DIFFRACTIVE ELEMENT FOR OPTICAL PICKUP DEVICE, METHOD AND DEVICE FOR GENERATING FOCUS ERROR SIGNAL, OPTICAL PICKUP DEVICE, AND OPTICAL INFORMATION PROCESSING DEVICE

摘要

PROBLEM TO BE SOLVED: To effectively decrease an offset in focus error signals caused by the movement of an objective lens by tracking control.;SOLUTION: In the optical pickup device, a returning light beam 20 reflected by the recording face 8A of an optical information recording medium 8 is divided into two beams having different diffraction angles from each other by a diffraction element 12, one of the divided beams is accepted by a photoreception element 4 in a halfway converging state and the other beam is accepted by a photoreception element 43 in a diverging state after convergence, and then focus error signals are generated based on the output of the photoreception elements 43, 44. In the device, the diffraction element 2 is formed by dividing each of two kinds of diffracting elements having different diffraction angles from each other into small fractions and densely combining the factions 12a, 12b into regular or random and dense arrangement to form a single body as a whole so that the whole diffraction region has an enough area to cover the range of changes in the incident position of the returning beam 20 and so that the quantities of two first-order diffracted light beams with different diffraction angles from each other are substantially equal to each other.;COPYRIGHT: (C)2002,JPO