| CPC G02B 6/0016 (2013.01) [G02B 6/0036 (2013.01); G02B 27/0081 (2013.01); G02B 27/0172 (2013.01)] | 19 Claims |
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1. A diffractive optical waveguide for optical pupil expansion, comprising:
a waveguide substrate; and
a grating structure disposed on a surface of the waveguide substrate or in the waveguide substrate and comprising a plurality of periodic structures arranged at intervals along a first direction and arranged at intervals along a second direction,
wherein the second direction is different from the first direction; a first distance between the centers of adjacent periodic structures in the first direction is smaller than a second distance between the centers of adjacent periodic structures in the second direction; the first distance is smaller than a projection distance of the second distance in a third direction perpendicular to the first direction, and the third direction is parallel to a plane where the grating structure is located; the first distance is P that satisfies the following relational expression:
 wherein, ε is an included angle between the third direction and the second direction, λ is a wavelength of incident light, (θ,φ) are an incidence angle and azimuth angle of light beam incident onto the grating structure through total reflection propagation in the waveguide substrate, nl is a waveguide refractive index, D is the projection distance, the grating structure is equivalent to a one-dimensional grating with a grating vector in a vertical direction of the first direction, and the vertical direction is parallel to the plane where the grating structure is located.
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