Patent ID: 6665257
Filing Date: 2003-12-16
Classification: G11B

Abstract:
An optical head device, comprising:a light source for emitting at least one of a coherent beam and a quasi-monochromatic beam; an optical element for receiving the beam emitted by the light source and dividing the beam into a first beam and a second beam; a collection optical system for receiving the first beam and the second beam and simultaneously converging the first and second beams into a microscopic spot on a single information memory medium; a beam branching element for receiving the first and second beams diffracted and/or reflected by the information memory medium and branching the first and second beams received by the beam branching element; a light detector for receiving at least one of the beams output from the beam branching element and outputting a signal in accordance with a light amount of the at least one of the beams received by the light detector; a signal processing section for receiving the signal from the light detector and performing an operation of the signal; and a driving section for determining relative positions of the collection optical system and the information memory medium based on the signal output from the signal processing section, wherein the first beam and the second beam have different effective numerical apertures when collected by the collection optical system, and the optical head device further includes a tracking error generation device for generating a tracking error signal using the first beam or the second beam which has a smaller effective numerical aperture when collected by the collection optical system.