US 6,473,387 B1Granted

Optical disc apparatus

AssigneeAsahi Kogaku Kogyo Kabushiki Kaisha

InventorsKoichi Maruyama, Takashi Yamanouchi

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Abstract

Disclosed is an optical disc apparatus that is adapted for DVD, CD and CD-R. The optical system includes a laser module and an objective lens that converges a divergent laser beam emitted from the laser module onto information layers of optical discs. The laser module is provided with a pair of emission points that are in close proximity to each other, and a pair of light receiving elements. A focusing mechanism moves the objective lens so that the beam spot follows an information layer of the optical disc. The objective lens is provided with the diffractive lens structure to have a wavelength dependence such that the spherical aberration varies in response to the change of the wavelength. Thereby, the variation of the spherical aberration due to the change of the thickness of the cover layer can be canceled by changing the wavelength.

Claims10

Dependent claims

An optical disc apparatus that is adapted for a plurality of kinds of optical discs whose cover layers are different in thickness, said apparatus comprising:

a light source portion that has a plurality of emission points in close proximity to each other, said emission points emitting divergent laser beams at different wavelengths, respectively, said emission points being switched in accordance with the thickness of said cover layer;
an objective lens for converging divergent laser beam from said light source portion onto an information layer of said optical disc through said cover layer thereof;
a light receiving portion that receives the reflected light beam from said optical disc to produce signals;
and
a focusing mechanism that moves said objective lens such that the distance between said objective lens and said optical disc increases as the thickness of said cover layer decreases,
wherein the distances between said respective emission points and the surfaces of said cover layers are constant regardless of the thickness of said cover layer.

3 more elements

Dependencies are inferred from the claim text.

Facts

Application: 09/655,880Filed 6 Sep 2000
Priority: JP 11-2519936 Sep 1999
Granted: 29 Oct 2002
Term ends: Not estimatedThe source records don’t support an estimate.

Classification7 codes

G11B 7/1353
Means for guiding the beam from the source to the record carrier or from the record carrier to the detector: diffractive elements, e.g. holograms…
G11B 7/123
Heads, e.g. forming of the optical beam spot or modulation of the optical beam: integrated head arrangements, e.g. with source and detectors…
G11B 7/1275
Lasers; Multiple laser arrays: two or more lasers having different wavelengths
G11B 7/1374
Lenses: objective lenses