Optical systems

Abstract

The optical system includes an optical waveguide and an image projection arrangement. The image projection arrangement includes a polarizing beam splitter prism having an oblique polarizing beam splitter surface that reflects light from the image generation matrix to the reflective collimating optical system. A coupling prism is positioned between the polarizing beam splitter surface and the optical waveguide inlet and provides a coupling surface that is coplanar with or parallel to one of the parallel main surfaces of the optical waveguide. The reference length RL is defined as the distance along the optical axis from the main plane of the collimating optical system to the polarizing beam splitter surface. Both the first optical path from the image plane to the main plane and the second optical path from the main plane to the optical waveguide inlet have lengths of less than 3 × RL.

Description

Technical Field

[0001] The present invention relates to an optical system, specifically, a small image projector integrated with an optical waveguide.

Background Art

[0002] U.S. Patent No. 10,564,417 discloses an advantageous small configuration integrating an image projector and an optical waveguide. Here, FIGS. 16 and 17 of that patent are reproduced with their original numbers as FIGS. 1A and 1B, respectively. These drawings illustrate an image projector including two polarization beam splitter (PBS) prisms. The first PBS prism 500 receives an S-polarized input illumination 505 that is reflected by a PBS surface 507 toward a reflective polarization modulation spatial light modulator such as an LCOS chip 509. The selectively modulated p-polarized divergent image light 511 passes through the PBS surface 507 and is converted to s-polarized light by a 1 / 2 wavelength retarder (not numbered) upon incidence on a second PBS prism 526 so as to be reflected toward a collimating reflective optical system 515 having a 1 / 4 retarder (not numbered) at a second PBS surface 513. The reflective optical system 515 collimates the image light into collimated light having p-polarization with a field of view 517 extending from the steepest angle ray 518a to the shallowest angle ray 518b, and that collimated light traverses the PBS surface 513 for coupling to the optical waveguide 503. The coupling to the optical waveguide is partially achieved by reflection at a surface 528 provided by a lower portion of the PBS prism 526 that forms a continuation of one of the surfaces of the optical waveguide. In FIGS. 1A and 1B, the range of angles used for the combined images is different, with a relatively high angle image presented in FIG. 1A while a shallower angle incident image is illustrated in FIG. 1B. Explanation of any reference numbers in FIGS. 1A and 1B not described above may be found in the '417 patent itself.

Summary of the Invention

[0003] The present invention is an optical system.

[0004] According to the teaching of one embodiment of the present invention, the provided optical system is an optical system having an optical waveguide inlet, having a pair of parallel main surfaces and supporting the propagation of image light by internal reflection at the main surfaces; (b) an image projection arrangement for generating a collimated image to be introduced into the optical waveguide, comprising (i) a polarizing beam splitter prism having a first surface, a second surface, and an oblique polarizing beam splitter surface; (ii) an image generation matrix associated with the first surface, defining an image plane; and (iii) a reflective collimating optical system associated with the second surface and arranged to collimate image light from the image plane reflected by the polarizing beam splitter surface, comprising a reflective collimating optical system having a main plane and an optical axis. An optical system is provided comprising: an image projection arrangement comprising: (c) a coupling prism between the polarizing beam splitter surface and the optical waveguide inlet, the coupling prism providing a coupling surface that is coplanar with or parallel to one of the parallel main surfaces, wherein the optical waveguide and coupling surface are inclined with respect to the optical axis such that a collimated image from a reflective collimating optical system passing through the polarizing beam splitter surface enters the optical waveguide inlet partially directly and partially after reflection from the coupling surface at an angle at which it undergoes internal reflection in the optical waveguide, a reference length RL is defined as the distance along the optical axis from the main plane to the polarizing beam splitter surface, a first optical path from the image plane to the main plane having a length of less than 3 × RL, and a second optical path from the main plane to the optical guide tube inlet having a length of less than 3 × RL.

[0005] According to further features of one embodiment of the present invention, the second optical path from the main plane to the optical waveguide entrance has a length of less than 2 × RL.

[0006] According to a further feature of one embodiment of the present invention, the collimated image rays entering the optical waveguide entrance span the field of view, the field of view is given by the image light that reaches the reflective collimating optical system from the image plane after reflecting off the active area on the surface of the polarizing beam splitter, and the active area extends on both sides of the plane of the coupled surface.

[0007] According to further features of one embodiment of the present invention, the entrance to the optical waveguide is defined by an optical cutoff edge between the optical waveguide and the coupled prism, and a plane passing through the optical cutoff edge perpendicular to the main surface intersects with the active area of ​​the polarizing beam splitter surface.

[0008] According to further features of one embodiment of the present invention, the image generation matrix is ​​a micro-LED array.

[0009] According to further features of one embodiment of the present invention, a field lens arrangement comprising at least one lens is also provided, the field lens arrangement being located between a micro-LED array and a first surface of a polarizing beam splitter prism.

[0010] According to further features of one embodiment of the present invention, at least one lens of the field lens arrangement is integrated with a micro-LED array.

[0011] According to further features of one embodiment of the present invention, the image generation matrix is ​​a reflected space light modulator (SLM), and the optical system further comprises an illumination arrangement interposed between the SLM and a first surface of a polarizing beam splitter prism, the illumination arrangement comprising an illumination optical waveguide having two mutually parallel surfaces for guiding illumination across the SLM by internal reflection within the illumination optical waveguide, the illumination optical waveguide including a set of internal partial reflection surfaces for gradually redirecting illumination from the illumination optical waveguide toward the SLM.

[0012] According to further features of one embodiment of the present invention, a field lens arrangement comprising at least one lens is also provided, the field lens arrangement being located between the SLM and a first surface of the polarizing beam splitter prism.

[0013] According to further features of one embodiment of the present invention, at least one lens of the field lens arrangement is integrated with the SLM.

[0014] According to the teaching of one embodiment of the present invention, the optical system also provided is (a) an optical waveguide having a pair of parallel principal surfaces supporting the propagation of image light by internal reflection at principal surfaces, wherein the optical waveguide has an optical waveguide inlet, and (b) an image projection arrangement for generating a collimated image to be introduced into the optical waveguide, comprising (i) first, second, and third micro-LED arrays configured to generate first, second, and third color images, respectively, and (ii) the first micro-LED array, the second micro-LED array, A dichroic combiner having first, second, and third input surfaces supporting a third micro-LED array, the dichroic combiner comprising: a first obliquely positioned dichroic reflector that is selectively reflective to a first color and transmissive to a second and third color; a second obliquely positioned dichroic reflector that is selectively reflective to a third color and transmissive to a second color; and (iii) a polarizing beam splitter plate associated with the dichroic combiner having a diagonal polarizing beam splitter surface. An image projection arrangement comprising: (iv) a reflective collimating optical system associated with the surface of a polarizing beam splitter prism, coupled by a dichroic combiner, and arranged to collimate image light from first, second, and third micro-LED arrays reflected by the polarizing beam splitter surface, the reflective collimating optical system having a main plane and an optical axis; and (c) a coupling prism between the polarizing beam splitter surface and the optical waveguide inlet, wherein the coupling prism is coplanar with one of the parallel main surfaces. An optical system is provided which provides a coupled surface that is parallel to or perpendicular to the optical axis, and the optical waveguide and coupled surface are inclined with respect to the optical axis, and the collimated image from the reflective collimating optical system passing through the polarizing beam splitter surface enters the optical waveguide entrance partially directly and partially after reflection from the coupled surface at an angle to which internal reflection occurs within the optical waveguide, and a reference length RL is defined as the distance along the optical axis from the main plane to the polarizing beam splitter surface, and the optical path from the main plane to the optical waveguide entrance has a length of less than 3 × RL, preferably less than 2 × RL.

[0015] According to further features of one embodiment of the present invention, the second dichroic reflector is transparent to the first color, and the second dichroic reflector is positioned non-parallel to the first dichroic reflector so as to intersect with the first dichroic reflector. [Brief explanation of the drawing]

[0016] In this specification, the present invention will be described only by reference to the accompanying drawings.

[0017] [Figure 1A] Figures 1A and 1B correspond to Figures 16 and 17 of U.S. Patent No. 10,564,417, respectively. [Figure 1B] Figures 1A and 1B correspond to Figures 16 and 17 of U.S. Patent No. 10,564,417, respectively. [Figure 2A] A schematic isometric diagram illustrating the propagation of an image from a projector through a two-dimensional aperture expansion optical waveguide. [Figure 2B] Schematic front view of the optical system shown in Figure 2A. [Figure 3] A schematic side view of an optical system comprising a miniature image projector integrated with an optical waveguide, constructed and operable according to the teachings of one embodiment of the present invention. [Figure 4A] A schematic side view of a further optical system integrated with an optical waveguide, constructed and operable according to the teachings of one embodiment of the present invention, and including a miniature image projector using a dichroic synthesizer arrangement and a micro-LED array. [Figure 4B] A schematic side view of an alternative implementation of a dichroic synthesizer configuration suitable for use in the optical system shown in Figure 4A. [Figure 5A] A schematic side view of a further optical system integrated with an optical waveguide, which is constructed and operable according to the teachings of one embodiment of the present invention, and includes a miniature image projector and uses a color micro-LED array. [Figure 5B] A schematic side view of a further optical system similar to the system in Figure 5A, implemented for incident images at shallower angles. [Figure 6] Schematic side view of a further optical system similar to the system of FIG. 5A, illustrating a further reduction in the size of the coupling prism so as to enable shortening of the optical path length from the collimating optical system to the entrance to the optical waveguide. [Figure 7A] Schematic side view similar to FIG. 6, illustrating an implementation mode having a coupling surface that is not on the same plane as the surface of the optical waveguide. [Figure 7B] Expanded view of the region of FIG. 7A designated VII. [Figure 8A] Schematic side view similar to FIG. 6, but using a reflective polarization modulation spatial light modulator illuminated via an illumination optical waveguide. [Figure 8B] A figure similar to FIG. 8A, illustrating a modified implementation mode of the illumination optical waveguide.

Mode for Carrying Out the Invention

[0018] The present invention is an optical system that provides a small image projector integrated with an optical waveguide.

[0019] The principle and operation of the optical system according to the present invention can be better understood by referring to the drawings and the accompanying description.

[0020] First, the present invention relates to various improvements to the small optical system described above with reference to FIGS. 1A and 1B, which typically use a small image projector integrated with an optical waveguide for delivering an image to the viewer's eyes in the context of an augmented reality display. In a particular preferred implementation mode, the optical system includes a two-dimensional optical aperture-expanded optical waveguide. The overall architecture of such an arrangement is schematically illustrated in FIGS. 2A and 2B.

[0021] FIGS. 2A and 2B show a schematic isometric view and a side view of an image projector 2 attached to an optical waveguide 10 having front and rear parallel planes 12a and 12b. The optical waveguide 10 has a first set of partial reflectors perpendicular to the optical waveguide surfaces 12a and 12b ( It incorporates 14 (also called "facets"). The second set of parallel partial reflectors (facets) 16 are inclined with respect to the optical waveguide surface.

[0022] The light beam 18a schematically represents the collimated image produced by the projector 2, which has a polarization orientation 20a (which may be referred to as P-polarization with respect to those surfaces) set perpendicular to surfaces 12a and 12b. This beam is represented as 18b and propagates through the optical waveguide 10 while maintaining its polarization. The light is schematically illustrated as a single arrow, but is angled to propagate by internal reflection from surfaces 12a and 12b. The beam 18b collides with facets 14. Since these facets 14 are perpendicular to surfaces 12a and 12b, the polarization 20b of the colliding beam 18b is parallel to the surface of facets 14 and corresponds to S-polarization with respect to those facets.

[0023] A partially reflected beam 18c (shown from one facet, but existing as a partially reflected beam from each of the facets) collides with facet 16. Due to the different orientations of facet 16, the colliding beam has P polarization with respect to these facets.

[0024] In certain cases, designing multilayer dielectric coatings to impart desired partial reflectivity and angular dependence to facets 14 and / or 16 may be easier for S-polarized light than for P-polarized light (with respect to the facets). Therefore, a projector arrangement that introduces P-polarized light into the optical waveguide 10 so that the image is essentially S-polarized with respect to facet 14 may be advantageous. This P-polarized incident light can be achieved by certain embodiments of the invention described below. Optionally, a half-wavelength delay plate may be included in the optical waveguide 10 interposed between two sets of facets to convert the light reaching facet 16 into S-polarized light with respect to those facets.

[0025] Referring now to Figure 3, this illustrates an optical system according to a first aspect of the present invention. The structure and function of this optical system are generally the same as those in Figure 1A, but structural simplification is achieved by mounting a portion of the PBS prism between PBS surfaces 510A and 510B as a single block. This facilitates the manufacture of PBS surfaces 510A and 510B integrated on the opposing surfaces of the parallel side prisms, preferably as a dielectric coating. This structure is made possible by rearranging the reflective polarization-modulating spatial light modulator (SLM) so that a polarization rotation element is not required between the PBS surfaces. The combination of the above-mentioned double PBS and the extension of the optical waveguide surface, i.e., the lower surface 528 of the PBS prism (coupled prism) parallel to the optical waveguide surface, enables a compact and efficient mounting configuration of the optical system.

[0026] All other features of this configuration are the same as those of the structure and function shown in Figure 1A above, and are labeled with the same reference numbers. This configuration can also be implemented at shallower incidence angles (similar to Figure 1B).

[0027] Referring here to Figure 4A, the teaching optical system of one embodiment of the present invention is adapted to generate an image using an active matrix image generator such as an OLED array, or more preferably a microLED array. In this embodiment, a set of three separate arrays, indicated as 605R, 605G, and 605B, each provide different color components of the image, indicated as solid, dashed, and dotted lines, respectively.

[0028] Accordingly, the optical system includes, in addition to the optical waveguide 10 having a pair of parallel main surfaces 12a and 12b, an image projection arrangement 2 for generating collimated images to be introduced into the optical waveguide, which includes first, second, and third micro-LED arrays 605R, 605G, and 605B, respectively, configured to generate images of first, second, and third colors such as red, green, and blue for full-color image generation. The dichroic combiner 606 has first, second, and third input surfaces supporting the first micro-LED array 605R, the second micro-LED array 605G, and the third micro-LED array 605B, respectively. The dichroic combiner 606 includes a first obliquely positioned dichroic reflector 600A that is selectively reflective to the first color and transmissive to the second and third colors, and a second obliquely positioned dichroic reflector 600B that is selectively reflective to the third color and transmissive to the second color.

[0029] The remainder of the image projection arrangement includes, as described above, a polarizing beam splitter prism 526 having an oblique polarizing beam splitter surface 510B and associated with a dichroic combiner, and a reflective collimating optical system 515 arranged to collimate image light from the first, second, and third micro-LED arrays, which is associated with the surface of the polarizing beam splitter prism 526 and combined by the dichroic combiner 606 and reflected by the polarizing beam splitter surface 510B. The reflective collimating optical system 515 has a main plane PP and an optical axis OA.

[0030] The coupling prism may be the entire prism between the polarizing beam splitter surface 510B and the optical waveguide inlet, but provides a coupling surface 528 that is coplanar with or parallel to one of the parallel main surfaces of the optical waveguide 10.

[0031] The optical waveguide 10 and the coupling surface 528 are inclined with respect to the optical axis OA, so that the collimated image from the reflective collimating optical system 515, which has passed through the polarizing beam splitter surface 510B, enters the optical waveguide entrance at an angle at which it undergoes internal reflection within the optical waveguide 10, partially directly and partially after reflection from the coupling surface 528.

[0032] The result of this structure is an advantageously compact optical arrangement. Throughout this document, the miniaturization of various configurations is quantified by reference to a “reference length” RL, defined as the distance along the optical axis OA from the main plane PP to the polarizing beam splitter surface (i.e., where OA intersects the plane of the PBS surface 510B). In this implementation, the optical path from the main plane to the optical waveguide entrance is preferably less than 3 × RL in length, and in some particularly preferred cases, less than 2 × RL in length. Optimal shortening of the distance from the collimating optics to the optical waveguide entrance can be achieved using a coupled prism configuration as described below with reference to Figure 6. The optical path from the image generating plane (micro-LED array) to the main plane of the reflective collimating optics, corresponding to the focal length of the collimating optics, is preferably 4 × RL or less.

[0033] In the embodiment of Figure 4A, the dichroic combiner 606 (which may be referred to as a “trichroic combiner” as it combines three different color sources) is illustrated as an “X cube,” where the first dichroic reflector 600A and the second dichroic reflector 600B intersect each other. In this case, the second dichroic reflector 600B is implemented to be transparent to the first color as well, thereby not interfering with the first color reaching the entire first dichroic reflector 600A. In certain cases, an alternative trichloric prism configuration, such as the trichloric combiner prism illustrated in Figure 4B, may be preferred, which corresponds to a prism structure common in 3CCD cameras. In this case, the light of the first color does not reach the second dichroic reflector, thereby easing the spectral requirements on the second dichroic reflector.

[0034] Both combiner prism configurations are illustrated here with first and third color images (and thus all principal rays visible in a single cross-section) input from opposite sides of the prism; however, the orientation of the dichroic reflector can alternatively be selected, for example, with a single color image introduced to the page from a direction, such that the first and third color images are input to adjacent faces of the prism. Furthermore, the entire illumination prism can be rotated by 90 degrees so that both the first and third images are introduced to and derived from the page.

[0035] If the active matrix image source generates unpolarized light, it may be possible to select S-polarized light depending on the PBS surface 510B and deliver it to the collimating optical system. In this case, the uncollimated P-polarized light passing linearly through the PBS surface remains on the lower surface of the coupling prism, exits there (as it is not at an angle for internal reflection), and is absorbed by an external absorbing material (not shown). Alternatively, a polarizer may be incorporated into the surface to which the active matrices 605A, 605B, and 605C are associated, or a single such polarizer may be positioned between the dichroic combiner prism 606 and the PBS surface 510B to remove P-polarized light before it reaches the PBS surface.

[0036] All other features of this configuration are the same as those of the structure and function shown in Figure 1A above, and are labeled with the same reference numbers. This configuration can also be implemented at shallower angles of the incident image (Figure 1B).

[0037] Referring now to the remaining Figures 5A to 8B, a family of implementations of optical systems according to the teachings of embodiments of the present invention is shown, where the image plane of the image generator is significantly reduced compared to the previously described embodiments, and it becomes possible to use a collimating optical system having a focal length that approximates (typically within about ±50%) the distance from the collimating optical system to the optical waveguide entrance. Similar to the previously described embodiments, the proximity of the collimating optical system to the optical waveguide entrance allows for a reduction in the size of the optical system relative to a given field of view (FOV). The reduction in the distance from the image plane of the image generator to the collimating optical system, and the corresponding reduction in the focal length of the collimating optical system, increases the efficiency of light collection from each pixel and allows for an expansion of the field of view relative to an image matrix of a given size. In addition, approximating the focal length from the optical system to the optical waveguide entrance reduces optical aberrations and simplifies the optical system required to correct aberrations.

[0038] In general terms, the optical system in Figures 5A–8B includes an optical waveguide 10 having a pair of parallel main surfaces 12a and 12b that support the propagation of image light by internal reflection at the main surfaces, the optical waveguide having an optical waveguide inlet with one side defined by a cutoff edge 523 on one side. The optical system also includes an image projection arrangement 2 for generating a collimated image introduced into the optical waveguide. The image projection arrangement 2 includes a polarizing beam splitter prism 536 having a first surface 630, a second surface 632, and an oblique polarizing beam splitter surface 610. An image generation matrix 611 or 612 (to be discussed further below) is associated with the first surface 630 and defines the image plane. A reflective collimating optical system 615 associated with the second surface 632 is arranged to collimate the image light from the image plane reflected by the polarizing beam splitter surface 610. The reflective collimating optical system 615 has a main plane PP and an optical axis OA.

[0039] The optical system also includes a coupling prism 637 between the polarizing beam splitter surface 610 and the entrance to the optical waveguide 10, which provides a coupling surface 638 that is coplanar with or parallel to one of the parallel principal surfaces 12b of the optical waveguide 10. The optical waveguide 10 and the coupling surface 638 are inclined with respect to the optical axis OA, so that the collimated image from the reflective collimating optical system 615 that has passed through the polarizing beam splitter surface 610 enters the optical waveguide entrance, partially directly and partially after reflection from the coupling surface 638, at an angle at which it undergoes internal reflection within the optical waveguide.

[0040] A characteristic feature of a group of embodiments of the present invention is that the first optical path from the image plane to the main plane and the second optical path from the main plane to the optical waveguide entrance are of similar dimensions and are both relatively short. Quantitatively, the reference length RL, defined as the distance along the optical axis OA from the main plane PP to the polarizing beam splitter surface 610, is again used. With respect to this reference length, the first optical path from the image plane to the main plane preferably has a length of less than 3 × RL, and the second optical path from the main plane to the optical waveguide entrance also preferably has a length of less than 3 × RL. In some cases, the second optical path from the main plane to the optical waveguide entrance has a length of less than 2 × RL. This results in a particularly compact and efficient optical system. Hereinafter, we consider some specific implementations of such an optical system.

[0041] In the implementations shown in Figures 5A to 7A, the image generation matrix is ​​an active matrix image source, which may be an OLED display, more preferably a micro-LED array 611. Most preferably, the micro-LED array is a color display comprising pixels of three primary colors, spaced close together or otherwise combined. Monolithic micro-LED color displays are commercially available from Jade Bird Display (JDB) in Shanghai, China, as the PHOENIX® series.

[0042] In this configuration, there is no external illumination, and light from the active matrix image source 611 enters directly onto the PBS prism 636. In some configurations, the field lens 616 may be mounted on the surface of the active matrix image source 611 and / or on the surface 630 of the PBS prism 636. This configuration does not require a separate illumination prism, which allows for a shorter effective focal length of the collimating optics 615, resulting in a larger illumination field and better light collection for the system. Shortening the distance from the reflective collimating optics 615 to the optical waveguide entrance 523 allows for a smaller and more compact optical system for a given field of view (FOV).

[0043] Figure 5A illustrates this configuration for a relatively steep image incidence angle, while Figure 5B illustrates such a configuration for a shallow image incidence angle to the optical guide path. In the latter case, the shallowest portion of the field labeled 518b contains rays substantially originating from the edge of the focusing optical system and therefore requires a relatively long internal coupling surface 638 extending from just below the PBS surface 610 and extended by the auxiliary coupling prism 535.

[0044] Further reduction of the distance between the collimating optical system 615 and the entrance to the optical waveguide can be achieved using the configuration illustrated in Figure 6. Figure 6 shows the case where the required dimensions of the PBS surface 610 are greater than the coupled prism entrance dimensions. This is suitable when a complex and wide optical system is required to project a wide field of view. Here, light projected from the image generator 611 passes through a field lens arrangement including a field lens 622A applied to the surface of the active matrix image source 611 and another field lens 622B mounted on the PBS prism surface 630. The illustrated sample ray path from the image source 611 to the reflective collimating optical system 615 through reflection in the PBS surface 610 requires the entire illustrated area of ​​the PBS surface 610, referred to as the “active area” of the PBS surface, and the optical waveguide entrance 523 is blocked over the entire desired FOV. Simultaneously, the ray path from the reflective collimating optical system 615 to the optical waveguide entrance 523 passes only through a sub-region of the PBS surface 610. This enables an implementation of the coupled prism 637 that contacts only the relevant sub-region of the PBS surface, allowing the optical waveguide entrance to be brought closer to the collimating optical system.

[0045] This configuration satisfies one or more of several characteristic geometric definitions. Firstly, it can be seen that the active area of ​​the PBS surface 610 extends onto both sides of the plane of the coupling surface 638. In addition, as defined above, the entrance to the optical waveguide 10 is defined by the optical cutoff edge 523 between the optical waveguide and the coupling prism 637. In this case, the plane passing through the optical cutoff edge 523 perpendicular to the main surfaces 12a and 12b intersects with the active area of ​​the polarizing beam splitter surface 610.

[0046] A further geometric definition that brings the optical waveguide inlet closer to the reflective collimating optical system is that the optical waveguide inlet preferably lies within a virtual cube which can be constructed by giving a mirror image of the upper PBS prism 636 beneath the PBS surface 610, represented by the ghost dashed line 639.

[0047] In all cases, the image light collimated by the optical system 615 preferably fills the optical waveguide aperture with rays corresponding to all portions of the FOV, both directly (rays propagating downward) and after reflection within the coupling surface 638 (rays propagating upward).

[0048] The reflective collimating optical system 615 is illustrated here in one preferred embodiment as a composite refractive reflective lens including a double lens 618 in front of the reflective surface. The presence of the double lens 618 provides design flexibility for correcting chromatic aberration that may be introduced by other parts of the optical system, including but not limited to the field lens arrangements 622A, 622B, and the combined output configuration for coupling the image toward the viewer's eye. The primary collimating light power is typically provided by the reflective surface of the optical system 615, which is itself achromatic.

[0049] Ignoring the details of the ray paths within the lens arrangement, the “principal plane” PP of the reflective collimated optical system 615 is defined in the conventional sense, corresponding to the plane on which parallel light entering from one side of the optical system intersects with the corresponding convergent ray from the other side of the optical system. The lens system has both a principal image plane and a principal subject plane, but due to the symmetry of the reflective lens system, these two planes generally coincide. As mentioned above, if the primary optical power of the collimated arrangement lies within the reflective surface, the principal plane is typically close to that surface.

[0050] As described above, the coupled reflector 638 may be coplanar with or parallel to the principal optical waveguide surface 12b. Here, with reference to Figures 7A and 7B, the particular importance of mounting a coupled surface 638 that is parallel to the principal surface 12b but slightly offset will be explained.

[0051] In practice, the mounting between the optical waveguide 10 and the coupling prism 637 presents technical challenges. Specifically, when the coupling prism 637 is attached to the optical waveguide 10 by an index-matching optical adhesive, it is difficult to achieve a high-quality continuous surface from the coupling surface 638 across the adhesive boundary to the optical waveguide surface 12b. Surface defects at that boundary can cause scattering that propagates within the optical waveguide and degrades image quality. This problem becomes more pronounced in designs that further hinder attempts to achieve a continuous high-optical-quality surface by introducing additional optical elements (such as waveplates, depolarizers, or other elements) at the interface between the coupling prism and the optical waveguide, resulting in additional transitions between different optical materials with different physical properties.

[0052] Figures 7A and 7B illustrate a method in which, even when an intervening optical element 700 is added, a small step difference between the elements at the junction between the coupling prism 637 and the optical waveguide 10 enters the optical waveguide 10 and the amount of scattered light induced within the optical waveguide 10 can be eliminated or at least reduced.

[0053] In the example illustrated here, the surface 638 of the coupled prism 637 is offset downward (outward) relative to the parallel surface 12b of the optical waveguide 10 so that not all light impacting the interface enters the optical waveguide. The range of the shift between 638 and 12b is preferably minimal, and is defined such that the last ray 702a impacting the front edge of surface 638 (of either the optical element 700 or the optical waveguide 10) at the boundary of the perturbation is reflected as ray 702b and enters the entrance end of 12b, while rays impacting the perturbation (i.e., at or beyond the interface boundary) and scattered (dashed arrow) do not enter the optical waveguide. This condition should be satisfied for the steepest rays entering the optical waveguide, and therefore for shallower rays as well.

[0054] Referring here to Figures 8A-8B, this particularly compact optical system can also be implemented using an image generation matrix implemented as a reflected space light modulator (SLM), such as a liquid crystal on silicon (LCOS) modulator 612. To shorten the optical path from the SLM to the collimating optics to less than 3 × RL, the optical system preferably uses an optical waveguide-based illumination arrangement interposed between the SLM 612 and the first surface 630 of the polarizing beam splitter prism 636. The illumination arrangement uses illumination optical waveguides 624A, 624B having two mutually parallel surfaces for guiding illumination across the SLM by internal reflection within the illumination optical waveguide, and a set of internal partial reflective surfaces 626 for gradually redirecting the S-polarized illumination toward the SLM. The P-polarized reflected image is reflected by the LCOS and passes through facet 626 into the PBS prism 636. To control polarization, the system may include a polarizer after the optical waveguide (above the PBS) to filter out non-image S-polarized light.

[0055] The image light entering the PBS prism 636 should typically be S-polarized with respect to the PBS surface 610. This can be achieved by including a 1 / 2 delay plate between the illumination waveguide (or subsequent polarizer) and the PBS prism, or by rotating the illumination arrangement 90 degrees relative to the PBS prism so that the illumination can be incident on the page of the drawing (not shown). As a result of this second option, the P-polarized image light for illumination facet 626 is S-polarized with respect to the PBS surface 610. Optionally, in either of these cases, the PBS surface 610 itself can act as a filter for the S-polarized image light from the LCOS. In such a case, any P-polarized light crossing the PBS surface 610 exits the optical system, reaching the underside of the coupled prism at an angle that does not undergo internal reflection, and is preferably absorbed by an absorbing material outside the optical arrangement.

[0056] Typically, it is advantageous to incorporate a field lens arrangement of at least one field lens 622A, 622B between the SLM 612 and the first surface of the polarizing beam splitter prism 630. In the example in Figure 8A, the illumination arrangement is directly related to the SLM, and the field lens is positioned between the illumination arrangement and the PBS prism 636.

[0057] Figure 8B illustrates a more preferred option in which at least one lens 622A of the field lens configuration is integrated with the SLM, and the illumination optical waveguide 624B is positioned on the side of the field lens, further away from the SLM 612. This architecture has the further advantage that the illumination optical waveguide 624B is significantly removed from the image plane, thereby reducing the risk that the facet pattern may be visible as an image perturbation.

[0058] Both the configurations in Figure 8A and Figure 8B illustrate that a very small image projector can be integrated with the optical waveguide 10 even when using a reflective SLM.

[0059] In all of the above configurations, the image projector configuration (unless intentionally modified further) directs P-polarized light into the optical waveguide. This polarization is preferred in many optical waveguide configurations, as discussed above with reference to Figures 2A and 2B.

[0060] The above description is intended to serve only as an example, and it will be understood that many other embodiments are possible within the scope of the invention as defined in the appended claims.

Claims

1. An optical system, (a) An optical waveguide having a pair of parallel main surfaces and supporting the propagation of image light by internal reflection at the main surfaces, and having an optical waveguide inlet, (b) An image projection arrangement for generating a collimated image to be introduced into the optical waveguide, (i) A polarizing beam splitter prism having a first surface, a second surface, and an oblique polarizing beam splitter surface, (ii) An image generation matrix associated with the first surface, comprising an image generation matrix that defines an image plane, (iii) A reflection collimating optical system associated with the second surface and arranged to collimate image light from the image plane reflected by the polarizing beam splitter surface, comprising: a reflection collimating optical system having a principal plane and an optical axis; (c) A coupling prism between the polarizing beam splitter surface and the optical waveguide inlet, which provides a coupling surface that is coplanar with or parallel to one of the parallel main surfaces, The optical waveguide and the coupling surface are inclined with respect to the optical axis such that the collimated image from the reflective collimating optical system passing through the polarizing beam splitter surface enters the optical waveguide entrance partially directly and partially after reflection from the coupling surface, at an angle at which it undergoes internal reflection within the optical waveguide. An optical system in which a reference length RL is defined as the distance along the optical axis from the main plane to the surface of the polarizing beam splitter, a first optical path from the image plane to the main plane having a length of less than 3 × RL, and a second optical path from the main plane to the entrance of the optical waveguide having a length of less than 3 × RL.

2. The optical system according to claim 1, wherein the second optical path from the main plane to the entrance of the optical waveguide has a length of less than 2 × RL.

3. The optical system according to claim 1, wherein the light rays of the collimated image entering the optical waveguide entrance span the field of view, the field of view is given by the image light that reaches the reflective collimating optical system from the image plane after reflection from the active area on the surface of the polarizing beam splitter, and the active area extends on both sides of the plane of the coupling surface.

4. The optical system according to claim 3, wherein the entrance to the optical waveguide is defined by an optical cutoff edge between the optical waveguide and the coupling prism, and a plane passing through the optical cutoff edge perpendicular to the main surface intersects the active area on the surface of the polarizing beam splitter.

5. The optical system according to claim 1, wherein the image generation matrix is ​​a micro-LED array.

6. The optical system according to claim 5, further comprising a field lens arrangement having at least one lens, wherein the field lens arrangement is located between the micro-LED array and the first surface of the polarizing beam splitter prism.

7. The optical system according to claim 6, wherein at least one lens of the field lens arrangement is integrated with the micro-LED array.

8. The optical system according to claim 1, wherein the image generation matrix is ​​a reflected space light modulator (SLM), and the optical system further comprises an illumination arrangement interposed between the SLM and the first surface of the polarizing beam splitter prism, the illumination arrangement comprising an illumination optical waveguide, the illumination optical waveguide having two mutually parallel surfaces for guiding illumination across the SLM by internal reflection within the illumination optical waveguide, and the illumination optical waveguide including a set of internal partial reflective surfaces for gradually redirecting illumination from the illumination optical waveguide toward the SLM.

9. The optical system according to claim 8, further comprising a field lens arrangement having at least one lens, wherein the field lens arrangement is located between the SLM and the first surface of the polarizing beam splitter prism.

10. The optical system according to claim 9, wherein at least one lens of the field lens arrangement is integrated with the SLM.

11. An optical system, (a) An optical waveguide having a pair of parallel main surfaces and supporting the propagation of image light by internal reflection at the main surfaces, and having an optical waveguide inlet, (b) An image projection arrangement for generating a collimated image to be introduced into the optical waveguide, (i) First, second, and third microLED arrays configured to generate first, second, and third color images, respectively, (ii) A dichroic combiner having first, second, and third input surfaces supporting the first, second, and third microLED arrays, comprising: a first obliquely positioned dichroic reflector that is selectively reflective to the first color and transmissive to the second and third colors; and a second obliquely positioned dichroic reflector that is selectively reflective to the third color and transmissive to the second color; (iii) A polarizing beam splitter prism associated with the dichroic synthesizer and having an oblique polarizing beam splitter surface, (iv) A reflective collimating optical system arranged to collimate image light from the first, second, and third micro-LED arrays, which are associated with the surface of the polarizing beam splitter prism, synthesized by the dichroic combiner, and reflected by the surface of the polarizing beam splitter, comprising: a reflective collimating optical system having a main plane and an optical axis; and an image projection arrangement. (c) A coupling prism between the polarizing beam splitter surface and the optical waveguide inlet, which provides a coupling surface that is coplanar with or parallel to one of the parallel main surfaces, The optical waveguide and the coupling surface are inclined with respect to the optical axis such that the collimated image from the reflective collimating optical system passing through the polarizing beam splitter surface enters the optical waveguide entrance partially directly and partially after reflection from the coupling surface, at an angle at which it undergoes internal reflection within the optical waveguide. An optical system in which a reference length RL is defined as the distance along the optical axis from the main plane to the surface of the polarizing beam splitter, and the optical path from the main plane to the entrance of the optical waveguide has a length of less than 3 × RL.

12. The optical system according to claim 11, wherein the optical path from the main plane to the entrance of the optical waveguide has a length of less than 2 × RL.

13. The optical system according to claim 11, wherein the second dichroic reflector is transparent to the first color, and the second dichroic reflector is arranged nonparallel to the first dichroic reflector such that it intersects with the first dichroic reflector.

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