| 摘要 |
PURPOSE:To obtain control signals for focusing and tracking simultaneously by inserting two oscillators into part of a main beam, obtaining two subordinate beams through intensity modulation, and extracting them by one array of four divided detectors. CONSTITUTION:The oscillators 13 and 14 impose intensity modulation upon a beam to obtain the main beam W and subordinate beams X and X', which are reflected by a disk 18 to illuminate the array of four divided detectors 19. When the respective detectors 19a-19d output electric signals A1-A4, a readout signal S is A1+A2+A3+A4. In case of defocusing, the subordinate beams shift in irradiation position from splitting points 19x and 19z and then the electric signals A1-A4 increase or decrease accordingly. Therefore, a foucus control signal F=Az+A3-(A1+A4) is obtained. In case of a shift in track, the beam is scattered by a track groove 24 and part of it does not reach the detectors 19. The tracking control signal T is obtained from the electric signals of the respective detectors based upon the splitting point 19y, and T=A1+A2-(A3+ A4). |
