Outward coupling suppression in waveguide display
A pupil replication waveguide for a projector display includes a slab of transparent material for propagating display light in the slab via total internal reflection. A diffraction grating is supported by the slab. The diffraction grating includes a plurality of tapered slanted fringes in a substrate for out-coupling the display light from the slab by diffraction into a blazed diffraction order. A greater portion of the display light is out-coupled into the blazed diffraction order, and a smaller portion of the display light is out-coupled into a non-blazed diffraction order. The tapered fringes result in the duty cycle of the diffraction grating varying along the thickness direction of the diffraction grating, to facilitate suppressing the portion of the display light out-coupled into the non-blazed diffraction order.
1. A method of manufacturing a pupil replication waveguide, the method comprising:
forming on a slab of transparent material a plurality of slanted fringes for out-coupling display light from the slab by diffraction into a blazed diffraction order, the slanted fringes having a first refractive index n 1 ;
forming on the plurality of slanted fringes and the slab a conforming layer forming gaps between the slanted fringes covered with the conforming layer, the conforming layer having a second refractive index n 2 ; and
forming an overcoat layer on the conforming layer, the overcoat layer filling the gaps between the slanted fringes covered with the conforming layer and having a third refractive index n 3 ;
wherein n 1 >n 2 >n 3 or n 1 <n 2 <n 3 .
2. The method of claim 1 , wherein the plurality of slanted fringes is formed by imprinting.
3. The method of claim 1 , wherein the plurality of slanted fringes is formed by etching.
4. The method of claim 1 , wherein the conforming layer is formed by atomic layer deposition (ALD).
5. The method of claim 1 , wherein the overcoat layer is formed by spin-coating.
6. A pupil replication waveguide comprising:
a slab of transparent material for propagating display light therein via total internal reflection;
a diffraction grating supported by the slab and comprising:
a plurality of slanted fringes for out-coupling display light from the slab by diffraction into a blazed diffraction order, the slanted fringes having a first refractive index n 1 ;
a conforming layer on the plurality of slanted fringes and the slab, the conforming layer forming gaps between the slanted fringes covered with the conforming layer, the conforming layer having a second refractive index n 2 ; and
an overcoat layer on the conforming layer, the overcoat layer being disposed in the gaps between the slanted fringes covered with the conforming layer and having a third refractive index n 3 ;
wherein n 1 >n 2 >n 3 or n 1 <n 2 <n 3 .
7. The pupil replication waveguide of claim 6 , wherein the plurality of slanted fringes is formed by imprinting.
8. The pupil replication waveguide of claim 6 , wherein the plurality of slanted fringes is formed by etching.
9. The pupil replication waveguide of claim 6 , wherein the conforming layer is formed by atomic layer deposition (ALD).
10. The pupil replication waveguide of claim 6 , wherein the overcoat layer is formed by spin-coating.
11. The pupil replication waveguide of claim 6 , wherein an effective refractive index profile of the diffraction grating along a thickness direction of the diffraction grating is symmetrical.
12. The pupil replication waveguide of claim 11 , wherein a refractive index contrast is larger at a middle than at both sides of the refractive index contrast profile.