Patent ID: 7948854
Filing Date: 2011-05-24
Classification: G11B

Abstract:
1. An optical head apparatus comprising: a light source; an objective lens focusing an output light emitted by said light source on a disc-shaped optical recording medium for which a groove or a pit for tracking is provided; a photo-detector receiving a reflected light reflected by said optical recording medium; a polarizing splitter unit splitting said output light and said reflected light; a quarter-wave plate disposed between said polarizing splitter unit and said objective lens; and a birefringence compensating unit reducing a change in an amplitude of a track error signal caused by birefringence in a protective layer of said optical recording medium, wherein said protective layer exhibits vertical birefringence, and in-plane birefringence varying depending on an in-plane position, and wherein said birefringence compensating unit provides compensation of said vertical birefringence for reducing the change in the amplitude of said track error signal depending on the variation in said in-plane birefringence.