| 摘要 |
PURPOSE:To miniaturize a tracking actuator by providing a means for photodetecting a part of a light beam which is made incident on an objective lens, and a means for varying a characteristic of the photodetected light beam in accordance with a movement of the objective lens. CONSTITUTION:In order to form a spot on an optical disk 10, a part of a laser luminous flux 29 which is made incident on an objective lens 20 fixed to a lens arm 23 is made incident on a mirror 6 and reflected, and made incident on two photodetectors 27, 28 roughly equally. When a lens holder 24 rotates and a position of the objective lens 20 is shifted from a neutral position, the mirror 26 also rotates and moves and the balance of the photodetecting quantity of the photodetectors 27, 28 is broken, and when a difference of the detected photodetecting quantity is inputted to a control system, a tracking actuator 22 is controlled so as to be always held in a neutral position.
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