Image projector with polarization catadioptric collimator

Abstract

An image projector for injecting a collimated image into an entrance aperture of a light guide employs collimation optics comprising a polarizing catadioptric arrangement to provide enhanced proximity of a main plane of the collimation optics to the entrance aperture of the light guide, thus, the size of the optical device is reduced or a larger field of view of an optical device of a given size is allowed. The disclosed embodiments modify a spatial light modulator (SLM), a laser scanning illumination arrangement with or without an SLM, with front-lit polarization via a polarization beam splitter (PBS) prism illumination at a 30 or 45 degree PBS angle; and an active matrix image generator combined via a dichroic combiner cube.

Description

[0001] Technical Field and Background Art

[0002] The present invention relates to near-eye displays, and in particular to an image projector with a polarizing catadioptric collimator for injecting an image into a light guide for an augmented reality display.

[0003] Near-eye augmented reality displays typically use an image projector to inject a collimated image into a light guide, which transmits the image to the user's eye while allowing the real world to be viewed through the light guide. In order to provide a uniform image, it is preferred that the injected image fill the thickness of the light guide. This requirement, along with the angular field of view (FOV) of the image, dictates the minimum size of the collimating optics that need to collimate the image before it is injected into the light guide. Figure 1A and Figure 1B Two such examples are schematically shown in FIG.

[0004] Specifically, in Figure 1A , an augmented reality display is schematically shown in which an image is generated by an LCOS (liquid crystal on silicon, LCOS) display chip 100 associated with the face of a prism 102. To simplify the presentation, the illumination arrangement is omitted. The image is reflected by a polarizing beam splitter (PBS) 104 toward a reflective collimating optical device 106, which collimates the image for delivery to an entrance aperture 110 of a light guide 112 via a coupling prism 108. The entrance aperture is shown as twice the thickness of the light guide because this is a geometric requirement to "fill" the entrance aperture with both the downwardly propagating image and the reflected upwardly propagating image. To simplify the presentation, the internal aperture expansion and / or outcoupling features of the light guide are also omitted.

[0005] It can be seen that the minimum size required for the prism is determined by tracing back from the entrance aperture to the outer limits of the desired field of view (FOV) and ensuring that the entire FOV is provided by the collimating optics 106. Since the distance from the entrance aperture to the collimating optics is the sum of the sizes of the coupling prism 108 and the PBS prism 102, the minimum size of the optics for a given field of view is relatively large.

[0006] Figure 1BSchematically illustrated is an augmented reality display employing a refractive collimating optical arrangement 114 to collimate an image from a display chip 116 for injection into an entrance aperture 110 of a light guide 112 via a coupling prism 108. Here, the size of the collimating optical arrangement is dictated by extrapolating the FOV from the entrance aperture 110 back outward to the front principal plane of the optical arrangement. In the example shown here, the FOV is significantly narrower than Figure 1A , but the size of the lens and the length of the optical arrangement are still large compared to the size of the coupling prism 108. Summary of the invention

[0007] The present invention is an image projector for injecting a collimated image into an entrance aperture of a light guide.

[0008] According to the teachings of an embodiment of the present invention, there is provided an image projector for injecting a collimated image into an entrance aperture of a light guide, the image projector comprising: (a) a polarization modifying spatial light modulator (SLM) disposed to modify the polarization of illumination based on image data provided to the SLM; (b) an illumination arrangement for illuminating the SLM with polarized illumination; (c) a polarization selecting element disposed to select light from the SLM corresponding to the image; and (d) a collimating optical device for collimating the light corresponding to the image to provide a collimated image at the entrance aperture of the light guide, wherein the collimating optical device comprises a polarization refractive-reflective arrangement comprising, in sequence: (i) a first quarter wave plate; (ii) a first optical surface implemented as a partial reflector; (iii) a second quarter wave plate; and (iv) a second optical surface implemented as a polarization selective reflector, wherein at least one of the first optical surface and the second optical surface is implemented as a non-planar surface having optical power, the non-planar surface acting on light twice, once as a refractive lens surface and once as a reflective lens.

[0009] According to further features in embodiments of the invention, the polarization selective element is a polarization beam splitter (PBS) integrated into the prism, and wherein the illumination arrangement directs the illumination to be reflected from the PBS towards the SLM.

[0010] According to another feature of an embodiment of the present invention, the PBS is inclined at an angle of 30 degrees relative to the surface of the SLM, the image projector also includes an angle selection reflector, the angle selection reflector is deployed to be arranged parallel to the SLM between the SLM and the PBS, the lighting arrangement guides the lighting to reflect from the angle selection reflector toward the PBS, and from the PBS toward the SLM, the angle selection reflector is reflective to visible light incident at an incident angle of 60 degrees and is substantially transparent to visible light incident at an incident angle of less than 30 degrees.

[0011] According to further features of an embodiment of the present invention, the PBS is inclined at a 45 degree angle relative to the surface of the SLM, and the image projector also includes a quarter wave plate and an illumination optical device reflective lens associated with the face of the prism, for directing illumination that has passed through the PBS back toward the PBS to be reflected toward the SLM at the PBS.

[0012] According to further features of embodiments of the invention, the illumination arrangement further comprises a light source associated with the illumination aperture, light propagates from the illumination aperture through the prism towards the illumination optics reflective lens, and wherein the illumination optics reflective lens and the collimating optics are configured to image the illumination aperture to an entrance aperture of the light guide.

[0013] According to further features of embodiments of the invention, the illumination arrangement further comprises a scanning mirror for scanning the illumination light beam over an angular range about at least one tilt axis, the scanning mirror being arranged to direct the illumination light beam through a prism toward a reflecting lens of the illumination optics, and wherein the reflecting lens of the illumination optics and the collimating optics are configured to image the scanning mirror to an entrance aperture of the light guide.

[0014] According to further features in embodiments of the invention, the second optical surface is a planar surface bonded to the image input surface of the light guide.

[0015] According to further features of embodiments of the invention, the first optical surface is a planar surface bonded to an output surface of the prism.

[0016] According to further features of embodiments of the invention, the first optical surface is a non-planar surface bonded to a corresponding non-planar output surface of the prism.

[0017] According to further features of an embodiment of the present invention, the lighting arrangement comprises a light guide having a pair of mutually parallel main surfaces for supporting propagation of illumination by internal reflection at the main surfaces and a plurality of mutually parallel partially reflective outcoupling surfaces, the pair of mutually parallel main surfaces being used to support propagation of illumination by internal reflection at the main surfaces, the plurality of mutually parallel partially reflective outcoupling surfaces being located inside the light guide and oriented obliquely relative to the main surfaces to couple the illumination out towards the SLM.

[0018] According to the teachings of an embodiment of the present invention, there is also provided an image projector for injecting a collimated image into an entrance aperture of a light guide, the image projector comprising: (a) a beam splitter integrated into a prism; (b) an image generator configured to generate an image at an image plane associated with a third face of the prism; and (c) a collimating optical device for collimating light of the image to provide a collimated image at the entrance aperture of the light guide, wherein the collimating optical device comprises a polarization refractive-reflective arrangement, the polarization refractive-reflective arrangement sequentially comprising: (i) a first quarter wave plate; (ii) a first optical surface implemented as a partial reflector; (iii) a second quarter wave plate; and (iv) a second optical surface implemented as a polarization-selective reflector, wherein at least one of the first optical surface and the second optical surface is implemented as a non-planar surface having optical power, the non-planar surface acting on light twice, once as a refractive lens surface and once as a reflective lens.

[0019] According to further features of an embodiment of the present invention, the beam splitter is a polarization beam splitter (PBS), and the image projector further includes: (a) an illumination arrangement including at least one light source and a scanning mirror, the at least one light source being used to generate a modulated intensity light beam; the scanning mirror being used to scan the illumination light beam over an angular range about at least one tilt axis, the scanning mirror being deployed to direct the light beam into a first face of a prism; (b) a first quarter wave plate and an illumination optical device reflecting lens associated with a second face of the prism, being used to direct light that has passed through the prism back toward the PBS; (c) a second quarter wave plate and a beam expansion reflector associated with a third face of the prism; and (d) a controller for synchronously modulating the intensity of the light source and controlling the scanning mirror to generate a time-averaged light intensity distribution corresponding to the image at the beam expansion reflector.

[0020] According to further features of an embodiment of the present invention, the beam splitter is a dichroic mirror, and wherein the image generator is a first active matrix image generator, which generates an image as light emission of at least a first wavelength, and the light of at least the first wavelength is reflected by the dichroic mirror, and the image projector also includes a second active matrix image generator associated with a second face of the prism, which generates an image as light emission of at least a second wavelength, and the light of at least the second wavelength is transmitted by the dichroic mirror to be combined with the light of the first wavelength when it reaches the collimating optical device.

[0021] According to another feature of an embodiment of the present invention, a second dichroic mirror is disposed in the prism and is not parallel to the dichroic mirror. The second dichroic mirror is transparent to light of the first wavelength and the second wavelength and is reflective to light of a third wavelength. The image projector also includes a third active matrix image generator associated with the first surface of the prism, which generates an image emitted as light of at least a third wavelength. The light of at least the third wavelength is reflected by the dichroic mirror to be combined with the light of the first wavelength and the second wavelength when it reaches the collimating optical device.

[0022] According to further features in embodiments of the invention, the second optical surface is a planar surface bonded to the image input surface of the light guide.

[0023] According to further features of embodiments of the invention, the first optical surface is a planar surface bonded to an output surface of the prism.

[0024] According to further features of embodiments of the invention, the first optical surface is a non-planar surface bonded to a corresponding non-planar output surface of the prism. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention is herein described, by way of example only, with reference to the accompanying drawings, in which:

[0026] Figure 1A is a schematic side view of a conventional near-eye augmented reality display employing the above-described projector with reflective collimating optics on a polarizing beam splitter prism;

[0027] Figure 1B is a schematic side view of a conventional near-eye augmented reality display employing the above-described projector with refractive collimating optics;

[0028] Figure 2A and Figure 2B is a schematic side view of a near-eye augmented reality display employing a projector constructed and operative in accordance with embodiments of the present invention, the projector employing polarizing catadioptric collimating optics deployed to inject a collimated image into an entrance aperture of a light guide via a coupling prism and via a coupling reflector, respectively;

[0029] Figure 3 According to a first implementation in which polarization catadioptric collimating optics are incorporated into a beam splitter prism Figure 2A and Figure 2B an enlarged schematic side view of a projector;

[0030] Figure 4 is with Figure 3 Similar views, Figure 4A variant implementation of a projector is shown in which polarization catadioptric collimating optics are bonded to the input surface of the light guide;

[0031] Figure 5 is with Figure 3 Similar views, Figure 5 Another variant implementation of a projector is shown in which polarization catadioptric collimating optics are incorporated into both the beam splitter prism and the input surface of the light guide;

[0032] Fig. 6A and Figure 6B is a schematic side view showing the embodiment of the invention when implemented using a reflective spatial light modulator (SLM) and a polarization beam splitter (PBS) tilted at 30 degrees relative to the SLM. Figures 3 to 5 Two possible lighting arrangements for use with a projector;

[0033] Figure 7 is a schematic side view of an additional implementation of a projector constructed and operative in accordance with an embodiment of the present invention, the projector being implemented using a 45 degree PBS;

[0034] Figure 8 is with Figure 7 A similar schematic side view, Figure 8 An implementation of a projector constructed and operated in accordance with an embodiment of the present invention is shown, the projector illuminating with a modulated scanning laser beam;

[0035] Fig. 9 is a schematic side view of another implementation of a projector constructed and operative in accordance with an embodiment of the present invention, the projector employing a light guide element to illuminate an SLM; and

[0036] Fig.10 is a schematic side view of an additional implementation of a projector employing a dichroic cube and an active matrix image generator, constructed and operative in accordance with an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The present invention is an image projector for injecting a collimated image into an entrance aperture of a light guide.

[0038] The principles and operation of an image projector according to the present invention may be better understood with reference to the drawings and accompanying description.

[0039] Now referring to the accompanying drawings, Figures 2A to 7 Various implementations of an image projector constructed and operative in accordance with various aspects of the present invention are shown for injecting a collimated image into an entrance aperture 26 ( Figure 2A and Figure 2B). Generally, these implementations include a polarization modifying spatial light modulator (SLM) 10, such as a liquid crystal on silicon (LCOS) display chip, which is deployed to modify the polarization of the illumination according to image data provided to the SLM from a suitable controller. For clarity, the illumination is arranged in Figures 2A to 5 is omitted and is referred to below FIG. 6A to FIG. 8 As described, the illumination arrangement is provided for illuminating the SLM 10. The polarization selective element 16, the polarization selective element 50 or the polarization selective element 160 selectively transmits (or selectively reflects, depending on the geometry) light corresponding to the desired image from the SLM. The collimating optics then collimate the light corresponding to the image to provide a collimated image at the entrance aperture 26 of the light guide 27.

[0040] A particular feature of one aspect of the invention is that the collimating optics comprises a polarizing catadioptric arrangement, such as Figures 3 to 5 As best shown, the polarization catadioptric arrangement sequentially has: a first quarter wave plate, typically integrated with a first optical surface 18 implemented as a partial reflector; and a second quarter wave plate, typically integrated with a second optical surface 20 implemented as a polarization selective reflector. At least one of the first optical surface 18 and the second optical surface 20 is implemented as a non-planar surface with optical power, which acts twice on light, once as a refractive lens surface and once as a reflective lens, thereby achieving greatly enhanced optical power with greatly shortened axial distance.

[0041] The projector of the present invention is mainly applicable to display structures that introduce the collimated image into the light guide 27 by means of geometrical optics coupling (i.e., no diffraction is involved). In this case, the main example of geometrical optics coupling is the use of a coupling prism 24 (e.g. Figure 2A as shown) and reflected coupling (as Figure 2B 26 ), a coupling prism 24 provides an appropriately angled coupling-in surface 22, and a mirror 28 is used for reflective coupling. In each case, the greatly reduced axial size of the collimating optics according to the present invention facilitates placing the principal plane of the collimating optics very close to the entrance aperture 26, thereby reducing the lateral size of the collimating optics required to provide a given angular field of view (FOV). In addition, by designing the collimating optics with a shorter focal length, the distance from the collimating optics to the image plane of the display chip and the corresponding size of any inserted optical elements (described below) can be minimized. Figure 2A The exemplary embodiment shown has an angular FOV of 65 degrees diagonal (46 x 46 degrees) and a focal length of 7.9 millimeters, resulting in a particularly compact implementation.

[0042] In a first subgroup of particularly preferred implementations of the invention, the polarization selective element is a polarization beam splitter (PBS) 16 or 50 integrated in a corresponding prism 15. The illumination arrangement directs illumination to the SLM 10 via the PBS (by reflection or transmission depending on the geometry).

[0043] The small diameter and short focal length of the catadioptric optics mentioned above, and the proximity of the optics to the entrance aperture of the light guide, facilitate the use of a variety of particularly compact PBS prism arrangements, as described in further detail below. Figure 2A and Figure 1A , it can be seen that in some cases the linear dimensions of the PBS prism 15 are approximately half the linear dimensions of an equivalent projector employing reflective collimating optics on the faces of a PBS cube. A 2x reduction in the linear dimensions of the PBS cube corresponds to an 8x reduction in the volume and mass of the prism, greatly facilitating the requirements for miniaturization of image projectors for near-eye augmented reality displays.

[0044] As previously mentioned, at least one of the first optical surface 18 and the second optical surface 20 is implemented as a non-planar surface with optical power that acts twice on light, once as a refractive lens surface and once as a reflective lens. Although in some embodiments, both optical surfaces are implemented with optical power, in some particularly preferred embodiments, it has been found to be advantageous to implement one of the surfaces as a planar surface, which can facilitate the manufacture and assembly of the projector. Figure 3 In the example shown, the first optical surface 18 is a planar surface. This option has particular synergy with the use of a PBS prism to support some or all other components of the projector, enabling the first optical surface to be bonded to the planar output surface of the prism, thereby simplifying assembly.

[0045] Figure 3Further details of the structure and operation of the implementation are as follows. The modulated light beam of the image is reflected from the LCOS10 (for clarity, one beam path is represented as an arrow). The light passes through the field lens surface 12, which is used to minimize the field curvature aberration. The light beam then passes through the angle selection reflector surface 14, which can be a layer or air gap of a low refractive index material that produces total internal reflection (TIR) ​​at a large angle. As will be described below, the function of the angle selection reflector 14 is to guide the illumination. The PBS surface 16 selects the light corresponding to the image, in this case by transmission, and the light propagates toward the first optical surface 18, which is the front surface of the catadioptric arrangement and includes a partial reflector. After passing through the surface 18, each light beam hits the curved second optical surface 20, which includes a polarizing reflector, such as a wire grid or dielectric polarizer commonly used in a pancake lens. The beam is then reflected to the first surface 18 which now partially reflects the beam, passes through the surface 20 and the air gap, then through the coupling surface 22, and into the coupling prism 24 (outline not shown) to reach the entrance aperture 26 of the light guide.

[0046] The configuration described here has the particular advantage of being compact and simple due to one or more of the following features:

[0047] 1. All or most of the optical collimation is achieved by using a "pie" mirror (surface 18 and surface 20) after the PBS.

[0048] 2. The pie mirror is attached directly to the PBS prism 15 at surface 18 (preferably a planar surface).

[0049] 3. The field lens is attached directly to the PBS prism 15 at the angle selective reflector surface 14.

[0050] 4. The angle of the PBS surface 16 is shown here as 30 degrees (instead of the usual 45 degrees), thereby reducing the thickness of the PBS prism 15.

[0051] All surfaces with optical power can advantageously be implemented as aspheric surfaces designed to reduce aberrations (as known in the art). The piezo mirror can be made as a doublet designed to reduce chromatic aberrations (also as known in the art).

[0052] Not all implementations need to be able to achieve all of the above features. For example, in some cases, a field lens may not be used. This can enable a shorter focal length design and thus a smaller projector size.

[0053] External surfaces other than the coupling-in surface 22 or the second optical surface 20 may be provided with a polarization rotator or any other depolarizer element, depending on the design and characteristics of the light guide and any associated aperture expansion and / or outcoupling arrangements, wherein a depolarized image is preferred. The present invention is applicable to various light guide structures, whether employing reflectors or diffractive optical elements, which redirect light internally within the light guide and couple the image out of the light guide towards the eye of the user. The details of the light guide design itself are not part of the present invention and therefore will not be described here.

[0054] Now turn to Figure 4 , Figure 4 A second option is shown, according to which the second optical surface 20 is a planar surface bonded to the input surface 22 of the coupling prism 24 for coupling the image light into the light guide. Thus, the first optical surface 18 is implemented as a curved surface that provides the optical power of the piezo mirror by acting twice on the image light. The first optical surface 18 is shown here as being separated from the surface 17, i.e. the planar end face of the PBS prism 15.

[0055] In this configuration, the planar end face of the projector (second optical surface 20) facilitates attachment of the projector to the coupling prism (surface 22) without any air gap and corresponding complex support mechanism. Implementing the polarization selective reflector 20 on a planar surface also facilitates manufacturing. In all other aspects, the structure and operation of this implementation are the same as those described above with reference to Figure 3 The structure and operation described are similar.

[0056] Figure 5 Shown with Figure 4 A similar, more compact design wherein the second optical surface 20 is bonded to the coupling-in surface 22 as before, and in addition, the PBS prism surface 17 is bonded to the first optical surface 18. In the implementation shown here, surfaces 18 and 17 are curved, while surfaces 20 and 22 are planar, but surfaces 20 and 22 may alternatively be implemented as curved surfaces. In this configuration, the number of air gaps present in the optics is reduced, thereby reducing the need for a support mechanism and further reducing the size of the projector. Manufacturing techniques for forming matching curved surfaces, aligning and bonding these curved surfaces are known, for example, in the context of doublet lens manufacturing, and these techniques may be readily applied to this application.

[0057] The air gap between the field lens 12 and the LCOS 10 can also be combined with glass and an inserted spacer to define the gap. In this case, fine adjustment of the focus can be performed by selecting the appropriate spacer from a set of spacers of different sizes. This eliminates another air gap.

[0058] Now turn to FIG. 6A to FIG. 9 , FIG. 6A to FIG. 9 Schematically shows the above Figures 3 to 5 Various implementations of any variation of the illumination light path shown in . Non-limiting examples of illumination arrangements will be described herein that employ a light source 30, such as: the exit end of a light pipe; an LED surface and a scanning mirror for a laser beam. An illumination optic 32 is preferably provided for collimating the illumination light and is preferably designed in conjunction with the collimating optics to image the illumination aperture 46 onto the exit aperture of the projector, which corresponds to the entrance aperture 26 of the light guide.

[0059] exist Fig. 6A and Figure 6B In the example of FIG. 1 , the PBS 16 is tilted at a 30 degree angle relative to the surface of the SLM 10, so that the distance between the LCOS and the "pie" mirror is shorter and the projector is smaller. To achieve correctly directed illumination to the LCOS, the illumination arrangement directs the illumination to reflect the illumination from the angle selective reflector 14 toward the PBS 16, where it is reflected toward the SLM 10. The polarization-modified light corresponding to the image is then transmitted through the angle selective reflector 14 and is selected by the PBS 16 to propagate toward the collimating optics (whose function is described above).

[0060] The angle selective reflector 14 is preferably disposed parallel to the SLM between the SLM 10 and the PBS 16. To support the above functions, the angle selective reflector should be reflective to visible light incident at an incident angle of 60 degrees (from the normal to the surface) within the region, and substantially transparent to visible light incident at an incident angle of less than 30 degrees from the normal to the surface. Such properties can be conveniently provided by leaving an air gap or by including a layer of low refractive index material that provides total internal reflection (TIR) ​​properties when the incident angle is greater than the critical angle. Alternatively, similar properties can be provided by a multilayer dielectric coating that is implemented to provide the desired angle selective reflection.

[0061] Fig. 6A and Figure 6B Two options for the geometry of light injection through the lighting arrangement are shown. Fig. 6A , light from light source 30 enters illumination prism 36 and is reflected by reflector 34 on the surface. The high angle illumination light is then reflected from surface 14 toward PBS surface 16 where it is reflected to illuminate LCOS 10. This geometry allows illumination to be injected along an axis parallel to the optical axis of the projector.

[0062] Figure 6B An alternative injection geometry is shown in which the illumination light is injected from a suitably angled facet at the side of the illumination prism 38. The reflector 34 is not required here.

[0063] Figure 7 An alternative implementation is shown in which the PBS surface 50 is tilted at a 45 degree angle relative to the SLM 10 surface. In this case, a quarter wave plate 53 and an illumination optics reflective lens 52 are associated with the face of the PBS prism for directing illumination that has passed through the PBS back into the PBS to be reflected by the PBS 50 towards the SLM 10. In this case, the illumination arrangement comprises a light source 42 associated with an illumination aperture 46 from which light propagates through the prism towards the illumination optics reflective lens 52. The illumination optics reflective lens 52 and collimating optics are preferably configured to image the illumination aperture 46 to the entrance aperture 26 of the light guide, thereby optimizing the efficiency of the optics (which has been limited using the "pie mirror" technique) and reducing stray light.

[0064] The pie mirror arrangement shown here is equivalent to Figure 4 , but it can also be like Figure 3 or Figure 5 Another variant feature shown here but applicable to any embodiment is that LCOS 10 is shown here as being attached directly to the PBS prism at surface 51 without the field lens and the resulting extra length and / or air gap. Focus adjustment can be made by adjusting the gap between surfaces 17 and 18.

[0065] According to a particularly preferred but non-limiting implementation shown here, light from a light source 42 propagates along a light pipe 44, which is preferably an extended light pipe. The light is reflected by a reflector 45 onto an aperture 46. As described above, the subsequent optics preferably image the plane 46 onto the exit aperture 26, thereby achieving minimal power loss. Improved uniformity can be achieved by implementing a diffuser in the light pipe or at the plane 46. Preferably, a polarizing filter should be placed in the plane 46 to transmit P polarization.

[0066] The P-polarized transmitted light passes through the PBS 50 and propagates onto the reflective lens 52. This lens contains a quarter wave plate, so the reflected light is now S-polarized and is reflected by the PBS 50 onto the LCOS 10.

[0067] In this context it will be appreciated that the optical arrangements shown here are supplemented by various control components which provide power and input data to update the SLMs and to synchronize the operation of the illumination arrangements to produce the desired output images. Figure 7 and Figure 8 In the figure, these components are schematically represented by the controller 90, and the controller 90 is omitted in other figures to simplify the description. For ordinary technicians in this field, the structure and operation of the controller 90 will be clear and will not be described in detail here.

[0068] Now turn to Figure 8 , Figure 8 A further option is shown in which the illumination arrangement includes a scanning mirror 60 for scanning an illumination beam, typically from a laser source 56, collimated by optics 58, over a range of angles about at least one tilt axis. The scanning mirror 60 is arranged to direct the illumination beam through a prism towards the illumination optics reflective lens 52, from which point the optical path is aligned with the illumination beam. Figure 7 Most preferably, the illumination optics reflective lens 52 and collimating optics are configured to image the scanning mirror 60 to the entrance aperture 26 of the light guide, thereby optimizing the energy transfer of the amount of laser illumination entering the light guide.

[0069] exist Figure 7 In the non-limiting implementation shown, the LCOS 10 is positioned opposite the collimating optical device, and the illumination prism and the illumination optical device are arranged on the side surface of the prism, wherein the light path undergoes a sequence of transmission-reflection-transmission at the PBS. It is understood that this arrangement can be changed, for example, a light path sequence of reflection-transmission-reflection is adopted, wherein it is reflected at the PBS, which selects the desired image light reflected from the LCOS. The overall function of image generation and collimation remains unchanged.

[0070] Thus, this configuration provides scanning laser illumination on the SLM such that both selective illumination of the SLM and modulation of the SLM contribute to image formation. The beam from the laser 56 is collimated by optics 58 onto a scanning mirror 60. The plane of the scanning mirror 60 is imaged by subsequent optics onto the output aperture 26 (at Figure 8 5 (shown as reduced size according to the laser beam width). The scanning beam 62 from the laser 56 is P polarized and therefore passes through the PBS 50 to the reflective lens 52. After polarization rotation, the S polarized beam is reflected from the PBS 50 to the LCOS 10. The LCOS 10 may include a microlens array or a diffuser to expand the beam as it propagates toward the aperture 26. Obviously, due to the narrower illumination of the laser beam, the PBS can be made smaller.

[0071] Although Figure 8It has been described as laser scanning on an LCOS, but according to another alternative implementation, the same structure can be adapted to employ laser scanning as the sole image generation mechanism. In this case, the LCOS is replaced by a beam expansion reflector, which is typically implemented as a reflective micro-lens array (MLA) associated with a quarter wave plate. The controller 90 varies the intensity of the laser beam synchronously with the scanning motion to generate a time-averaged light intensity distribution at the beam expansion reflector during the period of each image frame corresponding to the desired image. In all other respects, this arrangement is structurally and functionally the same as described above. Figure 8 The LCOS version in is similar.

[0072] Now turn to Fig. 9 , Fig. 9 An alternative implementation of the invention is shown which replaces the PBS prism in the previous embodiment with a sheet light guide for illuminating the SLM. This allows the focal length of the collimating optics to be further shortened, allowing further miniaturization of the LCOS and thus overall size and weight reduction compared to implementations using a 45 degree PBS cube (or 30 degree cube), and / or further increases in angular FOV.

[0073] Specifically, the lighting arrangement herein includes a light guide 156 having: a pair of mutually parallel main surfaces and a plurality of mutually parallel partially reflective outcoupling surfaces 158, wherein the pair of mutually parallel main surfaces are used to support the propagation of illumination by internal reflection at the main surfaces, and the plurality of mutually parallel partially reflective outcoupling surfaces 158 are located inside the light guide and are oriented obliquely relative to the main surfaces to couple the illumination toward the SLM 10.

[0074] Polarized illumination is coupled into a light guide 156 through a prism 154 for propagation by total internal reflection (TIR). The guided light impinges on a polarization selective partial reflector 158 for outcoupling onto a spatial light modulator (LCOS) 10. The reflected light is spatially modulated (e.g., by polarization rotation) and reflected. The reflected light passes through the partial reflector 158 and through the waveguide 156. The light also passes through a polarizer 160. The polarizer preferably provides some or all of the following functions:

[0075] Filter out the residual S polarization transmitted through the partial reflector 158 so that the image has proper contrast as modulated by the LCOS 10;

[0076] ensuring the correct input polarization to be followed by the pie optics, thereby avoiding losses at the first reflection from the second optical surface 168; and

[0077] The reflected light from the pie mirror is preferably also suppressed by absorbing most of the light reflected from the partial reflector 164 , which has passed through the wave plate 162A twice and is therefore polarized orthogonal to the transmission axis of the polarizer 160 .

[0078] The light beam continues to pass through quarter wave plate 162A and impinges on partial reflector 164 (corresponding to the first optical surface 18 described above). As the light beam propagates back and forth, it also passes through quarter wave plate 162B and reflective polarizer 168 (corresponding to the second optical surface 20 described above), and lenses 166A and 166B perform collimation (the optical path is schematically shown for one light beam).

[0079] The above system has a small size and can support a large field while using a short focal length and at the same time coupling light into the waveguide aperture 26 which is also located at a short distance from the collimating optics.

[0080] Now turn to Fig.10 It should be noted that the above reference Figures 3 to 8 The advantages of the various prism-based embodiments shown can be extended to essentially any image generation technology that can be associated with the image plane surface of a prism, allowing various implementations of beamsplitters to be utilized within the prism and maintaining short distances from the image plane to the collimating optics and from the collimating optics to the entrance aperture of the light guide (as previously shown). Fig.10 Further examples are shown in which the beam splitter is one or more dichroic mirrors and in which the image generator is an active matrix image generator, such as an OLED or micro-LED array.

[0081] In the particularly preferred but non-limiting example shown here, the image of each color (such as RGB) is generated by a different active matrix image generator (active matrix image generator 170R, active matrix image generator 170G and active matrix image generator 170B, respectively), and surfaces 172a and 172b are dichroic combiners (dichroic mirrors) that combine the color beams within the dichroic prism (as shown by the solid and dashed arrows, only the light from 170G is shown for clarity). Since the illumination from light source 170 may be unpolarized, an additional polarizer may be introduced directly adjacent to each light source or as the first element on surface 17. Here, similar to Figure 5 The catadioptric collimating arrangement and its association with the prism is shown in the form of , but may alternatively be based on Figure 3 or Figure 4 The structure shown.

[0082] In the embodiment shown here, a first active matrix image generator 170R generates an image emitted as at least a first wavelength of light (red) reflected by a dichroic mirror 172a, while a second active matrix image generator 170G associated with a second face of the prism generates an image emitted as at least a second wavelength of light (green) transmitted by the dichroic mirror 172a, to be combined with the red light when reaching the collimating optical device. The second dichroic mirror 172b is not parallel to the dichroic mirror 172a and is transparent to red and green light, while being reflective to a third wavelength of blue light. A third active matrix image generator 170B associated with another face of the prism generates an image emitted as at least a third wavelength of light (blue) reflected by the second dichroic mirror 170b, to be combined with the red and green light when reaching the collimating optical device. By generating images corresponding to the RGB color separation of the entire image to be displayed, these separate images are all combined and delivered to the collimating optical device for display to the user's eyes.

[0083] It will be understood that the above description is intended to be exemplary only and that many other embodiments are possible within the scope of the invention as defined in the appended claims.

Claims

1. An image projector for injecting a collimated image into an entrance aperture of a light guide, the image projector comprising: (a) a polarization modifying spatial light modulator (SLM) arranged to modify the polarization of the illumination in accordance with image data provided to said SLM; (b) an illumination arrangement for illuminating the SLM using polarized illumination; (c) a polarization selective element arranged to select light from the SLM corresponding to an image; as well as (d) collimating optics for collimating light corresponding to the image to provide the collimated image at an entrance aperture of the light guide, wherein the collimating optics comprises a polarizing catadioptric arrangement comprising, in sequence: (i) a first quarter wave plate; (ii) a first optical surface implemented as a partial reflector; (iii) a second quarter wave plate; and (iv) a second optical surface implemented as a polarization selective reflector, Wherein at least one of the first optical surface and the second optical surface is implemented as a non-planar surface with optical power, the non-planar surface acts on the light twice, once as a refractive lens surface and once as a reflective lens.

2. The image projector according to claim 1, wherein: The polarization selective element is a polarization beam splitter (PBS) integrated into a prism, and wherein the illumination arrangement directs illumination to be reflected from the PBS towards the SLM.

3. The image projector according to claim 2, wherein: The PBS is inclined at an angle of 30 degrees relative to the surface of the SLM, and the image projector also includes an angle selection reflector, which is disposed parallel to the SLM between the SLM and the PBS, and the lighting arrangement guides the illumination to reflect from the angle selection reflector toward the PBS and from the PBS toward the SLM, and the angle selection reflector is reflective to visible light incident at an incident angle of 60 degrees and is substantially transparent to visible light incident at an incident angle less than 30 degrees.

4. The image projector according to claim 2, wherein: The PBS is tilted at a 45 degree angle relative to the surface of the SLM, and the image projector also includes a quarter wave plate and an illumination optical device reflective lens associated with the face of the prism for directing illumination that has passed through the PBS back toward the PBS to be reflected at the PBS toward the SLM.

5. The image projector according to claim 4, wherein: The illumination arrangement further comprises a light source associated with an illumination aperture, light propagating from the illumination aperture through the prism towards the illumination optics reflective lens, and wherein the illumination optics reflective lens and the collimating optics are configured to image the illumination aperture to an entrance aperture of the light guide.

6. The image projector according to claim 4, wherein: The illumination arrangement further comprises a scanning mirror for scanning the illumination beam over an angular range about at least one tilt axis, the scanning mirror being arranged to direct the illumination beam through the prism towards the illumination optics reflective lens, and wherein the illumination optics reflective lens and the collimating optics are configured to image the scanning mirror to an entrance aperture of the light guide.

7. The image projector according to claim 2, wherein: The second optical surface is a planar surface bonded to the image input surface of the light guide.

8. The image projector according to claim 2, wherein: The first optical surface is a planar surface bonded to an output surface of the prism.

9. The image projector according to claim 2, wherein: The first optical surface is a non-planar surface bonded to a corresponding non-planar output surface of the prism.

10. The image projector according to claim 1, wherein: The lighting arrangement comprises a light guide having a pair of mutually parallel main surfaces for supporting propagation of illumination by internal reflection at the main surfaces and a plurality of mutually parallel partially reflecting outcoupling surfaces located inside the light guide and oriented obliquely relative to the main surfaces for outcoupling illumination towards the SLM.

11. An image projector for injecting a collimated image into an entrance aperture of a light guide, the image projector comprising: (a) Beam splitter integrated into the prism. (b) an image generator configured to generate an image at an image plane associated with a third face of the prism; as well as (c) collimating optics for collimating light of the image to provide a collimated image at an entrance aperture of the light guide, wherein the collimating optics comprises a polarizing catadioptric arrangement comprising, in sequence: (i) a first quarter wave plate; (ii) a first optical surface implemented as a partial reflector; (iii) a second quarter wave plate; and (iv) a second optical surface implemented as a polarization selective reflector, Wherein at least one of the first optical surface and the second optical surface is implemented as a non-planar surface with optical power, the non-planar surface acts on the light twice, once as a refractive lens surface and once as a reflective lens.

12. The image projector according to claim 11, wherein: The beam splitter is a polarizing beam splitter (PBS), and the image projector further comprises: (a) an illumination arrangement comprising at least one light source for generating a modulated intensity light beam and a scanning mirror for scanning the light beam over a range of angles about at least one tilt axis, the scanning mirror being arranged to direct the light beam into a first face of the prism; (b) a first quarter wave plate and an illumination optics reflective lens associated with a second face of the prism for directing light that has passed through the prism back toward the PBS; (c) a second quarter wave plate and a beam expansion reflector associated with a third face of the prism; and (d) a controller for synchronously modulating the intensity of the light source and controlling the scanning mirror to generate a time-averaged light intensity distribution corresponding to an image at the beam expansion reflector.

13. The image projector according to claim 11, wherein: The beam splitter is a dichroic mirror, and wherein the image generator is a first active matrix image generator, which generates an image as light emission of at least a first wavelength, and the light of at least the first wavelength is reflected by the dichroic mirror. The image projector also includes a second active matrix image generator associated with the second face of the prism, and the second active matrix image generator generates an image as light emission of at least a second wavelength, and the light of at least the second wavelength is transmitted by the dichroic mirror to combine with the light of the first wavelength when it reaches the collimating optical device.

14. The image projector of claim 13, further comprising a second dichroic mirror disposed within the prism and non-parallel to the dichroic mirror, the second dichroic mirror being transparent to light of the first wavelength and the second wavelength and being reflective to light of a third wavelength, the image projector further comprising a third active matrix image generator associated with the first face of the prism, the third active matrix image generator generating an image emitted as light of at least a third wavelength, the light of at least a third wavelength being reflected by the dichroic mirror to be combined with light of the first wavelength and the second wavelength when reaching the collimating optical device.

15. The image projector according to claim 11, wherein: The second optical surface is a planar surface bonded to the image input surface of the light guide.

16. The image projector according to claim 11, wherein: The first optical surface is a planar surface bonded to an output surface of the prism.

17. The image projector according to claim 11, wherein: The first optical surface is a non-planar surface bonded to a corresponding non-planar output surface of the prism.

Images