| 摘要 |
PURPOSE:To obtain the titled device which is excellent in S/N at the time of reproducing a signal, and to decrease a crosstalk, by using a diffraction grating in order to lead a reflected light from the surface of an optical disk, to a photodetector so that it can be attained to convert an optical system to a single axis. CONSTITUTION:An outgoing light of a semiconductor laser 1 passes through a diffraction grating 2, as a '0'-order diffracted light, converged to a disk surface 4 by a convergent lens 3, and its reflected light is diffracted by the diffraction grating 2 and reaches 2-split photodetectors 5, 6. The diffraction grating 2 is divided into the first and the second areas 9, 10, and in the first area 9, and in the second area, the gratings are formed in the direction orthogonal to a border line of both the areas 9, 10, and in the direction parallel to the border line, respectively. The 2-split photodetector 5 is provided on a converging direction of the diffracted light of the first area 9 so that the border line direction of the photodetecting surface coincides with the border line direction of the diffraction grating 2. When the disk surface has been varied, this diffracted light moves in the direction orthogonal to the border line in the same way as the wedge prism system, therefore, by a differential output of the 2-split photodetector 5, a focal error signal can be obtained. |
