Eyeglow suppression in waveguide-based displays

Abstract

Disclosed herein is a method and apparatus for suppressing eye glow in a waveguide system. Some embodiments of the method and apparatus include: a light source of image modulated light; a waveguide having a surface facing the eye and an outer surface facing the outside world; an input coupler for coupling light into a total internal reflection path in the waveguide; at least one grating for providing beam expansion and extracting light from the waveguide toward the eye box; and a polymer grating structure comprising a modulation depth and a grating pitch. The modulation depth is greater than the grating pitch over at least a portion of the polymer grating structure. Advantageously, the polymer grating structure is configured to diffract light entering the waveguide from the outside world or stray light generated within the waveguide to the outside world away from the light path refracted through the outer surface.

Description

[Technical field]

[0001] Cross-reference application This application claims priority to U.S. Provisional Patent Application No. 63 / 128,645, filed December 21, 2020, and U.S. Provisional Patent Application No. 63 / 129,270, filed December 22, 2020, the disclosures of which are incorporated by reference in their entireties herein.

[0002] The present invention relates generally to suppressing eye glow in waveguide systems. [Background technology]

[0003] A waveguide may be referred to as a structure with the ability to confine and guide waves (i.e., restrict the spatial region through which waves may propagate). One subclass includes optical waveguides, which are structures that can guide electromagnetic waves, typically electromagnetic waves in the visible spectrum. Waveguide structures can be designed to control the propagation path of waves using a number of different mechanisms. For example, planar waveguides can be designed to utilize diffraction gratings to diffract and couple incident light into the waveguide structure, so that the coupled-in light can continue to travel within the planar structure via total internal reflection (TIR).

[0004] Fabrication of the waveguide can include the use of material systems that allow for the recording of holographic optical elements within the waveguide. One class of such materials includes polymer-dispersed liquid crystal (PDLC) mixtures, which are mixtures containing a photopolymerizable monomer and a liquid crystal. A further subclass of such mixtures includes holographic polymer-dispersed liquid crystal (HPDLC) mixtures. Holographic optical elements, such as volume phase gratings, can be recorded in such liquid mixtures by irradiating the material with two mutually coherent laser beams. During the recording process, the monomer polymerizes and the mixture undergoes photopolymerization-induced phase separation, creating regions densely populated with liquid crystal microdroplets interspersed with regions of clear polymer. The alternating liquid crystal-rich and liquid crystal-depleted regions form the fringe planes of the grating. The resulting grating, commonly referred to as a switchable Bragg grating (SBG), has all the properties normally associated with a volume or Bragg grating, but has a much higher refractive index modulation range coupled with the ability to electrically tune the grating over a continuous range of diffraction efficiencies (fraction of incident light that is diffracted in a desired direction). A continuous range of diffraction efficiency can range from non-diffracting (clear) to diffracting with nearly 100% efficiency.

[0005] Waveguide optics such as those described above can be considered for a wide range of display and sensor applications. In many applications, waveguides containing one or more grating layers encoding multiple optical functions can be realized using a variety of waveguide architectures and material systems, enabling new innovations in near-eye displays for augmented reality (AR) and virtual reality (VR), compact head-up displays (HUD) and helmet-mounted or head-mounted displays (HMD) for road transportation, aviation, and military applications, and sensors for biometric authentication and laser radar (LIDAR) applications. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] US Patent Application Publication No. 2021 / 0063634 [Patent Document 2] US Patent Application Publication No. 2018 / 0284440 [Patent Document 3] International Publication No. 2022 / 015878 Summary of the Invention [Means for solving the problem]

[0007] Various embodiments are directed to a waveguide display including a light source of image modulated light, a waveguide having an eye-facing surface and an exterior surface facing an external environment, an input coupler for coupling the light into a total internal reflection path within the waveguide, at least one grating for providing beam expansion and extracting light from the waveguide toward an eyebox, and a polymer grating structure including a modulation depth and a grating pitch. The modulation depth is greater than the grating pitch over at least a portion of the polymer grating structure. The polymer grating structure is configured to diffract light entering the waveguide from the exterior environment or stray light generated within the waveguide toward the exterior environment away from a light path refracted through the exterior surface. The polymer grating structure does not substantially impede the propagation of image modulated light within the waveguide and the extraction of the image modulated light toward the eyebox. The stray light generated within the waveguide includes at least one selected from the group consisting of light scattered from a grating material, zero order diffraction image modulated light, and image modulated light propagating along an optical path that is not extracted from the waveguide towards the eyebox.

[0008] In various embodiments, the polymer lattice structure further includes a backfill material between adjacent polymer regions. The backfill material can have a refractive index that is higher or lower than the refractive index of the polymer regions.

[0009] In various further embodiments, the backfill material occupies the space at the bottom of the space between adjacent portions of the polymer lattice structure, and air occupies the space from above the top surface of the backfill material to the modulation depth.

[0010] In various further embodiments, the backfill material comprises an isotropic material.

[0011] In various further embodiments, the isotropic backfill material includes a birefringent material.

[0012] In various further embodiments, the birefringent material includes a liquid crystal material.

[0013] In various further embodiments, the modulation depth of the polymer grating structure is greater than the wavelength of visible light.

[0014] In various further embodiments, the grating pitch is the spacing between diffractive features of the polymer grating structure and the modulation depth is the depth of the polymer grating structure.

[0015] In further various embodiments, the grating pitch of the polymer grating structure is between 0.35 μm and 1 μm, and the modulation depth of the polymer grating structure is between 1 μm and 10 μm.

[0016] In further various embodiments, the ratio of the modulation depth of the polymer grating structure to the grating pitch spacing is in the range of 1:1 to 10:1.

[0017] In various further embodiments, the polymer grating structure is configured as a multiplexed grating.

[0018] In various further embodiments, a portion of the polymer grating structure is configured to outcouple light from the waveguide.

[0019] In various further embodiments, a portion of the polymer grating structure is configured as a beam expander.

[0020] In various further embodiments, a portion of the polymer grating structure is configured to couple image modulated light from a light source into a totally internally reflected path within the waveguide.

[0021] In various further embodiments, the modulation depth of the polymer grating structure is configured to provide a defined balance of S-polarized and P-polarized light with high efficiency.

[0022] In various further embodiments, the polymer grating structure further comprises alternating polymer regions and air gap regions, and the refractive index difference between the polymer regions and the air gap regions is in the range of 1.4 to 1.9.

[0023] In various further embodiments, the refractive index difference between the polymer region and the birefringent material is between 0.01 and 0.2.

[0024] In various further embodiments, the polymer lattice structure comprises a two-dimensional lattice structure or a three-dimensional lattice structure.

[0025] In various further embodiments, the polymer grating structure includes polymer diffractive features and a birefringent material between adjacent polymer diffractive features, the birefringent material having a higher refractive index than the polymer diffractive features.

[0026] In various further embodiments, the input coupler is a grating or a prism.

[0027] In various further embodiments, the modulation depth of the polymer grating structure varies across the waveguide to provide spatially varying polarization dependent diffraction efficiency characteristics.

[0028] In various further embodiments, the modulation depth of the polymer grating structure varies across the waveguide to provide spatially varying angle dependent diffraction efficiency characteristics.

[0029] In various further embodiments, at least one of the spatial, angular or polarization diffraction efficiency characteristics may be provided by backfilling the polymer grating structure with an optical material of a particular refractive index or birefringence.

[0030] In further various embodiments, the polymer grating structure is configured as a Bragg grating or a Raman-Nath grating.

[0031] In various further embodiments, a polymer grating structure is formed on the outer surface of the waveguide and / or on the eye-facing surface of the waveguide and at least partially overlaps with the input coupler and / or at least one grating for providing beam expansion and extracting light from the waveguide.

[0032] In further various embodiments, the polymer grating structure includes a region including a Bragg grating, a region including a Raman-Nath grating, and a grating-free region, the region at least partially covering the input coupler and at least one grating for providing beam expansion and light extraction.

[0033] In various further embodiments, the waveguide display further includes a light control layer overlying the grating-free regions of the polymer grating structure.

[0034] In further various embodiments, the light control layer provides at least one selected from the group consisting of polarization rotation, polarization selective absorption, polarization selective transmission, polarization selective diffraction, angle selective transmission, angle selective absorption, antireflection, and transmission within a defined spectral bandwidth.

[0035] In various further embodiments, the polymer grating structure comprises a rolled K-vector grating in which the tilt angle varies continuously or in piecewise steps.

[0036] In various further embodiments, the polymer grating structure comprises a grating having a spatially varying pitch.

[0037] In various further embodiments, light entering the waveguide from the outside world is provided by an external light source and enters the waveguide through the exterior and / or eye-facing surface of the waveguide.

[0038] In further various embodiments, light entering the waveguide from the outside world includes reflections from anatomical surfaces of a viewer of the display.

[0039] In various further embodiments, the waveguide includes two substrates and the polymer grating structure is sandwiched between the two substrates or disposed on the outer surface of either substrate.

[0040] In various further embodiments, the polymer lattice structure is a composite of at least one type of polymer and at least one other material.

[0041] In various further embodiments, the polymer lattice structure is a composite of a polymer and at least one other material, and the polymer is removed after formation of the polymer lattice structure.

[0042] In various further embodiments, the at least one other material includes nanoparticles.

[0043] In various further embodiments, the at least one other material includes a functionalized nanoparticle.

[0044] In various further embodiments, the polymer grating structure is coated with an optical material.

[0045] In various further embodiments, the polymer grating structure is coated with a reflective optical material.

[0046] In further various embodiments, the coating applied to the polymer grating structure provides an effective refractive index of up to 2.5.

[0047] In various further embodiments, a polymer grating structure is coated with a first material and the coated grating is backfilled with a second material having a higher refractive index than the first material.

[0048] In various further embodiments, a polymer grating structure is coated with a first material and the coated grating is backfilled with a second material having a refractive index lower than that of the first material.

[0049] In further various embodiments, the polymer grating structure includes a first grating structure disposed on the outer surface of the waveguide and a second grating structure disposed on the eye-facing surface of the waveguide.

[0050] In various further embodiments, the first grating structure and the second grating structure have different grating periods.

[0051] Various embodiments provide a method for reducing eye glow from a waveguide display, comprising: providing a source of image modulated light, a waveguide, an input coupler, and at least one grating for providing beam expansion and extracting light from the waveguide toward the eyebox, where the waveguide includes an eye-facing surface and an outer surface facing the outside world; providing a polymer grating structure comprising a modulation depth and a grating pitch, where the modulation depth is greater than the grating pitch over at least a portion of the polymer grating structure; directing the image modulated light into a total internal reflection path in a waveguide, beam expanding the light, and extracting it towards the eyebox; directing light propagating in the waveguide away from a refracted light path through an exterior surface to the outside world using a polymer grating structure; diffracting light entering the waveguide from the outside world, or stray light generated within the waveguide, away from a light path refracted through an exterior surface using a polymer grating structure; The present invention is further directed to a method, comprising:

[0052] Various embodiments provide a waveguide-based display device, comprising: a waveguide including an input coupling optical element and an output coupling optical element, the input coupling optical element configured to in-couple image modulated light and the output coupling optical element configured to out-couple the image modulated light towards a user, the waveguide including an outer surface and an inner surface opposite the outer surface, the inner surface being closer to the user than the outer surface; a partial light blocking layer on an outer surface of the waveguide opposite the user; Equipped with The partial light blocking layer is configured to prevent eye glow light exiting the exterior surface of the waveguide from entering the environment outside the exterior surface of the waveguide; Further of interest is a waveguide-based display device.

[0053] In various embodiments, eye glow light includes light that is directed out of the exterior surface, away from the user.

[0054] In various further embodiments, the eye glow light is light reflected by the output coupling optics, the input coupling optics, and / or the interior surfaces.

[0055] In various further embodiments, the waveguide allows the coupled light to be directed such that it undergoes total internal reflection (TIR) ​​between the inner and outer surfaces.

[0056] In various further embodiments, the partial light blocking layer absorbs light in a portion of the visible light spectrum.

[0057] In further various embodiments, the partial light blocking layer comprises a narrow band dye absorber layer.

[0058] In further various embodiments, the narrowband dye absorber layer comprises a light absorbing dye suspended in a transparent matrix.

[0059] Moreover, in various embodiments, the partial light blocking layer includes a meta-material absorbing layer.

[0060] In further various embodiments, the meta-material absorbent layer includes an absorber formed within the meta-material.

[0061] In various further embodiments, the partial light blocking layer deflects light in a portion of the visible light spectrum toward the user.

[0062] In various further embodiments, the partial light blocking layer comprises a dielectric or dichroic reflector.

[0063] In various further embodiments, the partial light blocking layer converts light in a portion of the visible light spectrum into non-visible radiation.

[0064] Additionally, in various embodiments, the partial light blocking layer includes quantum dots or phosphors.

[0065] In various further embodiments, the partial light blocking layer diffracts light in a portion of the visible light spectrum into a path that does not enter the environment.

[0066] In various further embodiments, the partial light blocking layer includes reflective or transmissive diffractive structures.

[0067] In various further embodiments, the partial light blocking layer includes a reflective grating layer.

[0068] In various further embodiments, the reflective grating layer is configured to direct light towards the light absorbing elements.

[0069] In various further embodiments, a reflective grating layer is disposed between two waveguide substrates.

[0070] In various further embodiments, the reflective grating layer includes a holographically recorded grating.

[0071] In various further embodiments, the partial light blocking layer includes a plurality of overlapping diffractive structures, each structure configured to diffract a unique angular bandwidth of the eye glow light and diffract it onto the light absorbing element.

[0072] In further various embodiments, the partial light blocking layer includes a plurality of multiple diffractive structures, each configured to diffract a unique angular bandwidth of the eye glow light onto the light absorbing agent.

[0073] In further various embodiments, the partial light blocking layer is coated directly onto the waveguide.

[0074] In further various embodiments, the partial light blocking layer is coated on a substrate disposed over the waveguide.

[0075] In various further embodiments, a spacer is disposed between the substrate and the waveguide to form a gap between the substrate and the waveguide.

[0076] In further various embodiments, the gap is an air gap.

[0077] In various further embodiments, the substrate includes a protective layer.

[0078] In various further embodiments, the display device further includes another waveguide disposed below the waveguide.

[0079] In various further embodiments, the display device further includes a spacer disposed between the waveguide and the other waveguide to form a gap between the waveguide and the other waveguide.

[0080] In various further embodiments, the gap comprises an air gap.

[0081] In various further embodiments, the display device further includes another partial shading layer, where the other waveguide is configured to display a different wavelength of light than the waveguide, where the partial shading layer is configured to block wavelengths of light that correspond to the wavelengths of light that the waveguide is configured to display, and where the other partial shading layer is configured to block wavelengths of light that correspond to the wavelengths of light that the other waveguide is configured to display.

[0082] In further various embodiments, the other waveguide is configured to display a different wavelength of light than the waveguide, and wherein the partial light blocking layer is configured to block wavelengths of light that correspond to the wavelengths of light of the waveguide and the other waveguide.

[0083] In various further embodiments, the waveguide is a first waveguide and the display device further comprises a second waveguide and a third waveguide.

[0084] In various further embodiments, the first waveguide, the second waveguide and the third waveguide are each configured to display a different wavelength of light.

[0085] In further various embodiments, the partial shading layer is a first partial shading layer, and the display device further includes a second partial shading layer and a third partial shading layer, where the first partial shading layer is configured to block wavelengths of light corresponding to the wavelengths of light that the first waveguide is configured to display, where the second partial shading layer is configured to block wavelengths of light corresponding to the wavelengths of light that the second waveguide is configured to display, and where the third partial shading layer is configured to block wavelengths of light corresponding to the wavelengths of light that the third waveguide is configured to display.

[0086] In various further embodiments, the second waveguide is disposed between the first waveguide and the second waveguide.

[0087] In various further embodiments, a second partial light blocking layer is formed on the top surface of the second waveguide.

[0088] In further various embodiments, a second partial light blocking layer is formed on a substrate disposed over the first waveguide.

[0089] In various further embodiments, the display device further includes a spacer disposed between the substrate and the first waveguide to form an air gap between the substrate and the first waveguide.

[0090] In various further embodiments, the substrate includes a protective layer.

[0091] In various further embodiments, the partial light blocking layer overlaps the output coupling optical elements but does not overlap the input coupling optical elements.

[0092] Further, various embodiments are directed to an augmented or mixed reality head-mounted display device that includes a display device as described throughout this disclosure and a projector configured to project image-bearing light toward the input coupling optical element.

[0093] In various further embodiments, the partial light blocking layer comprises a liquid crystal polymer or a cholesteric liquid crystal.

[0094] In various further embodiments, the partial light blocking layer includes a linear polarizer aligned with the principal k vector parallel to the outcoupling optical element.

[0095] In various further embodiments, the partial light blocking layer includes a phase scrambler that directs the light back into the waveguide by the phase scrambler so that it is out of phase with the image light output by the output coupling optical element towards the user.

[0096] In various further embodiments, the partial light blocking layer includes a microlouver film.

[0097] Further, various embodiments provide a method of suppressing eye glow, the method comprising: providing: Image modulation light source a waveguide having an inner reflective surface proximate to a user's eye and an outer reflective surface disposed above the inner reflective surface, said waveguide supporting an input coupling optical element and an output coupling optical element; and Partial light-shielding layer above the outer reflective surface coupling image modulated light from a source of image modulated light into a waveguide; extracting the image modulated light from the waveguide to a user for viewing using an output coupling optical element; using a partial light blocking layer to block the off-Bragg image modulated light from exiting the waveguide as eye glow light through the outer surface; The present invention relates to a method, comprising:

[0098] In various embodiments, blocking the off-Bragg image modulated light includes absorbing the off-Bragg image modulated light.

[0099] In various further embodiments, blocking the off-Bragg image modulated light includes deflecting the off-Bragg image modulated light towards a user.

[0100] In various further embodiments, blocking the off-Bragg image modulated light includes converting the off-Bragg image modulated light into non-visible radiation.

[0101] In various further embodiments, blocking the off-Bragg image modulated light includes diffracting the off-Bragg image modulated light into a path that does not enter the environment.

[0102] In various further embodiments, the method further includes absorbing the diffracted off-Bragg image modulated light.

[0103] In various further embodiments, the method further includes attenuating the diffracted off-Bragg image modulated light.

[0104] The description will be more fully understood with reference to the following figures, which are presented as exemplary embodiments of the invention and should not be construed as a complete recitation of the scope of the invention: [Brief description of the drawings]

[0105] [Figure 1A] 1 conceptually illustrates the eye glow phenomenon as a product of off-Bragg interactions, according to an embodiment of the present invention. [Figure 1B] 1 conceptually illustrates the eye glow phenomenon as a product of Fresnel reflection, in accordance with an embodiment of the present invention. [Diagram 2] 1 illustrates a waveguide display incorporating diffractive elements as eyeglow suppressing layers according to an embodiment of the present invention. [Figure 3A] 1 illustrates a waveguide display incorporating diffractive elements in the eyeglow suppression layer according to an embodiment of the present invention. [Figure 3B] 3 illustrates an example of an eyeglow suppression layer including transmissive diffractive elements, according to an embodiment of the present invention. [Figure 3C] 3 illustrates an example of an eyeglow suppressing layer including reflective diffractive elements, according to an embodiment of the present invention. [Figure 4] 1 illustrates a schematic diagram of a waveguide display incorporating a reflective grating as an eyeglow suppression structure, according to an embodiment of the present invention; [Diagram 5] 1 shows a waveguide display implementing a surface relief grating for eyeglow suppression according to an embodiment of the present invention. [Figure 6] 1 shows a reflective grating disposed on a separate substrate to suppress eye glow, according to an embodiment of the present invention. [Figure 7] 1 illustrates a waveguide display including a dichroic reflector coating according to an embodiment of the present invention. [Figure 8] 1 illustrates a waveguide-based display configuration including three different waveguides, according to an embodiment of the present invention. [Figure 9] 1 illustrates a waveguide-based display configuration including three different waveguides, according to an embodiment of the present invention. [Figure 10] 1 illustrates a waveguide-based display configuration including three different waveguides, according to an embodiment of the present invention. [Figure 11A] FIG. 2 shows a cross-sectional view of a waveguide-based display including a dichroic filter according to an embodiment of the present invention. [Figure 11B] FIG. 11B is a schematic plan view of the waveguide-based display shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0106] For purposes of describing the embodiments, some well-known features of optical technology known to those skilled in the art of optical design and visual displays have been omitted or simplified so as not to obscure the basic principles of the present invention. Unless otherwise stated, the term "on-axis" in relation to a light ray or beam direction refers to propagation parallel to an axis normal to the surface of the optical component described in relation to the present invention. In the following description, the terms light, ray, beam, and direction may be used synonymously and in conjunction with one another to indicate the direction of propagation of electromagnetic radiation along a straight trajectory. The terms light and illumination may be used in relation to the visible and infrared bands of the electromagnetic spectrum. Portions of the following description will be presented using terminology commonly adopted by those skilled in the art of optical design. As used herein, the term grating may, in some embodiments, encompass a grating comprised of a set of gratings. It should be understood that for illustrative purposes, the drawings are not drawn to scale unless otherwise stated.

[0107] In a waveguide-based display, light may also be diffracted toward and away from the user. Eye glow may include unwanted light originating from the front surface of the display waveguide (e.g., the waveguide surface furthest from the eye) and from the reflective surfaces of the eye, the waveguide reflective surfaces, and the surfaces of the grating (due to leakage, stray light diffraction, scattering, and other effects). Light that is diffracted away is commonly referred to as "eye glow" and raises security, privacy, and social acceptability obligations. "Eye glow" may refer to the phenomenon caused by light leakage from the display where the user's eyes appear to shine or glow through the eye display, which creates an aesthetic feature that may be unpleasant for some people. In addition to concerns regarding social acceptability in a fashion sense, eye glow may present a different challenge in that if there is sufficient clarity in the eye glow, viewers looking at the user may be able to see the projected image that is intended only for the user. Thus, eye glow may pose significant security concerns for many users. There are many sources of eye glow in near-eye displays, including but not limited to Fresnel reflection and off-Bragg diffraction. This can be a challenge for all diffractive waveguide solutions (surface relief gratings, volume Bragg gratings, etc.) and optical combiner methods that may utilize see-through. In addition to blocking the unwanted eye glow light, the waveguide can maintain high transparency that allows the observer to still see the real world. Furthermore, the need for eye contact drives highly transparent waveguides while blocking the eye glow light. Eye glow light suppression can be a selective light blocking technique for all waveguide and optical combiner augmented or mixed reality wearable devices. Eye glow suppression can also be applied to waveguide-based head-up displays, such as automotive head-up displays or head-up displays applied in aviation.

[0108] When eliminating eye glow from a waveguide display, it is advantageous to strike a balance between configuring the waveguide grating to maximize image light propagation into the eyebox and directing any stray light away from paths that may be refracted through the front surface of the waveguide. Here, stray light can include any image light that is not diffracted into the eyebox due to diffraction efficiency and haze caused by the grating material and grating imperfections. Stray light exiting the exterior surface of the waveguide can contribute to eye glow. In many cases, at least some of the stray light can exit the waveguide through the interior surface (near-eye surface) of the waveguide. Light from the interior surface may scatter from the user's face, which may result in some eye glow if it is refracted through the front surface of the waveguide. In order for the stray light to exit as eye glow, it may strike the exterior surface of the waveguide at an angle less than the critical angle. In many cases, the optical path taken by such light may have a polarization rotation relative to the image light propagating toward the eyebox. In many embodiments, the eye glow light may have high concentration around the grating region, where multiple beam-grating interactions may result in undesirable light extraction, such as in the case of folded and dual interaction gratings.

[0109] The disclosed eye glow suppression system can include one or more polymer grating structures that can provide advantages in terms of being able to divert stray light away from the front surface while aiding or not disrupting the propagation of image light towards the eyebox. In many embodiments, the polymer grating structure can be configured as a Bragg grating having a modulation depth and a grating pitch, where the modulation depth is greater than the grating pitch over at least a portion of the polymer grating structure. In some embodiments, the polymer grating structure can be configured as a Raman-Nath grating that operates in the Raman-Nath diffraction regime. The Raman-Nath grating can have a modulation depth less than the grating pitch over at least a portion of the polymer grating structure. The modulation depth of the polymer grating structure can be configured to provide high efficiency in-coupling of a defined balance of S-polarized and P-polarized light.

[0110] In many embodiments, the polymer grating structure can have properties of a Bragg grating over designated portions of the waveguide and properties of a Raman-Nath grating over other portions of the waveguide. In many embodiments, the polymer grating structure can operate functionally entirely in the Bragg regime, for eyeglow suppression, or entirely in the Raman-Nath regime. Bragg gratings can be used when high diffraction efficiency and polarization selectivity are advantageous. Bragg gratings can overlap folded grating regions, which are often associated with polarization rotation. Raman-Nath gratings can be advantageous when operation at large angles is beneficial, for example, to direct stray light toward absorbers or other types of light trapping mechanisms disposed around the edges of the waveguide.

[0111] The waveguide architectures described herein can mitigate or suppress eye glow using a variety of different methods that can be used separately or together as appropriate depending on the application. Turning now to the drawings, to better illustrate the problem of eye glow, a diagram showing the source of eye glow in a waveguide display according to an embodiment of the present invention is conceptually shown in Figure 1A. The waveguide 100 includes a grating layer 110 that includes one or more holographic gratings sandwiched between two substrates 111, 112.

[0112] Area 120 of waveguide 100 illustrates the intended operation of the waveguide display. In many embodiments, the holographic grating is designed to diffract a beam under Bragg diffraction toward the eye side of the waveguide display. As shown, beam 122 traveling a TIR path in waveguide 100, upon interaction with the grating in grating layer 110, is diffracted toward the eye side of waveguide 100 at a predetermined angle θ2 relative to the holographic grating and passes to the viewer's eye 113. In some embodiments, light may also be diffracted toward and away from the eye side. Light that is diffracted away is commonly referred to as "eye glow" and raises security, privacy and social acceptability obligations. Area 130 of waveguide 100 illustrates off-Bragg interactions, which are a substantial source of eye glow in many waveguide displays. The incident beam 132 is weakly diffracted due to off-Bragg interactions with the gratings of the grating layer 110, which causes a portion of the beam 132 to be diffracted at a predetermined angle θ1 as an eye glow beam 134 that passes through to the opposite side of the eye side (or the opposite side of the environment, i.e., output side) of the waveguide 100. This eye glow beam may be seen as eye glow by an outside observer. Although "eye side" is used herein to discuss the intended refraction direction, it can be easily understood that off-Bragg interactions may pose challenges for optical systems that are not designed to be worn on the eye, and thus the architecture described herein may be easily applied to any optical system that suffers from similar challenges. For example, in a sensor, the off-Bragg light path may result in stray light paths that may reduce the signal-to-noise ratio of the sensor. Eye glow may also be a challenge for infrared waveguides. For example, the off-Bragg paths in an eye tracker may result in detectable infrared radiation.

[0113] Although the eye glow phenomenon and intended operation are shown as occurring at separate locations of the waveguide 100, it should be understood that the eye glow phenomenon and intended operation may actually occur simultaneously throughout the entire waveguide display depending on the device architecture. Additionally, while significant contributors to eye glow are shown in FIG. 1A, it is contemplated that other factors may also contribute to eye glow. For example, eye glow may occur as a result of Fresnel reflections at the eye-side surface interfaces of the waveguide display. In some cases, scattering that may occur at the surface of the user's eye, or sunlight illumination entering and diffracted out of the waveguide may also contribute to eye glow.

[0114] An example of reflections that produce eye glow according to an embodiment of the present invention is conceptually illustrated in FIG. 1B. As shown, the beam diffracted toward the user's eye may have a portion reflected back at the surface interface, which represents a Fresnel reflection. Reflected beam 140a may travel through the waveguide and exit as an eye glow beam at the environment side of the waveguide. Reflected beam 140b may be generated by the grating layer 110. Note that FIG. 1A and FIG. 1B show general ray paths and interactions and may not fully depict the nature of the waveguide optics. For example, light rays entering and exiting the waveguide at a non-normal angle may result in a refractive change in angle at the waveguide surface. With this understanding of the different sources of eye glow, different proposed eye glow suppression structures are described in more detail below.

[0115] [Eye glow suppression structure] The architecture for suppressing eye glow according to various embodiments of the present invention attempts to mitigate the cause of eye glow by reflecting and / or redirecting eye glow beams. Eye glow suppression structures can be introduced multiple times in the same display system, and the specific structure can be based on the specific system. For example, in a system using multiple different waveguides (e.g., for different wavelengths and / or angle bands), multiple eye glow suppression structures can be included in the overall system. In many embodiments, a single eye glow suppression structure can be included that mitigate eye glow beams from multiple waveguides. In addition to blocking undesirable eye glow light, the waveguide has high transparency that allows the user to see the real world. For this reason, a highly transparent waveguide while simultaneously blocking eye glow light is advantageous. Suppressing eye glow light can be an optional light blocking technique for all waveguide and light combiner AR / XR wearables.

[0116] In many embodiments, a diffractive element such as at least one reflective grating may be implemented to suppress a large portion of eye glow in the waveguide display. In a multi-layered waveguide display system, a grating layer having at least one of such reflective gratings may be implemented for each waveguide layer. The reflective grating may be implemented in many different ways. In some embodiments, the reflective grating is implemented as a holographic grating in a grating layer in a secondary waveguide. This secondary reflective waveguide may be disposed adjacent to a base waveguide. In such a configuration, the substrates of the two waveguides may be index matched to provide a single TIR structure within which light can propagate. In some embodiments, the reflective waveguide and the base waveguide may be configured with an air gap between them. In many embodiments, the reflective grating is implemented in a grating layer that faces the environment and is disposed adjacent to a substrate opposite the grating layer of the base waveguide. In such a case, the waveguide display may include three substrate layers with two grating layers interleaved to form a single TIR structure. The reflective grating may also be implemented as a surface relief grating. For example, a surface reflective grating may be implemented on the environment-facing surface of the waveguide.

[0117] As explained above, each waveguide layer in a multi-layered waveguide display can include a reflective grating or reflective grating layer to suppress eye glow. Depending on the application, the reflective grating can be configured to reflect a predetermined wavelength and / or angle band. For example, in a three-layered RGB waveguide display system, each of the R, G and B layers can be implemented with a respective reflective grating or reflective grating layer configured to reflect the spectral wavelength band corresponding to the layer (i.e., a reflective grating designed to reflect red light can be implemented for the R layer of the waveguide display). In some embodiments, the reflective gratings can be multiplexed. In many embodiments, the reflective gratings can be recorded or formed with a grating vector that matches the rake angle of the waveguide display.

[0118] In addition to or instead of a reflective grating, a filter can be used to suppress eye glow. For example, a dichroic reflector or a dielectric mirror (e.g., a dielectric reflector) can be applied to the environment-facing surface of the waveguide to implement. Similar to the configuration described above, a multi-layered waveguide display system can include a dichroic reflector for each waveguide layer, where each dichroic reflector is configured to reflect a specific wavelength and / or angle band corresponding to the individual waveguide layer. In many embodiments, the waveguide display includes an additional protective layer. In such a case, one of the dichroic reflectors desired for implementation can be incorporated on the protective layer.

[0119] Another method for suppressing eye glow includes the use of quantum dots, whose structures can absorb light at a first wavelength and emit light at a second wavelength. In many embodiments, the quantum dots can be incorporated into a substrate adjacent to the environmental side of the waveguide. The quantum dots can be configured to absorb a particular wavelength of light corresponding to the particular waveguide layer in which they are incorporated. For example, quantum dots configured to absorb a particular red wavelength corresponding to a red light source can be incorporated into the substrate of a red waveguide layer. The quantum dots can be further configured to emit light shifted to a predetermined wavelength band (e.g., infrared) to allow for suppression of eye glow.

[0120] As can be easily understood, several methods and structures for suppressing eye glow may be suitably implemented according to various embodiments of the present invention. The specific configurations implemented may depend on the application. In many cases, the selection of the method and structure utilized may involve a balance of several factors, including but not limited to see-through transmission, suppression performance, cost, etc. Furthermore, as mentioned above, light rays interacting with the eye-side interface may be reflected due to Fresnel reflection, resulting in eye glow. In many embodiments, eye glow rays due to Fresnel reflection may be largely (or completely) mitigated using an anti-reflective coating on the eye-side surface of the waveguide. Next, optical structures, eye glow suppression structures, and related implementation and application methods are discussed below.

[0121] [Optical waveguides and grating structures] The optical structures recorded in the waveguide can include many different types of optical elements, such as, but not limited to, diffraction gratings. Gratings can be implemented to perform a variety of optical functions, including, but not limited to, coupling light, directing light, and preventing light transmission. In many embodiments, the grating is a surface relief grating present on the exterior surface of the waveguide. In other embodiments, the implemented grating is a Bragg grating (also called a volume grating), which is a structure with a periodic refractive index modulation. Bragg gratings can be fabricated using a variety of different methods. One process involves interference exposure of a holographic photopolymer material to form a periodic structure. Bragg gratings can have high efficiency, with only a small amount of light being diffracted into higher orders. The relative amount of diffracted zero-order light can be varied by controlling the refractive index modulation of the grating, a property that can be used to create lossy waveguide gratings for extracting light over a large pupil.

[0122] One class of Bragg gratings used in holographic waveguide devices is the switchable Bragg grating (SBG). SBGs can be fabricated by first placing a thin film of a mixture of photopolymerizable monomer and liquid crystal material between substrates. The substrates can be made of various types of materials such as glass and plastic. Often the substrates are in a parallel configuration. In other embodiments, the substrates form a wedge shape. One or both substrates can support electrodes, usually transparent tin oxide films, for applying an electric field across the film. The grating structure in SBGs can be recorded in a liquid material (often called a syrup) through photopolymerization-induced phase separation using interference exposure with spatially periodic intensity modulation. Factors such as, but not limited to, control of the illumination intensity, the component volume fractions of the materials in the mixture, and the exposure temperature can determine the resulting grating morphology and performance. As can be readily appreciated, a wide variety of materials and mixtures can be used depending on the specific requirements of a given application. In many embodiments, HPDLC materials are used. During the recording process, the monomers polymerize and the mixture undergoes phase separation. The LC molecules aggregate to form discrete or coalesced droplets periodically distributed within the polymer network on the scale of optical wavelengths. The alternating liquid crystal-rich and liquid crystal-depleted regions form a lattice fringe plane that can generate Bragg diffraction with strong optical polarization resulting from the orientational order of the LC molecules in the droplets.

[0123] The resulting volume phase grating can exhibit very high diffraction efficiency, which can be controlled by the magnitude of the electric field applied across the film. When an electric field is applied to the grating through transparent electrodes, the natural orientation of the LC droplets can change, reducing the refractive index modulation of the stripes and reducing the hologram diffraction efficiency to a very low level. Typically, the electrodes are configured such that the applied electric field is perpendicular to the substrate. In many embodiments, the electrodes are fabricated from indium tin oxide (ITO). In the OFF state, where no electric field is applied, the extraordinary axis of the liquid crystal is generally aligned normal to the stripes. The grating therefore exhibits high refractive index modulation and high diffraction efficiency for P-polarized light. When an electric field is applied to the HPDLC, the grating switches to the ON state, where the extraordinary axis of the liquid crystal molecules aligns parallel to the applied electric field and thus perpendicular to the substrate. In the ON state, the grating exhibits lower refractive index modulation and lower diffraction efficiency for both S-polarized and P-polarized light. Thus, the grating region no longer diffracts light. Each grating region may be divided into multiple grating elements, e.g., a pixel matrix as function of the HPDLC device. Typically, the electrodes on one substrate surface are uniform and continuous, while the electrodes on the opposing substrate surface are patterned according to multiple selectively switchable grating elements.

[0124] Typically, the SBG element is switched clear in 30 microseconds, with a longer relaxation time to switch on. The diffraction efficiency of the device can be tuned with the applied voltage over a continuous range. In many cases, the device exhibits close to 100% efficiency with no voltage applied, and essentially zero efficiency with a high enough voltage applied. In certain types of HPDLC devices, a magnetic field can be used to control the LC orientation. In some HPDLC applications, phase separation of the LC material from the polymer can be achieved to the extent that no discernible droplet structure results. SBGs can also be used as passive gratings. In this mode, its main benefit is the uniquely characteristic refractive index modulation. SBGs can be used to provide transmission or reflection gratings for free space applications. SBGs can be implemented as waveguide devices where the HPDLC forms either the waveguide core or the evanescent coupling layer adjacent to the waveguide. The substrates used to form the HPDLC cells provide a total internal reflection (TIR) ​​light guiding structure. When the switchable grating diffracts the light at an angle that exceeds the TIR condition, the light can be coupled out of the SBG.

[0125] In some embodiments, the LC can be extracted or evacuated from the SBG to provide an evacuated Bragg grating (EBG). The EBG can be characterized as a surface relief grating (SRG) with properties very similar to a Bragg grating due to the depth of the SRG structure (much greater than is practically achievable using surface etching and other conventional processes commonly used to fabricate SRGs). The LC can be extracted using a variety of different methods, including but not limited to flushing with isopropyl alcohol and solvents. In many embodiments, one of the transparent substrates of the SBG is removed and the LC is extracted. In further embodiments, the removed substrate is replaced. The SRG can be at least partially backfilled with a higher or lower refractive index material. Such gratings provide scope for tailoring efficiency, angular / spectral response, polarization, and other properties to suit various waveguide applications. Examples of EBGs and methods for manufacturing EBGs are discussed in U.S. Patent Application Publication No. 2010 / 0133994, filed August 28, 2020, entitled "Evacuating Bragg Gratings and Methods of Manufacturing," which is incorporated herein by reference in its entirety.

[0126] Waveguides according to various embodiments of the present invention can include various grating configurations designed for specific purposes and functions. In many embodiments, the waveguides are designed to implement grating configurations that can preserve the eyebox size while reducing the lens size by effectively expanding the exit pupil of the collimating optics. The exit pupil can be defined as a virtual aperture, and only light rays passing through said virtual aperture can enter the user's eye. In some embodiments, the waveguide includes an input grating optically coupled to the light source, a folded grating to provide beam expansion in a first direction, and an output grating to provide beam expansion in a second direction, typically orthogonal to the first direction, and provide beam extraction toward the eyebox. As can be readily appreciated, the grating configuration implementing waveguide architecture can depend on the specific requirements of a given application. In some embodiments, the grating configuration includes multiple folded gratings. In some embodiments, the grating configuration includes an input grating and a second grating to perform beam expansion and beam extraction simultaneously. The second grating can include gratings of different prescriptions arranged in separate overlapping grating layers or multiplexed into a single grating layer to propagate different portions of the field of view. Additionally, various types of gratings and waveguide architectures can also be utilized.

[0127] In some embodiments, the gratings in each layer are designed to have different spectral and / or angular responses. For example, in many embodiments, different gratings across different grating layers are stacked or multiplexed to increase the spectral bandwidth. In some embodiments, a full-color waveguide is implemented with three grating layers, each designed to operate in a different spectral band (red, green, and blue). In other embodiments, a full-color waveguide is implemented with two grating layers, a red-green grating layer and a green-blue grating layer. As can be easily understood, such techniques can be implemented to increase the angular bandwidth operation of the waveguide as well. In addition to multiplexing gratings across different grating layers, multiple gratings can be multiplexed within a single grating layer, i.e., multiple gratings can be stacked within the same volume. In some embodiments, the waveguide includes at least one grating layer with two or more grating prescriptions multiplexed within the same volume. In further embodiments, the waveguide includes two grating layers, each layer with two grating prescriptions multiplexed within the same volume. Multiplexing two or more grating prescriptions within the same volume can be achieved using various fabrication techniques. In many embodiments, the multiplexed master grating is utilized with an exposure configuration to form a multiplexed grating. In many embodiments, the multiplexed grating is fabricated by sequentially exposing an optical recording material layer with two or more exposure configurations, where each configuration is designed to form a grating prescription. In some embodiments, the multiplexed grating is fabricated by alternatingly exposing an optical recording material layer between two or more exposure configurations, where each configuration is designed to form a grating prescription. As can be easily understood, various techniques, including those well known in the art, can be used as needed to fabricate a multiplexed grating.

[0128] In many embodiments, the waveguide can incorporate at least one of an angle multiplexed grating, a color multiplexed grating, a folded grating, a double interaction grating, a roll K-vector grating, a cross folded grating, a mosaic grating, a chirped grating, a grating with a spatially varying refractive index modulation, a grating with a spatially varying grating thickness, a grating with a spatially varying average refractive index, a grating with a spatially varying refractive index modulation tensor, and a grating with a spatially varying average refractive index tensor. In some embodiments, the waveguide can incorporate at least one of a half wave plate, a quarter wave plate, an anti-reflective coating, a beam splitting layer, an alignment layer, a photochromic back layer for glare reduction, and a louver film for glare reduction. In some embodiments, the waveguide can support a grating that provides separate optical paths for different polarizations. In various embodiments, the waveguide can support a grating that provides separate optical paths for different spectral bandwidths. In many embodiments, the grating can be an HPDLC grating, a switching grating recorded in HPDLC (such a switchable Bragg grating), a Bragg grating recorded in a holographic photopolymer, or a surface relief grating. In many embodiments, the waveguide operates in a single color band. In some embodiments, the waveguide operates in a green band. In some embodiments, waveguide layers operating in different spectral bands, such as red, green, and blue (RGB), can be stacked to provide a three-layer waveguide structure. In further embodiments, the layers are stacked with air gaps between the waveguide layers. In various embodiments, the waveguide layers operate in broader bands, such as blue-green and green-red, to provide a two-waveguide layer solution. In other embodiments, the gratings are color multiplexed to reduce the number of grating layers. Various types of gratings can be implemented. In some embodiments, at least one grating in each layer is a switchable grating.

[0129] A waveguide incorporating optical structures as discussed above may be implemented in a variety of different applications including, but not limited to, a waveguide display. In various embodiments, the waveguide display is implemented with an eyebox of greater than 10 mm with an eye relief of greater than 25 mm. In some embodiments, the waveguide display includes a waveguide having a thickness of 2.0 mm to 5.0 mm. In many embodiments, the waveguide display can provide a diagonal image field of view of at least 50°. In further embodiments, the waveguide display can provide a diagonal image field of view of at least 70°. A waveguide display can employ many different types of picture generating units (PGUs). In some embodiments, the PGU can be a reflective or transmissive spatial light modulator, such as a liquid crystal on silicon (LCoS) panel or a microelectromechanical system (MEMS) panel. In many embodiments, the PGU can be an emissive device, such as an organic light emitting diode (OLED) panel. In some embodiments, the OLED display can have a brightness of greater than 4000 nits and a resolution of 4k x 4k pixels. In some embodiments, the waveguide can have an optical efficiency of greater than 10%, such that with an OLED display with a brightness of 4000 nits, an image brightness of greater than 400 nits can be provided. Waveguides implementing P gratings (i.e., gratings with high efficiency for P polarization) typically have a waveguide efficiency of 5% to 6.2%. Because P or S gratings can waste half of the light from an unpolarized source such as an OLED panel, many embodiments are directed to waveguides that can provide both S and P gratings to allow for an increase in the efficiency of the waveguide by up to 2x. In some embodiments, the S and P gratings are implemented in separate overlapping grating layers. Alternatively, a single grating can provide high efficiency for both p and s polarization under certain conditions.In some embodiments, the waveguide comprises a Bragg-like grating produced by extracting LC from an HPDLC grating as described above to enable high S and P diffraction efficiencies over certain wavelength and angular ranges for appropriately selected values ​​of grating thickness (typically in the range of 2 μm to 5 μm). Examples of waveguide-based display devices are discussed in U.S. Patent Application Publication No. 2013 / 0133994, filed March 30, 2018, entitled "Waveguide Display," which is incorporated herein by reference in its entirety.

[0130] [Waveguide with protective layer] Waveguides and waveguide displays can include protective layers according to various embodiments of the present invention. In many embodiments, the waveguide or waveguide display incorporates at least one protective layer. In further embodiments, the waveguide or waveguide display incorporates two protective layers, one on each side of the device. As discussed in the above section, the waveguide and waveguide display can be constructed with a transparent substrate that provides a TIR light guiding structure through its air interface. In these cases, the protective layer can be implemented and incorporated in such a way that it causes minimal disturbance to the air interface of the substrate. In some embodiments, the protective layer, due to its material properties and / or deposition method on the waveguide substrate, compensates for surface defects in the substrate, such as, but not limited to, surface ripples, scratches, and other non-uniformities that cause the surface shape to deviate from perfect planarity (or other desired surface shape). The protective layer can be implemented in a variety of thicknesses, shapes, and sizes. For example, a thicker protective layer can be utilized for applications that require a more durable waveguide. In many embodiments, the protective layer is sized and shaped similarly to the waveguide in which it is incorporated. In the case of a curved waveguide, the protective layer may also be curved. In further embodiments, the protective layer is curved with a curvature similar to that of the waveguide. The protective layer according to various embodiments of the present invention may be made from a variety of materials. As can be easily understood, the properties of the protective layer, including but not limited to thickness, shape and material composition, may be selected based on the specific requirements of a given application. For example, the protective layer may be implemented to provide structural support in various applications. In such cases, the protective layer may be made from sturdy materials such as, but not limited to, plastics and other polymers. Depending on the application, the protective layer may also be made from glass, silica, soda lime glass, polymethyl methacrylate (PMMA), polystyrene, polyethylene and other plastics / polymers.

[0131] In some embodiments, the protective layer may be incorporated with spacers to provide and maintain an air gap between the waveguide substrate and the protective layer. Such spacers may be implemented similarly to those described in the sections above. For example, a suspension of spacers and acetone may be sprayed onto the exterior surface of the waveguide. In many cases, it is desirable to spray the suspension evenly. The acetone is allowed to evaporate leaving the spacers behind. The protective layer (which may have had glue / adhesive / sealant / etc. applied to the edges) may then be placed in contact with the spacers and vacuumed down. In some applications, the spacers may move a small amount but will generally stay in place due to van der Waals forces. The spacers may be made from any of a wide variety of materials, including but not limited to plastics (e.g., divinylbenzene), silica, and conductive materials. In some embodiments, the spacer material is selected such that its refractive index does not substantially affect the propagation of light within the waveguide cell. The spacers may take any suitable shape, including but not limited to rods and spheres. Additionally, spacers of any suitable size may be utilized. For example, in many instances, the size of the spacer ranges from 1 μm to 30 μm. As can be readily appreciated, the shape and size of the spacer utilized may depend on the particular requirements of a given application. In some cases, the protective layer may be advantageously disposed further away from the waveguide. In such embodiments, a larger size spacer may be utilized.

[0132] The incorporation of protective layers can be implemented in different waveguide configurations, including single and multi-layered waveguides. For example, a multi-layered waveguide can incorporate two protective layers, one disposed near each of the outer surfaces. In addition to providing environmental isolation and structural support for the waveguide, protective layers can also be implemented for a wide variety of other applications. In many embodiments, the protective layers enable dimming and / or darkening. The protective layers can incorporate materials for photochromic or thermochromic functionality. The protective layers can also be configured to enable controllable dimming and / or darkening. In some embodiments, the protective layers implement electrochromic functionality. The protective layers can also provide a surface for other films, including but not limited to anti-reflective coatings and absorbing filters. Such films can be implemented to avoid seeing light from the outside. In many cases, such films cannot be placed directly on the waveguide, which may be due to the high temperature processes required or interference with general waveguiding properties. In many embodiments, the protective layers provide optical power. In further embodiments, the protective layer provides a variable, adjustable optical power. Such a focusable lens may be implemented using a fluid lens or SBG. In some applications, a screen generating unit may be implemented, requiring an unobstructed optical path between the PGU and the waveguide, since the protective layer may refract the input beam, resulting in position errors, depending on the application and design of the waveguide. In many cases, the incident beam contains rays at an angle to the waveguide substrate. These effects are exacerbated as the incident ray angle increases. Even in the case of an unrefracted incident beam, there is still a potential challenge, since the material used in the protective layer may affect the polarization of the beam and cause scattering. In such embodiments, the protective layer may be designed and shaped accordingly to prevent interference of the protective layer with the optical path.

[0133] [Eye glow suppression] A. Diffractive elements Eye glow suppression may be implemented in a partial light blocking layer that may include diffractive elements. The diffractive elements may be reflective gratings. In many embodiments, at least one reflective grating is implemented and utilized within a waveguide display system to suppress eye glow. The reflective grating may be introduced into the environment of the waveguide display to reflect otherwise leaking eye glow beams back into the waveguide. In many embodiments, this reflection occurs at an angle that matches the angle of the associated out-coupled light, preventing any distortion and ghost images from the viewer's perspective. A waveguide display incorporating a reflective grating as an eye glow suppression structure according to an embodiment of the present invention is conceptually shown in FIG. 2. As shown, the system includes a waveguide 200 that includes a grating layer 210 for providing in-coupling, propagation and out-coupling of light. In an exemplary embodiment, the system includes a second waveguide 230 having a grating layer 240 with at least one reflective grating. The reflective grating layer 240 may include one or more holographic gratings sandwiched between two substrates similar to the gratings described above. In such a configuration, the substrates of the waveguides 200 and 230 are index matched to form a single TIR structure within which light can propagate. In the intended mode of operation for the first waveguide 200 as shown in area 250, a beam 252 traveling a TIR path in the two waveguides 200, 230 can be outcoupled (254) towards a viewer by the grating in the grating layer 210.

[0134] In contrast, area 260 shows an example of an off-Bragg interaction that can cause eye glow. This example is not limiting, as other sources of eye glow exist and are discussed above in connection with FIG. 1A and FIG. 1B. As shown, ray 264 is the result of an off-Bragg interaction with the grating in the grating layer 210, originating from ray 262. Ray 264 passes through the waveguide 200 and is incident on a reflective grating in the grating layer 210, where a portion of ray 264 is diffracted into the second waveguide 230. Light absorbing layer 270 can absorb ray 264. Light absorbing layer 270 can absorb the eye glow light diffracted by the diffractive element and prevent any outside light from being diffracted toward light absorbing layer 270. The light absorbing layer 270 may be placed in many places throughout the waveguide display, such as toward the temple of a user with a side-mounted projector or absorbing frame of glasses; toward the nose of the user; upward toward a projector mounted in a top-down projector system; toward the edge of the frame that holds the waveguide; and toward other specific locations that have absorbing elements. The second waveguide 230 may include a thin substrate made of polycarbonate or glass. The thin substrate may be doped with a small amount of absorbing dye (e.g., about 5% coloring) at the desired wavelength. In some embodiments, through TIR, the eye glow light may have a long path through the second waveguide 230 that effectively absorbs all the light. The ambient light may have a short path through the second waveguide 230, but may remain unchanged during transmission through the waveguide 230. In many embodiments, a small portion of the eye glow light rays do not pass due to slight errors or physical limitations of the reflective grating layer 240 and continue through the waveguide 230, appearing as eye glow. However, these rays are significantly weaker than typical unmitigated eye glow rays.

[0135] Although FIG. 2 shows a particular configuration of a waveguide display implementing a reflective grating for eye glow suppression, many other configurations may be implemented as appropriate for the particular requirements of a given application. For example, in the embodiment of FIG. 2, the waveguide including the reflective grating is the same size and shape as the base waveguide. In other embodiments, the waveguide including the reflective grating is smaller than the base waveguide and covers a predetermined portion of the grating in the base waveguide. In addition, the reflective waveguide need not be positioned to contact the base waveguide. In many embodiments, a gap exists between the reflective waveguide and the base waveguide. In many embodiments, the gap is filled with air, but may be filled with any material, such as, but not limited to, an index matching material, as appropriate for the requirements of a particular application of an embodiment of the invention. A reflective grating eye glow suppression structure with an air gap according to an embodiment of the invention is shown in FIG. 3A. As shown, a waveguide 230 including a reflective grating 240 is separated from a base waveguide 200 by an air gap through the use of spacer beads 320. In such an embodiment, the TIR path of the main light ray is confined to the base waveguide 310.

[0136] In some embodiments, the reflective grating 240 may be a transmissive diffractive element capable of coupling light into the waveguide through transmissive diffraction. FIG. 3B illustrates an example of a diffractive element as a transmissive diffractive element, according to an embodiment of the invention. As shown, the transmissive diffractive element 240a couples inwardly directed light 352 into the waveguide through transmissive diffraction. The coupled light 354 travels through the waveguide by total internal reflection. In some embodiments, the reflective grating 240 may be a reflective diffractive element capable of coupling light into the waveguide through transmissive diffraction. FIG. 3C illustrates an example of a diffractive element as a reflective diffractive element, according to an embodiment of the invention. As shown, the reflective diffractive element 240b couples inwardly directed light 352 into the waveguide through transmissive diffraction. The coupled light 354 travels through the waveguide by total internal reflection.

[0137] In some embodiments, the reflective grating 240 may be a polymer grating structure. The polymer grating structure may be configured in many different ways depending on the waveguide region and light path that contributes to the eye glow. The primary waveguide region and light path may be determined using ray tracing techniques. In many embodiments, the polymer grating structure may be configured to provide beam expansion and at least partially overlap at least one of the grating and the input coupler for extracting light from the waveguide. The reflective grating 240 may be formed on at least one of the exterior surface of the waveguide (as shown in Figures 2 and 3A-3C) and the eye-facing surface of the waveguide (as described below).

[0138] In some embodiments, the reflective grating 240 may also be formed between the substrates of the waveguide 200 such that the reflective grating 240 is formed as a portion of the grating layer 210 of the waveguide 200. In some embodiments, a portion of the reflective grating 240 may be used as an input coupler to couple the image modulated light from the light source into a totally internally reflected path within the waveguide 200. In some embodiments, a portion of the reflective grating 240 may be used as an output coupler configured to output couple light from the waveguide 200. In some embodiments, a portion of the reflective grating 240 may be used as a folded grating configured as a beam expander. In some embodiments, the input coupler may be a grating or a prism.

[0139] FIG. 4 shows a schematic of a waveguide display incorporating a reflective grating as an eye glow suppression structure according to an embodiment of the present invention. FIG. 4 includes many of the same labeled elements from FIG. 2 that function similarly to FIG. 2. The description from FIG. 2 is applicable to the waveguide display of FIG. 4, and this description will not be repeated in detail. As shown, the waveguide 200 may be located between a top grating 240 and a bottom grating 241. In some embodiments, the top grating 240 and the bottom grating 241 may have different grating periods. The light rays that contribute to the eye glow that are incident on the top grating 240 and the bottom grating 241 may originate from different sources and may have followed different waveguide ray paths, and thus the top grating 240 and the bottom grating 241 may include different diffractive prescriptions to divert them from the eye glow path. In some embodiments, the top grating 240 and the bottom grating 241 may include different prescriptions that may differ not only in terms of their periods but also may include different grating modulations. For example, the bottom grating 241 may include a prescription for diffracting incident light (e.g., arising from an external light source) that enters the waveguide through its top surface at a relatively small angle relative to the normal to the bottom grating 241 at a much larger angle toward the light absorber 270a.

[0140] The top grating 240 and / or the bottom grating 241 can be polymer grating structures. In an exemplary embodiment, the system includes a waveguide 230a that houses the bottom grating 241. The bottom grating 241 can include one or more holographic gratings sandwiched between two substrates similar to the gratings described above. The substrates of the waveguides 200 and 231 can be index matched to form a single TIR structure within which light can propagate.

[0141] The light absorbing layer 270a can absorb the light rays 265. The light absorbing layer 270a can absorb the eye glow light 265 diffracted by the diffractive element and prevent any outside light from being diffracted towards the light absorbing layer 270a. The light absorbing layer 270a can be placed in many places throughout the waveguide display, such as towards the temple of a user with a side mounted projector or absorbing frame of glasses; towards the nose of the user; upwards towards a projector mounted in a top down projector system; towards the edge of the frame that holds the waveguide; and towards other specific locations with absorbing elements. The waveguide 231 can include a thin substrate made of polycarbonate or glass. The thin substrate can be doped with a small amount of absorbing dye (e.g., about 5% tint) at the desired wavelength. In some embodiments, through TIR, the eye glow light can have a long path through the waveguide 231, effectively absorbing all the light.

[0142] In some embodiments, the top grating 240 and the bottom grating 241 may be a combination of a Bragg grating and a Raman-Nath grating. In some embodiments, the top grating 240 and / or the bottom grating 241 may include a Bragg grating in some regions and a Raman-Nath grating in other regions. Depending on the nature of the beam-grating interaction in the waveguide, the input, folded and gratings may each have regions that overlap with a Bragg grating or a Raman-Nath grating. In many embodiments, the two types of gratings may be interspersed across the top grating 240 and / or the bottom grating 241. For example, the folded grating in the waveguide 200 may overlap with a Bragg grating in some regions of the folded grating and with a Raman-Nath grating in other regions. Any of the primary imaging gratings (e.g., the input grating, the folded grating and the output grating) may be at least partially covered by at least one selected from a Bragg grating region, a Raman-Nath grating region, and a region that does not include a grating. For example, top grating 240 and / or bottom grating 241 can include Bragg grating regions, Raman-Nath grating regions, and / or grating-free regions, each of which may overlap with portions of the folded grating due to complex ray paths and grating interactions. The grating-free regions may play a role in light management to support eyeglow suppression layers of the type described below.

[0143] 4 shows both the top grating 240 and the bottom grating 241, embodiments including only the top grating 240 (shown in FIG. 2) or only the bottom grating 241 (not shown) are also disclosed. In some embodiments, the top grating 240 and / or the bottom grating 241 may be formed on a separate substrate, which may include air separating the top grating 240 and / or the bottom grating 241 from the waveguide 200 used to propagate the image light towards the eyebox. An example of this is discussed in connection with FIG. 3A.

[0144] In many embodiments, the top grating 240 and / or bottom grating 241 may include regions containing Bragg gratings, regions containing Raman-Nath gratings, or regions that do not contain gratings. Any of the three types of regions may at least partially cover at least one of the input grating, the folded grating, and the output grating. In many embodiments, a light control coating may be applied to the grating-free regions of the top grating 240 and / or bottom grating 241. Many different types of light control coatings may be used to assist in eye glow management. In some embodiments, the light control coating provides at least one optical function selected from the group of polarization rotation, polarization selective absorption, polarization selective transmission, polarization selective diffraction, angle selective transmission, angle selective absorption, anti-reflection, and / or transmission within a defined spectral bandwidth. In some embodiments, the light control coating may provide spatial variation of the optical functions of the above examples.

[0145] In many embodiments, the top grating 240 and / or the bottom grating 241 can include roll K-vector gratings based on continuously or piecewise varying tilt angles. In many embodiments, the top grating 240 and / or the bottom grating 241 can include gratings with spatially varying pitch. In many embodiments, the top grating 240 and / or the bottom grating 241 can be configured as multiplexed gratings.

[0146] In many embodiments, light 265 entering the waveguide 200 from the outside world can include sunlight or indoor lighting that enters the waveguide 200 through the top surface of the waveguide 200 (e.g., the outside world side of the waveguide), or the bottom surface of the waveguide 200 (e.g., the eye-facing surface). Other sources of light 265 that potentially cause eye glow can include car headlights and laser sources. In many embodiments, light from an external light source can reflect off the eye of a viewer of the display after propagating through the waveguide. In many embodiments, image light reflected from an anatomical surface, such as the surface of the eye, can contribute to eye glow. In some embodiments, light entering the waveguide 200 from the outside world is provided by an external light source and enters the waveguide 200 through the exterior and / or eye-facing surfaces of the waveguide, which can contribute to eye glow.

[0147] In some embodiments, the top grating 240 and / or the bottom grating 241 may be a holographic reflection grating. The holographic reflection grating may be a Bragg grating and may be fabricated through holographic exposure as discussed above. In some embodiments, the holographic reflection grating may be an EBG and may be fabricated in a process discussed above. The EBG may be useful in generating deep SRGs, which may be Bragg gratings that may include a polymer grating structure including a modulation depth and a grating pitch, where the modulation depth is greater than the grating pitch over at least a portion of the polymer grating structure. In some embodiments, the EBG may be configured as a Raman-Nath grating that operates in the Raman-Nath diffraction regime. The Raman-Nath grating may have a modulation depth less than the grating pitch over at least a portion of the polymer grating structure. The EBG may be an emission periodic grating configured to operate in the Raman-Nath regime and may have a modulation depth less than the grating pitch in regions. Such gratings are not strictly in the Bragg regime. By controlling the fabrication process, EBGs can be useful in fabricating gratings that contain regions operating in the Bragg regime, regions operating in the Raman-Nagh regime, and / or regions with no grating.

[0148] In many embodiments, the polymer grating structure modulation depth may vary across the top grating 240 and / or bottom grating 241 to provide a spatially varying polarization-dependent diffraction efficiency characteristic according to the principles discussed in U.S. Patent Application Publication No. 2009 / 0239994, incorporated herein by reference in its entirety. In many embodiments, the polymer grating structure modulation depth may vary across the top grating 240 and / or bottom grating 241 to provide a spatially varying angle-dependent diffraction efficiency characteristic or a spatially varying polarization-dependent diffraction efficiency characteristic. When the top grating 240 and / or bottom grating 241 incorporate an EBG, at least one of the spatial, angular or polarization diffraction efficiency characteristics of the EBG can be tailored by backfilling the EBG with an optical material of a particular refractive index and / or birefringence. In some embodiments, the backfill material may be an isotropic material, such as a birefringent material. The backfill material may occupy the space at the bottom of the space between adjacent portions of the polymer grating structure, with air occupying the space from above the top surface of the backfill material to the modulation depth.

[0149] In some embodiments, the ratio of the modulation depth of the polymer grating structure to the spacing of the grating pitch is in the range of 1:1 to 10:1. In some embodiments, the grating pitch of the polymer grating structure is 0.35 μm to 1 μm, and the modulation depth of the polymer grating structure is 1 μm to 10 μm. The grating pitch can be the spacing of the diffractive features of the polymer grating structure, and the modulation depth can be the depth of the polymer grating structure. The polymer grating structure can have a modulation depth greater than the wavelength of visible light.

[0150] In many embodiments, the top lattice 240 and / or the bottom lattice 241 can include a polymer lattice structure, including a composite structure. A composite structure can include at least one type of polymer and at least one other material. In many embodiments, the polymer lattice structure can be a composite of a polymer and at least one other material, where the polymer is removed after formation of the lattice. In many embodiments, the at least one other material can be a nanoparticle. In many embodiments, the nanoparticle can be a functionalized nanoparticle. A lattice including nanoparticles is described in U.S. Patent Application Publication No. 2020 / 0133994, filed on July 14, 2021, entitled “Nanoparticle-Based Holographic Photopolymer Materials and Related Applications,” which is incorporated herein by reference in its entirety for all purposes.

[0151] In some embodiments, the top grating 240 and / or the bottom grating 241 can include a two-dimensional grating structure or a three-dimensional grating structure. The two-dimensional grating structure can be a 2D photonic crystal. An example of a 2D grating can be an array of diffractive cylinders with their bases on a surface. The three-dimensional grating structure can be a 3D photonic crystal. The 3D grating can include diffractive point-like regions.

[0152] In many embodiments, the top grating 240 and / or the bottom grating 241 may be coated with an optical material. In many embodiments, the top grating 240 and / or the bottom grating 241 may be coated with a reflective optical material. In many embodiments, the top grating 240 and / or the bottom grating 241 may be coated with a coating having an effective refractive index of up to 2.5. In many embodiments, the top grating 240 and / or the bottom grating 241 may be coated with a first material and the coated grating may be backfilled with a second material with a refractive index higher than the refractive index of the first material. In many embodiments, the top grating 240 and / or the bottom grating 241 may be coated with a first material and the coated grating may be backfilled with a second material with a refractive index lower than the refractive index of the first material.

[0153] In some embodiments, the top grating 240 and / or bottom grating 241 include polymer diffractive features and a birefringent material between adjacent polymer diffractive features, where the birefringent material has a higher refractive index than the polymer diffractive features. In some embodiments, the refractive index difference between the polymer diffractive features and the birefringent material is between 0.01 and 0.2. In some embodiments, the top grating 240 and / or bottom grating 241 include alternating polymer regions and air gap regions, where the refractive index difference between the polymer regions and the air gap regions is in the range of 1.4 to 1.9. In some embodiments, the birefringent material is a liquid crystal material.

[0154] In many embodiments, a method for reducing eye glow from a waveguide display includes: a) providing a source of image modulated light, a waveguide, an input coupler, and at least one grating for providing beam expansion and extracting light from the waveguide towards the eyebox; b) providing a polymer grating structure having a modulation depth greater than the grating pitch over at least a portion of the polymer grating structure; c) directing the image modulated light into a total internal reflection path in a waveguide to beam expand the light and extract it towards the eyebox; d) redirecting light propagating within the waveguide away from a light path refracted through the outer surface using a polymer grating structure; and e) diffracting light entering the waveguide from the outside world, or stray light generated within the waveguide, away from the light path refracted through the outer surface using a polymer grating structure; may include.

[0155] In addition to holographic reflective gratings, other types of structures may be utilized to achieve similar effects. For example, in some embodiments, reflective grating 240 may be a surface relief reflective grating.

[0156] In some embodiments, the reflective grating 240 may be etched directly onto the surface of the waveguide opposite the eye side. A waveguide display implementing a surface relief grating for eye glow suppression according to an embodiment of the present invention is conceptually shown in FIG. 5. The waveguide 400 includes a grating layer 410 and a surface relief reflective grating 420 disposed on the environment side surface of the waveguide 400. In a region 430 showing the intended operation of the waveguide display, a ray 432 in the TIR path in the waveguide 400 is diffracted by the output grating in the grating layer 410 and output to the eye side. In an area 440 showing off-Bragg interaction, a portion of the ray 442 is diffracted towards the environment side of the waveguide 400 as an eye glow ray 444. The eye glow ray 444 may be reflected by the surface relief reflective grating 420 and back towards the eye side as a ray 446. In many embodiments, the ray 446 is parallel to the corresponding normal output ray. Again, a portion of the light beam 446 may be reflected back towards the surface relief reflective grating due to Fresnel reflection, but may then be at least partially reflected by the relief reflective grating 420 (not shown). Although the light beam is shown passing through the reflective grating 420, in many embodiments this does not occur. However, due to imperfections and / or physical limitations, this may occur regardless. In some embodiments, the surface relief reflective grating 420 may be provided by a metasurface. Metasurfaces allow for a greater degree of wavefront phase and amplitude control resulting from the use of nanometer-scale pitch diffractive features. Conventional diffractive optical elements, such as Bragg gratings, have diffractive features with a micron-scale pitch, i.e., a diffractive feature pitch that is a large fraction of the visible band wavelength.

[0157] An advantage of a surface relief reflective grating is that it does not add significant volume to the display system. However, in many embodiments, the reflective grating 240 described in connection with FIG. 2 can be placed on a very thin substrate adjacent to the waveguide with similar results. In some embodiments, the substrate can be arranged such that there is a gap between the substrate and the waveguide. The gap can be filled with any material, including (but not limited to) air.

[0158] A reflective grating disposed on a separate substrate to suppress eye glow, according to an embodiment of the present invention, is conceptually shown in Figure 6. As shown, a waveguide 500 having a reflective grating 510 is separated from the base waveguide 200 using spacer beads 530. In an exemplary embodiment, the reflective grating 510 is disposed on a surface of the waveguide 500 that faces the environment side of the display. In other embodiments, the reflective grating 510 may be disposed on a surface that faces the base waveguide 200.

[0159] 2-6 depict specific reflective waveguide eye glow suppression structures, any number and / or arrangement of reflective waveguide optics may be used as appropriate for the requirements of a particular application of embodiments of the present invention. Additionally, any number of different types of gratings may be added to suppress eye glow rays. For example, an ejection Bragg grating may be used instead of a surface relief grating. Additionally, non-grating structures may be used to suppress eye glow. These structures are described in more detail below.

[0160] B. Reflective elements In some embodiments, eye glow suppression can be implemented in a partial light blocking layer that can include reflective elements. Reflective elements can include, but are not limited to, the use of filters such as dichroic reflectors and dichroic mirrors that can selectively pass certain wavelength bands precisely while reflecting others. A dielectric reflective coating can be applied to reflect the eye glow light back to the user. The reflective coating can be designed as a narrow notch filter around the illumination wavelength, effectively reflecting only certain wavelengths while transmitting all other visible wavelengths, making the waveguide appear nearly transparent with high transmission. The reflective coating can act as a mirror for the designed wavelengths, reflecting light at an angle equal to the angle incident on the reflective coating layer. However, the reflected light may create a ghost image for the user when superimposed with the desired image diffracted by the output grating. In some embodiments, filters such as dichroic filters can be designed to have angle-dependent reflection or transmission efficiency. Such filters can be multi-layered structures. The filters can be designed with polarization-sensitive efficiency. The use of one or more of the spectral, angular, and polarizing filter characteristics can help optimize the suppression of eye glow, in some embodiments, the eye glow suppression can balance a greater degree of eye glow suppression in the central portion of the user's field of view against residual eye glow in the periphery of the user's field of view.

[0161] The coating may be applied at various locations. For example, the coating may be applied to each waveguide individually, allowing for a larger angular deviation before ghosting becomes visible. The coating may also be applied to the front protective cover. It has been observed that the greater the distance from the user, the greater the deviation between the desired image and the ghost image. In some embodiments, the front protective cover may be placed farther away from the waveguide, thus providing slightly more light paths. The additional path length may be used to reduce the coherence of artifacts such as Newton's ring fringes in laser beam scanner (LBS) projectors. Advantageously, the reflection may be aligned with the "signal" image at the eye side. In some embodiments, the misalignment may be minimal, on the scale of the image-to-signal image resolution of the eye glow reflection, and if it does occur, this may result in a broadening of the point spread function, which may result in a loss of image sharpness, or if the reflection angle error is larger, a ghost image will result. Coherence of eye glow reflections may be considered especially for laser illumination solutions using laser beam scanners (LBS). In some embodiments, a phase scrambler on the non-eye side of the waveguide may bring the Fresnel reflections out of phase with the signal light, thereby reducing Newton ring fringe artifacts that may be seen with LBS projectors. Application of an "eye glow suppression" spectral notch reflective filter may increase the intensity of Newton ring fringes from the LBS, where the LBS Newton rings are caused by interference of the signal beam and the non-eye side reflection. In some embodiments, an anti-reflective coating on the non-eye side may be included, resulting in the reduction of both eye glow and LBS Newton ring fringes.

[0162] In some embodiments, the protective cover may be plastic. In this case, when a reflective coating is applied to the protective cover, the thermal property limitations in the coating may be minimal. For example, if the grating is made with a heat-sensitive material, a low temperature coating (e.g., 50°C to 60°C) may be beneficial. In embodiments where the protective cover is made from glass, a high temperature coating may be used. A reflective coating may be applied to one side of the protective cover for one waveband (e.g., a green reflective notch) and another reflective coating may be applied to the other side coated with a different waveband (e.g., a red / blue notch). It is understood that any combination of wavebands may be used (e.g., any other combination of R, G, B notches). The reflective coating may be combined with see-through AR, UV protection, gradient absorbing or photochromic coatings, scratch resistant or hard coat coatings.

[0163] It may be advantageous for the reflective layer to be flat and laminated to the waveguide to reduce reflected eye glow light and angular offset from the desired image. In some embodiments, materials can provide flatness between layers (e.g., thickness adjustment shims, spacer beads, etc.). The reflective layer may be laminated to the waveguide or waveguide stack. In some embodiments, the reflective layer may be a narrow notch reflector designed for lasers that specifically reduces LED eye glow when the notch is within the spectrum of the LED.

[0164] Depending on the structure, the reflective layer can pass a broad range of colors except for a specific band (or set of bands) that is reflected, or act as a high-pass or low-pass filter that reflects all wavelengths below or above a given wavelength, respectively. In some embodiments, alternating thin layers of dielectric material are coated to form the desired filter. As described herein, dichroic reflectors or dielectric mirrors can be applied to the waveguide to reflect eyeglow rays in a manner that produces results similar to those described above for reflective gratings, although the underlying operating principles are different.

[0165] The waveguide 600 includes a dichroic reflector 610 on the surface facing the environment. The waveguide 600 can include a grating layer 602 that is the same as the grating layer 210 discussed with respect to FIG. 2. The dichroic reflector 610 can be designed to reflect a predetermined wavelength band of light corresponding to the waveguide 600. For example, in a multi-layered waveguide display having three layers for R, G, and B, the dichroic reflector 610 for a given waveguide layer can be designed to reflect the light in which the given waveguide layer is intended to operate (e.g., a dichroic reflector for a red waveguide can be designed to reflect a wavelength band corresponding to red light from a light source). Similar to a surface relief grating, the dichroic reflector 610 can reflect at least a portion of the light rays that would otherwise leak out and return toward the viewer and appear as eye glow. 2-6, the intended light rays are shown in area 620, while the eye glow rays produced by off-Bragg interactions and their suppression are shown in area 630. Again, although the intended light rays and the eye glow rays are shown separately, it is readily understood that these rays occur simultaneously throughout the entire waveguide.

[0166] When using a dichroic reflector, the percentage of ambient light that can pass through the waveguide display to the viewer's eye can be reduced. Thus, while eye glow rays are reflected back to the eye, light from the outside world corresponding to a similar wavelength band can also be prevented from reaching the viewer's eye. This can cause problems in augmented reality systems where it may be desirable for the user to be able to see the outside world as clearly as possible. To address this, a dichroic reflector structure can be designed as a notch filter that can selectively reflect the wavelength band used in the waveguide (e.g., the color selected for the particular waveguide). For example, to suppress eye glow while leaving the rest of the visible spectrum (e.g., 440 nm to 640 nm) unaffected, narrow bands can be selected around 638 nm, 520 nm, and 455 nm (red, green, and blue in a standard display, respectively). As can be easily understood, the bands selected can correspond to the wavelength bands of the light source.

[0167] Furthermore, the dichroic reflector is often applied at high temperatures that may cause distortion of the waveguide depending on the structure of the waveguide and / or any anti-reflection coatings. To avoid this, a cooler dichroic reflector application process may be used. In many embodiments, the dichroic reflector may be included in a protective layer of the waveguide.

[0168] The dichroic reflector (or indeed the waveguides) may be applied in multiple iterations or in a single application depending on the needs of the overall system. For example, as explained above, in an RGB display where three different waveguides are used for each of R, G and B, the dichroic reflector (or reflective grating / reflective waveguide) may be interspersed between the three different waveguides or on the environment side of the waveguide stack.

[0169] Exemplary configurations for applying a dichroic reflector according to an embodiment of the present invention are shown in Figures 8-10. Figure 8 shows an example of a waveguide-based display including three different waveguides according to an embodiment of the present invention. The first waveguide 600a can be configured to display a first color, such as red, the second waveguide 600b can be configured to display a second color, such as green, and the third waveguide 600c can be configured to display a third color, such as blue. Each of the waveguides 600a, 600b, 600c can include features of the waveguide 200 described with respect to Figure 2. The dichroic reflector 610 described with respect to Figure 7 can be applied on top of the first waveguide 600a. A spacer 700 can be applied between adjacent waveguides. The gaps between adjacent waveguides can be filled with various materials, such as air.

[0170] FIG. 9 shows an example of a waveguide-based display including three different waveguides according to an embodiment of the present invention. This configuration includes many of the same features as the device of FIG. 8. This description is applicable and therefore will not be repeated. A dichroic reflector 610b can be applied on top of the second waveguide 600b, and a dichroic reflector 610c can be applied on top of the third waveguide 600c. A dichroic reflector 610a can also be on top of the first waveguide 600a. In this configuration, the dichroic filters 610a, 610b, 610c can be adapted to the specific waveguides 600a, 600b, 600c.

[0171] FIG. 10 shows an example of a waveguide-based display including three different waveguides according to an embodiment of the present invention. This configuration includes many of the same features as described in connection with FIG. 8 and FIG. 9. These descriptions are applicable, and therefore these descriptions will not be repeated. The dichroic filter 610b of the second waveguide 600b has been removed. Instead, a dichroic filter 910 disposed on a separate substrate 900 may be disposed above the first waveguide 600a. The separate substrate 900 may be a protective layer. The dichroic filter 910 on the separate substrate 900 may correspond to the second waveguide 600b. For example, the second waveguide 600b may be a green waveguide, and the dichroic reflector 910 may correspond to green and may be applied to the protective layer 900.

[0172] FIG 11A shows a cross-sectional view of a waveguide-based display including a dichroic filter according to an embodiment of the present invention. FIG 11B is a schematic plan view of the waveguide-based display of FIG 11B. The waveguide 600 includes an input coupling optical element 1006 and an output coupling optical element 1004. The dichroic filter 1004 overlaps the output coupling optical element 1004. In some embodiments, the dichroic filter 1004 may not overlap the input coupling optical element 1006.

[0173] As can be readily appreciated, any number of dichroic reflectors (or reflective gratings / reflective waveguides) may be used as appropriate for the requirements of a particular application of an embodiment of the present invention. For example, for a stack of three waveguides, only two dichroic reflectors may be used, depending on design requirements. It is further understood that any mixture of eye glow suppression structures may be used as appropriate for the requirements of a particular application of an embodiment of the present invention. Eye glow suppression structures do not necessarily need to reflect light. Alternative eye glow suppression structures are described below.

[0174] C. Absorption and conversion layers The eye glow suppression layer can include a light absorbing layer that can absorb light in a portion of the visible light spectrum. The light absorbing layer can be a narrow band dye absorber layer that can include a light absorbing dye suspended in a transparent matrix. The dye for absorption can be extremely narrow in the wavelengths absorbed. Any unwanted wavelengths are absorbed, causing the waveguide to have lower transmission, dimming the outside world and appearing dark. The location of the dye absorbing layer can vary. The dye absorber layer can be placed on the protective cover when multiple waveguides are used to guide a FOV of one color. If each waveguide is guiding only one color, the dye can be applied to the protective cover at the front of the waveguide stack. The dye can be angle insensitive and can cover a wide range of incidence angles of eye glow light. An exemplary dye in the visible light range is manufactured by Yamada Chemical Co., Ltd (Japan). High absorption efficiency, narrow spectral absorption bandwidth and thermal stability can be important selection criteria. One possible approach to improve absorber performance involves dilution of the dye in a transparent matrix, which can be an inert organic polymeric compound or an inorganic compound. The resulting absorber can give narrowband absorption and high out-of-band transmission. Multilayer constructions can allow absorption of more than one wavelength.

[0175] In some embodiments, the light absorbing layer can be a metamaterial absorbing layer. The metamaterial absorber can be made with an extremely narrow spectral bandwidth. The absorption can be highly sensitive to angular misalignment when having such narrowband absorption. The metamaterial absorbing layer can be placed on each waveguide individually when the color is not shared across multiple waveguides. The metamaterial absorbing layer can be placed on a protective cover above the top waveguide when the color is shared across the waveguides.

[0176] Many of the eye glow suppression solutions discussed can be implemented using metasurfaces, which may include surfaces patterned with one or more types of nanostructures. Metasurfaces can be configured for light absorption, beam deflection and polarization as a function of either or both wavelength or angle. Two or more of the above functions may be integrated into a single metasurface. Metasurfaces can provide a complete or partial solution to eye glow suppression contributed by specular reflections from the waveguide surface, the eye surface and scattering surfaces.

[0177] The eye glow suppression structure can include wavelength-changing elements such as quantum dots or phosphors. Quantum dots are nanoscale semiconductors that can absorb light at a first wavelength and emit light at a second wavelength. Quantum dots can be introduced into the substrate of the waveguide or applied to the loss side of the waveguide optics to suppress eye glow rays. For example, quantum dots that absorb eye glow rays at a specific wavelength and emit light at a non-visible wavelength (e.g., infrared) can suppress eye glow rays from generating visible eye glow rays. Eye glow rays may still leak out of the waveguide, but these eye glow rays can be changed to a non-visible range. In many embodiments, infrared bands and lower bands are desirable due to the biologically harmful properties of ultraviolet light. However, depending on the use of the waveguide optics, it may be acceptable to convert the light to ultraviolet bands or higher bands.

[0178] Depending on the available quantum dots, it may be difficult to shift higher frequency light (e.g., blue light) to the infrared band. In this situation, a series of different quantum dots can be used to stepwise shift the light wavelength, and / or quantum dots can be incorporated into a waveguide optics that also utilizes one or more of the alternative eye glow suppression structures described herein. Depending on the number of wavelengths used in the waveguide optics for display purposes, different sets of quantum dots can be applied to mitigate some or all of the different wavelengths.

[0179] As can be readily appreciated, quantum dots can be incorporated into systems that include any or all of the eye glow suppression structures described above. Indeed, while specific eye glow suppression structures are shown in the figures discussed above, any number of different architectures incorporating the eye glow suppression structures described herein can be used.

[0180] D. Embodiments Including Synchronization In many applications, it is desirable for a waveguide display to operate with a large eyebox. While convenient for the viewer, this can result in a large amount of unused light hitting the user's face (e.g., light that does not reach the user's pupil). Depending on the implementation of the waveguide display, this unused light can be highly visible to an outside observer. Thus, many embodiments of the present invention are directed to solutions for reducing the amount of unused light incident on the user's face while preserving the operating size of the eyebox.

[0181] In many embodiments, the waveguide display includes at least one switchable Bragg grating (SBG) for controlling the out-coupled light to reduce the amount of unused light. Typically, the eyebox size can be enlarged by multiplexing or duplicating the in-coupled light through the use of a diffraction grating. If a switchable Bragg grating is implemented, the display can be configured to control the propagation of light such that only light that reaches the viewer's eye is out-coupled, thereby reducing the amount of unused light emitted toward the user's face. In many embodiments, the necessary configuration to achieve such control is dynamically determined, since the user's eye is typically not stationary during operation. Thus, the configuration can be dynamically implemented once determined.

[0182] In some embodiments, a high brightness light source allows a small duty cycle (approximately 1%) to be used with the required output luminance. With this light source, an absorbing layer can be synchronized with the light source and switched on and off. It can absorb the eye glow light while the light source is on, but averaged over many cycles, appears transparent to the observer. In some embodiments, the absorbing layer can be a switchable grating such as SBG. The switchable grating can include diffractive eye glow elements. This reduces the number of times that potentially unwanted light is diffracted back towards the user through the diffractive elements. The switchable grating can be a switchable output grating. The switchable output grating can be a multiplexed grating scheme with a switching waveplate. In the case of multiplexed gratings, the output light can be polarized after mixing from multiple gratings. If the gratings are switched in time, each grating can produce a highly polarized output. In some embodiments, by switching waveplates synchronized with the switchable grating, the polarization of one or both outputs can be rotated to be orthogonal to the linear polarizer at the output, thereby blocking the eye glow light. In some embodiments, the eye glow light can be blocked without having a permanent linear polarizer for the output by switching the linear polarizer orthogonal to the light output from the switchable grating. In some embodiments, a switchable sub-wavelength grating (based on the principle of form birefringence) can provide a wavelength-specific optical retarder to synchronize the eye glow suppression to the light source. In some embodiments, the grating pitch can be much shorter than the wavelength of light. Thus, only the zeroth and diffracted waves propagate, and higher diffracted orders can be evanescent.

[0183] Determining the configuration required to only couple out light that reaches the user's eye can be accomplished in a variety of ways. In many embodiments, the waveguide display includes an eye tracker. The eye tracker can be implemented in many different ways. In some embodiments, a waveguide-based eye tracker is implemented to determine eye position and / or gaze information. Using information from the eye tracking sensor, the waveguide display can utilize a controller to implement configurations of the switchable Bragg grating's states to only couple out light that reaches the user's eye. In some embodiments, light that is coupled out of the waveguide would otherwise continue to propagate through the waveguide to the edge. As can be readily appreciated, the waveguide display according to various embodiments of the present invention can be designed to mitigate unused light leaking out of the edge of the waveguide. For example, the edge can be covered with a light absorbing material that can absorb any light that reaches the edge.

[0184] In the implementation of a switchable Bragg grating, the waveguide may include a transparent electrode, such as an indium tin oxide (ITO) or index-matched ITO (IMITO) layer on either side as an electrode for switching the grating between on / off states. In many embodiments, the waveguide includes a first ITO / IMITO layer on one side of the grating layer and a second ITO / IMITO layer on the opposite side. The second layer may be patterned to become selectively addressable elements. This allows for switching of discrete areas of the switchable Bragg grating. In some embodiments, the selectively addressable elements are large enough so as not to create line / gap artifacts, which may result in significant scattering and / or diffraction effects. As can be readily appreciated, various transparent conductive oxide layers may also be utilized.

[0185] By incorporating these layers, absorption losses due to the layers, which may be large, can be considered in the waveguide design. For example, some ITO layers may contribute absorption losses of about 0.25% per pass. Depending on the waveguide architecture, the total propagation loss along the waveguide may be large. For example, controlling the amount of out-coupled light may include switching a portion of the output grating to a diffractive state. The switching portion may correspond to the viewer's eye position and / or line of sight information. However, under such a scheme, the distance the light propagates through the waveguide may vary, which may result in varying losses in the out-coupled light when considering absorption losses due to the ITO / IMITO layers. By changing the output grating size and / or shape through the use of switching, the light propagation path may result in different amounts of TIR bounces within the waveguide (e.g., some configurations may result in a longer light path that interacts with the ITO / IMITO layer more times). For light paths that interact more with ITO / IMITO, the total loss in light intensity may be higher, resulting in non-uniformity between different configurations. Thus, many embodiments are directed to grating architectures and switching configurations designed to address these differences. In many embodiments, the waveguide display may be configured to include an output grating with independently addressable sections that are switchable between diffractive and non-diffractive states. In some embodiments, the waveguide display may be configured to provide a scrolling output (e.g., the output image may be displayed in sequentially scrolled sections). In such cases, the output configuration for a particular eye position / gaze setting may be configured to have a uniform profile. In some embodiments, the switching may include a feathering effect on the switching timing to preserve field uniformity.

[0186] E. Embodiments Including Antireflective Coatings Eye glow can be caused by several different effects. These effects can be divided into collimated leakage and scattered leakage. Scattered leakage can be generated by the hologram material, the waveguide material, or holographic haze (haze recorded in the hologram). Scattered leakage can scatter light out of the waveguide toward the eye. Collimated leakage, e.g., eye glow that emits light that retains the angular image components coupled into the waveguide, can be extracted with low diffraction efficiency. This can be especially true for light that is off-Bragg. Such eye glow can allow at least some of the displayed image to be seen from the outside world, which can present privacy and data security issues. In the holographic recording process, if ghost gratings arise as a result of stray light or scattering centers resulting from incomplete phase separation, obvious off-Bragg interactions can arise from the ghost gratings, which can appear in the multiplexed grating.

[0187] This type of grating may be weakly registered and difficult to separate from the off-Bragg grating. The effect may be to collimate light that leaves the waveguide and diffracts in the wrong direction. In the case of Fresnel reflection, light that is diffracted from the grating plane toward the user's eye may exit the waveguide. Fresnel reflection may occur at the interface between the waveguide (on the eye side) and the air. Reflection from this interface mostly exits the waveguide on the user side. However, a small portion of that light may then reflect back from the waveguide / air interface on the non-user side of the waveguide. In addition, some light interacts with the grating again following reflection from the waveguide / air eye side reflection. In some embodiments, Fresnel reflection may be mitigated by an AR coating on the waveguide. A waveguide that includes a higher index glass may have a higher Fresnel reflection. Thus, an AR coating may reduce eye glow. Additionally, the user's eye may contribute reflected light that may take the form of scattered and specular reflection, most commonly a mixture of the two. Contributions to scattering or reflection from the user's eye may occur at any of the surfaces or optical media at the eye and may include Purkinje reflections. Scattered light from the hologram and waveguide materials, as well as from haze recorded in the hologram, may have directional and isotropic properties that depend on the nature of the scattering centers. Some of this light may travel straight through the outer surface of the waveguide. Other exit paths may include reflections at the user's eye and at surfaces of the waveguide close to the user.

[0188] F. Embodiments Including a Liquid Crystal Layer In some embodiments, the liquid crystal layer may be supported by a waveguide to reduce eye glow. The liquid crystal layer may be a cholesteric liquid crystal layer. The liquid crystal layer may provide a narrow band reflective grating that can provide high diffraction efficiency. The liquid crystal layer may be inexpensive to manufacture. The liquid crystal layer may be configured with multi-layer stacking to cover multiple waveband notches (e.g., R / G / B laser light sources). Chiral dopants may be added to the liquid crystal layer to control the grating period.

[0189] In some embodiments, an eye glow control layer can be included in the waveguide. The eye glow control layer can include polymerizable liquid crystals called liquid crystal polymers (LCPs), also known as reactive mesogens. LCPs can have all the common properties of LCs, but can also be polymerized to form a solid material where the LC orientation and birefringence properties present in the liquid state are retained when the material is solidified in the polymer. UV orientation can be used to align the LC director in a desired direction while the LC is in the liquid state. LCPs can enable a wide range of optical functions such as selective color reflectors, retardation (quarter wave, half wave, etc.). LCPs can include liquid crystal monomers such as reactive acrylate end groups that polymerize with each other in the presence of photoinitiators and directional UV light to form a robust 2D or 3D network. As discussed throughout this disclosure, LCP eye glow control layers can be used in conjunction with other eye glow control layers. Exemplary LCP materials are developed by Merck KGaA (Germany). In some embodiments, the eye glow control layer may be based on a tunable reflection filter using reflective cholesteric reactive mesogen nanopost structures. The reflected wavelength may depend on the pitch of the nanoposts, which may be fabricated using printing techniques. The nanoposts may be formed as an array of features typically 10 microns to 500 nm in height with pitch ranging from 1 micron to 10 microns.

[0190] G. Embodiments Including Waveguide Output Polarization Design The leakage of output eye glow can be strong, but may not be fully polarized in a waveguide solution where the output grating may be represented with a single grating. In some embodiments, the leakage of strongly polarized eye glow can be minimized with a linear polarizer (e.g., analyzer) placed in front of the waveguide, but at the expense of see-through transmission. Output gratings with cross-multiplexed output gratings (e.g., integrated biaxially extended IDA designs) may not have a linear output polarization state, but in such gratings, the polarization matches the k-vector of each of the constituent multiplexing (MUX) gratings. If the MUX output gratings are at 90 degrees to each other, the output polarization may be mixed, and the linear analyzer then only serves to partially reduce the eye glow. In some embodiments, the MUX output grating minimizes the k-vector component of each grating in one particular direction (e.g., minimizes the vertical component of the k-vector), leaving only the horizontal component in the opposite direction. Even if the gratings are not perfectly aligned (in opposite directions) and are arranged to have a stronger output polarization in one direction than the orthogonal direction, the use of a linear analyzer is still beneficial. In some embodiments where the majority of the MUX output structure k vectors are in the opposite direction, the linear analyzer may not completely block the leakage of the eye glow, but an orientation may be obtained where the eye glow may be blocked by a factor greater than the loss factor in see-through transmission by the linear analyzer. In some embodiments, the orientation of the eye glow polarization may be strongly aligned with the k vector in the anisotropic output configuration and may be orthogonal to the k vector in the anisotropic lattice.

[0191] In some embodiments, a photochromic layer may be applied on top of the waveguide, which may reduce eye glow. However, the photochromic layer may also reduce optical see-through transmission. In some embodiments, the photochromic layer may be a passive photochromic layer or an active photochromic layer. The active photochromic layer may be an electrochromic or photochromic photochromic layer. In some embodiments, the active photochromic layer may provide a temporal transmission variation that is matched and synchronized with the brightness of the image content displayed by the projector (e.g., screen generating unit).

[0192] In some embodiments, a microlouver film can be applied to the top surface of the waveguide that can reduce eye glow. The microlouver film can be used to suppress eye glow at extreme angles that may be at the limit of the effective angular bandwidth of many of the grating and thin film coating solutions described throughout this disclosure. The microlouver film can be combined with a polarizer. An exemplary microlouver film is a light control film manufactured by 3M Company (Minnesota).

[0193] [The doctrine of equivalents] Although the above description contains many specific embodiments of the present invention, these should not be interpreted as limitations on the scope of the present invention, but rather as examples of one embodiment thereof. It is therefore to be understood that the present invention may be practiced in ways other than those specifically described without departing from the scope and spirit of the present invention. Thus, the embodiments of the present invention should be considered in all respects as illustrative and not restrictive. Therefore, the scope of the present invention should be determined not by the embodiments shown, but by the appended claims and their equivalents. [Explanation of symbols]

[0194] 100 Waveguide 110 lattice layer 111 Substrate 112 Substrate 113 Eyes 120 Area 122 Beam 130 Area 132 Injection beam 134 Eye Glow Beam 140a Reflected beam 140b Reflected beam 200 Waveguide 210 lattice layer 230 Waveguide 230a waveguide 231 Waveguide 240 Reflection grating layer, upper grating 240a Transmissive Diffractive Element 240b Reflective Diffractive Element 241 Bottom grid 250 Area 252 Beam 260 Area 262 Rays of light 264 Rays of light 265 Rays, Eyeglow Light 270 Light absorbing layer 270a Light absorbing layer 310 Base Waveguide 320 Spacer Beads 352 light 354 light 400 Waveguide 410 Lattice layer 420 Surface relief reflective grating 432 Ray of light 440 Area 442 Ray of light 444 Eyeglow Rays 446 Ray of light 500 Waveguide 510 Reflection grating 530 Spacer Beads 600 Waveguide 600a First Waveguide 600b Second waveguide 600c 3rd Waveguide 602 Lattice layer 610 Dichroic Reflector 620 Area 630 Area 700 Spacer 900 Substrate 1004 Output coupling optical elements, dichroic filters 1006 Input coupling optical element

Claims

1. 1. A waveguide display comprising: a source of image modulated light; a waveguide having an eye-facing surface and an outer surface facing the outside world; an input coupler for coupling the light into a totally internally reflected path within the waveguide; at least one grating for providing beam expansion and extracting light from the waveguide towards an eyebox; a surface relief reflective grating comprising a modulation depth and a grating pitch, the modulation depth being greater than the grating pitch over at least a portion of the polymer grating structure, the surface relief reflective grating being disposed on the outer surface of the waveguide; Including, the surface relief reflective grating is configured to redirect stray light generated within the waveguide away from a light path refracted through the exterior surface to the outside world and back out of the waveguide through the eye-facing surface; the surface relief reflective grating does not substantially impede propagation of image modulated light in the waveguide and extraction of the image modulated light towards the eyebox; A waveguide display, wherein the stray light generated within the waveguide includes at least one selected from the group consisting of light scattered from a grating material, zero order diffraction image modulated light, and image modulated light propagating along an optical path that is not extracted from the waveguide towards the eyebox.

2. 10. The waveguide display of claim 1, wherein the surface relief reflective grating further comprises a backfill material between adjacent polymer regions, the backfill material having a refractive index higher or lower than that of the polymer regions.

3. 3. The waveguide display of claim 2, wherein the backfill material occupies space at the bottom of the space between adjacent portions of the polymer grating structure, and the space above a top surface of the backfill material to the modulation depth is occupied by air.

4. The waveguide display of claim 2, wherein the backfill material comprises a birefringent material.

5. 5. The waveguide display of claim 4, wherein the birefringent material comprises a liquid crystal material.

6. 10. The waveguide display of claim 1, wherein the modulation depth of the surface relief reflective grating is greater than a wavelength of visible light.

7. 2. The waveguide display of claim 1, wherein said grating pitch is the spacing of diffractive features of said surface relief reflective grating and said modulation depth is the depth of said surface relief reflective grating.

8. 10. The waveguide display of claim 1, wherein the surface relief reflective grating further comprises alternating polymer regions and air gap regions, the refractive index difference between the polymer regions and the air gap regions being in the range of 1.4 to 1.

9.

9. 5. The waveguide display of claim 4, wherein the refractive index difference between said polymer domains and said birefringent material is between 0.01 and 0.

2.

10. The surface relief reflective grating comprises: A polymer diffraction mechanism; a birefringent material between adjacent polymeric diffractive features, the birefringent material having a higher refractive index than the polymeric diffractive features; 10. The waveguide display of claim 1, comprising:

11. 10. The waveguide display of claim 1, wherein the modulation depth of the surface relief reflective grating varies across the waveguide to provide spatially varying polarization-dependent or angle-dependent diffraction efficiency characteristics.

12. the surface relief reflective grating comprises an area containing a Bragg grating, an area containing a Raman-Nath grating, and an area without a grating; 10. The waveguide display of claim 1, wherein the region at least partially covers the input coupler and the at least one grating for providing beam expansion and light extraction.

13. 13. The waveguide display of claim 12 further comprising a light control layer overlying grating-free areas of said surface relief reflective grating.

14. 14. The waveguide display of claim 13, wherein the light control layer provides at least one selected from the group consisting of polarization rotation, polarization selective absorption, polarization selective transmission, polarization selective diffraction, angle selective transmission, angle selective absorption, anti-reflection, and transmission within a defined spectral bandwidth.

15. 10. The waveguide display of claim 1, wherein the surface relief reflective grating comprises a roll K-vector grating in which the tilt angle varies continuously or in discrete steps.

16. 10. The waveguide display of claim 1, wherein the surface relief reflective grating comprises a grating having a spatially varying pitch.

17. 10. The waveguide display of claim 1, wherein the light entering the waveguide from the outside world is provided by an external light source and enters the waveguide through the exterior and / or eye-facing surface of the waveguide.

18. 10. The waveguide display of claim 1, wherein the surface relief reflective grating is a composite of a polymer and at least one other material, the polymer being removed after formation of the polymer grating structure.

19. 20. The waveguide display of claim 18, wherein the at least one other material comprises nanoparticles.

20. 10. The waveguide display of claim 1, wherein a coating applied to the surface relief reflective grating provides an effective refractive index of up to 2.

5.

21. 10. The waveguide display of claim 1, wherein the surface relief reflective grating is coated with a first material and the coated grating is backfilled with a second material having a refractive index higher or lower than that of the first material.

22. 10. The waveguide display of claim 1 , wherein the surface relief reflective grating comprises a first grating structure disposed on the outer surface of the waveguide and a second grating structure disposed on the eye-facing surface of the waveguide.

23. 23. The waveguide display of claim 22, wherein the first grating structure and the second grating structure have different grating periods.

24. 1. A method for reducing eye glow from a waveguide display, comprising: providing a source of image modulated light, a waveguide, an input coupler, and at least one grating for providing beam expansion and extracting light from the waveguide towards the eyebox, the waveguide including an eye-facing surface and an outer surface facing the outside world; providing a polymer grating structure comprising a modulation depth and a grating pitch, the modulation depth being greater than the grating pitch over at least a portion of the polymer grating structure; directing image modulated light into a total internal reflection path within the waveguide, beam expanding the light, and extracting it towards the eyebox; directing light propagating in the waveguide away from a light path refracted through the outer surface towards the outside world using the polymer grating structure; diffracting light entering the waveguide from the outside world or stray light generated within the waveguide away from a light path refracted through the outer surface using a polymer grating structure; A method comprising:

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