Patent ID: 8036089

Claim:
An optical pick-up to perform recording or reproducing of information for a first optical recording medium with a first light beam of wavelength λ 1 , a thickness t 1 of a substrate thereof, and a numerical aperture NA 1 for use thereof and a second optical recording medium with a second light beam of wavelength λ 1 , a thickness t 2 (>t 1 ) of a substrate thereof, and a numerical aperture NA 2 (<NA 1 ) for use thereof, comprising: an objective lens to focus the first light beam or the second light beam; an aberration generation device configured to generate coma aberration or spherical aberration for the first light beam or the second light beam focused by the objective lens; and a control device configured to determine which of the first and second optical recording media is set and to perform a first control operation when the first optical recording medium is set or to perform a second control operation when the second optical recording medium is set; wherein the first control operation comprises: a first step of setting a quantity of the coma aberration generated by the aberration generation device to a predetermined stored value, a second step of varying a quantity of the spherical aberration generated by the aberration generation device to determine and store a driving condition of the aberration generation device, wherein the driving condition is a condition for which an amplitude of a recording information signal or a track error signal is at a maximum, and a third step of performing an operation of recording or reproducing while a quantity of the spherical aberration is added based on the driving condition; and wherein the second control operation comprises: a fourth step of setting a quantity of the spherical aberration generated by the aberration generation device to a predetermined stored value, a fifth step of varying a quantity of the coma aberration generated by the aberration generation device to determine and store a driving condition of the aberration generation device, wherein the driving condition is a condition for which an amplitude of a recording information signal or a track error signal is at a maximum, and a sixth step of performing an operation of recording or reproducing while the quantity of the coma aberration is added based on the driving condition, wherein the aberration generation device is controlled by the control device, wherein the objective lens is a lens providing a best aberration for the first optical recording medium and is provided with an aberration compensation element comprising a diffraction element or a phase shifter element between the objective lens and the aberration generation device, and wherein the aberration compensation element is provided with a diffraction element whereby recording or reproducing is made using light beams with selectively different diffraction orders dependent on an optical recording medium.