| 摘要 |
PROBLEM TO BE SOLVED: To provide an aspherical surface single objective lens, an optical pickup device and a recording/reproducing device which are used for recording and reproducing the information of an optical information recording medium, by which an image height characteristic is made excellent because a numerical aperture is se >0.85, which are made suitable for a high density optical pickup device using the light source of a short wavelength, by which an actuation distance is sufficiently secured and which are made light in weight. SOLUTION: This objective lens is a single lens whose at least one surface is aspherical, and satisfies the expressions of: 0.85<NA<0.98, 0.80<d/f<3.00, 0.5<Φ1<5.8 and 0.47<(X1-X 2)×(n-1)/(NA×f×√(1+|m|))<0.75, and then, NA means the numerical aperture of the objective lens on the side of the optical information recording medium, d (mm) means a thickness on an optical axis, f (mm) means a focal distance at an infinite object, Φ1 (mm) means the effective diameter of a surface on a light source side, X1 (mm) means a difference in an optical axis direction between a plane perpendicular to the optical axis and coming into contact with the apex of the surface on the light source side and the surface on the light source side in the most periphery of the effective diameter, X2 (mm) means a difference in the optical axis direction on the side of the optical information recording medium, (n) means a refractive index by a light source wavelength and (m) means image formation magnification. |
