Abstract: A device for calculating diffraction efficiencies of a diffraction lens divided into a plurality of regions, each region comprising at least one grating ring, comprises a first memory for storing information about diffraction efficiencies of the regions; a second memory for storing information about weights corresponding to the regions; and a first processor for retrieving information from the first and the second memory, and calculating diffraction efficiencies of the entire diffraction lens using the formula 1 E j = ∑ m = 1 M ⁢ W m ⁢ η mj ( 1 )

Abstract: An optical system for an optical disk, comprising a light source (61), a collimating optical system (63) for converting a luminous flux from the light source into parallel rays of light, and an object lens (66) for condensing the parallel rays onto the information recording surface (71) of an optical disk. The object lens consisting of two or three lenses and having a numerical aperture (NA) of at least 0.82 enables a high-density recording. Since a third-order astigmatism produced when the object lens is tilted 0.7 degree with respect to an optical axis is as small as up to 10 m&lgr;, a residual aberration, after a third-order comatic aberration produced when the optical disk is tilted due to warping or the like is corrected by tilting the optical lens, can be reduced. Therefore, a tilted optical disk still can ensure a satisfactory recording and/or reproducing quality.

Abstract: An objective lens (1) for an optical disk, which focuses a light beam from a light source, is designed so that a third-order coma aberration generated when the objective lens is inclined at a unit angle is larger than a third-order coma aberration generated when the optical disk (2) is inclined at the unit angle, mounted on an actuator for inclining the objective lens according to an inclination amount of the optical disk, and used. With this structure, it is possible to obtain an objective lens for an optical disk that has a large numerical aperture and is easy to manufacture and assemble, and in which the third-order coma aberration generated when the optical disk surface is inclined owing to a warp or the like can be corrected by small inclination of the objective lens, so as to reduce a residual astigmatism, which is generated according to the inclination amount, after the correction.

Abstract: A beam shaper is made up of a single lens whose both surfaces are toric surfaces. Assuming that directions where the beam divergence angle are larger and smaller in the far field from the semiconductor laser source are referred to as the vertical and horizontal directions, respectively, both of the toric surfaces have aspheric surfaces in a cross-section in the vertical direction, both of the toric surfaces have spherical surfaces in a cross-section in the horizontal direction, and both centers of curvature of the spherical surfaces are located substantially at a luminous point of the semiconductor laser source.

Abstract: A device for calculating diffraction efficiencies of a diffraction lens divided into a plurality of regions, each region comprising at least one grating ring, comprises a first memory for storing information about diffraction efficiencies of the regions; a second memory for storing information about weights corresponding to the regions; and a first processor for retrieving information from the first and the second memory, and calculating diffraction efficiencies of the entire diffraction lens using the formula E j = ∑ m = 1 M ⁢ W m ⁢ η mj ( 1 )

Abstract: In a lens array, a multiplicity of condenser lenses, each in a convex lens form, are arrayed in vertical and horizontal directions so as to correspond to pixel regions, respectively, and each condenser lens, when viewed from a direction perpendicular to a condenser lens-arrayed plane, takes a planar shape formed with a four straight sides along four sides of the pixel region and four circular arcs extending between the respective straight sides. A center of the four circular arcs substantially coincides with a center of the corresponding pixel region. This ensures an increase in area covered with the condenser lens in the pixel region, thereby causing more light rays to enter the condenser lens. In addition, a radius of curvature necessary for collecting can be obtained more easily. Consequently, light rays can be efficiently collected and guided to light receiving sections or the like provided in the pixel regions.