Optical lens and method of producing the same, method of producing optical lens array, focus error signal production method, and optical pickup apparatus

A method of producing an optical lens, comprising the steps of:

• forming, on a substrate made of an optical material, a mask layer corresponding to a shape of an optical lens having a pattern whose width in a first direction is different from a width thereof in a second direction perpendicular to the first direction;
• deforming the mask layer by heat treatment so that a surface area of the mask layer may be reduced;
• and
• removing the mask layer and the substrate simultaneously to transfer the shape of the mask layer to the substrate to form the shape of the optical lens.

A method of producing an optical lens array, comprising the steps of:

• forming, on a substrate made of an optical material, a plurality of mask layer portions corresponding to shapes of a plurality of optical lenses each having a pattern whose width in a first direction is different from a width thereof in a second direction perpendicular to the first direction;
• deforming the mask layer portions by heat treatment so that a surface area of each of the mask layer portions may be reduced;
• and
• removing the mask layer portions and the substrate simultaneously to transfer the shapes of the mask layer portions to the substrate to form the shapes of the optical lenses.

An optical pickup apparatus which irradiates light upon an optical recording medium and receives reflected light from the optical recording medium, comprising:

• a light emitting element for emitting light;
• a light receiving element for receiving the light emitted from said light emitting element;
• and
• an optical member for introducing the light emitted from said light emitting element so as to be irradiated upon the optical recording medium and introducing the reflected light from the optical recording medium to said light receiving element;
• said optical member including an optical lens which includes a substrate made of an optical material and a convex element formed integrally with said substrate and having a convex curved face so as to have a function as an optical lens, said convex element being configured such that a focal length on a first cross section including an axis in a focus direction of said optical lens and a focal length on a second cross section perpendicular to said first cross section and intersecting with said first cross section along the axis in the focus direction are different from each other.