Optical systems with partial reflectors on waveguides for maximizing pupil size coupling
A display may include a waveguide, a prism that directs a pupil of light into the waveguide, and a partial reflector between the prism and the waveguide. The partial reflector may reflect a second portion of the pupil incident from within the waveguide but not a first portion of the pupil incident from within the waveguide. This may couple some of the second portion of the pupil back into the waveguide that would otherwise be lost through the prism after a first reflection off the waveguide surface opposite the prism. The partial reflector may sacrifice luminance of the light to maximize the pupil size that can be uniformly coupled into the waveguide for propagation to the eye box while minimizing the thickness of the waveguide.
1 . An electronic device comprising:
a projector configured to generate light;
a waveguide;
a prism on the waveguide and configured to couple the light into the waveguide; and
a partial reflector between the prism and the waveguide, wherein the prism has a surface facing the waveguide and has a reflective surface, the prism is configured to receive the light through the waveguide and the surface, and the reflective surface is configured to reflect the light into the waveguide through the surface.
2 . The electronic device of claim 1 , wherein the waveguide has a first lateral surface and a second lateral surface opposite the first lateral surface, the prism is mounted to the second lateral surface, the image light comprises a pupil, the partial reflector is configured to transmit, into the waveguide, a first portion and a second portion of the pupil, the first portion of the pupil is configured to be incident, after a first reflection off the reflective surface, upon a portion of the first lateral surface that is non-overlapping with respect to the prism, and the second portion of the pupil is configured to be incident, after a second reflection off the first lateral surface, upon the partial reflector.
3 . The electronic device of claim 1 , wherein the partial reflector overlaps some but not all of the surface.
4 . The electronic device of claim 3 , wherein the partial reflector overlaps a first portion of the surface, a second portion of the surface is non-overlapping with respect to the partial reflector, and the partial reflector is configured to reflect a portion of the light that is transmitted into the waveguide through the second portion of the surface after a reflection in the waveguide.
5 . The electronic device of claim 4 , further comprising:
a transparent phase compensation layer between the prism and the waveguide, wherein the transparent phase compensation layer overlaps the second portion of the surface.
6 . The electronic device of claim 4 , wherein the partial reflector has an edge region at the second portion of the surface, the edge region having a gradual reflectivity.
7 . The electronic device of claim 6 , wherein the partial reflector has a tapered thickness in the edge region.
8 . The electronic device of claim 1 , wherein the prism has a surface facing the waveguide that is configured to transmit the light into the waveguide and the partial reflector overlaps an entirety of the surface.
9 . The electronic device of claim 1 , wherein the partial reflector comprises a metal layer.
10 . The electronic device of claim 1 , wherein the partial reflector comprises a dielectric film.
11 . The electronic device of claim 1 , wherein the partial reflector comprises a set of diffractive gratings.
12 . The electronic device of claim 1 , wherein the waveguide has a first lateral surface and a second lateral surface opposite the first lateral surface, wherein a quarter waveplate is on the first lateral surface of the waveguide and configured to receive the light coupled into the waveguide through the prism, wherein the partial reflector comprises a reflective polarizer on the second lateral surface, the prism being configured to couple the light into the waveguide through the reflective polarizer.
13 . An electronic device comprising:
a projector configured to generate light;
a waveguide;
a prism on the waveguide and configured to couple the light into the waveguide; and
a partial reflector between the prism and the waveguide, wherein the partial reflector comprises:
a reflective polarizer; and
a quarter waveplate on the reflective polarizer and interposed between the reflective polarizer and the waveguide.
14 . The electronic device of claim 13 , wherein the prism comprises a transmissive input coupling prism configured to couple the image light into the waveguide through the reflective polarizer and the quarter waveplate.
15 . The electronic device of claim 13 , wherein the prism comprises a reflective input coupling prism configured to receive the light through the quarter waveplate and the reflective polarizer and having a reflective surface configured to reflect the image light into the waveguide through the reflective polarizer and the quarter waveplate.
16 . An electronic device comprising:
a waveguide;
a prism on the waveguide and configured to receive a pupil of image light; and
a partial mirror between the prism and the waveguide, wherein the partial mirror has an edge region and has a tapered thickness in the edge region, and wherein the prism is configured to direct a first portion of the pupil and a second portion of the pupil into the waveguide and wherein the partial mirror is configured to receive, from within the waveguide, the second portion but not the first portion of the pupil.
17 . The electronic device of claim 16 , wherein the partial mirror is configured to transmit the first portion but not the second portion of the pupil into the waveguide from the prism.
18 . The electronic device of claim 17 , wherein the prism comprises a transmissive input coupling prism.
19 . The electronic device of claim 17 , wherein the prism comprises a reflective input coupling prism.
20 . The electronic device of claim 16 , wherein the edge region has a gradual reflectivity.