Patent ID: 8300513

Claim:
An optical head, comprising: a light source including a first emission point for emitting a first laser light having a first wavelength and a second emission point disposed away from the first emission point by a predetermined distance, and for emitting a second laser light having a second wavelength smaller than the first wavelength; a collimator lens for converting the first and second laser lights into substantially parallel lights; an objective lens for focusing the first laser light on an information recording layer of a first information recording medium and focusing the second laser light on an information recording layer of a second information recording medium different from the first information recording medium; and an objective lens driver for tilting the objective lens in a direction to decrease coma aberration generated by incidence of the first laser light oblique to an optical axis of the objective lens when the objective lens focuses the first laser light on the information recording layer of the first information recording medium, wherein the light source is arranged such that an optical axis of the second laser light substantially coincides with that of the objective lens, and such that an optical axis of the first laser light has a predetermined angle with respect to the optical axis of the objective lens, the light source is arranged such that the following Equation (1) is satisfied and the first laser light is incident from an outer peripheral side of the first information recording medium relative to the optical axis of the objective lens, if CMD (mλ/°) is a third-order coma aberration amount generated by the tilt of the first information recording medium per unit angle, CML (mλ/°) is a third-order coma aberration amount generated by the tilt of the objective lens per unit angle, δ (mm) is a distance between the first and second emission points of the first and second laser lights and fcl (mm) is the focal length of the collimator lens, and the objective lens driver tilts the objective lens to locate the inner peripheral end of the objective lens in the radial direction of the first information recording medium lower than the outer peripheral end thereof when the objective lens focuses the first laser light on an information recording layer of the first information recording medium to thereby correct comma aberration generated in the radial direction of the first information recording medium: 1.0≧(CMD+CML)×arctan(δ/ fcl )/CML>0 (1).