Patent ID: 7778141

Claim:
An optical pickup comprising: a light source that irradiates an optical beam being a divergent beam; a polarization adjustment plate made of crystal material provided with the birefringence, in which the crystal axis, along which direction the birefringence is not brought about, is so arranged as to be turned up from an orthogonal plane perpendicular to the optical axis of the optical beam to express the incidence angle dependence which the crystal material is provided with, and the thickness with respect to the optical axis is set up such that the phase difference to be brought about at the central part of the optical beam becomes low from a desired design value to make the optical beam emitted as a first linear polarization by a predetermined difference value, and which adjusts the ratio of the first linear polarization and a second linear polarization perpendicular to the first linear polarization such that the ratio of the first linear polarization at the rim part of the optical beam comes to be higher than that at the central part of the optical beam; a polarization beam splitter that splits off the first linear polarization and the second linear polarization in the adjusted optical beam; and an objective lens that condenses the first linear polarization, and makes the condensed first linear polarization go to an optical disc.