Patent ID: 8169704
Filing Date: 2012-05-01
Classification: G02B

Abstract:
1. An image display apparatus comprising: an image-forming element configured to form an original image; an optical system configured to guide 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, wherein the diffractive optical element includes plural diffraction grating portions formed of mutually different materials, the plural diffraction grating portions being disposed with a gap therebetween, wherein each of the diffraction grating portions includes plural grating rings each having a grating surface and a grating side surface, wherein, 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, and wherein the diffractive optical element satisfies the following conditions for a k-th grating ring of the plural grating rings in a j-th diffraction grating portion of the plural diffraction grating portions, at least when k=k where: λ represents a design wavelength of the diffractive optical element; θ θ m(j, k) represents the design diffraction order of the k-th grating ring in the j-th diffraction grating portion; P(j, k) represents a pitch between the k-th grating ring and a (k−1)-th grating ring; k M(k) represents a diffraction order of the diffractive optical element; n s represents a total number of the plural grating rings in the j-th diffraction grating portion; and θ represents an angle which the grating side surface forms with the normal to the enveloping surface.