OPTICAL DATA DEVICE FOR READOUT OF OPTICAL DISK WITH DIFFERENT THICKNESS IN AXIAL DIRECTION AND METHOD FOR DETECTION OF DATA FROM SAID OPTICAL DISK

摘要

The optical disc player reads the thin disc optical disc or the thick disc optical disc. The disc player optical system is designed to read thin disc optical discs and has an effective numerical aperture. A thick plate optical disc having a substrate thicker than a thin plate optical disc results in a laser beam reading such thick plate optical disc having sufficient spherical aberration to prevent reliable data detection. When the thick plate optical discs are read, the reading portion of the optical system is automatically changed to accommodate the undesired spherical aberration. The laser beam reflected by the thick plate optical disc is subject to annular filtering, which reduces spherical aberration to a degree sufficient to enable data and servo signal detection. The annular filtering is provided to the optical reading path by an effective opaque or translucent disc located in the center of the pupil of the laser beam optical filter disposed in the reading section. An oil-opening plate having an opening comparable to a known diffraction limited spot size is disposed between the laser beam filter and the photo detector. This oil-opening plate is disposed in the focus area of the lens in the optical read path.