| 摘要 |
<p>A means for correcting the spherical aberration due to variations in substrate thickness in optical disks is described. A portion of the lead-in region of an optical disk (1) is provided with a particular pattern of pit trains. An optical disk apparatus is provided with an aberration correction element (14) which varies the diverging or converging angle of the incoming light beam to the condenser (13), and control means (20) for controlling the adjustement of the aberration correction element. When the disk is inserted into the optical disk apparatus, the apparatus plays back the particular pattern while moving the condenser back and forth along the optical axis. The amplitude of a playback signal output from a photodetector (12) with respect to focus error amount is determined by an aberration detecting section (21). The aberration correction element is controlled to minimize the difference in amplitude due to the focus offset amounts.</p> |
