Waveguide display with total internal reflection band between color channels
A display may include a waveguide having a grating medium sandwiched between first and second substrates. A cross-coupler can direct light in the waveguide towards an output coupler. The output coupler may include volume holograms in the medium. The output coupler may couple the light out of the waveguide and towards an eye box. The cross-coupler may include a surface relief grating (SRG). The SRG may diffract an entirety of the fields of view of different color channels of light incident upon the SRG from within a total internal reflection (TIR) range of the waveguide onto angles at opposing sides of a TIR transition angle of the waveguide. This may prevent the formation of unsightly dark bands in one or more of the color channels at the eye box.
1 . An electronic device comprising:
a waveguide having a first substrate, a second substrate, and a grating medium sandwiched between the first substrate and the second substrate, wherein the first substrate is configured to propagate at least a first color channel and a second color channel of light via total internal reflection (TIR);
a third substrate on the waveguide;
a first optical coupler configured to couple the light into the waveguide;
a second optical coupler configured to couple the light out of the waveguide, the second optical coupler comprising volume holograms in the grating medium; and
a third optical coupler configured to redirect the light from the first optical coupler towards the second optical coupler, wherein the third optical coupler comprises a surface relief grating (SRG) in the third substrate, the SRG is configured to diffract the first color channel of the light onto first angles within a TIR range of the first substrate, and the SRG is configured to diffract the second color channel of the light onto second angles outside the TIR range of the first substrate.
2 . The electronic device of claim 1 , wherein the first substrate is configured to propagate a third color channel of the light via TIR and the SRG is configured to diffract the third color channel of the light onto third angles outside the TIR range of the first substrate.
3 . The electronic device of claim 2 , wherein the first color channel comprises red wavelengths, the second color channel comprises green wavelengths, and the third color channel comprises blue wavelengths.
4 . The electronic device of claim 1 , wherein the first substrate is configured to propagate a third color channel of the light via TIR and the SRG is configured to diffract the third color channel of the light onto third angles within the TIR range of the first substrate.
5 . The electronic device of claim 4 , wherein the first color channel comprises green wavelengths, the second color channel comprises red wavelengths, and the third color channel comprises blue wavelengths.
6 . The electronic device of claim 1 , wherein the third substrate is layered between the grating medium and the first substrate.
7 . The electronic device of claim 6 , wherein the grating medium contacts the first substrate, the SRG comprises grooves and troughs, and the grating medium fills the troughs.
8 . The electronic device of claim 1 , wherein the first color channel of the light has a first field of view, the second color channel of the light has a second field of view, an entirety of the first field of view is within the TIR range of the first substrate after diffraction by the SRG, and an entirety of the second field of view is outside the TIR range of the first substrate after diffraction by the SRG.
9 . The electronic device of claim 1 , further comprising:
an input coupling prism configured to couple the first color channel of the light and the second color channel of the light into the first substrate.
10 . An electronic device comprising:
a waveguide having a first substrate, a second substrate, a grating medium interposed between the first substrate and the second substrate, and a third substrate layered between the grating medium and the first substrate, the waveguide being configured to propagate light via total internal reflection (TIR);
volume holograms in the grating medium and configured to couple the light out of the waveguide; and
a surface relief grating (SRG) in the third substrate, wherein
the SRG is configured to receive the light from within the first substrate,
the SRG is configured to diffract the light towards the volume holograms,
the light has a first color channel,
the light has a second color channel different from the first color channel,
the SRG is configured to diffract the first color channel of the light onto a first side of a TIR transition angle of the first substrate, and
the SRG is configured to diffract the second color of the light onto a second side of the TIR transition angle of the first substrate.
11 . The electronic device of claim 10 , wherein the first color channel of the light has a first field of view, the second color channel of the light has a second field of view, and the SRG is configured to diffract an entirety of the first field of view onto first angles at the first side of the TIR transition angle.
12 . The electronic device of claim 11 , wherein the SRG is configured to diffract an entirety of the second field of view onto second angles at the second side of the TIR transition angle.
13 . The electronic device of claim 12 , wherein the TIR transition angle is between the first field of view and the second field of view after diffraction of the first color channel of the light and the second color channel of the light by the SRG.
14 . The electronic device of claim 10 , wherein the first color channel comprises red wavelengths and the second color channel comprises green wavelengths.
15 . The electronic device of claim 10 , wherein the first color channel of the light passes from the first substrate into the grating medium after a first interaction of the first color channel of the light with the SRG.
16 . The electronic device of claim 15 , wherein the second color channel of the light continues to propagate within the first substrate via TIR after a first interaction of the second color channel of the light with the SRG.
17 . The electronic device of claim 10 , wherein the grating medium has a first refractive index and the third substrate has a second refractive index greater than the first refractive index.
18 . An electronic device comprising:
a first substrate;
a second substrate;
a grating medium interposed between the first substrate and the second substrate, wherein the first substrate is configured to propagate at least a first color channel and a second color channel of light via total internal reflection (TIR);
a third substrate layered between the first substrate and the grating medium; and
a surface relief grating (SRG) in the third substrate, wherein the SRG is configured to
diffract the first color channel of the light from a first k-space region onto a second k-space region, and
diffract the second color channel of the light from the first k-space region onto a third k-space region, the first substrate having a TIR transition angle between the second k-space region and the third k-space region.
19 . The electronic device of claim 18 , wherein the first substrate is configured to propagate a third color channel of the light via TIR, the SRG is configured to diffract the third color channel of the light from the first k-space region onto a fourth k-space region different from the third k-space region, the TIR transition angle of the first substrate is between the second k-space region and the fourth k-space region, the first color channel comprises red wavelengths, the second color channel comprises green wavelengths, and the third color channel comprises blue wavelengths.
20 . The electronic device of claim 18 , further comprising:
volume holograms in the grating medium, wherein the volume holograms are configured to receive the first color channel and the second color channel of the light from the SRG, and wherein the volume holograms are configured to diffract the first color channel and the second color channel of the light towards an eye box.