| 摘要 |
PURPOSE:To obtain a stable head of less focus position slippage by arranging a focus plate, which divides the intensity of light into two and has a prescribed reflecting surface, in the optical path of reflected light and receiving the reflected light by a photodetector divided into six. CONSTITUTION:A focus plate 12 having an upper face 12a and a lower face 12b is arranged in the focusing optical path of the reflected light from a disc 7, and the reflected light divided into two is received by one photodetector 13 divided to six sections 13a-13f. A prescribed focus error signal is obtained in accordance with differences of output currents of individual sections. In this case, though light spots 14 and 15 are moved in the direction of an arrow Y when a light source 1 is displaced in the direction of the arrow Y, their variances are cancelled by each other not to change the focus position if the length between spots is sufficiently longer than the extent of displacement, and thus, stable recording and reproducing are performed. |
