DIFFRACTION OPTICAL ELEMENT

1 . A diffractive optical element comprising:

a body being composed of a first optical material, and having a diffraction grating on a surface thereof; and

an optical adjustment layer being composed of a second optical material, and provided on the body so as to cover the diffraction grating, wherein,

an envelope passing through an edge of the diffraction grating presents a curved an aspherical shape;

along an optical axis direction, an interval between the envelope passing through the edge of the diffraction grating and an envelope passing through grooves of the diffraction grating is constant; and

the optical adjustment layer has a uniform thickness along a normal direction from the envelope passing through the edge of the diffraction grating.

2 . The diffractive optical element of claim 1 , wherein a surface of the optical adjustment layer presents an aspherical shape different from the aspherical shape presented by the envelope passing through the edge of the diffraction grating.

3 . The diffractive optical element of claim 1 , wherein the second optical material comprises a resin.

4 . The diffractive optical element of claim 3 , wherein the second optical material further comprises inorganic particles, the inorganic particles being dispersed within the resin.

5 . The diffractive optical element of claim 1 , wherein a refractive index of the first optical material is smaller than a refractive index of the second optical material, and a wavelength dispersion of the refractive index of the first optical material is greater than a wavelength dispersion of the refractive index of the second optical material.

6 . The diffractive optical element of claim 1 , wherein the first optical material comprises another resin.