Lens for an optical disc recording and/or reproducing apparatus

Claim 2

A single focusing lens for an apparatus for recording and/or reproducing an optical disc having a substrate of a known thickness, the focusing lens comprising: a first aspherical surface; and a second aspherical surface; wherein the focusing lens has; a focal length such that the thickness of the substrate of the optical disc divided by the focal length is between 0.25 and 0.35, a lens thickness such that the thickness of the substrate of the optical disc divided by the lens thickness is between 0.3 and 0.4, and a numerical aperture substantially equal to 0.6.

Claim 3

A single focusing lens for an apparatus for recording and/or reproducing an optical disc, the focusing lens comprising: a first aspherical surface; and a second aspherical surface; wherein the focusing lens has: the following parameters in the first aspherical surface: K=-0.279372 (K: conic constant) A=-0.75198e-2 (mm.sup.-4) B=-0.313881e-2 (mm.sup.-6) C=+0.452206e-3 (mm.sup.-8) D=-0.434638e-3 (mm.sup.-10), and the following parameters in the second aspherical surface: K=-23.231301 K: conic constant) A=0.706198e-2 (mm.sup.-4) B=-0.186959e-2 (mm.sup.-6) C=-0.111016e-3 (mm.sup.-8) D=0.6295059e-3 (mm.sup.-10), an optical axis and a lens thickness near the optical axis of 1.9 millimeters, a refractive index of 1.582509 at a wavelength of 780 nanometers, and wherein the first aspherical surface and the second aspherical surface each have a radius of curvature, and are each defined by the relationship: z=cy.sup.2 /(1+{1-(1+K)c.sup.2 y.sup.2 }.sup.1/2)+Ay.sup.4 +By.sup.6 +Cy.sup.8 +Dy.sup.10, c=1/r, where z is the direction of the optical axis, y is the direction perpendicular to the optical axis, and r is the radius of curvature of the aspherical surface.

Claim 4

A single focusing lens for an apparatus for recording and/or reproducing an optical disc, the focusing lens comprising: a first aspherical surface; and a second aspherical surface; wherein the focusing lens has: the following parameters in the first aspherical surface: K=-0.279372 (K: conic constant) A=-0.75198e-2 (mm.sup.-4) B=-0.313881e-2 (mm.sup.-6) C=+0.452206e-3 (mm.sup.-8) D=-0.434638e-3 (mm.sup.-10), and the following parameters in the second aspherical surface: K=-23.231301 K: conic constant) A=0.706198e-2 (mm.sup.-4) B=-0.186959e-2 (mm.sup.-6) C=-0.111016e-3 (mm.sup.-8) D=0.6295059e-3 (mm.sup.-10), an optical axis and a lens thickness near the optical axis of 1.9 millimeters, a refractive index of 1.582509 at a wavelength of 780 nanometers, and wherein the first aspherical surface and the second aspherical surface each have a radius of curvature, and are each defined by the relationship: z=cy.sup.2 /(1+{1-(1+K)c.sup.2 y.sup.2 }.sup.1/2)+Ay.sup.4 +By.sup.6 +Cy.sup.8 +Dy.sup.10, c=1/r, where z is the direction of the optical axis, y is the direction perpendicular to the optical axis, and r is the radius of curvature of the aspherical surface.