| 摘要 |
<P>PROBLEM TO BE SOLVED: To suppress offset of a differential push-pull signal caused by lens shift even when detecting the differential push-pull signal as an origin of a track error signal for two kind of optical recording media having different groove pitches and an optical recording medium of two layers. <P>SOLUTION: An outgoing light from a semiconductor laser 1 is divided into a main beam of 0th order light and a sub-beam group of ±1st order diffracted light by a diffraction optical element 3 and condensed on a disk 7a by an objective lens 6. Reflected light of the main beam and the sub-beam group are received by a photodetector 10. A push-pull signal MPP of the main beam and a push-pull signal SPP of the sub-beam group are detected from the output of the photodetector 10, and a differential push-pull signal DPP as an origin of the track error signal is detected. Phase distribution of the main beam and the sub-beam group are different each other, when a sum signal of the main beam detected from the output of the photodetector 10 is defined as M and a sum signal of the sub-beam group is defined as SSUM, K is larger than MSUM/SSUM. <P>COPYRIGHT: (C)2008,JPO&INPIT |
