Patent ID: 7710650
Filing Date: 2010-05-04
Classification: G02B

Abstract:
1. A diffractive optical element comprising: a plurality of diffraction gratings which includes two diffraction gratings made of materials having different dispersive powers, the plurality of diffraction gratings including, wherein in the second diffraction grating, a height of the grating portion of the central circular zone from the second base surface is greater than a height of the grating portion of the peripheral circular zone from the second base surfaces, wherein a grating surface of the grating portion of the central circular zone of the second diffraction grating, and a grating surface of the grating portion of the central circular zone of the first diffraction grating are in a contact state, wherein an optical path difference function φ(r) of the diffractive optical element is determined as follows: where r is a distance from the center of the diffractive optical element, and C 1 , C 2 , C 3 , . . . are constants, and wherein a curvature radius R of each of the grating surfaces of the grating portions of the central circular zones of the first and second diffraction gratings in the contact state satisfies the following condition: where n 01 is a refractive index of the material of the first diffraction grating with a wavelength λ 0 , and n 02 is a refractive index of the material of the second diffraction grating with the wavelength λ 0 .