| 摘要 |
PURPOSE:To make a diffraction grating unnecessary and to simplify the constitution of a pickup by using a semiconductor laser which delivers three light beams from an element as a light source. CONSTITUTION:A semiconductor laser 21 which delivers three parallel light beams e-g is used as a light source to read out three adjacent bits on a disk 6. Then the focus control is performed with the read signal of the center bit 7b; while the tracking control is carried out with comparison between read signals of bits 7a and 7c, respectively. As a result, a diffraction grating which produces three laser beams is made unnecessary. In such a way the constitution of a pickup for optical digital disk is simplified. |
