Optical system for recording and reproducing for use in optical information recording medium

An optical system for recording or reproducing of information to or from an optical information recording medium, comprising

• (a) a light source;
• (b) a coupling lens for converting a diverging light emergent from the light source to a converging light;
• and
• (c) an objective lens for further converging the converted converging light and for focusing on an information recording surface of the optical information recording medium,
• wherein a lateral magnification of the objective lens in which a wavefront aberration within a Marechal criterion is minimum, and a numeral aperture satisfy the following conditional expressions,
• 0<m<1
• NA.multidot.(1.multidot.M).ltoreq.0.65, and
• 0.48.ltoreq.NA,
• where M represents the lateral magnification of the objective lens, and NA represents the numerical aperture on an image side of the optical system.

An optical system for recording or reproducing of information to or from an optical information recording medium, comprising:

• (a) a light source;
• (b) a coupling lens for converting a diverging light emergent from the light source to a converging light;
• and
• (c) an objective lens for further converging the converted converging light and for focusing on an information recording surface of the optical information recording medium,
• wherein a lateral magnification of the objective lens in which a wavefront aberration within a Marechal criterion is minimum, a lateral magnification of an entire optical system, and a numerical aperture satisfy the following conditional expressions,
• 0<M<1, and
• 0.06.ltoreq..vertline.M.sub.c .vertline..multidot.NA.ltoreq.0.21,
• where M represents the lateral magnification of the objective lens, M.sub.c represents a lateral magnification of an entire optical system, and NA represents a numerical aperture on an image side of the optical system.

An objective lens for use in an optical system for recording or reproducing an information to or from an optical information recording medium in which an incident converging light is light-formed on an information recording surface of the optical recording medium, the objective lens comprising:

• (a) a first surface;
• and
• (b) a second surface provided opposite the first surface, wherein when a wavefront aberration within a Marechal criterion is minimum, a lateral magnification M, a numerical aperture NA on an image side of the objective lens, a refractive index n of material of the objective lens, a vertex radius r.sub.2 of curvature of a surface on an image side of the objective lens, and a focal length F of the objective lens satisfy the following conditional expressions respectively, the objective lens is a single lens in which a surface on a light source side is aspherical,
• 0<M<1,
• 0.3.ltoreq.NA, and
• -0.30.ltoreq.F.multidot.(n-1)/r.sub.2 .ltoreq.0.7.

An objective lens for use in an optical system for recording or reproducing an information to or from an optical information recording medium in which an incident converging light is light-formed on an information recording surface of the optical recording medium, the objective lens comprising

• (a) a first surface;
• and
• (b) a second surface provided opposite the first surface, wherein when a wavefront aberration within a Marechal criterion is minimum, a lateral magnification M, a numerical aperture NA on an image side of the objective lens, a refractive index n of material of the objective lens, a difference x.sub.2 between an outermost periphery of effective diameter of on-axis ray of a surface on an image side of the objective lens and a vertex of the surface in an optical axis direction, and a direction in which as a point moves away from the optical axis, the point approaches toward an object side, is positive, and a focal length F of the objective lens satisfy the following conditional expressions respectively, the objective lens is a single lens in which a surface on a light source side is aspherical,
• 0<M<1,
• 0.3.ltoreq.NA, and
• -0.045.ltoreq.x.sub.2 .multidot.(n-1)/{F.multidot.(NA).sup.2 }.ltoreq.0.1.

An objective lens for use in an optical system for recording or reproducing an information to or from an optical information recording medium in which an incident converging light is light-formed on an information recording surface of the optical recording medium, the objective lens comprising:

• (a) a first surface;
• and
• (b) a second surface provided opposite the first surface, wherein when a wavefront aberration within a Marechal criterion is minimum, a lateral magnification M, a numerical aperture NA on an image side of the objective lens, a refractive index n of material of the objective lens, a difference .DELTA..sub.2 between an aspherical surface of an outermost periphery of effective diameter of on-axis ray of a surface on an image side of the objective lens, and a reference spherical surface having a vertex radius of curvature of the aspherical surface in an optical axis direction, and a direction in which as a point moves away from the optical axis, the point approaches toward an object side, is positive, and a focal length F of the objective lens satisfy the following conditional expressions respectively, the objective lens is a single lens in which a surface on a light source side is aspherical,
• 0<M<1,
• 0.3.ltoreq.NA, and
• -0.005.ltoreq..DELTA..sub.2 .multidot.(n-1).sup.3 /{F.multidot.(NA).sup.4 }.ltoreq.0.020.