Patent ID: 7468942

Claim:
An optical pickup comprising: a light source for emitting a plurality of laser beams with different wavelengths; and an objective lens for focusing the laser beams emitted from said light source on recording surfaces of plural types of information recording media, wherein a diffractive lens structure is provided in a light path of said laser beam, said structure including ring zone areas divided by a plurality of phase steps for correcting a wavefront aberration of said laser beam, a diameter of an outermost phase step of said diffractive lens structure is smaller than a second largest effective diameter of effective diameters required for reproduction of said plural types of information recording media, wherein a focused point of a reproducing laser beam which passes through said diffractive lens structure during reproducing at least one of those of said plural types of information recording media that are other than an information recording medium requiring a largest effective diameter for reproduction, resides between (i) a position at which an optical axis meets said laser beam passing through a height corresponding to an effective diameter required for reproduction of said information recording media, and (ii) a position at which the optical axis meets said laser beam passing through an innermost of an area outside said outermost phase step, and wherein the edge angles of all the phase steps are obtuse angles more than 90 degrees.