A diffractive optical element in which eclipse of rays at a grating side surface of a diffraction grating can be reduced is disclosed. In a diffractive optical element comprises a plurality of diffraction gratings made of different materials are laminated, at least one of the plurality of diffraction...http://www.google.ca/patents/US6947214?utm_source=gb-gplus-sharePatent US6947214 - Diffractive optical element and optical system having the same
