Image display system with beam multiplication - Patents.com

Abstract

The optical system for displaying an image includes a light-directing optical element (LOE) having a coupling input region and a propagation region, a coupling output arrangement associated with the propagation region of the LOE, an image projector for producing image illumination corresponding to a collimated image, and a beam multiplication arrangement external to the LOE. The beam multiplier is a transparent plate bonded to the LOE adjacent to the coupling input region. The transparent plate has a partially reflective surface between the LOE and the plate and a reflector on the opposite surface. The partially reflective surface and the reflector multiply the beam from the projector so as to fully illuminate the propagation region of the LOE with both the collimated image and a conjugate of the collimated image.

Description

[Technical field]

[0001] The present invention relates to optical systems, and in particular to image display systems employing a waveguide in which an illumination beam is multiplied.

[0002] As an exemplary context for implementations of the present invention, various optical displays employ light-guiding optical elements (LOEs) (interchangeably referred to as "waveguides" or "substrates") to transmit an image from an image projector toward a user's eye, where the image is typically coupled out toward the eye by an arrangement of partial reflectors or by a diffractive optical element.

[0003] To achieve uniformity in the viewed image, the waveguide should be uniformly "filled" with the projected image and its conjugate image, which imposes design constraints on the size of the image projector and various other aspects of the optical design. Summary of the Invention

[0004] The present invention is a light-directing optical system having a beam multiplication arrangement to compensate for insufficient aperture filling by an image projector.

[0005] In accordance with the teachings of one embodiment of the present invention, an optical system for displaying an image to an eye of a user includes: (a) a light-directing optical element (LOE) having two planar main exterior surfaces that are parallel to aid in propagation of image illumination within the LOE by internal reflection at the main exterior surfaces, the LOE having a thickness h between the main exterior surfaces, the LOE having a coupling input region and a propagation region; (b) a coupling output configuration associated with the propagation region of the LOE and configured to couple out at least a portion of the image illumination from the LOE towards the eye of the user; and (c) an image projector for producing image illumination corresponding to a collimated image, the image illumination being introduced into the coupling input region of the LOE and coupled out of the propagation region of the LOE by internal reflection. An optical system is provided comprising: (a) an image projector optically coupled to the LOE to propagate within the propagation region; and (b) a beam multiplication arrangement associated with the LOE and configured for beam multiplication of image illumination introduced into the coupling input region of the LOE, the beam multiplication arrangement including a transparent plate having mutually parallel outer surfaces, the transparent plate being adhered to a major outer surface of the LOE adjacent the coupling input region, the transparent plate providing a partially reflective surface between the LOE and the plate, and further providing a reflector, the partially reflective surface and the reflector being configured to reflect the image illumination introduced into the coupling input region into the propagation region, thus completely illuminating the propagation region with both a collimated image and a conjugate of the collimated image.

[0006] According to a further feature of an embodiment of the invention, the transparent plate has a thickness of h / 2.

[0007] According to a further feature of an embodiment of the invention, the beam multiplication arrangement is configured to compensate for half aperture filling of the combined input area by the image projector.

[0008] According to a further feature of an embodiment of the invention, the LOE includes a coupling input arrangement associated with the coupling input region of the LOE and configured to couple image illumination from an image projector into the LOE for propagation within the LOE by internal reflection.

[0009] According to a further feature of an embodiment of the present invention, the coupled input configuration includes a wedge prism positioned between the image projector and the coupled input area of ​​the LOE, or a beveled edge at one end of the LOE between the image projector and the coupled input area of ​​the LOE.

[0010] According to a further feature of an embodiment of the invention, the system includes a first beam multiplication arrangement configured to provide beam multiplication in a stimulated dimension of the LOE and a second beam multiplication arrangement configured to provide beam multiplication in a non-stimulated dimension of the LOE.

[0011] According to a further feature of an embodiment of the invention, the beam multiplication arrangement includes m partially reflective mutually parallel surfaces, m being a positive integer, the m surfaces being provided by m transparent plates, the beam multiplication arrangement being configured to compensate for an aperture filling of 1 / (m+1), each plate having a pair of major parallel outer surfaces, the m plates being bonded together at their respective major parallel surfaces to form a stack that is bonded to a major outer surface of the LOE, the reflector provided by the outer surface of the mth plate being the plate furthest from the LOE, and each of the m plates having a thickness equal to 1 / (m+1) of the thickness h of the LOE. [Brief description of the drawings]

[0012] The invention is herein described, by way of example only, with reference to the accompanying drawings.

[0013] [Figure 1A] 1A-1C are schematic side views illustrating an image projection waveguide with beam multiplication according to an embodiment of the present invention employing reflected and diffracted beam steering components, respectively. [Figure 1B]1A-1C are schematic side views illustrating an image projection waveguide with beam multiplication according to an embodiment of the present invention employing reflected and diffracted beam steering components, respectively. [Diagram 2] FIG. 1 is a schematic side view of a waveguide employing a coupled input wedge according to a conventional coupled input geometry. [Figure 3A] 3 shows the results of different sized illumination apertures introduced into the waveguide of FIG. 2, achieving full and partial filling of the waveguide, respectively. [Figure 3B] 3 shows the results of different sized illumination apertures introduced into the waveguide of FIG. 2, achieving full and partial filling of the waveguide, respectively. [Figure 4] 1A-1C are schematic side views of embodiments of an image display system for compensating for half aperture fill, one-third aperture fill, and one-quarter aperture fill, respectively. [Diagram 5] 1A-1C are schematic side views of embodiments of an image display system for compensating for half aperture fill, one-third aperture fill, and one-quarter aperture fill, respectively. [Figure 6] 1A-1C are schematic side views of embodiments of an image display system for compensating for half aperture fill, one-third aperture fill, and one-quarter aperture fill, respectively. [Figure 7] 1 shows the size of the coupling input area of ​​a conventional optical system using a wedge-type coupling input configuration. [Figure 8] 1 illustrates the size of the coupling input area of ​​an embodiment of the disclosed optical system using a wedge-type coupling input configuration. [Figure 9] 13 illustrates the size of the coupling input area of ​​an embodiment of the disclosed optical system using a diagonal edge coupling input configuration. [Figure 10] 1 is a schematic side view of an embodiment of the disclosed optical system in which the aperture is extended in the non-guiding dimension. [Figure 11] 1 is a schematic side view of an embodiment of the disclosed optical system in which the aperture is extended in the non-guiding dimension. [Figure 12] FIG. 12 is an isometric view of the optical system of FIGS. 10 and 11. [Figure 13] FIG. 1 is an isometric view of an optical system in which the aperture is elongated in both the guiding and non-guiding dimensions. [Figure 14] FIG. 1 is a schematic side view of one embodiment of the disclosed optical system using an air gap coupled input configuration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention is a light-directing optical system with beam multiplication, the principles and operation of which may be better understood with reference to the drawings and the accompanying description.

[0015] 1A and 1B show a schematic representation of one implementation of the teachings provided herein of an optical system for displaying an image to a user's eye 100 located within a region referred to as an eye motion box (EMB) 102. The system includes a light-directing optical element (LOE) 10 (interchangeably referred to as a "waveguide" or "substrate") having two planar major exterior surfaces 12, 14 that are parallel to aid in the propagation of image illumination within the LOE by total internal reflection (TIR) ​​at the major exterior surfaces 12, 14. The LOE of this system can be considered to be virtually divided along its width into at least functionally distinct regions, referred to herein as a "coupling input region" and a "propagation region," as described in more detail below.

[0016] A coupling-out arrangement is associated with at least a portion of the propagation region of the LOE and configured to couple out at least a portion of the image illumination from the LOE toward the user's eye 100. In certain embodiments, the coupling-out arrangement is implemented as a set of mutually parallel partially reflective surfaces 16 disposed within the LOE and oriented obliquely relative to the major exterior surface, as shown in FIG. 1A. In other embodiments, the coupling-out arrangement is implemented as at least one diffractive optical element 18 associated with the LOE 10 and configured to progressively couple out a portion of the image illumination toward the user's eye, as shown in FIG. 1B. In some embodiments, the coupling-out arrangement may be associated with the entire propagation region such that the image is coupled out progressively along the entire length of the propagation region. In other embodiments, the coupling-out arrangement may be associated with only a portion of the propagation region such that the propagation region includes a portion where the image only propagates without being coupled out.

[0017] An image projector 20, interchangeably referred to as a "POD," produces image illumination corresponding to a collimated image. Image projector 20 is optically coupled to LOE 10 to introduce image illumination into a coupling input region of the LOE for propagation within the LOE by internal reflection. The POD employed in the device of the present invention is preferably configured to produce a collimated image, i.e., an image in which the light for each image pixel is an infinitely collimated parallel beam, with the angular orientation corresponding to the pixel location. The image illumination thus spans an angular range corresponding to a two-dimensional angular field of view.

[0018] The image projector 20 includes at least one light source, such as an LCOS chip, typically arranged to illuminate a spatial light modulator. The spatial light modulator modulates the projection intensity of each pixel of the image, thereby generating the image. Other embodiments of the image projector 20 may include OLED or micro-LED illumination sources. Alternatively or additionally, the image projector may include a scanning configuration, typically implemented using a fast scanning mirror, that can scan illumination from a laser light source across the image plane of the projector while the intensity of the beam is changed synchronously with the movement on a pixel-by-pixel basis, thereby projecting the desired intensity of each pixel. In both cases, a collimating optical system is provided to generate an output projected image that is infinitely collimated. Some or all of the above components are typically configured on the surface of one or more polarizing beam splitter (PBS) cubes or other prism configurations, employing reflective optical systems, as is well known in the art. Alternatively, free-space optical implementations with reflective and / or refractive optical elements may be used. The details of the image projector are not per se part of the present invention and, for simplicity of presentation, the image projector is represented herein diagrammatically as a dash box without attempting to describe the individual components.

[0019] Optical coupling of the image projector 20 to the LOE 10 may be achieved by any suitable optical coupling, such as through one of the side edges and / or major exterior surfaces of the LOE, e.g., through a coupling input prism having an obliquely angled input face or through a reflective coupling configuration. An example of coupling inputs through a wedge prism may be found in PCT Publication No. WO2015 / 162611. Examples of various coupling inputs using mirrors may be found in PCT Publication No. WO2001 / 095027. Except as otherwise specified below, the details of the optical coupling between the image projector and the LOE are typically not important to the invention and are illustrated here diagrammatically as a non-limiting example of a wedge prism 22 applied to an edge surface of the LOE 10. Furthermore, implementations of the invention illustrated herein using a coupling input prism may similarly be implemented using a reflective coupling input configuration, and vice versa. A coupling input configuration is illustrated in FIG. 2 as a α-coupling input prism. POD Determine the angle between the POD and the LOE, denoted as:

[0020] One embodiment of the invention illustrated in Figures 1A, 1B and 4-14 relates to a range of configurations in which collimated image light is guided by a light-directing optical element (LOE) having a pair of major parallel exterior surfaces, but does not completely "fill" it (also referred to herein as "illuminating") it, and in particular propagates without the image being an image / image conjugate pair at all points along the LOE. In such situations, and in accordance with one embodiment of the invention, it has been found to be particularly useful to provide a beam multiplication arrangement associated with the coupled input region of the LOE and configured for beam multiplication of image illumination introduced into the coupled input region of the LOE, to completely illuminate the propagation region with the image and its conjugate, as described in more detail below.

[0021] 1A and 1B includes at least one transparent plate 26 disposed adjacent lower surface 12 of LOE 10. In the embodiment illustrated in FIGS. 1A and 1B, a single transparent plate 26 is shown. Transparent plate 26 includes a partially reflective surface 24 at or near surface 12 that acts as a beam splitter (also referred to as a "beam multiplier" and / or "beam duplicator") such that a portion of the light striking the beam splitter is reflected back into LOE 10 and a portion of the light is transmitted through plate 26 and reflected by the outer surface of plate 26 back into LOE 10. Further details of the beam multiplication configuration of the present invention are provided below.

[0022] To better illustrate the advantages provided by the beam multiplication configuration shown in Figures 1A and 1B, Figures 2 and 3A show a combined input configuration employing a wedge prism 22 according to a conventional approach without the currently disclosed beam multiplication configuration. The LOE should provide image illumination to the human eye with a uniform distribution across all light propagation angles (also referred to as "field" or "field of view" FOV) and throughout the EMB 102. To this end, the aperture of each field should be filled with light evenly. In other words, for any illumination angle corresponding to a pixel in the collimated image, the entire cross section of the LOE in a plane perpendicular to the main surface of the LOE is filled with both the image and its reflection (conjugate), and therefore at any point within the LOE volume, a ray should exist corresponding to every pixel in both the collimated image and its conjugate. To achieve this result, as shown in Figure 3A, a relatively large aperture image projector 20 was used with an extension to one major surface 12 of the LOE so that the aperture of LOE 10 received all of the direct illumination of the image and all of the reflected illumination of the conjugate image that was internally reflected from surface 12. To fill the LOE aperture in this manner, image projector 20 must have a correspondingly large aperture.

[0023] If the "fill" condition is not met, the light striking the eye will not be evenly distributed. An example of a narrow illumination beam that does not meet this criterion is shown in FIG. 3B, where a smaller image projector 20 is used that has an otherwise similar optical configuration to FIG. 3A. When aperture fill is lacking, the light exiting the LOE will not be evenly distributed. Non-uniformity in the filling of the LOE can occur for a number of reasons, including but not limited to the use of a projector with a small aperture, the use of a small coupling input geometry, and certain configurations of internal facet reflections.

[0024] 4-6, optical systems according to embodiments of the present invention that compensate for partial filling of an aperture are disclosed. Generally speaking, each of the optical systems includes a LOE 10 having two planar major exterior surfaces 12, 14 that are parallel to aid in propagation of image illumination within the LOE by internal reflection at the major exterior surfaces. The LOE has a thickness h between the major exterior surfaces. Along the length of the LOE, the LOE first includes a coupling input region 34, followed by a propagation region 36. Unlike the coupling input region, the propagation region is surrounded by an air barrier (or alternatively a reflective mirror), and thus image illumination introduced within the propagation region undergoes TIR between the major exterior surfaces 12, 14.

[0025] An image is introduced into the coupled input region 34 by a projector 20 configured to produce image illumination corresponding to a collimated image, and is optically coupled to the LOE so as to introduce the image illumination into the coupled input region of the LOE and propagate within the propagation region of the LOE by internal reflection.

[0026] The optical system further includes a beam multiplication arrangement associated with the LOE and configured for beam multiplication of image illumination introduced into a coupling input region of the LOE, the beam multiplication arrangement comprising m partially reflective mutually parallel surfaces 28, where m is a positive integer, and the m surfaces are external to the LOE and parallel to a major exterior surface of the LOE. The beam multiplication arrangement further comprises a reflector 30. The m surfaces and the reflector are configured to reflect the image illumination introduced into the coupling input region 34 into a propagation region 36 to fully illuminate the propagation region 36 with both the image and its conjugate.

[0027] The optical system further includes a coupling out arrangement, typically implemented as a facet 16 or a diffractive element 18 (omitted for clarity in Figures 4-6, but shown in Figures 1A and 1B), associated with the propagation region 36 and configured to couple out at least a portion of the image illumination from the LOE toward the user's eye.

[0028] Throughout this description, the partially reflective surface 28 is also referred to herein as a "partial reflector" and the fully reflective surface 30 is simply referred to as a "reflector". As will be explained in detail below, the reflectors and partial reflectors are provided by one or more transparent plates 26. Generally speaking, m plates are used to compensate for 1 / m aperture filling. The m plates provide m+1 reflective surfaces including one (1) reflector and m partial reflectors. The reflectors are typically implemented as the outer surfaces of the plates that completely reflect the impinging rays by TIR. Alternatively, in some embodiments, the reflectors can be implemented as mirrors.

[0029] 4, there is shown a cross-sectional schematic diagram of an optical system in which a beam multiplication configuration compensates for half (1 / 2) aperture filling by an image projector. In this case, a single transparent plate 26 provides a partial reflector 26 and a reflector 30 and is bonded to the exterior surface 12 (also referred to herein as the "lower" major exterior surface) of the LOE adjacent the coupling input region 34.

[0030] Transparent plate 26 extends partially along the length of the lower major exterior surface 12 of the LOE adjacent to the coupling input region 34. An end point 32 of plate 26 (referred to herein as the "critical point") marks the end of the coupling input region 34 and the entrance to the propagation region 36 of the LOE, although the distinction between the coupling input region and the propagation region is purely conceptual, as no physical barrier exists at the junction between these regions. In some embodiments, plate 26 includes an edge 38 at the critical point, which is perpendicular to the major exterior surface of the LOE. Importantly, image radiation cannot enter the propagation region after impinging on edge 38. In some embodiments, in the case of more than one plate, only the plate closest to the LOE (actually adjacent to the LOE) needs to extend completely along the coupling input region 34, terminating at edge 38 at point 32.

[0031] In this case, as shown in Figure 4, the beam multiplication configuration compensates for the 1 / 2 aperture fill by beam multiplication (also referred to herein as "beam duplication") of the image illumination entering the propagation region, so that the propagation region is fully illuminated by both the image (shown as a downward arrow) and its conjugate (shown as an upward arrow). As shown in Figure 4, each ray is duplicated by the beam splitter, with a portion of the ray reflecting off a partial reflector 28 and a portion of the ray reflecting off a full reflector 30, thereby effectively extending the critical point 32 further along the length of the LOE, so that each ray and its conjugate fills the propagation region 36 of the LOE, thereby compensating for the lesser aperture fill by the projector that would be insufficient to fully illuminate the propagation region with both the image and its conjugate. To achieve uniform intensity distribution in the image and conjugate image, the lower surface of transparent plate 26 acts as a perfect reflector 30 (e.g., via TIR or mirror coating) and ideally the upper surface of plate 26 should be coated to uniformly reflect 36%-40%, most preferably 38.2%, of the impinging light within the angular range of the image.

[0032] As a supplement, it should be understood that projector 20 may alternatively inject the conjugate of an image, in which case the downward arrow would in fact represent the conjugate and the upward arrow would represent the image. Thus, throughout this description, the terms "image" and "conjugate" should be understood to be interchangeable such that a reference to an "image" can also mean the conjugate of the image, in which case any reference to a "conjugate" will be understood as a reference to the image.

[0033] The optical system may, in some embodiments, include a coupled input arrangement of a wedge 22 between the projector 20 and the LOE 10.

[0034] As discussed above, compensation for smaller partial aperture filling is also contemplated. FIG. 5 shows an optical device that compensates for an injected beam that fills only 1 / 3 the size of the area filled by the full aperture injected beam (i.e., 1 / 3 the size of that filled by the beam shown in FIG. 3A). Without compensation, the LOE would only be partially filled (FIG. 3B). To compensate for 1 / 3 aperture filling (N=3), two (N-1=2) partial reflectors 28 are required. In the exemplary implementation shown in FIG. 5, the two partial reflectors are implemented using two transparent plates 26 with a total total thickness given by h*2 / 3, with each individual transparent plate 26 having a thickness of h / 3. In this case, the two transparent plates 26 form a "stack" that is glued together and then glued to the surface 12 of the LOE adjacent to the coupling input region 34. The two transparent plates are bonded at their major exterior surfaces and collectively provide two partial reflectors 28 and a reflector 30 .

[0035] To achieve uniform distribution of the image conjugate image, the interface between the top (first) plate and the LOE may include a partially reflective coating having a reflectance of 21% to 24%, preferably 22.8%. The interface between the bottom (second) plate and the top (first) plate may be coated with a partially reflective coating having a reflectance of 37% to 40%, preferably 38.2%. The lower major exterior surface of the bottom (i.e., second) transparent plate acts as a perfect reflector similar to that described with reference to FIG. 4.

[0036] 6 shows an optical device that compensates for an injected beam that fills only 1 / 4 the size of the area filled by the full aperture injected beam (i.e., 1 / 4 the size of that filled by the beam shown in FIG. 3A). To compensate for 1 / 4 aperture filling (N=4), three (N-1=3) partial reflectors 28 are required. In the exemplary implementation shown in FIG. 6, the three partial reflectors 28 are implemented using three transparent plates 26 with a total total thickness given by h*3 / 4, with each individual transparent plate having a thickness of h / 4.

[0037] To achieve a uniform distribution of the image conjugate image, the interface between the top (first) plate and the LOE may include a partially reflective coating having a reflectance of 15% to 17%, preferably 16.1%. The interface between the middle (second) plate and the top (first) plate may be coated with a partially reflective coating having a reflectance of 21% to 24%, preferably 22.8%. The interface between the middle (second) plate and the bottom (third) plate may be coated with a partially reflective coating having a reflectance of 37% to 40%, preferably 38.2%. The lower major external surface of the bottom (i.e., second) transparent plate acts as a perfect reflector, similar to that described with reference to Figures 4 and 5.

[0038] Generally speaking, the beam multiplication arrangement includes m partially reflective surfaces parallel to the main external LOE surface provided by m transparent plates, m being a positive integer. The number of partial reflectors is determined by the formula m=N-1, where 1 / N represents the fraction of the aperture filling to be compensated. The partial reflectors are arranged in a spaced relationship, with the first partial reflector placed at or near the lower main external surface 12 of the LOE. The spacing between the partial reflectors is proportional to the thickness h of the LOE and is determined by the thickness of the plates. A full reflector 30 is arranged below the partial reflectors, and in particular below the last partial reflector (which is also the first partial reflector when only one partial reflector is used). The full reflector is arranged in a spaced relationship relative to and below the last partial reflector such that the effective spacing between the full reflector and the lower main external surface 12 of the LOE (equivalently, or nearly equivalently, the first partial reflector) is also proportional to h. In general, the effective spacing between the full reflector and the lower major exterior surface of the LOE can be expressed by the formula h*(N-1) / N. To achieve such spacing, the thickness of each of the m plates should preferably be 1 / (m+1) of h.

[0039] In the case of more than one transparent plate, each interface between the plates and the interface between the first plate (i.e., the plate adjacent to the LOE) and the LOE includes a partially reflective coating. Several different coating methods are possible. For example, each plate can be coated on one surface and glued together and to the LOE, such that each interface includes a partially reflective coating. Alternatively, every other plate (i.e., every other plate in the stack) can each be coated with a partially reflective coating on both major exterior surfaces. Alternatively, partial reflectivity can be achieved by stacking plates (or using an optical adhesive) of different refractive index selected to produce the desired partial reflection at the interfaces between the plates. Alternatively, the optical adhesive between the plates can have a different refractive index than the plates, selected to produce the desired partial reflection.

[0040] To achieve uniform intensity of the image and the conjugate image, the top surface of plate i is

number

[0041] Preferably, the reflectivity of each of the m consecutive partial reflectors is R i The reflectivity is given using the formula for m = 1 / 2. However, the reflectivity percentage is a parameter that may not be precisely defined or precisely achievable in all cases, at least for the entire angular range of the image (field of view), and the intention here is to refer to a value close enough to the theoretical value that, if sampled, the resulting intensity distribution would be visually perceived as uniform across the thickness of the LOE. For a single partial reflector (m=1), a 5-10% error in reflectivity is visually acceptable even after half a cycle. More generally, a ±5% or even ±10% variation in reflectivity may, in certain cases, yield results close enough to the optimum to be visually acceptable. Parallelism between the partial reflector layer and the main external surface of the LOE should be maintained, and a thickness subdivision into equal parts is performed, within 10% accuracy, preferably more precisely, to avoid creating striped non-uniform intensities during the beam multiplication process.

[0042] Structurally, the partial reflectance of the beam multiplication configuration can be implemented using any suitable partially reflective layer or coating, including but not limited to metallic coatings, structural partial reflectors (e.g., polka dot pattern reflectors), and multi-layer dielectric coatings. In some embodiments, the partially reflective coating can be preferably implemented using an angle-dependent reflective coating, where the coating has a low reflectance at small angles (close to normal to the beam splitter) while having the desired reflectance according to the above sequence at angles in the range corresponding to the angle of image light propagation in the LOE, resulting in less attenuation of light from the directly viewed scene. Layers with such angle-dependent reflectance can be easily achieved using multi-layer dielectric coatings, and are easy to manufacture, since the required properties are essentially similar to Fresnel reflection properties. The design of multi-layer coatings to provide such angle-dependent reflectance can be done using standard software packages, as is customary in the art, and suitable coatings can be obtained commercially from a number of sources. Therefore, for simplicity of presentation, details will not be provided here.

[0043] While the embodiments described thus far have been directed to beam multiplication when using a wedge as the coupling input mechanism for injecting light into the LOE, other embodiments are possible in which other coupling input geometries are contemplated.

[0044] By way of introduction, FIG. 7 repeats the full aperture filling of the LOE when using a wedge 22 as the coupling input mechanism. The wedge is optically designed so that the aperture is completely filled, i.e., there is an upward and downward ray at every point of the cross section of the LOE in a plane perpendicular to the LOE's main exterior surface. The size of the coupling input region 34 is determined by the wedge and the field of view, and is designed so that the upward and downward rays overlap for every field inside the LOE. In a configuration where the chief ray is coupled out of the LOE perpendicular to the LOE, the angle of the wedge with respect to the LOE is selected to be perpendicular to the chief ray. However, if a slight tilt is applied to the LOE (e.g., for aesthetic reasons), the angle of the wedge should be adjusted to account for the tilt angle to minimize chromatic aberration. Furthermore, the length of the wedge is determined according to the shallowest ray that can be guided through the LOE. The propagation region 36 begins at the end of the coupling input region 34 and continues throughout the length of the LOE.

[0045] As discussed in detail above, partial aperture-filling techniques by beam multiplication (e.g., the semi-aperture-filling technique shown in FIG. 4 and reproduced in more detail in FIG. 8) rely on duplicating the incident light beam using one or more transparent plates 26 to completely fill the aperture. However, as is evident from FIG. 8, the transparent plates 26 increase the size of the coupled input region 34 (i.e., the transparent plates extend along a significant portion of the lower major exterior surface 12 of the LOE) when compared to the full aperture approach shown in FIG.

[0046] With the above in mind, FIG. 9 illustrates an optical device according to an embodiment of the present invention having a beam multiplication mechanism that simultaneously reduces the size of the coupled input region 34 when compared to the coupled input region 34 of FIG. 8. In such an embodiment, the entire aperture is illuminated, except that the wedge-shaped coupled input mechanism is replaced by a beveled edge 40 (i.e., an edge that is angled relative to the parallel major exterior surfaces of the LOE). In general, the particular angle of the beveled edge 40 is selected according to the same criteria used to select the angle of the wedge discussed above. Since there is no wedge to replicate the upward and downward light rays, the light rays are injected directly into the LOE via the beveled edge 40. A transparent plate 26 (similar to that described above) replicates and overlaps the upward and downward light rays. Furthermore, since there is no wedge acting as a coupled input mechanism, the overall input aperture of the optical device is smaller (compared to the optical device of FIG. 8) and the size of the coupled input region 34 (i.e., as defined by the length of the transparent plate) is smaller than the size of the coupled input region 34 of FIG. 8. As an aside, the reduced overall input aperture has the added benefit of reducing the overall form factor of the optical device, suitable for use in Near Eye Display (NED) systems.

[0047] Thus far, the discussion of input aperture extension has been discussed in terms of aperture extension in the guided dimension of the LOE 10. In some cases, aperture extension in the non-guided dimension is also required. As used herein, the "guided dimension" refers to the dimension between the major surfaces in which light is guided by TIR, and the "non-guided dimension" refers to the dimension extending parallel to the major surfaces in which the light path expands without being limited by internal reflection.

[0048] FIG. 10 shows an optical system in which the aperture is extended in the unguided dimension. To compensate for partial filling of the aperture when the light rays are not guided by TIR, a transparent plate 26 having a lower major surface 28 coated with a partially reflective coating is deployed between the wedge 22 and the edge of the LOE 10, such that a portion of the upper major outer surface of the transparent plate 26 acts as a mirror 30 and the lower major outer surface of the transparent plate acts as a partial reflector 28. The transparent plate effectively reflects the incident light rays such that the partially filled input light rays are replicated. To fill the entire aperture, the thickness h of the transparent plate 26 is reduced by 100 nm. m is chosen to comprise half the aperture stop S of the optical system.

[0049] FIG. 11 shows another depiction of the optical system of FIG. 10 with the addition of the illustration that the light rays from different fields (represented by a non-parallel set of parallel light rays) completely fill the stop S of the optical system (which is half the size of the original full aperture optical system).

[0050] Figure 12 is an isometric view of the optical system of Figures 10 and 11 showing transparent plate 26 coupled to the LOE input. For clarity, the coupling input configuration is not shown in Figure 12, but is assumed to be present. The two rays are duplicated by transparent plate 26 and then propagate through the LOE before reaching the coupling output configuration (shown in Figure 12 as a diagonal line representing the facets) and are coupled out towards the EMB (not shown).

[0051] FIG. 13 shows cross-sectional and isometric views, respectively, of one embodiment of an optical system similar to that of FIG. 12, but with an additional transparent plate 26' at the LOE input to perform beam duplication in the guiding dimension of the LOE (e.g., as discussed with reference to FIGS. 4-9).

[0052] FIG. 14 illustrates another optical system that performs beam multiplication in a non-guided dimension according to an embodiment of the present invention. It contrasts with the embodiment described with reference to FIGS. 10-12. In this embodiment, no wedge is used to couple the light beam into the LOE. Instead, the incident beam is injected from a projector (not shown) into the LOE through an air gap 44 (shown exaggerated for clarity). Similar to that described with reference to FIGS. 10-12, a transparent plate is disposed between the air gap 44 and the LOE 10. The beam expands due in part to the transparent plate 26 (as previously described) and in part to the refraction of the beam as it passes from the lower refractive index medium of the air gap 44 to the higher refractive index medium (e.g., the LOE, which is typically constructed from glass). The expansion due to refraction is referred to as beam diameter expansion. As shown in FIG. 14, a beam with diameter d1 impinges on a segment of length H of the transparent plate at an incidence angle θ1 (measured relative to the normal). The refracted beam has a beam diameter d2 and a refracted angle θ2 (measured relative to the normal). Using simple geometry, the following mathematical relationship can be easily derived:

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[0053] It should be emphasized that in the embodiments disclosed above with reference to Figures 1A and 1B and 4-14, light entering the propagation region of the LOE was previously only reflected by partial and / or full reflectors. In no case should light reflected from the edges of the transparent plate (i.e., the edges of transparent plate 26 perpendicular to LOE surfaces 12, 14) enter the propagation region of the LOE.

[0054] It will be appreciated that displays include various additional components, including a controller for operating an image projector, which typically employs power from a small on-board battery or some other suitable power source. It will be appreciated that the controller includes all the necessary electronic components, such as at least one processor or processing circuitry for driving the image projector, all as is well known in the art. These features are not part of the invention itself and will not be described in detail herein. All such features will be readily implemented by one of ordinary skill in the art.

[0055] In the present description, the expanded beam is said to "fully illuminate" the propagation region in the sense that the beam multiplication arrangement overcomes the limitations of the beam width provided by the image projector and ensures that the entrance aperture to the LOE is provided with both the image and its conjugate over its entire area. Clearly, "full" illumination is measured by the ability to produce a combined output image that has no significant holes or black lines that are perceived by the observer's eye and are disturbing. Minor imperfections in the filling of the LOE that do not significantly affect the user's experience are clearly acceptable and are encompassed by the expression "fully illuminated."

[0056] It will be understood that the above description is intended to serve as an example only, and that many other embodiments are possible within the scope of the invention as defined in the appended claims.

Claims

1. 1. An optical system for displaying an image to an eye of a user, comprising: (a) a light-directing optical element (LOE) having two planar major exterior surfaces that are parallel to assist propagation of image illumination within the LOE by internal reflection at the major exterior surfaces, the LOE having a thickness h between the major exterior surfaces, the LOE having a coupling input region and a propagation region; (b) a coupling-out arrangement associated with the propagation region of the LOE and configured to couple out at least a portion of the image illumination from the LOE towards the eye of the user; and (c) an image projector for producing image illumination corresponding to a collimated image, the image projector being optically coupled to the LOE such that the image illumination is introduced into the coupling input region of the LOE and propagated within the propagation region of the LOE by internal reflection; and (d) a beam multiplication arrangement associated with the LOE and configured for beam multiplication of the image illumination introduced into the coupling input region of the LOE, the beam multiplication arrangement comprising m partially reflective mutually parallel surfaces, m being a positive integer, the m surfaces being external to the LOE and parallel to the main exterior surface of the LOE, and further comprising a reflector, the m surfaces and the reflector being configured to reflect the image illumination introduced into the coupling input region into the propagation region to fully illuminate the propagation region with both the collimated image and a conjugate of the collimated image; the m surfaces are provided by m transparent plates, each transparent plate having a pair of major parallel exterior surfaces, the m transparent plates being bonded together at their respective major parallel surfaces to form a stack bonded to the major exterior surfaces of the LOE; 11. An optical system according to claim 10, wherein each of said m transparent plates has a thickness equal to l / (m+1) of h.

2. 2. The optical system of claim 1, wherein the reflector is provided by an outer surface of an mth transparent plate, the mth transparent plate being the farthest from the LOE, the outer surface being configured to be totally reflective via TIR.

3. The optical system of claim 1 , wherein the reflector is provided by a mirror.

4. The optical system of claim 1 , wherein a first transparent plate, which is the transparent plate closest to the LOE, extends along the length of the LOE adjacent the coupling input region.

5. An optical system for displaying an image to an eye of a user, comprising: (a) a light-directing optical element (LOE) having two planar major exterior surfaces that are parallel to assist propagation of image illumination within the LOE by internal reflection at the major exterior surfaces, the LOE having a thickness h between the major exterior surfaces, the LOE having a coupling input region and a propagation region; (b) a coupling-out arrangement associated with the propagation region of the LOE and configured to couple out at least a portion of the image illumination from the LOE towards the eye of the user; and (c) an image projector for producing image illumination corresponding to a collimated image, the image projector being optically coupled to the LOE such that the image illumination is introduced into the coupling input region of the LOE and propagated within the propagation region of the LOE by internal reflection; and (d) a beam multiplication arrangement associated with the LOE and configured for beam multiplication of the image illumination introduced into the coupling input region of the LOE, the beam multiplication arrangement comprising m partially reflective mutually parallel surfaces, m being a positive integer, the m surfaces being external to the LOE and parallel to the main exterior surface of the LOE, and further comprising a reflector, the m surfaces and the reflector being configured to reflect the image illumination introduced into the coupling input region into the propagation region to fully illuminate the propagation region with both the collimated image and a conjugate of the collimated image; The beam multiplication arrangement is configured to compensate for l / (m+1) filling of the combined input area by the image projector.

6. The optical system of claim 1, further comprising an additional beam multiplication arrangement configured to provide beam multiplication prior to propagation of the image illumination within the LOE by internal reflection at the main external surface.

7. 2. The optical system of claim 1, further comprising a coupling input arrangement associated with a coupling input region of the LOE and configured to couple the image illumination from the image projector into the LOE for propagation within the LOE by internal reflection.

8. The optical system of claim 7 , wherein the coupling input arrangement comprises a wedge prism positioned between the image projector and the coupling input region of the LOE.

9. The optical system of claim 7 , wherein the coupling input arrangement comprises a beveled edge at one end of the LOE between the image projector and the coupling input area of ​​the LOE.

10. The optical system of claim 1 , wherein the coupling output arrangement comprises a plurality of mutually parallel facets angled obliquely with respect to the major exterior surface of the LOE.

11. The optical system of claim 1 , wherein the output coupling arrangement comprises a diffractive element.

12. 1. An optical system for displaying an image to an eye of a user, comprising: (a) a light-directing optical element (LOE) having two planar major exterior surfaces that are parallel to assist propagation of image illumination within the LOE by internal reflection at the major exterior surfaces, the LOE having a thickness h between the major exterior surfaces, the LOE having a coupling input region and a propagation region; (b) a coupling-out arrangement associated with the propagation region of the LOE and configured to couple out at least a portion of the image illumination from the LOE towards the eye of the user; and (c) an image projector for producing image illumination corresponding to a collimated image, the image projector being optically coupled to the LOE such that the image illumination is introduced into the coupling input region of the LOE and propagated within the propagation region of the LOE by internal reflection; and (d) a beam multiplication arrangement associated with the LOE and configured for beam multiplication of the image illumination introduced into the coupling input region of the LOE, the beam multiplication arrangement comprising a transparent plate having mutually parallel exterior surfaces, the transparent plate being adhered to a major exterior surface of the LOE adjacent the coupling input region, the transparent plate providing a partially reflective surface between the LOE and the transparent plate, and further providing a reflector, the partially reflective surface and the reflector being configured to reflect the image illumination introduced into the coupling input region into the propagation region to fully illuminate the propagation region with both the collimated image and a conjugate of the collimated image; The optical system according to claim 1, wherein the transparent plate has a thickness of h / 2.

13. An optical system for displaying an image to an eye of a user, comprising: (a) a light-directing optical element (LOE) having two planar major exterior surfaces that are parallel to assist propagation of image illumination within the LOE by internal reflection at the major exterior surfaces, the LOE having a thickness h between the major exterior surfaces, the LOE having a coupling input region and a propagation region; (b) a coupling-out arrangement associated with the propagation region of the LOE and configured to couple out at least a portion of the image illumination from the LOE towards the eye of the user; and (c) an image projector for producing image illumination corresponding to a collimated image, the image projector being optically coupled to the LOE such that the image illumination is introduced into the coupling input region of the LOE and propagated within the propagation region of the LOE by internal reflection; and (d) a beam multiplication arrangement associated with the LOE and configured for beam multiplication of the image illumination introduced into the coupling input region of the LOE, the beam multiplication arrangement comprising a transparent plate having mutually parallel exterior surfaces, the transparent plate being adhered to a major exterior surface of the LOE adjacent the coupling input region, the transparent plate providing a partially reflective surface between the LOE and the transparent plate, and further providing a reflector, the partially reflective surface and the reflector being configured to reflect the image illumination introduced into the coupling input region into the propagation region to fully illuminate the propagation region with both the collimated image and a conjugate of the collimated image; An optical system, wherein the beam multiplication arrangement is configured to compensate for half-filling of the combined input area by the image projector.

14. 13. The optical system of claim 12, further comprising a coupling input arrangement associated with a coupling input region of the LOE and configured to couple the image illumination from the image projector into the LOE for propagation within the LOE by internal reflection.

15. The optical system of claim 12 , wherein the coupling input arrangement comprises a wedge prism positioned between the image projector and the coupling input region of the LOE.

16. The optical system of claim 12 , wherein the coupling input arrangement comprises a beveled edge at one end of the LOE between the image projector and the coupling input area of ​​the LOE.

17. The optical system of claim 12, further comprising an additional beam multiplication arrangement configured to provide beam multiplication prior to propagation of the image illumination within the LOE by internal reflection at the main external surface.

Images