Patent ID: 8483031
Filing Date: 2013-07-09
Classification: G11B

Abstract:
1. An optical head device which records or reproduces information on or from a first optical information medium having three or more recording layers, comprising: a first laser light source which emits a first light beam; a focusing optical system which focuses the first light beam emitted from the first laser light source onto one of the recording layers of the first optical information medium; a photodetector which receives the first light beam reflected by the recording layer of the first optical information medium and outputs an electric signal in accordance with an amount of the received first light beam; and a first light blocking region disposed on a light flux of the reflected light beam resulting from the reflection by the recording layer on which the first light beam is focused, to block, when there are at least two recording layers on a first light beam incident side of the recording layer on which the first light beam is focused or on a side thereof opposite to the first light beam incident side, reflected light beams resulting from reflection by the at least two recording layers which are incident on a region in the photodetector where the reflected light beams resulting from the reflection by the at least two recording layers interfere with each other, wherein the first light blocking region is not formed on an optical axis of the reflected light beam resulting from the reflection by the recording layer on which the first light beam is focused, the first light blocking region is a region surrounding the optical axis of the reflected light beam resulting from the reflection by the recording layer on which the first light beam is focused, and an outer edge of the first light blocking region is closer to the optical axis than an outer edge of an effective light flux of the reflected light beam resulting from the reflection by the recording layer on which the first light beam is focused.