An optical lens whose focal length is different on first and second planes perpendicular
to each other is provided. The optical lens is configured such that a convex element,
which is formed integrally with a substrate having a flat face, has a convex curved
face that functions as an optical lens and is shaped such that the curvature on
a first cross section and the curvature on a second cross section perpendicular
to and intersecting with the first cross section are different from each other,
whereby the focal lengths on the first and second cross sections are different
from each other. A groove of a substantially elliptical shape or a substantially
rectangular shape is formed along the boundary between the substrate and the convex
element. The optical lens is used to produce a focus error signal or is incorporated
into an optical pickup apparatus.
