PHASE STRUCTURE ON SURFACE-RELIEF GRATING-BASED WAVEGUIDE DISPLAY
A waveguide display includes a substrate transparent to visible light, a first grating on the substrate and configured to couple display light into or out of the substrate, and a phase structure on the substrate and configured to change a polarization state of the display light after or before the display light reaches the first grating. The first grating is characterized by a polarization-dependent diffraction efficiency. The first grating includes, for example, a surface-relief grating or a volume Bragg grating.
1 . A waveguide display comprising:
a substrate transparent to visible light;
a first surface-relief grating on the substrate and configured to couple display light into or out of the substrate, wherein the first surface-relief grating is characterized by a polarization-dependent diffraction efficiency; and
a phase structure on the substrate and configured to change a polarization state of the display light after or before the display light reaches the first surface-relief grating.
2 . The waveguide display of claim 1 , wherein the phase structure comprises a waveplate.
3 . The waveguide display of claim 2 , wherein the waveplate is characterized by a waveplate thickness between zero and one wavelength.
4 . The waveguide display of claim 1 , wherein the phase structure comprises a layer of a birefringent material.
5 . The waveguide display of claim 1 , wherein the phase structure comprises a subwavelength structure and an overcoat layer.
6 . The waveguide display of claim 5 , wherein the subwavelength structure is etched in the substrate.
7 . The waveguide display of claim 5 , wherein the subwavelength structure is etched in a material layer formed on the substrate.
8 . The waveguide display of claim 5 , wherein a difference between a refractive index of the substrate and an effective refractive index of the phase structure including the subwavelength structure and the overcoat layer is less than 0.35.
9 . The waveguide display of claim 1 , further comprising a second surface-relief grating on the phase structure, wherein the phase structure is between the substrate and the second surface-relief grating.
10 . The waveguide display of claim 9 , wherein a waveplate thickness of the phase structure is a quarter wavelength.
11 . The waveguide display of claim 9 , wherein the phase structure is arranged such that an angle between a fast axis of the phase structure and a grating vector of the first surface-relief grating is 45°.
12 . The waveguide display of claim 1 , further comprising a second surface-relief grating between the substrate and the phase structure.
13 . The waveguide display of claim 1 , wherein:
the first surface-relief grating is on a first surface of the substrate and is configured to couple the display light into the substrate; and
the phase structure is on a second surface of the substrate opposing the first surface and is configured to change the polarization state of the display light coupled into the substrate.
14 . The waveguide display of claim 1 , wherein the phase structure is in selected regions of the substrate.
15 . The waveguide display of claim 1 , wherein the phase structure is characterized by a spatially varying phase retardation across different regions of the phase structure.
16 . The waveguide display of claim 1 , wherein the phase structure is configured to convert s-polarized light to p-polarized light, convert p-polarized light to s-polarized light, convert linearly polarized light to circularly polarized light, or convert circularly polarized light to linearly polarized light.
17 . A waveguide display comprising:
a substrate transparent to visible light;
a first surface-relief grating on a first surface of the substrate and configured to couple display light into the substrate such that the display light propagates within the substrate through total internal reflection, wherein the first surface-relief grating is characterized by a polarization-dependent diffraction efficiency; and
a phase structure on a second surface of the substrate opposing the first surface, the phase structure configured to change a polarization state of the display light coupled into the substrate.
18 . The waveguide display of claim 17 , wherein the phase structure includes:
a layer of a birefringent material; or
a subwavelength structure formed in an isotropic material or the birefringent material.
19 . The waveguide display of claim 17 , wherein:
the phase structure includes a subwavelength structure and an overcoat layer; and
a difference between a refractive index of the substrate and an effective refractive index of the phase structure including the subwavelength structure and the overcoat layer is less than 0.35.
20 . The waveguide display of claim 17 , further comprising a second surface-relief grating on the phase structure, wherein the phase structure is between the substrate and the second surface-relief grating or the second surface-relief grating is between the substrate and the phase structure.