Faceted coupling-in element to a waveguide

Abstract

A conjugate coupler for coupling image light into a waveguide of a near-eye display comprises a coupling block having multiple facets oriented at conjugate elevation angles relative to a coupling-in mirror. The facets split incoming light rays into complementary ray sets, with at least one partially reflective surface reflecting a first portion and transmitting a second portion of the light. The conjugate coupler generates complementary ray sets that compensate for aperture-filling deficiencies by directing split light rays at varying incidence angles toward the coupling-in mirror, thereby improving illumination uniformity across the waveguide aperture. The first ray set impinges the coupling-in mirror at higher incidence angles than the second ray set, filling aperture regions that would otherwise be unilluminated and enhancing image quality at the eye box of the display.

Description

FACETED COUPLING-IN ELEMENT TO A WAVEGUIDECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application Serial No.63 / 759,607, filed February 18, 2025 titled FACETED COUPLING-IN ELEMENT TO A WAVEGUIDE, the entire disclosure of which is incorporated by reference herein.FIELD

[0002] The present disclosure relates to the field of near-eye display systems, such as head-mounted displays for augmented reality (AR). More specifically, the present disclosure relates to a compact waveguide system designed for near-eye displays (NEDs).BACKGROUND

[0003] Waveguide-based near-eye displays have emerged as a critical technology for augmented reality (AR) and mixed reality (MR) applications, enabling the projection of digital images directly into a user's field of view while maintaining transparency for real-world observation. These systems rely on optical waveguides to guide light from compact image projectors to the user's eyes through total internal reflection, providing a lightweight and unobtrusive display solution suitable for head-mounted devices such as smart glasses.

[0004] A fundamental challenge in waveguide display systems is achieving uniform illumination across the entire waveguide aperture. Traditional coupling methods, which typically employ a single coupling-in mirror or prism to direct light from the projector into the waveguide, often result in incomplete aperture filling. This occurs because the single reflection point cannot adequately distribute light to all regions of the waveguide that are necessary for total internal reflection propagation, creating aperture illumination gaps that manifest as visible non-uniformities, dark zones, or "holes" in the displayed image.

[0005] The aperture filling problem is particularly acute in consumer applications where high image quality and uniform brightness are essential for user acceptance. When certain angular and spatial regions within the waveguide remain unfilled by light, the resulting non-uniform illumination degrades the visual experience and creates noticeable artifacts in the displayed content. This issue becomes more pronounced as the field of view and eye boxDocket No. LMUS23PWO01requirements increase, making it difficult to achieve the performance standards expected in modem AR and MR systems.

[0006] Previous approaches to address illumination uniformity have included the use of optical homogenizers to blend light before entry into the waveguide and integrated projector designs that modify the input light geometry. However, these solutions typically increase system complexity, size, weight, and cost, making them less suitable for consumer applications where compactness and affordability are critical design constraints. Additionally, homogenizers can introduce optical losses and may not fully address the fundamental aperture filling limitations inherent in single-mirror coupling architectures.

[0007] There remains a need in the art for improved coupling techniques that can achieve uniform waveguide illumination without the drawbacks of existing approaches. Such techniques should be compatible with standard projector modules, maintain compact form factors suitable for wearable devices, and provide effective aperture filling to eliminate illumination non-uniformities while preserving optical efficiency and image quality.SUMMARY

[0008] According to an aspect, a conjugate coupler for coupling image light into a waveguide of a near-eye display comprises a coupling block having a plurality of facets, each facet oriented at a conjugate elevation angle relative to a coupling-in mirror of the waveguide and configured to split incoming light rays into multiple optical paths, wherein the plurality of facets includes at least one partially reflective surface configured to reflect a first portion of the incoming light rays and transmit a second portion of the incoming light rays, and wherein the conjugate coupler is configured to generate complementary ray sets that compensate for aperture-filling deficiencies and thereby improve illumination uniformity across a waveguide aperture by directing the split light rays at varying incidence angles toward the coupling-in mirror.

[0009] According to an embodiment, the coupling block further comprises a distal facet that is fully reflective.

[0010] According to an embodiment, at least one facet is a beam splitter with aDocket No. LMUS23PWO01reflectance between 30% and 70%.

[0011] According to an embodiment, facet reflectivities are non-uniform across the plurality of facets to equalize irradiance at the waveguide aperture.

[0012] According to an embodiment, the conjugate elevation angles are selected as a function of an angle p of the coupling-in mirror such that a facet tilt is approximately 2p.

[0013] According to an embodiment, is between 20° and 40°.

[0014] According to an embodiment, the complementary ray sets comprise a first ray set that impinges the coupling-in mirror at higher incidence angles than a second ray set.

[0015] According to an embodiment, the coupling block further includes multiple additional facets configured to increase spatial mixing of the complementary ray sets.

[0016] According to an embodiment, an auxiliary partial facet is disposed within the waveguide substantially parallel to the coupling-in mirror and configured to be highly reflective or absorbing for high-angle incidence and highly transmissive for low-angle incidence to recycle otherwise lost light.

[0017] According to an embodiment, anti-reflection coatings are provided at one or more optical interfaces of the coupling block.

[0018] According to an embodiment, at least one of a polarizer or a waveplate is disposed between the coupling block and a major surface of the waveguide.

[0019] According to an embodiment, a refractive index of the coupling block is different from a refractive index of the waveguide.

[0020] According to an embodiment, the coupling block is bonded to the waveguide with a low refractive index optical adhesive.

[0021] According to an embodiment, the coupling block comprises a single long fully reflective facet configured to generate the complementary beam without intermediate beam-splitting facets.

[0022] According to an embodiment, the coupler is external to and not integral with the waveguide to enable modular integration with different projector modules.Docket No. LMUS23PWO01

[0023] According to an embodiment, the plurality of facets comprises a fully reflective distal facet and at least one partially reflective facet.

[0024] According to an aspect, a waveguide display apparatus for a near-eye display comprises a planar waveguide having a major surface and a coupling-in mirror configured to direct image light for propagation by total internal reflection within the waveguide, and a conjugate coupler for coupling image light into the waveguide, the conjugate coupler comprising a coupling block having a plurality of facets, each facet oriented at a conjugate elevation angle relative to the coupling-in mirror and configured to split incoming image light into complementary ray sets including a first ray set reflected by at least one facet and a second ray set transmitted through the couplingblock, wherein the plurality of facets includes at least one partially reflective surface configured to reflect a first portion of the incoming light rays and transmit a second portion of the incoming light rays, wherein the first ray set impinges the coupling-in mirror at higher incidence angles than the second ray set such that, when coupled into the waveguide, the ray sets fill an aperture region that would otherwise be unilluminated using the coupling-in mirror alone.

[0025] According to an embodiment, the conjugate elevation angles are selected as a function of an angle p of the coupling-in mirror such that a facet tilt is approximately 2p.

[0026] According to an embodiment, is between 20° and 40°.

[0027] According to an embodiment, at least one facet of the coupling block is a partially reflective beam splitter.

[0028] According to an embodiment, a reflectance of the partially reflective facet is between 30% and 70%.

[0029] According to an embodiment, the coupling block further comprises a distal facet that is fully reflective.

[0030] According to an embodiment, the coupling block comprises multiple additional facets to enhance spatial mixing of the complementary ray sets.

[0031] According to an embodiment, an auxiliary partial facet is disposed substantially parallel to the coupling-in mirror and configured to be highly reflective or absorbing forDocket No. LMUS23PWO01high-angle incidence and highly transmissive for low-angle incidence to recycle lost light.

[0032] According to an embodiment, anti-reflection coatings are provided at one or more interfaces between the coupling block and the waveguide.

[0033] According to an embodiment, at least one of a polarizer or a waveplate is disposed between the coupling block and the major surface of the waveguide.

[0034] According to an embodiment, the conjugate coupler is juxtaposed external to the waveguide and not integral with the waveguide substrate.

[0035] According to an embodiment, a refractive index of the coupling block differs from a refractive index of the waveguide.

[0036] According to an embodiment, the coupling block is bonded to the waveguide with a low refractive index optical adhesive.

[0037] According to an aspect, a method of coupling image light into a waveguide using a conjugate coupler comprises emitting image light toward a couplingregion, positioning a conjugate coupler having a coupling block with facets oriented at conjugate elevation angles, splitting the image light at the facets into a first reflected ray set and a second transmitted ray set, and directing the first reflected ray set and the second transmitted ray set toward a coupling-in mirror at different angles of incidence such that, when coupled into the waveguide, the first reflected ray set and the second transmitted ray set filling an aperture region that would otherwise be unilluminated.

[0038] According to an embodiment, at least one facet is partially reflective with a reflectance between 30% and 70%.

[0039] According to an embodiment, facet orientations are selected as a function of such that a facet tilt is approximately 2p.

[0040] According to an embodiment, otherwise lost light is recycled by providing an auxiliary partial facet disposed substantially parallel to the coupling-in mirror and configured to be highly reflective or absorbing for high-angle incidence and highly transmissive for low-angle incidence.

[0041] The accompanying drawings, which are incorporated in and constitute a part ofDocket No. LMUS23PWO01the specification, illustrate various example systems, methods, and so on, that illustrate various example embodiments of aspects of the invention. It will be appreciated that the illustrated element boundaries (e.g., boxes, groups of boxes, or other shapes) in the figures represent one example of the boundaries. One of ordinary skill in the art will appreciate that one element may be designed as multiple elements or that multiple elements may be designed as one element. An element shown as an internal component of another element may be implemented as an external component and vice versa.Furthermore, elements may not be drawn to scale.BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Fig. 1 shows a prior art waveguide coupling system demonstrating incomplete aperture filling with a single coupling-in mirror.

[0043] Fig. 2 illustrates a waveguide coupling system with a conjugate coupler positioned adjacent to the coupling-in mirror to address aperture illumination gaps.

[0044] Fig. 3 shows the waveguide coupling system with enhanced detail of the partially reflective facets within the conjugate coupler.

[0045] Fig. 4 shows the waveguide coupling system with multiple additional facets.

[0046] Fig. 5 shows the waveguide coupling system with an auxiliary partial facet to recycle lost light from the extended facet configuration.

[0047] Fig. 6 illustrates a perspective view of smart glasses incorporating the waveguide display system with conjugate coupler technology according to some embodiments of the present disclosure.

[0048] Fig. 7 illustrates a block diagram of the overall near-eye display system illustrating the interconnection between a host computer and wearable device in accordance with some embodiments of the present disclosure.

[0049] Fig. 8 illustrates a flowchart of a method for coupling image light into a waveguide using the conjugate coupler according to the embodiments of the present disclosure.Docket No. LMUS23PWO01DETAILED DESCRIPTION

[0050] The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and / or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and / or configurations discussed.

[0051] Further, spatially relative terms, such as "beneath," "below," "lower," "above," "upper" and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

[0052] Numerical values in the specification and claims of this application should be understood to include numerical values which are the same when reduced to the same number of significant figures and numerical values which differ from the stated value by less than the experimental error of conventional measurement technique of the type described in the present application to determine the value. All ranges disclosed herein are inclusive of the recited endpoint.

[0053] The term "about" can be used to include any numerical value that can vary without changing the basic function of that value. When used with a range, "about" also discloses the range defined by the absolute values of the two endpoints, e.g., "about 2 toDocket No. LMUS23PWO01about 4" also discloses the range "from 2 to 4." The term "about" may refer to plus or minus 10% of the indicated number.

[0054] The numbers presented herein are representative of one possible implementation, and the skilled artisan will appreciate that variations regarding the numbers of bits or bytes utilized in the systems and methods presented herein are contemplated and incorporated herein. Such variations may include, for example and without limitation, numbers of bits or bytes that are greater than, or less than the examples utilized herein. Furthermore, the examples set forth herein are intended solely as nonlimiting examples of some of the embodiments disclosed and contemplated herein and are not to be construed as being definitive as to limits associated therewith.

[0055] Figure 1 illustrates a prior art waveguide coupling system 100 that demonstrates the technical problem addressed by the present embodiment. The system includes a waveguide 102 having a first major surface 104 and a second major surface 106, with a coupling-in mirror 108 positioned to direct light from a projector or projection optical device (POD) 110 into the waveguide 102. The waveguide 102 contains coupling out facets or outcoupling partial reflectors 112 configured to extract light toward an eye box 116. The waveguide 102 functions based on total internal reflection along its major surfaces 104, 106 to propagate light, with the coupling out facets 112 serving as outcoupling partial reflectors that progressively redirect image illumination

[0056] In this prior art configuration, the coupling-in mirror 108 creates an aperture illumination gap 114 in the waveguide's virtual aperture 118. In some embodiments, a virtual aperture 118 of the waveguide 102 is defined as an effective width of a region that is to be uniformly illuminated in order to avoid formation of unilluminated zones in the waveguide illumination pattern. The width of the image beam provided to the coupling-in region is selected to be at least equal to, and in certain examples greater than or equal to, a width of the virtual aperture so that missing rays do not create a hole in the waveguide illumination and a corresponding non-uniformity at an eye box 116. Light rays from the projector 110 are reflected by the coupling-in mirror 108 at a specific angle, but this single reflection point results in incomplete filling of the waveguide aperture. Specifically, certain regions of the first major surface 104 receive insufficient illumination, creating the apertureDocket No. LMUS23PWO01illumination gap 114 that corresponds to missing light rays that would otherwise contribute to uniform illumination across the waveguide 102. This problem is particularly acute in augmented reality (AR) and mixed reality (MR) headsets where uniform image quality is essential for user experience.

[0057] While in some circumstances, the coupling-in mirror 108 (or multiple mirrors), may completely fill the aperture, incomplete aperture filling may occur if the coupling-in mirror 108 alone, fails to redirect light to fill all angular and spatial regions within the waveguide 102 that are necessary for total internal reflection propagation. This deficiency results in non-uniform light distribution at the eye box 116, where the user observes the image. The aperture illumination gap 114 manifests as dark regions or reduced brightness zones in the displayed image, creating visible "holes" in the illumination that degrade the overall visual experience and image quality of the near-eye display system. Prior solutions to address this uniformity problem have included optical homogenizers to blend light before entry and integrated projectors that alter the input light geometry, but these approaches increase system size, complexity, and cost.

[0058] Figure 2 illustrates a waveguide coupling system 120 according to an embodiment that addresses the aperture illumination gap problem shown in Figure 1. The system 120 includes the same basic waveguide 102 with first major surface 104, second major surface 106, coupling-in mirror 108, and coupling out facets 112, but now incorporates a conjugate coupler 130 positioned adjacent to the coupling-in mirror 108. The conjugate coupler 130 comprises a coupling block having a plurality of facets, including a distal facet 132 and at least one partially reflecting facet 134, each facet oriented at a conjugate elevation angle p (angle 140) relative to the coupling-in mirror 108. In various embodiments, the conjugate elevation angle of the facets 132, 134 is selected as a function of an angle p 140 of the coupling-in mirror such that a facet tilt is approximately 2p 142. It is to be appreciated that 2p may be implemented for equal refractive indices, however 2p 142 may vary as a function of the refractive index. In some embodiments disclosed and contemplated herein, the waveguide 102 and the conjugate coupler 130 may have different refractive indices. This relationship arises from simple geometric ray tracing and ensures that a conjugate beam generated by the facets is redirected toward the coupling-in mirror at incidence angles that are complementary to those of a primary beam,Docket No. LMUS23PWO01so that the conjugate beam fills an aperture region that would otherwise be unilluminated by the primary beam alone.

[0059] The plurality of facets includes at least one partially reflective surface configured to reflect a first portion of the incoming light rays and transmit a second portion of the incoming light rays. The system demonstrates the angular relationship 2p (angle 142) that governs the facet orientation for optimal light splitting performance. The conjugate coupler 130 may be juxtaposed external to the waveguide 102 with an air gap or bonded using a low refractive index optical adhesive to maintain proper optical coupling while preserving total internal reflection conditions within the waveguide 102. In some embodiments, a polarizer, waveplate, etc., may be positioned between the conjugate coupler 130 and the second major surface 106, e.g., within the aforementioned airgap, adhesive, or the like. In some embodiments, the conjugate coupler 130 is tilted with respect to a major surface 104, 106 of the waveguide 102. A wedge element (not shown) having a refractive index lower than that of the waveguide 102 is disposed between the tilted conjugate coupler 130 and the waveguide 102. The wedge geometry and refractive index are selected so that total internal reflection conditions within the waveguide are maintained while still providing the desired mechanical and optical alignment between the coupler 130 and the waveguide 102. The conjugate coupler 130 may be mechanically and optically bonded directly to a projector 110 rather than to the waveguide 102. In such arrangements, the coupler 130 is positioned to receive an image beam from an output window of the projector 110 and to redirect and split the image beam toward the coupling-in mirror 108 of the waveguide 102, thereby enabling modular combinations of different projector modules with a given waveguide architecture.

[0060] The conjugate coupler 130 may be fabricated from various optical materials selected to achieve the desired refractive index characteristics and optical performance. Suitable materials for the coupling block include optical glasses such as BK7, SF11 , or other crown and flint glasses that provide appropriate refractive indices for the specific waveguide application. High-index materials such as sapphire, silicon, or titanium dioxide may be employed where increased optical path differences are desired between the conjugate coupler 130 and the waveguide 102. Alternatively, optical polymers including polycarbonate, cyclic olefin copolymers (COC), or specialized optical plastics may beDocket No. LMUS23PWO01utilized to reduce weight and manufacturing costs while maintaining optical clarity and dimensional stability. The facets 132, 134 may be formed through precision molding, diamond turning, or photolithographic processes, with partially reflective coatings applied using physical vapor deposition, chemical vapor deposition, or sol-gel coating techniques to achieve the desired reflectance characteristics. Anti-reflection coatings may be applied to non-functional surfaces to minimize unwanted reflections and optimize optical efficiency.

[0061] The facets 132, 134 themselves may be constructed from the same optical materials as the coupling block substrate or may incorporate specialized materials to achieve specific optical properties. For partially reflective facets 134, the reflective characteristics are typically achieved through thin-film coatings rather than bulk material properties. Common coating materials for partially reflective surfaces include metallic films such as aluminum, silver, or gold, which provide broadband reflectance characteristics suitable for visible light applications. Dielectric coatings comprising alternating layers of high and low refractive index materials, such as titanium dioxide (TiO2) and silicon dioxide (SiO2), tantalum pentoxide (Ta2O5) and magnesium fluoride (MgF2), or hafnium dioxide (HfO2) and aluminum oxide (AI2O3), may be employed to achieve precise reflectance values and spectral characteristics. These multilayer dielectric coatings enable fine control over the reflectance percentage, typically ranging from 30% to 70% as specified for optimal beam splitting performance.

[0062] For fully reflective facets, such as the distal facet 132, enhanced aluminum coatings with protective overcoats or silver-based mirror coatings may be utilized to achieve reflectance values exceeding 95% across the visible spectrum. The protective overcoats, typically comprising silicon dioxide or aluminum oxide, prevent oxidation and mechanical damage to the underlying metallic reflective layer. Alternatively, all-dielectric mirror coatings consisting of multiple quarter-wave layers of alternating high and low index materials may be employed where durability and environmental stability are essential. The coating thickness and layer count are optimized based on the specific wavelength range and reflectance of the near-eye display application, with typical coating thicknesses ranging from tens of nanometers for metallic films to several micrometers for complex multilayer dielectric stacks. In such embodiments, the conjugate coupler 130 comprises a plurality of facets 132, 134 having non-uniform reflectivities to equalize irradiance at the waveguideDocket No. LMUS23PWO01aperture, e.g., a fully reflective distal facet 132 and one or more partially reflective facets 134.

[0063] In another embodiment, the conjugate coupler 130 may be implemented with a single long fully reflective facet having a length sufficient to span at least a portion of the virtual aperture width. In such a configuration, a single conjugate mirror facet generates the complementary beam without intermediate beam-splitting facets. This embodiment can be advantageous in systems with a relatively small field of view, and may reduce manufacturing complexity while still providing improved aperture filling relative to a system that relies solely on the coupling-in mirror 108.

[0064] The conjugate coupler 130 operates by splitting incoming light rays from the projector 110 into complementary ray sets that follow different optical paths. A first ray set, shown as reflected light rays 148, is initially reflected by the partially reflecting facet 134 before impinging upon the coupling-in mirror 108 at higher incidence angles. A second ray set, shown as transmitted light rays 150, passes through the partially reflecting facet 134 and strikes the coupling-in mirror 108 at lower incidence angles. The distal facet 132 provides full reflection to prevent light loss at the far end of the coupling block. The partially reflecting facet 134 may be configured as a beam splitter with approximately 50% reflectance, though this reflectance can be optimized between 30% and 70% based on the specific illumination and field-of-view constraints of the display system.

[0065] This dual-path configuration enables the conjugate coupler 130 to fill the aperture illumination gap 114 that was present in the prior art system of Figure 1. The reflected light rays 148 and transmitted light rays 150 are directed at complementary angles such that when coupled into the waveguide 102, they collectively illuminate regions of the waveguide aperture that would otherwise remain unfilled by the coupling-in mirror 108 alone. The angle (140) is selected to optimize this complementary illumination, typically ranging between 20° and 40°, with the facet tilt being approximately 2p (142) to achieve the desired angular distribution of the ray sets within the waveguide 102. This approach provides a compact architecture that achieves uniform image brightness across the waveguide without bulky homogenizers or complex integrated projector modules,Docket No. LMUS23PWO01making it compatible with existing projector modules while maintaining scalability for different field-of-view applications.

[0066] Figure 3 illustrates the waveguide coupling system 120 with enhanced detail regarding the partially reflective nature of the facets within the conjugate coupler 130.Building upon the configuration shown in Figure 2, this embodiment demonstrates how the partially reflecting facet 134 operates as a beam splitter to create the complementary ray sets that address the aperture illumination gap. The partially reflecting facet 134 is configured with approximately 50% reflectance, though this value can be optimized between 30% and 70% depending on the specific illumination and desired balance between the reflected light rays 148 and transmitted light rays 150.

[0067] The beam-splitting operation of the partially reflecting facet(s) 134 enable precise control over the intensity distribution of the two ray sets. When incoming light from the projector 110 encounters the partially reflecting facet 134, a controlled portion is reflected to form the reflected light rays 148, while the remaining portion passes through to form the transmitted light rays 150. This splitting mechanism allows the system to balance the illumination contributions from each ray set, ensuring that neither path dominates the overall light distribution within the waveguide 102. The reflectance of the partially reflecting facet 134 can be tailored through appropriate coating design to achieve optimal uniformity at the eye box 116. Suitable coating materials for achieving the desired beam-splitting characteristics include metallic films such as aluminum, silver, or gold that provide broadband reflectance properties across the visible spectrum. Alternatively, dielectric coatings comprising alternating layers of high and low refractive index materials, such as titanium dioxide (TiO2) and silicon dioxide (SiO2), tantalum pentoxide (Ta2O5) and magnesium fluoride (MgF2), or hafnium dioxide (HfO2) and aluminum oxide (AI2O3), may be employed to achieve precise reflectance values typically ranging from 30% to 70% for optimal beam splitting performance. These multilayer dielectric coatings enable fine control over both the reflectance percentage and spectral characteristics, allowing the partially reflecting facet 134 to be optimized for specific wavelength ranges and displayapplications.Docket No. LMUS23PWO01

[0068] The controlled beam splitting shown in Figure 3 provides several advantages over the basic configuration. The partially reflecting facet 134 enables fine-tuning of the illumination balance between the high-angle reflected light rays 148 and the low-angle transmitted light rays 150, allowing the system to compensate for variations in projector beam characteristics or waveguide geometry. Additionally, the beam splitter configuration maintains high optical efficiency by utilizing both reflected and transmitted portions of the incident light, rather than blocking or absorbing unwanted rays. This approach results in improved illumination uniformity across the waveguide aperture while maintaining compatibility with standard projector modules and enabling modular integration with different near-eye display architectures.

[0069] Figure 4 illustrates the waveguide coupling system 120 with an extended configuration that includes multiple additional facets within the conjugate coupler 130. Building upon the configurations shown in Figures 2 and 3, this embodiment demonstrates how the addition of further facets can enhance spatial mixing of the complementary ray sets but may also introduce light loss challenges. The system retains the basic waveguide 102 with first major surface 104, second major surface 106, and coupling-in mirror 108, along with the conjugate coupler 130 having the distal facet 132 and partially reflecting facet 134, but now incorporates additional facets that provide increased optical path diversity.

[0070] The multiple additional facets in the conjugate coupler 130 create more complex ray splitting and redirection patterns, allowing for enhanced spatial mixing of the reflected light rays 148 and transmitted light rays 150. Each additional facet provides another opportunity for beam splitting, creating multiple sub-beams within each of the primary ray sets. This increased complexity in the optical paths can improve the uniformity of illumination distribution across the waveguide aperture by providing finer control over the angular and spatial characteristics of the light entering the waveguide 102. Furthermore, the multiple additional facets in the conjugate coupler 130 of Figure 4 avoid a non-uniform illumination of the coupling-in mirror 108 and then of the waveguide aperture. However, as shown in Figure 4, this configuration may result in lost light 152 that escapes through the first major surface 104 due to inadequate reflection conditions.Docket No. LMUS23PWO01

[0071] The lost light 152 occurs when certain ray paths within the extended facet structure do not maintain the proper angles for total internal reflection within the waveguide 102. As light undergoes multiple reflections and transmissions through the additional facets, some rays may be directed at angles that fall below the critical angle for total internal reflection at the first major surface 104, causing them to escape the waveguide rather than propagate toward the eye box 116. This light loss represents a reduction in optical efficiency and can create non-uniformities in the illumination pattern if not properly managed. The challenge illustrated in Figure 4 demonstrates the trade-off between increased spatial mixing capability and potential optical efficiency losses, highlighting the need for careful optimization of facet number, orientation, and reflectance characteristics to maximize the benefits while minimizing unwanted light loss.

[0072] Figure 5 illustrates the waveguide coupling system 120 with a solution to the light loss problem demonstrated in Figure 4. Building upon the extended facet configuration shown in Figure 4, this embodiment incorporates an auxiliary partial facet 160 positioned within the waveguide 102 to recycle the lost light 152 that would otherwise escape through the first major surface 104. The auxiliary partial facet 160 is disposed substantially parallel to the coupling-in mirror 108 and is strategically located to intercept light rays that fail to maintain total internal reflection conditions within the waveguide 102.

[0073] The auxiliary partial facet 160 is configured with angle-dependent reflectance characteristics, being highly reflective or absorbing for high-angle incidence and highly transmissive for low-angle incidence. This selective reflectance behavior enables the auxiliary partial facet 160 to capture and redirect the lost light 152 back into the waveguide propagation paths while allowing properly guided light to pass through unimpeded toward the eye box 116. When light rays strike the auxiliary partial facet 160 at high angles of incidence, corresponding to the lost light 152 from the extended facet structure of the conjugate coupler 130, the facet reflects these rays back into the waveguide 102 at angles that satisfy the total internal reflection conditions for continued propagation. The auxiliary partial facet 160 is disposed substantially parallel to the coupling-in mirror 108, typically oriented at an angle between 35° and 45° relative to the first major surface 104 of the waveguide 102, and positioned at a complementary angle relative to the conjugate coupler 130 facets to optimize light recycling efficiency. The angle-dependent reflectanceDocket No. LMUS23PWO01characteristics of the auxiliary partial facet 160 may be achieved through specialized coatings including dichroic filters comprising alternating layers of high and low refractive index materials such as titanium dioxide (TiO2) and silicon dioxide (SiO2), or tantalum pentoxide (Ta2O5) and magnesium fluoride (MgF2), designed to provide high reflectance for incident angles above approximately 60° while maintaining high transmittance for angles below 30°. Alternative coating approaches include gradient-index coatings that provide smooth transitions between reflective and transmissive regions, or polarization-selective coatings that combine angle-dependent and polarization-dependent reflectance characteristics to further optimize the light recycling performance for specific waveguide geometries and field-of-view applications.

[0074] The implementation of the auxiliary partial facet 160 provides several advantages for the overall system performance. The recycling of otherwise lost light improves the optical efficiency of the waveguide coupling system 120 by recovering light energy that would be wasted in the configuration shown in Figure 4. Additionally, the auxiliary partial facet 160 helps maintain illumination uniformity by preventing the creation of dark zones that would result from the lost light 152. The angle-selective properties of the auxiliary partial facet 160 ensure that the normal propagation of guided light rays within the waveguide 102 is not disrupted, while specifically targeting the problematic high-angle rays for redirection. This approach enables the benefits of the extended facet configuration with multiple additional facets to be realized without the associated efficiency penalties, providing enhanced spatial mixing of the complementary ray sets while maintaining high optical performance and uniform illumination at the eye box 116.

[0075] Figure 6 illustrates a perspective view of smart glasses 200 incorporating the waveguide display system with the conjugate coupler technology described in the previous figures. The smart glasses 200 comprise an eyeglasses frame 218 that supports the optical components and provides a wearable form factor suitable for augmented reality or mixed reality applications. The frame 218 houses a first waveguide section 201 and a second waveguide section 205, each corresponding to one eye of the user and incorporating the waveguide coupling system 120 with conjugate coupler 130 as described in Figures 2-5. A compact projector 212 is integrated within the frame 218 to provide image light to each waveguide section, and a controller 219 manages the operation of the display system.Docket No. LMUS23PWO01

[0076] The smart glasses 200 demonstrate the practical implementation of the conjugate coupler technology in a consumer-ready near-eye display device. Each waveguide section 201, 205 incorporates the conjugate coupler 130 positioned adjacent to its respective coupling-in mirror to achieve uniform illumination across the waveguide aperture, as described in the previous figures. The compact projector 212 generates image light that is directed through the conjugate coupler 130, where it is split into complementary ray sets that fill the aperture regions that would otherwise be unilluminated. The controller 219 coordinates the operation of the projectors and manages image rendering to provide synchronized binocular display functionality.

[0077] An exemplary implementation of a device in the form of a near-eye display according to the teachings of an embodiment of the present invention, generally designated 200, employing a waveguide system 215, is illustrated schematically in Figure 6. The near-eye display (NED) 200 employs a compact image projector 212 optically coupled so as to inject light beams corresponding to an image (interchangeably referred to as the "light," "light rays," the "image," or the "image light") into waveguide system (interchangeably referred to as "substrate" or "slab") 215 within which the image light is trapped in one dimension by internal reflection at a set of mutually-parallel planar external surfaces.

[0078] Optical aperture expansion is achieved within waveguide system 215 by one or more arrangements for progressively redirecting the image light, typically employing a set of partially-reflecting surfaces (interchangeably referred to as "facets" or "elements") that may be parallel to each other and inclined obliquely to the direction of propagation of the image light, with each successive facet deflecting a proportion of the image light into a deflected direction. As illustrated in Figure 6, two-dimensional aperture expansion is achieved by employing a first waveguide section 201 that transmits the light along the X direction and a first set of facets in waveguide section 201 to progressively redirect the image light within the waveguide system 215 in the Y direction, also trapped / guided by internal reflection.

[0079] The deflected image light then passes into a second waveguide section 205, which may be implemented as an adjacent distinct substrate or as a continuation of aDocket No. LMUS23PWO01single substrate, in which a coupling-out arrangement (for example, a further set of partially reflective facets) progressively couples out a portion of the image light in the Z direction towards the eye of an observer located within a section defined as the eye-motion box (EMB), thereby achieving a second dimension of optical aperture expansion. Similar functionality may be obtained using diffractive optical elements (DOEs) for redirecting and / or coupling-out of image light within one or both of waveguide sections 201 and 205. The overall device may be implemented separately for each eye and is preferably supported relative to the head of a user with each waveguide system 215 facing a corresponding eye of the user. In one embodiment, as illustrated here, a support arrangement is implemented as an eyeglasses frame 218 with sides for supporting the device relative to ears of the user. Other forms of support arrangement may also be used, including but not limited to head bands, visors or devices suspended from helmets.

[0080] Reference is made herein in the drawings and claims to an X axis which extends horizontally (or, in alternative embodiments, vertically), in the general extensional direction of the first section 201 of the waveguide system 215, a Y axis which extends perpendicular thereto, i.e. , vertically in Figure 6 (or, in alternative embodiments, horizontally), and a Z axis which extends perpendicular thereto, i.e., horizontal towards the eye of the user. In very approximate terms, the first waveguide section 201 of waveguide system 215 may be considered to achieve aperture expansion in the X direction while the second waveguide section 205 of waveguide system 215 achieves aperture expansion in the Y direction. The details of the spread of angular directions in which different parts of the field of view propagate will be addressed more precisely below. It should be noted that the orientation as illustrated in Figure 6 may be regarded as a "top-down" implementation, where the image illumination entering the second waveguide section 205 of the waveguide system 215 enters from the top edge, whereas an alternative orientation may be regarded as a "side-injection" implementation, where the axis referred to here as the Y axis is deployed horizontally.

[0081] Herein, the various features of certain embodiments of the present disclosure may be illustrated in the context of a "top-down" orientation, similar to Figure 6. However, it should be appreciated that all of those features are equally applicable to side-injection implementations, which also fall within the scope of the invention. In certain cases, otherDocket No. LMUS23PWO01intermediate orientations are also applicable, and are included within the scope of the present invention except where explicitly excluded. The two-dimensional expansion embodiments illustrated here are merely for the sake of example, but the invention is also applicable to embodiments in which only a single dimension of aperture expansion is performed by the waveguide system 215. It will be appreciated that the near-eye display 200 includes various additional components, typically including a controller 219 for actuating the image projector 212, typically employing electrical power from a small onboard battery (not shown) or some other suitable power source. It will be appreciated that controller 219 includes all necessary electronic components such as at least one processor or processing circuitry to drive the image projector 212. In embodiments, the near-eye display 200 may be implemented using the components of the wearable device 310 described with reference to Figure 7, discussed below.

[0082] Figure 7 illustrates a block diagram of the overall near-eye display system 300 showing the interconnection between a host computer 370 and a wearable device 310 that incorporates the conjugate coupler technology described in the previous figures. The system 300 demonstrates how the waveguide display apparatus with conjugate coupler integrates into a complete augmented reality or mixed reality platform. The host computer 370 includes a processor 374, computer-readable medium 380 containing instructions 378, and communicates with the wearable device 310 through image, control, status, and power signals 388 transmitted via signal and power bus 300, 302.

[0083] The wearable device 310 comprises several interconnected subsystems that work together to provide the near-eye display functionality. A controller 314 serves as the central processing unit for the wearable device 310 and interfaces with memory 316 for local data storage and processing. The controller 314 coordinates the operation of an image projector 326 that generates digital images 328 corresponding to the content received from the host computer 370. A power management module 320 regulates electrical power from a battery 322 to supply the various components of the wearable device 310, ensuring stable operation of the display system while maintaining portability and extended usage time.Docket No. LMUS23PWO01

[0084] The optical subsystem of the wearable device 310 includes the image projector 326 optically coupled to a light-guide optical element 330 that incorporates the conjugate coupler technology described in Figures 2-5. An optical engine 334 processes the digital images 328 from the image projector 326 and directs the resulting light through the conjugate coupler into the light-guide optical element 330, where the light undergoes the aperture expansion and uniform distribution processes previously described. The entire optical assembly is supported within a frame 338 that provides structural integrity and user comfort when worn as smart glasses or other head-mounted display configurations.

[0085] Figure 7 illustrates a block diagram of an optical system 300, in accordance with various examples of the present disclosure. Optical system 300 may include two or more devices or components and may be implemented generally as a hybrid system including various electronic, optical, and electro-optical elements. An optical device 302 may include one or more elements from optical system 300. The optical system 300 includes a wearable device 310, such as one or more near eye displays or smart glasses, which may be worn on or about the head of a user to convey optical information to one or more eyes of a user, and demonstrates the practical implementation of the conjugate coupler within a complete near-eye display ecosystem.

[0086] Wearable device 310 may include a controller 314 with a memory 316 where controller 314 may be configured to send and receive electrical signals to various other elements in optical system 300, to execute program instructions stored in memory 316 in order to process and provide information, to operate wearable device 310, and to interact with other systems outside wearable device 310, for example. Controller 314 may include a microcontroller, a processor, various discrete components, programmable logic devices, and / or various interface circuits that may access memory 316 which may be removable, replaceable, programmable, and reprogrammable to update instructions to controller 314.

[0087] Wearable device 310 may also include a power management module 320 having a battery 322, where power management module 320 may be configured to charge, discharge, and monitor power usage for battery 322. Various elements of wearable device 310 may receive power from battery 322, including controller 314, image projector 326, and optical engine 334, for example. Wearable device 310 may also includeDocket No. LMUS23PWO01one or more image projectors 326, each configured to produce a collimated image beam based on a digital image 328. The collimated image beam may be an illuminated representation of the digital image having an image field which is a two-dimensional representation of the digital image based on either a single graphical image (e.g., a static image) ora sequence of graphical images (e.g., a moving image). The collimated image beam may be collimated to infinity.

[0088] Wearable device 310 may also include one or more light-guide optical elements 330 (e.g., waveguides, also denoted as LOEs) comprising transparent materials configured to receive and propagate light, where light may enter into and exit through various external and internal surfaces of the light-guide optical element 330. For example, the transparent material comprising light-guide optical element 330 may include optical glass or other suitable material that is transformed into complex optical structures using a process that may include coating, stacking, slicing, polishing, and shaping the transparent materials. The process may include the addition of partially reflective or fully reflective materials such as mirror coatings, for example. Similarly, the process may also include the addition of partially opaque or fully opaque materials such as light covers to block light, for example. The conjugate coupler technology integrated within the light-guide optical element 330 ensures that the images generated by the image projector 326 are uniformly distributed across the waveguide aperture, resulting in high-quality visual experiences for the user.

[0089] Wearable device 310 may also include one or more optical engines 334 coupled to the one or more image projectors 326 and light-guide optical elements 330. Optical engine 334 may be configured to directly operate image projector 326 under the direction of the controller 314. For example, optical engine 334 may provide graphics processing for digital image 328 before projection of an illuminated representation of the digital image by image projector 326. Wearable device 310 may also include a frame 338 (e.g., a structure) for supporting and retaining one or more elements in wearable device 310. For example, frame 338 may support and retain a first image projector 326 in position next to a first light-guide optical element 330. Similarly, frame 338 may support and retain a second image projector 326 in position next to a second light-guide optical element 330. InDocket No. LMUS23PWO01this manner, frame 338 may support and retain one or two image projectors 326 and lightguide optical element 330 pairs on or about the head of a user, for example.

[0090] Optical system 300 may also include a host computer 370 that may include a processor 374 configured to read and execute operations based on instructions 378 stored in a computer-readable medium 380. Instructions 378 may include at least some instructions provided to controller 314 and stored in memory 316. Host computer 370 may communicate with one or more elements of wearable device 310 over a signal and power bus 388. In this manner, host computer 370 may provide power to charge battery 322, provide instructions to and receive status from controller 314, to control various other elements of wearable device 310, and to provide digital image data to optical engine 334.

[0091] The host computer 370 provides computational resources for rendering complex augmented reality or mixed reality content, while the wearable device 310 handles the realtime display functions including image projection and optical coupling. This distributed architecture enables the wearable device 310 to remain lightweight and comfortable while leveraging the processing power of the host computer 370 for demanding computational tasks, making the system suitable for extended use in professional, educational, and consumer applications where prolonged wear comfort and high-performance visual experiences are essential.

[0092] Figure 8 illustrates a flowchart of a method 400 for coupling image light into a waveguide 102 using the conjugate coupler 130 technology described in the previous figures. The method 400 provides a systematic approach to implementing the conjugate coupler solution for addressing aperture illumination gaps 114 in waveguide-based neareye displays. The flowchart demonstrates the sequential steps for achieving uniform illumination across the waveguide aperture through the coordinated operation of the conjugate coupler 130 and coupling-in mirror 108 components.

[0093] The method 400 begins at step 402 with emitting image light toward a coupling region of the waveguide system 120. This initial step involves activating the projector 110 or projection optical device to generate the image light that will be processed by the conjugate coupler 130 system. At step 404, the method proceeds with positioning a conjugate coupler 130 having a coupling block with facets oriented at conjugate elevationDocket No. LMUS23PWO01angles adjacent to the coupling-in mirror 108, establishing the spatial relationship for the faceted coupling block to intercept and process the incoming image light before it reaches the primary coupling mirror 108.

[0094] Step 406 involves orienting the facets 132, 134 at conjugate elevation angles, typically configured as a function of the mirror angle p 140 such that the facet tilt is approximately 2p 142. This angular relationship ensures that the facets 132, 134 are properly positioned to create the complementary ray sets that will address the aperture illumination gap 114. The conjugate elevation angles are selected to optimize the splitting and redirection of the incoming light rays, with typically ranging between 20° and 40° depending on the specific waveguide 102 geometry and field-of-view applications.

[0095] At step 408, the method performs the splitting of the image light at the facets into a first reflected ray set and a second transmitted ray set through interaction with the partially reflecting facet 134 of the conjugate coupler 130. The partially reflective surfaces, configured with reflectance values typically between 30% and 70%, divide the incoming light into two complementary paths. The first reflected ray set undergoes initial reflection from the facets 132, 134 before proceeding to the coupling-in mirror 108, while the second transmitted ray set passes through the facets and directly impinges upon the coupling-in mirror 108.

[0096] Step 410 directs the first reflected ray set and the second transmitted ray set toward the coupling-in mirror 108 at different angles of incidence. The first reflected ray set strikes the coupling-in mirror 108 at higher incidence angles, while the second transmitted ray set impinges at lower incidence angles. This angular differentiation enables the two ray sets to access different regions of the waveguide aperture when coupled into the waveguide 102 substrate, ensuring comprehensive coverage of the propagation space within the waveguide 102.

[0097] The method concludes at step 412 with the first reflected ray set and the second transmitted ray set filling an aperture region that would otherwise be unilluminated when using the coupling-in mirror 108 alone. The complementary ray sets, having been directed at varying incidence angles, collectively illuminate the entire waveguide 102 aperture including the regions that correspond to the aperture illumination gap 114 identified in theDocket No. LMUS23PWO01prior art configuration of Figure 1. This comprehensive aperture filling results in uniform illumination distribution at the eye box 116, eliminating the dark zones and brightness variations that would otherwise degrade the visual experience in the near-eye display system.

[0098] The method 400 provides several advantages over conventional single-mirror coupling approaches. The systematic splitting and redirection of image light through the conjugate coupler 130 enables uniform illumination without bulky homogenizers or complex integrated projector modifications. The method maintains compatibility with standard projector modules while achieving the aperture filling for high-quality augmented reality and mixed reality applications. The sequential nature of the method allows for optimization at each step, enabling fine-tuning of the facet orientations, reflectance values, and angular relationships to achieve optimal performance for specific waveguide 102 geometries and display applications.

[0099] While example systems, methods, and so on, have been illustrated by describing examples, and while the examples have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit scope to such detail. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the systems, methods, and so on, described herein. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the application is not limited to the specific details, the representative apparatus, and illustrative examples shown and described. Thus, this application is intended to embrace alterations, modifications, and variations that fall within the scope of the appended claims. Furthermore, the preceding description is not meant to limit the scope of the application. Rather, the scope of the application is to be determined by the appended claims and their equivalents.

Claims

Docket No. LMUS23PWO01CLAIMSWhat is claimed is:

1. A conjugate coupler for coupling image light into a waveguide of a near-eye display, comprising:a coupling block having a plurality of facets, each facet oriented at a conjugate elevation angle relative to a coupling-in mirror of the waveguide and configured to split incoming light rays into multiple optical paths;wherein the plurality of facets includes at least one partially reflective surface configured to reflect a first portion of the incoming light rays and transmit a second portion of the incoming light rays; andwherein the conjugate coupler is configured to generate complementary ray sets that compensate for aperture-filling deficiencies.

2. The conjugate coupler of claim 1 , wherein the coupling block further comprises a distal facet that is fully reflective.

3. The conjugate coupler of claim 1 , wherein at least one facet is a beam splitter with a reflectance between 30% and 70%.

4. The conjugate coupler of claim 1, wherein facet reflectivities are non-uniform across the plurality of facets to equalize irradiance at the waveguide aperture.

5. The conjugate coupler of claim 1, wherein the conjugate elevation angles are selected as a function of an angle p of the coupling-in mirror such that a facet tilt is approximately 2p.

6. The conjugate coupler of claim 5, wherein is between 20° and 40°.Docket No. LMUS23PWO017. The conjugate coupler of claim 1, wherein the complementary ray sets comprise a first ray set that impinges the coupling-in mirror at higher incidence angles than a second ray set.

8. The conjugate coupler of claim 1, wherein the coupling block further includes multiple additional facets configured to increase spatial mixing of the complementary ray sets.

9. The conjugate coupler of claim 8, further comprising an auxiliary partial facet disposed within the waveguide substantially parallel to the coupling-in mirror and configured to be highly reflective or absorbing for high-angle incidence and highly transmissive for low-angle incidence to recycle otherwise lost light.

10. The conjugate coupler of claim 1 , further comprising anti-reflection coatings at one or more optical interfaces of the coupling block.

11. The conjugate coupler of claim 1 , further comprising at least one of a polarizer or a waveplate disposed between the coupling block and a major surface of the waveguide.

12. The conjugate coupler of claim 1, wherein a refractive index of the coupling block is different from a refractive index of the waveguide.

13. The conjugate coupler of claim 1, wherein the coupling block is bonded to the waveguide with a low refractive index optical adhesive.

14. The conjugate coupler of claim 1, wherein the coupling block comprises a single long fully reflective facet configured to generate the complementary beam without intermediate beam-splitting facets.

15. The conjugate coupler of claim 1, wherein the coupler is external to and not integral with the waveguide to enable modular integration with different projector modules.Docket No. LMUS23PWO0116. The conjugate coupler of claim 1, wherein the plurality of facets further comprises a fully reflective distal facet and at least one partially reflective facet.

17. A waveguide display apparatus for a near-eye display, comprising:a planar waveguide having a major surface and a coupling-in mirror configured to direct image light for propagation by total internal reflection within the waveguide; and a conjugate coupler for coupling image light into the waveguide, the conjugate coupler comprising a coupling block having a plurality of facets, each facet oriented at a conjugate elevation angle relative to the coupling-in mirror and configured to split incoming image light into complementary ray sets including a first ray set reflected by at least one facet and a second ray set transmitted through the coupling block, wherein the plurality of facets includes at least one partially reflective surface configured to reflect a first portion of the incoming light rays and transmit a second portion of the incoming light rays;wherein the first ray set impinges the coupling-in mirror at higher incidence angles than the second ray set such that, when coupled into the waveguide, the ray sets fill an aperture region that would otherwise be unilluminated using the coupling-in mirror alone.

18. The apparatus of claim 17, wherein the conjugate elevation angles are selected as a function of an angle p of the coupling-in mirror such that a facet tilt is approximately 2p.

19. The apparatus of claim 18, wherein is between 20° and 40°.

20. The apparatus of claim 17, wherein at least one facet of the coupling block is a partially reflective beam splitter.

21. The apparatus of claim 20, wherein a reflectance of the partially reflective facet is between 30% and 70%.

22. The apparatus of claim 17, wherein the coupling block further comprises a distal facet that is fully reflective.Docket No. LMUS23PWO0123. The apparatus of claim 17, wherein the coupling block comprises multiple additional facets to enhance spatial mixing of the complementary ray sets.

24. The apparatus of claim 23, further comprising an auxiliary partial facet disposed substantially parallel to the coupling-in mirror and configured to be highly reflective or absorbing for high-angle incidence and highly transmissive for low-angle incidence to recycle lost light.

25. The apparatus of claim 17, further comprising anti-reflection coatings at one or more interfaces between the coupling block and the waveguide.

26. The apparatus of claim 17, further comprising at least one of a polarizer or a waveplate disposed between the coupling block and the major surface of the waveguide.

27. The apparatus of claim 17, wherein the conjugate coupler is juxtaposed external to the waveguide and not integral with the waveguide substrate.

28. The apparatus of claim 17, wherein a refractive index of the coupling block differs from a refractive index of the waveguide.

29. The apparatus of claim 17, wherein the coupling block is bonded to the waveguide with a low refractive index optical adhesive.

30. A method of coupling image light into a waveguide using a conjugate coupler, comprising:emitting image light toward a coupling region;positioning a conjugate coupler having a coupling block with facets oriented at conjugate elevation angles;splitting the image light at the facets into a first reflected ray set and a second transmitted ray set; andDocket No. LMUS23PWO01directing the first reflected ray set and the second transmitted ray set toward a coupling-in mirror at different angles of incidence such that, when coupled into the waveguide, the first reflected ray set and the second transmitted ray set filling an aperture region that would otherwise be unilluminated.

31. The method of claim 30, wherein at least one facet is partially reflective with a reflectance between 30% and 70%.

32. The method of claim 30, further comprising selecting facet orientations as a function of such that a facet tilt is approximately 2p.

33. The method of claim 30, further comprising recycling otherwise lost light by providing an auxiliary partial facet disposed substantially parallel to the coupling-in mirror and configured to be highly reflective or absorbing for high-angle incidence and highly transmissive for low-angle incidence.

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