Abstract An ojective lens for use in an optical pickup that is employed in a compact disk player, for example. The objective lens has a first aspherical surface on which parallel light rays impinge and a second spherical surface that faces the disk. The aspherical surface lies in a meridian plane of a cartesian coordinate system. The X-axis of this coordinate system is taken on the optical axis, the Y-axis is taken at the apex of the aspherical surface. The aspherical surface which is axially symmetrical is given by x=(y.sup.2 /r.sub.1)/{1+√1-(k+1) (y.sup.2 /r.sub.1.sup.2)}+d y.sup.4 +e Y 6 +f Y 8 +g y 10 where r 1 is the radius of curvature of a reference inscribed sphere at the apex of the aspherical surface, k is a conic constant, d, g, f, and g are expansion coefficients of the fourth, sixth, eighth, and tenth orders, respectively. The lens satisfies the following three relations: (1) 0.34<(N/2)-{N 2 -1)/N 2 }(r 1 /F)<0.38 (2) (1.1×N)-2.55<k<(0.5×N)-1.35 (3) N≧1.7. where N is the index of refraction of the medium of the lens at the wavelength of the incident light, and F is the focal length.
Inventors
👤 Masato Iwai
👤 Ichiro Morishita
👤 Masaru Nakayama
Bibliographic Details
Application Number—
JurisdictionUS
Data Sourcegoogle_patents
Last Synchronized2026-10-24 17:45
CPC Classifications
G; G02; G02B; G02B3/00; G02B3/02; G02B3/04
Claims Analysis
Total Claims: 2
Claim 1
Independent Claim
204 words
An objective lens for an optical pickup, said lens having a first aspherical surface on which parallel light rays impinge and a second spherical surface that faces an optical disk, the first aspherical surface lying in a meridian plane of a cartesian coordinate system whose X-axis is taken on the optical axis, the Y-axis is taken in a radial direction of the lens, and the origin is taken at the apex of the aspherical surface, the first aspherical surface which is axially symmetrical being given by x=(y.sup.2 /r.sub.1)/{1+√1-(k+1)(y.sup.2 /r.sub.1.sup.2)}+d y.sup.4 +e y.sup.6 +f y.sup.8 +g y.sup.10 where r 1 is the radius of curvature of a reference inscribed sphere at the apex of the aspherical surface, k is a conic constant, d is an expansion coefficient of the fourth order, e is an expansion coefficient of the sixth order, f is an expansion coefficient of the eighth order, and g is an expansion coefficient of the tenth order, the aspherical surface satisfying the following three conditions: (1) 0.34<(N/2)-{(N 2 -1)/N 2 }(r 1 /F)<0.38 (2) (1.1×N)-2.55<k<(0.5×N)-1.35 (3) N≧1.7 where N is the index of refraction of the medium of the lens at the wavelength of the incident light, and F is the focal length.
Claim 2
Dependent Claim
204 words
An objective lens for an optical pickup, said lens having a first aspherical surface on which parallel light rays impinge and a second spherical surface that faces an optical disk, the first aspherical surface lying in a meridian plane of a cartesian coordinate system whose X-axis is taken on the optical axis, the Y-axis is taken in a radial direction of the lens, and the origin is taken at the apex of the aspherical surface, the first aspherical surface which is axially symmetrical being given by x=(y.sup.2 /r.sub.1)/{1+√1-(k+1)(y.sup.2 /r.sub.1.sup.2)}+d y.sup.4 +e y.sup.6 +f y.sup.8 +g y.sup.10 where r 1 is the radius of curvature of a reference inscribed sphere at the apex of the aspherical surface, k is a conic constant, d is an expansion coefficient of the fourth order, e is an expansion coefficient of the sixth order, f is an expansion coefficient of the eighth order, and g is an expansion coefficient of the tenth order, the aspherical surface satisfying the following three conditions: (1) 0.34<(N/2)-{(N 2 -1)/N 2 }(r 1 /F)<0.38 (2) (1.1×N)-2.55<k<(0.5×N)-1.35 (3) N≧1.7 where N is the index of refraction of the medium of the lens at the wavelength of the incident light, and F is the focal length.