Patent attributes
An optical pickup includes: a light source; an objective lens; a beam splitter; a quarter wave plate that transforms the optical beam into a circularly polarized optical beam and also transforms the circularly polarized reflection optical beam into an optical beam whose polarization direction is perpendicular to the optical beam; a light detector; a neutral density filter section placed on a mutual optical path of those beams, reducing the intensity of the optical beam while maintaining the intensity of the reflection optical beam; and a filter drive section that puts the neutral density filter section in the mutual optical path or outside of it, wherein the intensity of the optical beam and the filter drive section are controlled such that the amount of the optical beam emitted to the optical disc is maintained at a predetermined level.
