| 摘要 |
PROBLEM TO BE SOLVED: To provide a relatively inexpensive two focal points optical pickup device capable of obtaining a stable reproducing signal. SOLUTION: When an SD system disk is reproduced, a voltage is applied to a TN(twist nematic) liquid crystal plate 8 from a circuit 20, and the twisted angle of a deflection surface is made 0 deg.. Beam from a laser diode 11 is deflected in the vertical direction, and the beam transmitting through the TN liquid crystal plate 8 isn't varied in the deflection surface, and transmits through a polarizing beam splitter 9, and is deflected by a 45 deg. reflection plate 10 by a 90 deg. to be made incident on an objective lens 2 through a 1/4 wavelength plate 12. The light reflected by the disk is made incident on the reflection beam splitter 9 through the wavelength plate 12 and the reflection plate 10. At the point of time, since the deflection surface of the beam is varied by a further 90 deg., the beam becomes the lateral deflection, and is reflected by the reflection beam splitter 9 to be made incident on a focal point and a tracking position detective part 13. Since the voltage isn't applied to the TN liquid crystal plate 8 when a CD is reproduced, the beam emitted from the laser diode 11 transmits through the TN liquid crystal plate 8, and is reflected by the reflection beam splitter 9 to be incident on the objective lens 1. |
