Patent ID: 6556534
Filing Date: 2003-04-29
Classification: G11B

Abstract:
An objective lens having two aspheric surfaces configured to be used in an optical system in which light from at least one light source is converged to respective data recording surfaces of two optical disks, and reflection light from the respective data recording surfaces is received by a light receiving element in recording or reading the two optical disks, and in recording or reading a first optical disk, a first wavelength &lgr;1 is used, and in recording or reading a second optical disk, a second wavelength &lgr;2 is used, comprising:a first phase shifter including ring-like step portions having a center coincident with an optical axis provided in a surface of the objective lens, the first shifter producing a phase difference with respect to light having the first wavelength &lgr;1, and a second phase shifter including ring-like step portions having a center coincident with the optical axis provided in the other surface of the objective lens, the second phase shifter producing a phase difference with respect to light having the second wavelength &lgr;2, wherein dimensions and a shape of the step portions of the first phase shifter are determined so that the phase difference caused by the light having the first wavelength &lgr;1 is equivalent to (0.9 &lgr;2 to 1.1 &lgr;2) times a natural number, and dimensions and a shape of the step portions of the second phase shifter are determined so that the phase difference caused by the light having the second wavelength &lgr;2 is equivalent to (0.9 &lgr;, to 1.1 &lgr;,) times a natural number.