Optical system and light guide optical element

Abstract

A light-guide optical element (LOE) for simultaneous viewing of a real scene and a projected image introduced into the LOE includes a transparent block along which light carrying the projected image propagates by internal reflection, and a plurality of internal partially reflective surfaces oriented at an angle and configured to outcouple a portion of the light, the reflectivity of each of the partially reflective surfaces being set so that the total power of the outcoupled light is less than one-third of the total power of the light introduced into the LOE. In some embodiments, the light of the projected image is polarized, and the reflectivity of the partially reflective surfaces is significantly reduced for light polarized in an orthogonal orientation. In some embodiments, the reflectivity of the partially reflective surfaces is significantly reduced for light that does not reach the viewer.

Description

Technical Field

[0001] The present invention generally relates to a head-mounted display device, and more particularly to a light guide optical element that is part of such a device.

Background Art

[0002] Devices worn by viewers for the simultaneous observation of the actual scene and the projected image from a display device are well known and are commonly referred to as "head-mounted displays" (HMDs) or "near-eye displays" (NEDs). Such devices are generally constructed as goggles or glasses, or helmets or visors, and are worn on the viewer's head, and also include one or two image projectors (each including an electro-optical display component) and optical components for transmitting the projected image to the viewer's eyes. In some configurations of HMDs known in the art, one of such optical components is a light guide positioned in front of each of the viewer's eyes.

[0003] Such a light guide (also referred to alternatively as a "waveguide" or "substrate") serves to expand the field of view (i.e., the angular size of the screen of the display component) and the viewing window (i.e., within this window the viewer's eyes are positioned to see the entire display screen, also known as the "eye motion box"). Generally, such a light guide is a block (or slab) of transparent material having two parallel main surfaces, and light that is projected from the display component and conveys a collimated image propagates along these main surfaces by total internal reflection. The block includes a structural coupling-out arrangement that functions such that a portion of that light is externally coupled through one of the main surfaces towards the corresponding viewer's eye.

[0004] In some configurations of light guides known as diffractive light guides, the external coupler includes a diffractive structure on one or both of the major surfaces. In reflective light guides and other configurations known particularly as "light guide optical elements (LOEs)", the external coupler includes a set of partially reflective surfaces that are angled obliquely and parallel to each other, alternatively known as facets, and are within the block.

[0005] In some cases where the HMD is in the form of glasses, it may be desirable for the external coupler to be difficult or invisible to an external observer. SUMMARY OF THE INVENTION MEANS FOR SOLVING THE PROBLEM

[0006] The present invention aims to provide improvements to light guides used in head-mounted displays (HMDs), or otherwise reduce undesirable visual effects experienced by an external observer when observing the face of a viewer wearing the HMD through such a light guide. Such effects are caused by a portion of the light reflected from the viewer's eyes and face being coupled into the light guide, thus dimming the light reaching the external observer and making the light guide appear clearly darker in the external observer's field of view, masking the viewer's face and eyes. Another undesirable visual effect in prior art light guides is caused by light within the light guide that is reflected at the end face and propagates rearward, being externally coupled towards the external observer and perceived as glare. Accordingly, embodiments of the present invention provide various techniques for increasing the transmission of light through the light guide between the viewer's face and the external observer and reducing the amount of other light radiated from the light guide towards the external observer.

[0007] As a non-exclusive example, improvements related to embodiments of the configuration of a light guide including a partially reflective surface are described. Such a reflective light guide, or a conventional light guide optical element (LOE), is described, for example, in U.S. Patent No. 6,829,095 entitled "Optical Beam Expander Conducted by a Substrate", which is incorporated herein by reference. However, the improvements according to the present invention are applicable, in whole or in part, to other embodiments and configurations of light guides for HMDs.

[0008] Specifically, a light guide optical element for simultaneous observation by a viewer's eye of an actual scene and a projected image introduced into the light guide optical element (LOE (Light-guide Optical Element)) is disclosed, the LOE being a block of a transparent material having a first main surface and a second main surface parallel to the first main surface, and light carrying the projected image introduced into the light guide optical element propagating within the light guide optical element by internal reflection at the first and second main surfaces, the block, and a plurality of mutually parallel, partially reflective surfaces disposed obliquely with respect to the first main surface within the block, the partially reflective surfaces being configured to externally couple a portion of the light through the second main surface, and comprising a plurality of mutually parallel, partially reflective surfaces. The reflectivity of each of the partially reflective surfaces is set such that the total power of the light externally coupled is less than 1 / 3 of the total power of the light carrying the projected image introduced into the light guide optical element.

[0009] In some embodiments, the reflectivity of each of the partially reflective surfaces is set such that the total power of the light externally coupled is less than 1 / 5, and in some embodiments less than 1 / 10, of the total power of the light carrying the projected image introduced into the light guide optical element.

[0010] In some embodiments, the reflectivity of each of the partially reflective surfaces is less than 13%, and in some embodiments less than 5%.

[0011] A light-guide optical element (LOE) for the simultaneous viewing by an observer's eye of an actual scene and a projected image carried by light polarized in a first orientation and introduced into the LOE is also disclosed. The LOE is a block of a transparent material having a first major surface and a second major surface parallel to the first major surface, and light carrying the projected image introduced into the light-guide optical element propagates within the light-guide optical element by internal reflection at the first and second major surfaces. The block includes a plurality of mutually parallel partially reflecting surfaces disposed obliquely with respect to the first major surface so as to externally couple a portion of the light toward the observer's eye. The reflectivity of each of the partially reflecting surfaces in a direction perpendicular to the first and second major surfaces with respect to light polarized in a second orientation orthogonal to the first orientation is less than 1 / 3 of its reflectivity in the direction with respect to light polarized in the first orientation.

[0012] The first polarization orientation can be S-polarized with respect to the partially reflecting surface. In some embodiments, the partially reflecting surface substantially transmits P-polarized light over an angular range of at least about 30 degrees including a direction perpendicular to the first major surface.

[0013] A light-guide optical element (LOE) for simultaneous observation by a viewer's eye of an actual scene and a projected image introduced into the LOE is also disclosed. The LOE is also disclosed as a block of a transparent material having a first major surface and a second major surface parallel to the first major surface. As a block of a transparent material having a first major surface and a second major surface parallel to the first major surface, light carrying the projected image introduced into the light-guide optical element propagates in a first direction within the light-guide optical element by internal reflection at the first and second major surfaces, and outside the first major surface and in a plane parallel thereto, an eye motion box of a predetermined size is defined. A block, and a plurality of mutually parallel and partially reflecting surfaces that are disposed in order along the first direction within the block and are oriented obliquely with respect to the first major surface so as to externally couple a part of the light toward the eye motion box. The reflectivity of the last one of the array of the partially reflecting surfaces with respect to a part of the light externally coupled from an arbitrary point within the eye motion box is at least twice its reflectivity with respect to light propagating in a direction perpendicular to the first and second major surfaces.

[0014] In some embodiments, the reflectivity of the last one of the array of the partially reflecting surfaces with respect to a part of the light externally coupled from an arbitrary point within the eye motion box is at least four times or more its reflectivity with respect to light propagating in a direction perpendicular to the first and second major surfaces.

[0015] In some of the embodiments, the block has an end face on which the light propagating within the light-guide optical element that has passed through the partially reflecting surfaces is incident, and the end face is coated with a light absorption layer configured to absorb light that is introduced into the light-guide optical element and not externally coupled. The light absorption layer can be implemented as a black paint applied to the rough end face.

[0016] An optical system for simultaneous observation by a viewer of a natural scene and an image on a near-eye image projector is also disclosed, the optical system comprising: a light guide optical element according to any one of claims 1 to 10; and a support structure provided for supporting the light guide optical element at a position facing at least one eye of the viewer on the head of the viewer.

Brief Description of the Drawings

[0017] The present invention is described herein by way of example only with reference to the following accompanying drawings.

Figure 1A

Figure 1B

Figure 2

Figure 3A

Figure 3B

Figure 4A

Figure 4B

Figure 4C

Figure 5A

Figure 5B

DETAILED DESCRIPTION OF THE INVENTION

[0018] FIG. 1A schematically shows, as a prelude, a head-mounted display (HMD) formed as glasses worn by a viewer in this example, including a light guide optical element (LOE) 10 having a partially reflective surface positioned in front of the viewer's eyes 20 when the HMD is worn. In addition, an image projector 22 (which thus includes a spatial light modulator such as an electro-optical display device or an LCOS device) that operates to generate an image in response to a signal supplied thereto, a collimating optical assembly (not shown in its entirety) configured to project light corresponding to the collimated image, and a coupling optical system 24 that couples the projected image to the LOE 10 are included.

[0019] In some configurations of the HMD, a single image projector is provided in relation to one eye, in other configurations, two image projectors each associated with one of the viewer's two eyes are provided, and in yet other configurations, a single image projector configured to project an image within two LOEs associated with the corresponding two eyes or within a single long LOE extending in front of both eyes is provided.

[0020] The light guide optical element (LOE) 10 is shown in a horizontal cross-sectional view in FIG. 1A, and selected light rays of an image that propagate within the LOE and are collimated to be emitted toward the viewer are traced. The LOE 10 is basically an elongated block 11, made of a transparent material, and has two mutually parallel major surfaces, a front surface 12 and a rear surface 14. Near one end of the block 11, a coupling-in arrangement associated with an incident window is provided, through which the collimated image is introduced into the LOE. In this example, it is an inclined reflecting surface 18, at which an incident window 19 is defined adjacent thereto at the rear surface 14. In other LOEs, for example, the incident window is an angled prism attached to one of the major surfaces, or the incident window can be an end face of the block. The block 11 has an array of inclined, partially reflecting surfaces 16 embedded therein, all parallel to each other, called "facets". Adjacent to the entire set of the partially reflecting surfaces 16, a viewing range 17 is defined at a distance from and parallel to the rear surface 14, also known as an eye motion box, indicating the region where the viewer's eyes are placed so as to be able to view the entire image, allowing some degree of freedom in the movement of the eyes and the location of the HMD with respect to the eyes 20.

[0021] Note that in the illustrated example the incident window is on the rear surface, but in other configurations of the HMD, the corresponding LOE can be configured to have the incident window on the front surface or on the end face of the block 11. The present invention also addresses such configurations.

[0022] As represented by the selected light rays, the image-carrying light from the coupling optics 24 enters the block 11 through the incident window 19 and, in this example, is deflected by the inclined reflecting surface 18 and propagates along the block 11 while undergoing total internal reflection from the major surfaces 12 and 14. In a configuration where the incident window is on the end face, the light incident thereon travels linearly (i.e., is not deflected) and propagates along the block. During this propagation process, the light is caught midway by the partially reflecting surfaces (facets) 16, and a part of it is deflected or externally coupled into the observation window (eye motion box) 17.

[0023] (Such as virtual reality devices and augmented reality devices) One of the main challenges in the design of LOEs for any near-eye display device is to maximize the optical throughput from the light source to the viewer's eyes in order to reduce energy consumption, and thus extend battery life. Therefore, a common approach in state-of-the-art reflective LOE designs is to maximize the reflectivity of all the facets and maximize the image intensity reaching the viewer's eyes. At the same time, in order to achieve an image of uniform intensity across the field of view and observation window perceived by the viewer, the reflectivity of the facets typically varies among them. More specifically, since light propagates along block 11 and a portion of it is externally coupled by the first facet, the intensity of the remaining light is reduced, and the subsequent facets are required to have a higher reflectivity at an equal rate so that the intensity of the externally coupled light is kept constant; that is, the last facet where the light intersects should have the maximum reflectivity.

[0024] Another challenge in the LOE design specific to the parts of the HMD is that the viewer must have sufficient transparency to clearly see the natural scene as well. This requirement is in conflict with the requirement for the maximum reflectivity of the above-mentioned facets in that a high reflectivity is actually equal to a low transmittance, and thus the light reaching the viewer's eyes from the natural scene is weakened. Therefore, conventional LOE designs for HMDs have compromised, and the reflectivity of the facets has been proportionally reduced so that the transmittance value for light from the natural scene achieves the desired minimum value.

[0025] Also, in a certain conventional LOE design, (as mentioned in the section of the means to be solved above) the facets are substantially visible to an external observer. This is because their transmittance is relatively low, and thus, the light reflected from the viewer's face and eyes 20 through the LOE block 11 in a direction generally perpendicular to its main faces 12 and 14 is reduced to the eyes (not shown) of the external observer. This effect is schematically demonstrated in FIG. 1B, which is a front view of the LOE 10 as seen by the eyes of an external observer. Here, the facet 16 is seen as a strip with changing darkness, blurring the viewer's face; the leftmost facet is the darkest because it is designed with the maximum reflectance and thus the minimum transmittance. In these designs, the facets may also generate glare seen by an external observer, because the remaining propagating light is reflected at the end face 15 of the block 11 and is externally coupled by the facet 16 through the front main face 12 towards the observer's eyes.

[0026] Exemplary embodiments of a light guide optical element including novel features designed to reduce the above-described effects, such as the visual recognition of facets by an external observer, will be described hereinafter. These features are described with respect to appropriate exemplary embodiments, although some other embodiments may include two or more of these features simultaneously, as will be readily envisioned by those skilled in the art. Furthermore, some or all of these features may be included in embodiments of LOEs of various configurations, particularly in reflective and diffractive LOEs.

[0027] The principle guiding certain embodiments of the present invention is to reduce the reflectance of the facet group, increase their overall transmittance with respect to the light passing through the LOE, make them appear transparent, and make them invisible to an external observer.

[0028] Furthermore, in a conventional typical optimized reflective LOE design, the reflectivity of the facets varies along the LOE from the first to the last incident facet in the range of the incident angle of interest, polarization azimuth, and wavelength band, typically ranging from 10% to 25%. The range of the incident angle of interest is determined by optical geometric considerations in the design of the LOE and the HMD where the LOE is a single part. The range of interest of the polarization azimuth and wavelength band is largely determined by the characteristics of the image projector or by the operating requirements. The optical design seeks to optimize the reflectivity of the facets within these ranges of interest, but the reflectivity values for any values of the incident angle, polarization azimuth, and wavelength band outside these ranges are typically not constrained in the design. Therefore, a further guiding principle of certain embodiments of the present invention is to reduce or minimize, to the extent possible, the reflectivity of one or more external facets of these ranges and increase their transmittance with respect to the light passing through the LOE.

[0029] In a first exemplary embodiment of the present invention, or according to a first aspect of the present invention, the overall reflectivity of each facet, including those within the angle range of interest, polarization state, and wavelength band, is substantially reduced by design compared to that of the prior art design described above.

[0030] Figure 2 is a comparative plot of the intensity of light propagating along the LOE (descending line group) and the reflectivity values of the facets (ascending line group). The horizontal axis is the relative distance along the LOE, and the vertical axis is the percentage of the maximum value. The dotted line represents the optimal value for an LOE designed for use in a virtual reality device (which is outside the scope of the present invention). Here, the optimal design is to externally couple all of the light energy incident on the LOE, maximizing the efficiency of viewing the display image while maintaining the intensity of the externally coupled light uniformly. Accordingly, the line 31 representing the intensity of the propagating light descends linearly to near zero, and the line 32 representing the reflectivity of the arrayed facets rises almost exponentially with the corresponding increase in reflectivity. As a result, the intensity of the light externally coupled towards the viewer is approximately uniform. Note that the lines represent the optimal set values; in reality, the slanted lines are somewhat step-like corresponding to the facets.

[0031] The dashed line represents typical values for a conventional LOE designed for use in a head-mounted display (HMD), and the reflectivity is selected to provide a relatively clear view of the natural scene. These lines appear similar to the dotted line, but with reduced slope. Accordingly, here too, the straight descending line 34 starting at 100 (which means the maximum intensity of the light incident on the LOE) reaches only about 50% at the end, meaning that only about 50% of the propagating light energy is externally coupled (towards the observation window). Correspondingly, the ascending line 35 reaches only about 42, meaning that the reflectivity of the last facet is only about 42%. This results in a transmittance of about 58% at an appropriate angle of incidence, and it is expected to be similarly high in the direction across the LOE along which the natural scene is viewed, high enough for the scene to appear satisfactorily clear.

[0032] As described above, the transmittance of the latter is not high enough to avoid blurring of the user's face and eyes of the HMD to an external observer and the visibility associated with the facet. To correct this, the reflectance of the facet of the exemplary embodiment of the invention corresponding to the first aspect of the invention is further sufficiently reduced as represented by the solid plot line in FIG. 2. Here, the rising solid line 38 reaches only about 13, and the total reflectance of the last (i.e., maximum reflectance) facet preferably does not exceed about 13% (in some specific preferred embodiments, does not exceed about 5%), and the linear solid line 39 drops only to about 63, meaning that only about 37% of the propagating light energy is externally coupled. As a result, the transmittance of the last facet rises to approximately 87%, which significantly reduces the visibility of the facet to an external observer observing the user's face; the transmittance of the other facets is even greater. Also, as a result, in this preferred example, at least 63% of the image intensity coupled into the LOE continues to propagate along the LOE beyond the last facet and thus is wasted. In other specific preferred examples, the ratio of the coupled-in illumination propagating beyond the last facet is greater than 2 / 3 and, in certain preferred cases, exceeds 80% or 90%. Thus, in this embodiment, a counterintuitive design compromise is made, and the optical efficiency of the LOE is significantly reduced to significantly reduce or make invisible the visibility of the facet observed by an external observer. Note that in the exemplary embodiment, the reduction in the reflectance of the last facet is a factor of 13% / 42% = 0.31 relative to that value of the prior art design. More generally, in embodiments according to this first aspect of the invention, the reflectance of the facet is reduced by a factor between 0.5 and 0.1, preferably between 0.4 and 0.25, compared to conventional optical designs.

[0033] In a second exemplary embodiment of the present invention, corresponding to a second aspect of the present invention, it is assumed that the image-carrying light incident on the LOE (or coupled into the LOE) is S-polarized with respect to the facet. This can be due to, in some HMD groups, the image projector (e.g., a liquid crystal display) itself that inherently emits polarized light, or a polarizing filter inserted in the optical path between the image projector (or collimating assembly) and the LOE. According to the novel feature of this second aspect, the reflectivity of the facet with respect to P-polarization is minimized or significantly reduced compared to their reflectivities with respect to S-polarization. In some embodiments, the facet is substantially transparent to P-polarization in an angular range of at least about 30 degrees including the light incident direction perpendicular to the first major surface. This maximizes the transmittance of the facet with respect to P-polarization, allowing more light emitted from the viewer's face to reach an external observer, thus making the facet more transparent and difficult to see for that person. It should be noted that this feature can be applied either by conventional means or in addition to the optimization of the reflectivity with respect to S-polarization according to the first aspect of the present invention. The term "substantially transparent" is used in its ordinary meaning. Quantitatively, it typically exhibits a transmittance exceeding 95%, most preferably exceeding 98%.

[0034] FIG. 3A shows, as an example, the reflectivities of typical facets in a conventional LOE for two polarization orientations, namely P-polarization and S-polarization orthogonal thereto, as a function of the angle of the incident light ray. FIG. 3B is a similar plot of the reflectivity for the LOE in an exemplary embodiment corresponding to the second aspect of the present invention. In this embodiment, the reflectivity of the incident light of S-polarization within the range of the incident angles of interest is optimized to a value representing a balance between efficient display image transmission and natural scene visibility, i.e., typically within the range of 10% to 25%, or a reduced reflectivity according to the first aspect of the present invention described above. However, compared to FIG. 3 A and FIG. 3As is clearly seen in B, the reflectance of incident P-polarized light in or near the direction perpendicular to the block main surface is significantly reduced. Preferably, this reduction is at least 4-fold, more preferably at least 8-fold. Additionally or alternatively, the value of the reflectance for P-polarized light in that direction preferably does not exceed 1 / 3, more preferably 1 / 5, of the value of the corresponding reflectance of the facet for S-polarized light.

[0035] In a third exemplary embodiment of the invention corresponding to a third side surface of the invention combinable with one or both of the previous two side surfaces, the reflectance of any of the facets at an angle of incidence different from the range of angles of incidence that deflect the image-carrying light that has propagated along the LOE and arrived towards the wearer's eye, more generally towards the eye motion box, is significantly reduced. The range of angles of incidence within which the reflectance is thus reduced includes, in particular, those corresponding to the direction of light transmitted across the LOE, such as from the viewer's face and eyes towards an external observer. This is equivalent to an increase in transmittance along that direction and makes the facets less visible.

[0036] Here, a third aspect of the present invention will be further described. For example, referring to FIG. 4A, a partial view of an exemplary typical LOE 10 is shown, and a light ray of a display signal (i.e., image-carrying light) propagates through it from the left end and is deflected (or externally coupled) by five facets 16 et al. The light rays shown are originally central light rays emitted from three points selected to span the displayed image. Specifically: the light ray illustrated by the solid line 42 is emitted from the central point of the image, the light ray illustrated by the long dashed line 41 is emitted from the extreme right of the image (as viewed by the viewer), and the light ray illustrated by the short dashed line 43 is emitted from the extreme left of the image (as viewed by the viewer). As clearly seen in the illustration, light rays from different image points reach the eye 20 through different facets. For example, the light ray (short dashed line) reaching the eye from the leftmost point mainly passes through the first (leftmost) facet 16a, the light ray reaching the eye from the central point (solid line) mainly passes through the third (central) facet 16b, and the light ray reaching the eye from the rightmost point (long dashed line) mainly passes through the fifth (rightmost) facet 16c. For such light rays, there is a unique angle of incidence at the corresponding facet. More generally, for each facet, there is a predetermined range of angles of incidence (from the corresponding part of the image) for directing the light ray towards any point within the eye motion box (EMB) 17, where the light ray is incident on the eye 20.

[0037] Focusing on the last (rightmost) facet 16c in the array of facets through which the image-carrying light propagates, this has the highest reflectivity by design (as described above and also shown, for example, at the right end of the plot in FIG. 2); thus, it has the minimum transmittance conventionally for the light passing through the LOE and is the most visible to an external observer (as demonstrated by the leftmost band in FIG. 1B, for example). This facet 16c and the light rays reflected thereby are shown enlarged in FIG. 4B, and the circular region detailed and appended in FIG. 4A is shown. As can be observed from the drawing, three representative light rays reach at their respective incident angles. Thus, in this example, the light ray from the left of the image (short dashed line) is incident at about 30 degrees, the light ray from the center of the image (solid line) is incident at about 23 degrees, and the light ray from the right of the image (long dashed line) is incident at about 16 degrees. Note that the same incident angles apply to all of the other facets.

[0038] In this case, only the one from the right side of the image (long dashed line) is the light ray of interest and only that reaches the EMB17. More generally, light rays emitted from near the region of the image within a range of incident angles near 16 degrees are reflected within the EMB17. This is the range in which the reflectivity has to be maintained high by design (or potentially reduced by the first and / or second aspects of the present invention). On the other hand, according to the third aspect of the present invention, the reflectivity of the facet 16c with respect to the optical signal arriving at an angle quite different from the above-described design range is reduced with respect to the value of the reflectivity in the design range.

[0039] Referring again to FIG. 4A, light crossing the LOE above the direction indicated by the vertical arrow 45, such as the light reflected from the viewer's face towards the external observer, is seen and passes through the facet 16c at an incident angle quite different from the above-described range (similar to all of the other facets). As observed in FIG. 4B, this angle is about 23 degrees. Thus, in this example, the range of incident angles of about 23 degrees is where the reflectivity of the facet 16c should be considerably reduced, increasing the transmittance in the transverse direction (arrow 45) and thus reducing the visibility of the facet.

[0040] More generally, in an embodiment according to the third aspect of the present invention, the reflectivity of the last facet of the array is preferably at least twice that of its reflectivity with respect to light propagating in a direction perpendicular to the main surface, for the portion of the light that is externally coupled from there towards any point within the eye motion box.

[0041] FIG. 4C schematically illustrates the design goals for facet 16c of FIG. 4A, and briefly, for the angle of incidence within the range of 16 to 21 degrees (for the light rays reaching the EMB), the reflectivity is relatively high as illustrated by rectangle 51, and for a high angle of incidence, preferably for the angle of incidence within the range of 22 to 25 degrees, the reflectivity is relatively low as illustrated by vertical lines 52. A plot 53 (solid line) of reflectivity versus angle of incidence for facet 16c of FIG. 4A is also seen in FIG. 4C to satisfy these requirements and is compared with a similar plot 54 (dashed line) for a conventional facet.

[0042] It should be noted that similar design considerations are applied to other facets in the LOE, and its visibility to an external observer can be further reduced.

[0043] A further aspect of the present invention, which is useful alone or in combination with any one or more of the above-described aspects of the present invention or applicable to the entire configuration of a light guide (including a diffractive waveguide), is disclosed here with reference to FIGS. 5A and 5B. As illustrated in FIG. 5A, the residual image-carrying light that propagates along the LOE 10 and is not externally coupled towards the observation window continues to propagate and reaches the end face 15# of the LOE. At least a part of this light is reflected back at its end face and propagates in the opposite direction 25 along the LOE, where the external coupler typically couples a part of this light outward 27 away from the user. This can result in an unwanted glow or glare emitted from the LOE and visible to an external observer. This effect can be particularly pronounced in the LOE according to the first aspect of the present invention because a relatively large portion of the injected image intensity propagates through all of the facets and reaches the end face 15.

[0044] To reduce this effect, according to this aspect of the present invention, also, as illustrated in FIG. 5B, a light absorption coating film or layer 35 is applied to the end face 15 of the LOE10. The light absorption coating can advantageously also be applied to any of the other three sides of the LOE. The light absorption coating 35 can conveniently be implemented as a layer of black paint. In some embodiments, the coating is configured to have a rough surface, which can be achieved by roughening the edges of the LOE before applying the paint, or by employing a rough film or layer that is bonded to the relevant side of the LOE using an optical adhesive or the like. It should be noted that the orientation of the LOE shown in the drawings is considered an implementation of the "side injection" type, where the image illumination incident on the LOE enters from near the side edge and propagates horizontally. It should be noted that all the features shown are equally applicable to an implementation of the "top-down" type, where the image is injected from the upper surface of the LOE and propagates downward, and is also within the scope of the present invention. In some cases, other intermediate orientations are also applicable and are included within the scope of the present invention unless explicitly excluded. The above numerical examples are merely examples and are understood to vary in the design optimization process. In various embodiments of the present invention, it is understood that two or more aspects of the present invention are combined in an optimized design. The above description is intended to serve only as an example, and it is understood that many other embodiments are possible within the scope of the present invention as defined by the appended claims.

[0045] As long as the appended claims are drafted without multiple dependencies, this is done only to satisfy the formal requirements in jurisdictions that do not allow such multiple dependencies. It should be noted that all possible combinations of the features suggested by making the claims multiply dependent are clearly contemplated and should be considered part of the present invention.

Claims

**Claim 1** An optical system for simultaneous viewing by a viewer of a natural scene and an image on a near-eye image projector, the optical system comprising: (a) a light-guide optical element (LOE (Light-guide Optical Element)); and (b) a support structure provided for supporting the light-guide optical element on the viewer's head at a position facing at least one eye of the viewer, wherein the light-guide optical element is a single light-guide optical element disposed between at least one eye of the viewer and the natural scene, and is a light-guide optical element for simultaneous viewing by at least one eye of the viewer of the natural scene and a projection image introduced into the light-guide optical element, a block of transparent material having a first major surface and a second major surface parallel to the first major surface, the light carrying the projection image introduced into the light-guide optical element propagating within the light-guide optical element by internal reflection at the first and second major surfaces, and a plurality of mutually parallel partially reflecting surfaces within the block and oriented obliquely with respect to the first major surface, the partially reflecting surfaces being configured to externally couple a portion of the light through the second major surface, wherein the reflectivity of each of the partially reflecting surfaces is set such that the total power of the externally coupled light is less than 1 / 3 of the total power of the light carrying the projection image introduced into the light-guide optical element, the light introduced into the light-guide optical element and carrying the projection image is S-polarized with respect to the plurality of mutually parallel partially reflecting surfaces, and the reflectivity of the plurality of mutually parallel partially reflecting surfaces with respect to P-polarized light is reduced relative to their reflectivity with respect to S-polarized light. An optical system. **Claim 2** The optical system according to claim 1, wherein the reflectivity of each of the partially reflecting surfaces is set such that the total power of the externally coupled light is less than 1 / 5 of the total power of the light carrying the projection image introduced into the light-guide optical element. **Claim 3** The optical system according to claim 1, wherein the reflectivity of each of the partially reflecting surfaces is less than 13%. **Claim 4** The optical system according to claim 1, wherein the block has an end face on which light propagating within the light guide optical element that has passed through the partially reflective surface is incident, and the end face is coated with a light absorption layer configured to absorb light that is introduced into the light guide optical element and not externally coupled.

5. The optical system according to claim 4, wherein the light absorption layer is implemented as a black paint applied to the rough end face.

6. A light guide optical element for simultaneous observation by a viewer's eye of an actual scene and a projected image introduced into a light guide optical element (LOE (Light-guide Optical Element)), A block of a transparent material having a first main surface and a second main surface parallel to the first main surface, wherein light that conveys the projected image introduced into the light guide optical element propagates within the light guide optical element by internal reflection at the first and second main surfaces, and A plurality of mutually parallel partially reflective surfaces that are within the block and are oriented obliquely with respect to the first main surface, and the partially reflective surfaces are configured to externally couple a part of the light through the second main surface, and the light guide optical element includes the plurality of mutually parallel partially reflective surfaces. The reflectivity of each of the partially reflective surfaces is set such that the total power of the light externally coupled is less than 1 / 10 of the total power of the light that conveys the projected image introduced into the light guide optical element. The light that is introduced into the light guide optical element and conveys the projected image is S-polarized with respect to the plurality of mutually parallel partially reflective surfaces. A light guide optical element in which the reflectivity with respect to P-polarization of the plurality of mutually parallel partially reflective surfaces is reduced compared to their reflectivity with respect to S-polarization.

7. A light guide optical element for simultaneous observation by a viewer's eye of an actual scene and a projected image introduced into a light guide optical element (LOE (Light-guide Optical Element)), A block of a transparent material having a first main surface and a second main surface parallel to the first main surface, wherein light that conveys the projected image introduced into the light guide optical element propagates within the light guide optical element by internal reflection at the first and second main surfaces, and A plurality of mutually parallel partially reflecting surfaces that are within the block and are oriented obliquely with respect to the first major surface, and the partially reflecting surfaces are configured to externally couple a part of the light through the second major surface, and the light guide optical element includes a plurality of mutually parallel partially reflecting surfaces. The reflectance of each of the partially reflecting surfaces is set such that the total power of the light externally coupled is less than 1 / 3 of the total power of the light that conveys the projection image introduced into the light guide optical element. The reflectance of each of the partially reflecting surfaces is less than 5%. The light introduced into the light guide optical element and conveying the projection image is S-polarized with respect to the plurality of mutually parallel partially reflecting surfaces. A light guide optical element in which the reflectance with respect to P-polarization of the plurality of mutually parallel partially reflecting surfaces is reduced compared to their reflectance with respect to S-polarization.

8. An optical system for simultaneous observation of a natural scene by a viewer and an image on a near-eye image projector, the optical system comprising: (a) a light guide optical element (LOE (Light-guide Optical Element)); and (b) a support structure provided to support the light guide optical element at a position facing at least one eye of the viewer on the viewer's head. The light guide optical element is a single light guide optical element disposed between at least one eye of the viewer and the natural scene, and is a light guide optical element for simultaneous observation of the natural scene and a projection image polarized in a first direction and conveyed by light introduced into the light guide optical element by at least one eye of the viewer. A block of a transparent material having a first major surface and a second major surface parallel to the first major surface, and the light that conveys the projection image introduced into the light guide optical element propagates within the light guide optical element by internal reflection at the first and second major surfaces, and the block. A plurality of mutually parallel partially reflecting surfaces that are within the block and are oriented obliquely with respect to the first major surface so as to externally couple a part of the light toward the viewer's eye. The reflectivities of the respective partially reflecting surfaces in the direction perpendicular to the first and second main surfaces with respect to the light polarized in the second direction orthogonal to the first direction are less than 1 / 3 of its reflectivity in the direction with respect to the light polarized in the first direction. The reflectivity of each of the partially reflecting surfaces is set such that the total power of the externally coupled light is less than 1 / 3 of the total power of the light that conveys the projection image introduced into the light guide optical element. The light introduced into the light guide optical element and conveying the projection image is S-polarized with respect to the plurality of mutually parallel partially reflecting surfaces. An optical system in which the reflectivity with respect to P-polarization of the plurality of mutually parallel partially reflecting surfaces is reduced compared to their reflectivity with respect to S-polarization. **Claim 9** The optical system according to claim 8, wherein the partially reflecting surface substantially transmits P-polarization for at least an angular range of about 30 degrees including the direction perpendicular to the first main surface.

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