Patent ID: 8040778

Claim:
A diffractive element, comprising: a transparent substrate; a grating portion including a plurality of convex portions provided on at least one principal plane of said transparent substrate having a first layer containing a first transparent material and a second layer containing a second transparent material, and extended in parallel to each other in a first direction as well as periodically arranged in a second direction orthogonal to said first direction; and a filling portion for filling a third layer containing a third transparent material at least between said plurality of convex portions, wherein the relationship α A <α C <0 and |α C |>|α B | is satisfied, wherein α A is the change rate of the refractive index with the change of temperature of said first transparent material, α B is the change rate of the refractive index with the change of temperature of said second transparent material, and α C is the change rate of the refractive index with the change of temperature of said third transparent material, wherein said first transparent material is an acrylic resin, an epoxy resin or a fluorine-containing aromatic polymer material.