Patent ID: 6207942
Filing Date: 2001-03-27
Classification: G11B

Abstract:
An error detection method for detecting, from a reflected beam of a beam converged on an information recording medium on which optical information is recorded in the form of tracks, a tracking error signal representing relative positions of a convergence spot and an information reading target point and a focus error signal representing a convergence state of the converged beam on the information recording medium, the error detecting method comprising:diffracting the reflected beam by a hologram having two divided regions and converging or diverging the diffracted beam;receiving respective .+-.1-order diffracted beams obtained by the regions of the hologram by using four light-receiving regions which are apart from a central point of the hologram through which an optical axis of the reflected beam passes by a distance optically equal to the distance between the central point of the hologram and a focal point of the 0-order reflected beam; andcausing the light-receiving regions to have a plural photoelectric conversion regions divided into two photoelectric conversion regions or three photoelectric conversion regions by combination, calculating signals obtained from the three photoelectric conversion regions of each of the light-receiving regions to obtain a focus signal, and, at the same time, calculating signals obtained from the two photoelectric conversion regions of each of the light-receiving regions to obtain a tracking signal.