| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to detect the tracking errors of optical disks varying in tack pitches and recording desisties with good accuracy bay a three- beam method without entailing the increase in the size of the device and the increase in its cost. SOLUTION: This device 1 has a composite diffraction grating 6 having a diffraction grating region forming three beams for a DVD by diffracting a laser beam and a diffraction grating region forming the three beams for the CD commonly having the main beam for the three beams. When the DVD is reproduced, the three beams for the DVD are condensed as a light spot to the position suitable for tracking error detection on the DVD via the object lens 8 (DVD) for the DVD. Similarly, the three beams for a CD are condensed as a light spot to the position suitable for the tracking error detection on the CD via the object lens 8 (CD) for the CD in reproducing the CD. Then, the tracking error detection of both of the DVD and the CD is exactly executed without requiring a mechanism for rotating the diffraction grating for forming the three beams and without making combination use of other tracking error detection methods. |
