| 摘要 |
<P>PROBLEM TO BE SOLVED: To acquire a good signal/noise ratio of an RF signal in detecting a radial tilt of a reproduction dedicated optical record medium. <P>SOLUTION: An outgoing beam from a semiconductor laser 1 is split into three beams by a diffraction optical element 3a: the zeroth order beam, which is main beam, and the plus and minus first diffraction beams, which are sub beams. Subsequently, a truck error signal is detected from each of the main and sub beams using a phase difference method. By function of the diffraction optical element 3a, intensity distributions of main and sub beams are different when incoming to an objective lens 6. Thereby, if a radial tilt exits in a disk 7, phases of the track error signals between main and sub beams are different. Based on the difference of phases of the track error signals, a radial tilt of the disk 7 is detected. <P>COPYRIGHT: (C)2004,JPO |
