Ghost reduction in near-eye displays

Abstract

A near-eye display (NED) system is provided with ghost image suppression using quarter-wave plates (QWPs). The system includes a projector (1) that generates an image and directs light through a polarizing beam splitter (PBS) prism (10). The image light exits the projector and passes through an intermediate optical element (2) before entering a lightguide (3), where it is guided toward the user's eye. Unwanted reflections from the intermediate optical element (2) can re-enter the projector (1), causing ghost images. A first QWP (41) is positioned between the projector exit (16) and the intermediate optical element (2) to alter the polarization state of these reflections, preventing them from retracing the original image path. A second QWP (42) may be positioned between the intermediate optical element (2) and the lightguide entrance aperture (17) to maintain or adjust polarization. This approach effectively reduces ghost artifacts while preserving image quality.

Description

[0001] Ghost Reduction in Near-Eye Displays

[0002] FIELD AND BACKGROUND OF THE INVENTION

[0003] The present invention relates to near-eye display (NED) systems, and more particularly to techniques for reducing ghost images that arise due to multiple reflections within optical elements of such systems.

[0004] Near-eye display (NED) systems, such as those used in augmented reality (AR) and virtual reality (VR) applications, rely on the precise control of light propagation to deliver high- quality images to the user's eye. These systems typically include a projector unit, which generates an image, and a lightguide, which conveys the projected image in front of the user’s eye via internal reflection within the lightguide. Internal components within the lightguide may achieve optical aperture expansion of the image from the projector in one or more directions, and a coupling out configuration redirects the image light out from the lightguide for viewing by the user.

[0005] A significant challenge in these systems is the occurrence of ghost images, which arise due to unwanted multiple reflections of light within the optical components. These ghost artifacts degrade image contrast and can introduce visual confusion or discomfort to the user.

[0006] Ghost images are particularly problematic in NED systems utilizing polarization-based optical elements, such as those employing reflective micro-displays (e.g., Liquid Crystal on Silicon (LCoS) or Digital Light Processing (DLP) systems) in combination with polarizing beam splitters (PBS). In such configurations, light originating from the projector may undergo unintended reflection from the lightguide or from other optical elements interposed between the projector and the lightguide, such as compensating prisms, and may re-enter the projector unit, following unintended light paths, and eventually reach the user’s eye as a distracting ghost. Such ghosts, originating from light generated by the projector, may be referred to as “display-on ghosts” since they appear only when the display is active. SUMMARY OF THE INVENTION

[0007] The present invention provides a near-eye display (NED) assembly for displaying an image to a viewer while reducing ghost images originating from display illumination.

[0008] According to an embodiment of the present invention, there is provided a NED assembly comprising: (a) a projector configured to project light corresponding to an image from a projector exit, the projector having an internal light path defined at least in part by a polarizing beam splitter (PBS) deployed such that the projected light emerges from the PBS through the projector exit with a first polarization; (b) a lightguide having a pair of mutually parallel major surfaces supporting propagation of light by internal reflection, the lightguide having an entrance aperture for receiving light from the projector and a coupling-out region for directing light toward an eye of the viewer; (c) at least one intermediate optical element interposed in a light path between the projector exit and the lightguide entrance aperture; and (d) a first quarter-wave retarder plate interposed between the projector exit and the at least one intermediate optical element and deployed such that reflected light re-entering the projector exit from the at least one intermediate optical element has a polarization that is orthogonal to the first polarization, ensuring that, upon reaching the PBS, the reflected light follows a path different from the internal light path of the projector.

[0009] According to another feature of an embodiment of the present invention, the NED assembly further comprises a second quarter-wave retarder plate interposed between the at least one intermediate optical element and the lightguide entrance aperture, deployed such that the light entering the lightguide entrance aperture is plane polarized with a lightguide-entrance polarization.

[0010] According to another feature of an embodiment of the present invention, a fast axis of the second quarter-wave retarder plate is aligned with a slow axis of the first quarter-wave retarder plate, ensuring that the lightguide-entrance polarization is the same as the first polarization.

[0011] According to another feature of an embodiment of the present invention, the lightguide is optimized to convey the lightguide-entrance polarization, and light that is reflected from a surface of the lightguide and then reflected from a surface of the at least one intermediate optical element passes twice through the second quarter-wave retarder plate, so that it reaches the lightguide entrance aperture with a polarization perpendicular to the lightguide-entrance polarization.

[0012] According to another feature of an embodiment of the present invention, the at least one intermediate optical element comprises at least one dispersion compensating prism, deployed to at least partially compensate for chromatic dispersion introduced by the projector and / or the lightguide.

[0013] According to another feature of an embodiment of the present invention, the first polarization is reflected at the PBS, while the reflected light re-entering the projector exit is transmitted by the PBS.

[0014] According to another feature of an embodiment of the present invention, the first polarization is transmitted by the PBS, while the reflected light re-entering the projector exit is reflected at the PBS.

[0015] According to another feature of an embodiment of the present invention, the projector comprises a polarization-modifying reflective spatial light modulator.

[0016] BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

[0018] FIG. 1 is a schematic diagram of a near-eye display (NED) projector unit employing a polarizing beam splitter (PBS) prism and a reflective collimating optical system integrated within the prism, wherein the final interaction of the image light with the PBS before exiting is reflection.

[0019] FIG. 2 is a schematic diagram of an alternative NED projector unit configuration similar to FIG. 1A, but wherein the final interaction of the image light with the PBS before exiting is transmission.

[0020] FIG. 3 is a schematic diagram of a NED projector unit employing a PBS prism, but with refractive collimating optics placed after the exit from the PBS prism.

[0021] FIG. 4 is a highly schematic block diagram showing a general relationship between an image projector, a lightguide (interchangeably referred to as a “waveguide” or WG) and intermediate optical elements, without showing details of the optical components or light paths, and illustrating one mechanism of unwanted ghost image formation in which light exiting the projector may undergo unintended reflections prior to entering the lightguide and consequently re-enter the projector unit.

[0022] FIG. 5 is a schematic ray-tracing diagram illustrating a specific ghost image formation mechanism, wherein light undergoes unintended reflections from an intermediate optical element, such as a compensating prism, before re-entering the projector unit.

[0023] FIG. 6 illustrates an embodiment of a ghost reduction solution employing quarter-wave plates (QWPs) positioned before and after the intermediate optical element, mitigating ghost formation by altering the polarization state of reflected light.

[0024] FIG. 7 illustrates a second ghost image formation mechanism where light reflected between the lightguide and the intermediate optical element would contribute to ghost artifacts, that is also addressed by the implementation of FIG. 6.

[0025] FIG. 8 is a schematic diagram similar to FIG. 4 illustrating a further mechanism of unwanted ghost image formation in which light exiting the projector is reflected from the lightguide and re-enters the projector unit. FIG. 9 is a schematic ray-tracing diagram illustrating formation of a ghost of the type illustrated schematically in FIG. 8.

[0026] FIG. 10 illustrates an alternative ghost reduction approach using a neutral density (ND) filter effective to reduce the intensity of the ghost image light of FIG. 9 by selectively attenuating multiple reflections.

[0027] DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The present disclosure describes multiple aspects of a near-eye display (NED) system, each of which is believed to be independently patentable. In particular, certain embodiments address ghost image reduction using quarter-wave plates (QWPs), as illustrated in FIGS. 1-7, while other embodiments provide ghost reduction using a neutral density (ND) filter, as illustrated in FIGS. 8-10. Each of these aspects of the invention, along with variants thereof, will be described in turn in the description below.

[0029] According to the first aspect of the present invention, a NED assembly is provided for displaying an image to a viewer while reducing ghost images originating from display illumination. The NED assembly includes a projector configured to project light corresponding to an image from a projector exit. The projector incorporates a polarizing beam splitter (PBS) prism to control the path of light between the various components of the projector resulting in a plane-polarized projected image.

[0030] The assembly further includes a lightguide having a pair of mutually parallel major surfaces that support propagation of light by internal reflection. The lightguide has an entrance aperture for receiving image light from the projector and a coupling-out region configured to direct the image light toward the viewer’s eye.

[0031] In scenarios of particular interest for this aspect of the present invention, the display system also includes at least one intermediate optical element interposed between the projector exit and the lightguide entrance aperture. According to certain preferred implementations, the intermediate optical element is a compensating prism deployed to at least partially compensate for chromatic dispersion introduced by the projector and / or the lightguide. One non-limiting example of such an element is described in PCT Patent Application Publication No. WO 2022 / 091087 Al.

[0032] According to this first aspect of the present invention, a quarter-wave plate (QWP) is used to reduce ghost image formation. Thus, a first quarter-wave retarder plate is preferably positioned between the projector exit and the intermediate optical element to alter the polarization state of light so that any unwanted reflections from the intermediate optical element re-entering the projector exit have a polarization orthogonal to the original projected polarization. As a result, when these reflections reach the PBS prism, they are directed along a different optical path, preferably preventing them from forming visible ghost images.

[0033] According to certain preferred implementations, a second quarter-wave retarder plate is positioned between the intermediate optical element and the lightguide entrance aperture. This preferably returns the state of the image light entering the lightguide aperture to be plane polarized, all as discussed in more detail below with reference to FIGS. 1-7.

[0034] Definitions of Terms

[0035] Before proceeding further with the detailed description, it will be useful to define various terminology as used herein in the description and claims. These definitions govern the interpretation of the corresponding terms throughout this document except where otherwise stated explicitly.

[0036] • Image projector: Refers to any system configured to generate and project an image, including but not limited to projectors based on different image generation technologies such as Liquid Crystal on Silicon (LCoS), Digital Light Processing (DLP), and microLED arrays. The image projector may include either a polarizing beam splitter (PBS) prism-based optical arrangement or open-space refractive optical components. This broad definition ensures applicability to both the first and second aspects of the invention.

[0037] • Polarizing Beam Splitter (PBS) prism: Includes any prism arrangement which includes a beam-splitting optical element that selectively transmits or reflects light based on polarization, and is not necessarily in the form of a cube.

[0038] • Polarization-modifying reflective spatial light modulator: A general term that includes LCoS as a non-limiting example.

[0039] • Retarder / Phase Plate / Wave Plate: These terms are used interchangeably and include quarter-wave plates, half-wave plates, and other phase-modifying optical elements.

[0040] • Intermediate optical element(s): This term broadly refers to any optical element interposed between the projector exit and the lightguide entrance aperture that is required for a particular implementation. By way of non-limiting example, the intermediate optical element(s) may include one or more compensating prisms formed from materials with differing refractive indices and / or differing Abbe numbers from adjacent materials, with surfaces oriented to compensate for chromatic dispersion that would otherwise be introduced by the optical design.

[0041] • Lightguide / Waveguide: These terms are used interchangeably to refer to an optical component that supports the propagation of image light by internal reflection. The lightguide may include various internal or associated components for image redirection and aperture expansion. In certain cases, the lightguide may by part of a compound lightguide arrangement in which the light is coupled out from a first lightguide into a second lightguide from which it is then delivered to the eye of the user. In this case, the first lightguide may be a rectangular cross-section lightguide in which light propagates by reflection at two orthogonal pairs of mutually parallel surfaces by four-fold internal reflection.

[0042] • Coupling-in mechanisms: Image light may enter the lightguide through various coupling mechanisms, including but not limited to: o Direct (non-deflected) coupling via a coupling prism with a suitably oriented coupling-in surface and a base that is a continuation of or parallel to one of the lightguide's major surfaces. o Reflective coupling using mirrors or prisms. o Diffractive optical elements (such as gratings) that redirect incoming light. No attempt is made to show the geometry of the coupling-in arrangement, as it is dictated by the details of the implementation.

[0043] • Multiple lightguides: In addition to the compound lightguide arrangement option mentioned above, the invention also contemplates implementations where multiple lightguides (or compound lightguide arrangements) are used, for example, each handling image light of a different color. This is particularly relevant in systems utilizing diffractive optical technology.

[0044] Turning now to the drawings, the first aspect of the invention is applicable to systems employing various projector configurations, such as those illustrated in FIGS. 1-3. Each configuration employs a PBS prism to define a compact light path between the components of the projector through polarization control. The projector configurations illustrated here differ in their optical collimation approach and in their light path geometry.

[0045] FIG. 1 illustrates a NED projector unit employing a PBS prism with an integrated reflective collimating optical system, wherein an S -polarized illumination ray 51 enters a PBS prism 10 from an illumination source (not shown) and is reflected at a PBS layer 12 toward a polarization-modifying reflective spatial light modulator 11 (e.g., an LCoS chip). The modulated P-polarized image light corresponding to the image reflected from the LCoS and passes through PBS layer 12 as ray 53 which traverses a quarter-wave plate 14 and is reflected and collimated by reflective collimating optics 13. The reflected collimated image ray 54 passes again through quarter-wave plate 14, becoming S-polarized so as to be reflected at PBS layer 12 to emerge from projector exit 16 as collimated image ray 55. Here and throughout the following description, the ray paths illustrated correspond to schematic exemplary rays corresponding to one part of the illumination, one pixel of an image and one part of the spatial field of a projected image to facilitate an understanding of the invention. It will be appreciated that the illumination preferably illuminated the entire active area of the LCoS chip with an appropriate field of illumination and the collimating optics preferably fills an exit aperture (which may be at the projector exit or more preferably at the entrance aperture of the lightguide) with light from each pixel of the image at a corresponding projection angle.

[0046] FIG. 2 shows a configuration similar to FIG. 1 , but wherein the final interaction of the image light with the PBS before exiting is transmission. In this case, illumination ray 51 is P- polarized, passing through PBS surface 12 to reach LCoS chip 11. The S-polarization image light ray 52 is reflected by PBS surface 12 towards reflective collimating optics 13, passing twice through quarter-wave plate 14 so as to become P-polarized collimated image ray 54. Image ray 54 passes through PBS surface 12 to emerge from projector exit 16.

[0047] FIG. 3 presents an alternative NED projector unit employing a PBS prism, but with refractive collimating optics 13 placed after the exit from the PBS prism 10. More specifically, the light path through the projector includes injection of P-polarized illumination ray 51 which passes through PBS layer 12, reflection of S-polarized image light ray 52 which is reflected at PBS layer 12 as image ray 53 which exits the PBS prism 10, and collimation by refractive optics 13 to generate collimated image ray 54 at the exit of the projector. In each of these cases, the projector and its components are shown only schematically.

[0048] For example, both the reflective collimating optics and the refractive collimating optics are shows simplistically, but may be implemented as compound optical components, such as a doublet, all as is known in the art.

[0049] FIG. 4 provides a high-level schematic representation of the system, illustrating the relationship between the image projector 1, intermediate optical element 2, and lightguide 3. This figure does not depict specific optical components or light paths but serves as a framework for understanding subsequent figures.

[0050] The first ghost formation mechanism is also described with reference to FIG. 4, showing that light exiting the projector 1 as collimated projected image ray 54 propagates through the intermediate optical element 2 before entering the lightguide 3. Unwanted reflected light 61 from the intermediate optical element 2 may return toward the projector 1, where it can cause secondary reflections that re-emerge as ghost image ray 73 directed toward the lightguide 3.

[0051] A significant proportion of the image light that re-enters the projector 1 and reaches the LCoS 11 will be reflected due to the high reflectivity of the LCoS 11. This includes both light reflected with rotated polarization (from active image pixels) and light reflected with the original polarization (from non-image pixels). As a result, a portion of the re-entering ghost light follows the original projection light path and forms a visible ghost image.

[0052] A more detailed depiction of this ghost formation mechanism is illustrated in FIG. 5, including specific ray paths. By way of non-limiting example, the device is illustrated using the projector structure of FIG. 3, but is equally applicable to other projector configures, particularly PBS-based projectors employing polarization-modifying reflective spatial light modulators (SLM) as the image source such as those of FIGS. 1 and 2. The projected image light 54 propagates through an intermediate optical element 2, such as a compensating prism, before reaching the lightguide entrance aperture 17. Unwanted ghost light 61 may be reflected from one or more surface of the intermediate optical element 2, returning as ray 62 (after the collimating optics) back into PBS prism 10.

[0053] This reflected light has the same polarization as the projected image, and therefore tends to follow the same light path as the projected image light (in reverse) until reaching the SLM. This is shown in FIG. 5 as reflection at PBS surface 12 as ray 63. If this ray falls on a nonimage pixel of the SLM, it is reflected without change of polarization (ray 71), to be again reflected at PBS surface 12 as ray 72 which passes through collimating optics 13, potentially reaching the lightguide entrance aperture as ghost ray 73. The high reflectivity of the SLM surface may result in such ghosts causing disturbing ghost images and / or a noticible reduction in image contrast. Furthermore, these effects may be most pronounced when only a small proportion of the SLM pixels are activated, resulting in bright ghosts specifically when much of the display is intended to be dark, thereby exacerbating the problem.

[0054] FIG. 6 illustrates an embodiment of the ghost suppression approach using quarter-wave plates (QWPs). A first QWP 41 is positioned between the projector exit 16 and the intermediate optical element 2. Light passing through QWP 41 undergoes a first quarter-wave retardation, and upon reflection at the intermediate optical element 2, the light passes through QWP 41 a second time, experiencing a second quarter-wave retardation, resulting in a cumulative halfwave retardation. This rotates the polarization by 90 degrees so that the reflected light (ray 61) follows a different path when re-entering the PBS prism 10. Rather than being directed toward the LCoS 11, where it would contribute to ghost image formation as described above, the reflected light with rotated polarization is instead typically directed toward the illumination source, which generally has much lower reflectivity than the LCoS, and which may include an absorptive polarizer for absorbing illumination other than the intended illumination polarization, thereby preventing ghost formation. In the example illustrated here, due to the effect of QWP 41, reflected ray 61 is here transmitted through PBS surface 12 instead of being reflected. The same would be true in a system based on the projector of FIG. 1. In a system based on the projector of FIG. 2, the reflected ray with rotated polarization would be reflected rather than transmitted. The overall resulting ghost reduction is equivalent in both cases.

[0055] In the particularly preferred but non-limiting embodiment illustrated here, a second QWP 42 is positioned between the intermediate optical element 2 and the lightguide entrance aperture 17. In one preferred implementation, the fast axis of QWP 42 is aligned with the slow axis of QWP 41, thereby canceling each other out and ensuring that the image light entering the lightguide 3 retains its intended polarization state. This is appropriate in cases in which the alignment of the projector and the lightguide are matched so that the output polarization of the projector should be preserved at the lightguide aperture. In other implementations, the presence of two QWPs may be used to advantage to rotate the output polarization of the projector to some other orientation of polarization that is the optimal input for a given lightguide design. This provides an additional degree of freedom in the system design, for example, allowing flexibility in the orientation of deployment of the projector.

[0056] In some implementations, QWP 42 may be omitted. For example, where the lightguide 3 is designed for use with non-polarized image light, a depolarizer may be inserted instead of QWP 42 to eliminate polarization dependency. If the lightguide is suitable for use with circularly polarized image light, QWP 42 may simply be omitted without substitution of an alternative element.

[0057] FIG. 7 illustrates a second ghost formation mechanism where light initially reflected at one or more surface of the lightguide 3 as ray 75 is then again reflected at a surface of the intermediate optical element 2 as ray 76, which may re-enter the lightguide 3 at an unintended angle generating a visible ghost. The presence of QWP 42 similarly modifies the polarization of this reflected light, rotating it to be polarized orthogonally to the injected image light. Where the lightguide is optimized for delivering image light of the intended input polarization to the user's eye, orthogonally polarized ghosts will typically be greatly attenuated, if not eliminated entirely, before reaching the eye.

[0058] Turning now to the second aspect of the invention, with reference to FIGS. 8-10, an alternative ghost suppression technique is provided utilizing a neutral density (ND) filter. Unlike the QWP-based solutions described previously, this approach is independent of polarization and is particularly applicable in cases where power efficiency is less critical, such as testing and metrology applications or tethered display systems that rely on an external power source rather than onboard batteries.

[0059] FIG. 8 illustrates an additional ghost formation mechanism in which light exiting the projector 1 as collimated projected image ray 54 undergoes unintended reflection at the lightguide 3, producing undesired reflection 61 that re-enters the projector 1. This stray light follows an unintended optical path, eventually re-emerging as ghost image ray 73, which propagates back into lightguide 3, causing image degradation.

[0060] A more detailed illustration of this ghost formation mechanism is provided in FIG. 9, where the unintended reflected light 61 re-enters the PBS prism 10, following an optical path similar to the projected image light but in reverse. The ray paths of image projection and of the ghost-forming rays within the projector as illustrated here are analogous to those described above with reference to FIG. 5 and are labelled similarly. However, as mentioned above, this aspect of the present invention is not limited to projectors employing PBS prisms, and may be used to advantage with a range of other internal projector reflections which may lead to reemission of a ghost image ray 73.

[0061] FIG. 10 presents a solution in which an ND filter 15 is introduced into the optical path at or near the projector exit 16. In the illustration shown here, ND filter 15 is actually located behind collimating optics 13 after PBS prism 10. In each implementation, the ND filter should be located closer to the projector exit than whatever reflective components or surfaces are likely to generate significant ghost reflections. ND filter 15 attenuates light intensity each time light passes therethrough without significant loss of image quality. The primary image illumination passes only once through the ND filter, resulting in a fixed and predefined attenuation of the image light. The projected intensity is chosen accordingly in order to provide the required output of image intensity. Ghost image suppression is achieved because ghost rays traverse the ND filter multiple times, resulting in an exponential reduction in brightness. If the ND filter has a transmission factor T, corresponding to the attenuation of the primary image, then ghost light passing through the filter three times (once forward, once reflected, and again forward) is attenuated by a factor of T3, giving a signal-to-noise ratio between the primary image and a ghost of T2For example, if the ND filter has a transmission coefficient of T = 10%, then the ghost image intensity is reduced by a factor of 100, significantly mitigating visual artifacts.

[0062] This approach is effective across various projector architectures, including those utilizing polarization-modifying reflective spatial light modulators (SLMs) as well as nonpolarized projectors. Since the method relies purely on intensity attenuation rather than polarization control, it is broadly applicable and can be integrated into systems where energy efficiency is a secondary concern. While ND filtering introduces some loss in the desired image signal, it remains a viable option in use cases such as metrology, calibration setups, and high- power tethered display applications, where an external power source is available.

[0063] The second aspect of the invention thus provides a complementary approach to ghost suppression, offering a robust solution in environments where polarization-based techniques may not be feasible or necessary.

[0064] It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the scope of the present invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A near-eye display (NED) assembly for displaying an image to a viewer with amelioration of ghosts originating from display illumination, the NED assembly comprising:(a) a projector configured to project light corresponding to an image from a projector exit, the projector having an internal light path defined at least in part by a polarizing beam splitter (PBS) deployed such that the projected light emerges from the PBS through the projector exit with a first polarization;(b) a lightguide having a pair of mutually parallel major surfaces supporting propagation of light by internal reflection, the lightguide having an entrance aperture for receiving light from the projector and a coupling-out region for coupling out the light towards an eye of the viewer;(c) at least one intermediate optical element interposed in a light path between the projector exit and the lightguide entrance aperture; and(d) a first quarter-wave retarder plate interposed between the projector exit and the at least one intermediate optical element and deployed such reflected light reflected from the at least one intermediate optical element and reentering the projector exit has a polarization that is orthogonal to the first polarization such that, on reaching the PBS, the reflected light follows a path different from the internal light path of the projector.

2. The NED assembly of claim 1, further comprising a second quarter- wave retarder plate interposed between the at least one intermediate optical element and the lightguide entrance aperture and deployed such that the light entering the lightguide entrance aperture is plane polarized with a lightguide-entrance polarization.

3. The NED assembly of claim 2, wherein a fast axis of the second quarter-wave retarder plate is aligned with a slow axis of the first quarter-wave retarder plate so that the lightguide-entrance polarization is the same as the first polarization.

4. The NED assembly of claim 2, wherein the lightguide is optimized to convey the lightguide-entrance polarization, and wherein light reflected from a surface of the lightguide and then reflected from a surface of the at least one intermediate optical element passes twice through the second quarter-wave retarder so as to reach the lightguide entrance aperture with a polarization perpendicular to the lightguide-entrance polarization.

5. The NED assembly of claim 1 , wherein the at least one intermediate optical element comprises at least one dispersion compensating prism deployed to at last partially compensate for a chromatic dispersion introduced by the projector and / or the lightguide.

6. The NED assembly of claim 1, wherein the first polarization is reflected at the PBS and wherein the reflected light reentering the projector exit is transmitted by the PBS.

7. The NED assembly of claim 1, wherein the first polarization is transmitted by the PBS and wherein the reflected light reentering the projector exit is reflected at the PBS.

8. The NED assembly of claim 1, wherein the projector comprises a polarizationmodifying reflective spatial light modulator.

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