Patent ID: 8259555

Claim:
An optical pickup for performing at least one of recording, reproducing, and erasing of information for at least two types of optical information recording media, the optical pickup comprising: an optical focusing system configured to focus a light beam from a light source onto a first recording layer of a first optical information recording medium via a first substrate having a first thickness t 1 with the use of a first numerical aperture NA 1 , and onto a second recording layer of a second optical information recording medium via a second substrate having a second thickness t 2 that is different from the first thickness t 1 with the use of a second numerical aperture NA 2 , wherein: the optical focusing system comprises an object lens designed to focus the light beam onto the first recording layer of the first optical information recording medium, and an aberration correction unit comprising at least one phase shifter surface that is divided into plural regions in a concentric manner according to steps having uneven shapes with different heights in a light axial direction, which phase shifter surface is configured to apply a phase difference to the light beam from the light source; the plural regions comprise a center region comprising an optical axis, an outside annular region extending from a position of the first numerical aperture NA 1 to a position of the second numerical aperture NA 2 , and a middle annular region positioned between the center region comprising the optical axis and the outside annular region; phase differences of the center region, the outside annular region, and the middle annular region are integral multiples of 2π with respect to a wavelength of the light beam; the steps having the uneven shapes are formed in a first annular region between the center region and the middle annular region and in a second annular region between the middle annular region and the outside annular region; and the steps are formed in such a manner as to reduce aberration that is caused by a difference between the first thickness t 1 of the first substrate and the second thickness t 2 of the second substrate.