| 摘要 |
PURPOSE:To decrease parts of an optical head, to reduce an adjusting part, to make the optical head inexpensive, and to improve the reliability by constituting the optical head so that both servo-signals can be received by a single photodetector in a prism. CONSTITUTION:A luminous flux which has been emitted by a semiconductor laser 1 is condensed by a recording disk 4, reflected thereby and returns in the direction opposite to going, but when it comes to a part of a half mirror 2, it is deflected vertically against the direction of the semiconductor laser 1, reaches a prism 7 and the luminous flux is divided into four, and reaches a photodetector 8. In this case, by a shift of a spot 11 from an objective lens 3 and a track groove 12 on the recording disk 4, intensity of a light spot on the photodetector 8 is varied, therefore, by catching this variation, a tracking servo-signal is obtained. On the other hand, each half of a 0th-order diffracted light 10 of the remaining luminous flux reaches the photodetector 8, and a shape of the light spot on the photodetector 8 is varied in accordance with whether the objective lens 3 and the recording disk 4 are far or near, therefore, by catching this variation, a focusing servo-signal is obtained. |
