Patent ID: 7236655

Claim:
An optical element, comprising: a first periodic structure having a period shorter than a wavelength of used light; and a second periodic structure that has a period shorter than the wavelength of the used light and in which a direction of the period is orthogonal to or substantially orthogonal to that of the first periodic structure, the second periodic structure being adjacent to the first periodic structure, wherein the period of the first periodic structure and the period of the second structure are different from each other, wherein with respect to a first plane including a periodic direction of the first periodic structure and a normal to a plane of the first periodic structure and a second plane including a periodic direction of the second periodic structure and a normal to a plane of the second periodic structure, the period of the periodic structure in one of the first and second planes in which a maximal incident angle of a used light beam is larger than that in the other plane is smaller than the period of the other periodic structure in the other plane of the first and second planes.