×

Astigmatic lens for use in detecting a focussing error in an optical pickup system

  • US 5,546,235 A
  • Filed: 11/04/1994
  • Issued: 08/13/1996
  • Est. Priority Date: 11/05/1993
  • Status: Expired due to Fees
First Claim
Patent Images

1. A convex astigmatic lens for use in an optical pickup system comprising:

  • an orthorhombic base, made of a refractive material, having a first and a second surfaces, and provided with a vertically directional centerplane, wherein the first and second surfaces are parallel to each other, each of the surfaces being provided with a pair of aerie sides and a pair of lengthwise sides, and the centerplane is perpendicular to the first and second surfaces; and

    two sets of M pentahedrons placed on the first surface of said orthorhombic base, each of the pentahedrons in each set being made of said refractive material and having a rectangular base surface, a rectangular inclined surface, a rectangular normal surface and a pair of right angled triangular parallel side surfaces, each of the three rectangular surfaces being provided with a pair of lengthwise sides and a pair of aerie sides and each of the triangular side surfaces having a base Rm, a height Hm, and an inclination, m being a natural number indicating the number of the order, said base, height and inclination of the pair of triangular side surfaces of each pentahedron being defined by the pair of aerie sides of the rectangular base, rectangular normal and rectangular inclined surfaces of the corresponding pentahedron, respectively, the height Hm of the triangular side surfaces in each of the M pentahedrons being equal, each of the pentahedrons being formed by joining one of the lengthwise sides of the rectangular inclined surface with one of the lengthwise sides of the rectangular normal surface at an angle Θ

    m, thereby forming a first edge, one of the lengthwise sides of the rectangular base surface with the remaining lengthwise side of the rectangular inclined surface at a right angle to thereby form a second edge, and the remaining lengthwise side of the rectangular base surface with the remaining lengthwise side of the rectangular inclined surface at an angle (Θ

    m <

    90°

    ), thereby forming a third edge, the first, second and third edges of the M pentahedrons being parallel to each other, the second edge of each of the M pentahedrons being collinear to the third edge of a neighboring pentahedron with the exception of the pentahedrons having the triangular side surfaces with the largest Rm and shortest Rm, the rectangular surfaces of the pentahedron having the triangular side surfaces with the largest base Rm from each set sharing the same rectangular surface, the third edge of the pentahedrons having the triangular side surfaces with the shortest Rm from each set being collinear to the lengthwise sides of the first surface, respectively, and the rectangular base surfaces of the M pentahedrons from the two sets and the first surface of the orthorhombic base being also coplanar, thereby allowing the two sets of M pentahedrons to be symmetrical with respect to the centerplane, the angle Θ

    m for each of the M pentahedrons being further determined by the Rm of the triangular side surfaces of the corresponding pentahedron, the base Rm being mathematically expressed as ##EQU7## wherein f represents the focus length and λ

    , the wavelength of the light source.

View all claims
  • 1 Assignment
Timeline View
Assignment View
    ×
    ×