Light guide integrated image projector for display

Abstract

An image projector integrated with a light guide 10 has a reflective or catadioptric lens 150 disposed on a surface 11 of the light guide itself or on a prism surface parallel to or coplanar with the surface of the light guide 10. In some cases, a polarizing beam splitter 158 deflects light reflected from the collimating lens, thereby coupling collimated image light directly into the light guide 10 for propagation within the light guide. In some cases, the collimating lens 150 is associated with the surface of the light guide or prism via an internal reflection-maintaining interface 154, such that at least a portion of the image light coupled into the light guide is reflected at the internal reflection-maintaining interface 154.

Description

[Technical Field]

[0001] The present invention relates to near-eye displays, and in particular to a light guide-integrated image projector for injecting images into a light guide of an augmented reality display. [Background technology]

[0002] Near-eye augmented reality displays typically use an image projector to inject a collimated image into a light guide that transmits the image to the user's eye while simultaneously allowing a view of the real world through the light guide. The image is coupled out of the light guide towards the user's eye by an output coupling arrangement, which may be a set of partially reflective, obliquely angled internal surfaces within the light guide or a diffractive optical element.

[0003] To provide a uniform image, it is typically preferred that the injected image should fill the thickness of the light guide. This requirement, together with the angular field of view (FOV) of the image and the distance of the collimating optics from the light guide entrance hole, determines the minimum size of the collimating optics needed to collimate the image prior to injection into the light guide. Summary of the Invention

[0004] The present invention is a light guide integrated image projector for injecting images into a light guide of an augmented reality display.

[0005] According to the teachings of one embodiment of the present invention, there is provided a display comprising: (a) a light guide formed from a transparent material having a first pair of mutually parallel major surfaces, the light guide supporting propagation of image light by internal reflection at the first pair of major surfaces; (b) an image generator for generating an image at an image plane; (c) a collimating optical arrangement including a reflective lens and an associated quarter-wave phase plate; and (d) a polarizing beam splitter (PBS), wherein the reflective lens is associated with one of the first pair of major surfaces or a surface of a prism parallel to or coplanar with one of the first pair of major surfaces via an internal reflection-maintaining interface, and the PBS is arranged such that image light from the image plane is coupled through the PBS to propagate within the light guide by internal reflection at the first pair of major surfaces, pass through the PBS, impinge on the reflective lens, be collimated by the reflective lens, and be reflected by the PBS, and at least a portion of the image light is reflected at the internal reflection-maintaining interface.

[0006] According to a further feature of an embodiment of the present invention, the normal to the PBS forms an angle of less than 45 degrees with the normal to the internal reflection-maintaining interface.

[0007] According to a further feature of an embodiment of the invention, the PBS is incorporated into a prism that is optically bonded to a light guide, the light guide having a thickness dimension in a direction perpendicular to the first pair of major surfaces, and the PBS occupies a thickness of the prism in the direction perpendicular to the first pair of major surfaces that is greater than the thickness dimension of the light guide.

[0008] According to a further feature of an embodiment of the invention, the optical element further comprises a second pair of mutually parallel major surfaces perpendicular to the first pair of major surfaces, the first and second pairs of major surfaces supporting propagation of the image light by four internal reflections at the first and second pairs of major surfaces.

[0009] According to a further feature of an embodiment of the present invention, the normal to the PBS is non-parallel to both of the first and second pairs of major surfaces.

[0010] According to a further feature of an embodiment of the present invention, the reflective lens has an optical axis that is non-parallel to both the first and second pairs of major surfaces.

[0011] According to a further feature of an embodiment of the invention, the prism comprises a first surface parallel to or coplanar with one of the first pair of major surfaces and a second surface parallel to or coplanar with one of the second pair of major surfaces, the first surface being provided with an internal reflection-maintaining interface.

[0012] According to a further feature of an embodiment of the invention, the PBS is incorporated into a prism optically bonded to a light guide, the light guide having a first thickness dimension in a direction perpendicular to a first pair of major surfaces and a second thickness dimension in a direction perpendicular to a second pair of major surfaces, and the PBS occupies a thickness of the prism in the direction perpendicular to the first pair of major surfaces that is greater than the first thickness dimension and a thickness of the prism in the direction perpendicular to the second pair of major surfaces that is greater than the second thickness dimension.

[0013] According to a further feature of an embodiment of the present invention, the internal reflection-maintaining interface is implemented as a layer of material having a refractive index lower than that of the light guide.

[0014] According to a further feature of an embodiment of the present invention, the internal reflection-maintaining interface incorporates an air gap.

[0015] According to further features of embodiments of the present invention, the internal reflection-maintaining interface is implemented as a multilayer dielectric coating configured to be substantially transparent to visible light within a first range of angles of incidence and reflective to visible light within a second range of angles of incidence, the second range being at a higher angle relative to the normal to the interface than the first range.

[0016] According to a further feature of an embodiment of the present invention, there is also provided a light-absorbing boundary disposed along at least two edges of the PBS so as to define an optical hole for the collimated image.

[0017] According to a further feature of an embodiment of the invention, the PBS is incorporated into a prism that is optically bonded to the light guide, and the image generator comprises an illumination arrangement for directing illumination from the illumination aperture through the prism to the image plane, wherein a first portion of the illumination undergoes an odd number of reflections from the illumination aperture to the image plane, and a second portion of the illumination undergoes an even number of reflections from the illumination aperture to the image plane.

[0018] According to a further feature of an embodiment of the present invention, a light guide is between the image plane and the reflecting lens.

[0019] According to a further feature of an embodiment of the invention, a PBS is between the first pair of major surfaces of the light guide.

[0020] According to a further feature of an embodiment of the invention, the collimating optical arrangement is a polarized catadioptric collimating arrangement in which the reflective lens has a partially reflective surface, the image plane is positioned to deliver image light by transmission through the partially reflective surface, and the image light is reflected back towards the partially reflective surface.

[0021] In accordance with the teachings of one embodiment of the present invention, a display is provided, comprising: (a) a light guide formed from a transparent material having a first major surface and a second major surface parallel to the first major surface, the light guide supporting propagation of image light by internal reflection at the first and second major surfaces; (b) an image generator for generating an image at an image plane; and (c) a polarizing catadioptric collimating and in-coupling arrangement, the polarizing catadioptric collimating and in-coupling arrangement including: (i) a non-planar partially reflective first reflector associated with the first major surface of the light guide; (ii) a second reflector associated with the second major surface of the light guide in facing relationship to the partial reflector; and (iii) a planar third reflector angled obliquely relative to the major surfaces. wherein one of the second reflector and the third reflector is a total reflector and another of the second reflector and the third reflector is a polarization-selective reflector interposed between the total reflector and the first reflector, and the polarizing catadioptric collimating and in-coupling arrangement further comprises at least one phase plate interposed between the polarization-selective reflector and the first reflector, whereby image light from the image plane is in-coupled and propagates within the light guide by internal reflection, partially transmitted through the partially reflective first reflector acting as a refractive lens, traversing at least a portion of the thickness of the light guide, reflected by the second reflector, partially reflected by the partially reflective first reflector acting as a reflective lens, and reflected by the third reflector, thereby providing a display.

[0022] According to a further feature of an embodiment of the invention, the second reflector is a total reflector and the third reflector is a polarization-selective reflector disposed within the thickness of the light guide.

[0023] According to a further feature of an embodiment of the invention, the second reflector is a polarization-selective reflector and the third reflector is a total reflector associated with a prism outside the thickness of the light guide.

[0024] According to a further feature of an embodiment of the invention, the second reflector is a planar reflector.

[0025] According to the teachings of one embodiment of the present invention, there is provided a projector for a display comprising: (a) a reflective spatial light modulator (SLM) for modulating the polarization of light reflected from an image plane; (b) an illumination source that outputs illumination from an illumination aperture; (c) a collimating optical arrangement including at least one lens; and (d) a prism that includes a polarizing beam splitter (PBS), wherein the PBS is arranged to reflect the illumination from the illumination aperture towards the SLM and allow light corresponding to an image reflected from the SLM to pass through the PBS and reach the collimating optical arrangement, and a surface of the prism adjacent to the SLM is provided with an internal reflection-maintaining interface, and a portion of the illumination from the illumination aperture is reflected at the interface such that a first portion of the illumination from the illumination aperture undergoes an odd number of reflections from the illumination aperture to the SLM and a second portion of the illumination undergoes an even number of reflections from the illumination aperture to the SLM, and is then reflected from the PBS before entering the SLM. [Brief explanation of the drawings]

[0026] The invention is herein described, by way of example only, with reference to the accompanying drawings.

[0027] [Figure 1A] FIG. 1 is a schematic side view of a light guide-integrated projector for injecting an image into a light guide of an augmented reality display constructed and operative in accordance with one embodiment of the present invention, using a polarized catadioptric collimating arrangement; [Figure 1B] FIG. 1 is a schematic side view of a light guide-integrated projector for injecting an image into a light guide of an augmented reality display constructed and operative in accordance with one embodiment of the present invention, using an alternative polarized catadioptric collimation arrangement. [Figure 1C] FIG. 1C is a schematic side view similar to FIG. 1B, showing an embodiment using a reflective spatial light modulator for image generation. [Figure 1D]1B is a schematic side view similar to FIG. 1A illustrating the use of multiple light guide-integrated projectors to inject images of different colors. [Figure 2A] 2A-2C are schematic side views of a light guide-integrated projector for injecting an image into a light guide of an augmented reality display constructed and operative in accordance with an embodiment of the present invention, using a reflective collimating arrangement and a polarizing beam splitter located within the light guide, within a prism adjacent to the light guide, and within a prism above the light guide, respectively. [Figure 2B] 2A-2C are schematic side views of a light guide-integrated projector for injecting an image into a light guide of an augmented reality display constructed and operative in accordance with an embodiment of the present invention, using a reflective collimating arrangement and a polarizing beam splitter located within the light guide, within a prism adjacent to the light guide, and within a prism above the light guide, respectively. [Figure 2C] 2A-2C are schematic side views of a light guide-integrated projector for injecting an image into a light guide of an augmented reality display constructed and operative in accordance with an embodiment of the present invention, using a reflective collimating arrangement and a polarizing beam splitter located within the light guide, within a prism adjacent to the light guide, and within a prism above the light guide, respectively. [Figure 2D] FIG. 2D is a schematic side view similar to FIG. 2C illustrating the use of multiple light guide-integrated projectors to inject images of different colors. [Figure 2E] 2C is a schematic side view illustrating an alternative structure of the light guide-integrated projector of FIG. 2B. [Figure 3A] FIG. 2C is an isometric view of a light guide arrangement corresponding to FIG. 2B implemented using a rectangular light guide. [Figure 3B] FIG. 3B is a view similar to FIG. 3A illustrating the placement of a polarizing beam splitter at an oblique angle relative to both axes of the rectangular light guide. [Figure 3C] FIG. 3C is a view similar to FIG. 3B, but with the polarizing beam splitter replaced by a reflector. [Figure 3D] 3D and 3E are similar to FIGS. 3B and 3C, respectively, with the polarizing beam splitter or reflector reduced in size to fit within the dimensions of a rectangular light guide. [Figure 3E] 3D and 3E are similar to FIGS. 3B and 3C, respectively, with the polarizing beam splitter or reflector reduced in size to fit within the dimensions of a rectangular light guide. [Figure 3F] FIG. 3B is a view similar to FIG. 3A illustrating additional components of the projector arranged to create a tilted optical axis. [Figure 4A] 2C is a side view of a light guide-integrated projector generally similar to FIG. 2B illustrating an arrangement for flood illumination of a reflective spatial light modulator. [Figure 4B] 4B is a side view similar to FIG. 4A illustrating an arrangement for scanned laser illumination of a reflective spatial light modulator. [Figure 5A] 5A and 5B are side and isometric views, respectively, of a light guide-integrated projector similar to FIG. 4A, illustrating various arrangements for spatial filtering of the projected image. [Figure 5B] 5A and 5B are side and isometric views, respectively, of a light guide-integrated projector similar to FIG. 4A, illustrating various arrangements for spatial filtering of the projected image. [Figure 6A] 6A and 6B are side views similar to FIGS. 2B and 2C, respectively, illustrating polarization control options for achieving plane polarization of the image entering the light guide. [Figure 6B] 6A and 6B are side views similar to FIGS. 2B and 2C, respectively, illustrating polarization control options for achieving plane polarization of the image entering the light guide. [Figure 6C] 6C and 6D are side views similar to FIGS. 2B and 2C, respectively, illustrating polarization control options for achieving circular polarization of the image entering the light guide. [Figure 6D]6C and 6D are side views similar to FIGS. 2B and 2C, respectively, illustrating polarization control options for achieving circular polarization of the image entering the light guide. [Figure 7A] 7A and 7B are side and top views of a further embodiment of a light guide-integrated projector for injecting an image into a light guide of an augmented reality display constructed and operative in accordance with an embodiment of the present invention, further illustrating an illumination light path that uses a rectangular light guide and undergoes total internal reflection. [Figure 7B] 7A and 7B are side and top views of a further embodiment of a light guide-integrated projector for injecting an image into a light guide of an augmented reality display constructed and operative in accordance with an embodiment of the present invention, further illustrating an illumination light path that uses a rectangular light guide and undergoes total internal reflection. [Figure 7C] 7B is a view similar to FIG. 7A illustrating ray paths corresponding to additional image points not shown in FIG. 7A. [Figure 7D] FIG. 7B is an isometric view of the light guide-integrated projector of FIG. 7A. [Figure 8A] 8A and 8B are schematic side views illustrating design considerations in the illumination arrangement of a reflective spatial light modulator. [Figure 8B] 8A and 8B are schematic side views illustrating design considerations in the illumination arrangement of a reflective spatial light modulator. [Figure 8C] 10 is a schematic side view illustrating a preferred embodiment of an illumination arrangement for a reflective spatial light modulator according to a further aspect of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention is a light guide integrated image projector for injecting images into a light guide of an augmented reality display.

[0029] The principles and operation of a display according to the present invention may be better understood with reference to the drawings and accompanying descriptions.

[0030] By way of preamble, the present invention provides several different configurations in which an image projector is integrated with a light guide in such a manner as to place at least a portion of the collimating optics particularly close to the bore of the light guide, thereby providing a particularly compact projector configuration. In some cases, a reflective or catadioptric lens is disposed on the surface of the light guide itself, while in other cases, the lens is disposed on a prism surface that is parallel to or coplanar with the surface of the light guide. In some cases, a polarizing beam splitter (PBS) deflects light reflected from the collimating lens, thereby coupling the collimated image light directly into the light guide, thereby propagating within the light guide. In some cases, the collimating lens is associated with the surface of the light guide or prism via an internal reflection-maintaining interface, such that at least a portion of the image light coupled into the light guide is reflected at the internal reflection-maintaining interface. Examples of each of these features are illustrated below.

[0031] Referring now to the drawings, Figures 1A-1D schematically illustrate several light guide integrated projectors that use polarized catadioptric collimating optics associated with the major surfaces of the light guide for use in a display.

[0032] Specifically, these examples show a light guide 10 formed from a transparent material having first and second major surfaces 11 and 12 that are parallel and support propagation of image light within the light guide by internal reflection at major surfaces 11 and 12. Continuation of the light guide and output coupling arrangement has been omitted for ease of presentation.

[0033] The image generator generates an image at an image plane and may be an active matrix image generator 4, a reflective or transmissive spatial light modulator (SLM) such as an LCOS chip 166, a digital light processor, or any other desired image generator.

[0034] The device further includes a polarizing catadioptric collimating and in-coupling arrangement including: 1. A lens 150 having a non-planar surface providing a partially reflective first reflector 152, the base of the lens being associated with the first major surface 11 of the light guide 10; 2. a second reflector, typically but not necessarily planar, associated with the second major surface 12 of the light guide 10 in facing relationship to the first reflector 152; and 3. A planar third reflector angled obliquely relative to the major surface.

[0035] One of the second reflector and the third reflector is a total reflector, and the other of the second reflector and the third reflector is a polarization-selective reflector interposed between the total reflector and the first reflector. At least one phase plate 156 is interposed between the polarization-selective reflector and the first reflector, such that image light from the image plane is coupled in and propagates within the light guide 10 by internal reflection, partially transmitted through the partially reflective first reflector 152 acting as a refractive lens, traverses at least a portion of the thickness of the light guide 10, is reflected by the second reflector, partially reflected by the partially reflective first reflector 152 acting as a reflective lens, and is reflected by the third reflector.

[0036] 1A and 1D, the second reflector is a polarization-selective reflector 158, and the third reflector is a total reflector 8 associated with a prism 9 outside the thickness of the light guide 10. In FIGS. 16B and 16C, the second reflector is a total reflector 8, and the third reflector is a polarization-selective reflector 158. In the case illustrated here, the polarization-selective reflector is disposed within the thickness of the light guide. In the latter case, it is also possible to mount the total reflector 8 on a plane external to and parallel to the plane of surface 12, in which case the polarization-selective reflector 158 can also extend outside the thickness of the light guide, as long as it does not extend beyond the plane of the total reflector.

[0037] More specifically, in FIG. 1A , image source 4 (e.g., a micro LED or OLED) transmits light onto lens 150. The light passes through a partially transmitting curved surface (first partial reflector) 152 and through an internal reflection-preserving interface 154, such as a layer of low refractive index material or an air gap, before entering light guide 10. After traversing the light guide, the beam passes through wave plate 156 (which may alternatively be located above interface 154) and is reflected by polarizer reflector 158. The reflected beam passes through interface 154 and is partially back-reflected by first reflector 152. The reflected beam passes through light guide 10 a second time and, after second-pass wave plate 156, passes through polarizer reflector 158, with the orthogonal polarization as reflected by reflector 152. The beam maintains its polarization and thus passes through polarizer reflector 158 and is guided by light guide 10. The portion of the beam that impinges on interface 154 undergoes total internal reflection.

[0038] 1B shows a more compact architecture in which a polarizer reflector 158, also referred to as a polarizing beam splitter (PBS), is positioned at an angle within the light guide 10. The beam entering the light guide is linearly polarized (orthogonal to the beam entering FIG. 1A) and therefore passes through the PBS 158 to be reflected from reflector 8. The beam passes through the PBS 158, interface 154, and wave plate 156 and is partially back-reflected by the first reflector 152. After the second pass wave plate 156, the beam is orthogonally polarized and therefore reflected by the PBS 158 to be in-coupled and guided within the light guide 10.

[0039] 1C shows a variant embodiment similar to FIG. 1B but using an LCOS image projector. Similar variants can also be implemented based on FIG. 1A. Light from a light source 160 (which may be, for example, LED illumination or a scanning laser beam) is reflected by a focusing reflective lens 164 onto a PBS surface 162, illuminating an LCOS matrix 166. The light modulated by the LCOS passes through the PBS 162, enters the lens 150, and then follows the same sequence as described above in the context of FIG. 1B.

[0040] Configurations such as that of Figure 1A can be combined in sequence with dichroic coatings adjacent to wave plates 156 along the light guide 10, as shown in Figure 1D, where 190A represents the dichroic surface, allowing for sequential in-coupling of different color images along the light guide.

[0041] 1B and 1C illustrate a particularly compact in-coupling arrangement in which a PBS located near a reflecting lens is used to couple into a light guide in a collimated image, and an internal reflection-preserving interface allows image light to be guided at an interface below the reflecting lens. This approach is not limited to the catadioptric optical arrangements of these examples and is illustrated below with reference to alternative optical arrangements using reflecting-only lenses.

[0042] 2A-2E, which illustrate a portion of a display including a light guide 10 formed from a transparent material having a first pair of parallel major surfaces 11, 12 for supporting propagation of image light by internal reflection, and an image generator for generating an image at an image plane 4. The device also includes a collimating optical arrangement including a reflective lens 150 and associated quarter-wave retarder 156, and a polarizing beam splitter (PBS) 158. The reflective lens 150 is associated with one of the major surfaces 12, or surface 112, of a prism 161, which is parallel to or coplanar with major surface 12 via an internal reflection-preserving interface 154 that maintains or simulates a total internal reflection (TIR) ​​condition. PBS 158 is arranged so that image light from image plane 4 is coupled into and propagates within light guide 10 by internal reflection at major surfaces 11 and 12, passes through PBS 158, impinges on reflective lens 150, is collimated by the reflective lens, and is then reflected by PBS 158. At least a portion of the image light is reflected at internal reflection-preserving interface 154.

[0043] More specifically, FIG. 2A illustrates an image source 4 (e.g., an OLED, microLED, or LCOS) arranged to transmit image light through the major surface 11 of the light guide 10, through interface 154, through PBS 158 (polarized for transmission, preferably P), through quarter-wave plate 156, and onto reflective lens 150. In this case, the outer surface of lens 150 is highly reflective (preferably at least 95%, typically close to 100%), acting as a reflective collimating lens. This reflected light passes through quarter-wave plate 156 and interface 154 again. Here, because the polarization is orthogonal (preferably S) to the initial polarization introduced, it is reflected by PBS 158 into the range of angles guided by light guide 10. Internal reflection-preserving interface 154 ensures internal reflection of the angled reflected light, thereby achieving efficient in-coupling. The angle of PBS 158 is chosen according to the desired range of angles over which the image light should propagate within the light guide. The PBS typically forms an angle of less than 45 degrees with the major surfaces and the Internal Reflection-Maintaining Interface, and in certain preferred embodiments may be at an angle of about 25 to 40 degrees with the major surfaces / interfaces. When referring to an angle between two planes or surfaces herein, this may be defined as the angle between the normal to the first surface and the normal to the second surface.

[0044] 2A is particularly compact because the light guide 10 is located between the image plane 4 and the reflecting lens 150, and additionally because the PBS 158 is located between the major surfaces 11 and 12, which are entirely contained within the thickness of the light guide 10. This compactness may come at the expense of some lack of uniformity due to incomplete "filling" of the light guide thickness at all fields of view of the image. This can be remedied by the use of uniformity-enhancing arrangements such as "mixer" partial reflectors located within the light guide parallel to the major surfaces, and most preferably a 50% reflector located at the center plane of the light guide.

[0045] 2B depicts an architecture that more uniformly illuminates the light guide. To this end, PBS 158 extends beyond the plane of light guide 10. Structurally, PBS 158 is now incorporated into a prism 161 that is optically bonded to light guide 10. PBS 158 occupies the thickness of the prism perpendicular to major surfaces 11, 12, which is greater than the thickness dimension of light guide 10 perpendicular to major surfaces 11, 12.

[0046] If the light guide 10 is a rectangular cross-section light guide that directs light by reflection at two orthogonal sets of major surfaces, the PBS 158 should extend beyond both dimensions of the light guide, as illustrated below with reference to Figures 3A-3C and 3F.

[0047] Figure 2C shows a simplified configuration in which a light guide 10 is included in the path of the projector optics. Here, a PBS prism 163 is placed on top of the light guide 10, and the reflecting lens 150 and associated components are implemented as in Figure 2A. Although the focal length in such a system is longer than in Figure 2B, integration of such a system is simpler. This configuration can achieve uniform light guide illumination by appropriately choosing the length of the PBS 158.

[0048] FIG. 2D shows a cascade configuration based on the structure of FIG. 2C, where image sources 4a and 4b are of different wavelengths (colors) and surface 190a is a dichroic coating.

[0049] 2E shows another embodiment for integrating a PBS prism onto a light guide 10. Here, the light guide 10 is polished to create a flat surface 159. This flat surface serves as a reference base for a PBS prism 161a. This prism is placed on top to create a flat surface on which the PBS 158 is positioned, and another prism 161b is added to support the image generator 4. The resulting structure is optically equivalent to the structure of FIG. 2B.

[0050] As illustrated generally by the thick arrow 160 in Figures 2B and 2E, or shown in more detail with reference to Figure 1C, each of the above configurations can be implemented using an LCOS image generator in which illumination is injected from a side illumination source.

[0051] As previously mentioned, embodiments of the present invention can be implemented to inject image light into a "rectangular light guide," i.e., a light guide having a first pair of mutually parallel major surfaces 11, 12 and a second pair of mutually parallel major surfaces 13, 14 (see FIG. 3A ) that are perpendicular to the first pair of major surfaces. Such a light guide supports propagation of the image light by four internal reflections at the first and second pairs of major surfaces. Such a rectangular light guide is typically used as the first dimension of an optical aperture extension in combination with a slab-type light guide (having only one pair of major surfaces) that delivers image light to the user's eye. Suitable configurations for combining a rectangular light guide with a second light guide are disclosed in applicant's patent publications US10133070B2 and WO2023 / 131959A1.

[0052] Image light introduced into a rectangular light guide should be injected in a direction oblique to both axes of the light guide. This can be achieved by using a "twisted" tilt of the PBS, where the normal to the PBS is non-parallel to both pairs of major surfaces, and / or by tilting the optical element so that the reflecting lens has an optical axis non-parallel to both pairs of major surfaces. These options are illustrated with reference to Figures 3A-3F. Rectangular light guide embodiments relate to each of the variations illustrated in Figures 2A-2E.

[0053] FIG. 3A shows a schematic isometric view of FIG. 2B, where surface 158 is within prism 161. This configuration is suitable when light guide 10 is a slab light guide having only two reflective outer surfaces (top and bottom). When used with a rectangular light guide, it can be seen that the normal to the PBS is parallel to the second pair of major surfaces 13, 14. Tilting of the image light can be achieved using suitable tilting of optical elements (not shown), as illustrated in FIG. 3F.

[0054] Figure 3B shows coupling into a rectangular light guide 10. Here, the PBS surface 158T is tilted in both dimensions, which facilitates correct tilting of the reflected beam to in-couple, propagate through four reflections, and completely fill the light guide 10 with all four images. Figure 3C shows the PBS surface 158M as an external reflector for an embodiment similar to that of Figure 1A, i.e., an embodiment in which image light is injected from below (in the orientation illustrated here).

[0055] 3A-3C, the PBS is incorporated into a prism 161 optically bonded to the light guide, with the PBS occupying a thickness of the prism that is greater than the thickness of the light guide in both lateral dimensions. This allows the image light to fill the light guide with all four times the image. Additionally, to couple light reflected from the PBS to provide all four times the image at the entrance to the light guide, prism 161 provides two surfaces that are parallel to, and most preferably coplanar with, two adjacent surfaces of the rectangular light guide, which act as a continuation of those surfaces for coupling purposes.

[0056] A more compact prism size can be achieved by implementing the PBSs shown in Figures 3D and 3E, which are equivalent to prisms 2A and 1A, respectively. These configurations do not fill the light guide with all of the image and its reflections, but subsequent filling can be achieved using mixer elements as described above.

[0057] 3F expands on FIG. 3A, showing PBS 158 at a right angle to one of the pair of major surfaces of the rectangular light guide. To achieve the range of tilt angles required to inject image light into the rectangular light guide, the plane of image generator 4 and the plane of collimating lens 150 are tilted, thereby creating the tilted principle optical axis required for injection into light guide entrance 170.

[0058] 3A-3F, where the optical axis and / or PBS has a tilt in two directions relative to the light guide and prism axes, the required polarization orientation is determined according to how the propagating beam encounters the PBS and does not correspond to the axis of the light guide. In certain cases, polarization rotation is required before the light enters the light guide. For this purpose, a wave plate or polarizer can be introduced at the entrance 170 to the light guide.

[0059] As noted above, all of the embodiments described herein can be implemented with any suitable image generator. Structurally, if the image generator is a micro LED array disposed at image plane 4, no additional structure may be required to complete the optical arrangement. The supporting electronics (such as power supplies, data storage and processing components, and controllers) required to operate all embodiments are well known to those skilled in the art and are not shown herein.

[0060] If the image generator is a reflective spatial light modulator (SLM), such as a liquid crystal on silicon (LCOS) chip, additional optics are required to direct illumination, such as from an LED or laser, to illuminate the LCOS at image plane 4. As an example, FIG. 4A illustrates an LED 200 illuminating an LCOS at plane 4. Light from the LED is expanded within a light guide 202, and optionally, a diffuser 204 is introduced at the end of the light guide. A reflector 206 reflects the light onto a PBS. Optionally, further beam collimation is performed by a Fresnel lens 208 placed just before the PBS.

[0061] In FIG. 4B, laser 220 illuminates a pair of scanning mirrors 222A and 222B (one or both of which are driven in a scanning motion by suitable drive components not shown) through Fresnel lens 208 onto PBS 158 and LCOS 4.

[0062] A further aspect of the invention relates to spatial filtering of the image light injected into the light guide. Scattered light within the projector can reduce image contrast, and large beam divergence can reduce resolution due to aberrations. Spatial filters (holes) can be implemented to block this scattered light and limit the beam numerical aperture (divergence) to a nominal value.

[0063] 5A and 5B show various spatial filtering configurations that may be implemented in any of the embodiments described herein. Any combination of filters is possible. As one non-limiting example, the configurations shown herein are illustrated in the context of the design described above with reference to FIG. 2C.

[0064] 5A shows that the entrance to the light guide 10 includes an edge 250 that performs vertical spatial filtering of the light entering the light guide. Preferably, the prismatic surface 252 is coated with an absorptive coating to prevent scattering of the light striking the surface, thereby enhancing the vertical filtering effect.

[0065] In this configuration, beam 254 is the lowest beam reflected into the light guide from surface 256. This reflection is close to edge 258 of reflecting lens 150. By making surface 258 an absorber, efficient trimming of the excess beam is achieved.

[0066] In a preferred embodiment, the three sets of beams (illuminating 260, diverging 262, and collimating 264) impinging on the PBS 158 impinge on the same overlapping region of 158, as shown in FIG. 5A. Therefore, in accordance with a further feature of the present invention, an efficient spatial filter (hole) can be implemented in the plane of this PBS. Arrow 266 indicates the aperture of this spatial filter, while absorber 268 is located around its periphery. FIG. 5B is an isometric view showing that the spatial filter in the PBS plane also has a lateral width 270, where absorber 268 is positioned around the aperture of the PBS 158. For clarity and simplicity of presentation, FIG. 5B omits 252 and additional portions of the prisms that provide the illumination arrangement optics.

[0067] FIG. 5B also illustrates further options for spatial filtering in the in-plane direction of the light guide, which may be used in addition to or instead of holes in the plane of the PBS. Lateral holes 274 may be created at location 250 by eliminating TIR associated with beams diverging outside of the holes. Elements 272 (shown only in FIG. 5B and omitted from FIG. 5A for clarity) are attached to surface 256, thereby spatially selectively eliminating TIR on this plane. Beams within the light guide 10 that impinge on these elements 272 are either outcoupled or absorbed. The shape of elements 272 allows for the guidance and transmission of the image beam through lateral holes 274 and vertical holes 250. Elements 272 may be located on the opposite (top) side of the light guide 10, or on both sides. The shape of elements 272 illustrated here is one non-limiting example; shorter or longer shaped elements, or elements of different shapes, may be used. Furthermore, in certain cases, such as when separate projectors are deployed to inject images of different colors, the elements may be configured to selectively absorb only one color. This shape may also extend beyond the aperture 274, providing additional image beam steering.

[0068] Figures 6A-6D illustrate options for polarization management in the configurations described in Figures 2A-2E. As an example, the configuration of Figure 2B is the basis for Figures 6A and 6C, and Figure 2C is the basis for Figures 6B and 6D. Herein, polarization orientation is defined relative to the PBS 158, with double-headed arrows across the beam representing P-polarized light and black dots representing S-polarized light. Circularly polarized light is represented as a curved arrow with the same direction indicated for the reflected circularly polarized light for clarity.

[0069] The example shown here illustrates the normal operation of the PBS 158, which is optimally to reflect S-polarized light and transmit P-polarized light. However, it will be understood that this is by way of example only, and that embodiments are not limited to this option, as some polarizers can operate in other directions (e.g., wire grid polarizers).

[0070] In FIG. 6A, P-pol light from the LCOS4 passes through PBS 158 and subsequently through quarter-wave retarder (QW) 156, thereby generating circularly polarized light. (Note that the terms "retarder," "phase plate," and "wave plate" are used interchangeably herein.) Lens 150 reflects the circularly polarized light to pass through QW 156 a second time, thereby generating S-pol light that reflects from PBS 158. If the requirement is to inject S-pol light into light guide 10, no further elements are required. However, if P-pol light is required, then a half-wave retarder (HW) is implemented on surface 300. If unpolarized light is required, a birefringent depolarizing agent can be introduced into this surface.

[0071] Introducing elements into plane 300 can cause scattering at the interface. To remedy this problem, it is possible to implement prism 161, slightly enlarged and shifted by step 302, so that light scattered from the edge does not enter light guide 10. The surface of prism 161 formed by internal reflection-preserving interface 154 must still be parallel to the surface of the light guide, as it is responsible for the in-coupling of image light reflected by PBS 158.

[0072] The half-wave retarder may alternatively be implemented on the plane 159 or adjacent to (and below) the PBS 158. In such cases, the polarization progression is equivalent to that described below for FIG. 6B.

[0073] In Figure 6B, a half-wave phase plate is placed on surface 304, which is part of one of the main light guide surfaces. The P-pol polarization passing through PBS 158 is rotated to S-pol polarization after 304. The beam polarization is rotated to P-pol polarization after reflection from 150 and passes through QW 154 a second time. After passing through 304 again, the beam is S-pol polarization and is therefore reflected by PBS 158. The third pass 304, if necessary, rotates the beam to P-pol polarization as it enters light guide 10. In this configuration, S-pol injection into light guide 10 is simply achieved by omitting the HW from surface 304.

[0074] 6C and 6D illustrate configurations for injecting circularly polarized light into light guide 10. In FIG. 6C, QW 156B is placed at some distance from PBS 158 or adjacent to PBS 158 (and not next to interface 154). P-pol divergent image light passing through PBS 158 and QW 156B becomes circularly polarized. After reflecting from 150 and passing through QW 156B again, it is S-pol and is reflected from PBS 158. This reflected light now passes through QW 156B a third time to produce circularly polarized light that is injected into light guide 10.

[0075] Alternatively, a QW retarder can be implemented on plane 300 of Figure 6A to generate circularly polarized light in light guide 10. In Figure 6D, the QW is placed on plane 156C (instead of adjacent to the PBS), but achieves similar polarization management as in Figure 6C.

[0076] As discussed above with reference to Figures 3A-3F, coupling an image into a rectangular light guide requires that the projector's optical axis be tilted in two axes relative to the light guide axis, thereby initiating four image propagations within the light guide. Figures 7A-7D illustrate a further particularly preferred embodiment as an alternative to the configuration of Figure 3F. In this embodiment, the bottom surface of the lens (150 in Figure 3F) is immediately adjacent to the TIR interface (154 in Figure 3F), thereby simplifying integration.

[0077] 7A-7D can be used for an emissive image matrix such as a microLED array, but can also be implemented using an illumination spatial light modulator (SLM) such as an LCOS chip. The example shown here is for an illumination LCOS where the illumination section itself incorporates partial TIR according to a further aspect of the invention, as explained further below. With this combination of features, the projector uses a prism that includes three different surfaces that provide TIR properties.

[0078] 7A shows a side view and FIG. 7B shows a top view of the beam propagation associated with one point in the projected field of view. Polarization elements will not be described in detail herein but will be apparent to those skilled in the art.

[0079] As seen in FIG. 7A , light from light source 348 is projected onto prism 357a, which, along with prism 357b, comprises PBS 356. The light source may be an arrangement of one or more LEDs, or the exit aperture of a light guide that homogenizes illumination from one or more LED sources. Central beam 350a (shown as a dotted line) propagates into PBS 356, reflects through surface 354 onto lens 358, and is reflected by SLM (e.g., LCOS) 360. The reflected beam propagates through lens 358, surface 354, PBS 356, and surface 363 to be reflected by reflective lens 362. The reflected beam passes through surface 363, is reflected by PBS 356, passes through prism 357b, and prism extension 357c, and reaches exit aperture 366, the entrance to light guide 10. Two other beams associated with the same image point are shown. Beam 350b (shown as a dashed line) also propagates directly onto PBS 356 via prism 357a, while beam 350c (solid line) is first reflected by surface 354 before striking PBS 356. Thus, a portion of the illumination undergoes an odd number of reflections between the illumination aperture and the SLM image plane, while another portion of the illumination undergoes an even number of reflections. These odd and even reflections are part of the optical path that images light source 348 onto exit aperture 366, as explained further below.

[0080] As described in the previous configuration, some of the beam (in this case beam 350c) is reflected by TIR from surface 363 to exit aperture 366, thereby facilitating filling of the light guide aperture. There is no correlation between the light rays that undergo TIR at surface 354 and the light rays that undergo TIR at surface 363.

[0081] 7B shows central ray 350a and other rays (350d (solid line) and 350e (dashed line), both of which follow a similar path as ray 350a). Ray 350e originates from illumination aperture 348, strikes PBS 356 (from the top, shown as ray 370), reflects from LCOS 360 (ray 372), reflects from top reflecting lens 362 (ray 374), PBS 356 (ray 376), and reflects from side surface 378 (this surface is not visible in the side view of FIG. 7A) onto prism extension 357c, and reflects back into light guide 10 via exit aperture 366.

[0082] The prism configuration provides two surfaces that are parallel or coplanar with the major surfaces of the rectangular light guide and participate in the in-coupling of all four images required for the four propagations into the light guide at exit aperture 366. The extent to which these surfaces need to extend depends on the implementation details. In the case illustrated here, surface 378 is provided partially by extension prism 357c and partially by prism section 357b, as seen in FIG. 7B. The other in-coupling surface is provided by interface 363 on prism 357c and its extension, as seen in FIG. 7A. The overall resulting shape of the projector prism is best seen in FIG. 7D.

[0083] For clarity, Figure 7C shows the beam propagation at a different point in the image. Although the reflections are at different angles, the principle of the optical path is the same as that shown in Figure 7A.

[0084] Optimal coupling of light from illumination aperture 348 to exit aperture 366 is achieved when exit aperture 366 is imaged onto the plane of illuminator aperture 348, with surface 354 ending at the center of this image. In this case, the vertical size of illumination aperture 348 is effectively doubled by reflection at plane 354, so the illumination source can be half the size of the exit aperture (a 1:1 imaging ratio in this example). Laterally (as shown in the top view of FIG. 7B ), the size of illumination aperture 348 is equal to twice the width of the image on 366 (as required for uniform illumination / filling of the light guide).

[0085] The configurations illustrated in Figures 7A and 7C can also be advantageously used to project an image into a slab-type (one-dimensional) light guide, where the other dimension of the prism allows for divergence of the image in the in-plane dimension of the light guide (i.e., without surface 378).

[0086] The illumination architecture described in relation to Figures 7A-7D is considered to be the invention in itself, independent of the additional features disclosed above. To clarify the features of this aspect of the invention, Figures 8A-8C illustrate the design considerations of an illumination arrangement for an SLM in the context of an otherwise conventional image projector for near-eye displays, with Figure 8C corresponding to a preferred implementation of the illumination arrangement.

[0087] Thus, according to this aspect of the invention, a projector for a display includes a reflective spatial light modulator (SLM) 506 for modulating the polarization of light reflected from an image plane, an illumination source outputting illumination from an illumination aperture 500B, a collimating optical arrangement including at least one lens 508, and a prism including a polarizing beam splitter (PBS) 502B. The PBS 502B is positioned to reflect illumination from the illumination aperture 500B towards the SLM 506 and to allow light corresponding to the image reflected from the SLM to pass through the PBS and reach the collimating optical arrangement 508.

[0088] A particular feature of this embodiment of the invention is that surface 512 of the prism adjacent to SLM 506 is provided with an internal reflection-preserving interface, such that a portion of the illumination from illumination aperture 500B is reflected at the interface and then reflected off the PBS before entering the SLM. As a result, a first portion of the illumination undergoes an odd number of reflections along its path from illumination aperture 500B to SLM 506, and a second portion of the illumination undergoes an even number of reflections from illumination aperture 500B to SLM 506.

[0089] 8A illustrates a simplified architecture of an image projector based on an LCOS image generator using a conventional illumination arrangement to better explain the significance of this aspect of the present invention. An illumination source 500A projects light onto a first PBS 502A, which reflects the light through a field lens 504A onto an LCOS chip 506. The modulated light is reflected off a collimating reflecting lens 508, which reflects the light to a second PBS 507, which reflects collimated image light into an exit aperture 510. For optimal power efficiency, the plane of the illumination source 500A is imaged onto the aperture plane 510.

[0090] PBSs 502A and 507 in this schematic representation can be combined into a single PBS, similar to the arrangement of FIG. 7A.

[0091] 8B shows an attempt to reduce the size of the projector's illumination portion, where the angle of PBS 502B is shallower compared to 502A. However, this geometric change results in some of the light from light source 500A having to pass through the field lens (dashed arrow) in a way that redirects and distorts the light.

[0092] 8C illustrates a practical solution according to this aspect of the invention, in which field lens 504B is moved to be on top of LCOS 506, where the bottom surface of prism 512 serves to perform total internal reflection of a portion of the light emitted by illumination source 500B. Additionally, in this configuration, the emission source can be reduced in size because it is imaged twice onto output aperture 510 (once directly and once by reflection off surface 512).

[0093] Field lens 504 can still be implemented on a prism surface as shown in FIG. 8A, in which case an internal reflection-preserving interface must be introduced to maintain TIR at plane 512.

[0094] Optionally, a phase element (either refractive or reflective, having a continuous profile or Fresnel type) may be introduced at the surface of source 500B to direct the beam and produce uniform illumination of pupil 510. This phase element redirects the beam from a non-illuminating direction (e.g., along surface 512) to an illuminating direction.

[0095] Emission source 500B may be the exit hole of a light guide, with or without a diffuser, that can be used to mix illumination from multiple light sources.

[0096] Throughout this document, whenever reference is made to an "internal reflection-maintaining interface," the term is used generically to refer to any and all implementations of an interface that maintains or simulates total internal reflection (TIR) ​​properties. Accordingly, such an interface may be implemented as a layer of material having a refractive index lower than that of the light guide, or as a structure incorporating an air gap adjacent to the surface, thereby creating the classical conditions for TIR at an interface between a material having a higher refractive index and a material having a lower refractive index (or air). Alternatively, the internal reflection-maintaining interface may be implemented as a multilayer dielectric coating configured to be substantially transparent to visible light within a first range of angles of incidence and reflective to visible light within a second range of angles of incidence, the second range being at a higher angle relative to the normal to the interface than the first range, thereby mimicking TIR properties.

[0097] It will be understood that the above description is intended to act by way of example only, and that many other embodiments are possible within the scope of the invention as defined in the appended claims.

Claims

1. A display, (a) a light guide formed from a transparent material having a first pair of mutually parallel major surfaces, the light guide for supporting propagation of image light by internal reflection at the first pair of major surfaces; (b) an image generator for generating an image at an image plane; (c) a collimating optical arrangement including a reflective lens and an associated quarter wave phase plate; (d) a polarizing beam splitter (PBS); a reflective lens associated with one of the first pair of major surfaces or a surface of a prism parallel to or coplanar with one of the first pair of major surfaces via an internal reflection-maintaining interface, and the PBS is arranged such that image light from the image plane is coupled through the PBS to propagate within the light guide by internal reflection at the first pair of major surfaces, pass through the PBS, impinge on the reflective lens, be collimated by the reflective lens, and be reflected by the PBS, and at least a portion of the image light is reflected at the internal reflection-maintaining interface.

2. 10. The display of claim 1, wherein a normal to the PBS forms an angle of less than 45 degrees with a normal to the internal reflection-maintaining interface.

3. 2. The display of claim 1, wherein the PBS is incorporated into a prism optically bonded to the light guide, the light guide having a thickness dimension in a direction perpendicular to the first pair of major surfaces, and the PBS occupies a thickness of the prism in the direction perpendicular to the first pair of major surfaces that is greater than the thickness dimension of the light guide.

4. 2. The display of claim 1, wherein the light guide further comprises a second pair of mutually parallel major surfaces perpendicular to the first pair of major surfaces, the first and second pairs of major surfaces supporting propagation of image light by four internal reflections at the first and second pairs of major surfaces.

5. 5. A display as claimed in claim 4, wherein the normal to the PBS is non-parallel to both of the first and second pairs of major surfaces.

6. 5. The display of claim 4, wherein the reflective lens has an optical axis that is non-parallel to both of the first and second pairs of major surfaces.

7. 5. The display of claim 4, wherein the prism comprises a first surface parallel to or coplanar with one of the first pair of major surfaces and a second surface parallel to or coplanar with one of the second pair of major surfaces, the first surface being provided with the internal reflection-maintaining interface.

8. 5. The display of claim 4, wherein the PBS is incorporated into a prism optically bonded to the light guide, the light guide having a first thickness dimension in a direction perpendicular to the first pair of major surfaces and a second thickness dimension in a direction perpendicular to the second pair of major surfaces, and the PBS occupies a thickness of the prism in the direction perpendicular to the first pair of major surfaces that is greater than the first thickness dimension and a thickness of the prism in the direction perpendicular to the second pair of major surfaces that is greater than the second thickness dimension.

9. The display of claim 1 , wherein the internal reflection-maintaining interface is implemented as a layer of material having a refractive index lower than that of the light guide.

10. The display of claim 1 , wherein the internal reflection-maintaining interface incorporates an air gap.

11. 10. The display of claim 1, wherein the internal reflection-maintaining interface is implemented as a multilayer dielectric coating configured to be substantially transparent to visible light within a first range of angles of incidence and reflective to visible light within a second range of angles of incidence, the second range being at a higher angle relative to a normal to the interface than the first range.

12. 10. The display of claim 1, further comprising a light-absorbing boundary disposed along at least two edges of the PBS to define an optical hole for the collimated image.

13. 10. The display of claim 1, wherein the PBS is incorporated into a prism optically bonded to the light guide, and the image generator comprises an illumination arrangement for directing illumination from an illumination aperture through the prism to the image plane, wherein a first portion of the illumination receives an odd number of reflections from the illumination aperture to the image plane and a second portion of the illumination receives an even number of reflections from the illumination aperture to the image plane.

14. The display of claim 1 , wherein the light guide is between the image plane and the reflective lens.

15. 15. The display of claim 14, wherein the PBS is between the first pair of major surfaces of the light guide.

16. 10. The display of claim 1, wherein the collimating optical arrangement is a polarized catadioptric collimating arrangement in which the reflective lens has a partially reflective surface, the image plane being positioned to deliver image light by transmission through the partially reflective surface, and the image light being reflected back towards the partially reflective surface.

17. A display, (a) a light guide formed from a transparent material having a first major surface and a second major surface parallel to the first major surface, the light guide supporting propagation of image light by internal reflection at the first and second major surfaces; (b) an image generator for generating an image at an image plane; (c) a polarizing catadioptric collimating and in-coupling arrangement, the polarizing catadioptric collimating and in-coupling arrangement comprising: (i) a non-planar partially reflective first reflector associated with the first major surface of the light guide; (ii) a second reflector associated with the second major surface of the light guide in facing relationship to the partial reflector; (iii) a planar third reflector angled obliquely relative to the major surface; and wherein one of the second reflector and the third reflector is a total reflector, and another of the second reflector and the third reflector is a polarization-selective reflector interposed between the total reflector and the first reflector, and the polarizing catadioptric collimating and in-coupling arrangement further comprises at least one phase plate interposed between the polarization-selective reflector and the first reflector, whereby image light from the image plane is in-coupled and propagates within the light guide by internal reflection, being partially transmitted through the partially reflective first reflector acting as a refractive lens, traversing at least a portion of the thickness of the light guide, being reflected by the second reflector, being partially reflected by the partially reflective first reflector acting as a reflective lens, and being reflected by the third reflector.

18. 18. The display of claim 17, wherein the second reflector is the total reflector and the third reflector is the polarization-selective reflector disposed within the thickness of the light guide.

19. 18. The display of claim 17, wherein the second reflector is the polarization-selective reflector and the third reflector is the total reflector associated with a prism outside the thickness of the light guide.

20. 18. The display of claim 17, wherein the second reflector is a planar reflector.

21. 1. A projector for a display, the projector comprising: (a) a reflective spatial light modulator (SLM) for modulating the polarization of light reflected from the image plane; (b) an illumination source that outputs illumination through the illumination aperture; (c) a collimating optical arrangement including at least one lens; (d) a prism including a polarizing beam splitter (PBS); the PBS is positioned to reflect illumination from the illumination aperture towards the SLM and to allow light corresponding to an image reflected from the SLM to pass through the PBS and reach the collimating optical arrangement; a surface of the prism adjacent to the SLM is provided with an internal reflection-maintaining interface, and a portion of the illumination from the illumination aperture is reflected at the interface such that a first portion of the illumination undergoes an odd number of reflections from the illumination aperture to the SLM and a second portion of the illumination undergoes an even number of reflections from the illumination aperture to the SLM, and is then reflected off the PBS before entering the SLM.

Images