Optical system using a dual reflector coupled incidence method for light guides

Abstract

The optical system (1) includes a light guide (100) and an image projector (200). The combined incidence configuration includes a first planar reflector (250) that forms an acute angle [3] with the main surface (101) of the light guide and extends over the thickness h of the light guide, and a second planar reflector (271) that is outside the light guide and inclined thereto at an angle 2 [3]. Light rays passing through the first portion (Di) of the projector exit aperture are incident directly on the first planar reflector (250), reflected and incident on the main surface (101) of the light guide at a first incidence angle, and light rays passing through the second portion (D2) of the projector exit aperture are incident on the second planar reflector (271), reflected toward the first planar reflector (150), and incident on the second main surface (102) at the same incidence angle.

Description

[Technical Field]

[0001] The present invention relates to an optical system, and more particularly to an optical system that couples an image to a light guide optical element using a dual reflector arrangement. [Background technology]

[0002] Light guide-based displays typically employ a slab-shaped light guide with parallel front and rear surfaces to guide the image in front of the user's eyes and display it by merging and emitting it toward the eyes. In some cases, the light guide can achieve one-dimensional or two-dimensional optical aperture expansion by progressively redirecting the light within the light guide and / or during the merging emission process. This progressive redirection of light is usually achieved by a collection of embedded partial reflectors or by diffractive optical elements.

[0003] Combining an image with a light guide presents design challenges. Optimal image uniformity is achieved when the image light "fills" the thickness of the light guide, that is, when all rays of the image and its reflections are present at every point within the thickness of the light guide. This often requires relatively large projectors and combined configurations, and determines a geometric layout that can conflict with ergonomic and aesthetic design considerations. [Overview of the project]

[0004] This invention is an optical system that uses a dual reflector arrangement to couple an image to a light guide optical element.

[0005] According to the teachings of embodiments of the present invention, (a) a light guide having first and second parallel principal surfaces for supporting the propagation of image light by internal reflection on principal surfaces, wherein the principal surfaces are separated by the thickness of the light guide, and the light guide includes a coupled emission arrangement for coupled emission of image light from the light guide toward the observer's eye; (b) an image projector for projecting light corresponding to a collimated image through a projector emission aperture; and (c) a coupled incidence arrangement configured to coupled and propagate light from the image projector within the light guide, comprising (i) a first planar reflector forming an acute angle β with the principal surfaces and extending throughout the thickness of the light guide; and (ii) a first outside the light guide. An optical system is provided, comprising: a second planar reflector associated with the first main plane, the plane of the second planar reflector inclined with respect to the first main plane at an angle 2β such that the plane of the second planar reflector corresponds to the first main plane under reflection in the plane of the first planar; the image projector is aligned in a coupled incident configuration, and for each pixel of a collimated image, a ray corresponding to that pixel passing through a first portion of the projector exit aperture is incident directly on the first planar reflector, reflected and incident on the first main plane at a first angle of incidence; and a ray corresponding to that pixel passing through a second portion of the projector exit aperture is incident on the second planar reflector, reflected toward the first planar reflector, reflected from the first planar reflector and incident on the second main plane at a first angle of incidence.

[0006] According to further features of one embodiment of the present invention, the second planar reflector is formed on the surface of the prism attached to the first main surface.

[0007] According to further features of one embodiment of the present invention, the light guide is mainly formed from a material having a first refractive index, and the prism is formed from a material having a second refractive index.

[0008] A further feature of one embodiment of the present invention also provides a compensating wedge formed from a material having a first refractive index, which is interposed between the prism and the first main surface.

[0009] According to further features of one embodiment of the present invention, a portion of the light guide adjacent to the first planar reflector is formed from a material having a second refractive index, the second refractive index being greater than the first refractive index.

[0010] According to further features of one embodiment of the present invention, the image projector is integrated with a prism, and the image projector includes a polarizing beam splitter positioned within the prism to guide light from the image plane toward first and second planar reflectors via a reflective collimating optical system.

[0011] According to further features of one embodiment of the present invention, a reflective collimating optical system is located behind a second plane reflector, and light from the image plane passes through the second plane reflector to the reflective collimating optical system, passes through the second plane reflector again and is reflected obliquely to the second plane reflector by a polarizing beam splitter and coupled to a light guide.

[0012] According to further features of one embodiment of the present invention, the angle β is between 35 and 55 degrees.

[0013] According to further features of one embodiment of the present invention, the second planar reflector is perpendicular to the first main plane of the light guide. [Brief explanation of the drawing]

[0014] The present invention is described herein for illustrative purposes only, with reference to the accompanying drawings. [Figure 1A] This is a schematic isometric view of an optical system configured and operating according to an embodiment of the present invention, which is incorporated as a binocular near-eye display with one-dimensional aperture magnification of the projected image within a light guide. [Figure 1B]This is a schematic isometric view of an optical system configured and operating according to an embodiment of the present invention, which is incorporated as a binocular near-eye display with two-dimensional aperture magnification of the projected image within a light guide. [Figure 2A] This is a schematic side view illustrating the coupled incidence of an image with reflective coupled emission onto a light guide. [Figure 2B] This is a schematic side view illustrating the coupled incidence of an image with diffractive coupled emission onto a light guide. [Figure 3A] This is a partially schematic side view similar to Figure 2A, illustrating the ray path for the principal ray of the image. [Figure 3B] This is a partially schematic side view similar to Figure 2A, illustrating the ray path for the light rays at the shallowest angle in the image. [Figure 3C] This is a partially schematic side view similar to Figure 2A, illustrating the ray paths for the sharpest angle rays in the image. [Figure 3D] This figure is similar to Figures 3A-3C and illustrates the size parameters of the coupled incident prism required to capture both the shallowest and steepest angle rays to satisfy the light guide. [Figure 4A] This is a schematic top view showing the inclination direction of the eyeglass frame light guide relative to the user's line of sight. [Figure 4B] This is a schematic side view showing the inclination direction of the eyeglass frame light guide relative to the user's line of sight. [Figure 5A] These are schematic side views illustrating the coupled incident configuration from the optical system shown in Figures 1A and 1B, showing the ray path of the principal ray of the image, starting from the first portion of the projector output aperture. [Figure 5B] This is a schematic side view illustrating the coupled incident configuration from the optical system shown in Figures 1A and 1B, showing the ray path of the principal ray of the image, starting from the second portion of the projector exit aperture. [Figure 5C]A schematic side view illustrating a combined incident arrangement from the optical systems of FIGS. 1A and 1B, showing the ray path of the chief ray of an image starting from the entire projector emission aperture. [Figure 6A] A schematic side view similar to FIGS. 5A - 5C, illustrating the ray path of the light ray at the shallowest angle of the image. [Figure 6B] A schematic side view similar to FIGS. 5A - 5C, illustrating the ray path of the light ray at the steepest angle of the image. [Figure 6C] A figure similar to FIGS. 6A and 6B, illustrating the size parameters of the combined incident prism necessary to fill the light guide by capturing both the light ray at the shallowest angle and the light ray at the steepest angle. [Figure 7] A figure similar to FIGS. 5A - 5C, showing the ray path that may generate a ghost image in a particular embodiment of the optical system. [Figure 8] A schematic side view similar to FIG. 7, illustrating the modification of the combined incident configuration to remove the ghost ray path of FIG. 7. [Figure 9A] A figure similar to FIGS. 5A - 5C, illustrating another ray path that may generate a ghost image in a particular embodiment of the optical system. [Figure 9B] A schematic side view similar to FIG. 9A, illustrating the change in the combined incident configuration to remove the ghost ray path of FIG. 9A. [Figure 10A] A schematic side view similar to FIGS. 5A - 5C, illustrating options when the high refractive index portion of the light guide adjacent to the combined incident region is provided without a correction wedge prism. [Figure 10B] A schematic side view similar to FIGS. 5A - 5C, illustrating options when the high refractive index portion of the light guide adjacent to the combined incident region is provided with a correction wedge prism. [Figure 11] A schematic side view similar to FIGS. 5A - 5C, illustrating a first option for integrating a combined prism for coupling an image into a light guide and an image projector. [Figure 12]This schematic side view, similar to Figures 5A-5C, illustrates a second option for integrating a coupling prism and an image projector for compositing an image onto a light guide. [Modes for carrying out the invention]

[0015] This invention is an optical system that uses a dual reflector arrangement to couple an image to a light guide optical element.

[0016] The principle and operation of the optical system according to the present invention can be better understood by referring to the drawings and accompanying descriptions.

[0017] First, Figures 1A–4B illustrate typical use scenarios of the present invention, illustrate some conventional methods for coupled injection configurations for such applications, and define various terms and parameters used to describe the features of the present invention. Next, details of various preferred embodiments of the present invention are shown with reference to Figures 5A–511.

[0018] Figures 1A and 1B are schematic isometric views of a head-mounted display 1. An image is projected by a projector 200 and coupled to a light guide optical element (LOE) 100, synonymous with "waveguide" or "substrate," which is supported by a support structure shown here in the form of an eyeglass frame 106. The waveguide typically consists of an optical substrate having two parallel main surfaces. The light corresponding to the projected image coupled to the waveguide 100 is captured by total internal reflection (TIR). Due to TIR, the image in Figure 1A propagates mainly in the x-axis direction. The waveguide 100 includes embedded elements that gradually couple light from the cavity toward the observer's eye, thereby achieving optical aperture expansion in the x-direction. These elements are located within region 110 and may be partially reflective surfaces (i.e., "facets") 111 embedded within the substrate, as shown in Figure 2A, or a volume grid or surface grid 112, as shown in Figure 2B. Although the embodiments described in the disclosure below primarily refer to embodiments comprising partial reflective surfaces, the teachings of the present invention are equally applicable throughout to waveguides comprising diffractive elements or combinations of diffractive and reflective elements.

[0019] The waveguide 100 may include more than one set of co-parallel elements, as shown in Figure 1B, where the embedded elements in the first region 120 progressively redirect the image light within the substrate, thereby expanding the effective optical aperture approximately in the y-axis direction, while the embedded elements in the second region 110 expand the light approximately in the x-axis direction. Here again, two-dimensional aperture expansion can employ reflective elements, diffracting elements, or a combination of both.

[0020] Figures 2A-23D illustrate conventional geometric shapes for coupling light corresponding to an image to a waveguide, shown in a one-dimensional magnification scenario, but applicable to a two-dimensional aperture magnification scenario. In Figures 2A and 2B, the image from the display 210 is collimated by the lens 220 and coupled to the waveguide 100 through the coupled incident prism 230. The upward rays 11b and downward rays 11a represent the image and conjugate (inverted) image, which are confined by TIR between the main surfaces 101 and 102 of the waveguide, as their energy is exchanged as they propagate through the waveguide. When rays 11b are reflected by one of the embedded partial reflecting surfaces 111 in Figure 2A or by the diffractive optical element 112 in Figure 2B, they are redirected to rays 13 that are no longer confined by TIR and are thus coupled out of the waveguide toward the “eye motion box” (EMB) corresponding to the area where the user’s eye 2 views the image.

[0021] The image coupled to the waveguide consists of different fields of view (different pixels reaching different locations on the user's retina), each of which can be represented by a pair of parallel rays. Figure 3A shows downward rays 12a and upward rays 12b representing the central field of view. To obtain a uniform image at output, the effective aperture 20 must be satisfied. The size of the effective aperture 20 in the direction perpendicular to the waveguide (z-axis in Figure 3A) is twice the thickness of the waveguide and is defined between the cutoff end at the end of the prism 230 and its mirror image on the lower waveguide surface 102. Typically, the prism 230 is configured such that the light incidence plane is perpendicular to the central field of view, thereby minimizing dispersion artifacts.

[0022] Figures 3B and 3C show the waveguide system 1 at an angle α with respect to the main surface of the waveguide. min and α max This shows two extreme field of view positions propagating through [the specified path]. In Figure 3B, the ray is at the minimum angle α with respect to the main plane. minpropagates and becomes the downward ray 11a and the upward ray 11b. In FIG. 3C, the light propagates at the maximum angle α with respect to the major surface of the waveguide. max propagates and becomes the downward ray 13a and the upward ray 13b. The field of view (FoV) guided by the waveguide in the x-z plane is given by the following equation. FoV = α max -α min

[0023] Considering the input structure in these figures, as shown in FIG. 3D, for a waveguide with a thickness h whose required projector size can be estimated based on (a) the size D defined as the area where the light rays enter to reach the aperture 20 in the required field of view at the back surface (light incident surface) of the prism 230, and (b) the distance a between the center of the incident aperture 20 and the back surface of the prism 230, these size parameters are given by the following equations.

[0024]

Equation

[0025] These parameters diverge when the value of α min is small, and accordingly, the size of the projector in a waveguide with a small α min becomes large. Since the orientation of the projector in FIGS. 2A to 3D is determined by the geometric parameters of the waveguide, especially when α min is small, this may lead to a complicated system. Therefore, it is advantageous to design an input coupling arrangement that provides additional flexibility regarding the orientation of the projector. Additionally, the waveguide is often tilted for aesthetic or other reasons, as illustrated in FIGS. 4A and 4B, and is often desired to be arranged and oriented so that the image projector can be conveniently and compactly incorporated into the frame 106.

[0026] In the context described above, a particular embodiment of the present invention, as shown in Figures 5A to 11, provides an optical system 1, which is typically a display system as shown in Figures 1A and 1B, and includes a light guide 100 having first and second parallel main surfaces 101, 102 for supporting the propagation of image light 12a, 12b by internal reflection at the main surfaces. The main surfaces 101, 102 are separated by a thickness h of the light guide. The light guide also includes a coupled emission configuration, as shown in Figure 2A or 2B described above, for coupled emission of image light from the light guide toward the observer's eye. The optical system also includes an image projector for projecting light corresponding to a collimated image through a projector emission aperture D. The projector is schematically represented in Figure 6C as an image source 210 and a collimating optical system 220.

[0027] In particular features of a particular preferred embodiment of the present invention, an optical system 1 is arranged to coupled incident light from an image projector to propagate within a light guide, the light guide further includes a coupled incident configuration comprising a first planar reflector 250 and a second planar reflector 271, which form an acute angle β with the main surface and extend across the thickness of the light guide 100. The second planar reflector 271 is associated with the first main surface 101 outside the light guide 100 and is inclined at an angle 2β with respect to the first main surface 101. Thus, the plane of the second planar reflector 271 corresponds to the plane of the first main surface 101 under reflection in the plane of the first planar reflector 250. The plane of the second planar reflector can be considered a “conjugate plane” with respect to the first main surface 101 under reflection in the plane of the first planar reflector 250. The plane of the first planar reflector 250 also typically bisects the angle between the first main surface 101 and the plane of the second planar reflector 271, but may be slightly offset from the line of intersection between these planes, as will be described later.

[0028] In the combined incidence configuration, the image projector alignment is such that, for each pixel of the collimated image, a ray 11 corresponding to that pixel passes through the first portion D1 of the projector output aperture, is directly incident on the first planar reflector 250, reflected as ray 12a, and selected to incident on the first main surface 101 at a first incidence angle α, as shown in Figure 5A. Also, as shown in Figure 5B, a ray 11 corresponding to a pixel passes through the second portion D2 of the projector output aperture, is incident on the second planar reflector 271, reflected toward the first planar reflector 250, reflected from the first planar reflector as ray 12b, and incident on the second main surface 102 at a first incidence angle α. Thus, the combined rays emanating from the entire projector output aperture D fill the light guide, as shown in Figure 5C.

[0029] At this stage, it should be understood that the coupled incidence configuration of the present invention provides additional design flexibility, particularly useful for implementing eyeglass form factors using projector deployments that extend outward from the plane of a light guide adjacent to or integrated with the side of the eyeglass frame. The angle β can be selected according to various design considerations and is typically in the range of 35 to 55 degrees. The corresponding angle of the second planar reflector 271 is 70 to 110 degrees with respect to the main plane 101. In certain cases, employing a second planar reflector 271 deployed perpendicular to the main plane 101 may be preferable for ease of manufacture and may also avoid the need for a dispersion-correcting wedge prism, as will be discussed later. This corresponds to an angle β of 45 degrees with respect to the inclination of the first planar reflector 250.

[0030] Figure 5A shows the trajectory of a ray 11 incident on the coupled incident mirror 250. As shown, the ray 11 is reflected by the coupled incident mirror 250 and becomes a downward ray 12a that is confined within the substrate by total internal reflection. The figure also shows the entire aperture 20 of the waveguide, which has a size of 2h (where h is the thickness of the waveguide) as previously mentioned, and also shows a virtual ray 12a' which represents the trajectory of the ray 12a if it were not reflected by the main surface 101. The ray 12a' represents the size of the aperture 20 filled by the mirror 250, which is given by the following equation.

[0031]

number

[0032] Figure 5B shows the trajectory of a ray 11 incident on the coupled mirror 271. Ray 11 is reflected by the coupled incident mirror 271 to become ray 13, which then incident on the coupled incident mirror 250, which then reflects ray 13 to become the upward ray 12b. The figure also shows the aperture 20, along with ray 12b', which represents the mirror image of ray 12b reflected from 271 and 250 around the main surface 101. Ray 12b' represents the relative portion of the aperture 20 filled by ray 11 incident on the mirror 271, which is given by the following equation.

[0033]

number

[0034] Clearly, the trajectories of the light rays 11 in Figures 5A and 5B combine to fill the entire aperture 20, as shown in Figure 5C.

[0035] Figures 6A and 6B show the trajectory of the extreme field in optical system 1, at an angle α with respect to the main plane of waveguide 100. min and α maxThe entire field of view determines the illumination required for the incident aperture of the waveguide. To minimize chromatic aberration, it is advantageous to position a coupled incident prism 270 having an incident plane perpendicular to the central field of view illuminated from the projector, as shown in Figure 6C. The prism may be bonded to the waveguide 100 using a low refractive index adhesive, or mounted with a small air gap from the waveguide 100, thereby maintaining the conditions for TIR of the coupled incident rays 12a on the main surface 101. The sides of the prism 270 may be coated to form a second planar reflector 271, or its function may also be provided by TIR depending on the range of incident angles to be treated. For clarity of presentation, the prism 270 is not shown in all drawings. However, it should be understood that the prism 270 is present in most cases unless otherwise specified.

[0036] As shown in Figure 3D above, the size D of the ray footprint on the incident prism 270, along with the distance a1+a2 from the center of the aperture 20 to the coupled incident surface of the prism 270, determines the required size of the projector. This configuration is a "folded" version of the arrangements in Figures 2A to 3D, and therefore a=a1+a2 and D are given by the same equations cited above. If the material of 270 differs from the material of the waveguide substrate, the coupled incident structure may produce chromatic aberration and / or mismatch between the coupled incident lower image 12a and upper image 12b. A corrective wedge prism 272 (further described later with reference to Figure 10B, and may be composed of several materials - not shown) can correct such distortion.

[0037] Figures 7-9B illustrate certain specific cases of ray paths that can lead to ghost images and how they can be suppressed. Referring to Figure 7, this is the steepest angle α in the waveguide. max If the elevation angle β of the planar reflector 250 is greater than the elevation angle α, then α maxThe case of >β is illustrated. In this case, as shown in Figure 7, upward rays 12b are incident on the reflector 250 and reflected by harmful rays 14, thereby potentially forming a ghost image. This ghost image can be suppressed by mounting the reflector 250 to protrude slightly from the main surface 102, as shown in Figure 8, thereby forming a cutoff edge that trims off unwanted rays 14. This solution comes at the cost of a slight decrease in efficiency, as some of the image rays 12b are incidentally trimmed and discarded.

[0038] Figure 9A shows that when the coupled incident mirror 250 is "missed," the light ray 11 incident on the coupled incident mirror 271 can be reflected by the light ray 13 and coupled to the waveguide. This can produce a ghost image in the output. In an optimally designed system, the illumination optical system associated with the image source (not detailed herein), together with the collimating optical system, should be able to achieve "pupil imaging" from the illumination pupil to the incident portion of the light guide 20, thereby largely eliminating stray rays such as the light ray 13 in Figure 9A. However, if such rays prove to be problematic, the resulting ghost can be eliminated by polarization control, as illustrated with reference to Figure 9B.

[0039] Specifically, to eliminate this ghosting, the embodiment shown in Figure 9B includes a quarter-wave plate 260 positioned near the first planar reflector 250, thereby rotating the polarization of all rays 13 reflected by the reflector 250. When the injected rays are polarized, the polarization of rays 12a and 12b in the waveguide is perpendicular to the polarization of rays 13 coupled to the waveguide. Therefore, harmful rays 13 inside the waveguide can be suppressed by placing a polarizer inside the waveguide or by applying a highly polarization-sensitive coating to the waveguide facets.

[0040] In certain preferred embodiments of the present invention, the coupled prism 270 is formed from a material having the same refractive index as the light guide 100, thereby avoiding chromatic aberration and image blurring or duplication problems that may occur at the interface between materials with different refractive indices. However, in certain cases, there may be advantages to using a material with a higher refractive index than that typically used for the light guide 100. Specifically, the light ray 11 must penetrate the waveguide, and the light ray 12a must be reflected by the coupled incident reflector (mirror) 250 and then confined within the waveguide by TIR. In particular, when the prism 270 is bonded to the light guide using a low refractive index adhesive, the relatively small difference in refractive index between the light guide material and the low refractive index adhesive imposes strict constraints on the angular orientation of the light rays 11 and 12, as well as on the coupled incident reflector 250. As shown in Figure 10A, this limitation can be relaxed if at least the coupled incident region of the waveguide is made from a material having a higher refractive index n2. By using a higher refractive index n2 in the prism 260 positioned below the coupled incident mirror 250, it is possible to maintain a larger difference between the refractive index of the prism 260 and the low refractive index adhesive used to attach the coupled prism, for example, thereby increasing design flexibility and enabling a larger field of view. Although the entire light guide 100 could, in principle, be made from a material having a refractive index n2, high refractive index materials may be more expensive and / or heavier than other optical materials, and matching may be more difficult if a refractive index matching adhesive is required. For these reasons, it may be preferable to form only the coupled incident region from a high refractive index material and provide a junction where the rest of the light guide switches to a low refractive index material. To minimize chromatic aberration and / or mismatch between the coupled incident lower image 12a and the upper image 12b, the interface between the prism 260 and the waveguide substrate is most preferably approximately perpendicular to the main plane of the waveguide.

[0041] The interface between the coupled prism 270 and the waveguide 100 or prism 260 can also be a source of chromatic aberration and mismatch between the coupled incident lower image 12a and upper image 12b if the coupled prism 270 has a different refractive index than the material of the waveguide 100 or prism 260 beneath it. While the above description has assumed the orientation of the second planar reflector 271 is at angle 2β, it is possible to achieve at least partial correction for the refractive index difference between the light guide and the waveguide or coupled prism by changing the orientation so that the plane of the reflector 271 still reflects the light guide even after considering the refractive index difference. Typically, such correction is not optimal because it does not work uniformly across different fields of view of the image, and is typically only sufficient for displays with small FOVs.

[0042] A more comprehensive correction for refractive index mismatches that could cause image blurring or duplication is illustrated in Figure 10B. In this case, an additional wedge prism 272 made from the same material as prism 260 (or waveguide if prism 260 is not used) is inserted between the coupled prism 272 and the first main surface 101, such that it presents a front surface equally inclined with respect to rays 11 and 13. The wedge angle is (90-2β) degrees, resulting in the front surface being perpendicular to the reflector 271. In this way, rays 11 and 13 associated with the same field of view receive the same refractive deflection at the interface between the coupled incident prism 270 and the wedge prism 272. A low refractive index adhesive or air gap must be present between the wedge prism 260 and the waveguide, as previously described.

[0043] Next, looking at Figures 11 and 12, in a particular advantageous embodiment, instead of a separate, self-contained image projector juxtaposed with the prism 270, the image projector may be integrated with the prism by using a polarizing beam splitter 273 positioned within the prism to guide light from the image plane toward the first and second planar reflectors via a reflective collimating optical system. This results in a more compact structure.

[0044] A first such embodiment is shown in Figure 11, in which the prism 270 includes a polarizing beam splitter (PBS) 273. Typically, a display device 280 defining the image plane is positioned near one face of the PBS prism 270, and a collimating lens (reflective collimating optical system) 290 is positioned on the other face of the PBS prism 270. In this case, the reflective collimating optical system 290 is positioned behind the second planar reflector 271 such that image light from the display device 280 passes through the PBS 273, through the second planar reflector 271 to reach the reflective collimating optical system 290, passes through the second planar reflector 271, is reflected and bounced back, and is further reflected at an oblique angle by the polarizing beam splitter 273 to both the first planar reflector 250 and the second planar reflector 271 and coupled to a light guide.

[0045] The display device may consist of a silicon liquid crystal (LCOS) display, a liquid crystal display (LCD), an OLED or micro-LED display, or a spatial light modulator (SLM) such as a scanning laser configuration. According to these different examples, the display device 280 may be self-emissive or, optionally, illuminated by an external light source, such as an RGB LED, through the reflection of polarized light from the PBS surface 273. The reflective collimating optical system 290 may be a single lens, a doublet, or a combination of other lenses including at least one reflective surface. The reflective collimating optical system 290 may preferably be separated from the prism surface / reflector 271 by an air gap or bonded to it using a low refractive index material, providing the required reflectivity at the relevant angles for coupled incidence of image light to the light guide as described above.

[0046] A ray 15 projected from a single pixel on the display device 280 is collimated by the optical system 290, reflected from 290, and then oriented as ray 17. A quarter-wave plate (not shown) is placed between 270 and 290, which rotates the polarization of the light after it is reflected from the collimating lens 290. In this way, ray 17 is reflected by ray 11 at surface 273 and coupled into the waveguide.

[0047] Figure 12 shows a modified embodiment of optical system 1 that is structurally and functionally similar to Figure 11. This embodiment employs the reflection of image rays 15 from a display device 280 onto a PBS surface 273, followed by collimation by a reflective collimating optical system 290, and rotation of polarization by a quarter-wave plate associated with the collimating optical system. After this, the collimated rays are transmitted by the PBS surface 273 as rays 11 for coupled incidence into a waveguide.

[0048] The above description is provided for illustrative purposes only, and it will be understood that many other embodiments are possible within the scope of the invention as defined by the attached claims.

Claims

1. An optical system, (a) A light guide having first and second parallel principal surfaces to support the propagation of image light by internal reflection on the principal surfaces, wherein the principal surfaces are separated by the thickness of the light guide, and the light guide includes a coupled emission arrangement for coupled emission of image light from the light guide toward the observer's eye, (b) An image projector for projecting light corresponding to a collimated image through a projector output aperture, (c) A coupled incidence configuration provided for coupled incidence of light from the image projector so as to propagate within the light guide, wherein the coupled incidence configuration is (i) A first planar reflector that forms an acute angle β with the main surface and extends over the entire thickness of the light guide, (ii) A second planar reflector, which is associated with the first main surface outside the light guide and is inclined at an angle 2β with respect to the first main surface, such that the plane of the second planar reflector corresponds to the first main surface under reflection by the plane of the first planar reflector, A coupled incident configuration comprising, Equipped with, The image projector is aligned with the coupled incidence configuration, so that for each pixel of the collimated image, a ray corresponding to the pixel passing through the first portion of the projector output aperture is directly incident on the first planar reflector and reflected, incident on the first main surface at a first incidence angle, and a ray corresponding to the pixel passing through the second portion of the projector output aperture is incident on the second planar reflector, reflected toward the first planar reflector, and further reflected from the first planar reflector and incident on the second main surface at a first incidence angle. Optical system.

2. The optical system according to claim 1, wherein the second planar reflector is formed on the surface of a prism attached to the first main surface.

3. The optical system according to claim 2, wherein the light guide is mainly formed from a material having a first refractive index, and the prism is formed from a material having a second refractive index.

4. The optical system according to claim 3, further comprising a correcting wedge formed of a material having the first refractive index, interposed between the prism and the first main surface.

5. The optical system according to claim 3, wherein a portion of the light guide adjacent to the first planar reflector is formed from a material having a second refractive index, the second refractive index being greater than the first refractive index.

6. The optical system according to claim 2, wherein the image projector is integrated with the prism, and the image projector includes a polarizing beam splitter disposed within the prism to guide light from the image plane toward the first and second planar reflectors via a reflective collimating optical system.

7. The optical system according to claim 6, wherein the reflective collimating optical system is located behind the second planar reflector, and light from the image plane passes through the second planar reflector to the reflective collimating optical system, is reflected and bounced back through the second planar reflector, is reflected at an oblique angle from the second planar reflector by the polarizing beam splitter, and is coupled and incident to the light guide.

8. The optical system according to claim 1, wherein the angle β is between 35 degrees and 55 degrees.

9. The optical system according to claim 1, wherein the second planar reflector is perpendicular to the first main surface of the light guide.

Images