Patent ID: 8611199
Filing Date: 2013-12-17
Classification: G02B,G11B

Abstract:
1. An objective lens element that has optical function surfaces on an incident side and an exit side, that converges a first incident light beam of a wavelength λ 1 through a base plate having a thickness t 1 to form a spot, and that converges a second incident light beam of a wavelength λ 2 longer than the wavelength λ 1 through a base plate having a thickness t 2 larger than the thickness t 1 to form a spot, wherein: at least either one of the optical function surfaces is divided into a first region that includes a rotational symmetry axis and through which the first and second incident light beams that substantially contribute to spot formation pass, and a second region that is a ring-shaped region surrounding the first region and through which only the first incident light beam that substantially contributes to spot formation passes; the first region is provided with a first diffraction structure; the second region is provided with a second diffraction structure, the second diffraction structure being different from the first diffraction structure; and the objective lens element satisfies the following conditions: where: DO DO DO DO