Objective lens, optical head, optical system, and design method for objective lens
AssigneeHitachi Maxell, Ltd.
InventorsYutaka Makino, Yasuyuki Sugi
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Abstract
An objective lens of this embodiment is used in an optical head in which a distance between a DVD laser and a CD laser is fixed. The objective lens focuses a laser beam emitted from the DVD laser on a DVD by a numerical aperture of 0.60, and focuses a laser beam emitted from the CD laser on a CD by an numerical aperture of 0.47. The wavefront aberration in design for CD is set greater than the wavefront aberration in design for DVD.
Claims9
An objective lens for use in an optical head having a fixed distance between a first laser emitting a laser beam with a wavelength λ1 and a second laser emitting a laser beam with a wavelength λ2 being longer than the wavelength λ1, the objective lens focusing the laser beam emitted from the first laser on a first optical disk by a first numerical aperture and focusing the laser beam emitted from the second laser on a second optical disk by a second numerical aperture being smaller than the first numerical aperture,
- wherein wavefront aberration in design for the second optical disk is greater than wavefront aberration in design for the first optical disk, and a ratio t1/(t1+t2) of a distance t1 from an optical axis to the first laser and a distance (t1+t2) between the first laser and the second laser is smaller than 0.80.
An objective lens for use in an optical head having a fixed distance between a first laser emitting a laser beam with a wavelength λ1 and a second laser emitting a laser beam with a wavelength λ2 being longer than the wavelength λ1, the objective lens focusing the laser beam emitted from the first laser on a first optical disk by a first numerical aperture and focusing the laser beam emitted from the second laser on a second optical disk by a second numerical aperture being smaller than the first numerical aperture,
- wherein composite aberration (C22+AS22)1/2 of coma aberration C2 and astigmatism AS2 of the second optical disk in design is greater than composite aberration (C12+AS12)1/2 of coma aberration C1 and astigmatism AS1 of the first optical disk in design.
A design method for an objective lens for use in an optical head having a fixed distance between a first laser emitting a laser beam with a wavelength λ1 and a second laser emitting a laser beam with a wavelength λ2 being longer than the wavelength λ1, the objective lens focusing the laser beam emitted from the first laser on a first optical disk by a first numerical aperture and focusing the laser beam emitted from the second laser on a second optical disk by a second numerical aperture being smaller than the first numerical aperture,
- wherein wavefront aberration in design for the second optical disk is greater than wavefront aberration in design for the first optical disk, and if coma aberration and astigmatism of the first optical disk in design are C1 and AS1, respectively, and coma aberration and astigmatism of the second optical disk in design are C2 and AS2, respectively, values of C1, AS1, C2, and AS2 are determined so as to satisfy:
- 0.25<(C12+AS12)1/2(C22+AS22)1/2<0.80.
A design method for an objective lens for use in an optical head having a fixed distance between a first laser emitting a laser beam with a wavelength λ1 and a second laser emitting a laser beam with a wavelength λ2 being longer than the wavelength λ1, the objective lens focusing the laser beam emitted from the first laser on a first optical disk by a first numerical aperture and focusing the laser beam emitted from the second laser on a second optical disk by a second numerical aperture being smaller than the first numerical aperture,
- wherein wavefront aberration in design for the second optical disk is greater than wavefront aberration in design for the first optical disk, and a ratio t1/(t1+t2) of a distance t1 from an optical axis to the first laser and a distance (t1+t2) between the first laser and the second laser is smaller than 0.80.
An objective lens for use in an optical head having a fixed distance between a first laser emitting a laser beam with a wavelength λ1 and a second laser emitting a laser beam with a wavelength λ2 being longer than the wavelength λ1, the objective lens focusing the laser beam emitted from the first laser on a first optical disk by a first numerical aperture and focusing the laser beam emitted from the second laser on a second optical disk by a second numerical aperture,
- wherein composite aberration (C12+AS12)1/2 of coma aberration C1 and astigmatism AS1 of the first optical disk and composite aberration (C22+AS22)2 of coma aberration C2 and astigmatism AS2 of the second optical disk satisfy:
- 0.25<(C12+AS12)1/2/(C22+AS22)1/2<0.80.
Dependencies are inferred from the claim text.