Patent ID: 6741539
Filing Date: 2004-05-25
Classification: G11B

Abstract:
An optical system for an optical head employed in an optical disc drive, said optical disc drive using a plurality of optical discs, cover layers of the plurality of optical discs having different thickness, the optical system comprising:a light source unit provided with a plurality of light emitting points that are arranged close to each other, a plurality of diverging light beams having different wavelengths being emitted from said plurality of light emitting points, respectively, one of said plurality of light emitting points being used depending on a thickness of a cover layer of an optical disc; an objective lens that converges each of the plurality of diverging light beams emitted from said plurality of light emitting points on a data recording surface of an optical disc; and a light receiving unit that receives a light beam reflected by the data recording surface of the optical disc and generates electronic signals corresponding to the received beam, wherein an image magnification M of said objective lens satisfies the following condition for each of the plurality of diverging light beams: âˆ’0.144<M