to suppress a divergence angle variation in response to a temperature variation, or a converging angle variation in response to a temperature variation, for the first light flux emitted from the coupling lens. ### Claim 19 (depends on 18) The optical pickup apparatus of claim 18, wherein: a recording density of the first optical disk is larger than that of the second optical disk, the coupling lens is a plastic lens, and the optical pickup apparatus satisfies the following formula: {NA1·(1−m1)}4·(f12/fC)·|c1+(c2−c1)·PD/PC|<0.13·λ1 where NA1 is a numerical aperture of the objective lens unit at the time of information recording and/or representing on the first optical disk, m1 is a magnification of the objective lens unit at the time of information recording and/or representing on the first optical disk, f1 (mm) is a focal length of the objective lens unit for the first wavelength λ1 at the time of information recording and/or representing on the first optical disk, λ1 (mm) is the first wavelength, fC is a focal length of the coupling lens for the first wavelength λ1, n is a refractive index of the coupling lens for the first wavelength λ1, α is a linear expansion coefficient of the coupling lens, PD (mm−1) is a paraxial power of the diffractive surface for the first wavelength λ1, PC (mm−1) is a paraxial power of the coupling lens for the first wavelength λ1, dn/dλ is a change rate in a refractive index resulting from a temperature variation in the coupling lens, dλ/dt is a wavelength change rate resulting from the temperature variation, and c1 and c2 are defined by the following formulas: c1=1/(n−1)·dn/dt+1/(n−1)·dn/dλ·dλ/dt−α c2=1/λ1·dλ/dt−2α and where an added optical path length caused by the diffractive structure is defined by an optical path difference function represented by the formula: PD=−2·n1·B2·(λ1/λB) and n1 is a diffraction order of a diffracted ray with a largest diffraction efficiency among diffracted rays caused when the first light flux enters into the diffractive structure, and PD is defined by an added optical path length quantity caused by the following formula: ϕ b = n × ( λ / λ ⁢ ⁢ B ) × ∑ j = 0 ⁢ B 2 ⁢ j ⁢ h 2 ⁢ j where h (mm) is a height in a perpendicular direction to the optical path, B2j is an optical path difference function coefficient, n is a diffraction order of a diffracted ray with a largest diffraction efficiency among diffracted rays of an incident light flux, λ (nm) is a wavelength of an incident light flux to the diffractive structure and λB (nm) is a construction wavelength, or a blazed wavelength, of the diffractive structure. ### Claim 20 (depends on 19) The optical pickup apparatus of claim 19 which satisfies the following formula: |c1+(c2−c1)·PD/PC|/fC<0.08·λ1 (mm) ### Claim 21 (depends on 1) The optical pickup apparatus of claim 1, wherein the chromatic aberration correcting optical element comprises at least one optical surface with negative paraxial power and is an one-group optical element which conducts the first light flux almost parallel to the optical axis and emits an almost parallel light flux. ### Claim 22 (depends on 1) The optical pickup apparatus of claim 1, wherein the objective lens unit comprises at least two kinds of objective lenses: a first objective lens for recording and/or reproducing information on a first optical disk with a first pre-defined recording density; and a second objective lens for recording and/or reproducing information on a second optical disk with a second pre-defined recording density, wherein the pickup apparatus further comprises a switching mechanism for selectively switching the first and second objective lenses. ### Claim 23 (depends on 1) The optical pickup apparatus of claim 1, wherein the recording density of the first optical disk is larger than that of the second optical disk, and wherein a numerical aperture of the objective lens unit, when information recording and/or reproducing is conducted on the first optical disk, is 0.8 or more. ### Claim 24 (depends on 1) The optical pickup apparatus of claim 1, wherein the recording density of the first optical disk is larger than that of the second optical disk, a first protective layer has a thickness in the range of 0.07 mm-0.13 mm on the first information surface on the first optical disk, the second protective layer has a thickness in the range of 0.55 mm-0.65 mm on the second information surface of the second optical disk, and the optical pickup apparatus conducts recording and/or reproducing of information on the first optical disk and the second optical disk by converging the first light flux on each of the information recording surfaces of the first optical disk and the second optical disk. ### Claim 25 (depends on 1) An optical information recording and reproducing apparatus which comprises the optical pickup apparatus of claim 1 and is adapted to conduct at least one of recording information on the first to third optical disks and reproducing information recorded on the first to third optical disks. ### Claim 26 A coupling lens for an optical pickup apparatus comprising a first light source for emitting a first light flux with a first wavelength λ1 of 450 nm or less; a second light source for emitting a second light flux with a second wavelength λ2 which is in the range of 600 nm-700 nm; a third light source for emitting a third wavelength λ3 which is in the range of 730 nm-830 nm; an objective lens unit to converge the first light flux emitted by the first light source onto a first information recording surface of a first optical disk, to converge the second light flux emitted by the second light source onto a second information recording surface of a second optical disk, and to converge the third light flux emitted by the third light source onto a third information recording surface of a third obtical disk, wherein the second optical disk has a different recording density from that of the first optical disk, wherein the third optical disk has a different recording density from those of the first and the second optical disks, wherein the coupling lens is arranged between all of the first light source, the second light source, the third light source, and the objective lens unit, and wherein the coupling lens is in a common optical path of the first to third light fluxes, the coupling lens comprises a chromatic aberration correcting optical element which includes a diffractive surface on at least one optical surface of the chromatic aberration correcting optical element such that a diffractive structure which is constructed by a plurality of ring-shaped zones separated by fine steps is formed on the diffractive surface; the coupling lens is designed so that a diffraction order n2 for a diffracted ray having a largest diffraction efficiency among diffracted rays when the second light flux enters into the diffractive structure is a lower order than a diffraction order n1 for a diffracted ray having a largest diffraction efficiency among diffracted light rays when the first light flux enters into the diffractive structure; the coupling lens comprises a plurality of lens groups, and changes a slope angle of a marginal ray in an incident light flux to the objective lens unit by variably adjusting an interval between at least one lens group of the coupling lens and the objective lens unit; and the coupling lens satisfies one of the following combinations: (n1, n2, n3)=(2, 1, 1), (4, 2, 2), (6, 4, 3), (8, 5, 4), (10, 6, 5) where n1, n2 and n3 are diffraction orders of diffracted rays, wherein the diffracted rays have their largest diffraction efficiencies when the first, second, and third light fluxes enter into the chromatic aberration correcting optical element, respectively. ### Claim 27 (depends on 26) The coupling lens of claim 26, wherein a refractive index for the first wavelength λ1 of a lens constructing the chromatic aberration correcting optical element and including the diffractive surface is in the range of 1.5-1.6, the Abbe number for the d line of 587.6 nm is in the range of 50-60 and the depth (d0) of a step which is along an optical axis and closest to the optical axis satisfies one of the following: 1.2 μm