Patent ID: 7612941
Filing Date: 2009-11-03
Classification: G02B

Abstract:
1. An optical system comprising: a diffractive optical element including a plurality of diffraction gratings laminated and being composed of at least two materials having different dispersions; and a refractive optical element, wherein at least one of the diffraction gratings includes a plurality of grating parts having a curved grating surface and grating tips that connect to define a curved envelope face, wherein the grating surface has a radius of curvature larger than a radius of curvature of the envelope face, wherein an absolute value of the radius of curvature of the envelope face is between one-fifteenth of a focal length of the optical system to one-half of the focal length of the optical system, inclusive, wherein the grating parts of the diffraction grating are arranged concentrically with respect to each other, and the grating side of the grating part is substantially parallel to an optical axis of the optical system, and wherein the plurality of diffraction gratings are bonded together at an area where the grating parts are not formed.