Patent ID: 7933189
Filing Date: 2011-04-26
Classification: G11B

Abstract:
1. An optical-disc focus optical system comprising: an optical modulating section for modulating or polarizing emitted light from a light source; an objective lens for converging emitted light, which has been modulated or polarized by the optical modulating section, onto an optical disc; an optical path diverging section for diverging, from an optical axis of the emitted light, reflected light reflected from the optical disc; an astigmatic optical system which includes a converging lens, a cylindrical lens and a 4-division detector with a dead zone placed on its dividing lines orthogonally intersecting each other, and by which reflected light diverged by the optical path diverging section is made to be received on the 4-division detector via the converging lens and the cylindrical lens by using an astigmatic method; and a lens drive unit for, based on a result of detection of reflected light by the 4-division detector, adjusting a position of the objective lens so that a spot shape of emitted light converged on the optical disc via the objective lens becomes closer to a focused point shape, wherein in the astigmatic optical system, the 4-division detector is positioned relative to an optical axis of the astigmatic optical system so that one of the dividing lines is placed along a longitudinal direction of an interference fringe of reflected light appearing on the 4-division detector, while the cylindrical lens is positioned relative to the optical axis of the astigmatic optical system so that a cylindrical axis of the cylindrical lens is placed at a 45° skew to the dividing line of the 4-division detector.