| 摘要 |
PROBLEM TO BE SOLVED: To enable inexpensive and simple adjustment and to stabilize characteristics by arranging a mirror at the position of a disk, expressing with the reflected light beam in a waveform a relation between the position of the lens and the output of a photodetector, and displacing a diffraction element to obtain a prescribed waveform. SOLUTION: With a hologram element 18 fixed, a half mirror 46 is placed on the turntable 44. A laser beam from a light source element 16 is divided into the main beam and a sub-beam by a pattern 28, and converged on the half mirror 46 with an objective lens 20, while the reflected light of the main beam is diffracted by a pattern 30 and converged on the three light receiving elements of a photodetector 22. With the objective lens 20 displaced vertically, a relation is grasped between the position in the direction orthogonally crossing the face of the disk 14 and the output from the three light receiving elements of the photodetector 22, in the form of a graph by a computer 36. The minimum point of the jitters is obtained by positioning the hologram element 18 in the manner that the point P where the focus servo is actuated is superposed on the maximum value output point Q. |
