| 摘要 |
PURPOSE: To embody an exact tracking control by detecting the light in which the zero-order diffracted light and first-order diffracted light interfere with each other among the reflected light rays from a beam spot and detecting the intensity of the reflected light rays of this beam spot. CONSTITUTION: In the reflected light rays of sub-spots 302, 303, the diffracted light of high order are distributed. A tracking signal photodetector 101 detects the region where the zero-order diffracted light and the +1st-order diffracted light interfere and, therefore, if the sub-spots 302, 303 exist on pits, the intensity of the reflected light rays thereof is minimized. The intensity increases gradually as going further from the pits and becomes the max. value when the subs-spots deviate completely from the pits and, therefore, there is no disorder in the tracking error signal obtd. by subtraction with a subtractor 304. The exact control of the tracking position of a main spot 301 is thus made possible. |
