| 摘要 |
PROBLEM TO BE SOLVED: To facilitate the offset adjustment of a focusing error signal(FES signal) by arranging two diffracted lights so as to be received by two sets of respectively bisected photodetectors, making them be diffracted to two points different in distances from a light source and making beam spreads on the photodetectors of the two diffracted lights so that the size of the beam spread distant from the light source is smaller than the size of the beam spread near to the light source. SOLUTION: The beam spreads of lights to be diffracted by a hologram are made so that the beam spread 11A at the photodetectors 5A, 5D side of a side nearer to a light source 1 is larger than the beam spread of 11B at the photodetectors 5B, 5C side of a side farther from the light source 1. Since ratios in which photodetector parting lines are moved with respect to respective beam diameters at the time of rotating the hologram are made to be changed and by changing two beam diameters, then, the offset to be generated by the signal processing of the FES signal is changed largely. Thus, a larger offset can be generated. |
