Objective lens, optical pickup, and optical drive device
AssigneeSony Corporation
InventorsKenji Yamamoto, Noriaki Nishi, Kimihiro Saito
Life of this patent
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Abstract
Provided is an objective lens, which is provided in an optical pickup including a spherical aberration correction mechanism which performs a spherical aberration correction with respect to laser light applied to a recording layer of an optical recording medium, having the recording layer on which information can be recorded at a plurality of positions in a depth direction, via the objective lens, and a tilt correction unit which varies a lens tilt angle which is a tilt angle of the objective lens, thereby performing a tilt correction.
Claims8
An objective lens, which is provided in an optical pickup including a spherical aberration correction mechanism which performs a spherical aberration correction with respect to laser light applied to a recording layer of an optical recording medium, having the recording layer on which information can be recorded at a plurality of positions in a depth direction, via the objective lens, and a tilt correction unit which varies a lens tilt angle which is a tilt angle of the objective lens, thereby performing a tilt correction,
- wherein, when a third-order spherical aberration variation (λrms) corresponding to an error of a condensed position of the laser light with respect to a predetermined reference layer position set inside the recording layer is denoted by ΔSA, the lens tilt angle (radian) is denoted by Ltilt, a third-order comatic aberration variation (λrms) generated by the lens tilt angle Ltilt is denoted by ΔCA, and a relationship therebetween is given by ΔCA/Ltilt=α*ΔSA, the objective lens is designed such that a value of α has a value in an allowable difference range which has an ideal value indicated by α=−6.32·NA (where NA is an effective numerical aperture of the objective lens), as a reference, and has a value in the allowable difference range set based on the third-order comatic aberration variation ΔCA and a Marechal criterion when the third-order spherical aberration variation ΔSA is the maximum and the lens tilt angle is the maximum.
An optical pickup comprising:
- a spherical aberration correction mechanism that performs a spherical aberration correction with respect to laser light applied to a recording layer of an optical recording medium, having the recording layer on which information can be recorded at a plurality of positions in a depth direction, via an objective lens;
- and
- a tilt correction unit that varies a lens tilt angle which is a tilt angle of the objective lens, thereby performing a tilt correction,
- wherein, when a third-order spherical aberration variation (λrms) corresponding to an error of a condensed position of the laser light with respect to a predetermined reference layer position set inside the recording layer is denoted by ΔSA, the lens tilt angle (radian) is denoted by Ltilt, a third-order comatic aberration variation (λrms) generated by the lens tilt angle Ltilt is denoted by ΔCA, and a relationship therebetween is given by ΔCA/Ltilt=α*ΔSA, the objective lens is designed such that a value of α has a value in an allowable difference range which has an ideal value indicated by α=−6.32·NA (where NA is an effective numerical aperture of the objective lens), as a reference, and has a value in the allowable difference range set based on the third-order comatic aberration variation ΔCA and a Marechal criterion when the third-order spherical aberration variation ΔSA is the maximum and the lens tilt angle is the maximum.
An optical drive device comprising an optical pickup which includes:
- a spherical aberration correction mechanism that performs a spherical aberration correction with respect to laser light applied to a recording layer of an optical recording medium, having the recording layer on which information can be recorded at a plurality of positions in a depth direction, via an objective lens;
- and
- a tilt correction unit that varies a lens tilt angle which is a tilt angle of the objective lens, thereby performing a tilt correction,
- wherein, when a third-order spherical aberration variation (λrms) corresponding to an error of a condensed position of the laser light with respect to a predetermined reference layer position set inside the recording layer is denoted by ΔSA, the lens tilt angle (radian) is denoted by Ltilt, a third-order comatic aberration variation (λrms) generated by the lens tilt angle Ltilt is denoted by ΔCA, and a relationship therebetween is given by ΔCA/Ltilt=α*ΔSA, the objective lens is designed such that a value of α has a value in an allowable difference range which has an ideal value indicated by α=−6.32·NA (where NA is an effective numerical aperture of the objective lens), as a reference, and has a value in the allowable difference range set based on the third-order comatic aberration variation ΔCA and a Marechal criterion when the third-order spherical aberration variation ΔSA is the maximum and the lens tilt angle is the maximum, and
- wherein the optical drive device performs information recording and/or reproduction for the optical recording medium.
Dependencies are inferred from the claim text.