| 摘要 |
PURPOSE: To enable a correct detection of a tracking error by a simple construction by preventing occurrence of a DC bias in a tracking error signal even when a track slippage of an optical pickup occurs. CONSTITUTION: A return light from a optical disk 13 is reflected by a half- mirror surface 15a of a beam splitter 15 and cast on sensor parts formed by dividing a photodetector 16 in two. Based on a tracking error signal TE showing a difference between the lights cast thereon, an objective lens 14 is moved in a direction P being oblique at an angle of about 45 degrees to the direction of the radius of the optical disk 13 and correction is executed so that the TE be zero. In the case when a track slippage of the objective lens 14 occurs at this time, a spot on the photodetector 16 shifts along the line of division of the sensor, no change occurs in the ratio between the quantities of the incident light of the spot on the two sensor parts and, accordingly, no DC bias occurs in the signal TE. By this constitution, an accurate tracking error signal can be detected without necessitating a circuit for correcting the DC bias. |
