Patent ID: 7283452

Claim:
An optical device comprising: an objective lens including, aspheric surfaces at a first surface and a second surface, and a phase shifter provided with annular step portions having a center coincident with an optical axis of the objective lens formed in at least one of the first and second surfaces of the objective lens; and a light receiving element, wherein, light having a first wavelength is converged to a data recording surface of a first optical disk via the objective lens and reflection light from the data recording surface of the first optical disk is received by the light receiving element in recording or reading the first optical disk, light having a second wavelength which is different from the first wavelength is converged to a data recording surface of a second optical disk via the objective lens and reflection light from the data recording surface of the second optical disk is received by the light receiving element in recording or reading the second optical disk, the phase shifter is configured to produce a phase difference for reducing on-axial and off-axial aberration resulting from recording or reading the first optical disk with respect to the light having the first wavelength, and the phase shifter is configured to produce a phase difference for reducing on-axial and off-axial aberration resulting from recording or reading the second optical disk with respect to the light having the second wavelength.