EP-4740048-A1 - WAVEGUIDE DISPLAY HAVING GRATINGS WITH CONTINUOUS PHASE SHIFTING

Abstract

A display may include a waveguide that directs image light to an eye box. The waveguide may include an optical coupler that redirects and replicates the light. The coupler may include a surface relief grating (SRG). The SRG may have a pitch that varies continuously along an axis orthogonal its ridges. The pitch may vary sinusoidally, linearly, parabolically, or according to other continuous and differentiable functions of position along the axis. The SRG may diffract the light. Upon diffracting the light, the SRG may impart a phase to the light. The phase may vary continuously as a function of position along a first axis and may, if desired, vary continuously as a function of position along a second axis orthogonal to the first axis. The SRG may prevent formation of coherent light paths after replication, thereby maximizing the efficiency of the system.

Inventors

• BORN, BRANDON
• ZHU, Wencong
• HONG, Jong, Young
• OH, Se, Baek

Assignees

• Apple Inc.

Dates

Publication Date

20260513

Application Date

20240820

Claims (20)

1. 1. An electronic device comprising: a waveguide configured to propagate light; and an optical coupler configured to redirect and replicate the light, wherein the optical coupler includes a substrate on the waveguide, and a surface relief grating (SRG) in the substrate, wherein the SRG has ridges with a pitch that varies continuously as a function of position along an axis orthogonal to the ridges.
2. 2. The electronic device of claim 1, wherein the pitch varies periodically as a function of position along the axis.
3. 3. The electronic device of claim 2, wherein the pitch varies sinusoidally as a function of position along the axis.
4. 4. The electronic device of claim 3, wherein the ridges follow periodic paths.
5. 5. The electronic device of claim 4, wherein the periodic paths comprise sinusoidal paths.
6. 6. The electronic device of claim 1, wherein the pitch varies parabolically as a function of position along the axis.
7. 7. The electronic device of claim 6, wherein the SRG has a length along the axis and the SRG has a minimum pitch halfway along the length.
8. 8. The electronic device of claim 6, wherein the SRG has a length along the axis and the SRG has a minimum pitch that is offset from halfway along the length.
9. 9. The electronic device of claim 1, further comprising: an additional SRG in the substrate and overlapping the SRG, wherein the additional SRG has additional ridges oriented non-parallel with respect to the ridges in the SRG, and wherein the additional ridges have an additional pitch that varies continuously as a function of position along an additional axis orthogonal to the additional ridges.
10. 10. The electronic device of claim 1, wherein the waveguide has a first lateral surface, a second lateral surface opposite the first lateral surface, and the substrate is layered on the first lateral surface, the electronic device further comprising: an additional substrate layered on the second lateral surface; and an additional SRG in the additional substrate and overlapping the SRG, wherein the additional SRG has additional ridges oriented non-parallel with respect to the ridges in the SRG, and wherein the additional ridges have an additional pitch that varies continuously as a function of position along an additional axis orthogonal to the additional ridges.
11. 11. The electronic device of claim 1 , further comprising: an input coupler configured to couple the light into the waveguide; and an output coupler configured to couple the light out of the waveguide, the optical coupler comprising a cross-coupler configured to redirect the light from the input coupler towards the output coupler.
12. 12. An electronic device comprising: a waveguide configured to propagate light; and an optical coupler configured to redirect and replicate the light, wherein the optical coupler includes a substrate on the waveguide, and a diffractive grating in the substrate, wherein the diffractive grating is configured to impart a phase to the light upon diffracting the light and wherein the phase varies continuously as a function of position along an axis.
13. 13. The electronic device of claim 12, wherein the function is a continuous and differentiable function.
14. 14. The electronic device of claim 13, wherein the continuous and differentiable function is a sinusoidal function.
15. 15. The electronic device of claim 13, wherein the continuous and differentiable function is a parabolic function.
16. 16. The electronic device of claim 12, wherein the continuous and differentiable function is a linear function.
17. 17. The electronic device of claim 12, wherein the phase varies continuously as a function of position along an additional axis orthogonal to the axis.
18. 18. The electronic device of claim 17, wherein the phase varies parabolically along the axis and varies parabolically along the additional axis.
19. 19. The electronic device of claim 12, wherein the diffractive grating comprises a surface relief grating.
20. 20. An electronic device comprising: a waveguide configured to propagate light; and an optical coupler configured to redirect and replicate the light, wherein the optical coupler includes a substrate on the waveguide, and a surface relief grating (SRG) in the substrate, wherein the SRG has ridges and troughs that follow sinusoidal paths.

Description

Waveguide Display Having Gratings with Continuous Phase Shifting This application claims priority to U.S. Patent Application No. 18/805,955, filed August 15, 2024, and U.S. Provisional Patent Application No. 63/583,085, filed September 15, 2023, each of which are hereby incorporated by reference herein in their entireties. Background [0001] This disclosure relates to optical systems such as optical systems in electronic devices having displays. [0002] Electronic devices can include displays that provide images near the eyes of a user. Such electronic devices often include virtual or augmented reality headsets with displays having optical elements that allow users to view the displays. If care is not taken, components used to display images can be bulky and might not exhibit desired levels of optical performance. For example, coherent light paths in the display can produce destructive interference that reduces the efficiency of the display. Summary [0003] An electronic device may include a display having a waveguide that directs image light to an eye box. The waveguide may include an optical coupler that redirects and replicates the image light. The optical coupler may include one or more surface relief gratings (SRGs). The SRG may have a pitch that varies continuously along an axis orthogonal to the ridges of the SRG. The pitch may vary sinusoidally, linearly, parabolically, or according to other continuous and differentiable functions of position along the axis. [0004] The SRG may diffract the image light. Upon diffracting the image light, the SRG may impart a phase to the image light. The phase may vary continuously as a function of position along a first axis and may, if desired, vary continuously as a function of position along a second axis orthogonal to the first axis. The SRG may, for example, exhibit a parabolic or paraboloid phase map. If desired, the ridges and troughs of the SRG may follow sinusoidal paths. The SRG may prevent formation of coherent light paths after replication, thereby maximizing the efficiency of the system. Continuously varying the pitch or phase may prevent the formation of smear artifacts in the image light associated with sharp boundaries between regions of different pitch or phase. Brief Description of the Drawings [0005] FIG. 1 is a diagram of an illustrative system having a display in accordance with some embodiments. [0006] FIG. 2 is a top view of an illustrative optical system for a display having a waveguide with optical couplers in accordance with some embodiments. [0007] FIGS. 3A-3C are top views of illustrative waveguides provided with a surface relief grating in accordance with some embodiments. [0008] FIG. 4 is a front view of an illustrative waveguide having optical couplers formed from surface relief gratings in accordance with some embodiments. [0009] FIG. 5 is a front view of an illustrative waveguide having an optical coupler with first and second overlapping surface relief gratings oriented in different directions in accordance with some embodiments. [0010] FIG. 6 is a front view showing how a surface relief grating having constant pitch can produce coherent light paths in a pupil replicating optical coupler in accordance with some embodiments. [0011] FIG. 7 is a front view of an illustrative surface relief grating having a continuously varied pitch across its lateral area in accordance with some embodiments. [0012] FIG. 8 is a front view of an illustrative surface relief grating having ridges that follow periodic paths in accordance with some embodiments. [0013] FIG. 9 is a plot showing how an illustrative surface relief grating may have a pitch that continuously varies in a parabolic pattern across its lateral area in accordance with some embodiments. [0014] FIG. 10 is a one-dimensional phase map showing how an illustrative surface relief grating may impart a phase to diffracted light that varies parabolically along a first axis in accordance with some embodiments. [0015] FIG. 11 is a two-dimensional phase map showing how an illustrative surface relief grating may impart a phase to diffracted light that varies parabolically along a first axis in accordance with some embodiments. [0016] FIG. 12 is a one-dimensional phase map showing how an illustrative surface relief grating may impart a phase to diffracted light that varies parabolically along a second axis in accordance with some embodiments. [0017] FIG. 13 is a two-dimensional phase map showing how an illustrative surface relief grating may impart a phase to diffracted light that varies parabolically along first and second orthogonal axes in accordance with some embodiments. [0018] FIG. 14 is an exploded front view showing how the ridges of an illustrative surface relief grating provided with a phase map of the types shown in FIGS. 10-13 may follow curved paths in accordance with some embodiments. Detailed Description [0019] System 10 of FIG. 1 may be a head-mounted device having one or more display