| 摘要 |
<p>[PROBLEMS] To provide an optical head device capable of obtaining a desirable track error signal and a lens position signal for both two types of optical media having different groove pitches. [MEANS FOR SOLVING PROBLEMS] Light emitted from a light source is divided by a diffraction optical element (3a) into a main beam that is transmitted light, a first sub beam that is ± first-order diffraction light, and a second sub beam that is ± second-order diffraction light. The phase of the ± first-order diffraction light from regions (13a, 13c) and that of the ± first-order diffraction light from regions (13b, 13d) are shifted from each other by 180 degrees, and the phase of ± second-order diffraction light from regions (13a, 13d) and that of the ± second-order diffraction light from regions (13b, 13c) are shifted from each other by 180 degrees. For a light recording medium having a narrow groove pitch, the difference between a main beam push-pull signal and a first sub beam push-pull signal is set as a track error signal. For a light recording medium having a wide groove pitch, the difference between a main beam push-pull signal and a second sub beam push-pull signal is set as a track error signal.</p> |
