Multiplexed volume holographic coupler for augmented reality waveguide

Abstract

Volume holographic couplers are multiplexed into the same volume to increase the field of view of components in the waveguide assembly, such as augmented reality (AR) waveguide assemblies for use in electronic eyewear devices. The multiplexing may be performed in any direction perpendicular to the optical axis. The multiplexing of the volume holographic coupler combines the different functions of the waveguide assembly into a diffractive optical element (DOE) in the form of an input coupler or an output coupler. For example, each volume holographic grating of the input coupler and the output coupler has a different refraction angle, a different periodicity, or both relative to any other volume holographic grating in the same volume. The resulting DOE reduces re-interaction loss, reduces thickness, reduces the number of DOEs as well as the number of layers and air gaps, and improves robustness (surface relief that may be scratched or broken by volume contrast).

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. application serial number 17 / 850,983, filed on June 27, 2022, the contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] Examples described herein relate generally to volume hologram couplers for waveguides, and specifically to volume hologram couplers that multiplex multiple volume holograms into a single optical device that implements the functionality of a single state-of-the-art volume hologram and increases the field of view of a system including an augmented reality (AR) waveguide. Background Art

[0004] Volume holography has been used in AR devices, such as eye-worn devices with limited eye box size and limited field of view. The eye box is a three-dimensional space in which the user can place their eyes to correctly see the entire virtual image without moving the head or making any other adjustments. Multiplexing and layering have been used with diffractive optical elements and combiner optics to achieve multicolor performance, but have not yet been used to achieve increased field of view or one- or two-dimensional eye box expansion in AR devices.

[0005] The state-of-the-art in augmented reality waveguide combiner optics uses broadband surface relief structures and diffractive optical elements. Specifically, output couplers based on surface relief gratings (SRGs) have light incident at angles far from the Bragg condition and therefore have low diffraction efficiency. This approach allows for multiple interactions with the SRGs and provides eyebox expansion. However, eyebox expansion comes at the expense of optical efficiency and increased power draw of the light source of the AR device. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] In the accompanying drawings, which are not necessarily drawn to scale, like numbers may describe similar components in different views. Some non-limiting examples are shown in the figures of the accompanying drawings, in which:

[0007] Figures 1A to 1E is a graph showing thickness (d) versus diffraction angle of a grating, demonstrating that increasing the thickness of a diffractive optical element increases the diffraction efficiency but decreases the angular and wavelength bandwidth.

[0008] FIG. 2A to FIG. 2C is an illustration of a volume grating where several structures are multiplexed in the same volume but operated independently.

[0009] Figure 3Ais an illustration of a diffractive optical element (DOE) used in augmented reality (AR) glasses to capture light in a waveguide through total internal reflection (TIR) ​​and force the light to exit at a desired location, such as in front of the user's eyes.

[0010] Figure 3B An illustration of a real or AR image presented to the user's eyes in an eye box.

[0011] Figure 4 The operation of a matched input coupler (IC) and output coupler (OC) in reflection mode is shown, whereby light (kp) incident on the IC is diffracted (kd) at an angle greater than the critical angle and captured in the waveguide by TIR.

[0012] Figure 5A and Figure 5B is a graph of the incident angle and diffraction of light on a matched IC / OC waveguide assembly using a single volume holographic grating and the corresponding intensity of the diffracted light.

[0013] Fig. 6A and Figure 6B It is shown Figure 4 Illustration of the IC-OC matched volume grating in transmission mode of matched IC and OC.

[0014] Figure 7 is a diagram of a waveguide, where each arrow pointing upward represents an image extracted from the waveguide each time a light wave captured by TIR interacts with the OC.

[0015] Figure 8 is an illustration of a folded grating in an example configuration.

[0016] Fig. 9A and Fig. 9B is an illustration of a volume grating using multiplexing in an example configuration to allow multiple gratings to occupy the same volume simultaneously to increase the field of view of a waveguide assembly.

[0017] Fig. 10A and Fig. 10B is a graph of the angle of propagation of light from the normal to the waveguide / air interface of a matched IC / OC waveguide using volume holographic gratings, and a graph of the corresponding intensity of light diffraction from a simulation result of angular multiplexing of different parts of the image using 9 (9x) gratings.

[0018] Fig.11 yes Figure 7 Isometric view of FIG. 1 showing the IC positioned at a single internal reflection of light from the OC or within multiple internal reflections from the OC for one-dimensional eye box expansion.

[0019] Fig.12is a diagram illustrating that re-interaction losses may occur when a light wave captured by TIR is incident on an IC before reaching the portion of the waveguide between the IC and the OC or the portion of the waveguide that includes an interface with the OC.

[0020] Fig.13 is a graph of incident angle and diffraction of light on an IC using a volume grating, and the corresponding light intensity, where the range of incident angles is shown within the range captured by TIR.

[0021] Fig.14 is an illustration of a waveguide with a folded hologram that simultaneously folds and splits an input beam that is captured by TIR but does not outcouple the light.

[0022] Fig.15 Using volume grating Fig.14 Graph of the incident angle and diffraction of light on a folded hologram and the corresponding intensity of the diffraction of light showing the diffraction efficiency of a 10x grating multiplexed to achieve a folded hologram, where 5x is used in the +y direction and 5x is used in the -y direction but no light is coupled out.

[0023] Fig.16 is an illustration of a waveguide assembly with a multiplexed volume holographic splitter-fold-OC (SFO) grating that combines the splitter, fold and output coupler functions into one multiplexed volume holographic.

[0024] Fig.17 Is implemented Fig.16 Illustration of a side view of the waveguide assembly coupling light outside the SFO grating.

[0025] Fig.18 Is implemented Fig.16 Illustration of a top view of the waveguide assembly coupling light outside the SFO grating.

[0026] Fig.19 yes Fig.16 A graph of the incident angle and diffraction of light on the components of and the corresponding intensity of the diffracted light, showing the division and folding of light by the SFO grating.

[0027] Fig. 20 is an illustration of a waveguide assembly having a multiplexed volume holographic folded grating (FOLD) layered with an unfolded output coupler (UOC).

[0028] Fig.21 Yes Fig. 20 Illustration of a side view of the waveguide assembly coupling light outside the UOC grating.

[0029] Fig. 22 Yes Fig. 20Illustration of a top view of the waveguide assembly coupling light outside the UOC grating.

[0030] Fig.23 With folded grating Fig. 20 A graph of the incident angle and diffraction of light on a waveguide assembly and the corresponding intensity of the diffracted light, showing the output light from a multiplexed OC stacked on a folded grating.

[0031] Fig.24 is a diagram of a waveguide assembly with a multiplexed volume holographic IC-splitter-fold (ICSF) grating and an unfolded output coupler (UOC).

[0032] Fig.25 Is implemented Fig.24 Illustration of a side view of an ICSF grating coupling light within a waveguide assembly.

[0033] Fig.26 Is implemented Fig.24 Illustration of a top view of the ICSF grating to couple light within the waveguide assembly.

[0034] Fig. 27 Is has Fig.24 A graph of the incident angle and diffraction of light on the waveguide assembly of the ICSF grating and the corresponding intensity of the diffracted light, showing the light output by the ICSF grating.

[0035] Fig.28 is a graph of the incident angle and diffraction of light on a divided and folded IC and the corresponding intensity of the diffracted light, showing Fig.24 The ICSF raster shows individual segments of the field of view (FOV) of each UOC. DETAILED DESCRIPTION

[0036] Multiplexing volume holographic couplers into the same volume increases the field of view of each component in a waveguide assembly, such as an augmented reality (AR) waveguide assembly for use in an electronic eyewear device. Multiplexing can be performed in any direction perpendicular to the optical axis. Multiplexing of volume holographic couplers can be used to combine different functions of an AR waveguide assembly into one diffractive optical element (DOE) in the form of an input coupler or output coupler. For example, each volume holographic grating of the input coupler and output coupler has a different refraction angle, a different periodicity, or both relative to any other volume holographic grating in the same volume. The resulting DOE reduces re-interaction losses, reduces thickness, reduces the number of DOEs as well as the number of layers and air gaps, and improves robustness (volume vs. surface relief that may be scratched or cracked).

[0037] The device described herein includes a DOE in the form of an input coupler, an output coupler, and a waveguide assembly (including one or more of such input couplers and output couplers). In an example configuration, the waveguide assembly includes a waveguide, an input coupler, and an output coupler. The waveguide propagates light at an incident angle greater than the critical angle at which total internal reflection (TIR) ​​occurs. The input coupler includes at least two gratings within a first three-dimensional (3D) volume. Each grating within the first 3D volume responds to input light of different wavelengths and reflects or transmits the input light into the waveguide as propagated light. Each grating within the first 3D volume has the same periodicity but different orientations, the same orientation but different periodicity, or both, to provide a different refractive index relative to each other grating within the first 3D volume. The output coupler similarly includes at least two gratings within a second 3D volume. Each grating within the second 3D volume responds to light of different wavelengths propagating in the waveguide within the incident angle of the output coupler, and the propagated light is reflected or transmitted out of the waveguide at the incident angle. Each grating within the second 3D volume has the same periodicity but a different orientation, the same orientation but a different periodicity, or both, to provide a different refractive index relative to each other grating within the second 3D volume.

[0038] Now, reference will be made to FIGS. 1 to Fig.28 Description Detailed Description. While this description provides detailed descriptions of possible implementations, it should be noted that these details are intended to be exemplary and in no way limit the scope of the inventive subject matter.

[0039] DOEs operate by diffracting light. The design of a DOE controls the intensity and direction of light when it interacts with structures that are approximately the size of the wavelength of the light of interest.

[0040] Typically, light propagation occurs in isotropic media (vacuum, air, plastic, glass) where the dielectric constant and absorption constant are equal and constant regardless of the direction of the light wave. For the purposes of this description, non-isotropic media are used for light propagation. More specifically, this description focuses on periodic variations of the dielectric constant (e.g., the periodicity of a grating), and therefore, periodic variations of the refractive index in a volume.

[0041] The direction of light when it is scattered by a periodic medium (e.g., a grating) can be determined by finding a condition where the scattered waves are superimposed in phase (constructive interference). A more complete solution is found by solving Maxwell's equations using spatially dependent dielectric constants (intensity and direction). This condition can be satisfied by using integer multiples (or periodicity) of the incident wavelength. As the thickness of the DOE (interaction length of the incident light with the periodic structure) increases, constructive interference is restricted to a narrower set of parameter conditions. When the DOE is considered thick, it is considered to operate in the Bragg regime, where the diffraction efficiency is high and the diffraction is within a narrow band (i.e., the incident angle / wavelength range of high diffraction efficiency is narrow).

[0042] Figures 1A to 1E is a graph showing the thickness (d) in micrometers versus the diffraction angle of the grating, indicating that increasing the thickness of the DOE increases the diffraction efficiency but decreases the angular and wavelength bandwidth. In Figure 1, the thickness increases from 6 micrometers ( Figure 1A ) varies up to 3 microns ( Figure 1E As shown in the figure, increase the thickness (in Figures 1A to 1E (from right to left in the figure) increases the diffraction efficiency but reduces the bandwidth of diffraction angles and wavelengths. As used herein, diffraction efficiency is the performance of a diffractive optical element (especially a diffraction grating) in terms of power throughput. Diffraction efficiency is a measure of how much optical power is diffracted into a specified direction compared to the power incident on the diffractive element.

[0043] This disclosure focuses on Bragg-regime gratings. Volume gratings or thick gratings are defined as periodic variations of the refractive index in a dielectric volume that operate in the Bragg regime. Note that the grating can be viewed as a hologram of a single wavelength of light (and hence the term holographic grating used in the art).

[0044] Another feature of volume gratings is that several structures can be multiplexed (i.e. partially or completely overlapped) in the same volume as appropriate to achieve a desired field of view. Multiplexing of volume gratings is described in more detail below with reference to FIG2 . Multiple different wavelengths of light can be recorded in the same volume, which will operate independently (within some limitations). Volume gratings can be the same periodic structure but different orientations (angles), the same orientation but different periods, or both.

[0045] FIG. 2A to FIG. 2C shows volume grating, where several structures are multiplexed in the same volume but operated independently. Figure 2A , an incident plane wave / light 210 interacts with an interference pattern 220 of the volume grating 200 to produce diffracted light represented by a vector K that is perpendicular to the interference pattern 220 of the volume grating 200 . Figure 2BA volume grating 230 is shown with two different interference patterns 220 and 240 at different angles multiplexed within the same volume. Thus, the volume grating 230 diffracts the incident plane wave / light 210 to produce diffracted light represented by vectors K and K' that are perpendicular to the respective interference patterns 220 and 240. Figure 2C In FIG. 2 , the volume grating 250 has two different multiplexed interference patterns 260 and 270 having different lengths (periodicity) but the same orientation, thereby generating diffracted light represented by vectors K′ and K″ in response to the incident plane wave / light 210.

[0046] Since the direction of diffracted light can be controlled by the periodicity of the medium, DOEs can be used in augmented reality (AR) glasses as a means of capturing light in a piece of glass or plastic (a waveguide) via TIR and forcing it to exit at a desired location (e.g., in front of the user's eyes). Figure 3A A DOE is shown for use in augmented reality (AR) glasses 300 to capture light in a waveguide via TIR and force the light to exit at a desired location, such as along an optical axis 302 leading from a page toward a user's eye. Figure 3B As shown, AR glasses 300 can force light to exit along an optical axis 302 toward a user's eyes 304. As shown, a real or AR image 306 is presented to the user's eyes 304 in an eye box 308, which is a three-dimensional space in which the user can see the entire image 306 without moving her head or making any other adjustments to her eyes 304.

[0047] Figure 3A A rear view of a right optical assembly 310 is shown of an example hardware configuration of the electronic eyewear device 300. The right optical assembly 310 includes a waveguide assembly 320 including at least one of an output coupler 324 positioned in front of the wearer's eye 304 and an input coupler 326 typically located at a side edge of the right optical assembly 310, and a waveguide 322. The electronic eyewear device 300 may take other forms and may be incorporated into other types of frames, such as headgear, headphones, or helmets.

[0048] The electronic eyewear device 300 may include a plurality of visible light cameras forming a stereo camera, wherein a right visible light camera (not shown) is located on the right temple 330, and a left visible light camera (not shown) is located on the left temple. Figure 3AAs shown, the electronic eyewear device 300 includes a frame 340, a bridge 350, a right rim 360 including an aperture 362 for holding a right optical assembly 310, a right temple 330 extending from a right lateral side 370 of the frame 340, and a see-through image display in the right optical assembly 310 including a waveguide assembly 320 having an output coupler 324, the see-through image display presenting a graphical user interface to the user's eye 304, for example, in an eye box 308. A right hinge 372 connects the right temple 330 to an articulated arm 374 of the electronic eyewear device 300. Corresponding elements can be found on the left side of the electronic eyewear device 300. During operation, the right visible light camera connected to the frame 340 or the right temple 330 simultaneously captures respective images of partially overlapping scenes with the left visible light camera. The captured images can be input into the waveguide assembly 320 as an image source of the optical assembly 310. although Figure 3A Not shown, but a processor is coupled to the electronic eye-mounted device 300 and is connected to the visible light camera and a processor-accessible memory within the electronic eye-mounted device 300 itself.

[0049] exist Figure 3A In the right optical assembly 310 of FIG. 1 , the input coupler (IC) 326 is a DOE that diffracts the incident light 380, 382, ​​384 within the waveguide 322 at an angle where it is totally internally reflected and thus captured. Since the light cannot be transmitted to the outside of the waveguide 322, all the light is propagated by the waveguide 322 until the propagation angle θ is changed by the output coupler (OC) 324. The OC 324 diffracts the incident light 380, 382, ​​384 at an angle where it is totally internally reflected and thus captured. Since the light cannot be transmitted to the outside of the waveguide 322, all the light is propagated by the waveguide 322 until the propagation angle θ is changed by the output coupler (OC) 324. θ (This angle is greater than the critical angle at which light will escape the waveguide 322 and thus be captured by TIR) and diffracted light 380', 382', 384' emerges from the waveguide assembly 320 toward the wearer's eye 304. As is known to those skilled in the art, the critical angle θ c is determined by Snell's law from the refractive index of the material between the two interfaces. In this example, the waveguide / air interface is of interest.

[0050] Figure 4 A matched input coupler (IC) 400 and output coupler (OC) 410 with corresponding volume gratings 402 and 412 are shown, whereby light (kp) incident on IC 400 is reflected by air-waveguide interface 430 via TIR (center-top) and is incident on OC 410 in reflection mode. Light kd is diffracted by IC 400 or OC 410 and is incident on air-waveguide interface 430 (center-top). When light kd is diffracted at a greater angle θ than the critical angle θ at which light will escape waveguide 420, the light kd will be diffracted by IC 400 or OC 410 and will be incident on air-waveguide interface 430 (center-top).c At an angle θ, light kd is captured in waveguide 420 by TIR at interface 430. IC 400 is matched to OC 410 if IC 400 outputs light at an angle within the acceptance angle range of OC 410, where the minimum acceptance angle is the maximum angle of incidence at which the optical element or material captures light by TIR. c ), the light is trapped in the waveguide 420 by TIR until it changes direction at the OC 410 (see, for example, Figure 7 When light captured by TIR is incident on OC 410, the light escapes from waveguide 420 at an angle α ( Figure 4 ) diffraction because α is less than the critical angle.

[0051] Figure 5A and Figure 5B Graphs 500 and 510 are graphs of incident angle and diffraction of light on a matched IC / OC waveguide assembly 320 using a single volume holographic grating, and the corresponding intensity of the diffracted light, respectively. Figure 5A and Figure 5B , the xy plane represents the angle of incidence on the waveguide / air interface. The bar 520 on the right side of each graph indicates the intensity of the light. Any light within the small circle 530 propagates at an angle less than the critical angle and is therefore not captured by TIR. Any light outside the outer circle 540 represents an angle greater than 90 degrees where propagation is not possible. Light in the "ring" 535 between the concentric circles 530 and 540 is incident on the interface between the critical and 90 degrees and is therefore captured by TIR. In these graphs, the "ring" 535 between the inner circle 530 and the outer circle 540 represents the propagation angle at which light is captured by TIR. Increasing the size of the "ring" 535 increases the field of view (FOV) that the waveguide can maintain.

[0052] Figure 5A The effect of the interaction of IC 400 with light is shown, where light from a source with a flat (angled) diffraction intensity profile is represented by the strong rectangle 550 in the center. Possible diffraction is represented by rectangle 560 on the right. Given a single volume grating in Figure 5A As shown in , for a very narrow angular range (at or near Bragg), performance is efficient and therefore the overall diffraction efficiency is low as shown by rectangle 560. Portions of the source outside this range are lost, making the field of view of the image very narrow. Figure 5B The effect of the interaction of OC 410 with light is shown, where the propagating light in the waveguide is diffracted by OC 410 back to the same angular range of source 570 at different diffraction angles, as shown at 580 .

[0053] above Figure 4The description of FIG5 is based on reflection mode diffraction. In this case, the incident beam and the diffracted beam are on the same side of the air-waveguide interface. Fig. 6A and Figure 6B As shown, it can be Figure 4 This IC-OC matching is achieved in the transmission mode of the matched IC and OC. Fig. 6A As shown, in the transmission mode, light (kp) incident on IC 400 is transmitted through IC 400 as diffracted light (kd). Figure 6B As shown, in the transmission mode, light (kp) incident on the OC 410 is transmitted through the OC 410 as diffracted light (kd).

[0054] Whereas a system that creates a single image in a specific place would be very limited (i.e., the user's eye must be in exactly one place or risk not seeing the image at all), multiple internal reflections of light in the waveguide at the interface with OC 410 can be used to create many images to extend the eye box 308. Figure 7 is a simplified diagram showing a waveguide 700, where each arrow 710 pointing upward represents a single input image 740 that is input at the IC 720, reflected within the waveguide 700, and output from the waveguide 700 at 710 each time the light wave captured by TIR interacts with the OC 730. The light escapes at 710 because it is diffracted by the OC 730 to an angle less than the critical angle. This is achieved by controlling the diffraction efficiency of each interaction with the waveguide / OC interface. Typically, the amplitude of the modulation of the refractive index is a function of x and / or y, so the first interaction encounters a refractive index modulation with the same period but "weaker". Towards the end of the interaction, the period is the same, but the modulation is much "stronger". At Figure 7 , reflective mode diffraction is shown; however, it will be understood that transmissive mode diffraction can also be used, as it is possible to mix and match reflective and transmissive modes (e.g., reflective IC with transmissive OC, or vice versa). In the latter case, the user's eyes will be on opposite sides of the waveguide 700.

[0055] The use of diffraction of light waves captured by TIR is not limited to extracting light, as diffraction can also be used to change the angle of light waves captured by TIR to another angle greater than the critical angle and thus maintain capture by TIR. For example, the grating can also be used to redirect the propagation direction of the light waves by 90° (for example, the light waves captured by TIR can propagate from the plane (on the page and from left to right inside the waveguide, as shown in FIG. Figure 7 Gratings that perform these operations are called folded gratings and are Figure 8As shown, the waveguide 800 receives light input at IC 810, and the incident light passes through the fold grating 820 to propagate the light into or out of the page along a range of angles at OC 830. It will be appreciated that the fold grating 820 can be used to provide a two-dimensional pupil expansion for the eye box 308.

[0056] Since users expect full-color images at large angles, wide-angle and wide-spectrum performance is required to implement AR devices. The configuration described below addresses these needs in the art by operating in a Bragg manner, whereby the conditions for non-negligible diffraction are wide.

[0057] As mentioned above, multiplexing volume holographic couplers (with multiple gratings) into the same volume can be used to increase the number of Figure 3A An eye box 308 ( Figure 3B ) to address these needs in the art. Multiplexing can be done in any direction perpendicular to the optical axis 302 to obtain high diffraction efficiency. In addition, multiplexing of volume holographic couplers can be used to combine different functions of the waveguide components of the AR-enabled electronic eyewear 300 into one DOE in the form of an input coupler with a fold, an output coupler with a fold, or separate folding directions combined into one device, where light is directed toward the user's eye 304, such as Figure 3B Any number of gratings (greater than one) can be multiplexed into a volume. The resulting DOE has reduced re-interaction losses, reduced thickness, reduced number of DOEs as well as layers and air gaps, and improved robustness (volume vs. surface relief that may be scratched or cracked).

[0058] Fig. 9A and Fig. 9B An IC 900 with volume gratings 910 and 920 and an OC 930 with volume gratings 940 and 950 are shown, respectively, which use multiplexing to allow multiple gratings to occupy the same volume simultaneously to increase the field of view of the corresponding waveguide assembly 320. Fig. 9A and Fig. 9B Two interference patterns are shown as an example, but it will be understood that more than two interference patterns k1 to kn may be provided in the IC 900 and / or the OC 930. Fig. 9A , the incident light kp and kp' of each wavelength (eg, from the electronic eyewear device 300 equipped with the waveguide assembly 320 as described herein) Figure 3A) is provided to the IC 900 at different angles and is diffracted by individual gratings 910 and 920 having different multiplexed interference patterns at angles indicated by vectors K and K', thereby changing the direction of the incident light to generate light at angles kd and kd'. Fig. 9B In FIG. 1 , incident light kp” and kp′” provided to OC 930 at different angles is reflected by individual gratings 940 and 950 having different multiplexed interference patterns at angles represented by vectors K” and K′”, thereby changing the direction of the incident light to generate light at angles kd” and kd′”. Fig. 9A As shown, gratings 910 and 920 simultaneously occupy the same volume 960, and as Fig. 9B As shown, gratings 940 and 950 simultaneously occupy the same volume 960'. This configuration reduces the number of layers required and therefore reduces the overall thickness of the DOE 900, 930 by requiring fewer layers, fewer separate DOEs, and eliminating the need for air gaps between these layers. Since the corresponding volume gratings 910, 920 and 940, 950 are located within the volume 960 and are not surface relief features surrounded by air, the DOE 900, 930 is inherently less prone to fracture, thereby improving robustness.

[0059] Fig. 10A is a graph 1000 of the angle of propagation of light from the normal to the waveguide / air interface of the waveguide. The "ring" 1035 between the inner circle 1030 and the outer circle 1040 represents the propagation angle at which light is captured via TIR. Increasing the size of the "ring" 1035 increases the field of view (FOV) that the waveguide can sustain. Incident light 1050 is diffracted into TIR captured light 1060 using the IC 900 including a volume multiplexed holographic grating. Fig. 10B The corresponding intensity of light diffraction of a simulation result using 9 9x gratings that angularly multiplex different angular parts of the image is shown in FIG. Fig. 10B is a graph 1010 of the angles of incidence 1070 and diffraction 1080 of light on the OC 930 using a multiplexed volume holographic grating. Fig. 10B The corresponding intensity of light diffraction for a simulation result using nine 9x gratings that angularly multiplex different angular portions of the image is shown in . The bars 1020 on the right side of each graph represent the intensity of the incident and diffracted light. Increasing the size of the "ring" 1035 increases the FOV that the waveguide can sustain. Fig. 10A and Fig. 10B From the simulation results, it can be seen that when Figure 5A and Figure 5B When compared, the system's FOV is greatly increased.

[0060] Fig. 10AThe effect of the interaction of IC 900 with light from a rectangular shaped source having a flat diffraction intensity profile represented by the strong rectangle 1050 in the center. Possible diffraction is represented by rectangle 1060 on the right. Figure 5A and Figure 5B When compared, performance is optically efficient for a larger angular range of a given FOV. Similarly, Fig. 10B The effect of the interaction of OC 930 with light 1070 diffracted by IC 900 is shown. It will be appreciated that light 1060 and light 1070 are essentially the same light, except that light 1060 is captured by TIR and propagates down the waveguide until it reaches OC 930 as light 1070.

[0061] Light diffracted by OC 930 is shown at 1080. Again, performance is optically efficient for a larger range of angles for a particular FOV.

[0062] Fig. 9A The IC 900 may be adapted to achieve pupil expansion by not diffracting all of the input light after the first interaction with the OC 930. For example, the efficiency of each outcoupling may be increased to keep the power output the same for each "pupil". The eye may be located at the edge of the eyebox so that only the last two diffracted beams are seen. If the diffraction efficiency is 100% at the first interaction, 100% of the light will exit and no light will reach the eye at the edge of the eyebox.

[0063] Fig.11 1 shows a one-dimensional eye box extension in the form of a waveguide assembly 1100. As used herein, a waveguide assembly 1100 may include a plurality of waveguide junctions connecting waveguides 1110. The waveguide junctions may include at least one of an IC 900 or an OC 930 of the type described herein.

[0064] like Fig.11As shown, the OC 930 has a length in the propagation direction of the light within the waveguide 1110 that is orthogonal to the light 1120 input into the IC 900 (in the y-direction in this example), whereby the propagating light interacts with the OC 930 multiple times (at least twice) in the propagation direction. It will be appreciated that the interface between the IC 900 or the OC 930 and the waveguide 1110 is assumed to be lossless. The light interacts with the IC 900 or the waveguide-air interface (either TIR-trapped after the IC 900 or out-coupled after interacting with the OC 930) or interacts with the OC 930. The light is diffracted by the OC 930 to an angle less than the critical angle to escape the waveguide 1110 as a corresponding image 1140 that provides a one-dimensional eyebox expansion in the propagation direction (y-direction). In an example configuration, the OC 930 can have a diffraction efficiency profile as a function of length that is suitable for controlling the intensity of the output light 1140, whereby the light 1140 output by the OC 930 has a desired diffraction intensity profile in the propagation direction along the length of the OC 930. For example, the diffraction efficiency profile of the OC 930 can be selected whereby each output light wave 1140 escaping the waveguide 1110 has approximately the same intensity, thereby providing a consistent intensity along the length of the OC 930, and therefore the eyebox.

[0065] An advantage of this configuration over a surface relief grating (SRG) is reduced re-interaction losses, which occur when a light wave captured by TIR is incident on IC 900 before reaching portion 1150 of waveguide 1110 between IC 900 and OC 930 or portion 1160 of waveguide 1110 (including interface 1130 with OC 930). In this case, there is a possible diffraction condition (non-Bragg) that can diffract the light wave out of waveguide 1110.

[0066] Fig.12 It is shown that when an incident light wave 1200 captured by TIR strikes the IC 900 before reaching the portion 1150 of the waveguide 1110 between the IC 900 and the OC 930 or the portion 1160 of the waveguide 1110 (including the interface 1130 with the OC 930), re-interaction losses may occur. Fig.12As shown, the incident light wave 1200 may include possible diffraction from the IC 900, which diffracts the input light 1200 to an angle less than the critical angle, thereby allowing the input light 1200 to escape the waveguide 1110 before reaching the OC 930. Such a light wave 1210 is undesirable anywhere in the waveguide assembly 1100, except at the OC 930. On the other hand, the desired light wave 1220 may be diffracted by the IC 900 to an angle greater than the critical angle, thereby capturing the light wave 1210 through TIR. Since the undesired diffraction of the light wave 1200 at the IC 900 is not in Bragg (outside the range where the IC 900 diffraction efficiency is high), the re-interaction losses are minimized.

[0067] exist Fig.12 In the configuration, at least one of the volume gratings can diffract light waves captured by TIR at IC 900 so as to reduce re-interaction losses that occur when the light waves captured by TIR interact with IC 900 (e.g., reflecting light wave 1220 at an incident angle greater than the critical angle to capture light wave 1220 by TIR rather than allowing diffracted light wave 1210 to escape).

[0068] This can be Fig.13 The reinteraction loss is seen in the simulation shown. Fig.13 is a graph 1300 of incident angle and diffraction of light on IC 900 using a volume grating, and the corresponding light intensity, where the range of incident angles is shown within the range captured by TIR. The angular range and intensity of diffraction corresponds to the re-interaction losses. Graph 1300 shows the effect of re-interaction on the IC diffraction efficiency, where the bar 1310 on the right side indicates the intensity of the light. In graph 1300, the "ring" 1325 between the inner circle 1320 and the outer circle 1330 represents the field of view (FOV). In Fig.13 The incident angle range (originally diffracted by the multiplexer IC 900) is Fig.12 The light waves 1200 in FIG. 1200 are shown to be efficient for the intensity versus angle of the incident light marked at 1340, within the range captured by TIR. However, the diffraction 1350 from the re-interaction of the escaping light is shown to have very low diffraction efficiency.

[0069] Fig.14 A waveguide assembly 1400 is shown that includes a folded hologram 1410 that simultaneously folds and splits an input beam that is captured in a waveguide 1420 by TIR but does not couple the light out. The folded hologram includes two or more folded gratings (e.g., Figure 8 The folded grating 820) is multiplexed in the same volume to change the direction of part of the in-coupled light 1450 by an angle around the z-axis through IC900. Fig.14As shown in the example geometry in FIG, the light wave captured by IC900 in the waveguide 1420 is divided into light waves 1430 and 1440 by the folded hologram (having two volume folded gratings) 1410, and the light waves 1430 and 1440 rotate around the z-axis in the xy plane. Therefore, the light waves 1430 and 1440 propagate in the +y, +x and -y, -x planes, respectively. Fig.14 The folded hologram 1410 need not be part of the IC 900 or the OC 930, but can be a separate light steering device adapted to fold and split a light beam captured within the waveguide 1420 by TIR. In this example, the folded hologram 1410 outputs light waves 1430 and 1440 that have been diffracted at different angles and captured in the waveguide 1420 by TIR, but at different angles than the input light wave received by the folded hologram 1410. In the example configuration, the folded hologram 1410 has a diffraction efficiency selected to control the intensity of each of the two split light waves 1430 and 1440 output by the folded hologram 1410. In addition, the folded hologram 1410 can be configured so that the incident light wave received by the folded hologram 1410 matches the output light wave of the IC 900, and the two light waves output by the folded hologram 1420 match the input of the OC 930.

[0070] Fig.15 yes Fig.14 Graph 1500 of incident angle and diffraction of light on a folded hologram 1410 and the corresponding intensity of the diffracted light showing the efficiency of a 10x grating multiplexed to achieve the folded hologram 1410. Graph 1500 shows the division and folding efficiency, with the bar 1510 on the right side indicating the intensity of the light. In graph 1500, the "ring" 1525 between the inner circle 1520 and the outer circle 1530 represents the field of view (FOV). As shown in graph 1500, a 5x grating is used in the +y direction (arrow 1540), and a 5x grating is used in the -y direction (arrow 1550). Note that the simulated efficiency of 86% for the incident light 1560 includes two diffracted light waves (i.e., 43% in the +y angle range 1570 and 43% in the -y angle range 1580). It can also be seen that this configuration does not outcouple light (i.e., no intensity is shown in the inner circle 1520).

[0071] Fig.16 A waveguide assembly 1600 is shown having a multiplexed volume holographic Splitter-Fold-OC (SFO) 1610 that Fig.11 and Fig.14The splitter, folding and output coupler functions of the grating of the SFO 1610 are combined into a multiplexed volume hologram. In this configuration, each SFO 1610 can have a diffraction efficiency selected to control the out-coupled light 1620 of each of the two split and folded lights and the intensity of the out-coupled wave output by the SFO grating 1610. In this example configuration, the light wave captured in the waveguide 1600 by the IC 900 is divided into three waves: one is folded to the +x, +y direction, one is folded to the -x, +y direction, and one is out-coupled 1620.

[0072] Fig.17 Shows the implementation Fig.16 Side view of the SFO grating 1610 with the waveguide assembly 1600 out-coupling light at 1620. Fig.18 Shows the implementation Fig.16 A top view of the waveguide assembly 1600 of the SFO grating 1610.

[0073] exist Fig.18 , the out-coupled light 1620 extends out of the page along the z-axis. It will be appreciated that the out-coupled light 1620 extends the eyebox 308 in the x and y directions.

[0074] Fig.19 is the light from the normal to Fig.16 1900 of the angles of propagation of the waveguide assembly 1600, which shows the TIR capture of incident light 1910 by IC 900 at 1910A, the fold 1940 into the +x, +y direction and the fold 1950 into the -x, +y direction by the SFO grating 1610, and the outcoupling 1950A from the +x, +y direction, the outcoupling 1940A from the -x, +y direction, and the outcoupling 900A from the coaxial direction. In the graph 1900, the "ring" 1925 between the inner circle 1920 and the outer circle 1930 represents the propagation angles at which light is captured by TIR. As shown, the incident light 1910 is divided by the SFO 1610 into diffracted light waves 1940 and 1950 of high diffraction efficiency. As shown, the corresponding diffracted light waves 1940 and 1950 can be diffracted back out of the waveguide assembly 1600.

[0075] Fig. 20 A waveguide assembly 2000 is shown, which includes a multiplexed volume holographic folded grating (FOLD) 2010 layered with an Unfolding Output Coupler (UOC) 2020, which layers the FOLD grating 2010 and the configuration of the IC 900 described above. In this case, the IC 900 and the FOLD grating 2010 are as described above with reference to Fig.14However, in the example configuration, the IC 900 and the FOLD grating 2010 are disposed in a first layer of the waveguide assembly 2000, and the UOC 2020 is disposed in a second layer of the waveguide assembly 2000, the second layer being different from the first layer. As also shown, when the light 2030 interacts with the FOLD grating 2010, the UOC 2020 outcouples the light 2030.

[0076] Fig.21 FIG. 2 shows a UOC 2020 including a FOLD grating 2010 for dividing and folding light and an out-coupled light 2030. Fig. 20 A side view of the waveguide assembly 2000 is shown. Fig. 22 Shows Fig. 20 900B. The UOC 2020 couples the remaining light (OC) on the y-axis (directly from the IC 900), while the OC+ and OC- couple the light folded by the FOLD grating 2010 in each tilted direction.

[0077] exist Fig. 22 , the out-coupled light 2030 extends out of the page along the z-axis. It will be appreciated that the out-coupled light 2030 extends the eyebox 308 in the x and y directions.

[0078] Fig.23 is a graph 2300 of the angle of propagation of light from the normal to the waveguide / air interface of the waveguide assembly 2000 including the FOLD grating 2010 and the corresponding intensity of the light diffraction, showing Fig. 20 Figure 2300 shows the light output of UOC 2020. Incident light 2310 is captured by IC900 in direction 2310A. Captured light 900B is folded by FOLD hologram 2010 into +x, +y directions 2350 and -x, +y directions 2340. UOC 2020 outcouples part of 900B light into direction 900A, and outcouples all folded light 2350, 2340 into directions 2350A and 2340A, respectively. In graph 2300, the "ring" 2325 between the inner circle 2320 and the outer circle 2330 represents the propagation angle at which light is captured by TIR. As shown, incident light 2310 is divided and folded by UOC 2020 into diffracted light waves 2340 and 2350 with high diffraction efficiency. As shown, for each tilt direction, the respective diffracted light waves 2340 and 2350 and the remaining original light 900B may be outcoupled as OC, OC+, and OC-.

[0079] Fig.24A waveguide assembly 2400 with a multiplexed volume holographic IC-Splitter-Fold (ICSF) grating 2410 in reflection mode and an unfolded output coupler (UOC) 2020 is shown. This configuration multiplexes the incoupling, splitting and folding functions into the input coupler (ICSF grating 2410). The UOC 2020 is matched to outcouple light at 2420 from corresponding coaxial and oblique directions 2410A, 2410B and 2410C. In this example configuration, the ICSF 2410 includes an IC 900 multiplexed with two other ICs 900 in oblique directions at angles around the z-axis, which corresponds to the propagation directions coaxial 2410A and oblique in 2410B and 2410C.

[0080] Fig.25 Shows the implementation Fig.24 A side view of the waveguide assembly 2400 for coupling light within the ICSF grating 2410. Fig.26 Shows Fig.24 2400. UOC 2020 includes three (3x) multiplexed ICs, each matching a different propagation direction in the xy plane. UOC 2020 outcouples the remaining light (UOC) from ICSF grating 2410 at each tilt direction (2410A, 2410B, 2410C) at 2420.

[0081] exist Fig.26 , the out-coupled light 2420 extends out of the page along the z-axis. It will be appreciated that the out-coupled light 2420 extends the eye box 308 in the x and y directions.

[0082] Fig. 27 is a graph 2700 of the angle of propagation of light from the normal to the waveguide assembly 2400 including the ICSF grating 2410, showing the input light 2710, the light entering the TIR capture in a coaxial 2710A, and the light passing through Fig.24 2710B and 2710C of the ICSF grating 2410. In the diagram 2700, the "ring" 2725 between the inner circle 2720 and the outer circle 2730 represents the propagation angle at which light is captured by TIR. As shown, the incident light 2710 is diffracted on the axis 2710A and is diffracted obliquely by the ICSF 2410 at 2710B and 2710C into three equally effective captured propagation directions (on-axis 2410A, oblique 2410B and 2410C). As shown, for each on-axis and oblique direction, the corresponding diffracted light waves 2410A, 2410B and 2410C can be coupled out through the UOC 2020 diffractions 2420A, 2420B and 2420C.

[0083] Fig.28 2800 is a graph of simulation results of the angle of propagation of light from a waveguide assembly 2400 including only ICSF gratings 2410. The bars 2810 on the right side indicate the intensity of the light. In the graph 2800, the "ring" 2825 between the inner circle 2820 and the outer circle 2830 represents the propagation angle at which the light is captured by TIR. Each IC 900 has a 7x grating to increase the FOV. This can be seen in the bar-like appearance of the intensity profile. The incident light propagation 2840 is diffracted by each IC 900 of the ICSF grating 2410 into propagation directions 2850, 2860, and 2870.

[0084] Although the multiplexed volume holographic couplers described herein have been described for use in augmented reality waveguides, it will be understood that the use of the multiplexed volume holographic couplers is not so limited. The multiplexed volume holographic couplers described herein may be used in input couplers, output couplers, waveguide assemblies, or any combination thereof, for other types of waveguide assemblies other than those used in augmented reality glasses. For example, the techniques described herein may be used in optical systems to process optical signals.

[0085] Although various embodiments have been described above, it should be understood that they are presented by way of example only and are not limiting. For example, any element associated with the above-described systems and methods may employ any desired functionality set forth above. Therefore, the breadth and scope of the preferred embodiments should not be limited by any of the above-described example embodiments.

[0086] Those skilled in the art will appreciate that while the disclosure contained herein is about electronic eyewear having a waveguide, it should be understood that this is only one of many possible applications and that other configurations are possible. Therefore, all such applications are included within the scope of the following claims.

Claims

1. A coupler for a waveguide, comprising: At least two gratings within a three-dimensional (3D) volume, each grating reflecting or transmitting input light into or out of the waveguide in response to a different wavelength of input light, each grating within the 3D volume having at least one of (1) the same periodicity but different orientations or (2) the same orientation but different periodicity to provide a different refractive index relative to each other grating within the 3D volume.

2. The coupler according to claim 1, wherein: The coupler is an input coupler, and the waveguide propagates light at an incident angle greater than a critical angle at which total internal reflection occurs, and each grating is oriented to receive an input light wave at an incident angle to the waveguide less than the critical angle, and to transmit or reflect the input light wave to form an output light wave propagating in the waveguide at an incident angle greater than the critical angle.

3. The coupler according to claim 2, wherein: At least one of the gratings has a refractive index that diffracts the output lightwave upon a second interaction with the input coupler, whereby the diffracted output lightwave has an angle of incidence greater than the critical angle.

4. The coupler according to claim 1, wherein: The coupler is an input coupler, and the waveguide propagates light at an incident angle greater than a critical angle at which total internal reflection occurs, and each grating is oriented to receive an input light wave at an incident angle greater than the critical angle and transmit or reflect the input light wave to form an output light wave that propagates in the waveguide at an incident angle greater than the critical angle and different from the incident angle of the input light wave.

5. The coupler according to claim 1, wherein: The coupler is an output coupler, and the waveguide propagates light at an incident angle greater than a critical angle for total internal reflection to occur, and each grating is oriented to receive an input light wave from the waveguide at an incident angle greater than the critical angle and to transmit or reflect the input light wave to form an output light wave having an incident angle less than the critical angle so as to escape the waveguide.

6. The coupler according to claim 5, wherein: The output coupler extends in a propagation direction of an input light wave within the waveguide so as to have at least two interactions with the input light wave as it propagates in the propagation direction within the waveguide.

7. The coupler according to claim 6, wherein: The output coupler has a diffraction efficiency profile as a function of length, which is suitable for controlling the intensity of the output light wave at each interaction with the output coupler, whereby the light output by the output coupler has a desired intensity profile along the length of the output coupler.

8. A waveguide assembly comprising: a waveguide that propagates light at an incident angle greater than a critical angle at which total internal reflection occurs; an input coupler comprising at least two gratings within a first three-dimensional (3D) volume, each grating within the first 3D volume being responsive to input light of a different wavelength by reflecting or transmitting the input light into the waveguide as propagating light, each grating within the first 3D volume having at least one of (1) the same periodicity but different orientations or (2) the same orientation but different periodicity to provide a different refractive index relative to each other grating within the first 3D volume; and An output coupler comprising at least two gratings within a second 3D volume, each grating within the second 3D volume being responsive to light of a different wavelength propagating in the waveguide within an incident angle propagating through the output coupler, the propagating light being reflected or transmitted out of the waveguide at the incident angle, each grating within the second 3D volume having at least one of (1) the same periodicity but different orientations or (2) the same orientation but different periodicity to provide a different refractive index relative to each other grating within the second 3D volume.

9. The waveguide assembly according to claim 8, wherein: The propagated light output by the input coupler is reflected or transmitted by the waveguide to the output coupler, whereby the reflected or transmitted propagated light output by the input coupler has an incident angle within the acceptance angle of the output coupler when interacting with the output coupler.

10. The waveguide assembly according to claim 8, wherein: The output coupler extends in a propagation direction of the propagating light within the waveguide so as to have at least two interactions with the propagating light as it propagates in the propagation direction within the waveguide.

11. The waveguide assembly according to claim 10, wherein: The refractive index of each grating of the second 3D volume has a value whereby propagating light of different wavelengths can be reflected or transmitted by the output coupler to an angle less than the critical angle in order to escape the waveguide.

12. The waveguide assembly according to claim 11, wherein: The output coupler has a diffraction efficiency profile as a function of length, which is suitable for controlling the intensity of the propagating light at each interaction with the output coupler, whereby light output by the output coupler has a desired intensity profile along the length of the output coupler.

13. The waveguide assembly according to claim 8, wherein: The input coupler also includes a volume holographic folding grating that simultaneously folds and splits an incident input light wave into two light waves that rotate about an axis perpendicular to a plane including the waveguide.

14. The waveguide assembly according to claim 13, wherein: The volume holographic folded grating reflects or transmits two light waves output by the volume holographic folded grating to propagate in the waveguide within an incident angle of the output coupler.

15. The waveguide assembly according to claim 8, wherein: The output coupler also includes a volume holographic folding grating that simultaneously folds and splits the propagating light into two light waves that rotate about an axis perpendicular to a plane including the waveguide, and outcouples the folded and split light out of the waveguide.

16. The waveguide assembly of claim 15, wherein: The output coupler also includes at least two multiplexed volume holographic folded gratings, each of which matches a different propagation direction in the waveguide and folds the received propagating light to outcouple the folded light in each direction.

17. The waveguide assembly of claim 16, wherein: The input coupler further comprises a volume holographic folded grating, which simultaneously folds and divides the propagating light into at least two light waves, which rotate around an axis perpendicular to a plane including the waveguide and are coupled out of the waveguide by the output coupler.

18. The waveguide assembly of claim 17, wherein: The input coupler is disposed in a first layer of the waveguide and the output coupler is disposed in a second layer of the waveguide, wherein the second layer is different from the first layer.

19. The waveguide assembly of claim 8, wherein: The input coupler includes at least two volume holographic folded gratings oriented to receive an input light wave incident at an angle of incidence to the waveguide that is less than a critical angle of the waveguide, and to transmit or reflect the input light wave to form an output light wave that propagates in the waveguide at an angle of incidence that is greater than the critical angle and different from the angle of incidence of the input light wave, and the output coupler includes at least two volume holographic folded gratings oriented to receive propagated light from the waveguide at an angle of incidence that is greater than the critical angle, and to transmit or reflect the propagated light to form an output light wave having an angle of incidence that is less than the critical angle so as to escape from the waveguide.

20. An eyewear device comprising: Image source; a display including an eye box; a waveguide that propagates light at an incident angle greater than a critical angle at which total internal reflection occurs; an input coupler comprising at least two gratings within a first three-dimensional (3D) volume, each grating within the first 3D volume being responsive to input light of a different wavelength from the image source to reflect or transmit the input light into the waveguide as propagating light, each grating within the first 3D volume having at least one of (1) the same periodicity but different orientations or (2) the same orientation but different periodicity to provide a different refractive index relative to each other grating within the first 3D volume; and An output coupler comprising at least two gratings within a second 3D volume, each grating within the second 3D volume being responsive to light of a different wavelength propagating in the waveguide within an incident angle propagating through the output coupler, the propagating light being reflected or transmitted out of the waveguide to an eyebox of the display at the incident angle, each grating within the second 3D volume having at least one of (1) the same periodicity but different orientations or (2) the same orientation but different periodicity to provide a different refractive index relative to each other grating within the second 3D volume.

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