| 摘要 |
<p>Outgoing light from a semiconductor laser is split into a main beam and two sub-beams by a diffraction optical element, and collected to a recording layer of a disc. Reflection light of the main beam reflected by the recording layer of the disc and the reflection light of the two sub-beams pass through a composite wavelength plate and are received by a light detector. As the composite wavelength plate, a composite wavelength plate (11a) having a region (12a) and a region (12b) is used. Light passed through the region (12a) and light passed through the region (12b) orthogonally intersect with each other in polarized status. A differential push-pull signal is calculated based on output from the light detector.</p> |
