| 摘要 |
PURPOSE:To minituarize the constitution of the device without the interference of a light beam by radiating three diffracted light beams reflected by a parallel flat plate on a recording medium, giving astigmatism into reflected lights via the parallel flat plate and individually detecting them as a transmitted light and a reflected light. CONSTITUTION:A light beam from a light source is made into three light beams of 0 order and + or -1st order at a diffraction grating 2, reflected on the side surface 31 of a parallel flat surface 3, radiated on a recording medium 100 passing through an objective optical system 4, one of the reflected lights is received by the first detecting means 5 transmitting through the side surface 31 of the flat plate 3 and a focusing control is operated while a reproduced signal is taken out. The other reflected light is reflected on the side surface 32, given astimagtism at the side surface 31, made incident on the second detecting means 6 in the vicinity of the focusing position of the astimagtism as an linear image and a tracking error is detected. By providing these two detecting means, a recessed lens is made unnecessary for enlarging a transmitted light interval, the size of a detector is reduced by receiving the light of the linear image, the interference of the means 6 of an outgoing light from the light source to the parallel flat plate is eliminated and thus, the constitution of the device is reduced. |
