Dual projector system and image light guide

Abstract

An image light guide for conveying a virtual image comprising a first surface and an opposing second surface and a first incoupling diffractive optical element disposed along one of the first and second surfaces, the first incoupling diffractive optical element including a first set of diffractive features. A second incoupling diffractive optical element disposed along one of the first and second surfaces, the second incoupling diffractive optical element including a second set of diffractive features. The image light guide further comprises an outcoupling diffractive optical element disposed along at least one of the first and second surfaces, the outcoupling diffractive optical element including a plurality of zones each having a different set of diffractive features than adjacent zones, the plurality of zones including a first zone optimized to diffract incoupling light from both the first incoupling diffractive optical element and the second incoupling diffractive optical element.

Description

[Technical Field]

[0001] The present disclosure relates generally to electronic display devices, and more particularly to optical image light guide systems having diffractive optical elements operable to transmit image-bearing light to a viewer. [Background technology]

[0002] Head-mounted displays (HMDs) are being developed for a wide range of applications, including military, commercial, industrial, firefighting, and entertainment applications. In many of these applications, there is value in creating a virtual image that can be visually superimposed on a real-world image in the HMD user's field of view. Optical image light guides can deliver image-bearing light to the viewer in a small space to direct the virtual image toward the viewer's pupil and enable this superimposition function.

[0003] In general, HMD optics must meet several basic requirements for viewer acceptance, including pupil size and field of view (FOV). Pupil size requirements are based on physiological differences in the viewer's facial structure and gaze direction during viewing. A minimum entrance pupil diameter of approximately 10 mm has been found to be desirable for the typical viewer. A wide field of view is preferred for many tasks and operations. Additionally, the virtual image produced should have sufficient brightness for visibility and viewer comfort.

[0004] In addition to optical requirements, HMD designs must address practical factors such as an acceptable form factor, with expected shrinking size for comfort when worn, weight, cost, and ease of use. Thus, there is a need for an image light guide system that provides increased FOV and brightness while maintaining a small form factor. Summary of the Invention

[0005] It is an object of the present disclosure to advance the art of virtual image presentation using head-mounted devices. Advantageously, embodiments of the present disclosure provide an optical coupling solution that is compatible with the common form factor of eyeglasses.

[0006] These and other aspects, objects, features, and advantages of the present invention will be more clearly understood and appreciated from the following detailed description of embodiments and appended claims, and by reference to the accompanying drawings. In an exemplary embodiment, the present disclosure provides an image light guide for conveying a virtual image including a first surface and an opposing second surface, and a first incoupling diffractive optical element disposed along one of the first and second surfaces, the first incoupling diffractive optical element including a first set of diffractive features. A second incoupling diffractive optical element is disposed along one of the first and second surfaces, the second incoupling diffractive optical element including a second set of diffractive features. The image light guide further includes an outcoupling diffractive optical element disposed along at least one of the first and second surfaces, the outcoupling diffractive optical element including a plurality of zones each having a different set of diffractive features than adjacent zones, the plurality of zones including a first zone optimized to diffract incoupling light from both the first incoupling diffractive optical element and the second incoupling diffractive optical element.

[0007] In an exemplary embodiment, the outcoupling diffractive optical element includes a first zone, a second zone disposed outward from the first zone in a first direction, a third zone disposed outward from the second zone in the first direction, a fourth zone disposed outward from the first zone in a second direction, and a fifth zone disposed outward from the fourth zone in the second direction.

[0008] In an exemplary embodiment, the second and fourth zones are mirrored over the first zone, and the third and fifth zones are mirrored over the first zone.

[0009] In an exemplary embodiment, the second and fourth zones are linear and oriented at opposite angles relative to an imaginary axis that bisects the first zone.

[0010] In an exemplary embodiment, the first zone includes linear diffractive features arranged to bisect the first surface and oriented parallel to an imaginary axis that is parallel to the first surface, the imaginary axis extending between a first edge of the first surface adjacent the first incoupling diffractive optical element and the second incoupling diffractive optical element, and a second edge of the first surface adjacent the outcoupling diffractive optical element.

[0011] In an exemplary embodiment, the third zone includes linear diffractive features oriented at a first angle relative to the diffractive features of the first zone, and the fifth zone includes linear diffractive features oriented at a second angle relative to the diffractive features of the first zone, e.g., the second angle may be equal and opposite to the first angle.

[0012] In an exemplary embodiment, the second zone includes a first set of linear diffractive features parallel to the diffractive features of the first zone and a second set of linear diffractive features parallel to the diffractive features of the third zone.

[0013] In an exemplary embodiment, the fourth zone includes a first set of linear diffractive features parallel to the diffractive features of the first zone and a second set of linear diffractive features parallel to the diffractive features of the fifth zone.

[0014] In an exemplary embodiment, the second zone includes diffractive features having a first grating vector parallel to the grating vector of the first zone and a second grating vector parallel to the grating vector of the third zone, and the fourth zone includes diffractive features having a first grating vector parallel to the grating vector of the first zone and a second grating vector parallel to the grating vector of the fifth zone.

[0015] In an exemplary embodiment, the first zone, the second zone, the third zone, and the fourth zone of the outcoupling diffractive optical element form a first output region optimized to diffract the image-bearing light beam incoupled by the first incoupling diffractive optical element, and the first zone, the second zone, the fourth zone, and the fifth zone of the outcoupling diffractive optical element form a second output region optimized to diffract the image-bearing light beam incoupled by the second incoupling diffractive optical element.

[0016] In an exemplary embodiment, the present disclosure provides an image source for generating an angularly coded image-bearing light beam, the image source comprising: a light source system; a first beam splitter having two opposing output faces through which polarized portions of the light exit the polarizing beam splitter, the first beam splitter being operable to polarize light from the light source system into a first optical path and a second optical path; a second beam splitter positioned in the first optical path to receive light emitted from the first beam splitter; a third beam splitter positioned in the second optical path to receive light emitted from the first beam splitter; a first imaging engine positioned in the first optical path to receive light from the second beam splitter; and a second imaging engine positioned in the second optical path to receive light from the third beam splitter.

[0017] In an exemplary embodiment, the light source system includes a first wavelength source, a second wavelength source, and a third wavelength source, the first wavelength source, the second wavelength source, and the third wavelength source operable to emit light that is incident on the first beam splitter.

[0018] In an exemplary embodiment, the light source system further includes lenses positioned between each of the wavelength sources to collimate the light emitted thereby.

[0019] In an exemplary embodiment, the first beam splitter comprises a polarizing beam splitter operable to split unpolarized light from the light source system into linearly polarized light.

[0020] In an exemplary embodiment, the image source includes a first prism disposed in the first optical path and a second prism disposed in the second optical path, the first prism and the second prism operable to direct polarized light along the first optical path and the second optical path, respectively.

[0021] In an exemplary embodiment, the first imaging engine and the second imaging engine include liquid crystal on silicon (LCOS) panels, for example, the LCOS panels are front-emitting.

[0022] In an exemplary embodiment, the first imaging engine and the second imaging engine comprise digital light processing (DLP) projectors.

[0023] In an exemplary embodiment, a first wave plate is positioned to redirect the polarization of light emitted by the first imaging engine, and a second wave plate is positioned to redirect the polarization of light emitted by the second imaging engine.

[0024] The accompanying drawings are incorporated herein as part of this specification. The drawings described herein illustrate embodiments of the disclosed subject matter and illustrate selected principles and teachings of the present disclosure. However, the drawings do not illustrate every possible implementation of the disclosed subject matter and are not intended to limit the scope of the present disclosure in any way. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a top view of an image light guide with an exaggerated thickness to illustrate the propagation of light from an image source along the image light guide to an eyebox within which a virtual image can be displayed. [Figure 2] FIG. 2 is a perspective view of an image light guide that includes an incoupling diffractive optical element, which is a rotating diffractive optical element, and an outcoupling diffractive optical element for managing the propagation of an image-bearing light beam. [Figure 3A] FIG. 3A shows a side view of an image light guide according to an exemplary embodiment of the disclosed subject matter. [Figure 3B] FIG. 3B is a side view of an embodiment of an image light guide according to FIG. 3A. [Figure 4A] FIG. 4A is a top view of an embodiment of an image light guide according to FIG. 3A, with an exaggerated thickness. [Figure 4B] FIG. 4B is a top view of another embodiment of an image light guide according to FIG. 3A, with an exaggerated thickness. [Figure 4C] FIG. 4C is a top view of yet another embodiment of an image light guide according to FIG. 3A, having an exaggerated thickness. [Figure 5] FIG. 5 shows a side view of an image light guide including a waveguide stack, according to an exemplary embodiment of the disclosed subject matter. [Figure 6A] FIG. 6A shows a top perspective view of an image light guide with an image source according to an exemplary embodiment of the disclosed subject matter. [Figure 6B] FIG. 6B shows a schematic top perspective view of an image light guide with an image source, according to an exemplary embodiment of the disclosed subject matter. [Figure 7] FIG. 7 is a schematic top view of an image source system according to an exemplary embodiment of the disclosed subject matter. [Figure 8] FIG. 8 is a front view of the image source system according to FIG. DETAILED DESCRIPTION OF THE INVENTION

[0026] It should be understood that the present invention may assume various alternative orientations and step arrangements unless expressly specified to the contrary. It should also be understood that the specific assemblies and systems illustrated in the accompanying drawings and described in the following specification are merely exemplary embodiments of the inventive concepts defined herein. Accordingly, specific dimensions, orientations, or other physical characteristics relating to the disclosed embodiments are not to be considered limiting unless expressly stated otherwise. Also, although not applicable, like elements in the various embodiments described herein may be generally referred to within this section of the specification using like reference numerals.

[0027] Those skilled in the relevant art will recognize that the elements and techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In some instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects of the disclosure. Throughout this specification, references to "one embodiment," "an exemplary embodiment," or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the disclosure. Thus, appearances of the phrases "in one embodiment," "in an exemplary embodiment," or "in an embodiment" throughout this specification do not necessarily refer to the same embodiment. However, particular features, structures, or characteristics described may be combined in any suitable manner in one or more embodiments.

[0028] As used herein, terms such as "first," "second," etc. do not necessarily imply any order, sequence, or priority relationship, but are merely used to more clearly distinguish one element or set of elements from another, unless otherwise specified.

[0029] As used herein, the terms "viewer," "operator," "observer," "wearer," and "user" are considered equivalent and refer to a person or machine wearing a device having an imaging light guide and / or viewing an image using a device having an imaging light guide.

[0030] As used herein, the term "set" refers to a non-empty set, as the concept of a collection of elements or members of a set is commonly understood in elementary mathematics. As used herein, the term "subset," unless explicitly stated otherwise, is used to refer to a non-empty proper subset, i.e., a subset of a larger set that has one or more members. For a set S, a subset may include the complete set S. However, a "proper subset" of set S is strictly contained in set S and excludes at least one member of set S.

[0031] As used herein, the terms "coupled," "coupler," or "coupling" in the optical context refer to a connection in which light travels from one optical medium or device to another.

[0032] As used herein, the terms "wavelength band" and "wavelength range" are equivalent and have the standard meaning used by those skilled in the art of color imaging, and refer to a continuous range of light wavelengths used to represent a multicolor image.

[0033] As used herein, the term "beam expansion" is intended to mean the duplication of a beam through multiple encounters with optical elements to provide an exit pupil expansion in one or more directions. Similarly, as used herein, "expanding" a beam or a portion of a beam is intended to mean the duplication of the beam through multiple encounters with optical elements to provide an exit pupil expansion in one or more directions.

[0034] Optical systems such as HMDs can generate virtual images. Unlike methods for forming real images, virtual images are not formed on a display surface. That is, when a display surface is positioned at the perceived location of the virtual image, no image is formed on the surface. Virtual images have many advantages unique to augmented reality displays. For example, the apparent size of the virtual image is not limited by the size or location of the display surface. Furthermore, the source object of the virtual image can be small; for example, a magnifying glass provides a virtual image of the object. Compared to systems that project real images, a more realistic viewing experience can be provided by forming a virtual image that appears to be at a certain distance. Providing a virtual image also eliminates the need to correct for screen artifacts, which may be required when projecting a real image.

[0035] FIG. 1 is a schematic diagram showing a simplified cross-sectional view of one conventional configuration of an image light guide system 10. The image light guide system 10 includes a planar image light guide 12, an incoupling diffractive optical element IDO, and an outcoupling diffractive optical element ODO. The image light guide 12 includes a transparent substrate S, which may be made of optical glass or plastic, having plane-parallel front and back surfaces 14 and 16. In this example, the incoupling diffractive optical element IDO is shown as a transmission grating disposed on, within, or otherwise engaged with the front surface 14 of the image light guide 12. However, the incoupling diffractive optical element IDO may alternatively be a reflection grating or other type of diffractive optical element (such as a volume hologram or other holographic diffractive element) that diffracts an incident image-bearing light beam WI into the image light guide 12. The incoupling diffractive optical element IDO is located on or within the front surface 14 or back surface 16 of the image light guide 12, or otherwise engages with the front surface 14 or back surface 16, and may be a combination of transmissive or reflective, depending on the direction from which the image-bearing light beam WI approaches the image light guide 12.

[0036] When used as part of a near-eye or head-mounted display system, the incoupling diffractive optical element IDO of conventional image light guide system 10 couples an image-bearing light beam WI from an image source 18 of a real, virtual, or hybrid image into the substrate S of the image light guide 12. Any real image or image dimension formed by the image source 18 is first converted into an array of overlapping, angle-related, collimated beams that encode different locations within the virtual image for presentation to the incoupling diffractive optical element IDO. Typically, the light rays in each bundle forming one of the angle-related beams extend parallel, but the angle-related beams are relatively oblique to one another through an angle that may be defined by two angular dimensions corresponding to the linear dimensions of the image.

[0037] When the angle-related beams engage the incoupling diffractive optical element IDO, at least a portion of the image-bearing light beam WI is diffracted (typically by a first diffraction order) and thereby redirected by the incoupling diffractive optical element IDO into the planar image light guide 12 as an angularly encoded image-bearing light beam WG for further propagation along the length dimension x of the image light guide 12 by total internal reflection (TIR) ​​between the plane-parallel front and back surfaces 14, 16. Although diffracted into different combinations of angle-related beams along the boundaries established by the TIR, the image-bearing light beam WG preserves the image information in an angularly encoded form derivable from the parameters of the incoupling diffractive optical element IDO. The outcoupling diffractive optical element ODO receives the encoded image-bearing light beam WG and diffracts at least a portion of the image-bearing light beam WG from the image light guide 12 as an image-bearing light beam WO (typically also by a first diffraction order) toward a nearby spatial region referred to as the eyebox E, within which a transmitted virtual image can be seen by a viewer's eye or other optical component. The outcoupling diffractive optical element ODO can be designed symmetrically with respect to the incoupling diffractive optical element IDO to restore the original angular relationship of the image-bearing light beam WI from between the output angularly related beams of the image-bearing light beam WO. Furthermore, the outcoupling diffractive optical element ODO can modify the angular relationship of the original field point positions to generate an output virtual image at a finite focusing distance.

[0038] However, to increase one dimension of overlap between the angle-related beams injected into the eyebox E (which defines the size of the area in which the virtual image can be seen), the outcoupling diffractive optical element ODO is positioned with the limited thickness T of the image light guide 12 to encounter the image-bearing light beam WG multiple times, diffracting only a portion of the image-bearing light beam WG at each encounter. The multiple encounters along the length (e.g., in the first direction) of the outcoupling diffractive optical element ODO have the effect of replicating the image-bearing light beam WG and expanding or widening at least one dimension of the eyebox E where the replicated beams overlap. The expanded eyebox E reduces the sensitivity to the position of the viewer's eyes for viewing the virtual image.

[0039] The outcoupling diffractive optical element ODO is shown as a transmissive diffraction grating disposed on or affixed to the front surface 14 of the image light guide 12. However, like the incoupling diffractive optical element IDO, the outcoupling diffractive optical element ODO may be located on, within, or otherwise engaged with the front surface 14 or back surface 16 of the image light guide 12, and may be a combination of transmissive and reflective types, depending on the direction in which the image-bearing light beam WG is intended to exit the image light guide 12. In addition, the outcoupling diffractive optical element ODO may be formed as another type of diffractive optical element, such as a volume hologram or other holographic diffractive element, which diffracts the image-bearing light beam WG propagating from the image light guide 12 as an image-bearing light beam WO propagating toward the eyebox E.

[0040] 2 shows a perspective view of a conventional image light guide system 10 arranged to expand the eyebox E in two dimensions, i.e., along both the x-axis and y-axis of the intended image. To achieve the second dimension of eyebox expansion, the incoupling diffractive optical element IDO is oriented to diffract at least a portion of the image-bearing light beam WG along its grating vector k1, along the image light guide 12, toward the intermediate rotation optical element TO, and its grating vector k2 is oriented to diffract at least a portion of the image-bearing light beam WG in a reflective mode, along the image light guide 12, toward the outcoupling diffractive optical element ODO. It should be appreciated that only a portion of the image-bearing light beam WG is diffracted by each of its multiple encounters with the intermediate rotation optical element TO, thereby laterally replicating each of the angularly related beams of the image-bearing light beam WG as it approaches the outcoupling diffractive optical element ODO. Before exiting the image light guide 12 as the image-bearing light beam WO, the intermediate rotating optical element TO redirects the image-bearing light beam WG towards the outcoupling diffractive optical element ODO (with grating vector k3) to longitudinally replicate an angularly related beam of the image-bearing light beam WG in a second direction. The grating vectors, such as the depicted grating vectors k1, k2, and k3, extend in respective directions perpendicular to the diffractive features (e.g., grooves, lines, or rulers) of the diffractive optical element in the parallel plane of the image light guide 12 and have inverse magnitude to the period or pitch d (i.e., the center-to-center distance between the diffractive features) of the diffractive optical elements IDO, TO, and ODO, respectively.

[0041] As shown in FIG. 2, the incoupling diffractive optical element IDO receives an incident image-bearing light beam WI, which includes a series of angularly related beams corresponding to individual pixels or equivalent locations in an image generated by an image source 18, such as a projector. The full range of angularly coded beams for generating a virtual image can be generated by a physical display device in combination with collimating or other optical components, by a beam scanner to more directly set the beam angle, or by a combination of a one-dimensional physical display device used with a scanner. In this configuration, the image light guide 12 outputs a series of replicated angularly related beams (replicated in two dimensions) by providing multiple encounters of the image-bearing light beam WG with both the intermediate rotation optical element TO and the outcoupling diffractive optical element ODO at different orientations. In the illustrated orientation of the image light guide 12, the intermediate rotation optical element TO provides eyebox expansion in a first direction, e.g., the y-axis direction, and the outcoupling diffractive optical element ODO provides a similar eyebox expansion in a second direction, e.g., the x-axis direction. The relative orientations and respective periods d of the diffractive features of the incoupling optical element IDO, the intermediate rotation optical element TO, and the outcoupling diffractive optical element ODO provide eyebox expansion in two dimensions while maintaining the intended relationship between the angularly related beams of the image-bearing light beam WI that are output from the image light guide system 10 as the image-bearing light beam WO. It will be appreciated that the periods d of the incoupling diffractive optical element IDO, the intermediate rotation optical element TO, and the outcoupling diffractive optical element ODO can each include diffractive features having a common pitch d, and the common pitch d of each optical element can be different.

[0042] In the illustrated configuration, the image-bearing light beam WI input to the image light guide 12 is encoded into a series of different angle-related beams by the incoupling diffractive optical element IDO, but the information necessary to reconstruct the image is preserved by considering the systematic effects of the incoupling diffractive optical element IDO. The intermediate rotation optical element TO, located at an intermediate position between the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, can be positioned so as not to induce any significant changes to the encoding of the image-bearing light beam WG. Therefore, the outcoupling diffractive optical element ODO can be positioned symmetrically with respect to the incoupling diffractive optical element IDO, for example, including diffractive features that share the same period d. Similarly, the period of the intermediate rotation optical element TO can also match the common period of the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO. Although the grating vector k2 of the intermediate rotation optical element TO is shown oriented at 45 degrees relative to the other grating vectors, with possible orientations maintained, the grating vector k2 of the intermediate rotation optical element TO can be oriented at 60 degrees relative to the grating vectors k1 and k3 of the incoupling and outcoupling diffractive optical elements IDO and ODO, such that the image-bearing light beam WG is rotated by 120 degrees. By orienting the grating vector k2 of the intermediate rotation optical element TO at 60 degrees relative to the grating vectors k1 and k3 of the incoupling and outcoupling diffractive optical elements IDO and ODO, the grating vectors k1 and k3 of the incoupling and outcoupling diffractive optical elements IDO and ODO are also oriented at 60 degrees relative to each other. Using the common pitch of the incoupling diffractive optical element IDO, the intermediate rotation diffractive optical element TO, and the outcoupling diffractive optical element ODO as the basis for the magnitude of the grating vectors, the three grating vectors k1, k2, and k3 (as directed line segments) form an equilateral triangle and sum to a zero vector magnitude, thereby avoiding asymmetric effects that may result in undesirable aberrations, including chromatic dispersion. Such asymmetric effects can also be avoided by having the grating vectors k1, k2, and k3 have unequal magnitudes in their relative orientations, such that the sum of the three grating vectors k1, k2, and k3 has a zero vector magnitude.

[0043] In a broader sense, the image-bearing light beam WI directed into the image light guide 12 is effectively encoded by the incoupling diffractive optical element IDO, regardless of whether the incoupling optics IDO uses a grating, hologram, prism, mirror, or some other mechanism. Light reflection, refraction, and / or diffraction occurring at the input should be decoded accordingly by the output to recreate the virtual image presented to the viewer. It may be relevant whether any symmetry is maintained between the intermediate rotation optical element TO, the incoupling optics IDO, and the outcoupling diffractive optical element ODO, or whether changes to the angle-related beam encoding of the image-bearing light beam WI occur along the image light guide 12, the intermediate rotation optical element TO, the incoupling diffractive optical element IDO, and the outcoupling diffractive optical element ODO, so that the image-bearing light beam WO output from the image light guide 12 retains or otherwise maintains the original or desired form of the image-bearing light beam WI to generate the intended virtual image.

[0044] As shown in FIG. 2 , the letter “R” represents the orientation of the virtual image as seen by a viewer with their eyes positioned within the eyebox E. As shown, the orientation of the letter “R” in the represented virtual image coincides with the orientation of the letter “R” encoded by the image-bearing light beam WI. A change in rotation about the z-axis or angular orientation of the incident image-bearing light beam WI relative to the xy plane causes a corresponding symmetric change in the rotation or angular orientation of the output light from the outcoupling diffractive optical element (ODO). From the image orientation perspective, the intermediate rotation optical element TO simply acts as a type of optical relay, providing one-dimensional eyebox expansion through angle-encoded beam replication of the image-bearing light beam WG along one axis of the image (e.g., along the y-axis). The outcoupling diffractive optical element ODO further provides a second dimension of eyebox expansion through angle-encoded beam replication along another axis (e.g., along the x-axis) while maintaining the original orientation of the virtual image encoded by the image-bearing light beam WI. The intermediate rotating optical element TO is typically a tilted or square grating, or alternatively may be a blazed grating, and is typically disposed on one of the plane-parallel front and back surfaces of the image light guide 12. Of course, the representation of the virtual image "R" created by the image source consists of light focused at infinity, which requires a lens (e.g., the lens of the human eye) to focus the image so that the orientation discussed above can be detected.

[0045] Collectively, the incoupling diffractive optical element IDO, the rotating diffractive optical element TO, and the outcoupling diffractive optical element ODO preferably preserve the angular relationships between the beams of different wavelengths that define the virtual image upon transport from an offset position to a near-eye position of the viewer by the image light guide 12. Meanwhile, the incoupling diffractive optical element IDO, the rotating diffractive optical element TO, and the outcoupling diffractive optical element ODO can be positioned and oriented relative to one another in different ways to control the overall shape of the image light guide 12 and the overall orientation at which angularly related beams can be directed into and out of the image light guide 12.

[0046] FIG. 3A shows an exemplary embodiment of a waveguide 102 according to the present disclosure. In the exemplary embodiment, the waveguide 102 includes an at least partially transparent substrate S (see FIGS. 4A-4C ) and has plane-parallel front and back surfaces 104 and 106 (also shown in FIGS. 4A-4C ). For example, the waveguide 102 may be made of optical glass or plastic. The waveguide 102 includes a first incoupling diffractive optical element IDOA and a second incoupling diffractive optical element IDOB. In one example, the first incoupling diffractive optical element IDOA and the second incoupling diffractive optical element IDOB may be laterally offset relative to each other (i.e., in the x-direction or the y-direction) and disposed on the front surface 104 and / or the back surface 106. In another example, the first incoupling diffractive optical element IDOA and the second incoupling diffractive optical element IDOB are laterally offset with respect to each other, with at least one of the first incoupling diffractive optical element IDOA or the second incoupling diffractive optical element IDOB disposed on the front surface 104 and the other of the first incoupling diffractive optical element IDOA or the second incoupling diffractive optical element IDOB disposed on the back surface 106. As shown in FIG. 3A , in an exemplary embodiment, the first incoupling diffractive optical element IDOA and the second incoupling diffractive optical element IDOB are disposed symmetrically about an imaginary axis AA that bifurcates the waveguide 102. In one example, the imaginary axis AA bisects the waveguide 102. As shown in FIG. 3A , the first incoupling diffractive optical element IDOA includes a first diffraction pattern 108, and the second incoupling diffractive optical element IDOB includes a second diffraction pattern 110. The first diffraction pattern 108 includes a plurality of diffractive features that are periodic in at least a first direction represented by a grating vector k1. The second diffraction pattern 110 includes a plurality of other diffraction features that are periodic in at least a second direction represented by the grating vector k2. For example, the first diffraction pattern 108 and the second diffraction pattern 110 may include linear diffraction features.Although other shapes are possible, the waveguide 102 is generally formed as an inverted trapezoid, for example, with the first incoupling diffractive optical element IDOA and the second incoupling diffractive optical element IDOB positioned adjacent to the longer of the two parallel sides of the trapezoid.

[0047] Continuing with reference to FIG. 3A , in an exemplary embodiment, the waveguide 102 includes an outcoupling diffractive optical element ODO having multiple zones of diffractive features, e.g., a first zone 112, a second zone 114A, a third zone 114B, a fourth zone 116A, and a fifth zone 116B of diffractive features. The outcoupling diffractive optical element ODO is arranged symmetrically about an imaginary axis AA. In the exemplary embodiment, the first zone 112 defines a generally V-shaped and / or triangular region and is centrally disposed within the outcoupling diffractive optical element ODO such that the imaginary axis AA diverges the first zone 112. The second zone 114A is disposed outward from the first zone 112 in the −x-axis direction (e.g., to the left in FIG. 3A ), and the third zone 114B is disposed outward from the second zone 114A in the −x-axis direction (e.g., to the left in FIG. 3A ). The fourth zone 116A and the fifth zone 116B are mirrored across a plane with a surface parallel to the imaginary axis AA relative to the second zone 114A and the third zone 114B, respectively. In an exemplary embodiment, the second zone 114A and the fourth zone 116A are generally linear and oriented at angles ±α, respectively, relative to the imaginary axis AA. The third zone 114B and the fifth zone 116B may have a generally triangular shape.

[0048] In the exemplary embodiment, the diffraction features of the first zone 112 are oriented parallel to the imaginary axis AA and approximate linear diffraction features with grating vectors ±k3, the diffraction features of the third zone 114B are oriented at an angle β relative to the diffraction features of the first zone 112 and approximate linear diffraction features with grating vector k4, and the diffraction features of the fifth zone 116B are oriented at an angle −β relative to the diffraction features of the first zone 112 and approximate linear diffraction features with grating vector k5. The second zone 114A includes diffraction features defining grating vectors k3 and k4. For example, the second zone 114A includes overlapping diffraction features of the first zone 112 (with grating vector k3) and the third zone 114B (with grating vector k4). Similarly, the fourth zone 116A includes diffraction features defining grating vectors k3 and k5. For example, the fourth zone 116A includes overlapping diffractive features of the first zone 112 (with grating vector k3) and the fifth zone 116B (with grating vector k5).

[0049] In one exemplary embodiment, the first zone 112, the second zone 114A, the third zone 114B, and the fourth zone 116A of the outcoupling diffractive optical element ODO are optimized to diffract the image-bearing light beam incoupled by the first incoupling diffractive optical element IDOA, and the first zone 112, the second zone 114A, the fourth zone 116A, and the fifth zone 116B of the outcoupling diffractive optical element ODO are optimized to diffract the image-bearing light beam incoupled by the second incoupling diffractive optical element IDOB. Thus, the image-bearing light beam incoupled by the first incoupling diffractive optical element IDOA and the second incoupling diffractive optical element IDOB utilizes at least the diffractive features of the central first zone 112 in the optical path to the eyebox E. In another embodiment, the image-bearing light beam incoupled by the first incoupling diffractive optical element IDOA and the second incoupling diffractive optical element IDOB utilizes the diffractive characteristics of the first zone 112, the second zone 114A, and the fourth zone 116A.

[0050] 3B and 6B, the first zone 112, the second zone 114A, the third zone 114B, and the fourth zone 116A of the outcoupling diffractive optical element ODO may form a first output area 118A optimized to diffract an image-bearing light beam incoupled by the first incoupling diffractive optical element IDOA. The first zone 112, the second zone 114A, the fourth zone 116A, and the fifth zone 116B of the outcoupling diffractive optical element ODO may form a second output area 118B optimized to diffract an image-bearing light beam incoupled by the second incoupling diffractive optical element IDOB.

[0051] In an exemplary embodiment, the second zone 114A of the outcoupling diffractive optical element ODO includes diffractive features comprising generally diamond-shaped posts, each diamond-shaped post including two sides generally parallel to the diffractive features of the first zone 112 (e.g., perpendicular to the grating vector k3) and two sides generally parallel to the diffractive features of the third zone 114B (e.g., perpendicular to the grating vector k4). Similarly, the fourth zone 116A may include diffractive features comprising generally diamond-shaped posts, each diamond-shaped post including two sides generally parallel to the diffractive features of the first zone 112 (e.g., perpendicular to the grating vector k3) and two sides generally parallel to the diffractive features of the fifth zone 116B (e.g., perpendicular to the grating vector k5).

[0052] 3A , in the exemplary embodiment, the waveguide 102 provides a first optical path for a first wavelength range of light (e.g., red light in the wavelength range of 620-750 nm) through the first zone 112, second zone 114A, third zone 114B, and fourth zone 116A of the first incoupling diffractive optical element IDOA and outcoupling diffractive optical element ODO, and a second optical path for a second, different wavelength range of light (e.g., green light in the wavelength range of 500-565 nm) through the first zone 112, second zone 114A, fourth zone 116A, and fifth zone 116B of the second incoupling diffractive optical element IDOB and outcoupling diffractive optical element ODO. The zoned outcoupling diffractive optical element ODO allows the waveguide 102 to utilize the same pattern of diffractive features in the first zone 112 (as well as diffractive features in the second zone 114A and fourth zone 116A) for both optical paths. With respect to virtual image alignment, utilizing the same pattern of diffractive features in the first zone 112, the second zone 114A, and the fourth zone 116A for both optical paths prevents disconnection in the waveguide 102 where the image-bearing light intersects without physically overlapping diffractive optical element regions (e.g., diffraction gratings).

[0053] Furthermore, the diffractive features in the first zone 112 of the outcoupling diffractive optical element ODO, as well as portions of the diffractive features in the second zone 114A and fourth zone 116A, are oriented vertically (i.e., oriented parallel to the imaginary axis AA) to prevent image noise produced by overhead point sources in use. In other words, the vertical orientation of the diffractive features in the first zone 112 (and in at least some embodiments the second zone 114A and fourth zone 116A) prevents or mitigates overhead point sources that induce "rainbows."

[0054] 4A , in an exemplary embodiment, the first incoupling diffractive optical element IDOA, the second incoupling diffractive optical element IDOB, and the outcoupling diffractive optical element ODO are disposed on the front surface 104 of the waveguide 102. Similarly, in another exemplary embodiment, the first incoupling diffractive optical element IDOA, the second incoupling diffractive optical element IDOB, and the outcoupling diffractive optical element ODO may be disposed on the back surface 106 of the waveguide 102. In yet another embodiment, the first incoupling diffractive optical element IDOA and the second incoupling diffractive optical element IDOB are disposed on the front surface 104 of the waveguide 102, and the outcoupling diffractive optical element ODO is disposed on the back surface 106 of the waveguide 102. Now referring to FIG. 4B , in an exemplary embodiment, the first incoupling diffractive optical element IDOA is disposed on the front surface 104, and the second incoupling diffractive optical element IDOB is disposed on the back surface 106 of the waveguide 102. Similarly, as shown in FIG. 4C, in an exemplary embodiment, the first incoupling diffractive optical element IDOA may be positioned on the back surface 106 and the second incoupling diffractive optical element IDOB may be positioned on the front surface 104 of the waveguide 102.

[0055] 5 , utilizing two waveguides, for example, a first waveguide 102A and a second waveguide 102B in a waveguide stack, creates six effective diffraction regions to facilitate transmitting a multicolor image to the eyebox E. For example, the first waveguide 102A may include two incoupling diffractive optical elements IDOA and IDOB, where the diffractive features within both of the incoupling diffractive optical elements IDOA and IDOB of the first waveguide 102A are optimized to incouple an image-bearing light beam of a first wavelength range, for example, red light, and the second waveguide 102B may include two incoupling diffractive optical elements IDOA and IDOB, where the diffractive features within both of the incoupling diffractive optical elements IDOA and IDOB of the second waveguide 102B are optimized to incouple an image-bearing light beam of a second, different wavelength range, for example, green light and / or blue light. In these embodiments, the first incoupling diffractive optical element IDOA of the first waveguide 102A and the first incoupling diffractive optical element IDOA of the second waveguide 102B are coaxial about an imaginary axis that is disposed through both the first incoupling diffractive optical element IDOA and through both planes of the first waveguide 102A (e.g., the imaginary axis is oriented perpendicular to the plane of the waveguide). Similarly, the second incoupling diffractive optical element IDOB of the first waveguide 102A and the second incoupling diffractive optical element IDOB of the second waveguide 102B are coaxial about an imaginary axis that is disposed through both the second incoupling diffractive optical element IDOB and through both planes of the first waveguide 102A (e.g., the imaginary axis is oriented perpendicular to the plane of the waveguide). In this way, two image sources or a single image source with a split exit pupil can utilize six different diffractive zones or regions (e.g., diffractive optical elements) to form a fully polychromatic virtual image with a wide field of view utilizing two waveguides in a single waveguide stack.

[0056] 6A and 6B, in an exemplary embodiment, an image light guide system 200 includes waveguides 102, 102A, and 102B, or 102A and 102B, which also include two image sources 18A and 18B. As shown in FIGS. 6A and 6B, one or more optical couplers 202, including but not limited to prisms, can be utilized to direct the image-bearing light to the incoupling diffractive optical elements IDOA and IDOB, respectively. The first image source 18A directs a first portion of the image-bearing light to the first incoupling diffractive optical element IDOA, for example, via optical coupler 202A. The second image source 18B directs a second portion of the image-bearing light to the second incoupling diffractive optical element IDOB, for example, via optical coupler 202B. In the exemplary embodiment, the first image source 18a and the second image source 18B are disposed in a transverse orientation relative to each other. For example, a first image source 18A may be positioned generally parallel to the imaginary axis AA (as shown in FIG. 3A), and a second image source 18B may be positioned generally perpendicular to the first image source 18A.

[0057] In the exemplary embodiment, the first image source 18A is operable to emit image-bearing light corresponding to a first half of the field of view (FOV) of the image transmitted to the eyebox, and the second image source 18B is operable to emit image-bearing light corresponding to a second half of the field of view (FOV) of the image transmitted to the eyebox. The first incoupling diffractive optical element IDOA is optimized to diffract the image-bearing light from the image source 18A, and the second incoupling diffractive optical element IDOB is optimized to diffract the image-bearing light from the image source 18B. This arrangement allows each incoupling diffractive optical element IDOA, IDOB to diffract half of the image transmitted to the eyebox into the waveguide 102, which, when outcoupled from the outcoupling diffractive optical element ODO, combine into a single wide-field virtual image. This provides the advantage of doubling the FOV of the image transmitted to the user without compromising the brightness of the virtual image. In an exemplary embodiment, the FOV emitted from each image source 18A, 18B may be greater than half of the total FOV, such that the FOVs emitted by each image source 18A, 18B overlap within the eyebox.

[0058] 7 and 8, in an exemplary embodiment, an image light guide system 200 including a waveguide 102 includes an image source 18C having a light source system 19. The light source system 19 may include a first wavelength source 302A (e.g., a red wavelength range source), a second wavelength source 302B (e.g., a green wavelength range source), and a third wavelength source 302C (e.g., a blue wavelength range source) operable to emit light incident on a combiner 304, such as an X-cube. Lenses 306A, 306B, and 306C disposed between the wavelength sources 302A, 302B, and 302C may be utilized to collimate the light emitted by the wavelength sources 302A, 302B, and 302C. For example, but not limited to, the lenses 306A, 306B, and 306C may be formed of glass or plastic.

[0059] In an exemplary embodiment, image source 18C includes a polarizing beam splitter 310. Unpolarized light 308 is emitted from combiner 304 of light source system 19 and is incident on polarizing beam splitter 310. Polarizing beam splitter 310 is configured to split the light path according to polarization. In an exemplary embodiment, polarizing beam splitter 310 comprises a cube-shaped beam splitter having polarizing coatings 312 arranged along the diagonal corners of the cube and a reflector coating paired with a quarter-wave plate 314 (e.g., at 45°) arranged along a surface 316 of the cube, surface 316 being oriented transverse to the path of unpolarized light 308.

[0060] For example, polarizing beam splitter 310 splits unpolarized light 308 into S-polarized light 318A and P-polarized light 318B. The linearly polarized light portions 318A and 318B exit polarizing beam splitter 310 and are incident on first and second prisms 320A and 320B, respectively. In an exemplary embodiment, first and second prisms 320A and 320B are operable to direct the linearly polarized light portions 318A and 318B along desired nominal angular paths. For example, first and second prisms 320A and 320B may be wedge prisms.

[0061] 7, in an exemplary embodiment, image source 18C includes lenses 322A and 322B optically positioned between polarizing beam splitter 310 and homogenizing elements 324A and 324B. Lenses 322A and 322B, in conjunction with lenses 306A, 306B, and 306C, collimate the light emitted by wavelength sources 302A, 302B, and 302C. Homogenizing elements 324A and 324B are configured to make the pupil more uniform. For example, homogenizing elements 324A and 324B may be light pipes, lenslet arrays, or scattering elements.

[0062] Referring now to FIG. 8 , which shows a top-view schematic diagram of image source 18C, in an exemplary embodiment, image source 18C includes beam splitters 326A and 326B positioned in the optical path to capture light emitted from homogenizing elements 324A and 324B, respectively. Respective beam splitters 326A and 326B direct linearly polarized light 318A and 318B toward first liquid crystals on first and second LCOS (liquid crystal on silicon) panels 328A and 328B, respectively. First and second LCOS panels 328A and 328B are front-emitting. The collimated light leaves first and second LCOS panels 328A and 328B and is incident on incoupling diffractive optical elements IDOA and IDOB, respectively. In other words, image source 18C includes two imaging engines with LCOS panels 328A, 328B configured to receive light generated by a single light source system 19. In one or more exemplary embodiments, imaging optics may be provided downstream of LCOS panels 328A, 328B. Because LCOS panels are typically polarization-sensitive, in some examples, some form of retarder or waveplate can be positioned between polarizing beam splitter 310 and one of the LCOS panels, e.g., 328A or 328B, to optimize the orientation of the linear polarization of the portion of the light exiting polarizing beam splitter 310. In this way, both portions of linear polarization are oriented for optimal engagement with both LCOS panels.

[0063] Advantageously, this design provides two display panels illuminated by a single (polychromatic) light source system 19 (e.g., light sources 302A, 302B, 302C), with light of each polarization utilized by transmitting linearly polarized light 318A, 318B to two respective LCOS panels 328A, 328B, thereby increasing system efficiency. In an exemplary embodiment, quarter-wave plates 330A, 330B are utilized to align the polarization of light emitted by one or more of the panels 328A, 328B with the diffractive features of the incoupling diffractive optical elements IDOA, IDOB, increasing the overall coupling efficiency within the waveguide 102. As noted above, LCOS panels are typically polarization-sensitive. This means that, when coupled with a polarizing beam splitter, most image sources utilize only half of the potential light intensity generated by the light source system, while the other portion of the linearly polarized light is unused by the system. The exemplary configuration described herein allows for the use of both linearly polarized portions of light by using a portion of linearly polarized light passing through the first LCOS panel 328A and a second portion of oppositely polarized linearly polarized light passing through the second LCOS panel 328B. Thus, the exemplary configuration described above allows for the utilization of all or most of the light generated by the light source system 19. This exemplary configuration offers the potential to double the outcoupling efficiency without doubling the power requirements of the system.

[0064] In another embodiment, the first LCOS panel 328A and the second LCOS panel 328B are replaced by a DLP (digital light processing) projector. Advantageously, this design does not require unpolarized light 308 to be polarized by the polarizing beam splitter 310, and a beam splitter can be utilized to direct the light into two optical paths.

[0065] One or more features of the embodiments described herein may be combined to create additional embodiments not shown. While various embodiments have been described in detail above, it should be understood that they are presented for illustrative purposes, and not for limiting purposes. It will be apparent to those skilled in the relevant art that the subject matter of the present disclosure may be embodied in other specific forms, variations, and modifications without departing from the scope, spirit, or essential characteristics thereof. The above-described embodiments are therefore to be considered in all respects as illustrative and not restrictive. The scope of the invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.

Claims

1. 1. An image light guide for conveying a virtual image, comprising: a first surface and an opposing second surface; a first incoupling diffractive optical element disposed along one of the first surface and the second surface, the first incoupling diffractive optical element including a first set of diffractive features; a second incoupling diffractive optical element disposed along one of the first surface and the second surface, the second incoupling diffractive optical element including a second set of diffractive features; an outcoupling diffractive optical element disposed along at least one of the first surface and the second surface, the outcoupling diffractive optical element including a plurality of zones each having a different set of diffractive characteristics than adjacent zones, the plurality of zones including a first zone optimized to diffract light incoupled from the first incoupling diffractive optical element and the second incoupling diffractive optical element.

2. 2. The image light guide of claim 1, wherein the outcoupling diffractive optical element includes the first zone, a second zone disposed outward from the first zone in a first direction, a third zone disposed outward from the second zone in the first direction, a fourth zone disposed outward from the first zone in a second direction, and a fifth zone disposed outward from the fourth zone in the second direction.

3. The image light guide of claim 2 , wherein the second zone and the fourth zone are mirrored over the first zone, and the third zone and the fifth zone are mirrored over the first zone.

4. 4. The image light guide of claim 2 or 3, wherein the second zone and the fourth zone are linear and oriented at opposite angles relative to an imaginary axis that bisects the first zone.

5. 5. The image light guide of claim 1, wherein the first zone comprises linear diffractive features arranged to bisect the first surface and oriented parallel to an imaginary axis that is parallel to the first surface, the imaginary axis extending between a first edge of the first surface adjacent the first incoupling diffractive optical element and the second incoupling diffractive optical element, and a second edge of the first surface adjacent the outcoupling diffractive optical element.

6. 6. The image light guide of claim 5, wherein the third zone includes linear diffractive features oriented at a first angle relative to the diffractive features of the first zone, and the fifth zone includes linear diffractive features oriented at a second angle relative to the diffractive features of the first zone.

7. The image light guide of claim 6 , wherein the second angle is equal to and opposite to the first angle.

8. 8. The image light guide of claim 6 or 7, wherein the second zone includes a first set of linear diffractive features parallel to the diffractive features of the first zone and a second set of linear diffractive features parallel to the diffractive features of the third zone.

9. 8. The image light guide of claim 6 or 7, wherein the fourth zone includes a first set of linear diffractive features parallel to the diffractive features of the first zone and a second set of linear diffractive features parallel to the diffractive features of the fifth zone.

10. 8. The image light guide of claim 6 or 7, wherein the second zone includes diffractive features having a first grating vector parallel to the grating vector of the first zone and a second grating vector parallel to the grating vector of the third zone, and the fourth zone includes diffractive features having a first grating vector parallel to the grating vector of the first zone and a second grating vector parallel to the grating vector of the fifth zone.

11. 3. The image light guide of claim 2, wherein the first zone, the second zone, the third zone, and the fourth zone of the outcoupling diffractive optical element form a first output area optimized to diffract an image-bearing light beam incoupled by the first incoupling diffractive optical element, and the first zone, the second zone, the fourth zone, and the fifth zone of the outcoupling diffractive optical element form a second output area optimized to diffract an image-bearing light beam incoupled by the second incoupling diffractive optical element.

12. 1. An image source for generating an angularly coded image-bearing light beam, comprising: a light source system; a first beam splitter having two opposing output faces through which polarized portions of light exit the polarizing beam splitter, the polarizing beam splitter operable to polarize light from the light source system into a first optical path and a second optical path; a second beam splitter positioned in the first optical path to receive light emitted from the first beam splitter; and a third beam splitter positioned in the second optical path to receive light emitted from the first beam splitter. an image source including a first imaging engine positioned in the first optical path to receive light from the second beam splitter, and a second imaging engine positioned in the second optical path to receive light from the third beam splitter.

13. the light source system comprises: a first wavelength source; and a second wavelength source; and 13. The image source of claim 12, wherein the first wavelength source, the second wavelength source, and the third wavelength source are operable to emit light that is incident on the first beam splitter.

14. 14. The image source of claim 13, wherein the light source system comprises lenses positioned between each of the wavelength sources to collimate the emitted light.

15. The image source of claim 12 , wherein the first beam splitter comprises a polarizing beam splitter operable to split unpolarized light from the light source system into linearly polarized light.

16. 13. The image source of claim 12, further comprising a first prism disposed in the first optical path and a second prism disposed in the second optical path, the first prism and the second prism operable to direct the polarized light along the first optical path and the second optical path, respectively.

17. The image source of claim 12 , wherein the first imaging engine and the second imaging engine include liquid crystal on silicon (LCOS) panels.

18. 18. The image source of claim 17, wherein the LCOS panel is front-emitting.

19. 13. The image source of claim 12, wherein the first imaging engine and the second imaging engine comprise digital light processing (DLP) projectors.

20. 18. The image source of claim 17, further comprising a first wave plate positioned to reorient the polarization of light emitted by the first imaging engine, and a second wave plate positioned to reorient the polarization of light emitted by the second imaging engine.

Images