Objective lens, optical head apparatus, optical information recording/reproducing apparatus

摘要

An objective lens for converging a light beam emitted from a first light source on a recording surface (17a) of a first optical information recording medium covered with a transparent substrate (7a) and converging a light beam emitted from a second light source on a recording surface (17b) of a second optical information recording medium covered with a transparent substrate (7b) having a thickness greater than the transparent substrate (7a). On an incident plane for the light beam, there are formed a center region (A1), an intermediate region (A2) surrounding the center region (A1), and a peripheral region (A3) surrounding the intermediate region (A2). A diffraction grating (11) is provided on the lens surface of the intermediate region (A2). Between the intermediate region (A2) and the center region (A1), and also between the intermediate region (A2) and the peripheral region (A3), stepped portions (12) are provided for causing an advance or a delay of a phase of a light beam passing through the intermediate region (A2) with respect to the phases of the light beams passing through the center region (A1) and the peripheral region (A3). The stepped portions (12) are formed so that a value of a tertiary spherical aberration on the recording surface (17b) of the second optical information recording medium becomes a value that makes a jitter value of a reproduction signal from the second optical information recording medium not more than 15%.