Patent ID: 8953428
Filing Date: 2015-02-10
Classification: G02B,G11B

Abstract:
1. An objective lens, comprising: a first area substantially concentrically formed on a laser light source side surface of the objective lens with respect to an optical axis; a second area formed on an outside of the first area; and a third area formed on an outside of the second area, a diffraction structure is formed on the first area, the second area, and the third area, the first area, the second area, and the third area being configured to converge, on an information recording surface of a first information recording medium having a light transmissive layer of a first thickness t the first area and the second area being configured to converge, on an information recording surface of a second information recording medium having a light transmissive layer of a second thickness t the first area being configured to converge, on an information recording surface of a third information recording medium having a light transmissive layer of a third thickness t assuming that third-order coma aberration [mλ/deg] per unit angle generated by tilt of the first information recording medium in recording information on the first information recording medium or reproducing information from the first information recording medium is CMD a sine condition deviation amount SC a sine condition deviation amount SC the sine condition deviation amount SC assuming that a focal length [mm] in recording information on the first information recording medium or reproducing information from the first information recording medium is f the focal length f