Patent ID: 7394733

Claim:
An information recording or reproducing method for performing information recording or reproducing with respect to an optical disk that is an information recording medium by utilizing an optical disk device, the optical disk device including: an optical head including: a light source, an objective lens operable to focus an light beam emitted from the light source on the information recording medium, a photodetector operable to detect the light beam reflected from the information recording medium, a defocusing correction element operable to correct a defocused state caused by a wavelength change and a wavelength broadening, and spherical aberration correction element as a separate element from the defocusing correction element, the defocusing correction element and the spherical aberration correction element are provided in an optical path between the light source and the information recording medium: the information recording or reproducing method comprising: emitting a light beam from the light source, passing the emitted light beam through the spherical aberration correction element and the defocusing correction element, focusing the emitted light beam that has passed through the respective elements on the information recording medium by the objective lens, and passing the light beam reflected from the information recording medium through the objective lens, the defocusing correction element, and the spherical aberration correction element to be focused on the photodetector, so that a signal is detected, wherein when the emitted light beam passes through the spherical aberration correction element and the defocusing correction element, the spherical aberration correction element substantially corrects a spherical aberration occurring due to the defocusing correction element in accordance with an amount of the spherical aberration.