Patent ID: 8305868

Claim:
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: the light receiving portion includes a four-divided light receiving portion having four sensor portions each in a square shape, the return light is return light of the zeroth-order light of the first laser beam reflected from the signal recording layer of the first optical disc or return light of the zeroth-order light of the second laser beam reflected from the signal recording layer of the second optical disc, a focus error signal is generated from the return light of the zeroth-order light of a laser beam having the shorter wavelength of the first wavelength and the second wavelength, wherein the laser beam having the shorter wavelength is focused on the respective optical disc, and 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.