| 摘要 |
An optical element has at least one surface divided into a plurality of regions and includes: a first region configured to converge light with a wavelengthλ1 onto a storage surface of a first optical disc and converge light with a wavelengthλ2 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 wavelengthλ1 onto the storage surface of the first optical disc. The second region has a concave-convex structure concentrically formed on an aspheric surface and having a cross section being a saw teeth shape. The concave-convex structure is formed by a plurality of different saw teeth shapes, and the plurality of different saw teeth shapes respectively give different phase differences corresponding to substantially integer multiples of the wavelengthλ1, for light with the wavelengthλ1. |
