Patent ID: 8681593
Filing Date: 2014-03-25
Classification: G02B,G11B

Abstract:
1. An objective lens used in an optical head which records information onto or reproduces information from an information recording medium, wherein at least one surface of the objective lens includes an optical surface formed of a plurality of partitioned surfaces including an approximately stair-shaped cross section and annularly partitioned centered around an optical axis of the objective lens, and a plurality of connecting surfaces connecting mutually adjacent partitioned surfaces, of the plurality of partitioned surfaces, to each other, the plurality of connecting surfaces includes a first connecting surface formed of a cylindrical surface centered around the optical axis of the objective lens, a second connecting surface formed of a cylindrical surface centered around the optical axis of the objective lens, and a third connecting surface formed of a conical surface centered around the optical axis of the objective lens, the plurality of partitioned surfaces includes a first partitioned surface, a second partitioned surface adjacent to the first partitioned surface, a third partitioned surface adjacent to the second partitioned surface, and a fourth partitioned surface adjacent to the third partitioned surface, the first partitioned surface is closer to the optical axis of the objective lens than the second partitioned surface, the second partitioned surface is closer to the optical axis of the objective lens than the third partitioned surface, the third partitioned surface is closer to the optical axis of the objective lens than the fourth partitioned surface, when a plane in contact with the optical surface at an intersection of the optical surface and the optical axis of the objective lens is assumed as a reference plane, the first connecting surface connects the first partitioned surface and the second partitioned surface, the second connecting surface connects the second partitioned surface and the third partitioned surface, the third connecting surface connects the third partitioned surface and the fourth partitioned surface, a length of each of the first connecting surface and the second connecting surface in a direction of the optical axis of the objective lens is shorter than a length of the third connecting surface in the direction of the optical axis of the objective lens, the objective lens has a numerical aperture of 0.8 or higher and is made of synthetic resin, the optical surface has a diffractive structure with an approximately stair-shaped cross section, and an angle θ where λ