Patent ID: 7525896

Claim:
An optical head for use in an optical disk apparatus which performs recording and/or reproduction of information for first and second optical recording media by using, respectively, light of a first wavelength and light of a second wavelength which is different from the first wavelength, comprising: a first light source for emitting light of the first wavelength; a second light source for emitting light of the second wavelength which is different from the first wavelength, the second light source being disposed adjacent to the first light source; a converging lens for converging the light emitted from the first and second light sources toward the first and second optical recording media; and an optical device disposed between: the first and second light sources; and the converging lens, the optical device reducing a spherical aberration which occurs due to a combination of: at least one of the light of the first wavelength and light of the second wavelength; at least corresponding one of the first and second optical recording media; and the converging lens, wherein an optical axis of the optical device is shifted with respect to an optical axis of the converging lens so as to reduce a coma which occurs due to an optical axis of at least one of the light of the first wavelength and light of the second wavelength not coinciding with the optical axis of the converging lens; the first and second optical recording media include a recording layer on which to form recording marks, and a substrate provided on a surface of the recording layer; the converging lens is structured to optimize the spherical aberration with respect to an optical recording medium whose substrate has a thickness t (where t satisfies the relationship t 1 <t<t 2 ), wherein t 1 and t 2 are thicknesses of the substrates of the first and second optical recording media; and the optical device reduces the spherical aberration which occurs due to the converging lens and the substrates of the first and second optical recording media with respect to the light of the first wavelength and light of the second wavelength by changing transmitted wave fronts of the light of the first wavelength and light of the second wavelength.