| 摘要 |
PROBLEM TO BE SOLVED: To lighten an actuator and to improve a high speed vibration characteristic for tracking and focusing operation by providing a liquid crystal unit on a fixed part of an optical pickup. SOLUTION: The actuator 17 makes a movable part containing an objective lens 18 and a polarizing plate 30, etc., and makes a light source 11, a beam splitter 12, a collimation 13 and the liquid crystal unit 20, etc., a fixed part. Then, in the state that a voltage from a power source isn't applied to a liquid crystal layer 21, a polarization direction of an incident beam is twisted by 90 deg., and in the state that the voltage from the power source is applied to the liquid crystal layer 21, the incident beam is made pass through as it is without converting the polarization direction. When the voltage is applied or isn't applied to the liquid crystal unit 20 based on a kind of an optical disk, the size of the beam transmitted to the objective lens 18 is adjusted so as to become an optimum numerical aperture according to the kind of the optical disk by actions of the liquid crystal unit 20 and the polarizing plate 30. |
