Optical head, LD module, optical recording-and-reproducing apparatus and diffraction element used in the optical recording-and-reproducing apparatus

摘要

A beam emitted from a light source 1 is separated into a main beam and a sub beam by a diffraction element 2. Because the diffraction element 2 has a diffraction pattern shaped like sinusoidal wave, the spot of the sub beam becomes larger than that of the main beam. As a result, the sub beam little contains any tracking cross component which is generated when the spot crosses any one of tracks of an optical disk 5. Accordingly, when a signal output from a detector provided for detecting the sub beam is subtracted from a push pull signal of the main beam, it is possible to obtain a tracking error signal or a focusing error signal substantially containing no DC offset component.