| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an objective lens for use in an optical pickup which focuses three light beams having different wavelengths onto a signal recording surface, using a single common objective lens, while reducing the spherical aberrations due to the fluctuations of temperature. <P>SOLUTION: A diffraction portion 50, on an incident surface onto which a light beam is incident of the objective lens 34, has a first region 51 provided at an innermost circumferential portion, a second region 52 provided outside the first region 51, and the third region 53 provided outside the second region 52. The diffraction portion is formed so that a light beam of λ1 has an aperture diameter corresponding to the first to third regions 51-53; a light beam of λ2 has an aperture diameter corresponding to the first and second regions 51 and 52; and a light beam of λ3 has an aperture diameter corresponding to the first region 51. In the first region 51, a staircase-like periodic structure 511, in which staircase shapes having an orbicular zone shape and a predetermined height are formed periodically in a radial direction of the orbicular zone, and a step structure 512 having the same depth d in each period of the staircase-like periodic structure are superimposed in an aspheric lens shape. <P>COPYRIGHT: (C)2011,JPO&INPIT |
