| 摘要 |
PROBLEM TO BE SOLVED: To precisely detect the thickness of a light transmission layer and to correct spherical aberration in an optical recording and reproducing device for recording and reproducing information on optical recording mediums such as an optical disk. SOLUTION: The optical recording and reproducing device 10 receives a return light reflected from a surface of the light transmission layer 16 in the optical recording medium 18 and an information recording surface 14 of a laser beam emitted through objective lenses 2 from a laser beam source 20 with a first photodetector 30 and a second photodetector 66. The device 10 detects a first and second focus error signal when a converging point of the laser beam passes through the surface of the light transmission layer 16 and along the information recording surface 14. The device 10 detects zero crossing points within a specific time after these signals exceed the thresholds, detects difference of driving voltages in a focusing direction of a two-axis actuator 26 in these zero crossing points, compares both of the detected value and the reference value, calculates an amount of compensation of the spherical aberration due to the thickness error of the light transmission layer 16, and drives a spherical aberration correcting element 28. |
