Image projector for near-eye display system and method of assembly

Abstract

An image projector (14) for a near-eye display includes a polarizing beam-splitter prism (72) having a first face (72a) adjacent to an image generator (70), a second face (72b) adjacent to a reflective lens arrangement (80), and a third face (72c) separated by an air gap (104) from a refractive lens arrangement (100). Collimating optical power is subdivided between the reflective and refractive lens arrangements, thereby relaxing the optical design requirements on each and enhancing performance. The width of the air gap (104) is selected during assembly to adjust image focus, enabling collimation of the output light for injection into a lightguide (12) while simplifying deployment of the image generator. A corresponding method of assembly is provided. The system allows compact integration and precise optical alignment using objective image quality metrics.

Description

[0001] Image Projector for Near-Eye Display System and Method of Assembly

[0002] FIELD AND BACKGROUND OF THE INVENTION

[0003] The present invention relates to compact image projectors suitable for use in near-eye display systems, and more particularly to projector architectures employing a polarizing beamsplitter prism and optical arrangements configured to collimate image light for injection into a lightguide.

[0004] In many conventional projector architectures, collimation is provided by a reflective optical element that directs light from the PBS prism into the waveguide. Focus adjustment is commonly achieved by varying the spacing between the image generator and the PBS prism. Alignment and focus adjustments are typically performed during assembly using adjustable supports or jigs, and fixed by bonding or mechanical retention after calibration.

[0005] SUMMARY OF THE INVENTION

[0006] The present invention is an image projector for near-eye display systems and a corresponding method of assembly of an image projector.

[0007] According to the teachings of an embodiment of the present invention, an image projector is provided for a near-eye display system, the image projector comprising: (a) a polarizing beamsplitter (PBS) prism having a first face, a second face, and a third face; (b) an image generator defining an image plane from which light corresponding to an image emanates, the image plane being disposed adjacent to the first face of the PBS prism; (c) a reflective lens arrangement associated with the second face of the PBS prism, the reflective lens arrangement having a first positive optical power and including a quarter-wave retarder plate; and (d) a refractive lens arrangement disposed in facing relation to the third face of the PBS prism, the front lens arrangement having a second positive optical power and being spaced from the third face of the PBS prism by an air gap, wherein the PBS prism includes a polarizing beam-splitter surface deployed to define a light path for image light from the image plane to the reflective lens arrangement and from the reflective lens arrangement to the front lens arrangement, and wherein the first positive optical power, the second positive optical power and a width of the air gap are chosen so that the image light emerging from the refractive lens arrangement corresponds to a collimated image for coupling into a lightguide for display to a user.

[0008] According to a further feature of an embodiment of the present invention, the image projector further comprises a field lens disposed between the image generator and the first face of the polarizing beam-splitter prism. According to a further feature of an embodiment of the present invention, the field lens is a doublet with planar external surfaces and is optically bonded to both the image generator and the first face of the polarizing beam-splitter prism.

[0009] According to a further feature of an embodiment of the present invention, the field lens is separated from the image generator or the polarizing beam-splitter prism by an air gap less than 100 microns.

[0010] According to a further feature of an embodiment of the present invention, the air gap between the refractive lens arrangement and the polarizing beam-splitter prism is at least about 300 microns.

[0011] According to a further feature of an embodiment of the present invention, the image projector further comprises an adjustable support configuration configured to allow adjustment of the air gap between the refractive lens arrangement and the polarizing beam-splitter prism for focus adjustment during assembly.

[0012] According to a further feature of an embodiment of the present invention, the image generator comprises a reflective liquid crystal on silicon (LCoS) device.

[0013] According to a further feature of an embodiment of the present invention, the image projector further comprises: (a) a lightguide for conveying the collimated image by internal reflection for display to a user, the image projector being deployed to introduce the collimated image via an optical coupling arrangement into the lightguide; and (b) illumination optics configured to project light from an illumination stop through the PBS prism to illuminate the image plane, wherein the illumination optics together with the reflective lens arrangement and the refractive lens arrangement are configured to achieve pupil imaging of the illumination stop onto an entrance of the lightguide.

[0014] According to a further feature of an embodiment of the present invention, the image generator comprises a multi-color microLED array.

[0015] According to a further feature of an embodiment of the present invention, the image generator comprises at least two microLED arrays configured to generate images of at least two different colors, said at least two microLED arrays being mounted on respective faces of a dichroic combiner prism.

[0016] According to a further feature of an embodiment of the present invention, the image generator comprises at least one microLED array, and the polarizing beam-splitter (PBS) prism has a fourth face having associated therewith a second reflective lens arrangement with the first positive optical power and including a quarter-wave retarder plate, wherein the polarizing beamsplitter surface is deployed to define said light path for image light of a first polarization component from the image plane to the reflective lens arrangement and from the reflective lens arrangement to the front lens arrangement, and to define an additional light path for image light of a second polarization component from the image plane to the second reflective lens arrangement and from the second reflective lens arrangement to the front lens arrangement, said first and second polarization components being combined in the collimated image for coupling into a lightguide.

[0017] There is also provided according to the teachings of an embodiment of the present invention, a method is provided for assembling an image projector for a near-eye display system, the method comprising: (a) providing: (i) a polarizing beam-splitter (PBS) prism having a first face, a second face, and a third face; (ii) an image generator defining an image plane from which light corresponding to an image emanates; (iii) a reflective lens arrangement with a first positive optical power and including a quarter-wave retarder plate; and (iv) a refractive lens arrangement with a second positive optical power; (b) aligning and affixing the image generator adjacent to the first face of the PBS prism such that the image plane is optically coupled to the PBS prism, and aligning and affixing the reflective lens arrangement adjacent to the second face of the PBS prism; (c) positioning the refractive lens arrangement in facing relation to the third face of the PBS prism, separated by an air gap; (d) adjusting a width of the air gap to achieve optical collimation of image light emerging from the refractive lens arrangement; and (e) fixing the position of the refractive lens arrangement after adjustment of the air gap.

[0018] According to a further feature of an embodiment of the present invention, the refractive lens arrangement is positioned with an air gap of at least about 300 microns from the third face of the polarizing beam-splitter prism prior to fixation.

[0019] According to a further feature of an embodiment of the present invention, adjusting the width of the air gap includes using an adjustable support configuration for focus adjustment during assembly.

[0020] According to a further feature of an embodiment of the present invention, the method further comprises aligning the refractive lens arrangement in an in-plane direction to maintain boresight alignment of the collimated image.

[0021] According to a further feature of an embodiment of the present invention, the method further comprises affixing a field lens between the image generator and the first face of the polarizing beam-splitter prism.

[0022] According to a further feature of an embodiment of the present invention, the field lens is a doublet with planar external surfaces and is optically bonded to both the image generator and the polarizing beam-splitter prism.

[0023] According to a further feature of an embodiment of the present invention, the field lens is spaced from the image generator or the polarizing beam-splitter prism by an air gap of less than 100 microns. According to a further feature of an embodiment of the present invention, the image generator comprises a reflective liquid crystal on silicon (LCoS) device.

[0024] According to a further feature of an embodiment of the present invention, the method further comprises projecting light from an illumination stop through the polarizing beam-splitter prism to illuminate the image plane, wherein the illumination optics, the reflective lens arrangement, and the refractive lens arrangement achieve pupil imaging of the illumination stop onto an entrance of a lightguide.

[0025] According to a further feature of an embodiment of the present invention, the image generator comprises at least two microLED arrays mounted on respective faces of a dichroic combiner prism.

[0026] According to a further feature of an embodiment of the present invention, the image generator comprises at least one microLED array, and the method further comprises: (a) providing a second reflective lens arrangement with the first positive optical power and including a quarterwave retarder plate, the second reflective lens arrangement being associated with a fourth face of the PBS prism; and (b) directing image light of two orthogonal polarization components from the image plane along two respective optical paths through the first and second reflective lens arrangements for recombination at the PBS surface to form the collimated image.

[0027] BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

[0029] FIGS. 1 A and IB are schematic isometric views of an optical system including two displays each implemented using a lightguide optical element (LOE), constructed and operative according to the teachings of an embodiment of the present invention, illustrating a top-down and a sideinjection configuration, respectively.

[0030] FIG. 2 is a schematic optical layout of an image projector according to an embodiment of the present invention, illustrating the optical path through a PBS prism from a reflective image generator to a reflective lens arrangement and a refractive lens arrangement, and coupling into a lightguide via a coupling prism and a coupling mirror.

[0031] FIG. 3 is a schematic optical layout similar to FIG. 2, but according to an alternative embodiment of the present invention, in which a field lens is disposed between the image generator and the PBS prism.

[0032] FIG. 4 is a schematic optical layout of an image projector according to another embodiment of the present invention, in which a non-polarized image generator is used in conjunction with a polarization beam-splitting prism and two reflective lens arrangements to process orthogonal polarization components for recombination into a collimated image. FIG. 5 is a schematic optical layout similar to FIG. 4, according to a further embodiment of the present invention, in which three monochrome image generators are coupled to the PBS prism via a dichroic combiner cube.

[0033] FIG. 6 is a schematic diagram of an assembly system according to an embodiment of the present invention, illustrating a configuration for aligning and assembling optical components of an image projector using adjustable jigs, a test image generator, and an optical metrology system.

[0034] FIG. 7 is a flow diagram illustrating a method of assembling an image projector according to an embodiment of the present invention.

[0035] DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] The present invention is an image projector for near-eye display systems and corresponding methods of assembling such a projector.

[0037] The principles and operation of image projectors and corresponding methods of assembly according to the present invention may be better understood with reference to the drawings and the accompanying description.

[0038] By way of introduction, an exemplary non-limiting implementation of a near-eye display, generally designated 10, in which context the projector of the present invention may be used is illustrated schematically in FIGS. 1A and IB. The near-eye display 10 employs a compact image projector assembly 14 integrated so as to inject an image into a lightguide optical element (LOE, interchangeably referred to as a “waveguide,” a “substrate” or a “slab”) 12 within which the image light is trapped in one dimension by internal reflection at a set of mutually-parallel planar external surfaces.

[0039] The LOE typically includes an arrangement for expanding the optical aperture of the injected image in one or two dimensions, and for coupling-out the image illumination towards the eye of the observer, typically based either on the use of internal partially-reflecting surfaces or on diffractive optical elements. In one non-limiting set of implementations, the light injected into LOE 12 by image projector assembly 14 impinges of a set of partially-reflecting surfaces (interchangeably referred to as “facets”) that are parallel to each other, and inclined obliquely to the direction of propagation of the image light, with each successive facet deflecting a proportion of the image light into a deflected direction, also trapped / guided by internal reflection within the substrate. This first set of facets are not illustrated individually in FIGS. 1A and IB, but are located in a first region of the LOE designated 16. This partial reflection at successive facets achieves a first dimension of optical aperture expansion.

[0040] The first set of partially-reflecting surfaces deflect the image illumination from a first direction of propagation trapped by total internal reflection (TIR) within the substrate to a second direction of propagation, also trapped by TIR within the substrate. The deflected image illumination then passes into a second substrate region 18, which may be implemented as an adjacent distinct substrate or as a continuation of a single substrate, in which a coupling-out arrangement (either a further set of partially reflective facets or a diffractive optical element) progressively couples out a proportion of the image illumination towards the eye of an observer located within a region defined as the eye-motion box (EMB), thereby achieving a second dimension of optical aperture expansion. The overall device may be implemented separately for each eye, and is preferably supported relative to the head of a user with the each LOE 12 facing a corresponding eye of the user. In one particularly preferred option as illustrated here, a support arrangement is implemented as an eye glasses frame with sides 20 for supporting the device relative to ears of the user. Other forms of support arrangement may also be used, including but not limited to, head bands, visors or devices suspended from helmets.

[0041] Reference is made herein in the drawings and claims to an X axis which extends horizontally (FIG. 1A) or vertically (FIG. IB), in the general extensional direction of the first region of the LOE, and a Y axis which extends perpendicular thereto, i.e., vertically in FIG. 1A and horizontally in FIG. IB. In very approximate terms, the first LOE, or first region 16 of LOE 12, may be considered to achieve aperture expansion in the X direction while the second LOE, or second region 18 of LOE 12, achieves aperture expansion in the Y direction. It should be noted that the orientation as illustrated in FIG. 1A may be regarded as a “top-down” implementation, where the image illumination entering the main (second region) of the LOE enters from the top edge, whereas the orientation illustrated in FIG. IB may be regarded as a “side-injection” implementation, where the axis referred to here as the Y axis is deployed horizontally. In certain cases, other intermediate orientations are also applicable, and are included within the scope of the present invention except where explicitly excluded. Although illustrated herein in the context of an LOE which achieves two-dimensional expansion, it should be noted that the present invention is also applicable to devices in which an LOE performs only a single dimension of expansion. For simplicity of presentation in the drawings presented below, only a single dimension of expansion will be shown, but it will be understood in each case that the principles described apply equally to two-dimensional aperture expansion lightguides.

[0042] The image injected into the lightguides of the present invention is preferably a collimated image, i.e., in which the light of each image pixel is a parallel beam, collimated to infinity, with an angular direction corresponding to the pixel position. The image illumination thus spans a range of angles corresponding to an angular field of view in two dimensions.

[0043] It will be appreciated that the near-eye display 10 includes various additional components, typically including a controller 22 (FIG. 1A-1B) for actuating the image projector 14, typically employing electrical power from a small onboard battery (not shown) or some other suitable power source. It will be appreciated that controller 22 includes all necessary electronic components such as at least one processor or processing circuitry to drive the image projector, all as is known in the art.

[0044] Implementations of the present invention provide an image projector for a near-eye display system, including an optical architecture suitable for collimating image light and coupling the collimated image into a lightguide. As illustrated in various embodiments shown in FIGS. 2-5, the image projector includes a polarizing beam-splitter (PBS) prism having at least three optical faces. An image generator is disposed adjacent to a first face of the PBS prism and defines an image plane from which image light emanates. A reflective lens arrangement is optically coupled to a second face of the PBS prism and has a positive optical power. A refractive lens arrangement is positioned in facing relation to a third face of the PBS prism, also with a positive optical power, and is spaced from the prism by an air gap, which preferably has a width of at least about 300 microns. The PBS prism includes an internal beam-splitting surface configured to direct image light from the image plane toward the reflective lens arrangement and to subsequently redirect the reflected light toward the refractive lens arrangement.

[0045] The optical powers of the reflective and refractive lens arrangements, together with the spacing between the refractive lens and the PBS prism, are selected so that image light emerging from the refractive lens arrangement corresponds to a collimated image suitable for injection into a lightguide, such as a substrate-based waveguide optical element. The projector may be implemented with a reflective image generator, such as a liquid crystal on silicon (LCoS) display illuminated by polarized light, or with an emissive image generator, such as a microLED array. In some implementations, the optical architecture includes a single reflective lens arrangement; in others, multiple reflective lens paths are used to process orthogonal polarization components for recombination into the output image. The refractive lens arrangement may be a compound lens and may include in-plane and axial alignment features to maintain optical quality.

[0046] The various implementations of the projector described herein are compatible with a range of coupling architectures for light injection into a lightguide. In one example, image light is coupled through a prism and reflected internally by a coupling mirror. In other examples, direct bonding or refractive coupling arrangements may be used. The projector structure supports compact integration and high image quality. In particular, the separation of collimating optical power between multiple elements reduces the optical power required from the reflective optics while the combination of reflective and refractive elements provides additional design flexibility to optimize performance and minimize aberrations.

[0047] In association with the optical architecture, the present invention also encompasses methods for assembling and aligning such image projectors. These methods include mechanical and optical alignment of the image generator and refractive lens arrangement relative to the PBS prism, including focus adjustment based on collimation criteria. Certain embodiments allow for coarse and fine alignment stages, with verification via optical metrology systems. The method steps correspond to the assembly configurations and procedures illustrated schematically in FIGS. 6 and 7.

[0048] Turning now to FIG. 2, an image projector assembly 14 according to an embodiment of the present invention is shown in schematic form. This embodiment illustrates an optical architecture in which collimating optical power is distributed between a reflective lens arrangement 80 and a refractive lens arrangement 100.

[0049] The non-limiting preferred example illustrated here employs a reflective spatial light modulator (SLM), such as a liquid crystal on silicon (LCOS) image generator, and therefore requires an illumination arrangement. Accordingly, FIG. 2 illustrates one or more light sources 60 that emit light via an illumination stop 62 and illumination optics 64 that include a polarizer, before entering a polarizing beam-splitter (PBS) prism 72 through a light-input face 72e. The light entering the prism is linearly polarized by the polarizer according to the intended light propagation path within the PBS prism, as discussed below.

[0050] The PBS prism 72 includes an internal polarization beam-splitting surface 76, which reflects light of one linear polarization (typically s-polarization) and transmits the orthogonal polarization. An image generator 70, such as a reflective liquid crystal on silicon (LCoS) device, is mounted adjacent to an image input face (“first face”) 72a of the PBS prism. The image generator 70 may be affixed directly to the PBS prism 72 using an optically clear adhesive, or spaced by a thin air gap (not separately numbered here), preferably of width less than 100 microns. If an air gap is used, the facing surfaces of the image generator 70 and the PBS prism 72 are preferably treated with anti-reflective coatings.

[0051] Polarized light entering the PBS prism 72 is s-polarized so as to be reflected by the PBS surface 76 upward toward the image generator 70. After modulation by the image generator 70, the light is reflected back into the PBS prism 72. The modulation process selectively alters the polarization state of the image light according to the image content, so that the image light passes through PBS surface 76 and propagates downward toward a reflective-optics face (“second face”) 72b of the PBS prism.

[0052] At second face 72b, the image light enters a reflective lens arrangement 80, which may be a simple reflective lens or a compound lens with refractive and reflective components, having positive optical power. A quarter-wave retarder plate 78 is disposed between the PBS prism 72 and the reflective lens 80, such that the light passes through it before and after reflection, resulting in a net rotation of the polarization state by 90 degrees upon the round trip. The reflected image light re-enters the PBS prism 72, and is reflected by the PBS surface 76 toward a third face 72c, which serves as the output face of the PBS prism. From there, the image light crosses an air gap 104 and passes through the refractive lens arrangement 100, which may be a singlet or a compound lens (e.g., a doublet). The air gap 104 is selected and fixed during assembly to adjust focus, thereby achieving a collimated image output.

[0053] The collimated image light emerging from the refractive lens arrangement 100 is preferably delivered into a lightguide for expansion and delivery to the eye of a user. In the non-limiting example illustrated here, the collimated image enters a coupling prism 102 that provides an entrance surface for introducing the light into a lightguide 12. In the illustrated embodiment, the light is internally deflected by a coupling mirror 106 within the lightguide 12, which redirects the image light to propagate by total internal reflection within the lightguide substrate. Alternative coupling-in arrangements, such as coupling prisms without reflectors, reflectors without coupling prisms or diffractive coupling arrangements, may also be employed.

[0054] In order to optimize illumination efficiency, the illumination optics 64 together with the reflective lens arrangement 80 and the refractive lens arrangement 100 are configured to achieve pupil imaging of the illumination stop 62 onto an entrance of the lightguide.

[0055] Turning now to FIG. 3, an image projector assembly 14 according to another embodiment of the present invention is shown in schematic form. This embodiment is structurally and functionally similar to that described above with reference to FIG. 2, and like features are identified with like reference numerals. The key distinction in this embodiment is the inclusion of a field lens 108 between the image generator 70 and the PBS prism 72, disposed adjacent to the image input face 72a. The additional flexibility in optical design provided by the use of a reflective lens arrangement and a refractive lens arrangement spaced apart along the optical path may in many cases make the use of a field lens adjacent to the image plane unnecessary. Nevertheless, particularly in cases with very large fields of view, a field lens may be advantageous.

[0056] In the particularly preferred but non-limiting example illustrated here, field lens 108 is implemented as a compound (doublet or triplet) lens having planar external surfaces and a curved internal interface, e.g., a biplanar doublet lens. The planar external surfaces facilitate direct optical bonding to both the image generator 70 and the PBS prism 72, thereby eliminating the need for an air gap at this interface. Alternatively, the field lens may be affixed to one of the two elements (image generator or PBS prism), with a small air gap — preferably less than 100 microns — remaining between the field lens and the other element. In such cases, the facing surfaces are preferably provided with anti-reflective coatings to reduce reflections, and the non-bonded surface may also have curvature. The function of the field lens is to improve image quality, particularly in wide field-of- view implementations, by reducing field curvature and improving edge resolution. Inclusion of the field lens does not otherwise alter the optical path within the projector. As in FIG. 2, light from one or more light sources 60 passes through an illumination stop 62 and illumination optics 64, which include a polarizer, and enters the PBS prism 72 through a light-input face 72e. The polarized light is reflected upward by the PBS surface 76 toward the image generator 70. After modulation by the image generator 70, the image light is transmitted through the PBS surface 76 and propagates to the reflective lens arrangement 80 via the second face 72b. A quarter-wave retarder plate 78 positioned at the interface rotates the polarization state of the image light on its forward and return passes. Upon reflection, the collimated or partially collimated light returns through the quarter-wave plate 78, is reflected by the PBS surface 76, and exits through the third face 72c of the PBS prism.

[0057] The output light crosses a fixed air gap 104 and passes through the refractive lens arrangement 100, which provides final collimation. The collimated light is then directed through a coupling prism 102 into a lightguide 12, where it is redirected by a coupling mirror 106 and guided by total internal reflection. As with the embodiment of FIG. 2, other coupling-in configurations may alternatively be used.

[0058] This embodiment illustrates one option for implementing a field lens between the PBS prism and the image generator, without altering the remainder of the projector architecture. The field lens may be included or omitted depending on system requirements, such as field curvature correction or compactness constraints.

[0059] In the various embodiments described thus far, and similarly below, mention has been made of additional air gaps, other than air gap 104, which may be present between certain components of the projector assembly. It should be appreciated that these additional air gaps, if present, are conceptually distinct in structure and function from air gap 104. In certain cases, a constructional air gap is introduced between adjacent components to facilitate mechanical assembly, particularly where one or both of the facing optical surfaces are non-planar, thereby allowing the components to be brought into position without collision or interference. For this purpose, the width of the constructional air gap is preferably kept as small as is practically feasible, which in the context of micro-projectors for near-eye displays, is typically less than 100 microns. In contrast, the air gap 104 described between the PBS prism 72 and the refractive lens arrangement 100 is a functional air gap chosen to be large enough to allow a range of adjustment of the spacing and to thereby achieve precise collimation of the projected output image over a range of likely manufacturing tolerances. For this purpose, a relatively larger air gap width, typically in excess of 300 microns, is used. By way of one illustrative but non-limiting example, the nominal design of the projector assembly may set the target air gap width at about 500 microns, with a range of adjustment during assembly adjustment of ±200 microns.

[0060] Throughout the above discussion, where an air gap is provided between surfaces which are non-planar, the air gap width referred to is the minimum spacing between the component surfaces at any region through which image illumination ray paths pass. In the case of convex surfaces, this typically corresponds to the width of the air gap as measured along the optical axis.

[0061] Turning now to FIG. 4, an image projector assembly 14 according to another preferred but non-limiting embodiment of the present invention is shown in schematic form. This embodiment differs from the previous examples by employing a non-polarized image generator 70, such as a multi-color microLED array, and a polarization recombination architecture within a PBS prism 72 configured to process orthogonal polarization components via two reflective lens arrangements.

[0062] In this embodiment, the PBS prism 72 is implemented as a cubic prism in cross-section, oriented such that its optical faces lie at 45 degrees relative to the vertical and horizontal axes of the drawing. The image generator 70 is positioned adjacent to a first face 72a of the PBS prism, here located on the lower right of the prism in the illustrated orientation.

[0063] The image light emitted by generator 70 is unpolarized, and thus splits upon reaching the PBS surface 76. A first polarization component (e.g., s-polarized) is reflected upward and rightward toward a first reflective lens arrangement 80a, mounted at a second face 72b of the PBS prism. A second polarization component (e.g., p-polarized) is transmitted through the PBS surface 76 and propagates upward and leftward toward a second reflective lens arrangement 80b, mounted at a fourth face 72d of the PBS prism.

[0064] Each of the reflective lens arrangements 80a and 80b is associated with a corresponding quarter-wave plate, denoted 78a and 78b, positioned at the respective prism interfaces. The light in both paths passes through the quarter-wave plate before and after reflection. This double pass rotates the linear polarization of the image light by 90 degrees, converting the s- and p-polarized components into their orthogonal counterparts upon re-entry into the PBS prism.

[0065] As a result of this polarization rotation, the component reflected from 80a (now p- polarized) passes through the PBS surface 76 while the component reflected from 80b (now s- polarized) is reflected by the PBS surface 76. These two components recombine co-linearly within the PBS prism and exit through the third face 72c.

[0066] The combined and partially collimated image light exits across a fixed air gap 104 and passes through a refractive lens arrangement 100, which is illustrated here as a doublet lens with planar external surfaces, which achieves full collimation of the output image of the projector. The lens 100 may be affixed to a coupling prism 102, which serves as the injection interface to a lightguide 12. In this embodiment, the coupling prism is oriented so that the light enters the lightguide without requiring a coupling mirror. The input angle is selected such that the injected light propagates by total internal reflection within the lightguide substrate. The planar external surfaces of lens 100 facilitate direct bonding to the input surface of the coupling prism 102.

[0067] This architecture allows efficient use of unpolarized light sources by splitting and recombining polarization components with symmetrical optical paths, maintaining high optical efficiency and compact packaging. The reflective lens arrangements 80a and 80b are preferably identical, and each only achieves partial collimation of the image light, which is then completed by the refractive lens 100.

[0068] Turning now to FIG. 5, an image projector assembly 14 according to another preferred but non-limiting embodiment of the present invention is shown in schematic form. This embodiment builds upon the polarization recombination architecture of FIG. 4, but instead of using a single multi-color microLED array, employs three separate monochrome image generators — 70R, 70G, and 70B — corresponding to red, green, and blue image components, respectively. The three image generators are optically coupled to the projector input via a dichroic combiner prism 110, such as an X-cube or trichroic prism.

[0069] The three image generators are mounted on different external faces of the combiner 110:

[0070] • Red array 70R generates a red image whose light is reflected within the cube by a dichroic reflector 112R, which reflects red light while transmitting green and blue.

[0071] • Green array 70G generates a green image whose light passes directly through the cube without deflection.

[0072] • Blue array 70B generates a blue image whose light is reflected by a dichroic reflector 112B, which reflects blue light while transmitting red and green.

[0073] The result is a combined multi-color image beam emerging from the dichroic combiner prism 110 and entering the PBS prism 72 through its first face 72a. As in FIG. 4, the image light is unpolarized and is split at the PBS surface 76 into orthogonal polarization components, following a subsequent light path identical to that described above with reference to FIG. 4. Although the illustrated geometry appears to be larger due to the presence of the additional dichroic combiner prism 110, it should be noted that this is not necessarily to scale, since high resolution monochrome microLED arrays may be smaller than a color array of similar color pixel count. This may facilitate compact implementations in which all of the components are correspondingly smaller.

[0074] Although FIG. 5 illustrates the use of an X-cube combiner 110, it will be appreciated that other types of dichroic combiners may also be used in this architecture. For example, in some implementations, two or more color channels may be combined sequentially using planar dichroic reflectors or other spectrally selective elements. More generally, the image generator may include at least two microLED arrays configured to generate images of different colors, with their outputs optically combined for injection into the PBS prism. The number, arrangement, and combination sequence of image generating arrays may vary based on various design considerations, details of which are beyond the scope of this disclosure.

[0075] Turning now to FIG. 6, this illustrates a schematic assembly and alignment system for an image projector assembly 14 according to an embodiment of the present invention. The figure shows a configuration for aligning and assembling the optical components of the projector during manufacturing, using a combination of mechanical positioning elements, electronic image driving hardware, and optical metrology tools. The non-limiting example presented here illustrates assembly of the projector structure of FIG. 2. The required modifications, additional components and / or additional alignment steps required for assembly of the other illustrated implementations or variations thereof will be clear to a person having ordinary skill in the art.

[0076] A common optical bench 30 provides a stable reference frame for the assembly process. A jig 32 holds the PBS prism 72 in a fixed position, with the reflective lens arrangement 80 and associated quarter- wave plate 78 preferably pre-mounted at the second face 72b. A second jig 34 is used to position and align the image generator 70, such as an LCoS device, relative to the first face 72a of the PBS prism. Jig 34 is configured to allow adjustment in two lateral directions X, Y within the image plane, and rotation (0) about an axis perpendicular to the image plane, enabling precise centering and angular alignment of the image content.

[0077] A third jig 36 supports the refractive lens arrangement 100 facing the third face 72c of the PBS prism, across an air gap. Jig 36 provides adjustment in two lateral directions X, Y perpendicular to the optical axis, and Z parallel to the optical axis, allowing in-plane and axial positioning of the refractive lens. The axial positioning (Z-direction) is used for focus adjustment, while in-plane positioning ensures boresight alignment of the output image.

[0078] A processing system 38 is connected to the image generator 70 and includes drivers 40 for generating one or more calibration images suitable for various stages of the assembly process, which may include crosshairs and / or alignment frames that are preferred for alignment, and / or periodic structures optimized for modulation transfer function (MTF) analysis. A support structure 42 maintains the position of a camera 44, aligned along the intended optical axis of the projector output, downstream of the refractive lens 100. The camera captures projected test images and relays them to the processing system where they are typically handled by an image analysis module 46, which may include software for computing MTF, edge sharpness, and field uniformity.

[0079] Optionally, the jigs 34 and 36 may be provided with automated actuators 48 that are operated under semi-automated or fully automated control by processing system 38 under feedback from the image analysis system 46 to adjust alignment. In other implementations, the adjustments may be performed manually under operator supervision, with visual or software- guided indicators of alignment quality.

[0080] This assembly setup allows independent and sequential alignment of the image generator and the refractive lens, using projected test images and objective image quality metrics. It supports both coarse and fine adjustments and accommodates a wide range of projector configurations. A typical alignment and assembly sequence for implementation using this system will now be described with reference to FIG. 7.

[0081] Turning now to FIG. 7, a flow diagram is shown illustrating a method of assembling an image projector assembly according to an embodiment of the present invention. The method includes a sequence of alignment and fixation steps suitable for constructing a projector of the type illustrated, for example, in FIG. 2. The method may be implemented using an assembly system of the type shown in FIG. 6, although variations are possible depending on the specific embodiment.

[0082] In step 200, the core optical components of the projector are provided. These include a PBS prism 72, an image generator 70, a reflective lens arrangement 80, and a refractive lens arrangement 100.

[0083] In step 202, the reflective lens arrangement 80 and its associated quarter-wave plate 78 are affixed to the PBS prism 72, preferably in advance of the alignment procedure as part of a subassembly process. The lens is typically mounted at the second face 72b of the PBS prism employing a “passive alignment” process, i.e., relying on physical features of the components to align them correctly to sufficient accuracy, with any fine variations in alignment being compensated for during the active alignment of other components performed is subsequent steps. In implementations such as those of FIGS. 4 and 5 where two identical reflective lens arrangements 80a and 80b must be arranged in highly precise symmetrical deployment relative to the plane of PBS surface 76, one of the reflective lens arrangement, e.g., 80a, is preferably deployed at this stage using passive alignment, while the other should be deployed using active alignment (further discussed below). Where an LCOS image generator or other reflective SLM is used, the illumination components are preferably also pre-assembled together with the PBS prism 72 at this stage by passive alignment, and are treated as a unitary assembly with the PBS prism in the subsequent alignment and integration steps.

[0084] In step 204, the PBS prism 72 (i.e., the PBS prism assembly with its associated preassembled components), image generator 70, and refractive lens arrangement 100 are arranged in an assembly jig system that provides adjustable positioning and includes an optical metrology system. This system typically includes the jigs 32, 34, and 36, a processing system 38 with associated drivers 40 and image analysis module 46, and a camera 44 supported by structure 42 along the optical output axis, all as described above with reference to FIG. 6. In step 206, the image generator 70 is activated to display one or more calibration images. These may include crosshairs, bounding boxes, or line structures, optionally switching between different calibration images optimized for each type of adjustment during the assembly process.

[0085] In step 208, a coarse focus adjustment is preferably performed by displacing the refractive lens arrangement 100 in the Z direction, using jig 36, to bring the image into approximate collimation. This step enables sufficient image quality to proceed with image generator alignment.

[0086] In step 210, the image generator 70 is adjusted laterally in X and Y directions, i.e., parallel to prism face 72a, and in rotation (0) about the optical axis, to achieve centering and proper orientation of the projected image. This may be done manually, guided by visual display of the calibration image superimposed on displayed guide features, or under closed-loop control, based on analysis of the captured image. This alignment may optionally be performed simultaneously with X-Y adjustment of the refractive lens arrangement 100 (i.e., perpendicular to the optical axis of the projected image emerging from face 72c).

[0087] In implementations such as those of FIGS. 4 and 5 where two identical reflective lens arrangements 80a and 80b must be arranged in highly precise symmetrical alignment, positioning and X-Y alignment of the second reflective lens arrangement, typically supported by an additional adjustable jig (not shown), may be performed at this point. The two images can be distinguished by use of a linear polarizer at the exit from the projector, and correct alignment will result in exact combination (perfect overlap) of the two images to appear as a single image.

[0088] In step 212, a fine focus adjustment is performed by readjusting the refractive lens 100 in Z and, optionally, in X and Y, to achieve collimation of the output beam. The term “collimated” in this context refers to an optical condition in which the light emerging from each image pixel propagates in a well-defined direction corresponding to an image angle, with all rays parallel to one another, such that the image is focused at infinity. This is typically verified by maximizing a modulation transfer function (MTF) or other optical quality metric measured by the image analysis system 46.

[0089] In step 214, once optimal alignment is achieved, the image generator 70 and the refractive lens 100 are fixed in position. Fixation may be achieved by curing of UV adhesives, clamping within the projector housing, or mechanical fastening.

[0090] In optional step 216, a final verification of image quality is performed to confirm proper alignment, focus, and uniformity. This step may include analysis of sharpness, field curvature, and boresight alignment.

[0091] The method as described allows staged adjustment of image alignment and collimation under objective assessment and may be adapted to different image generator types, coupling architectures, and lens configurations. It will be appreciated that the above descriptions are intended only to serve as examples, and that many other embodiments are possible within the scope of the present invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. An image projector for a near-eye display system, the image projector comprising:(a) a polarizing beam-splitter (PBS) prism having a first face, a second face, and a third face;(b) an image generator defining an image plane from which light corresponding to an image emanates, the image plane being disposed adjacent to the first face of the PBS prism;(c) a reflective lens arrangement associated with the second face of the PBS prism, the reflective lens arrangement having a first positive optical power and including a quarter-wave retarder plate; and(d) a refractive lens arrangement disposed in facing relation to the third face of the PBS prism, the front lens arrangement having a second positive optical power and being spaced from the third face of the PBS prism by an air gap, wherein the PBS prism includes a polarizing beam-splitter surface deployed to define a light path for image light from the image plane to the reflective lens arrangement and from the reflective lens arrangement to the front lens arrangement, and wherein the first positive optical power, the second positive optical power and a width of the air gap are chosen so that the image light emerging from the refractive lens arrangement corresponds to a collimated image for coupling into a lightguide for display to a user.The image projector of claim 1, further comprising a field lens disposed between the image generator and the first face of the polarizing beam-splitter prism.

2. The image projector of claim 0, wherein the field lens is a doublet with planar external surfaces and is optically bonded to both the image generator and the first face of the polarizing beam-splitter prism.

3. The image projector of claim 0, wherein the field lens is separated from the image generator or the polarizing beam-splitter prism by an air gap less than 100 microns.

4. The image projector of claim 1, wherein the air gap between the refractive lens arrangement and the polarizing beam-splitter prism is at least about 300 microns.

5. The image projector of claim 1, further comprising an adjustable support configuration configured to allow adjustment of the air gap between the refractive lens arrangement and the polarizing beam-splitter prism for focus adjustment during assembly.

6. The image projector of claim 1, wherein the image generator comprises a reflective liquid crystal on silicon (LCoS) device.

7. The image projector of claim 6, further comprising:(a) a lightguide for conveying the collimated image by internal reflection for display to a user, the image projector being deployed to introduce the collimated image via an optical coupling arrangement into the lightguide; and(b) illumination optics configured to project light from an illumination stop through the PBS prism to illuminate the image plane, wherein the illumination optics together with the reflective lens arrangement and the refractive lens arrangement are configured to achieve pupil imaging of the illumination stop onto an entrance of the lightguide.

8. The image projector of claim 1, wherein the image generator comprises a multi-color microLED array.

9. The image projector of claim 1, wherein the image generator comprises at least two microLED arrays configured to generate images of at least two different colors, said at least two microLED arrays being mounted on respective faces of a dichroic combiner prism.

10. The image projector of claim 1, wherein the image generator comprises at least one microLED array, and wherein the polarizing beam-splitter (PBS) prism has a fourth face having associated therewith a second reflective lens arrangement with the first positive optical power and including a quarter- wave retarder plate, wherein the polarizing beam-splitter surface is deployed to define said light path for image light of a first polarization component from the image plane to the reflective lens arrangement and from the reflective lens arrangement to the front lens arrangement, and to define an additional light path for image light of a second polarization component from the image plane to the second reflective lens arrangement and from the second reflective lens arrangement to the front lens arrangement, said first and second polarization components being combined in the collimated image for coupling into a lightguide.I L A method of assembling an image projector for a near-eye display system, the method comprising:(a) providing:(i) a polarizing beam-splitter (PBS) prism having a first face, a second face, and a third face;(ii) an image generator defining an image plane from which light corresponding to an image emanates;(iii) a reflective lens arrangement with a first positive optical power and including a quarter- wave retarder plate; and(iv) a refractive lens arrangement with a second positive optical power;(b) aligning and affixing the image generator adjacent to the first face of the PBS prism such that the image plane is optically coupled to the PBS prism, and aligning and affixing the reflective lens arrangement adjacent to the second face of the PBS prism;(c) positioning the refractive lens arrangement in facing relation to the third face of the PBS prism, separated by an air gap;(d) adjusting a width of the air gap to achieve optical collimation of image light emerging from the refractive lens arrangement; and(e) fixing the position of the refractive lens arrangement after adjustment of the air gap-12. The method of claim 12, wherein the refractive lens arrangement is positioned with an air gap of at least about 300 microns from the third face of the polarizing beam-splitter prism prior to fixation.

13. The method of claim 12, wherein adjusting the width of the air gap includes using an adjustable support configuration for focus adjustment during assembly.

14. The method of claim 12, further comprising aligning the refractive lens arrangement in an in-plane direction to maintain boresight alignment of the collimated image.

15. The method of claim 12, further comprising affixing a field lens between the image generator and the first face of the polarizing beam-splitter prism.

16. The method of claim 16, wherein the field lens is a doublet with planar external surfaces and is optically bonded to both the image generator and the polarizing beam-splitter prism.

17. The method of claim 16, wherein the field lens is spaced from the image generator or the polarizing beam-splitter prism by an air gap of less than 100 microns.

18. The method of claim 12, wherein the image generator comprises a reflective liquid crystal on silicon (LCoS) device.

19. The method of claim 19, further comprising projecting light from an illumination stop through the polarizing beam-splitter prism to illuminate the image plane, wherein the illumination optics, the reflective lens arrangement, and the refractive lens arrangement achieve pupil imaging of the illumination stop onto an entrance of a lightguide.

20. The method of claim 12, wherein the image generator comprises at least two microLED arrays mounted on respective faces of a dichroic combiner prism.

21. The method of claim 12, wherein the image generator comprises at least one microLED array, and wherein the method further comprises:(a) providing a second reflective lens arrangement with the first positive optical power and including a quarter-wave retarder plate, the second reflective lens arrangement being associated with a fourth face of the PBS prism; and(b) directing image light of two orthogonal polarization components from the image plane along two respective optical paths through the first and second reflective lens arrangements for recombination at the PBS surface to form the collimated image.

Images