Patent ID: 8305868
Filing Date: 2012-11-06
Classification: G11B

Abstract:
1. An optical pickup apparatus comprising: an objective lens formed with an annular diffraction grating according to a numerical aperture so that a first laser beam having a first wavelength and a second laser beam having a second wavelength are focused onto a signal recording layer of a first optical disc and a signal recording layer of a second optical disc respectively, the first and second optical discs respectively including cover layers different in thickness covering the signal recording layers; a first diffraction grating configured to split the first laser beam and a second diffraction grating configured to split the second laser beam into zeroth-order diffracted light and ±first-order diffracted light; and a photodetector including a square-shaped light receiving portion for being irradiated with return light as a spot, wherein: a length of a diagonal line of the light receiving portion is substantially equal to a length of a diameter of an elliptical spot formed in a direction of the diagonal line when the focus error signal is at a maximum level.