Patent ID: 6950383
Filing Date: 2005-09-27
Classification: G11B

Abstract:
1. An objective lens for use in an optical pickup apparatus for recording and/or reproducing information of an optical information recording medium, wherein the objective lens is a single lens comprising an aspherical surface on at least one surface; wherein the objective lens is a finite conjugate type to converge a divergent light flux from a light source onto an information recording plane of the optical information recording medium and satisfies the following formula: where NA is an image-side numerical aperture necessary for conducting recording and/or reproducing information of the optical information recording medium, and wherein the following formula is satisfied: where f is a focal length, where n is a refractive index of the objective lens for a used wavelength, where m is a lateral magnification of the objective lens defined with the formula of NA where X1 is a difference (mm) in the direction of an optical axis between a plane that is perpendicular to the optical axis and is tangent to the vertex of a light source side surface and a light source side surface at the outermost periphery in the effective diameter (at a position on a light source side surface where the marginal ray at the above NA enters), and where X1 takes a positive sign when it is measured in the direction toward the optical information recording medium from the tangent plane that serves as a reference point, and X1 takes a negative sign when it is measured in the direction toward the light source, and where X2 is a difference (mm) in the direction of the optical axis between a plane that is perpendicular to the optical axis and is tangent to the vertex of an optical information recording medium side surface and an optical information recording medium side surface at the outermost periphery in the effective diameter (at a position on an optical information recording medium side surface where the marginal ray at the above NA enters), and where X2 takes a positive sign when it is measured in the direction toward the optical information recording medium from the tangent plane that serves as a reference point, and X2 takes a negative sign when it is measured in the direction toward the light source.