US Patent 7342865 Objective lens for optical recording/reproducing device

There is provided an objective lens which has positive refractive power and has a single lens element having an incident surface from which the collimated beam enters and an exit surface from which the collimated beam emerges. Further, the incident surface and the exit surface are configured to be rotationally symmetrical aspherical surfaces. At least within an effective diameter of the single lens element, the incident surface and the exit surface are symmetrical with respect to a plane perpendicular to an optical axis of the single lens element and have the same shape.