Patent ID: 8059515
Filing Date: 2011-11-15
Classification: G11B

Abstract:
1. An optical pickup apparatus comprising: a light source; an objective lens for condensing light emitted from the light source on a surface of an optical recording medium; a diffraction element in which the light reflected from the optical recording medium enters; a light-receiving element in which a light beam diffracted by the diffraction element enters, the light-receiving element having a plurality of light-receiving regions, each of which produces an output signal responsive to the light quantity of the incident light beam; and a control-driving section that obtains differences among the output signals produced by a plurality of the light-receiving regions by calculation to derive a push-pull signal, and drives the objective lens under control on the basis of the push-pull signal, the diffraction element including: a forward region that serves to let a light beam enter, out of a plurality of the light-receiving regions, the one for producing an output signal bearing a same-sign relation to the push-pull signal; a reverse region that serves to let a light beam enter, out of a plurality of the light-receiving regions, the one for producing an output signal bearing an opposite-sign relation to the push-pull signal; a bright-dark contrast area where, out of light beams reflected from the optical recording medium, diffraction reflected light from a track borne on the surface of the optical recording medium enters; and a simple area where, out of the light beams reflected from the optical recording medium, simple reflected light from the optical recording medium enters and the diffraction reflected light does not enter, the light-receiving region including: a push-pull light-receiving region where light diffracted by the bright-dark contrast area enters; and an offset light-receiving region where the light diffracted by the bright-dark contrast area does not enter but light diffracted by the simple region enters, and the diffraction element including: a first diffraction region for diffracting incident light so that it can be directed to the push-pull light-receiving region; and a second diffraction region for diffracting incident light so that it can be directed to the offset light-receiving region, a plurality of the first diffraction regions and the second diffraction regions being arranged alternately in the tangential direction.