| 摘要 |
The image display apparatus includes an image-forming element, an optical system guiding light from the image-forming element to an exit pupil, and a diffractive optical element disposed between the image-forming element and the optical system or between the optical system and the exit pupil. The diffractive optical element includes plural diffraction grating portions formed of mutually different materials. Each of the diffraction grating portions includes plural grating rings each having a grating surface and a grating side surface. In each of the grating rings, the grating side surface is inclined oppositely to the grating surface with respect to a normal to an enveloping surface passing through apexes of the plural grating rings. The diffractive optical element satisfies the following conditions at least when k=kE: thetad(j, k)=sin-1 [{ni.sin thetai(j, k)-m(j, k).lambda/P(j, k)}/nd]<=thetai(j, k), M(k)=Sigma{m(j, k)}=const, and thetad(j, k)<=thetai(j, k).
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