Light Guide Optical Assembly

Abstract

To provide an optical assembly for optical aperture expansion.SOLUTION: An optical assembly combines facet reflective technology with diffractive technology. At least two diffractive components having opposite optical power (matching) are used so that chromatic dispersion introduced by a first diffractive component will then be canceled by a second diffractive component. The two diffractive components are used in combination with a reflective optical component to achieve more efficient aperture expansion (for near-eye display), reducing distortions and noise, while also reducing design constraints on a system and individual components, as compared to conventional techniques. The assembly eliminates and / or reduces the need for polarization management while enabling a wider field of view. In addition, since distortion patterns of the two technologies do not correlate, nonuniformity can be reduced, as compared to conventional single technology implementations.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates generally to optical assemblies and, more particularly, to optical aperture enlargement. [Background technology]

[0002] Referring to Figure 7A, a rough schematic of conventional optical aperture expansion using diffractive components within a waveguide is shown. In the current illustration, the incident light (image) is perpendicular from off-page to on-page. A coupling-in element (1001) couples the incident light to a lateral expansion element (1002), which expands the light laterally (from left to right in the current illustration). The laterally expanded light then couples to a vertical expansion element (1003), which expands the light vertically (from top to bottom in the current illustration) and outcouples the light to the user (viewer's eye).

[0003] Conventional diffractive elements introduce chromatic dispersion, where light rays with different wavelengths are diffracted at different angles. A narrowband light source (such as a laser) can be used to reduce chromatic dispersion. A more practical solution is to design diffractive components to cancel each other's dispersion.

[0004] Referring to FIG. 7B, a diagram of the diffraction direction of light propagating in angular regions (angle intervals) is shown. The dashed and solid arrows indicate two different typical wavelengths. The starting angle in region (1005) represents the angle of the light ray when it hits the first diffractive element (internal coupling element (1001)) that couples into the light guide. Region (1007) represents the direction of the light ray after the internal coupling element (1001), region (1009) represents the direction of the light ray after the lateral magnification element (1002), and region (1005) further represents the angle of the light ray after coupling out of the light guide by the vertical magnification element (1003). The direction of the light ray entering the light guide is equal to the direction of the light ray coupled out of the light guide to minimize chromatic dispersion. When different wavelengths of light propagate into the light guide, they have different directions and have the same direction when they exit the light guide.

[0005] Basic Technology Figure 1 illustrates a conventional prior art folded optical structure, in which a substrate (2) is illuminated by a display source (4). The display is collimated by collimating optics (6) (e.g., a lens). Light from the display source (4) is coupled to the substrate (2) by a first reflective surface (8) so that the main light ray (11) is parallel to the substrate plane. A second reflective surface (12) couples the light from the substrate to the viewer's eye (14). Despite its compactness, this structure suffers from significant drawbacks. In particular, only a very limited FOV can be achieved.

[0006] Referring now to FIG. 2, a side view of a typical light directing optical element (LOE) is shown. To alleviate the above limitations, an array of selectively reflective surfaces can be used and fabricated within the light directing optical element (LOE). A first reflective surface (16) is illuminated by a collimated viewing light beam (18) emanating from a light source (not shown) positioned behind the device. For simplicity of illustration, only one light beam, the incident light beam (38) (also referred to as the "beam" or "incident ray"), is generally depicted. Other rays of incident light, such as beams (18A) and (18B), may also be used to designate the edges of the entrance pupil, such as the left and right edges of the entrance pupil. Note that, generally, whenever an image is represented herein by a light beam, the light beam is a sample beam of the image, which is typically formed by multiple beams at slightly different angles, each corresponding to a point or pixel of the image. Unless specifically referred to as the tip of the image, the illustrated beam is typically the centroid of the image.

[0007] The reflective surface (16) reflects incident light from a light source, which is captured within the light guide (20) by total internal reflection. The light guide (20) is also referred to as a "waveguide," "planar substrate," and "optically transmitting substrate." The light guide (20) includes at least two parallel (major) surfaces, shown in the drawings as the rear (major) surface (26) and the front (major) surface (26A). Note that the designations "front" and "back" relative to the major surfaces (26) and (26A) are for convenience of reference, as the light guide (20) is typically symmetrical (thus, references to the major surfaces (26) and (26A) can be interchanged with the same result). The light guide (20) is referred to in the context of this specification as a one-dimensional (1D) waveguide, guiding an injected image in only one dimension between a pair of parallel surfaces (in this case, the major surfaces (26) and (26A)).

[0008] An incident light ray (38) enters the substrate at the substrate's proximal end (right side of the figure). The light propagates through the light guide and one or more facets, usually at least several facets, and typically several facets, toward the light guide's distal end (left side of the figure). The light propagates through the light guide in both the original propagation direction (28) and an alternate propagation direction (30).

[0009] After several reflections from the surface of the substrate 20, the trapped waves reach an array of selectively reflective surfaces 22, which couple the light from the substrate to the viewer's eyes 24. In an alternative configuration, the selectively reflective surfaces 22 enter the substrate immediately after the light ray 18, without first reflecting off the surface of the substrate 20.

[0010] Internal partially reflective surfaces, such as selectively reflective surface 22, are generally referred to as "facets" in the context of this specification. At the limit, a facet can be fully reflective (100% reflectivity or a mirror, e.g., the last facet at the distal end of a substrate) or minimally reflective. For enhanced reality applications, the facet is partially reflective, allowing light from the real world to enter through the top surface 26A, traverse the substrate containing the facet, and exit the substrate through the bottom surface 26A to the viewer's eye 24. For virtual reality applications, the facet may have an alternative reflectivity, such as a first internally coupled mirror with 100% reflectivity, since image light from the real world does not need to traverse this mirror. Internal partially reflective surfaces 22 generally traverse the light guide 20 at least partially at an oblique angle (i.e., neither parallel nor perpendicular) to the direction of elongation of the light guide 20.

[0011] References to reflectivity generally refer to nominal reflectivity. Nominal reflectivity is the total reflection required at a particular location in the substrate. For example, if a facet's reflectivity is referred to as 50%, this generally refers to 50% of the nominal reflectivity. If the nominal reflectivity is 10%, then 50% reflectivity would result in a facet reflectivity of 5%. Those skilled in the art will understand the use of percentage reflectivity from the context of use. Partial reflection can be achieved by a variety of techniques, including, but not limited to, transmitting a percentage of light or using polarization.

[0012] Figures 3A and 3B illustrate the desired reflectivity behavior of a selectively reflective surface. In Figure 3A, light ray 32 is partially reflected from facet 34 and coupled out of substrate 20 (38B). In Figure 3B, light ray 36 is transmitted through facet 34 without significant reflection.

[0013] Figure 4A is a detailed cross-sectional view of an array of selectively reflective surfaces that couples light into a substrate and then into the viewer's eye. As shown, a light ray (38) from a light source (4) strikes a first partially reflective surface. A portion of the light ray (41) continues its original direction and is coupled out of the substrate. Another portion of the light ray (42) is coupled into the substrate by total internal reflection. The trapped light ray is gradually coupled out of the substrate by two other partially reflective surfaces (22) at point (44). The coating properties of the first reflective surface (16) do not necessarily have to be similar to those of the other reflective surfaces (22) and (46). This coating can be metallic, dichroic, or a hybrid metallic-dichroic, more simply a beamsplitter. Similarly, for non-see-through systems, the final reflective surface (46) can be a simple mirror.

[0014] Figure 4B shows a detailed cross-section of a device including an array of reflective surfaces, with the last reflective surface (46) being a fully reflective mirror. The leftmost portion of the last reflective surface (46) cannot be optically active in this case, and cannot couple the marginal rays (48) out of the substrate. Thus, the output aperture of the device is slightly smaller. However, the optical efficiency can be much higher, and the manufacturing process for the LOE can be much simpler.

[0015] It is important to note that, unlike the structure shown in FIG. 2, there are constraints on the orientation of reflective surfaces 16 and 22. In the previous structure, all light is coupled into the substrate by reflective surface 16. Therefore, surface 16 does not need to be parallel to surface 22. Furthermore, the reflective surface may be oriented so that light is coupled out of the substrate in a direction opposite to the direction of the input wave. For the structure illustrated in FIG. 4A, however, a portion of the input light is not reflected by surface 16 but continues in the original direction of input light 38 and is immediately coupled out of the substrate as output light 41. Therefore, not only must all reflective surfaces 22 be parallel to each other, but surfaces 16 must be parallel to surfaces 22 as well, to ensure that all light rays originating from the same plane wave have the same output direction.

[0016] Referring again to Figure 4A, a system is shown with two reflective surfaces for coupling light out of the substrate; however, any number of reflective surfaces can be used depending on the required output aperture of the optical system and the thickness of the substrate. Of course, only one outcoupling surface may be required; in that case, the output aperture is effectively twice the size of the input aperture of the system. The only reflective surfaces required in the final configuration are a simple beamsplitter and mirror.

[0017] In the device described in this figure, light from the display source is coupled into the substrate at the edge of the substrate, however, in some systems it is preferable to have a symmetrical system, i.e. the input light should be coupled into the substrate at the center of the substrate.

[0018] FIG. 4C is a diagram illustrating a detailed cross-section of a one-dimensional (1D) light guide for lateral pupil dilation with a symmetrical structure. This figure illustrates how two identical substrates can be combined to create a symmetrical light module. As can be seen, a portion of the light from the display source (4) exits the substrate directly through the partially reflective surfaces. Another portion of the light is coupled into the right side (20R) and left side (20L) of the substrate by partially reflective surfaces (16R) and (16L), respectively. The captured light is then gradually outcoupled by reflective surfaces (22R) and (22L), respectively. Obviously, the output aperture is three times the size of the input aperture of the system, the same magnification as described in FIG. 5B. However, unlike the previous system, this system is symmetric about the interface (29) of the right and left substrates.

[0019] Referring now to Figures 5A and 5B, exemplary implementations of Figures 4B and 4C are shown on top of the light guide. The configurations of Figures 4B and 4C are horizontally expanded versions of the incident image. The apparatus of Figure 4B can be used to implement the first LOE (20a) of Figure 5A, the apparatus of Figure 4C can be used to implement the first LOE (20a') of Figure 5B, and the apparatus of Figure 2 can be used to implement the second LOE (20b).

[0020] FIG. 5A illustrates an alternative method for expanding a beam along two axes using a dual LOE configuration. An input wave (90) is coupled by a first reflective surface (16a) into a first LOE (20a), which has an asymmetric structure similar to that illustrated in FIG. 4B, and then propagates along the η axis. A partially reflective surface (22a) couples the light out of the first LOE (20a), where it is then coupled into a second, asymmetric LOE (20b) by a reflective surface (16b). The light then propagates along the ξ axis and is then outcoupled by a selectively reflective surface (22b). As shown, the original beam (90) is expanded along both axes, where the overall expansion is determined by the ratio between the lateral dimensions of elements (16a) and (22b). The configuration given in FIG. 5A is merely one example of a dual LOE setup. Other configurations are also possible in which two or more LOEs are combined together to form a complex optical system.

[0021] Referring now to FIG. 5B, a diagram illustrating another method for expanding a beam along two axes using a dual LOE configuration is shown. Typically, the area where light is coupled by surface 16b to second LOE 20b cannot be transparent to external light and is not part of the see-through area. Therefore, first LOE 20a does not need to be transparent. As a result, even for see-through systems, it is usually possible to design first LOE 20a to have a symmetrical structure, as can be seen in this diagram. Second LOE 20b has an asymmetrical structure that allows the user to see outside. In this configuration, a portion of the input beam (90) continues along its original direction (92) to the inter-coupling mirror (16b) of the second LOE (20b), while another portion (94) is coupled by reflective surface (16a) to the first LOE (20a'), propagating along the η-axis, and then coupled by selective reflective surface (22a) to the second LOE (20b). Both portions are then coupled by reflective surface (16b) to the second asymmetric LOE (20b), propagating along the ξ-axis, and then coupled by selective reflective surface (22b).

[0022] FIG. 6 illustrates an example of LOEs 20a / 20a' and 20b embedded in a standard eyeglass frame 107. The display source 4, folding optics, and collimating optics 6 are assembled within the arm portion 112 of the eyeglass frame, directly beside the LOEs 20a / 20a', located at the edge of the second LOE 20b. If the display source is an electronic device, such as a small CRT, LCD, or OLED, the drive electronics 114 for the display source may be assembled within the rear portion of the arm 112. A power and data interface 116 can be connected to the arm 112 by leads 118 or other communication means, including wireless or optical transmission. Alternatively, a battery and miniature data link electronics may be integrated into the eyeglass frame. This diagram is an example, and other possible head-mounted display configurations can be constructed, including assemblies in which the display source is mounted parallel to the LOE plane or above the LOE.

[0023] Additional details of this underlying technology can be found in U.S. Pat. No. 7,643,214 and PCT / IL2018 / 050025, which has not been published and does not constitute prior art to the present invention. Summary of the Invention

[0024] According to the teachings of this embodiment, an apparatus for optical aperture expansion is provided, the apparatus including at least one light guide; a set of three optical components associated with the at least one light guide, the set of three optical components including a pair of first and second coincident diffractive optical components; and a reflective optical component including an array of multiple partially reflective, mutually parallel surfaces; and cooperating optical components for expanding in-coupled light into out-coupled light, wherein the in-coupled light is coupled into the at least one light guide, and the expansion is two-dimensional.

[0025] In an optional embodiment, a first optical component of the set is configured to direct the intercoupled light in a first direction of magnification within a first light guide, thereby generating a first expanded light; and a second optical component of the set is configured to couple the first expanded light into a second light guide in a second direction of magnification, thereby generating a second expanded light; and a third optical component of the set configured to outcouple the second expanded light as outcoupled light in a third direction; where the first, second, and third directions are not parallel to one another.

[0026] Another optional embodiment further includes a non-diffractive optical element configured to direct light into at least one light guide as in-coupled light; wherein the at least one light guide is a single light guide including: a first diffractive optical element configured to direct the in-coupled light in a first direction of magnification within the single light guide, thereby generating a first expanded light; a second diffractive optical element configured to magnify the first expanded light in the single light guide in a second direction of magnification, thereby generating a second expanded light; and a reflective optical element configured to out-couple the second expanded light in a third direction as out-coupled light; wherein the first, second, and third directions are not parallel to one another.

[0027] Another optional embodiment further includes a pair of third and fourth matching diffractive optics; and a pair of fifth and sixth matching diffractive optics.

[0028] In another optional embodiment, each of the optical components of the matched pair has a diffraction interval that is different from the other optical components of the matched pair, such that each optical component of the matched pair refracts different wavelengths through similar angles from the other optical components of the matched pair.

[0029] In another optional embodiment, the wavelengths are red, green, and blue light.

[0030] In another optional embodiment, a first light guide of the at least one light guide includes a pair of first and second matching diffractive optical elements; a second light guide of the at least one light guide includes a pair of third and fourth matching diffractive optical elements; and a third light guide of the at least one light guide includes a pair of fifth and sixth matching diffractive optical elements.

[0031] In another optional embodiment, the reflective optical element is configured to magnify the in-coupled light in a first direction of magnification within the first light guide, thereby generating a first expanded light; the first, third, and fourth diffractive optical elements are configured to magnify respective wavelengths of the first expanded light in the respective first, second, and third light guides in a second direction of magnification, thereby generating respective second expanded lights; and the second, fourth, and sixth diffractive optical elements are configured to out-couple the respective second expanded lights in a third direction as out-coupled lights; wherein the first, second, and third directions are not parallel to one another. [Brief explanation of the drawings]

[0032] The present embodiments are herein described, by way of example only, with reference to the accompanying drawings. [Figure 1] 1 is a side view of a prior art foldable optical device. [Figure 2] 1 is a side view of a typical light guide optical element. [Figure 3] A and B illustrate the desired reflectance and transmittance characteristics of the selectively reflecting surface for two ranges of angles of incidence. [Figure 4] A is a diagram illustrating a typical configuration of a light guide optical element; B is a diagram illustrating another configuration of a light guide optical element; and C is a diagram illustrating a detailed cross-sectional view of a lateral pupil-dilation one-dimensional light guide having a symmetrical structure. [Figure 5]FIG. 1A is a diagram illustrating a method for expanding a beam of light along two axes utilizing a dual LOE configuration; FIG. 1B is a diagram illustrating another method for expanding a beam of light along two axes utilizing a dual LOE configuration. [Figure 6] An example of an LOE embedded in a standard eyeglass frame is shown. [Figure 7] 7A is a rough schematic diagram of conventional optical aperture expansion using a diffractive component in a waveguide, and FIG. 7B is a diagram of the diffraction direction of light propagating in the angular domain of FIG. 7A. [Figure 8] 8A and 8B are rough schematic side and front views, respectively, of an exemplary embodiment of diffraction-reflection-diffraction; C is a rough schematic of an exemplary embodiment of reflection-diffraction; and D is a diagram of the diffraction direction of light propagating in the angular domain of FIG. 8A and FIG. 8B. [Figure 9] 9A and 9B are side and front views, respectively, of a rough schematic diagram of an exemplary embodiment of diffraction-diffraction-reflection, and FIG. 9C is a diagram of the diffraction direction of light propagating in the angular domain of FIG. 9A and FIG. 9B. [Figure 10] 1A and 1B are rough schematic side and front views, respectively, of an exemplary embodiment of a diffraction-reflection device. [Figure 11] 1A and 1B are rough schematic side and front views, respectively, of an exemplary embodiment of diffraction-diffraction-reflection, and FIG. 1C is a rough schematic front view of an exemplary embodiment of overlapping diffraction-reflection-diffraction. [Figure 12] A and B are side and front views, respectively, of a rough schematic of an exemplary embodiment of diffraction-reflection, and C is a front view of a rough schematic of an exemplary embodiment of diffraction-diffraction-reflection. [Figure 13] 1A and 1B are rough schematic side and front views, respectively, of an exemplary embodiment of a diffraction-diffraction-reflection system with separate diffraction lateral expanders. [Figure 14]A and B are side and front views, respectively, of a rough schematic of an exemplary embodiment of diffraction-reflection, and C is a front view of a rough schematic of an exemplary embodiment of diffraction-diffraction-reflection. [Figure 15] 15A, B, and C are side, front, and plan views, respectively, of a rough schematic of a typical reflection-diffraction-diffraction embodiment, and FIG. 15D is a diagram of the diffraction direction of light propagating in the angular domain of FIG. 15A, FIG. 15B, and FIG. 15C.

[0033] Abbreviations and Definitions For ease of reference, this section contains a concise list of abbreviations, acronyms, and short definitions used in this specification. This section should not be considered limiting of the invention. More complete descriptions can be found below and in applicable standards. 1D - one dimension 2D - two dimensions CRT - cathode ray tube EMB - Eye Motion Box FOV - field of view HMD - Head Mounted Display HUD - Heads Up Display LCD - Liquid Crystal Display LOE - Light Guide Optical Element OLED - Organic Light Emitting Diode Array OPL - Optical path length SLM - Spatial Light Modulator TIR - total internal reflection DETAILED DESCRIPTION OF THE INVENTION

[0034] Detailed Description - Figure 8A to Figure 15D The principles and operation of the device described in this embodiment may be better understood with reference to the drawings and accompanying description. The present invention is an optical assembly for optical aperture expansion. The device combines diffractive technology (diffractive component) and faceted reflection technology (reflective component). An innovative embodiment using a diffractive component uses at least two components with opposing optical powers (matching), so that wavelength dispersion introduced by the first diffractive component is subsequently canceled by the second diffractive component. Two diffractive components are used in combination with reflective optics (for near-eye displays), thereby achieving more effective aperture expansion and reducing distortion and noise, while also reducing design constraints on the system and individual components compared to conventional technologies.

[0035] Currently, conventional optical aperture expansion uses a single technique for both expansion (lateral and vertical). Current advances in the field are to optimize and improve any one of these techniques. The two main techniques used are: 1) Reflection by angled coated facets (e.g., U.S. Patent No. 7,457,040 to Lumus, Ltd.). This reflection technique has a broad spectrum and can therefore project the entire visible spectrum from a single light guide. Although the facets typically both partially reflect and transmit the propagating light, for simplicity herein, this technique will be generally referred to as being implemented by "reflective optics." This reflection is typically polarization dependent. 2) Diffraction patterns on the light guide surface. As known in the art, a diffraction grating (pattern) reflects or transmits propagating light rays depending on the structure of the diffraction grating. For brevity herein, this technique will be generally referred to as being implemented by "diffractive optics." This diffractive technique is both spectrally and angularly limited. However, this technique has low polarization dependency.

[0036] By using an arrangement of reflective and diffractive components in various quantities and orders (alternating and vice versa), the need for polarization management is eliminated and / or reduced while allowing for a wider field of view. Additionally, the distortion patterns of the two techniques are uncorrelated, allowing for reduced non-uniformity in embodiments compared to conventional single-technique implementations.

[0037] Generally, an apparatus for optical aperture expansion includes at least one light guide and a set of three optical components associated with the at least one light guide. The set of three optical components includes a pair of matching diffractive optical components and a reflective optical component. The reflective optical component includes an array of multiple, at least partially reflective, parallel surfaces. The optical components are configured to cooperate to achieve two-dimensional expansion of outcoupled light. In other words, the components cooperate to expand incoupled light into outcoupled light. Incoupled light is light that is coupled into at least one light guide, and the expansion is two-dimensional.

[0038] In the context of this description, the term "matched" with respect to diffractive optical components generally refers to the grating and / or spacing of the grating elements being substantially exactly equal, so that the optical power of the diffractive components is equal and usually reciprocal. Although the overall physical dimensions of the components may differ, similar gratings result in matching optical power of the components.

[0039] In the context of this description, the term "component" is used for optical elements, particularly reflective and diffractive optical elements. Design and production techniques for reflective components and optical elements are known in the art. Based on this description, components can be implemented as needed in a variety of shapes and sizes of reflective and diffractive optical elements, and various operating parameters include wavelength, power, and angle.

[0040] Diffractive optics, also referred to in the context of this description as "diffraction gratings" and "diffraction patterns," may be embedded in a light guide or configured or attached to a surface of the light guide. For example, diffractive optics may be implemented as diffraction gratings or holographic elements. Diffractive components are available from companies such as Horiba Scientific (Kyoto, Japan), and reflective components are available from Lumus (Ness Ziona, Israel), such as the OE50.

[0041] Referring now to Figures 8A and 8B, a rough schematic diagram of a typical diffraction-reflection-diffraction embodiment is shown in side and front views, respectively. A combination of different optical components magnifies light along different axes. Optical light guide 10 is a two-dimensional (2D) light guide with an elongation direction arbitrarily illustrated herein as corresponding to the "X-axis." Light guide 10 is referred to as a 2D waveguide, meaning that light guide 10 guides the injected image in two dimensions by reflection between two sets of parallel surfaces, as indicated in Figure 8A by the four arrows inside light guide 10. An array of multiple internal partially reflective surfaces 40 at least partially traverses light guide 10 at an oblique angle (i.e., neither parallel nor perpendicular) to the elongation direction.

[0042] Incident light (38) is coupled into the light guide (10) by the diffractive component (5). The in-coupled light enters the light guide (10), which acts as a first lateral light guide expander in a first direction. From the light guide (10), expanded light (38C) is coupled into the light guide (2000). The optical light guide (2000) guides light primarily along the "Y-axis." The expanded light (38C) continues to reflect within the light guide (2000), expanding in a second expansion direction (Y-axis), as indicated by the arrow in the side view of FIG. 8A. The light in the light guide (2000) is referred to in this context as the second expanded light (38D). When the second expanded light (38D) encounters the diffraction pattern (25), it is out-coupled (38B) from the light guide (2000) to the observer (47). A feature of this embodiment is that the diffractive components are not parallel to each other.

[0043] Typically, a set of three optical components includes a first optical component (diffractive component (5)) configured to direct in-coupled light (38) in a first expansion direction (X-axis) within a first light guide (light guide (10)), thereby generating a first expanded light (38C). A second optical component (array of partially reflective surfaces (40)) of the set is configured to couple the first expanded light (38C) in a second expansion direction (Y-axis) into a second light guide (2000), thereby generating a second expanded light (38D). A third optical component (diffractive component (25)) of the set is configured to out-couple the second expanded light (38D) in a third direction as out-coupled light (38B).

[0044] In the context of this description, the term "direction" generally refers to the average direction of propagation within the light guide, typically along the optical axis (usually the length) of the light guide. In other words, the course or normal path that light captured in the light guide slab by total internal reflection (TIR) ​​takes along the light guide slab, i.e., the course of expansion in the plane of the light guide slab (the in-plane component of the light ray propagating in the substrate of the light guide).

[0045] The first, second, and third directions are not parallel to each other.

[0046] Referring now to FIG. 8D, a diagram of the diffraction direction of light propagating in the angular regions (angle intervals) of FIGS. 8A and 8B is shown. The dotted and solid lines indicate two different exemplary wavelengths. Direction region 1005 is the angle of incidence as described with respect to FIG. 7B. Region 1007 represents the direction of the light ray (or simply "ray") after lateral expansion and reflection by the array of partially reflective surfaces 40. The partially reflective surfaces 40 redirect the light ray to region 1011. However, this reflection from region 1007 to region 1011 does not introduce additional dispersion and simply mirrors the direction of propagation around a mirror direction (shown as dashed line 1008). The mirror direction 1008 is determined by the tilt of the partially reflective surfaces 40. The final diffractive element 25 diffracts the light ray into region 1013. Once the light rays are diffracted into the diffractive component (5) in a compensatory manner, the output direction (1013) is not dispersed, but need not overlap (1005). In this embodiment, dispersion is eliminated, but the output angle of the outcoupled light (38B) does not have to match the input angle of the incoupled light (38).

[0047] Referring now to Figure 8C, a rough schematic diagram of an exemplary reflective-diffractive embodiment is shown. This diagram is similar to Figures 8A and 8B, except that incident light (38) is coupled into light guide (10) by tilted prism (7) (instead of diffractive component (5)). Because this embodiment contains only one diffractive element (diffractive element (25)), chromatic dispersion is significant compared to the embodiment of Figures 8A and 8B, which contains two coincident diffractive elements ((5) and (25)). Chromatic dispersion (aberration) can be reduced by using a narrowband light source.

[0048] 9A and 9B, side and front views, respectively, of a roughly schematic diagram of an exemplary embodiment of a diffraction-diffraction-reflection system are shown. The light guide (2010) is a 2D light guide. In this embodiment, the first optical component of the set is implemented by a diffractive component (5A) configured to direct the inter-coupled light (38) within the light guide (2010) in a first expansion direction (X-axis), thereby generating a first expanded light (38C). The second optical component of the set is implemented by a diffractive component (370) configured to couple the first expanded light (38C) into the light guide (20) in a second expansion direction (Y-axis), thereby generating a second expanded light (38D). The third optical component of the set is implemented by an array of partially reflective surfaces (facets) (45) at least partially traversing the light guide (20), preferably at an oblique angle to the plane of the light guide (20), configured to outcouple the second expanded light (38D) in a third direction as outcoupled light (38B).

[0049] Referring now to Figure 9C, a diagram of the diffraction direction of light propagating in the angular domain (angle interval) of Figures 9A and 9B is shown. The angle vectors are also shown, with (1005) being the incoming direction and (1007) being the direction after the first element (5A). The diffractive element (370) has a corresponding optical power, so light is coupled from the light guide (2010) into the light guide (20) with the same direction but no chromatic dispersion (overlap (1005)). The facet (45) reflects the light without dispersion into the preferred direction (1013) without chromatic dispersion. Some chromatic dispersion may be introduced by the reflective component, and the remaining diffraction can compensate for this.

[0050] Referring now to Figures 10A and 10B, a rough schematic diagram of a typical diffraction-reflection embodiment is shown in side and front views, respectively. The light guide (2011) is a 2D light guide. Lateral magnification is achieved by a diffractive component, while vertical magnification is achieved by reflective facets. The method of coupling into the light guide (2011) is not shown. Light propagates within the light guide (2011), encounters a diffractive surface (component) (35), and is diffracted toward the light guide (20). The diffractive component (35) can be on any surface of the light guide (2011) (shown at the top, in this illustration). As the light propagates within the light guide (20), it is outcoupled (38B) toward the eye (47) by a facet (45). This configuration does not require polarization management between the light guide (2011) and the light guide (20). The injected polarization of the light can be oriented to match the required facet (45).

[0051] Referring now to Figures 11A and 11B, a rough schematic diagram of a side view and a front view, respectively, of an exemplary embodiment of a diffraction-diffraction-reflection system is shown. A non-diffractive optical element (501) is configured to direct light into a light guide (2002) as an intercoupled beam, shown as beam (38). In this embodiment, a single light guide (2002) is used, and two diffractive components are implemented as part of the light guide (2002). A first diffractive optical element (502) is configured to direct the intercoupled beam (38) in a first magnification direction (X-axis) within the single light guide (2002), thereby generating a first magnified beam (38C). A second diffractive optical element (50) is configured to magnify the first magnified beam (38C) in the single light guide (2002) in a second magnification direction (Y-axis), thereby generating a second magnified beam (38D). The reflective optic (array of facets 45) is configured to outcouple the second expanded light 38D in a third direction as outcoupled light 38B. As in the previous embodiment, the first, second, and third directions are not parallel to one another.

[0052] A feature of this embodiment is the use of a single, one-dimensional light guide. Coupling to the light guide is via a non-diffractive component (501), and the light is diverted by a strong diffractive pattern (502). The light propagates from left to right along the diffractive component (50), guided in one dimension and therefore expanding in another. When the light encounters the diffractive pattern (50), it is also diverted downward. While propagating downward, the light is reflected by the reflective facet (45) (shown in side view in Figure 11A) toward the observer (47). This configuration involves a single light guide and does not require polarization management (the polarization of the light injected into the light guide can be appropriate for the reflective facet (45)). The combination of the diffractive pattern (502) and the diffractive pattern (50) results in no chromatic dispersion.

[0053] Referring now to FIG. 11C, a rough schematic diagram of a front view of an exemplary embodiment of overlapping diffraction-reflection-diffraction is shown. Using different techniques, diffractive and reflective elements can be positioned on top of each other on the same light guide. In this illustration, a diffraction grating component (1110) expands the in-coupled light (38) in a first direction to create a first expanded light (38C). The lateral aperture expansion is achieved by overlapping the oblique facets (1114) that laterally couple the light from the front and back, expanding the light in a second direction (38D) without introducing chromatic aberration. A diffraction pattern (1112) is used to couple light out of the waveguide.

[0054] Referring now to Figures 12A and 12B, rough schematic diagrams of side and front views, respectively, of an exemplary embodiment of a diffraction-reflection system are shown. Lateral expansion is based on a one-dimensional light guide (2012) (see, for example, U.S. Patent No. 7,643,214 to Lumus Ltd.). In Figure 12B, coupling into the light guide (2012) is achieved by highly reflective (i.e., partially reflective and reflecting most of the energy) internal facets (65), which reflect most of the coupled-in light (38) to the left and right sides of the light guide (2012), while a portion of the coupled-in light (38) passes through the internal facets (65) into the light guide (20). As this embodiment includes only one diffractive element, chromatic dispersion becomes significant compared to the embodiment of Figure 12C below. Chromatic dispersion (aberration) can be reduced by using a narrowband light source.

[0055] 12C, a rough schematic diagram of a front view of an exemplary diffraction-diffraction-reflection embodiment is shown. In this embodiment, coupling into the light guide (2013) is achieved by a highly efficient diffractive component (66), which reflects most of the in-coupled light (38) to the left and right sides of the light guide (2013), while a portion of the in-coupled light (38) passes through the diffractive component (66) into the light guide (20).

[0056] Similar to the illustration in FIG. 9B, the first expanded light (38C) is diffracted by diffractive component (67) in FIG. 12B and by diffractive component (68) in FIG. 12C to produce a second expanded light (38D) in the light guide (20).

[0057] As can be seen from the exemplary embodiments, the diffractive component can generally be placed on any side of the light guide, and as in the previous embodiment, no further management is required for the device by injection of the appropriate polarization.

[0058] Different wavelengths of light are refracted by diffraction patterns in different directions. This phenomenon can be used, for example, by near-eye displays by implementing a separate light guide for each wavelength. An exemplary embodiment is three light guides, one for each wavelength corresponding to red (R), green (G), and blue (B) colored light. Separate diffractive side aperture expanders (one for each color) are combined into a single vertical reflective aperture expander.

[0059] Referring now to Figures 13A and 13B, a rough schematic diagram of an exemplary embodiment of a diffraction-diffraction-reflection system with individual diffractive lateral expanders is shown, showing side and front views, respectively. This embodiment is based on the embodiment described above with reference to Figures 9A and 9B. The light guide (2010) in Figure 9B is replaced with a set of light guides (103), (102), and (101). Each set of light guides has a first diffractive component ((133R), (133G), and (133B), respectively) configured for a specific wavelength in this example, red, green, and blue. Each set of light guides has a second diffractive component ((134R), (134G), and (134B), respectively) that matches the first diffractive component. The inter-coupled light (38) is injected through the first diffractive component. Each of these first diffractive components is wavelength specific, diffracting a particular associated wavelength of light and passing other wavelengths of light. The specific diffraction of wavelengths into each light guide can be improved by adding a set of dichroic reflectors (133R1, 133G1, and 133B1, respectively) after each first diffractive component (133R), (133G), and (133B). The dichroic reflectors can be based on coated reflectors or diffractive reflectors, so that different wavelengths are coupled into different respective light guides (103), (102), and (101). The wavelengths of light diffracted by the first diffractive components (133R), (133G), (133B) expand and propagate laterally in the respective light guides (103), (102), and (101) as respective first expanded rays (38CR), (38CG), (38CB). Each light guide (103), (102), (101) has a respective second diffractive component (134R), (134G), (134B) that diffracts the respective first expanded rays (38CR), (38CG), (38CB) towards the light guide (20).Because the second diffractive components (134G, 134B) are wavelength selective or have low diffraction efficiency for other wavelengths, light from the upper light guide passes through the lower light guide where distortion is least. In the light guide (20), an array of multiple partially reflective surfaces (45) reflects all wavelengths to the eye (47).

[0060] An alternative description of this embodiment is that the pair of first (133R) and second (134R) matching diffractive optical elements is augmented with 1) a pair of third (133G) and fourth (134G) matching diffractive optical elements, and 2) a pair of fifth (133B) and sixth (134B) matching diffractive optical elements. The diffraction interval of each matching pair of diffractive optical elements is different from the other matching pairs of diffractive optical elements. The diffraction intervals are such that each matching pair of diffractive optical elements refracts different wavelengths through similar angles from the other matching pairs of diffractive optical elements. The first light guide (103) includes a pair of first (133R) and second (134R) matching diffractive optical elements. The second light guide (103) includes a pair of fourth (133G) and fourth (134G) matching diffractive optical elements. The third light guide (103) includes a pair of fifth (133B) and sixth (134B) matching diffractive optics.

[0061] In this configuration, one light guide may be in front of the eye (47), and there is no ability to arbitrarily manage polarization between light guides (103), (102), (101), and (20). In this configuration, the light guides may be placed directly on top of each other (typically, an air gap is used between the light guides to maintain TIR).

[0062] Referring now to Figures 14A and 14B, there are shown rough schematic diagrams of a side view and a front view, respectively, of an exemplary embodiment of a diffraction-reflection system. This embodiment is similar to the operation described with respect to Figures 12A and 12B, except that light guide 2012 has been replaced / augmented (replaced with three light guides 160R, 160G, and 160B). In-coupling of light 38 into each light guide 160R, 160G, and 160B is via respective highly reflective internal facets / central splitting mirrors 165R, 165G, and 165B. The lateral (sideways) expansion is diffractive in each light guide (160R), (160G), (160B), and the first expanded light (38C) is then diffracted / diverted into the light guide (20) for outcoupling into the user's eye (47).

[0063] Referring now to Figure 14C, a rough schematic diagram of a front view of an exemplary diffraction-diffraction-reflection embodiment is shown. This embodiment is similar to the operation described with respect to Figure 12C, except that the diffractive component 66 is replaced / augmented by a set of diffractive components 133R, 133G, and 133B, and each first diffractive component 133R, 133G, and 133B at the center of each respective light guide 159R, 159G, and 159B is followed by a dichroic reflector (133R1, 133G1, and 133B1, respectively). The corresponding diffractive elements 134R, 134G, and 134B are replaced with multiple diffractive elements 134R1, 134R2, 134G1, 134G2, 134B1, and 134B2 on either side of the central diffractive components 133R, 133G, and 133B.

[0064] Referring now to Figures 15A, 15B and 15C, there are shown rough schematic side, front and top views, respectively, of an exemplary diffract-reflect-reflect embodiment. In this embodiment, the reflective aperture expander precedes the diffractive expander. Four light guides are used: a reflective component (201) and three diffractive components (205), (206), and (207). The reflective component (201) is a light guide that expands reflections laterally. This reflective light guide (201) can be a 1D light guide (similar to light guide (20) in FIG. 4A) or a 2D light guide (similar to light guide (10) in FIG. 8C). The light coupled into the reflective light guide (201) includes all wavelengths of the inter-coupled light (38); therefore, the reflective light guide (201) can include a reflector (such as the reflective surface (16) in FIG. 4A) or a prism (such as the tilted prism (7) in FIG. 8C).

[0065] Facet 203 (depicted in plan view in FIG. 15C) diverts guided light forward and from light guide 201 to light guides 205, 206, and 207. Each of light guides 205, 206, and 207 has a respective inter-coupling grating 209R, 209G, and 209B. These inter-coupling gratings 209R, 209G, and 209B have different periods for each light guide, and therefore different wavelengths will be coupled by each inter-coupling grating into their associated light guide.

[0066] Light propagates within light guides (205), (206), and (207) and is outcoupled (38B) towards the observer (47) by respective gratings (25R), (25G), and (25B) designed according to the wavelength within each light guide and matched to respective in-coupling gratings (209R), (209G), and (209B).

[0067] Generally, the reflective optics (facets (203)) are configured to expand the incoupled light (38) in a first direction of expansion within the first light guide (201), thereby generating a first expanded light (38C). The first diffractive optic (209R), third diffractive optic (209G), and fourth diffractive optic (209B) are configured to couple each wavelength of the first expanded light into the first light guide (205), second light guide (206), and third light guide (207), respectively. The second diffractive optic (25R), fourth diffractive optic (25G), and sixth diffractive optic (25B) are configured to expand and outcouple each light in a third direction as outcoupled light (38B).

[0068] Referring now to Figure 15D, there are shown the diffraction direction diagrams of Figures 15A, 15B, and 15C for light propagating within the angular field (angle interval). A front view of the angular direction of a single light guide shown in Figures 15A-15C is shown in Figure 15D. Light is coupled in direction (1005), and a reflecting mirror (203) redirects the light beam into direction (1007) without dispersing it. The intra-diffractive coupling component (one of (209R), (209G), or (209B)) redirects the light beam downwards with dispersion, while the diffractive component (one of (25R), (25G), or (25B)) has an opposing optical power, so the light is coupled into the overlapping direction (1007) without dispersion.

[0069] This configuration has strong anti-dispersion properties and therefore can use a small number of components to transmit one or more color channels (R, G, B) in a narrow field (angular spectrum). For example, the three light guides (205), (206) and (207) can be implemented as a single light guide, or a combination of two color channels can be implemented in a single light guide (such as the set {red and green, blue} or {red, green and blue}).

[0070] It should be noted that the above examples, symbols used, and exemplary calculations are intended to aid in the explanation of this embodiment, and that inadvertent typographical errors, mathematical errors, and / or the use of simplistic calculations do not detract from the utility and fundamental advantages of the present invention.

[0071] To the extent that the appended claims have been drafted without multiple dependencies, this has been done solely to accommodate formal requirements in jurisdictions that do not permit such multiple dependencies. Note that all combinations of features implied by making the claims multiple dependent are expressly contemplated and should be considered part of the invention.

[0072] It will be understood that the above description is intended to be given by way of example only, and that many other embodiments are possible within the scope of the invention as defined in the appended claims.

Claims

1. An optical system for redirecting light generated by a display module towards an observer's eye, the optical system comprising: a waveguide having a pair of parallel major surfaces; a non-diffractive input coupler configured to directly couple the light produced by the display module into the waveguide so as to propagate within the waveguide in an input direction by internal reflection at the major surface; a diffractive arrangement integrated with the waveguide, configured to diffract the light propagating in the waveguide in the input direction through a first diffractive section that redirects the light to propagate in the waveguide in a first direction non-parallel to the input direction by internal reflection at the major surface, and through a second diffractive section that progressively redirects the light in the waveguide to propagate in the waveguide in a second direction parallel to the input direction by internal reflection at the major surface while expanding the light in the first direction; an output coupler including a plurality of partially reflective surfaces angled obliquely relative to the major surfaces of the waveguide, the output coupler progressively coupling the light expanded in the first direction by the diffractive arrangement from the waveguide toward the eye of the observer while expanding the light in the second direction.

2. The optical system of claim 1 , wherein the diffractive arrangement includes a first diffractive optical element and a second diffractive optical element.

3. 3. The optical system of claim 2, wherein the first diffractive optical element is a diffractive element and the second diffractive optical element is configured to progressively diffract the light while expanding the light in the first direction.

4. 3. The optical system of claim 2, wherein the first diffractive optical element and the second diffractive optical element have matching optical powers such that a second one of the diffractive sections cancels chromatic dispersion introduced by a first one of the diffractive sections.

5. The optical system of claim 1 , wherein the diffractive arrangement is configured such that a second one of the diffractive sections cancels chromatic dispersion introduced by a first one of the diffractive sections.

6. The optical system of claim 1 , wherein the diffractive arrangement comprises at least one grating on a surface of the waveguide.

7. The optical system of claim 1 , wherein the diffractive arrangement comprises at least one diffraction grating embedded in the waveguide.

8. The optical system of claim 1 , wherein the diffractive arrangement comprises at least one holographic element.

Images