Patent ID: 9001635
Filing Date: 2015-04-07
Classification: G11B

Abstract:
1. An optical element having at least one surface divided into a plurality of regions, the optical element comprising: a first region including an optical axis and configured to converge light with a wavelength λ1 onto a storage surface of a first optical disc and converge light with a wavelength λ2 onto a storage surface of a second optical disc; and a second region formed around the outer circumference of the first region and configured to converge light with the wavelength λ1 onto the storage surface of the first optical disc and converge light with the wavelength λ2 onto the storage surface of the second optical disc, wherein the first region has a first diffraction structure cyclically formed on an aspheric surface and having a step-like cross section, the second region has a second diffraction structure cyclically formed on an aspheric surface and having a step-like cross section, and in the first region, the number of steps included between top portions of the first diffraction structure is different from the number of steps included between the optical axis and a top portion that is closest to the optical axis in the first diffraction structure.