| 摘要 |
PROBLEM TO BE SOLVED: To interchangeably reproduce optical disks varying in substrate thicknesses with one piece of optical pickup. SOLUTION: Voltage is not impressed on TN type liquid crystals 4 at the time of reproducing the optical disk of a thin type. At this time, the laser beam of a short wavelength emitted from a semiconductor laser 1 is reflected half at a half mirror 2 and is made into parallel beams by a collimator lens 3. These parallel beams are rotated 90 deg. in the polarization direction by the TN type liquid crystals 4 and are nearly completely transmitted through a polarization filter 5. The transmitted beams are made incident on an objective lens 6 and are condensed onto a signal recording surface 7a. The voltage is impressed on the TN type liquid crystals 4 at the time of reproducing the optical disk of the standard thickness. At this time, the laser beam emitted from the collimator lens 3 is shielded in its outer peripheral part by the polarization filter 5 and is made incident on the objective lens 6, by which the light is condensed to the signal recording surface 7a. |
