| 摘要 |
<P>PROBLEM TO BE SOLVED: To smoothly derive an S curve with respect to a proper focus even when a plurality of focuses are generated in the vicinity of a photodetector by the diffraction operation of a diffraction type objective lens. <P>SOLUTION: A hologram element (HOE) for separating a infrared laser beam into a main beam and a subbeam and diffusing the subbeam is arranged before a photodetector. The separated main and sub beams are received by different sensor patterns. Two focus error signals FE1 and FE2 generated from the detection signal of each sensor pattern have a relation shown in Fig. 4. The focus error signal FE2 is amplified so that the amplitude of an S curve is roughly equal in size to the amplitude of an S curve generated in the focus error signal FE1 in the same timing. By executing FE=FE-α×FE2, a focus error signal having an unnecessary S curve offset is obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT |
