Patent ID: 8107348
Filing Date: 2012-01-31
Classification: G11B

Abstract:
1. An optical pickup apparatus for use on a multi-layered optical information storage medium, comprising: a laser light source; an irradiation focusing optical system that focuses laser light from the laser light source on a recording layer of the multi-layered optical information storage medium; an astigmatic lens system that imparts astigmatism to reflected light that is reflected from the recording layer of the multi-layered optical information storage medium; a detector that detects light that has passed through the astigmatic lens system; a first segmented wave plate that is provided between a posterior focal line position of the astigmatic lens system for the reflected light from the recording layer and a posterior focal line position for reflected light from an adjacent layer that is further from the laser light source than the recording layer, the first segmented wave plate making polarization states of transmitted light from two regions of the first segmented wave plate be in a mutually orthogonal state; a second segmented wave plate that is provided between the posterior focal line position for the reflected light from the recording layer and the detector, the second segmented wave plate comprising wave plate regions that are the same as or are inverted relative to those of the first segmented wave plate; and the astigmatic lens system is provided between the laser light source and the first segmented wave plate.