Patent ID: 6822800
Filing Date: 2004-11-23
Classification: G02B,G11B

Abstract:
An objective lens for an optical pickup having a single lens element having two refraction surfaces, one of said two refraction surfaces being divided into a central area including an optical axis of said objective lens and a peripheral area outside said central area, a step providing a level difference along a direction of the optical axis being formed at a boundary between said central area and said peripheral area, said step providing a phase shift between light passing through said central area and light passing through said peripheral area, said phase shift suppressing deterioration of wavefront aberration due to a change of temperature, said level difference being formed such that a thickness on the peripheral area side is greater than a thickness on the central area side at the boundary, said objective lens being configured to satisfy a condition:0.83wherein,hx is a radius of the boundary, and hmax is an effective radius defining a numerical aperture of said surface formed with the step.