Light guide with polarization selective body reflector

Abstract

A light guide having a partially reflective tilted polarization selective body mirror is disclosed. The light guide may be used for a near-eye display having a polarized image source. The polarization selective mirror reflects the light of the polarized image source and completely transmits the orthogonally polarized light so that the mirror is less apparent to the external viewer while maintaining efficient delivery of the image light to the viewer.

Description

Technical Field

[0001] The present disclosure relates to visual display devices and related components, modules, and methods. Background Art

[0002] Visual displays provide information including still images, videos, data, etc. to one or more viewers. Visual displays have applications in different fields including entertainment, education, engineering, science, professional training, advertising, etc. (to name just a few examples). Some visual displays (such as televisions) display images to multiple users, and some visual display systems (such as near-eye displays (NEDs)) are intended for a single user.

[0003] An artificial reality system typically includes an NED (e.g., a headset or a pair of glasses) configured to present content to a user. A near-eye display can display virtual objects or images of combined reality objects and virtual objects, as in virtual reality (VR), augmented reality (AR), or mixed reality (MR) applications. For example, in an AR system, a user can view an image of a virtual object (e.g., computer-generated images (CGIs)) superimposed on the surrounding environment through a transparent "combiner" component. The combiner of a wearable display is typically transparent to external light but includes some optical elements of an optical path that direct display light into the user's field of view.

[0004] Since the display of an HMD or NED is typically worn on a user's head, a large, bulky, unbalanced, and / or heavy display device with a heavy battery would be difficult and uncomfortable for the user to carry. Thus, a head-mounted display device can benefit from a compact and efficient configuration, including an efficient light source and illuminator that provide illumination for the display panel, high-throughput lenses, and other optical elements in the imaging train. Additionally, for better social acceptance and to facilitate visual eye contact with an NED wearer, it may be desirable to make such optical elements less visible to external viewers. Summary of the Invention

[0005] According to a first aspect of the present disclosure, there is provided a light guide for transmitting image light in a display device, the light guide comprising: a light guide body including a first surface and an opposite second surface extending parallel to each other, the light guide body configured to cause image light to propagate in a zigzag optical path within the light guide body, the zigzag optical path being defined by alternating reflections of the image light on the first surface and the second surface; and an array of polarization-selective tilted volume reflectors along the zigzag optical path within the light guide body, the array configured to out-couple light in a first polarization state while allowing light in a second orthogonal polarization state to transmit therethrough, whereby in operation, a laterally offset polarization portion of the image light is out-coupled from the light guide body towards an eyebox of the display device.

[0006] In some embodiments, each of the polarization-selective tilted volume reflectors of the array comprises a multi-layer birefringent polymer film.

[0007] In some embodiments, the spectral bandwidth of the polarization-selective tilted volume reflector can be tuned by applying at least one of an electric field or a magnetic field, whereby the optical transmissivity of outside light through the polarization-selective tilted volume reflector is variable.

[0008] In some embodiments, the polarization-selective tilted volume reflector comprises at least one of helicoidal cholesteric liquid crystals or ferroelectric nematic liquid crystals.

[0009] In some embodiments, for a color channel of the image light propagating within the light guide body, the polarization-selective tilted volume reflector has a reflection bandwidth of less than 40 nm.

[0010] In some embodiments, the polarization-selective tilted volume reflector is configured to reduce reflection of outside light therefrom when the outside light impinges on the light guide body at an incident angle of less than 70 degrees.

[0011] In some embodiments, the polarization-selective tilted volume reflectors of the array have a reflectivity range of between 4% and 80% for image light in the first polarization, and a reflectivity of less than 1% for image light in the second orthogonal polarization.

[0012] In some embodiments, the polarization-selective tilted volume reflectors of the array have a refractive index greater than 1.65.

[0013] In some embodiments, the light guide further includes an elastic layer located between the polarization-selective volume reflector of the array and the light guide body.

[0014] In some embodiments, the light guide body includes: a first light guide body portion including a first surface of the light guide body on one side and a first ridged surface on the opposite side, the first ridged surface including a plurality of first inclined facets; and a second light guide body portion including a second surface of the light guide body on one side and a second ridged surface on the opposite side, the second ridged surface including a plurality of second inclined facets, wherein: the polarization-selective inclined volume reflectors of the array of polarization-selective inclined volume reflectors are sandwiched between corresponding inclined facets of the plurality of first inclined facets and the plurality of second inclined facets located in the first light guide body portion and the second light guide body portion, respectively.

[0015] In some embodiments, the light guide further includes: a first adhesive layer located between the polarization-selective volume reflector of the array and the inclined facets of the plurality of first inclined facets; and a second adhesive layer located between the polarization-selective volume reflector of the array and the inclined facets of the plurality of second inclined facets.

[0016] In some embodiments, the light guide body includes a polymeric material that maintains the polarization state of the image light propagating therein.

[0017] In some embodiments, for the propagating image light, the difference between the ordinary indices of refraction and the extraordinary index of the polymeric material is less than 0.1.

[0018] In some embodiments, the polymeric material has an elastic modulus of less than 1 GPa.

[0019] In some embodiments, the light guide body includes a polarizer that polarizes the image light propagating along a zigzag optical path to have a first polarization state.

[0020] According to a second aspect of the present disclosure, there is provided a method for manufacturing a light guide for transmitting image light in a display device, the method including: obtaining a plurality of polymer plates, each having a reflective polarizer bonded thereto; bonding the polymer plates together to form a stack; and cutting the stack at an acute angle to obtain a light guide body including an array of polarization-selective inclined volume reflectors, each polarization-selective inclined volume reflector including one of the polymer plates having one of the reflective polarizers bonded thereto.

[0021] In some embodiments, the method further includes polishing a first surface and an opposite second surface of the light guide body, and assembling the light guide body into the light guide.

[0022] According to a third aspect of the present disclosure, there is provided a display device including: a light engine configured to provide image light carrying an image in an angular region; and a light guide configured to expand the image light above the oculus of the display device, the light guide including: a light guide body including a first surface and an opposite second surface extending parallel to each other, the light guide body configured to cause the image light to propagate along a zigzag optical path within the light guide body, the zigzag optical path being defined by alternating reflections of the image light on the first surface and the second surface; and an array of polarization-selective tilted volume reflectors along the zigzag optical path within the light guide body, the array configured to outcouple light in a first polarization state while transmitting light in a second orthogonal polarization state, whereby, in operation, a laterally offset polarized portion of the image light is outcoupled from the light guide body toward the oculus of the display device.

[0023] In some embodiments, the display device further includes a transmissive polarizer coupled to the first surface of the light guide body for polarizing incident ambient light to have the second polarization state.

[0024] In some embodiments, the light engine is configured to emit polarized light and includes at least one of: a liquid crystal display, a micro-LED display, a liquid crystal on silicon (LCoS) display, or a laser diode coupled to a tiltable reflector. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Exemplary embodiments will now be described with reference to the drawings, in which:

[0026] Figure 1A is a side cross-sectional view of a light guide of the present disclosure showing the image-carrying property of the light guide;

[0027] Figure 1B is showing the optical paths of the image light and the external light Figure 1A of the light guide;

[0028] Figure 2A is an enlarged side cross-sectional view of a light guide having a 50% reflective polarizer;

[0029] Figure 2B is an enlarged side cross-sectional view of a light guide having a non-polarizing 50% reflector for comparison with Figure 2A ;

[0030] Figure 2C is an enlarged side cross-sectional view of a light guide having a non-polarizing 25% reflector for comparison withFigure 2A Make a comparison;

[0031] Figure 3A Is a simulated front view of a person wearing AR glasses with a light guide having a polarized partial point reflector;

[0032] Figure 3B Is a simulated front view of a person wearing AR glasses with a light guide having a non - polarized partial point reflector, which is more obvious;

[0033] Figure 3C Is a simulated front view of a person wearing AR glasses with a light guide having a polarized partial stripe reflector;

[0034] Figure 3D Is a simulated front view of a person wearing AR glasses with a light guide having a non - polarized partial stripe reflector, which is more obvious;

[0035] Figure 4 Is an enlarged side cross - sectional view of a light guide of the present disclosure having a polarized reflector and an external polarizer;

[0036] Figure 5 Is an enlarged side cross - sectional view of a light guide of the present disclosure having a birefringent layer polarizer;

[0037] Figure 6 Is an enlarged side cross - sectional view of a light guide of the present disclosure having a dielectric layer stack polarizer;

[0038] Figure 7 Is an enlarged side cross - sectional view of a light guide of the present disclosure having a wire grid polarizer;

[0039] Figure 8 Is a side cross - sectional view of a light guide having a polarized partial reflector supported by a transparent elastic layer;

[0040] Figure 9 Is a side cross - sectional view of a light guide body portion including a ridged surface having a plurality of inclined facets;

[0041] Figure 10 Is including a pair of matching Figure 9 3D view of a light guide of the light guide body portion;

[0042] Figure 11 Is Figure 10 Side cross - sectional view of the light guide;

[0043] Figure 12 Is a cross - sectional view of a reflective polarizer having a stress - applying side layer;

[0044] Figure 13 Is a side cross - sectional view of a bent light guide of the present disclosure;

[0045] Figure 14 is a side cross-sectional view of an optical waveguide of the present disclosure having an embedded transmissive polarizer;

[0046] Figure 15 is a side cross-sectional view of an optical waveguide of the present disclosure having an array of optical retarders coupled to a partially reflective polarizer;

[0047] Figure 16 is a spectrogram showing the spectral transmittance of a reflective polarizer according to an embodiment;

[0048] Figure 17A is a flowchart of a method of manufacturing an optical waveguide of the present disclosure;

[0049] Figure 17B is for using Figure 17A a side cross-sectional view of a stack of reflective polarizers for manufacturing an optical waveguide by the method;

[0050] Figure 18 is a combined side view and plan view of a pupil replication optical waveguide having an inclined partially polarization-selective stripe reflector;

[0051] Figure 19 is a schematic view of a near-eye display including an optical waveguide of the present disclosure;

[0052] Figure 20 is a view of a wearable display of the present disclosure having a form factor of a pair of glasses; and

[0053] Figure 21 is a three-dimensional view of a head-mounted display (HMD) of the present disclosure. DETAILED DESCRIPTION

[0054] Although the present teachings are described in connection with various embodiments and examples, the present teachings are not intended to be limited to these embodiments. On the contrary, as will be understood by those skilled in the art, the present teachings include various alternatives and equivalents. All statements of principles, aspects, and embodiments of the present disclosure set forth herein, as well as specific examples thereof, are intended to encompass their structural and functional equivalents. In addition, such equivalents are intended to include both currently known equivalents and equivalents developed in the future, i.e., any elements developed to perform the same function regardless of structure.

[0055] As used herein, unless expressly stated otherwise, the terms "first," "second," etc. are not intended to imply an order of sequencing, but rather to distinguish one element from another. Similarly, the order of method steps does not imply the order in which they are performed, unless expressly stated. In Figures 1A to 1B , Figures 2A to 2C , Figures 3A to 3D ,Figures 4 to 8 , Figure 11 , Figures 13 to 15 and Figure 18 in, like reference numerals generally represent like elements.

[0056] Near-eye displays and augmented reality displays can use a pupil replication light guide to expand image light carrying a projected image above the oculus of the display, i.e., above the region where the user's eyes may be located during normal operation of the display. The pupil replication light guide can include a parallel plate of a transparent material that causes the image light to propagate in a zigzag pattern by total internal reflection (TIR) on top and bottom surfaces of the light guide that extend parallel to each other. A partial volume reflector can be used to out-couple a portion of the image light along the zigzag optical path of the image light. The reflectivity of the partial volume reflector can be selected to gradually decrease from an upstream reflector to a downstream reflector to counteract the decrease in optical power of the image light as a portion thereof is out-coupled by one or more upstream partial reflectors. In this document, contrary to diffraction structures that are not considered volume reflectors, such as volume Bragg gratings or polarization volume holograms, the term "volume reflector" refers to a continuous, non-diffractive surface that can at least partially reflect light, such as a Fresnel surface, a metal surface, a wire grid surface, etc.

[0057] One disadvantage of a light guide having a partial reflector output coupler is that the partial reflector may be visible to an external viewer. A visible partial reflector may obscure or distract the eyes of a near-eye display wearer, thereby reducing the social acceptance of the display and deterring the display owner from wearing the display in public.

[0058] According to the present disclosure, by making the partial reflector polarization selective, the partial volume reflector of the light guide can be made less visible, i.e., less obvious, to an external viewer. The polarization selective partial volume reflector partially reflects light of a first polarization while allowing light of a second orthogonal polarization to transmit therethrough. Since ambient light is not polarized, such a reflector may be less visible to an external viewer. Additionally, by placing a transmissive polarizer at the distal side of the light guide, the ambient light can be polarized to have a second polarization state in which the light freely propagates through the partial reflective polarizer, rendering the latter almost completely invisible. In embodiments where an external polarization dimming device is used upstream of the display for any reason, such as to reduce glare, reduce the brightness of external images, etc., the incoming light can be polarized by the polarization dimming device to have a second polarization state.

[0059] According to the present disclosure, there is provided a light guide for transmitting image light in a display device. The light guide includes a light guide body including a first surface and an opposite second surface that extend parallel to each other, and the light guide body is configured to cause image light to propagate along a zigzag optical path within the light guide body. The zigzag optical path is defined by alternating reflections of the image light on the first and second surfaces. The light guide further includes an array of polarization-selective tilted volume reflectors along the zigzag optical path within the light guide body, and the array is configured to out-couple light in a first polarization state while allowing light in a second orthogonal polarization state to transmit therethrough. In operation, a laterally offset polarized portion of the image light is out-coupled from the light guide body toward an eyebox of the display device.

[0060] Each of the polarization-selective tilted volume reflectors of the array may include a multilayer birefringent polymer film, a cholesteric liquid crystal, a dielectric layer stack, a dichroic layer stack, a wire grid polarizer, and the like. In some embodiments, the polarization-selective tilted volume reflectors of the array may have a reflectance range, for example, between 4% and 80% for image light of one polarization, while having a reflectance of about 0%, for example, less than 1% for image light of the other orthogonal polarization; and / or the polarization-selective tilted volume reflectors of the array may have a refractive index high enough, for example, greater than 1.65.

[0061] The polarization-selective tilted volume reflectors may be configured to reduce reflection of external light from the polarization-selective tilted volume reflectors when the external light is incident on the first surface of the light guide body at a normal incidence angle. In some embodiments, the polarization-selective tilted volume reflectors may be configured to reduce reflection of external light from the polarization-selective tilted volume reflectors when the external light is incident on the light guide body at an incidence angle less than 70 degrees with respect to the normal of the light guide body. The light guide may include an elastic layer between the array of polarization-selective volume reflectors and the light guide body.

[0062] In some embodiments, the light guide body includes a first light guide body portion including the first surface of the light guide body on one side and a first ridged surface on an opposite side, the first ridged surface including a plurality of first tilted facets; and a second light guide body portion including the second surface of the light guide body on one side and a second ridged surface on an opposite side, the second ridged surface including a plurality of second tilted facets. The first light guide body portion and the second light guide body portion match each other when combined together. The polarization-selective tilted volume reflectors of the array of polarization-selective tilted volume reflectors are sandwiched between corresponding tilted facets of the plurality of first tilted facets and the plurality of second tilted facets respectively located in the first light guide body portion and the second light guide body portion.

[0063] The light guide may further include a first adhesive layer located between the polarization-selective volume reflector of the array and the inclined facets of the plurality of first inclined facets; and a second adhesive layer located between the polarization-selective volume reflector of the array and the inclined facets of the plurality of second inclined facets.

[0064] In some embodiments, the polarization-selective inclined volume reflector of the array includes a polarization-selective reflective layer and a pair of stress-imparting layers on opposite sides of the polarization-selective reflective layer for applying compressive stress thereto. In such embodiments, the stress-imparting layer may have a higher coefficient of thermal expansion than the polarization-selective reflective layer. The stress-imparting layer may be thermally laminated to the polarization-selective reflective layer. The first surface and the second surface may be flat, form a meniscus shape with a simple or complex shape, and the like.

[0065] In some embodiments, the spectral bandwidth of the polarization-selective inclined volume reflector can be tuned by applying at least one of an electric field or a magnetic field, whereby the optical transmissivity of external light through the polarization-selective inclined volume reflector is variable. In such embodiments, the polarization-selective inclined volume reflector may include at least one of a chiral nematic liquid crystal or a ferroelectric nematic liquid crystal.

[0066] In some embodiments, for the color channels of the image light propagating in the light guide body, the polarization-selective inclined volume reflector has a reflection bandwidth of less than 40 nm. The polarization-selective inclined volume reflector may be configured to reduce the reflection of external light therefrom when the external light is incident on the dielectric layer stack at an incident angle greater than 70 degrees. In embodiments where the light guide body includes a polymer material that maintains the polarization state of the image light propagating in the light guide body, the difference between the ordinary refractive index and the extraordinary refractive index of the polymer material may be less than 0.1, and / or the polymer material may have an elastic modulus of less than 1 GPa.

[0067] In some embodiments, the light guide further includes a transmissive polarizer coupled to the first surface of the light guide body for polarizing the incident external light to have a second polarization state. The light guide may further include an array of optical retarders along a zigzag optical path in the light guide body for changing the polarization state of the image light propagating along the zigzag optical path. The retarder can be tuned by applying a control signal.

[0068] According to the present disclosure, a display device is provided that has an optical engine and an optical waveguide of the present disclosure. The optical engine is configured to provide image light carrying an image in an angular region, and the optical waveguide is configured to expand the image light above the eyebox of the display device. The optical engine may include, for example, a liquid crystal display, a liquid crystal on silicon (LCoS) display, a micro-LED display, and / or a laser diode coupled to a tiltable reflector. The optical engine may include a light source having a spectral bandwidth including red, green, and blue light.

[0069] According to the present disclosure, a method for manufacturing an optical waveguide for transmitting image light in a display device is provided. The method includes: obtaining a plurality of polymer sheets, each polymer sheet having a reflective polarizer bonded to the corresponding polymer sheet; bonding the polymer sheets together to form a stack; and cutting the stack at an acute angle to obtain an optical waveguide body including an array of polarization-selective tilted reflectors, each polarization-selective tilted reflector including one of the polymer sheets having one of the reflective polarizers bonded to the corresponding polymer sheet. The first surface and the opposite second surface of the optical waveguide body may be polished, and the optical waveguide body may be assembled into an optical waveguide.

[0070] Now referring to Figure 1A , the optical waveguide 100 can be used to transmit image light 104 to the eyebox 101 of a display device (e.g., a near-eye display device). The optical waveguide 100 includes an optical waveguide body 102, and the optical waveguide body 102 includes a first surface 111 and an opposite second surface 112. The first surface 111 and the second surface 112 may be flat, curved, etc. as shown as long as they extend parallel to each other. The first surface 111 and the opposite second surface 112 may be the outer surfaces of the optical waveguide body 102. The optical waveguide body 102 may include a transparent substrate, such as a glass substrate, a plastic substrate, an oxide substrate, or an inorganic crystal substrate. The transparent substrate may have a flat or curved outer surface and may be coated with a low-refractive-index material to prevent dust and fog.

[0071] Image light 104 is in-coupled through an optional in-coupler 106, which is a prism in-coupler in this example. The image light 104 propagates along a zigzag optical path 108 within the light guide body 102, which is defined by the alternating reflections of the image light 104 on the first surface 111 and the second surface 112 of the light guide body 102. The image light 104 carries the image to be displayed. The image light 104 carries an image in the angular domain, that is, where each image element (pixel) is represented by the light angle of a fan of light rays covering the entire field of view (FOV) of the image. The brightness and / or color of the pixels of the image in the angular domain are represented by the brightness and / or color of the light rays of the corresponding light angles.

[0072] An array of tilted partial volume reflectors 110A, 110B, and 110C (collectively 110) is disposed within the light guide body 102 along the zigzag optical path 108. More than three partial volume reflectors 110 may be provided. The partial volume reflectors 110 may be tilted in a parallel manner, that is, they may be parallel to each other at the same tilt angle. In this document, the term "tilted" means forming an acute angle with the first surface 111 and the second surface 112 of the light guide body 102. In operation, the tilted partial volume reflectors 110 out-couple the laterally offset portion 105 of the image light 104 from the light guide body 102 towards the eyebox 101.

[0073] Figure 1B Also shown is how the light guide 100 can transfer an image to the eyebox 101. The image carried by the image light 104 is an image in the angular domain, where the pixels of the image are represented by the light angles of the light rays of the image light emitted by the pixels. Thus, different pixels are represented by different light angles. In Figure 1BIn this case, the image in the angular region is represented by a fan of light rays including a first light ray 121, a second light ray 122, and a third light ray 123 at different light angles. In operation, the inner coupler 106 inner-couples the first light ray 121, the second light ray 122, and the third light ray 123 into the light guide body 102. The first light ray 121, the second light ray 122, and the third light ray 123 are totally internally reflected from the second surface 112 of the light guide body 102 and are then partially reflected by the leftmost inclined partial volume reflector 110A, providing a first beam portion 121A, a second beam portion 122A, and a third beam portion 123A that maintain the light ray angles of the original first light ray 121, second light ray 122, and third light ray 123 of the image light 104. The remaining portion of the image light 104 propagates in the light guide 100 through a series of total internal reflections on the first surface 111 and the second surface 112 (not shown for simplicity), generating beam portions 121B, 122B, and 123B reflected from the central inclined partial volume reflector 110B, beam portions 121C, 122C, and 123C reflected from the right inclined partial volume reflector 110C, etc., effectively distributing the image light over the oculus 101. Since the light ray angles of the beam portions are preserved, the viewer can see the image carried by the image light 104 anywhere within the oculus 101. Additionally, since the light guide body 102 is transparent, the viewer can see the image of the external world carried by the external light 130 (also referred to as ambient light 130) through the light guide body 102.

[0074] As described above, one disadvantage of an optical waveguide having a partial volume reflector (such as, for example, optical waveguide 100) is that the inclined partial volume reflectors 110A, 110B, and 110C may be readily noticeable to an external viewer. It is socially and aesthetically unacceptable for a user to wear such augmented reality goggles in most public settings. In accordance with the present disclosure, the inclined volume reflector 110 can be made polarization selective. An inclined partial volume reflector that is polarization selective out-couples light in a first polarization state while transmitting light in a second orthogonal polarization state. By providing image light in a first polarization state, the image light can be reflected more efficiently than non-polarized external light, thereby making the partial inclined volume reflector less noticeable and / or improving the efficiency of out-coupling of the laterally offset polarized portion of the image light. Additionally, by polarizing the external light to have a second polarization state, the partial inclined volume reflector can be made nearly invisible to an external viewer because light in the second polarization state propagates through the polarization selective volume reflector substantially without reflection. As a non-limiting illustrative example, a polarization selective inclined volume reflector can have a reflectivity ranging from 4% to 80% for one polarization of image light and a reflectivity approaching 0% for another orthogonally polarized image light. In some embodiments, the polarization selective inclined volume reflector can have a refractive index greater than 1.65.

[0075] The effect of a polarization selective partial volume reflector on saliency is as Figure 2A , Figure 2B and Figure 2C shown. Figure 2A Shown is an optical waveguide 200A having a polarization selective partial volume reflector, while Figure 2B and Figure 2C show an optical waveguide 200B and an optical waveguide 200C, respectively, where the non-polarization selective partial volume reflectors have reflectivities of 50% and 25%, respectively.

[0076] First, referring to Figure 2A, the light guide 200A includes a light guide body 202 having a first surface 211 and a second surface 212. In this example, the flat outer surfaces extend parallel to each other. The partial reflection polarizer 210A reflects 50% of the P-polarized light and substantially does not reflect the S-polarized light. That is, the P-reflectivity RP is 50%, and the S-reflectivity RS is 0%. The image light 104 is P-polarized, so the partial reflection polarizer 210A will reflect 50% of the image light 104, as shown. The external light 130 (i.e., the ambient light 130) is unpolarized, so its P-polarized component and S-polarized component have equal optical power. In other words, each of the P-polarized component and S-polarized component of the ambient light 130 is 50% of the total optical power of the ambient light 130. Half of the P-component of the ambient light 130 is reflected by the partial reflection polarizer 210A, so 25% of the total optical power of the ambient light 130 is transmitted. The entire S-polarized component of the ambient light 130 can propagate through, so another 50% of the total optical power of the ambient light 130 is transmitted. Therefore, the total transmission power ratio is 75%.

[0077] Figure 2B A light guide 200B with a non-polarization-selective partial volume reflector is shown for comparison with Figure 2A In Figure 2B , the partial volume reflector 210b has a reflectivity of 50%, so the partial reflection polarizer 210B will reflect 50% of the image light, as shown. The external light 130 will also be transmitted at 50%. By comparing Figure 2B and Figure 2A it can be seen that the reflectivity of the image light 104 is 50% in both cases. In Figure 2A 's case (i.e., with the polarization-selective partial reflection polarizer 210A), the transmittance of the external light 130 is 75%, while in Figure 2A (i.e., with the non-polarization-selective partial reflection polarizer 210B), the transmittance of the external light 130 is only 50%. In other words, at the same efficiency of transmitting the image light to the oculus, Figure 2A 's polarization-selective tilted volume reflector 210A transmits 25% more light than Figure 2B 's non-polarization-selective tilted volume reflector 210B. Therefore, at the same image light utilization efficiency corresponding to a reflectivity of 50%, Figure 2A 's polarization-selective tilted volume reflector 210A is less visible to both the wearer of the near-eye display and external viewers.

[0078] Moving on to Figure 2C, the partial volume reflector 210C of the light guide 200C is non-polarization selective at a reflectivity of 25%. Thus, only 25% of the image light 104 will be reflected by the first partial volume reflector 210C. Similarly, 25% of the external light will be reflected by the partial volume reflector 210C, and thus, the transmittance of the external light 130 will be 75%. Therefore, under the same apparentness as that of the Figure 2A case, the image light utilization efficiency will be reduced by 50% (i.e., 25%, instead of Figure 2A 50%). Therefore, the utilization of the polarization selective tilted partial reflector in the light guide improves at least one of the image light utilization rate or the unapparentness of the tilted volume reflector.

[0079] The latter point is shown in Figure 3A to FIG. 3F. Figure 3A An AR goggle including a light guide 300A having a polarization selective tilted volume reflector 310A with small dots is depicted. Figure 3B An AR goggle including a light guide 300B having a non-polarization selective tilted dot reflector 310B that appears more opaque and thus more apparent to an external observer is depicted. Figure 3A The AR goggles of Figure 3B may be more socially acceptable than the AR goggles of

[0080] Figure 3C because the polarization selective tilted volume reflector 310A is less apparent at the same image light utilization efficiency of the goggle light guide. An AR goggle including a light guide 300C having a polarization selective tilted volume reflector 310C in an elongated stripe shape is depicted. Figure 3D An AR goggle including a light guide 300D having a non-polarization selective tilted stripe reflector 310D that appears more opaque and thus more apparent to an external observer is depicted. Figure 3C The AR goggles of Figure 3D may be more socially acceptable than the AR goggles of

[0081] As a non-limiting illustrative example, the polarization selective tilted volume reflectors of the present disclosure, such as Figure 2A the polarization selective tilted volume reflector 210A of Figure 3A the polarization selective tilted volume reflector 310A of Figure 3CThe polarization - selective tilted volume reflector 310C and the other reflectors considered below can have a reflectance range between 4% and 80% for image light of one polarization, and a reflectance close to 0% (e.g., less than 1% or 0.1%) for image light of the other orthogonal polarization. In some embodiments, the polarization - selective tilted volume reflector 210A can have a refractive index greater than 1.65, for example.

[0082] Turning to Figure 4 and further referring to Figure 2A , the light guide 400 ( Figure 4 ) is similar to Figure 2A the light guide 200A of Figure 2A and includes elements that are the same as or similar to those of the light guide 200A of Figure 4 , that is, a light - guide body 402 having a first surface 411 and a second surface 412 that extend parallel to each other. The first surface 411 and the second surface 412 are flat surfaces in this example.

[0083] Now referring to Figure 5 and further referring to Figure 2A , the light guide 500 is similar to Figure 2A the light guide 200A of Figure 5 and includes similar elements.

[0084] Figure 5 The light guide 500 of

[0084] includes a light - guide body 502 having opposite, flat and parallel first outer surface 511 and second outer surface 512. The image light 104 propagates in the light - guide body 502 through a series of internal reflections on the first surface 511 and the second surface 512. The partial - reflection polarizer 510 (only one is shown) partially out - couples the image light 104 for viewing by a viewer. The partial - reflection polarizer 510 includes a layer 515 of birefringent material having an ordinary refractive index and an extraordinary refractive index, one of which can match the refractive index of the light - guide body 502, enabling light at the polarization corresponding to the matched refractive index to propagate through the partial - reflection polarizer 510 with substantially no reflection loss. Due to the refractive - index mismatch, light at the other orthogonal polarization will experience Fresnel reflection.In some embodiments, the birefringent layer 515 includes a cholesteric liquid crystal that reflects circularly polarized light of one chirality while transmitting circularly polarized light of the opposite chirality, such as, for example, a tilted helix (ChOH) cholesteric liquid crystal or an N tb *cholesteric liquid crystal. In some embodiments, the birefringent layer 515 includes a ferroelectric nematic liquid crystal, such as, for example, an NF* ferroelectric nematic liquid crystal. Using a liquid crystal allows tuning of the spectral bandwidth of the polarization-selective tilted reflector by applying at least one of an electric field or a magnetic field, whereby the optical transmissivity of external light through the polarization-selective tilted reflector can be made variable. Additionally, in some embodiments, the birefringent layer 515 can include a multilayer birefringent polymer film having a multilayer birefringent polymer.

[0085] Turning to Figure 6 and further referring to Figure 2A , the light guide 600 is similar to Figure 2A the light guide 200A of Figure 6 and includes similar elements. The light guide 600 of Figure 6 includes a light guide body 602 having opposite, flat, and parallel first and second outer surfaces 611 and 612. Image light 104 propagates in the light guide body 602 by a series of internal reflections (e.g., total internal reflections) on the first surface 611 and the second surface 612. A partial reflection polarizer 610 (only one is shown) externally couples a portion of the image light for viewing by a viewer. The partial reflection polarizer 610 includes a dielectric layer stack 615. The thicknesses and refractive indices of the layers of the dielectric layer stack 615 are selected to optimize the reflection of light having only one polarization (typically linearly polarized) while reducing the reflection of light of the orthogonal polarization, thereby making the dielectric layer stack 615 a partial polarization-selective linear polarizer. Additionally, in some embodiments, the dielectric layer stack is optimized to reduce the reflection of external light, thereby making such a partial reflector less visible to an external viewer. For example, the dielectric layer stack 615 can be configured to reduce the reflection of external light from the dielectric layer stack 615 when the external light impinges on the dielectric layer stack 615 at an incident angle less than 45 degrees, which can correspond to an incident angle on the light guide 600 of less than 70 degrees. Other types of polarization-selective tilted reflectors can also be configured to reduce the reflection of external light at incident angles within a specified range or a similar range.

[0086] Referring to Figure 7 and further referring to Figure 2A , the light guide 700 is similar to Figure 2A the light guide 200A of Figure 7The light guide 700 includes a light guide body 702 having opposite, flat and parallel first and second outer surfaces 711 and 712. Image light 104 propagates in the light guide body 702 by a series of internal reflections on the first and second surfaces 711 and 712. A partial reflector polarizer 710 (only one is shown) externally couples a portion of the image light for viewing by a viewer. The partial reflector polarizer 710 includes a wire grid polarizer 715. The length, direction, and composition of the nanowires of the wire grid polarizer 715 are selected such that the wire grid polarizer 715 at least partially reflects light of a first polarization while substantially non-reflectively transmitting light of a second orthogonal polarization.

[0087] Go to Figure 8 And further refer to Figure 2A , the light guide 800 is similar to Figure 2A the light guide 200A and includes similar elements. Figure 8 The light guide 800 includes a light guide body 802 having opposite, flat and parallel first and second outer surfaces 811 and 812. As shown, image light 104 propagates in the light guide body 802 by a series of internal reflections on the first and second surfaces 811 and 812. An array of polarization-selective volume reflectors 810 externally couples a portion 105 of the image light 104 for viewing by a viewer. The light guide 800 includes an elastic layer 820 located between the polarization-selective volume reflectors 810 and the light guide body 802 surrounding them. The purpose of the elastic layer 820 is to compensate for a mismatch in the coefficients of thermal expansion (CTEs) of the materials of the light guide body 802 and the polarization-selective volume reflectors 810. In the absence of the elastic layer 820, the CTE mismatch may cause the polarization-selective volume reflectors 810 to delaminate from the light guide body 802, resulting in a structural failure.

[0088] In Figure 8 the illustrated embodiment, the polarization-selective volume reflectors 810 extend from the first surface 811 to the second surface 812 of the light guide body 802. In some embodiments, the polarization-selective tilted volume reflectors do not extend completely between the outer surfaces of the light guide body but are "embedded" or disposed within the light guide body without extending all the way from one surface of the light guide body to the other surface. Figure 9 , Figure 10 and Figure 11 One such embodiment is shown in

[0089] First refer to Figure 9, which shows a light guide body portion 900 including inclined facets (e.g., facets 905 and 915) and steps (e.g., steps 910 and 920). In this example, the light guide body portion 900 generally has linear facets. In some examples, the facets may include circular facets or other facet shapes, such as oval, elliptical, annular, and linear (e.g., rectangular), etc.

[0090] Figure 10 A light guide body 1000 is shown, which includes a light guide body portion 1010, a filling layer 1020 that planarizes the upper surface of the light guide body 1000, and polarization-selective inclined body reflectors 1040 and 1050 disposed on the facets of the light guide body portion 1010. In this example, the polarization-selective inclined body reflectors 1040 and 1050 can generally be rectangular. However, the polarization-selective inclined body reflectors 1040 and 1050 sized to cover the corresponding facets of the light guide body portion can be of any suitable shape. A step 1060 can be located between adjacent polarization-selective inclined reflectors 1040 and 1050. In Figure 10 the illustrated embodiment, the step 1060 does not support the polarization-selective inclined body reflector.

[0091] In some examples, the light guide body can include a light guide body portion and a polarizer. The light guide body portion has a faceted surface on one side and a non-faceted surface on the other side, and the polarizer is located on the non-faceted surface, such as a transmissive polarizer or a reflective polarizer. As a non-limiting illustrative example, the polarizer can be located on a flat surface, a concave surface, or a convex surface of the light guide body portion. In some examples, a filling layer can be used to smooth (e.g., planarize) the faceted surface, and the polarizer can be located on the filling layer. In some examples, the filling layer can have a first surface conforming to the faceted surface of the light guide body portion and a second surface that is a flat surface or a non-faceted (smooth) curved surface (such as a concave surface or a convex surface). In some examples, the polarizer can be located on the second surface of the filling layer. In some examples, a reflective polarizer can be located on the inclined facet of the light guide body portion, and the filling layer can be located above the reflective polarizer and the light guide body portion and can act as a protective layer.

[0092] In some examples, the light guide body can include a light guide body portion (such as Figure 9 and Figure 10 those shown in), which forms a reflective polarizer on at least one facet. The exemplary light guide body portion can also include an outer peripheral edge coated with a light-absorbing coating. In some examples, the light guide body portion can include a curved surface (such as a convex surface or a concave surface) without facets. In some examples, the light guide body portion can include a curved surface having facets and steps. The steps can allow for a reduction in the thickness of the light guide.

[0093] In some instances, the light guide body may include a pair of mating light guide body portions, each light guide body portion having a flat surface and an opposing surface including facets and stepped portions. Figure 11 An example of such a light guide is shown. The light guide body 1102 has a first surface 1111 and an opposing second surface 1112 for propagating image light through a series of internal reflections on the first surface 1111 and the second surface 1112 within the light guide body 1102. The light guide body 1102 also includes an array of polarization-selective tilted volume reflectors 1110 for out-coupling a portion of the image light from the light guide body 1102.

[0094] The light guide body 1102 includes a first light guide body portion 1131 that includes the first surface 1111 of the light guide body 1102 on one side and a first ridged surface 1141 on the opposing side. The first ridged surface 1141 includes a plurality of first tilted facets 1151. The light guide body 1102 also includes a second light guide body portion 1132 that includes the second surface 1112 of the light guide body 1102 on one side and a second ridged surface 1142 on the opposing side. The second ridged surface 1142 includes a plurality of second tilted facets 1152. The first light guide body portion 1131 and the second light guide body portion 1132 mate with each other when assembled together. The polarization-selective tilted volume reflectors 1110 may be sandwiched between the corresponding tilted facets 1151 and 1152 of the first light guide body portion 1131 and the second light guide body portion 1132, respectively.

[0095] In some embodiments, the light guide body 1102 also includes a first bonding layer 1161 and a second bonding layer 1162, the first bonding layer being located between the polarization-selective volume reflector 1110 and the plurality of first tilted facets 1151, and the second bonding layer being located between the polarization-selective volume reflector 1110 and the plurality of second tilted facets 1151. The first bonding layer 1161 and / or the second bonding layer 1162 may serve as a filling layer and may include, for example, an adhesive layer and / or a polymer layer. The adhesive and / or polymer layer may be elastic to accommodate mechanical stresses due to CTE mismatches between the polarization-selective volume reflector 1110 and the first portion 1131 and the second portion 1132 of the light guide body 1102, similar to Figure 8 the elastic layer 820 of the light guide 800 in. At least one of the first bonding layer 1161 or the second bonding layer 1162 may have an elastic modulus between 0.1 GPa and 10 GPa, or between 0.5 GPa and 5 GPa, or in some embodiments greater than 1 GPa. Another way to mitigate mechanical stresses caused by CTE mismatches between the tilted partial reflector and the supporting light guide body is to fabricate the light guide body from an isotropic polymer material having an elasticity between.5 GPa and 10 GPa.

[0096] The light guides of the present disclosure may use an array of partial reflectors that include stress-applying layers. One such partial reflector is shown as Figure 12 Reflector 1200 includes a polarization-selective reflector layer 1210 and a pair of stress-applying layers 1271, 1272 located on opposite sides of the polarization-selective reflector layer 1210 for applying compressive stress to the polarization-selective reflector layer 1210. The stress-applying layers 1271, 1272 may be made of a transparent isotropic material having a CTE closer to the CTE of the surrounding light guide body than the CTE of the polarization-selective reflector layer 1210. In some embodiments, the stress-applying layers 1271, 1272 have a coefficient of thermal expansion higher than that of the polarization-selective layer. For such embodiments, the stress-applying layers 1271, 1272 may be thermally laminated onto the polarization-selective reflector layer 1210 such that, upon cooling to the normal operating temperature, the polarization-selective reflector layer 1210 is under compressive stress.

[0097] As described above, the light guide body of the present disclosure may include a pair of opposing surfaces that extend parallel to each other. The surfaces need not be flat, so long as they remain parallel. Referring to the non-limiting illustrative example of Figure 13 , light guide 1300 includes a meniscus-shaped light guide body 1302 having a first curved surface 1311 and an opposing second curved surface 1312 that extend parallel to each other.

[0098] The meniscus shape may follow a simple curve or a complex curve in the XZ plane (i.e., in a cross-section including one of the length or width dimension and the thickness dimension of the light guide body 1302). As used herein, the term "simple curve" means a curve that is an easily formed curve, such as by bending a flat plate or similar simple operation. An example is a cylindrical meniscus shape. The term "complex curve" refers to a meniscus shape such as a spherical or aspherical shape.

[0099] To maintain the image-carrying characteristics of the light guide body 1302, the latter may be made of a material having a refractive index that varies along the thickness dimension of the light guide body 1302 (i.e., Figure 13 the X-axis in ). The refractive index at the bottom of the meniscus-shaped light guide body 1302 may be greater than the refractive index at the top of the meniscus-shaped light guide body 1302. In operation, image light propagates along a zigzag optical path within the light guide body 1302, which is defined by the refractive index gradient and the alternating reflections of the image light on the first surface 1311 and the second surface 1312. The partially tilted polarization-selective body reflector 1310 out-couples a portion of the image light 104 from the light guide body 1302.

[0100] Now turning to Figure 14 and further referring toFigure 2A , the light guide 1400 is similar to Figure 2A the light guide 200A and includes similar elements. Figure 14 The light guide 1400 includes a light guide body 1402 having opposite, flat and parallel first and second outer surfaces 1411 and 1412. Image light 104 is internally coupled into the light guide body 1402 through a prism internal coupler 1406. The internally coupled image light 104 propagates in the light guide body 1402 along a zigzag optical path 1408 through a series of internal reflections on the first and second surfaces 1411 and 1412. An array of polarization-selective volume reflectors 1410 externally couples a portion 105 of the image light 104 for viewing by a user. The light guide 1400 also includes a set of polarizers 1442 that are configured to polarize the image light 104 propagating along the zigzag optical path 1408 to have a first polarization state, i.e., the polarization state in which the image light 104 will be reflected by the polarization-selective volume reflectors 1410. The polarizers 1442 (e.g., linear transmission polarizers) help maintain the desired polarization of the image light 104. At least one polarizer 1442 may be provided. Ambient light 130 may be polarized by an upstream linear transmission polarizer 1428 to have a second polarization state.

[0101] Referring to Figure 15 and further referring to Figure 2A , the light guide 1500 is similar to Figure 2A the light guide 200A and includes similar elements. Figure 15 The light guide 1500 includes a light guide body 1502 having a first surface 1511 and an opposite second surface 1512 that extend parallel to each other. The light guide body 1502 may include a transparent substrate such as, for example, a glass substrate, a plastic substrate, an oxide substrate, and / or an inorganic crystal substrate. The light guide 1500 includes an input coupler (e.g., an internal coupling prism (as shown) and / or an internal coupling mirror) that is configured to couple the image light 104 into the light guide body 1502. For example, the input coupler 1506 may include a polarization element (such as a linear polarizer).

[0102] The light guide body 1502 also includes a plurality of polarization-selective tilted volume reflectors or mirrors 1510. The polarization-selective tilted volume reflectors 1510 may be parallel to each other. As shown, after being coupled into the light guide body 1502 through the input coupler 1506, the image light 104 propagates in the light guide body along a zigzag optical path 1508 through a series of total internal reflections (TIRs) on the first and second surfaces 1511 and 1512 of the light guide body.

[0103] The light guide body 1502 may further include an array of optical retarders 1580 arranged along a zigzag optical path 1508 within the light guide body 1502, and the array of optical retarders is configured to change the polarization state of the image light 104 propagating along the zigzag optical path 1508. At least some of the optical retarders 1580 may have tunable optical retardation. The optical retardation can be tuned by applying an external signal. For example, some of the optical retarders 1580 may include liquid crystals or liquid crystal (LC) cells. As shown in the figure, the LC cells 1580 may be arranged in the optical path 1508 upstream of each polarization-selective tilted volume reflector 1510, but in some embodiments, the LC cells 1580 may be arranged downstream of the corresponding polarization-selective tilted volume reflector 1510. The LC cells 1580 may include a pair of transparent electrodes configured to perform uniform polarization control over the entire LC cell 1580. As shown in the figure, the LC cells 1580 may be disposed near and / or parallel to the corresponding volume reflectors 1510 and may form a stack with the corresponding volume reflectors 1510.

[0104] The purpose of the LC cells 1580 is to control the polarization state of the image light 104 along the optical path 1508 and, correspondingly, to control the spatial distribution of the out-coupled portion 105 of the image light 105 via the polarization state of the image light 105. For example, if the polarization-selective tilted volume reflector 1510 is configured to reflect light of a first linear polarization and transmit light of a second orthogonal polarization, one or more LC cells 1580 may be tuned to convert the polarization state of the image light 104 to the first polarization state when out-coupling through one or more corresponding downstream volume reflectors 1510 is desired. By the same principle, when the corresponding volume reflector 1510 is to transmit the image light 104 through the polarization-selective tilted volume reflector 1510, one or more LC cells 1580 may be tuned to convert the polarization state of the image light 105 to the second polarization state. Of course, in an intermediate polarization state of the image light 104, a controllable portion 105 of the image light 104 may be out-coupled, and one or more LC cells 1580 may be tuned according to the desired spatial profile of the optical power distribution of the image light portion 105 to provide the desired one or more controllable portions 105 of the image light 104 that will be out-coupled from the light guide body 1502.

[0105] Refer to Figure 16, presents the reflection spectra of S1601 and P1602 of an embodiment of an inclined body reflector that can be used in an optical waveguide of the present disclosure. The S reflection spectrum 1601 is represented by a solid line, that is, the spectrum of the S-polarized image light propagating in the optical waveguide body. The P reflection spectrum 1602 is represented by a dashed line, that is, the spectrum of the P-polarized image light propagating in the optical waveguide body. The P reflection spectrum 1602 is a straight line with a reflectivity close to zero, for example, a reflectivity of <1%, or in some embodiments, <0.1%, while the S reflection spectrum 1601 has a non-zero reflectivity in the first spectral band 1611, the second spectral band 1612, and the third spectral band 1613, such that the inclined body reflector of this embodiment has polarization selectivity in those spectral bands. Outside the first spectral band 1611, the second spectral band 1612, and the third spectral band 1613, the inclined body reflectors of this embodiment are substantially transparent, that is, they substantially (i.e., within 1%) do not reflect the image light propagating in the optical waveguide body, and they substantially do not reflect external light, such that the polarization-selective inclined body reflectors are less obvious to external viewers.

[0106] In some embodiments, the first spectral band 1611, the second spectral band 1612, and the third spectral band 1613 respectively correspond to the blue 1621, green 1622, and red 1623 color channels of the image light. The bandwidths of the first spectral band 1611, the second spectral band 1612, and the third spectral band 1613 (i.e., the reflection bandwidths of the polarization-selective inclined body reflectors) can be reduced to respectively cover the spectral bandwidths of the blue 1621, green 1622, and red 1623 color channels of the image light. In some embodiments, the reflection bandwidth of the polarization-selective inclined body reflector is less than 40 nm, for example, between 5 nm and 40 nm. Such a configuration can make the polarization-selective inclined body reflector less obvious to external viewers. To provide the spectral bands, the polarization-selective inclined body reflector can include liquid crystal materials.

[0107] Now refer to Figure 17A and Figure 17B , a method 1700 for manufacturing an optical waveguide for transmitting image light in a display device of the present disclosure is given ( Figure 17A ). The method 700 includes obtaining a plurality of polymer plates, each polymer plate having a bonded reflective polarizer, such as polymer plate 1720 ( Figure 17B ), each polymer plate having a reflective polarizer 1722 bonded to the corresponding polymer plate 1720. The reflective polarizer can be solvent-bonded (1702) to the corresponding polymer plate. The polymer plates can be bonded together ( Figure 17A ; 1704) to form a stack 1730.

[0108] The stack 1730 can be cut (1706) at an acute angle along the thick dashed line 1732( Figure 17B ) to obtain an optical waveguide body including an array of polarization-selective tilted volume reflectors, each polarization-selective tilted volume reflector including one of the polymer sheets, the polymer sheet having one of the reflective polarizers bonded to the sheet. The cutting angle is determined by the tilt angle required for the polarization-selective volume reflectors within the optical waveguide. The plurality of polymer sheets 1720 can be provided, for example, by bonding a larger polarizer to a larger polymer sheet and cutting the larger polymer sheet into a plurality of polymer sheets, each polymer sheet having a bonded reflective polarizer. Then, the cut stack 1730 can be processed (1708) to polish the first and opposite second surfaces of the optical waveguide body. Then, the optical waveguide body can be assembled (1710) into an optical waveguide.

[0109] Go to Figure 18 , the pupil-copying optical waveguide 1800 can be based on any of the optical waveguides contemplated herein. As shown, the pupil-copying optical waveguide 1800 includes an optical waveguide body 1802 that supports an array of two tilted polarization-selective partial volume reflectors, a vertical array 1810V that extends along the Y-axis and is tilted about the Z-axis, and a horizontal array 1810H that extends along the X-axis and is tilted about the Y-axis. In operation, the image light 104 is internally coupled into the optical waveguide body 1802 through the internal coupler 1806. The horizontal array 1810H expands the image light 104 in the vertical dimension (i.e., along the Y-axis) to provide a horizontal image light portion 105H. The vertical array 1810V receives the horizontal image light portion 105H and expands the image light in the horizontal dimension (i.e., along the X-axis) to provide a vertical image light portion 105V. A stress-relieving filler or elastic layer can be provided for the tilted polarization-selective partial volume reflectors of the vertical array 1810V and / or the horizontal array 1810H, as explained above with reference to Figure 10 and Figure 11 . The optical waveguide body 1802 can be made of a transparent isotropic plastic or polymeric material, glass, inorganic crystal, etc. As a non-limiting example, the difference between the ordinary refractive index and the extraordinary refractive index of the plastic or polymeric material for the propagating image light can be less than 0.1, and even less than 0.01. The elastic modulus of the plastic or polymeric material can be less than 1 GPa, such as in polydimethylsiloxane (PDMS). These birefringence and elasticity ranges also apply to any other optical waveguide disclosed herein.

[0110] Now refer to Figure 19 and further refer to Figure 1A, the display device 1990 includes an image projector 1933 and an optical waveguide 1900. The image projector is configured to provide image light 1904 carrying an image in an angular field, and the optical waveguide is configured to transmit the image light 1904 carrying the image in the angular field to the oculus 1950 for viewing by the user's eyes 1980. The optical waveguide 1900 may include, for example Figures 1A to 1B optical waveguide 100 of Figure 2A optical waveguide 200A of Figure 4 , Figure 5 , Figure 6 , Figure 7 and Figure 8 optical waveguides 400, 500, 600, 700, 800 of Figure 11 , Figure 13 and Figure 14 optical waveguides 1100, 1300 and 1400 of

[0111] The image projector 1933 may be, for example, a scanned image projector that includes a laser diode coupled to a tiltable reflector (such as a microelectromechanical system (MEMS) reflector). The image projector 1933 may also be based on a microdisplay panel coupled to a collimator and / or a micro-LED display, such as, for example, a liquid crystal display or a liquid crystal on silicon (LCoS) display. The image projector 1933 (also referred to herein as the "light engine") may include a light source having a spectral bandwidth including red, green, and blue light. In the illustrated embodiment, the display device 1990 is a near-eye display device that provides image light 104 to the oculus 1950. Figure 15 As explained above, in an embodiment having a controllable optical retarder in the optical path of the image light inside the optical waveguide 1900, for example, as described above with reference to

[0112] The controller 1931 may be operatively coupled to the controllable optical retarder. In operation, the controller 1931 operates the image projector 1933 to display an image or video to the user's eyes 1980 and may attenuate the ambient light to a level where the ambient light does not overwhelm the displayed image or video.

[0113] The controller 1931 can be operatively coupled to an eye tracking system 1970 that is configured to determine an instantaneous position of a pupil 1981 of an eye 1980 within an oculus frame 1950 of a display device 1990 based on a determined position and orientation of the eye 1980. The eye tracking system 1970 can update information regarding the position of the pupil 1981 of the user's eye 1980 in real time. The controller 1931 can be configured to control an optical retarder based on information received from the eye tracking system 1970 and / or based on a current FOV portion displayed by an image projector 1933. The controller 1931 can be configured to increase an image light portion directed at the eye pupil 1981 while attenuating an image light portion 1905 of the image light that lacks the eye pupil 1981, to conserve power by better utilizing the image light 1904. By re - distributing the image light portion 1905 to primarily propagate towards the eye pupil 1981, the controller 1931 increases the light level of the image light 1904 reaching the eye pupil 1981, thereby significantly increasing the electro - optical conversion efficiency (wall plug efficiency) of the display device 1990.

[0114] Figure 20 The AR near - eye display 2000 includes a frame 2001 that supports for each eye: a light engine or image projector 2008 that is configured to provide an image beam carrying an image in an angular field; a pupil - replicated light guide 2010 based on any of the light guides disclosed herein that is configured to provide a plurality of offset portions of the image beam to spread the image across the oculus frame 2012 in the angular field; and a plurality of oculus frame illuminators 2006 that are shown as black dots that extend around an effective aperture of the pupil - replicated light guide 2010 on a surface facing the oculus frame 2012. An eye tracking camera 2004 can be provided for each oculus frame 2012.

[0115] The purpose of the eye tracking camera 2004 is to determine the position and / or orientation of the user's two eyes. The oculus frame illuminators 2006 illuminate the eyes at the corresponding oculus frames 2012, allowing the eye tracking camera 2004 to obtain an image of the eyes, and providing a reference reflection (i.e., a blink). The blink can be used as a reference point in the captured eye image that facilitates determination of the eye gaze direction by determining the position of the eye pupil image relative to the position of the blink. To avoid the light from the oculus frame illuminators 2006 distracting the user, the latter can be made to emit light that is invisible to the user. For example, infrared light can be used to illuminate the oculus frames 2012.

[0116] Go to Figure 21, the HMD 2100 is an example of an AR / VR wearable display system that surrounds the user's face for greater immersion in the AR / VR environment. The HMD 2100 can generate fully virtual 3D images. The HMD 2100 can include a front body 2102 and a strap 2104 that can be fixed around the user's head. The front body 2102 is configured to be placed in front of the user's eyes in a reliable and comfortable manner. A display system 2180 can be provided in the front body 2102 for presenting AR / VR images to the user. The display system 2180 can include any one of the display devices and illuminators disclosed herein. The side 2106 of the front body 2102 can be opaque or transparent.

[0117] In some embodiments, the front body 2102 includes a locator 2108 and an inertial measurement unit (IMU) 2110 for tracking the acceleration of the HMD 2100, and a position sensor 2112 for tracking the position of the HMD 2100. The IMU 2110 is an electronic device that generates data indicating the position of the HMD 2100 based on measurement signals received from one or more position sensors 2112, which generate one or more measurement signals in response to the movement of the HMD 2100. Examples of the position sensor 2112 include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor for detecting movement, a type of sensor for error correction of the IMU 2110, or some combination thereof. The position sensor can be located outside the IMU, inside the IMU, or some combination thereof.

[0118] The locator 2108 is tracked by an external imaging device of the virtual reality system so that the virtual reality system can track the position and orientation of the entire HMD 2100. The information generated by the IMU 2110 and the position sensor 2112 can be compared with the position and orientation obtained by tracking the locator 2108 to improve the tracking accuracy of the position and orientation of the HMD 2100. Accurate position and orientation are very important for presenting a suitable virtual scene to the user when the user moves and rotates in 3D space.

[0119] The HMD 2100 can also include a depth camera assembly (DCA) 2111 that captures data describing the depth information of a local area around part or all of the HMD 2100. To more accurately determine the position and orientation of the HMD 2100 in 3D space, the depth information can be compared with the information from the IMU 2110.

[0120] The HMD 2100 may also include an eye tracking system 2114 that is configured to determine the direction and position of the user's eyes in real time. The obtained position and direction of the eyes also allow the HMD 2100 to determine the user's gaze direction and, accordingly, adjust the images generated by the display system 2180. The determined gaze direction and vergence angle can be used to adjust the display system 2180 to reduce vergence-accommodation conflict. As disclosed herein, the direction and vergence can also be used for exit pupil control of the display. In addition, the determined vergence and gaze angle can be used to interact with the user, highlight objects, bring objects to the foreground, create additional objects or pointers, etc. An audio system may also be provided, which includes, for example, a set of small speakers built into the front body 2102.

[0121] Non-limiting illustrative embodiments of the light guides and devices of the present disclosure are provided below.

[0122] Example 1 A light guide for transmitting image light in a display device, the light guide comprising:

[0123] A light guide body including a first surface and an opposite second surface that extend parallel to each other, the light guide body configured to cause image light to propagate in a zigzag optical path within the light guide body, the zigzag optical path being defined by alternating reflections of the image light on the first and second surfaces; and

[0124] An array of polarization-selective tilted volume reflectors in the light guide body along the zigzag optical path, the array configured to outcouple light in a first polarization state while transmitting light in a second orthogonal polarization state, whereby in operation, a laterally offset polarization portion of the image light is outcoupled from the light guide body toward the oculus of the display device.

[0125] Example 2 The light guide according to Example 1, wherein the polarization-selective tilted volume reflectors of the array include at least one of: a dielectric layer stack; a cholesteric liquid crystal; or a ferroelectric nematic liquid crystal.

[0126] Example 3 The light guide according to Example 1, wherein the polarization-selective tilted volume reflectors are configured to reduce reflection of external light therefrom when the external light impinges on the first surface of the light guide body at a normal angle of incidence.

[0127] Example 4 The light guide according to Example 1, wherein each of the polarization-selective tilted volume reflectors of the array includes a wire grid polarizer.

[0128] Example 5 The light guide according to Example 1, wherein the light guide body includes:

[0129] A first light guide body portion, the first light guide body portion including a first surface of the light guide body on one side and a first ridged surface on the opposite side, the first ridged surface including a plurality of first inclined facets; and

[0130] A second light guide body portion, the second light guide body portion including a second surface of the light guide body on one side and a second ridged surface on the opposite side, the second ridged surface including a plurality of second inclined facets, wherein:

[0131] The first light guide body portion and the second light guide body portion match each other when combined together; and / or

[0132] The polarization-selective tilted body reflectors of the array of polarization-selective tilted body reflectors are sandwiched between corresponding inclined facets of a plurality of first inclined facets and a plurality of second inclined facets respectively located on the first light guide body portion and the second light guide body portion.

[0133] Example 6 The light guide according to Example 5, the light guide further comprising:

[0134] A first bonding layer, the first bonding layer being located between the polarization-selective body reflector of the array and the inclined facets of the plurality of first inclined facets;

[0135] A second bonding layer, the second bonding layer being located between the polarization-selective body reflector of the array and the inclined facets of the plurality of second inclined facets.

[0136] Example 7 The light guide according to Example 6, wherein:

[0137] At least one of the first bonding layer or the second bonding layer includes at least one of a bonding layer or a polymer layer; and / or

[0138] Wherein, at least one of the first bonding layer or the second bonding layer has a modulus of elasticity between 0.1 GPa and 10 GPa; or in some embodiments, between 0.5 GPa and 5 GPa.

[0139] Example 8 The light guide according to Example 1, wherein each of the polarization-selective tilted body reflectors of the array includes:

[0140] A polarization-selective reflective layer; and

[0141] A pair of stress-applying layers on opposite sides of the polarization-selective reflective layer for applying compressive stress thereto.

[0142] Example 9 The light guide according to Example 8, wherein:

[0143] The coefficient of thermal expansion of the stress-applying layer is higher than that of the polarization-selective reflective layer; and / or

[0144] The stress-applying layer is thermally laminated onto the polarization-selective reflection layer.

[0145] Example 10 The optical waveguide according to Example 1, wherein the first surface and the second surface are parallel to each other within 0.1 degree or better, and / or the first surface and the second surface have a roughness of less than 8 nm.

[0146] Example 11 The optical waveguide according to Example 1, wherein the optical waveguide body comprises an isotropic material having a refractive index between 1.45 and 1.85.

[0147] Example 12 The optical waveguide according to Example 1, wherein the first surface and the second surface of the optical waveguide body form a meniscus shape.

[0148] Example 13 The optical waveguide according to Example 12, wherein the meniscus shape follows a simple curve or a complex curve in a cross section including one of the length dimension or the width dimension of the optical waveguide body and the thickness dimension.

[0149] Example 14 The optical waveguide according to Example 1, further comprising an array of optical retarders along a zigzag optical path within the optical waveguide body, the array of optical retarders being configured to change the polarization state of image light propagating along the zigzag optical path.

[0150] Example 15 The optical waveguide according to Example 14, wherein the optical retarders of the array of optical retarders are tunable by applying an external signal.

[0151] Example 16 The optical waveguide according to Example 14, wherein the optical retarders of the array of optical retarders comprise liquid crystals.

[0152] Embodiments of the present disclosure may include or be implemented in conjunction with an artificial reality system. Before being presented to a user, the artificial reality system adjusts sensory information about the external world obtained through senses such as visual information, audio, touch (haptic) information, acceleration, balance, etc. in some manner. As a non-limiting example, artificial reality may include virtual reality (VR), augmented reality (AR), mixed reality (MR), hybrid reality, or some combination and / or derivative thereof. Artificial reality content may include fully generated content or content generated in combination with captured (e.g., real-world) content. Artificial reality content may include video, audio, body or haptic feedback, or some combination thereof. Any of these contents may be presented in a single channel or multiple channels, such as in a stereoscopic video that produces a three-dimensional effect for a viewer. Additionally, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof for creating content in artificial reality and / or otherwise for use in artificial reality (e.g., to perform activities therein). An artificial reality system that provides artificial reality content may be implemented on a variety of platforms, including an HMD connected to a host computer system, a stand-alone HMD, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.

[0153] The scope of the present disclosure is not limited to the specific embodiments described herein. Indeed, various other embodiments and modifications will be apparent to those of ordinary skill in the art from the foregoing description and drawings in addition to those described herein. Accordingly, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Moreover, although the present disclosure is described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be advantageously implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be interpreted in view of the full breadth of the present disclosure described herein.

Claims

1. A light guide for transmitting image light in a display device, the light guide comprising: A light guide body including a first surface and an opposite second surface extending parallel to each other, the light guide body configured to cause the image light to propagate along a zigzag optical path within the light guide body, the zigzag optical path being defined by alternating reflections of the image light on the first surface and the second surface; and An array of polarization-selective tilted volume reflectors along the zigzag optical path within the light guide body, the array configured to out-couple light in a first polarization state while transmitting light in a second orthogonal polarization state, whereby in operation, a laterally offset polarization portion of the image light is out-coupled from the light guide body towards an eyebox of the display device.

2. The optical waveguide according to claim 1, wherein, Each of the polarization-selective tilted volume reflectors of the array includes a multi-layer birefringent polymer film.

3. The optical waveguide according to claim 1 or 2, wherein The spectral bandwidth of the polarization-selective tilted volume reflector can be tuned by applying at least one of an electric field or a magnetic field, whereby the optical transmissivity of external light through the polarization-selective tilted volume reflector is variable.

4. The optical waveguide according to claim 3, wherein, The polarization-selective tilted volume reflector includes at least one of a cholesteric liquid crystal or a ferroelectric nematic liquid crystal.

5. The optical waveguide according to any one of the preceding claims, wherein, For a color channel of the image light propagating within the light guide body, the polarization-selective tilted volume reflector has a reflection bandwidth of less than 40 nm.

6. The optical waveguide according to any one of the preceding claims, wherein The polarization-selective tilted volume reflector is configured to reduce reflection of external light incident on the light guide body at an incident angle of less than 70 degrees; and / or preferably, the polarization-selective tilted volume reflectors of the array have a reflectivity range of between 4% and 80% for the image light in the first polarization and a reflectivity of less than 1% for the image light in the second orthogonal polarization.

7. The light guide according to any one of the preceding claims, wherein, The polarization-selective tilted volume reflectors of the array have a refractive index greater than 1.65; and / or preferably, the light guide further includes an elastic layer between the polarization-selective volume reflectors of the array and the light guide body.

8. The optical waveguide according to any one of the preceding claims, wherein, The light guide body includes: A first light guide body portion including the first surface of the light guide body on one side and a first ridged surface on an opposite side, the first ridged surface including a plurality of first tilted facets; and A second light guide body portion including the second surface of the light guide body on one side and a second ridged surface on an opposite side, the second ridged surface including a plurality of second tilted facets, wherein: The first light guide body portion and the second light guide body portion match each other when combined; The polarization-selective tilted volume reflectors of the array of polarization-selective tilted volume reflectors are sandwiched between corresponding tilted facets of the plurality of first tilted facets and the plurality of second tilted facets respectively located on the first light guide body portion and the second light guide body portion; and / or preferably, the light guide body further includes: A first adhesive layer located between the polarization-selective volume reflectors of the array and the tilted facets of the plurality of first tilted facets; A second adhesive layer, the second adhesive layer being located between the polarization-selective volume reflector of the array and the inclined facets of the plurality of second inclined facets.

9. The optical waveguide according to any one of the preceding claims, wherein, The light guide body includes a polymer material that maintains the polarization state of the image light propagating therein.

10. The optical waveguide according to claim 9, wherein, For the propagating image light, the difference between the ordinary refractive index and the extraordinary refractive index of the polymer material is less than 0.1; and / or preferably, wherein the polymer material has an elastic modulus of less than 1 GPa.

11. The optical waveguide according to any one of the preceding claims, wherein, The light guide body includes a polarizer that polarizes the image light propagating along the zigzag optical path to have a first polarization state.

12. A method for manufacturing a light guide for transmitting image light in a display device, the method comprising: Obtaining a plurality of polymer plates, each polymer plate having a reflective polarizer bonded thereto; Bonding the polymer plates together to form a stack; And Cutting the stack at an acute angle to obtain a light guide body including an array of polarization-selective inclined volume reflectors, each polarization-selective inclined volume reflector including one of the polymer plates having one of the reflective polarizers bonded thereto.

13. The method according to claim 12, wherein, The method further includes polishing a first surface and an opposite second surface of the light guide body, and assembling the light guide body into the light guide.

14. A display device, the display device comprising: A light engine configured to provide image light carrying an image in an angular domain; And A light guide configured to expand the image light above the oculus of the display device, the light guide including: A light guide body including a first surface and an opposite second surface extending parallel to each other, the light guide body configured to cause the image light to propagate along a zigzag optical path within the light guide body, the zigzag optical path being defined by alternating reflections of the image light on the first surface and the second surface; and An array of polarization-selective inclined volume reflectors along the zigzag optical path within the light guide body, the array configured to out-couple light in a first polarization state while transmitting light in a second orthogonal polarization state, whereby in operation, a laterally offset polarized portion of the image light is out-coupled from the light guide body towards the oculus of the display device.

15. The display device according to claim 14, the display device further including a transmissive polarizer coupled to the first surface of the light guide body for polarizing incident ambient light to have the second polarization state; and / or preferably, wherein the light engine is configured to emit the polarized light and includes at least one of the following: a liquid crystal display, a micro-LED display, a liquid crystal on silicon (LCoS) display, or a laser diode coupled to a tiltable reflector.

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