Patent ID: 6909687

Claim:
An optical pickup apparatus, comprising: a light source emitting a light beam; a first diffraction element diffracting a returned light beam based on the light beam emitted from said light source; and a first photodetector detecting the returned light beam diffracted by said first diffraction element, wherein said first diffraction element having two regions in first diagonal positions among four regions, divided by a first dividing line at an approximately 45° to a direction of diffracting the returned beam and a second dividing line orthogonal to the first dividing line, as first and second regions, and third, fourth, fifth and sixth regions obtained by equally dividing the remaining two regions in second diagonal positions by a third dividing line, wherein said first photodetector has four photodetection parts sectioned by a first section line substantially parallel to the direction in which a condensed spot of the returned light beam diffracted by said first diffraction element is moved by a variation in the wavelength of said light source and a second section line orthogonal to said first section line, wherein the returned light beam diffracted in said first and second regions of said first diffraction element forms first and second condensed spots at positions apart from each other on opposite sides on said first section line with respect to the intersection of said first and second section lines of said photodetector, wherein the returned light beam diffracted in said third, fourth, fifth and sixth regions of said first diffraction element forms condensed spots on the four photodetection parts of said first photodetector or on said first section line, wherein the first, second, third, fourth, fifth and sixth regions of said first diffraction element provides each light beam with a spatial variation corresponding to a focus state on an optical recording medium so that the focus state can be detected by operating the outputs of the four photodetection parts in said first photodetector, and wherein the spatial variation corresponding to said focus state provided by at least said first and second regions is astigmatism, and wherein said first and second condensed spots each move among the different photodetection parts depending on said focus state.