Optical pickup device, error detection device, and detection method therefore

An error detection device 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 detection device comprising:

• a hologram element having first and second divided regions, for diffracting the reflected beam in different directions in units of the regions, and having a lens function;
• a first light-receiving element region, having four divided photoelectric conversion regions, for receiving a ±1-order diffracted beam diffracted by the first region of the hologram element;
• a second light-receiving element region, having four divided photoelectric conversion regions, for receiving a −1-order diffracted beam diffracted by the first region of the hologram element;
• a third light-receiving element region, having four divided photoelectric conversion regions, for receiving a +1-order diffracted beam diffracted by the second region of the hologram element;
• and
• a fourth light-receiving element region, having four divided photoelectric conversion regions, for receiving a −1-order diffracted beam diffracted by the second region of the hologram element;
• wherein a region division line of the hologram element and photoelectric conversion region division lines of the first to fourth light-receiving element regions are set in a predetermined direction, and the first to fourth light-receiving element regions are arranged apart from a central point of the hologram through which an optical axis of the reflected beam passes by a distance almost optically equal to the distance between the central point of the hologram and a focal point of the 0-order reflected beam.

An optical pickup device for converging a beam emitted from a semiconductor laser beam source on an information recording medium on which optical information is recorded in the form of tracks through an optical system, and for detecting, from a reflected beam obtained from the information recording medium at this time, at least 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 optical pickup device comprising:

• a hologram element having first and second divided regions, for diffracting the reflected beam in different directions in units of the regions, and having a lens function;
• a first light-receiving element region, having four divided photoelectric conversion regions, for receiving a +1-order diffracted beam diffracted by the first region of the hologram element;
• a second light-receiving element region, having four divided photoelectric conversion regions, for receiving a −1-order diffracted beam diffracted by the first region of the hologram element;
• a third light-receiving element region, having four divided photoelectric conversion regions, for receiving a +1-order diffracted beam diffracted by the second region of the hologram element;
• and
• a fourth light-receiving element region, having four divided photoelectric conversion regions, for receiving a −1-order diffracted beam diffracted by the second region of the hologram element;
• wherein a region division line of the hologram element and photoelectric conversion region division lines of the first to fourth light-receiving element regions are set in a predetermined direction, and the first to fourth light-receiving element regions are arranged apart from a central point of a hologram by a distance almost optically equal to the distance between the central point of the hologram and a focal point of the 0-order reflected beam.