Patent ID: 6144623
Filing Date: 2000-11-07
Classification: G11B

Abstract:
An optical pickup apparatus for irradiating an optical recording medium with a beam and detecting a returned beam from said optical recording medium, comprising:a light source for emitting said beam;a objective lens for irradiating said optical recording medium with said beam emitted from said light source;a first diffraction element for diffracting said returned beam supplied from said optical recording medium through said objective lens; anda photodetector having first and second photodetection parts for detecting said returned beam being diffracted by said first diffraction element, whereinsaid first diffraction element has four regions being divided by a first dividing line extending substantially along a radial direction of said optical recording medium and a second dividing line perpendicular to said first dividing line,said objective lens is provided to be movable substantially along the radial direction of said optical recording medium for a tracking operation,said first photodetection part of said photodetector detects parts of said returned beam being diffracted in two of said four regions of said first diffraction element being located on first diagonal positions and said second photodetection part detects parts of said returned beam being diffracted in remaining two of said four regions of said first diffraction element being located on second diagonal positions, each of said first and second photodetection parts having a length not shorter than the distance of movement of a condensed spot of said diffracted returned beam resulting from wavelength fluctuation of said light source.