Diffractive optical elements with mitigation of rebounce-induced light loss and related systems and methods
Display devices include waveguides with in-coupling optical elements that mitigate re-bounce of in-coupled light to improve overall in-coupling efficiency and/or uniformity. A waveguide receives light from a light source and/or projection optics and includes an in-coupling optical element that in-couples the received light to propagate by total internal reflection in a propagation direction within the waveguide. Once in-coupled into the waveguide the light may undergo re-bounce, in which the light reflects off a waveguide surface and, after the reflection, strikes the in-coupling optical element. Upon striking the in-coupling optical element, the light may be partially absorbed and/or out-coupled by the optical element, thereby effectively reducing the amount of in-coupled light propagating through the waveguide. The in-coupling optical element can be truncated or have reduced diffraction efficiency along the propagation direction to reduce the occurrence of light loss due to re-bounce of in-coupled light, resulting in less in-coupled light being prematurely out-coupled and/or absorbed during subsequent interactions with the in-coupling optical element.
1. A display system comprising:
a waveguide including a first major surface and a second major surface opposite the first major surface;
projection optics configured to project a beam of light toward the second major surface of the waveguide; and
an in-coupling optical element disposed on the second major surface of the waveguide, the in-coupling optical element including a diffractive region configured to in-couple light that is incident on the diffractive region such that the light propagates by total internal reflection in a first direction within the waveguide,
wherein the diffractive region is configured, to mitigate re-bounce of in-coupled light propagating in the waveguide, such that a first portion of the beam of light is incident on the diffractive region and at least partly in-coupled into the waveguide, and wherein a second portion of the beam of light impinges on the waveguide without being incident on the diffractive region, and
wherein the diffractive region is configured to reduce a length of the diffractive region along which re-bounce occurs for an in-coupled, outward angled beam component of the beam of light.
2. The display system of claim 1 , wherein the in-coupling optical element is disposed beyond a focal distance of the projection optics, and wherein the light projected by the projection optics is diverging when it reaches the in-coupling optical element.
3. The display system of claim 1 , wherein the in-coupling optical element is disposed closer to the projection optics than a focal distance of the projection optics, and wherein the light projected by the projection optics is converging when it reaches the in-coupling optical element.
4. The display system of claim 1 , wherein the diffractive region is asymmetric about a beam axis that extends from the projection optics and is perpendicular to the second major surface of the waveguide.
5. The display system of claim 4 , wherein the diffractive region is radially asymmetric about the beam axis.
6. The display system of claim 4 , wherein the diffractive region is reflectively asymmetric about an axis of symmetry that is perpendicular to the first direction at the beam axis.
7. The display system of claim 1 , wherein the diffractive region is a high-efficiency diffractive region, and wherein the in-coupling optical element further includes a low-efficiency diffractive region configured such that the second portion of the beam of light from the projection optics is incident on the low-efficiency diffractive region.
8. The display system of claim 7 , wherein the high-efficiency diffractive region is a reflective diffractive region comprising a metalized grating portion, and wherein the low-efficiency diffractive region comprises a non-metalized grating portion.
9. The display system of claim 1 , wherein the second portion of the beam of light propagates out of the waveguide through the second major surface without being in-coupled into the waveguide.
10. The display system of claim 1 , wherein the second portion of the beam of light is in-coupled into the waveguide at a lower efficiency relative to the first portion of the beam of light.
11. The display system of claim 1 , further comprising a waveguide stack including the waveguide, the waveguide stack further comprising:
a second waveguide comprising a first major surface and a second major surface; and
a second in-coupling optical element disposed on the second major surface of the second waveguide, the second in-coupling optical element comprising a second diffractive region covering a larger proportion of an area defined by a second beam of light from the projection optics, relative to a proportion covered by the diffractive region of an area defined by the beam of light.
12. The display system of claim 11 , wherein the second diffractive region is configured to in-couple substantially all of the second beam of light.
13. The display system of claim 11 , wherein the diffractive region is asymmetric about a beam axis that extends from the projection optics and is perpendicular to the second major surface of the waveguide, and wherein the second diffractive region is symmetric about the beam axis.
14. The display system of claim 13 , wherein the diffractive region is radially asymmetric about the beam axis, and wherein the second diffractive region is radially symmetric about the beam axis.
15. The display system of claim 13 , wherein the diffractive region is reflectively asymmetric about an axis of symmetry that is perpendicular to the first direction at the beam axis, and wherein the second diffractive region is reflectively symmetric about the axis of symmetry that is perpendicular to the first direction at the beam axis.
16. The display system of claim 13 , wherein a width of the diffractive region is different than a length of the diffractive region, to reduce an occurrence of the re-bounce of the in-coupled light propagating in the waveguide relative to a diffractive region of substantially equal length and width.
17. The display system of claim 16 , wherein the width of the diffractive region parallel to the first direction is shorter than the length of the diffractive region perpendicular to the first direction.
18. The display system of claim 17 , wherein the width is less than 80% of the length.
19. The display system of claim 11 , wherein the second waveguide is disposed between the waveguide and the projection optics, and wherein the waveguide is spaced from the projection optics by a distance greater than a focal distance of the projection optics.