Fixed focus image light guide system

Abstract

The image light guide system includes: an image light guide positioned to direct an image-bearing light beam of a virtual object toward an eyebox at a first focused distance; a first corrective optical element positioned between the image light guide and the real-world object, the first corrective optical element having a spherical light output contribution operable to converge or diverge the real-world image-bearing light beam before the eyebox to a second focused distance that is smaller than the first focused distance; an outcoupling optical element disposed along the image light guide, the outcoupling optical element having a spherical light output contribution operable to converge or diverge the virtual image-bearing light beam before the eyebox to a second focused distance that is smaller than the first focused distance; and a second corrective optical element positioned between the image light guide and the eyebox, the second corrective optical element having a cylindrical optical contribution operable to reduce optical aberrations associated with viewing the real-world object and virtual object at the second focused distance.

Description

[Technical Field]

[0001] The present disclosure relates generally to augmented reality systems, 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 increasingly taking the form of traditional eyeglasses with unobtrusive optics for conveying virtual image content with a low obstruction of the surrounding environment. An image generator may be supported along the eyeglass temples, and a substantially transparent image light guide conveys the generated image to the wearer's eyes as a virtual image projected into the wearer's real-world field of view as seen through the image light guide.

[0003] Virtual image content can be transmitted along an image light guide as a set of angularly related beams, with the relative angular orientation of each beam in two angular dimensions corresponding to a different location (e.g., pixel) in the generated image. Typically, the beams themselves are collimated as if they correspond to distant point sources located at unique angular positions in the field of view. Thus, when the collimated beams are directed to overlapping positions in a common eyebox, the wearer's eyes view the generated image from the eyebox as a virtual image located at a distance approaching infinity. However, real-world objects of interest to the wearer may be located much closer and require some significant eye accommodation to focus. Viewing virtual and real-world objects requiring different focus accommodations in the same scene can cause eye strain.

[0004] Vision problems in the wearer's eyes caused by refractive errors such as myopia (nearsightedness), hyperopia (farsightedness), and astigmatism can also pose challenges to low-profile HMDs, which resemble traditional eyeglasses. If the wearer's traditional eyeglasses (including corrective lenses) must be removed to accommodate the low-profile HMD, the wearer's view of both real-world and virtual objects through the HMD can be impaired. Summary of the Invention

[0005] The present disclosure is directed to one or more exemplary embodiments of an image light guide system that manages focus discrepancies between real-world and virtual objects presented to a viewer, manages vision issues that affect a particular viewer's ability to adjust focus, and reduces the viewer's ocular requirements to see virtual objects alongside real-world objects in the same field of view.

[0006] In a first exemplary embodiment, the present disclosure provides an image light guide system for viewing virtual objects and real-world objects within a common field of view, the image light guide system including: an image light guide having an inner surface and an outer surface, positioned to direct an image-bearing light beam of the virtual object toward an eyebox at a first focused distance; a first corrective optical element positioned between the image light guide and the real-world object, the first corrective optical element having a spherical light output contribution operable to converge or diverge the real-world image-bearing light beam before the eyebox to a second focused distance that is shorter than the first focused distance; an outcoupling optical element positioned along the image light guide, the outcoupling optical element having a spherical light output contribution operable to converge or diverge the virtual image-bearing light beam before the eyebox to the second focused distance that is shorter than the first focused distance; and a second corrective optical element positioned between the image light guide and the eyebox, the second corrective optical element having a cylindrical optical contribution operable to reduce optical aberrations associated with viewing the real-world object and the virtual object at the second focused distance.

[0007] In a second exemplary embodiment, the present disclosure provides an image light guide system for viewing virtual objects and real-world objects within a common field of view, the image light guide system including: an image light guide having an inner surface and an outer surface, positioned to direct an image-bearing light beam of the virtual object toward an eyebox at a first focused distance; a first corrective optical element positioned between the image light guide and the real-world object, the first corrective optical element having a spherical light output contribution operable to converge or diverge the real-world image-bearing light beam before the eyebox to a second focused distance that is shorter than the first focused distance; and an outcoupling optical element positioned along the image light guide, the outcoupling optical element having a composite light output contribution operable to converge or diverge the virtual image-bearing light beam before the eyebox to the second focused distance that is shorter than the first focused distance and a cylindrical optical contribution operable to reduce optical aberrations associated with viewing the real-world object and the virtual object at the second focused distance.

[0008] In a third exemplary embodiment, the present disclosure provides an image light guide system for viewing virtual objects and real-world objects within a common field of view, the image light guide system including: an image light guide having an inner surface and an outer surface, the image light guide positioned to direct an image-bearing light beam of the virtual object toward an eyebox at a first focused distance; an outcoupling optical element disposed along the image light guide; a digital spherical corrector element disposed between the image light guide and the eyebox, the digital spherical corrector element having a spherical light output contribution operable to converge or diverge the real-world image-bearing light beam and the virtual image-bearing light beam before the eyebox to a second focused distance that is smaller than the first focused distance; and a cylindrical corrector element disposed between the digital spherical corrector element and the eyebox, the cylindrical corrector optical element having a cylindrical optical contribution operable to reduce optical aberrations associated with viewing the real-world object and the virtual object at the second focused distance.

[0009] In a fourth exemplary embodiment, the present disclosure provides a binocular image light guide system for viewing virtual objects and real-world objects within a common field of view, comprising: an image light guide having an inner surface and an outer surface, the image light guide arranged to incouple a collimated image-bearing light beam of a virtual object; and first and second outcoupling optical elements arranged along the image light guide, the first and second outcoupling optical elements each comprising diffractive features having a pitch configured to position a convergence point of the virtual object closer than a focal plane at infinity. [Brief explanation of the drawings]

[0010] 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.

[0011] [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 3] FIG. 3 is a plan schematic view of a portion of an image light guide system according to an exemplary embodiment of the disclosed subject matter. [Figure 4] FIG. 4 is a simplified plan view schematic diagram of a portion of an imaging light system showing a common field of view according to an exemplary embodiment of the disclosed subject matter. [Figure 5]FIG. 5 is a simplified plan view schematic diagram of a portion of an imaging light system having a negative power optical element, according to an exemplary embodiment of the disclosed subject matter. [Figure 6] FIG. 6 is a simplified plan view schematic diagram of a portion of an imaging light system having negative and positive output optical elements, according to an exemplary embodiment of the disclosed subject matter. [Figure 7] FIG. 7 is a simplified plan view schematic diagram of a portion of an imaging light system having a negative power optical element, a positive power optical element, and a corrective optical element, according to an exemplary embodiment of the disclosed subject matter. [Figure 8A] FIG. 8A is a simplified side schematic diagram of a portion of an imaging light system having a negative power optical element, a positive power optical element, and a multifocal corrective optical element, according to an exemplary embodiment of the disclosed subject matter. [Figure 8B] FIG. 8B is a simplified side schematic diagram of a portion of an imaging light system having a negative power optical element, a positive power optical element, and a multifocal correcting optical element, according to an exemplary embodiment of the disclosed subject matter. [Figure 9] FIG. 9 is a simplified side schematic diagram of a portion of an imaging light system having a negative power optical element, a positive power optical element, and a multifocal correcting optical element, according to an exemplary embodiment of the disclosed subject matter. [Figure 10] FIG. 10 is a simplified plan view schematic diagram of a portion of an imaging light system having a multi-function optical element according to an exemplary embodiment of the disclosed subject matter. [Figure 11] FIG. 11 is a simplified plan view schematic diagram of a portion of an imaging light system having a multi-function optical element and a lens carrier, according to an exemplary embodiment of the disclosed subject matter. [Figure 12] FIG. 12 is a simplified side schematic diagram of a portion of an imaging optical system having first and second metamaterials, according to an exemplary embodiment of the disclosed subject matter. [Figure 13A] FIG. 13A is a simplified side schematic diagram of a portion of an imaging light system that provides spherical correction to virtual image-bearing light via an outcoupling diffractive optical element, according to an exemplary embodiment of the disclosed subject matter. [Figure 13B]FIG. 13B is a schematic perspective view of a portion of the imaging light system according to FIG. 13A. [Figure 13C] FIG. 13C is a schematic top view of a portion of the imaging light system according to FIG. 13A. [Figure 13D] FIG. 13D is a schematic side view of a portion of the imaging light system according to FIG. 13A. [Figure 13E] FIG. 13E is another simplified side schematic diagram of a portion of an imaging light system that provides spherical correction to virtual image-bearing light via an outcoupling diffractive optical element, according to an exemplary embodiment of the disclosed subject matter. [Figure 14A] FIG. 14A is a cross-sectional side view of a portion of a diffractive optic showing a gradual change in pitch along a first dimension of the diffractive optic to create a virtual focal point for one dimension of an image. [Figure 14B] FIG. 14B is a top view of an image light guide system in which the image light guide is oriented at a chevron angle, according to an exemplary embodiment of the disclosed subject matter. [Figure 14C] FIG. 14C is a top view of an image light guide system in accordance with an exemplary embodiment of the subject matter of the present disclosure, in which the image light guide is oriented at a chevron angle and configured to change the convergence point of a virtual object conveyed by an output image-bearing light beam. [Figure 14D] FIG. 14D is a top view of an image light guide system configured to change the convergence point of a virtual object conveyed by an output image-bearing light beam, according to an exemplary embodiment of the disclosed subject matter. [Figure 14E] Figure 14E is a top view of an image light guide system in accordance with an exemplary embodiment of the subject matter of the present disclosure, in which the image light guide is oriented at a chevron angle and configured to change the convergence point and focal plane of a virtual object conveyed by an output image-bearing light beam. [Figure 14F] FIG. 14F is a top view of an image light guide system configured to change the convergence point and focal plane of a virtual object conveyed by an output image-bearing light beam, according to an exemplary embodiment of the disclosed subject matter. [Figure 14G]FIG. 14G is a top view of an image light guide system in which an image light guide having an optical wedge configured to change the convergence point of a virtual object carried by an output image-bearing light beam is oriented at a chevron angle, according to an exemplary embodiment of the subject matter of the present disclosure. [Figure 15] FIG. 15 is a perspective view of a portion of a diffractive optical element showing a gradual variation in the orientation angle of the diffractive features along a second direction of the diffractive optical element. [Figure 16] FIG. 16 is a front view of a portion of an outcoupling diffractive optical element showing an array of contoured zones, each with parallel diffractive features of equal pitch, but with each zone varying in pitch along one direction of the array and varying in orientation angle along the other direction of the array. [Figure 17] FIG. 17 is a front view of a portion of an outcoupling diffractive optical element showing an array of zones according to an exemplary embodiment of the subject matter of the present disclosure, each zone having a common pitch between each diffractive feature of the first and second sets of output diffractive features, the common pitch being configured to vary between zones in at least a first direction. [Figure 18] FIG. 18 is a front view of a portion of an outcoupling diffractive optical element showing multiple patterns of diffractive features according to an exemplary embodiment of the disclosed subject matter. [Figure 19A] FIG. 19A is a simplified side schematic diagram of a portion of an image lighting system that provides spherical and cylindrical correction to real-world image-bearing light, according to an exemplary embodiment of the disclosed subject matter. [Figure 19B] FIG. 19B is a simplified side schematic diagram of a portion of an imaging lighting system that provides cylindrical correction for real-world image-bearing light and virtual image-bearing light, according to an exemplary embodiment of the disclosed subject matter. [Figure 19C] FIG. 19C is a simplified side schematic diagram of a portion of an image lighting system that provides spherical and cylindrical correction for real-world image-bearing light, and cylindrical correction for virtual image-bearing light, according to an exemplary embodiment of the subject matter of the present disclosure. [Figure 20A]FIG. 20A is a simplified side schematic diagram of a portion of an image lighting system that provides digital spherical correction for real-world image-bearing light and virtual image-bearing light, and cylindrical correction for real-world image-bearing light and virtual image-bearing light, in accordance with an exemplary embodiment of the subject matter of the present disclosure. [Figure 20B] FIG. 20B is a simplified side schematic diagram of a portion of an image lighting system that provides digital spherical correction for real-world image-bearing light and virtual image-bearing light, and digital cylindrical correction for real-world image-bearing light and virtual image-bearing light, according to an exemplary embodiment of the subject matter of the present disclosure. [Figure 20C] FIG. 20C is a simplified side schematic diagram of a portion of an image lighting system that provides digital spherical correction for real-world image-bearing light and cylindrical correction for real-world image-bearing light and virtual image-bearing light, according to an exemplary embodiment of the subject matter of the present disclosure. [Figure 20D] FIG. 20D is a simplified side schematic diagram of a portion of an image lighting system that provides digital spherical correction for real-world image-bearing light and digital cylindrical correction for real-world image-bearing light and virtual image-bearing light, according to an exemplary embodiment of the subject matter of the present disclosure. [Figure 21] FIG. 21 is a perspective view of an image light guide system in the form of a head-mounted display according to an exemplary embodiment of the disclosed subject matter. DETAILED DESCRIPTION OF THE INVENTION

[0012] 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 configurations related 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.

[0013] 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" or "embodiments" mean that a particular configuration, structure, or feature described in connection with an embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" throughout this specification do not necessarily refer to the same embodiment. However, particular configurations, structures, or features described may be combined in any suitable manner in one or more embodiments.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] When the angle-related beam engages 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.

[0024] 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.

[0025] 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.

[0026] 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 grating vector k1, along the image light guide 12, toward the intermediate rotation optical element TO, and its diffractive component and grating vector k2 are 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 toward 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. Grating vectors, such as the depicted grating vectors k1, k2, and k3, extend in respective directions parallel to the periodic direction of the diffractive features of the diffractive optical element (e.g., parallel to the grooves, lines, or rulers) within the parallel planes of the image light guide 12 and have opposite magnitudes to the period or pitch d (i.e., the center distance between the diffractive features) of the diffractive optical elements IDO, TO, and ODO, respectively. It will be apparent to those skilled in the art that light can also be directed into diffracted orders corresponding to the grating vectors -k1, -k2, and -k3.

[0027] 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 is output from the image light guide system 10 as the image-bearing light beam WO. Of course, 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 (e.g., constant) pitch d, and the common pitch d of each diffractive optical element IDO, TO, ODO can be different.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] FIG. 3 shows a planar schematic view of a portion of an exemplary head-mounted image light guide system 100 according to the present disclosure. In some embodiments, the image light guide system 100 can take the form of a head-mounted display (shown in FIG. 19 ) or other head-mounted optical system. As shown in FIG. 3 , the exemplary image light guide system 100 includes an image light guide 102 in the form of a planar waveguide. Although not shown, the image light guide 102 can include the same structure, function, materials, and / or configuration as described above with respect to the image light guide 12; for example, the image light guide 102 can include an incoupling diffractive optical element, an intermediate rotating optical element, and an outcoupling diffractive optical element. While illustrated as a planar waveguide, it should be understood that the image light guide 102 can be a non-planar waveguide, e.g., a curved waveguide. Additionally, the image light guide 102 includes a transparent substrate, which can be made of optical glass, quartz, or plastic, for example, having plane-parallel front and back surfaces 104 and 106, respectively. It will be appreciated that, similar to image light guide system 10 described above, image light guide system 100 and image light guide 102 are configured to receive angularly related image-bearing light beams and couple the angularly related image-bearing light beams into image light guide 102 by an incoupling diffractive optical element (located on the front surface 104 or back surface 106 of the image light guide and configured as a transmissive or reflective diffractive element). Once coupled into image light guide 102, the angularly encoded image-bearing light beams are configured to propagate along the length dimension of image light guide 102 and exit image light guide 102 by interaction with the outcoupling diffractive optical element, such that at least one image is formed within eyebox E for observation by a viewer or other optical components. As described above with respect to image light guide 12, image light guide 102 can also utilize one or more encounters with intermediate rotating or outcoupling optical elements to increase the size of eyebox E in one or more dimensions.

[0033] As shown in FIG. 3 , image light guide system 100 also includes image source 108. In some embodiments, image source 108 is a projector including a light source and one or more optical components for focusing and / or collimating light generated by the light source. In some embodiments, image source 108 includes one or more light-emitting diodes (LEDs), organic LEDs (OLEDs), or ultra-light-emitting diodes (uLEDs). In other embodiments, image source 108 is a color-field sequential projector system operable to pulse image-bearing light of multiple wavelength bands, e.g., light from within the red, green, and blue wavelength bands, to a digital light modulator / micromirror array (“DLP”) or liquid crystal on silicon (“LCOS”) display. In further embodiments, image source 108 includes one or more pico projectors, each configured to generate a single primary color band (e.g., red, green, or blue). In another embodiment, image source 108 includes a single pico projector arranged to generate at least three primary color bands (e.g., red, green, and blue). In one example, the three primary color bands include a green band having wavelengths ranging between 495 nm and 570 nm, a red band having wavelengths ranging between 620 nm and 750 nm, and a blue band having wavelengths ranging between 450 nm and 495 nm. The substantially collimated light produced by the pico projector, when coupled and transmitted through image light guide 102, can be used by image light guide system 100 to form one or more virtual images viewed by a user's eyes or other optical components positioned within eyebox E.

[0034] Continuing to refer to FIG. 3 , image light guide system 100 also includes a frame 110 including a right-eye rim section 112 having a right temple 114 and a nose bridge portion 116. Between temple 114 and nose bridge portion 116, frame 110 includes a right opening 118 configured to receive image light guide 102 such that image light guide 102 is configured to form at least one image associated with one or more virtual objects in a viewer's right eye 120 during operation of image light guide system 100. While only right-eye rim section 112 and right eye 120 are illustrated in FIG. 3 , it will be appreciated that frame 110 may be symmetrical, i.e., may include a right-eye rim section 112 and a left-eye rim section (not shown), each of which may both include a respective temple and a respective image light guide 102 configured to form respective virtual images associated with one or more virtual objects in a viewer's right and left eyes. In other words, image light guide system 100 and frame 110 can be configured as a binocular display system that forms images for both the right and left eyes of a viewer. In some embodiments, frame 110 is made of a metal, plastic, or wood material (or any combination thereof) and is intended to be opaque, i.e., not transmit visible light. In some embodiments, image light guide 102 is removably secured between temples 114 and nose bridge portion 116, i.e., image light guide 102 can be removed and / or replaced using additional tools. Furthermore, it should be understood that in one or more exemplary embodiments of image light guide system 100 (whether a binocular system as described above or a monocular system), image light guide system 100 can include multiple stacked image light guides 102. For example, one image light guide 102 in the stack is configured to incouple and propagate light in a first wavelength range (e.g., light in the red portion of the visible spectrum), and another image light guide 102 in the stack is configured to incouple and propagate light in a second wavelength range (e.g., light in the green and / or blue portions of the visible spectrum).

[0035] 3, the image light guide system 100 may further include a cover window or other protective outer cover 122. In some embodiments, an anti-reflective coating may be provided on the front and / or back surface of the protective outer cover 122. In some embodiments, because the protective outer cover 122 is located between the image light guide 102 and the real-world object RWO, the protective outer cover 122 may provide filtering or other optical functionality that affects the viewer's view of the real-world object RWO without affecting the viewer's view of the virtual object VO. Furthermore, the image light guide system 100 may include an optical coupler 124. The optical coupler 124 may take the form of an incoupling diffractive optical element, such as a plurality or set of surface relief gratings or a volume hologram. In some embodiments, the optical coupler 124 may take the form of a prism configured to receive image-bearing light from the projector 106 and redirect and / or incouple the image-bearing light into the image light guide 102. In some embodiments, optical coupler 124 includes an incoupling diffractive optical element as well as a prism.

[0036] 4 illustrates a simplified schematic plan view of one exemplary configuration of the right-eye rim section 112 of the image light guide system 100, with certain components of the frame 110 removed for clarity. As shown, the image light guide system 100 is configured to receive virtual image-bearing light 126 generated by an image source (e.g., the image source 108 shown in FIG. 3 ) and form an image related to a virtual object VO (depicted as a triangular symbol with the letter “V” encircled) within the eyebox E using at least the in-coupling, TIR, and out-coupling mechanisms of the image light guide 102. Additionally, within the common field of view FOV, the image light guide 102 is also operable to receive and transmit to the eyebox E image-bearing light 128 reflected from a real-world object RWO (depicted as a star-shaped symbol with the letter “R” encircled). Thus, the viewer's right eye 120 is configured to form an image related to the virtual object VO and an image related to the real-world object RWO from within the common field of view FOV. Of course, the common field-of-view FOV can encompass a wider or narrower field-of-view angle than the field-of-view shown; for example, the common field-of-view FOV may be wide enough to completely encompass the image light guide 102, or it may cover only a portion of the image light guide 102. As shown in FIGS. 4-7 , the dotted lines associated with virtual image-bearing light 126 (discussed below) indicate virtual projections associated with virtual images originating from a virtual source location. In other words, the dotted lines illustrate the virtual image-bearing light tracing back to a virtual focal point in the environment, such that the light used to form the virtual object VO in the eyebox E appears to originate from the virtual location of the virtual object VO in the environment and within the common FOV. As shown in FIG. 4 , the virtual image-bearing light 126 is incoupled into the image light guide 102, propagates along the length dimension of the image light guide 102 (the vertical direction in FIG. 4 ), and is outcoupled as virtual image-bearing light 128, operable to form one or more images in the eyebox associated with one or more virtual objects VO from within the environment.Additionally, real-world image-bearing light 130 is transmitted through image light guide 102 and travels to eyebox E and is operable to form one or more images within eyebox E associated with one or more real-world objects RWO from within the environment and from within the common field of view FOV as virtual objects VO.

[0037] As described above, image source 108 is configured to generate substantially collimated virtual image-bearing light 126. In embodiments of image light guide system 100 in which the incoupling and outcoupling diffractive optical elements do not introduce optical power into incoupled virtual image-bearing light 126, images associated with virtual objects VO formed within eyebox E are focused at optical infinity. For some users, particularly those with certain forms of eye disease such as myopia (nearsightedness) or astigmatism, generating images of virtual objects focused at optical infinity may not be desirable. Instead, it may be desirable to focus those objects at a closer focusing distance, i.e., a focusing distance shorter than optical infinity.

[0038] FIG. 5 shows a simplified schematic plan view of one example configuration of the right-eye rim section 112 of the image light guide system 100. While not shown in FIGS. 5-7 for clarity, it should be understood that virtual image-bearing light 126 may be incoupled into the image light guide 102 and can propagate by TIR along the length dimension of the image light guide 102 (the vertical direction in FIGS. 5-7 ) until it is outcoupled from the image light guide 102 as virtual image-bearing light 128A. Furthermore, although not shown in FIG. 5 , it should be understood that the virtual object VO and the real-world object RWO are within a common field of view, as shown and described with respect to FIG. 4 above. As shown in FIG. 5 , the image light guide system 100 may also include a negative-power optical element 132 that provides a negative light output contribution 134 to the image light guide system 100. As shown, the negative-power optical element is positioned between the image light guide 102 and the viewer's right eye 120. The negative output optical element 132 operates to branch the incident image-bearing light, reducing the apparent focal length of the incident image-bearing light. By positioning the negative output optical element 132 between the image light guide and the user's eye 120, the negative output optical element 132 operates to reduce the focal length of a virtual object originally focused at optical infinity. For example, the negative output optical element 132 is configured to branch the virtual image-bearing light 128A such that the focal length of the virtual object VO is reduced from a first focal length FD1 (e.g., optical infinity) associated with the virtual image-bearing light 128B to a second focal length FD2, the second focal length being shorter than the first focal length (e.g., less than optical infinity). 5, it should be appreciated that negative power optical element 132 may be formed as, but is not limited to, a plano-concave lens, a bi-concave lens, a negative meniscus lens, or any optical element that diverges incident light in a predictable manner to form at least one image whose focused distance to the viewer is reduced from its actual distance. In some embodiments, second focused distance FD2 is between 0.005 m and 6 m. In other embodiments, second focused distance FD2 is selected from the range of 0.005 m and 4 m.

[0039] As a result of placing a negative power optical element (e.g., negative power optical element 132) between image light guide 102 and eyebox E, virtual image-bearing light 128B is focused by viewer's eye 120 such that virtual object VO appears at a second focusing distance FD2 (shown in FIG. 5 by a dotted triangle). Here, second focusing distance FD2 is shorter than first focusing distance FD1 for eyebox E. Furthermore, when negative power optical element 132 is positioned between eyebox E and real-world object RWO, negative power optical element 132 also operates to diverge real-world image-bearing light 130A such that the focusing distance of any real-world object RWO is shortened, for example, from first focusing distance FD1 to second focusing distance FD2 (shown in FIG. 5 by a dotted star). Of course, real-world object RWO need not be located at a distance greater than 6 meters (20 feet), i.e., at an infinite focusing distance, to be affected by the negative light output contribution of the negative power optical element. For example, the perceived focusing distance of a real-world object RWO located at a finite focusing distance, e.g., 1-5 meters from the viewer, is also reduced. If the viewer wishes to view the virtual object VO at a closer focusing distance without changing the perception of distance to any real-world object RWO, then the negative light output contribution 134 of the negative power optical element 132 must offset the real-world image-bearing light 130A.

[0040] 6, this figure shows a simplified schematic plan view of one example configuration of the right-eye rim section 112 of image light guide system 100 having both a negative output optical element 132 and a positive output optical element 136, where the positive output optical element 136 is provided with a positive light output contribution 138 that offsets, cancels, or nullifies the negative light output contribution 134 of the negative output optical element 132 to an image formed from light reflected from a real-world object RWO in the environment. As shown, the positive output optical element 136 is positioned between the image light guide 102 and the real-world object RWO, i.e., on the opposite side of the image light guide 102 from the negative output optical element 132. The positive output optical element 136 operates to focus incident image-bearing light, increasing the apparent focused distance of any real-world object RWO. By positioning the positive output optical element 136 between the image light guide 102 and the real-world object RWO having an environment, before the real-world image-bearing light 130A reaches the image light guide 102 and / or the negative output optical element 132, the positive output optical element 136 increases the focal length of the real-world object RWO and offsets, cancels, or nullifies the reduction in the focal length of the image of the real-world object RWO caused by the negative output optical element 132. Of course, the positive output optical element 136 may be formed as at least a portion of the cover window 122, and / or the positive optical contribution 138 may be provided at least in part by the cover window 122.

[0041] In some embodiments, the negative light output contribution 134 and the positive light output contribution 138 are measured in diopters. In these embodiments, the diopter value of the negative output optical element 132 is equal to and opposite to the light output provided by the positive output optical element 134. For example, the negative light output contribution 134 may be selected as at least one of −0.5, −0.75, −1, −1.5, −2 diopters, etc. Thus, to preemptively offset the effect of this negative light output contribution 134 on the image of the real-world object RWO, the positive light output contribution 138 of the positive output optical element 136 is selected to be at least one of +0.5, +0.75, +1, +1.5, +2 diopters, such that the converging effect of the positive output optical element 136 and the diverging effect of the negative output optical element 132 are completely canceled out such that there is no net effect on the real-world position of the real-world object RWO as perceived by a viewer or other sensor positioned within the eyebox E. In other words, the net effect of providing a negative power optical element 132 between the image light guide 102 and the eyebox E, and a positive power optical element 136 between the image light guide 102 and the real-world object RWO in the environment (where the light output contributions of each optical element 132, 136 have the same magnitude and cancel each other out), is that the virtual object VO appears at a focal distance less than optical infinity, while the focal distance of the real-world object RWO remains unchanged.

[0042] As shown in FIG. 6, virtual image-bearing light 126 (shown in FIGS. 3 and 4) is outcoupled from image light guide 102 as substantially collimated virtual image-bearing light 128A. As virtual image-bearing light 128A refracts through negative power optic 132, the light diverges (shown as virtual image-bearing light 128B). Virtual image-bearing light 128B enters eyebox E and forms an image of virtual object VO at a second focusing distance FD2 (shown as a triangle formed by dotted lines in FIG. 6). Additionally, real-world image-bearing light 130A reflected from real-world object RWO in the environment propagates into image light guide system 100 and encounters positive output optic 136, which converges real-world image-bearing light 130A to form real-world image-bearing light 130B. In this example, positive output optic 136 may be formed with a positive light output contribution of +2 diopters. The real-world image-bearing light 130B is then transmitted through the image light guide 102 and encounters the negative output optical element 132, which has a negative light output contribution 134 of -2 diopters. As the real-world image-bearing light 130B refracts through the negative output optical element 132, the light diverges such that the net effect of the positive light output contribution 138 of the positive light output element 136 and the negative light output contribution 134 of the negative light output element 132 cancels out, and the real-world image-bearing light 130C is operable to form images of the real-world objects RWO at their true locations in the environment.

[0043] It should be understood that the embodiment described above with respect to +2 and −2 diopter values ​​is merely one example, and that in operation, image light guide system 100 may utilize any conceivable diopter setting for both negative light output contribution 134 and positive light output contribution 138. In some embodiments, these two diopter values ​​cancel each other out, with no net effect on the perceived focused distance of real-world object RWO. It should also be understood that, although shown schematically in FIG. 6 , positive output optical element 132 may be formed as, but is not limited to, a plano-convex lens, a bi-convex lens, a positive meniscus lens, or any optical element that converges incident light in a predictable manner to form at least one image with an increased focused distance from its actual distance to the viewer.

[0044] In addition to the foregoing, it may be desirable to correct for a particular viewer's optical aberrations associated with various refractive disorders, such as myopia (nearsightedness), hyperopia (farsightedness), or astigmatism. To that end, as shown in FIG. 7 , the image light guide system 100 may also include one or more corrective optical elements 140 that provide corrective optical contributions 142 to both the virtual image-bearing light 128 and the real-world image-bearing light 130. The corrective optical elements 140 may be configured as monofocal, bifocal, or multifocal optical elements, such as refractive lenses, diffraction gratings, holographic optical elements (HOEs), or any combination thereof. As such, the corrective optical elements 140 can provide spherical or cylindrical corrections specific to a particular observer.

[0045] As shown in FIG. 7, virtual image-bearing light 126 (shown in FIGS. 3 and 4 ) is outcoupled from image light guide 102 as substantially collimated virtual image-bearing light 128A. As virtual image-bearing light 128A refracts through negative power optical element 132, the light diverges (shown as virtual image-bearing light 128B). Virtual image-bearing light 128B continues toward eyebox E until it encounters and refracts corrective optical element 140. Corrective optical element 140 provides corrective optical contribution 142, which can be customized to offset the viewer's particular eye condition, e.g., myopia (nearsightedness). Corrected virtual image-bearing light 128C then operates to form one or more images of virtual object VO at a corrected distance CD. In an embodiment, if corrective optical element 140 is selected to correct myopia, corrective optical contribution 142 provides a negative light output, reducing the apparent distance to virtual object VO (shown as a black triangle in FIG. 7 ). It will also be appreciated that when the corrective optical contribution 142 of the negative output optical element 132 and the negative contribution of the negative light output contribution 134 are positioned in series, the negative output is combined and the virtual object VO appears at a corrected distance CD that appears closer to the viewer than the second focusing distance FD2.

[0046] Additionally, real-world image-bearing light 130A reflected off real-world object RWO in the environment propagates into image light guide system 100 and encounters positive output optical element 136, which converges real-world image-bearing light 130A forming real-world image-bearing light 130B. In this example, positive output optical element 136 may be formed with a positive light output contribution of +2 diopters. Real-world image-bearing light 130B is then transmitted through image light guide 102 and encounters negative output optical element 132, which has a negative light output contribution 134 of -2 diopters. As real-world image-bearing light 130B refracts through negative output optical element 132, the light is converged such that the net effect of the positive light output contribution 138 of positive light output element 136 and the negative light output contribution 134 of negative light output element 132 cancels out to form real-world image-bearing light 130C, which represents the true position of real-world object RWO in the environment. Real-world image-bearing light 130C continues to propagate toward eyebox E and encounters corrective optics 140. Continuing with the example above in which corrective optics 140 is selected to correct myopia (nearsightedness), corrective optics contribution 142 provides a negative light output, reducing the apparent distance to real-world object RWO (shown as a black star in FIG. 7). Not surprisingly, the negative output of corrective optics 140 operates to form an image in eyebox E of real-world object RWO at a corrected distance CD that appears closer to the viewer than the real-world object RWO's true location (e.g., first focusing distance FD1).

[0047] In some embodiments, FIGS. 8A-8B depict side views of an image light guide system 100 according to the present disclosure, and the corrective optical element 140 can be a multifocal optical element, such as a bifocal optical element ( FIG. 8A ) or a trifocal optical element ( FIG. 8B ). In FIG. 8A , for example, the image light guide system 100 can include a bifocal corrective optical element 140. As such, the bifocal corrective optical element 140 is comprised of multiple corrective sections 144A-144B. The first corrective section 144A and the second corrective section 144B (collectively referred to herein as “multiple corrective sections 144” or “corrective section 144”) are intended to be integral sections of a single corrective optical element. However, it should be understood that each corrective section 144 can be an individual optical element positioned adjacent to one another, as shown in FIG. 8A .

[0048] As shown, each correction section 144 provides a different correction light output than any adjacent correction section, such that the different light outputs properly focus images from objects at different distances to correct for optical aberrations of a particular viewer at each distance. For example, FIG. 8A shows two real-world objects RWO, RWO' present in an environment. The first real-world object RWO may be positioned farther away from the eyebox E than the second real-world object RWO'. For example, the first real-world object RWO may be positioned at a distance of more than 6 meters from the eyebox E, while the second real-world object RWO' may be positioned at a closer distance to the first real-world object RWO, e.g., 3 meters from the eyebox E.

[0049] With respect to the first real-world object RWO, light reflected from that object propagates as real-world image-bearing light 130A until it reaches positive output optic 136, where it converges to form real-world image-bearing light 130B. Real-world image-bearing light 130B continues to propagate through image light guide 102 and encounters negative output optic 132, where it diverges in a manner equal to or opposite to the converging effect of positive output optic 136 to form real-world image-bearing light 130C. Real-world image-bearing light 130C continues to propagate toward eyebox E until it encounters first corrector section 144A of bifocal corrector optic 140. Upon transmission through first correction section 144A, real-world image-bearing light 130C is formed into real-world image-bearing light 130D, which is used to form an image of real-world object RWO, e.g., appearing closer than the real-world object RWO's true location in the environment, i.e., at first corrected focusing distance 146. Additionally, light reflected from second real-world object RWO' propagates as real-world image-bearing light 130A' until it reaches positive output optic 136, where real-world image-bearing light 130A' converges to form real-world image-bearing light 130B'. Real-world image-bearing light 130B' continues to propagate through image light guide 102 and encounters negative output optic 132, where it diverges in a manner equal to or opposite to the converging effect of positive output optic 136, forming real-world image-bearing light 130C'. The real-world image-bearing light 130C' continues to propagate in the direction of the eyebox E until it encounters the second correction section 144B of the bifocal correction optics 140. Upon transmission through the second correction section 144B, the real-world image-bearing light 130C' is formed into a real-world image-bearing light 130D', which is used to form an image of the real-world object RWO' that appears closer than the real-world object RWO's true position in the environment, i.e., at the second corrected focusing distance 148, for example.

[0050] 8A , it should be understood that the first correction section 144A provides a first corrected light output, and the second correction section 144B provides a second corrected light output, where the first corrected light output is different (e.g., larger) than the second corrected light output. For example, if the correction output of the bifocal correction optics 140 is selected to correct myopia (nearsightedness), the change in focal distance between the true position of the real-world object RWO and the first focal distance 146 is greater than the change in focal distance between the true position of the real-world object RWO′ and the second focal distance 148. It should be understood that the light output of each correction section 144 may also be selected to correct other refractive disorders, such as hyperopia (farsightedness), in which case the light output of each correction section 144 is selected to have less (if any) effect on objects over 6 meters.

[0051] FIG. 8B shows a side view of image light guide system 100 according to the present disclosure, in which corrective optics 140 are trifocal optics. Real-world image-bearing lights 130A-130D (associated with real-world object RWO) and real-world image-bearing lights 130A'-130D' (associated with real-world object RWO') are similar to those described in connection with FIG. 8A. However, as shown in FIG. 8B, corrective optics 140 includes a third corrective section 144C that provides a third corrected light output that is different from the first corrected light output and the second corrected light output associated with first corrective section 144A and second corrective section 144B. Additionally, a third real-world object RWO'' is provided in the environment. Additionally, light reflected from third real-world object RWO'' propagates as real-world image-bearing light 130A'' until it reaches positive output optic 136, where real-world image-bearing light 130A'' converges to form real-world image-bearing light 130B''. Real-world image-bearing light 130B'' continues to propagate through image light guide 102 and encounters negative output optic 132, where it diverges in a manner equal to or opposite to the converging effect of positive output optic 136 to form real-world image-bearing light 130C''. Real-world image-bearing light 130C'' continues to propagate toward eyebox E until it encounters third corrective section 144C of trifocal corrective optic 140. Upon transmission through the third correction section 144C, the real-world image-bearing light 130C'' is formed into real-world image-bearing light 130D'', which is used to form an image of the real-world object RWO'' that appears, for example, closer than the true position of the real-world object RWO'' in the environment, i.e., at the third corrected focusing distance 150.

[0052] 8A-8B illustrate the effect of multifocal corrective optics 140 on real-world image-bearing light 130A-130D, 130A'-130D', and 130A''-130D'', and, for clarity of illustration only, do not illustrate the effect of multifocal corrective optics 140 on virtual image-bearing light 128. However, it should be understood that the effects described above with respect to real-world image-bearing light 130B-130D, 130B'-130D', and 130B''-130D'' may equally be applied to virtual image-bearing light 128 before it enters eyebox E.

[0053] As illustrated in FIG. 9 , it should be appreciated that correction optics 140 may be positioned between image light guide 102 and real-world objects RWO, RWO′, and RWO″. For example, with respect to a first real-world object RWO, light reflected from that object propagates as real-world image-bearing light 130A until it reaches correction optics 140, where real-world image-bearing light 130A encounters first correction section 144A to form real-world image-bearing light 130B. Real-world image-bearing light 130B continues to propagate until it reaches positive output optics 136, where the light converges to form real-world image-bearing light 130C. Real-world image-bearing light 130C continues to propagate through image light guide 102 and encounters negative output optics 132, where it diverges in a manner equal to or opposite to the converging effect of positive output optics 136 to form real-world image-bearing light 130D. After transmitting through negative power optic 132, real-world image-bearing light 130D continues into eyebox E and is used to form an image of real-world object RWO, e.g., appearing closer than the real-world object RWO's true location in the environment, i.e., at first corrected focusing distance 146. Additionally, light reflected from second real-world object RWO' propagates as real-world image-bearing light 130A' until it reaches correcting optic 140, where real-world image-bearing light 130A' encounters second correcting section 144B and forms real-world image-bearing light 130B'. Real-world image-bearing light 130B' continues to propagate until it reaches positive power optic 136, where the light converges to form real-world image-bearing light 130C'. Real-world image-bearing light 130C' continues to propagate through image light guide 102 and encounters negative output optic 132, where it diverges in a manner equal to or opposite to the focusing effect of positive output optic 136 to form real-world image-bearing light 130D'. After transmitting through negative output optic 132, real-world image-bearing light 130D' continues into eyebox E and is used to form an image of real-world object RWO', e.g., appearing closer than the real-world object RWO's true location in the environment, i.e., at second corrected focusing distance 148.As shown, it should be appreciated that the positive power optical element 136 and the corrective optical element 140 may be formed as a single multi-function optical element 152, as described below.

[0054] It should be appreciated that while shown as two or three integrated correction sections, i.e., correction sections 144A-144C, correction optic 140 may include more than two correction sections 144. For example, correction optic 140 may include four, five, ten, fifteen, twenty, thirty, or more correction sections. Multiple correction sections 144 may provide seamless transitions between correction sections 144, with each correction section 144 operating to focus the image formed in the viewer's eye at a different focusing distance.

[0055] FIG. 10 shows a planar schematic view of a portion of an exemplary head-mounted image light guide system 100 according to the present disclosure. As shown, the image light guide system 100 may include at least one multifunction optical element 152 configured to perform the functions of one or more of the optical elements described above. In the example shown in FIG. 10 , the negative power optical element 132 and the corrective optical element 140 are formed as a single multifunction optical element 152 arranged to perform the functions of both optical elements 132, 140, as described above. As shown, the single multifunction optical element 152 may be formed as a doublet lens positioned between the image light guide 102 and the eyebox E and includes both the light output contributions of the corrective optical element 140 (e.g., the corrective optical contribution 142) and the negative light output contribution 134 of the negative power optical element 132. It should be appreciated that the multifunction optical element 152 may also be arranged to perform the functions of the positive power optical element 136 and the corrective optical element 140. This single multifunction optical element 152 can be formed as a doublet lens positioned between the image light guide 102 and the real-world object RWO and includes both light output contributions of the corrective optical element 140 (e.g., the corrective optical contribution portion 142) as well as the positive light output contribution 138 of the positive output optical element 136.

[0056] Furthermore, as shown schematically in Figures 7-9, it will be appreciated that corrective optic 140, negative power optic 132, and positive output optic 136 may be separate optical elements separated by air or other medium. For example, negative power optic 132 and corrective optic 140 may be separate lenses positioned between image light guide 102 and eyebox E, as shown in Figures 7-8B. Alternatively, positive power optic 136 and corrective optic 140 may be separate lenses positioned between image light guide 102 and real-world object RWO, as shown in Figure 9.

[0057] 11 , the right eye rim section 112 can further include a removable lens carrier 154 positioned between the nose bridge section 116 and the right temple 114, configured to be removably engaged or disengaged with the right eye rim section 112 using an additional tool. Furthermore, in each of the above configurations, each of the above lenses can be configured to be placed into and removed from a respective slot in the lens carrier 154 such that each lens is removable and / or replaceable. By having the lens carrier 154 as well as the lenses themselves removable from the image light guide system 100, a viewer can easily customize the light output contribution of each lens to customize their viewing experience to compensate for their particular optical aberrations.

[0058] 12 , the image light guide system 100 may include one or more electromagnetic metamaterials engaged with or embedded within one or more surfaces of the image light guide system 100. For example, metamaterials may be formed on or embedded within one or both surfaces of (i) the front surface 104 of the image light guide 102, (ii) the back surface 106 of the image light guide 102, and (ii) the cover window or protective outer cover 122 to form one or more electromagnetic metasurfaces. Accordingly, one or more optical elements within the scope of the present disclosure, such as the negative power optical element 132, the positive power optical element 136, or the corrective optical element 140, may be formed from an optically translucent structure, such as the image light guide 102, that includes one or more metamaterials configured to converge, diverge, or correct, respectively, image-bearing light passing through the optically translucent structure. Of course, the material properties of the metamaterial can be selected from any material having subwavelength structures configured to mimic the optical properties of a lens, e.g., concave, convex, or other optical element, without requiring that the surfaces of the optical structures be curved. In other words, while the image light guide 102 and / or protective outer layer 122 disclosed in this disclosure may include flat surfaces, a metamaterial disposed on one or more surfaces of these structures may cause light rays and / or electromagnetic wavefronts associated with light passing through these features to behave as if they were passing through a shaped lens.

[0059] FIG. 12 illustrates one exemplary embodiment of a portion of an image light guide system 100 that includes one or more metamaterials instead of a lens. In this example, rather than a lens, a linear grating structure, or a holographic optical element (HOE), the image light guide system 100 provides the negative light output contribution 134, the positive light output contribution 138, or the aforementioned corrective light output contribution 142. As shown in FIG. 12 , in one embodiment, the image light guide system 100 includes a first metamaterial 156 located on or embedded within the inner surface 104 of the image light guide 102 and a second metamaterial 158 located on or embedded within the outer surface 106 of the image light guide 102. As shown, the first metamaterial 156 is configured to diverge the virtual image-bearing light 128 and the real-world image-bearing light 130, and is therefore operable to provide the negative light output contribution 134. The second metamaterial 158 is configured to focus the real-world image-bearing light 130, and is therefore operable to provide the positive light output contribution 138. Of course, as with other exemplary embodiments described herein, the diopter values ​​of the negative light output contribution 134 and the positive light output contribution 138 can be equal and opposite so that they cancel each other out with respect to real-world image-bearing light 130.

[0060] In the example shown in FIG. 12 , virtual image-bearing light 126 (shown in FIGS. 3 and 4 ) propagates within image light guide 102 via TIR and is outcoupled from image light guide 102 as substantially collimated virtual image-bearing light. Upon outcoupling from image light guide 102, virtual image-bearing light 128 engages first metamaterial 156, which has a negative light output contribution 134. Upon transmitting through first metamaterial 156, the light diverges (shown as virtual image-bearing light 128B) and enters eyebox E, forming an image of virtual object V O at a second focusing distance FD2 (shown as a triangle formed by dotted lines in FIG. 12 ). Additionally, real-world image-bearing light 130A reflected from real-world object RWO in the environment propagates into image light guide system 100 and encounters second metamaterial 158, which converges real-world image-bearing light 130A forming real-world image-bearing light 130B. In this example, the positive light output contribution 138 of the second metamaterial 158 is selected as +2 diopters. The real-world image-bearing light 130B is then transmitted through the image light guide 102 and encounters the first metamaterial 156, which has a negative light output contribution 134 of -2 diopters. As the real-world image-bearing light 130B refracts through the first metamaterial 156, the light is focused such that the net effect of the positive light output contribution 138 of the second metamaterial 158 and the negative light output contribution 134 of the first metamaterial is canceled, and the real-world image-bearing light 130C is operable to form images of real-world objects RWO at their true locations in the environment.

[0061] It should be appreciated that at least one of first metamaterial 156 and second metamaterial 158 may also include an optical structure or configuration that operates to provide corrective optical contribution 142. That is, it should be appreciated that either (i) first metamaterial 156 can provide both negative light output contribution 134 and corrective optical contribution 142, (ii) second metamaterial 158 can provide both positive light output contribution 138 and corrective optical contribution 142, or (iii) first metamaterial 156 can provide both negative light output contribution 134 and a portion of corrective optical contribution 142, while second metamaterial 158 can provide both positive light output contribution 138 and a portion of corrective optical contribution 142. It should also be appreciated that one or both of first metamaterial 156 and second metamaterial 158 can include one or more corrective sections 144A-144C, as described above in connection with FIGS. 8A-8B , and thus can provide multifocal correction capabilities.

[0062] It will also be appreciated that first metamaterial 156 and / or second metamaterial 158 may be located on or embedded in one or more surfaces of protective outer cover 122 rather than, or in addition to, being located on or embedded in image light guide 102. It will further be appreciated that first metamaterial 156 and / or second metamaterial 158 may be disposed on or embedded in a standalone optical component, such as a transparent or semi-transparent planar substrate, positioned between eyebox E and image light guide 102 and / or between the image light guide and real-world object RWO.

[0063] In an exemplary embodiment, as shown in FIG. 13A , light guide system 100 includes first corrective optical element 140 (i.e., a corrective optical element providing a spherical correction, e.g., a spherical or hemispherical lens), image light guide 102 having at least incoupling optical element IDO and outcoupling optical element ODO, and second corrective optical element 180 (i.e., a corrective optical element providing a cylindrical correction, e.g., a cylindrical lens). For example, incoupling optical element IDO, any intermediate optical element TO, and outcoupling optical element ODO may be any combination of volume holograms, holographic polymer dispersed liquid crystals (HPDLC), diffractive surface relief gratings, partially reflective surfaces, prisms, diffractive polarization gratings, or other liquid crystal (LC)-formed grating structures. First corrective optical element 140 is disposed between image light guide 102 and real-world object RWO. For example, light reflected from real-world object RWO propagates as real-world image-bearing light 130A until it reaches first corrective optics 140, where real-world image-bearing light 130A forms real-world image-bearing light 130B. Real-world image-bearing light 130B continues to propagate through image light guide 102 and encounters second corrective optics 180, where real-world image-bearing light 130B forms real-world image-bearing light 130C. After transmitting through second corrective optics 180, real-world image-bearing light 130C continues into eyebox E and forms an image of real-world object RWO that appears closer than the real-world object RWO's true location in the environment, and is used to correct for certain viewer optical aberrations, such as astigmatism. In some embodiments, first corrective optics 140 may be configured as at least a portion of cover window 122 (shown in FIGS. 4-12, 13B, and 13C).

[0064] Continuing with FIG. 13A , in the exemplary embodiment, outcoupling optics ODO are configured to provide spherical correction to virtual image-bearing light 128 outcoupled toward eyebox E (i.e., outcoupling optics ODO provides refractive power). Spherically corrected virtual image-bearing light 128A is outcoupled from image light guide 102 and propagates to second corrective optics 180. As virtual image-bearing light 128A refracts through second corrective optics 180, the light converges or diverges and propagates toward eyebox E as virtual image-bearing light 128B. Second corrective optics 180 provides a corrective optical contribution that the viewer can customize to offset the viewer's particular asymmetric ocular condition, e.g., astigmatism. The corrected virtual image-bearing light 128B operates to form one or more images of virtual object VO at a corrected distance, corrected for the viewer's particular condition. In embodiments in which second corrective optics 180 is selected to correct for parallax, the corrective optics contribution provides an asymmetric optical output about the planar axis of the second corrective optics that operates to correct for the parallax of a particular viewer. In this embodiment, real-world image-bearing light 130 and virtual image-bearing light 128 are spherically and cylindrically corrected, respectively.

[0065] 13B-13D, first corrective optics 140, image light guide 102, and second corrective optics 180 are positioned side-by-side and adjacent to one another to form a substantially stacked configuration. In an exemplary embodiment, first corrective optics 140 may be eyeglasses that provide spherical correction to real-world image-bearing light 130. When positioned between image light guide 102 and a real-world object, first corrective optics 140 may be configured to provide the functionality of protective cover window 122. As such, cover window 122 may include one or more coatings, such as a scratch-resistant coating or an anti-reflective coating, on its interior or exterior surfaces. In an exemplary embodiment, the illustrated stacked configuration is a first stacked configuration optically coupled to a user's right eye, and a second stacked configuration optically coupled to the user's left eye to form a substantially binocular image light guide system. In such a binocular imaging light guide system, first corrective optic 140, outcoupling optic ODO, and second corrective optic 180 are aligned to a particular user's interpupillary distance (IPD). With continued reference to FIG. 13D , alignment point AP of first corrective optic 140 is schematically illustrated as overlapping with at least a portion of outcoupling optic ODO of imaging light guide 102. When assembled, the optical centers of first corrective optic 140 and / or second corrective optic 180 are configured to align with alignment point AP that overlaps with the outcoupling diffractive optic and are selected based on a particular user's interpupillary distance (IPD). Alignment of first corrective optical element 140, second corrective optical element 180, and alignment point AP is necessary to prevent or limit two-dimensional shifting of real-world image-bearing light 130 (e.g., causing double images and / or eye distortion) and two-dimensional shifting of virtual image-bearing light 128 (e.g., causing double images and / or eye distortion) in binocular image light guide system 100. In one or more embodiments, sealing members may be disposed around and / or between various components within a given stacked arrangement to prevent or limit the amount of contamination from external elements from interfering with the optical function of one or more elements of the stack.

[0066] 13E, light guide system 100 includes a first corrective optical element 140 (e.g., a spherical or hemispherical lens) and an image light guide 102 having at least an incoupling optical element IDO and an outcoupling optical element ODO. First corrective optical element 140 is disposed between image light guide 102 and real-world object RWO. For example, light reflected from real-world object RWO propagates as real-world image-bearing light 130A until it reaches first corrective optical element 140, where real-world image-bearing light 130A forms real-world image-bearing light 130B. Real-world image-bearing light 130B continues to propagate through image light guide 102 into eyebox E and is used, for example, to form an image of real-world object RWO closer than the real-world object RWO's true location in the environment.

[0067] Continuing with FIG. 13E , outcoupling optic ODO is configured to provide spherical and / or cylindrical correction to virtual image-bearing light 128 outcoupled toward eyebox E (i.e., outcoupling optic ODO provides refractive power). Spherically and / or cylindrically corrected virtual image-bearing light 128A is outcoupled from image light guide 102 and propagates toward eyebox E as virtual image-bearing light 128B. Outcoupling optic ODO configured to provide both spherical and cylindrical correction to virtual image-bearing light 128 may be referred to in this disclosure as providing a combined light output contribution. In this embodiment, real-world image-bearing light 130 and virtual image-bearing light 128 are each spherically corrected, and virtual image-bearing light 128 is cylindrically corrected and / or spherically corrected.

[0068] To provide spherical correction to the outcoupled virtual image-bearing light 128, each of the angularly related beams of image-bearing light 128A is no longer collimated, i.e., diverges from a point at infinity, but instead appears to diverge or converge from a point located much closer to or farther away from the image light guide 102. One mechanism for converting the dimensions of the collimated image-bearing light 128 propagating along the image light guide 102 into multiple diverging beams representing near-focus positions in the virtual image is shown in FIG. 14A as a stepped, chirped outcoupling diffractive optical element ODO. The grating vector k5 extends parallel to the x-axis, in a direction opposite to the direction along which the collimated image-bearing light 128 propagates. The period d of the diffractive features of the outcoupling diffractive optical element ODO increases in steps along the same propagation direction. Because the angle through which a given beam of image-bearing light 128 is diffracted is inversely proportional to the period d of the diffractive feature, the angle through which the collimated beam is diffracted decreases with successive encounters of the collimated beam along the stepped chirped outcoupling diffractive optical element ODO. At the beginning of the outcoupling grating ODO, where the collimated beam is first encountered, the period d is relatively short so that the diffraction angle increases, and at the end of the outcoupling diffractive optical element ODO, the period d is relatively long so that the diffraction angle decreases. The stepped chirped diffractive feature applies cylindrical power to the outcoupling diffractive optical element ODO.

[0069] 14B , in an exemplary embodiment, image light guide system 100 includes left-eye image light guide 102A and right-eye image light guide 102B that are disposed at a “chevron” angle φ with respect to imaginary horizontal axis A1. Chevron angle φ may also be referred to as a “rake” angle in this disclosure. Left-eye image light guide 102A includes an incoupling diffractive optical element IDOA and an outcoupling diffractive optical element ODOA disposed along surface 104 of image light guide 102A. It will be understood that at least one of incoupling diffractive optical element IDOA and outcoupling diffractive optical element ODOA may be disposed along surface 106 of image light guide 102A as an alternative configuration. Similarly, right-eye image light guide 102B includes an incoupling diffractive optical element IDOA and an outcoupling diffractive optical element ODOA disposed along surface 104 of image light guide 102B. It will be appreciated that at least one of the incoupling diffractive optical element IDOA and the outcoupling diffractive optical element ODOA may alternatively be disposed along the surface 106 of the image light guide 102B.

[0070] The image-bearing light beams 128AL, 128AR are emitted by the outcoupling diffractive optical elements ODOA, ODOB from surface 104 in the same direction as the image-bearing beam WI is incident on the incoupling diffractive optical elements IDOA, IDOB at an exit angle 36 equal to the incidence angle 30, causing the image-bearing light beams WI and 128AL, 128AR to be parallel in angle space. Figure 14B shows a configuration in which an image-bearing light beam WI incident on surface 106 at an incidence angle 30 of one hundred degrees (100°) relative to surface 106 generates image-bearing light beams 128AL, 128AR that are emitted from surface 104 at an exit angle 36 of one hundred degrees (100°) relative to surface 104. As shown in Figure 14B, the incidence angle 30 and the exit angle 36 are equal relative to surfaces 106 and 104.

[0071] It will be appreciated that the horizontal angular relationship of the incoming image-bearing light WI and the output image-bearing light beams 128AL, 128AR is independent of the alignment and orientation of the image light guides 102A, 102B. For example, changing the angle φ does not cause any angular change in the output image-bearing light beams 128AL, 128AR. As such, the angle φ may be selected based on one or more of form factor, ergonomics, aesthetics, and system size.

[0072] Referring now to FIG. 14C, in an exemplary embodiment, the incoupling diffractive optical elements IDOA, IDOB are configured as clouding gratings or clouding diffractive features. The pitch of the outcoupling diffractive optical elements ODOA, ODOB is configured to angle the output image-bearing light beams 128AL, 128AR to change the relative alignment / orientation of the incoupling image-bearing light beams and the output image-bearing light beams 128AL, 128AR. Changing the alignment of the output image-bearing light beams 128AL, 128AR changes the convergence point of the virtual object carried by the output image-bearing light beams 128AL, 128AR at infinity. In an exemplary embodiment, the convergence point is not so close to the eyebox as to create convergence containment issues (e.g., the convergence point may vary from infinity to 1-4 meters or 3-4 meters from the eyebox). By varying the pitch of the outcoupling diffractive optical elements ODOA, ODOB as described, the grating vectors of the incoupling diffractive optical elements IDOA, IDOB and the respective diffractive features in the outcoupling diffractive optical elements ODOA, IDOB do not sum to zero (i.e., the grating vectors do not form triangular vector diagrams that sum to zero). For example, the grating vectors of the outcoupling diffractive optical elements are configured such that the grating vectors do not sum to zero.

[0073] 14D , in an exemplary embodiment, the left-eye image light guide 102A and the right-eye image light guide 102B described in FIG. 14C may be replaced with a single planar image light guide 102 including incoupling diffractive optical elements IDOA, IDOB and outcoupling diffractive optical elements ODOA, ODOB disposed along at least one of surfaces 104 or 106 of the image light guide 102. In an exemplary embodiment, the incoupling diffractive optical elements IDOA, IDOB may be replaced with a single incoupling diffractive optical element IDO configured to direct substantially 50% of the incoupling image-bearing light to each of the outcoupling diffractive optical elements ODOA, ODOB. For example, the diffractive features of the incoupling diffractive optical element IDO may be a symmetrically tilted grating.

[0074] 14E, in an exemplary embodiment, the pitch of the outcoupling diffractive optical elements ODOA, ODOB is configured to angle the output image-bearing light beams 128AL, 128AR to change the relative alignment of the incoupled image-bearing light beams and output image-bearing light beams 128AL, 128AR with the outcoupling diffractive optical elements ODOA, ODOB, and the outcoupling diffractive optical elements ODOA, ODOB have a zone-segmented pattern with an angular change between linear diffractive features between zones along one dimension of the outcoupling optics, configured to change the focal plane of the output image-bearing light beams 128AL, 128AR, as described above. For example, when bringing vergence to a point within 1 meter or 1-3 meters of the eyebox E, the image light guide system benefits from changing the focal plane of the virtual object by adding refractive power to the outcoupling diffractive optical elements ODOA, ODOB, e.g., to reduce eye strain.

[0075] 14F, in an exemplary embodiment, the left-eye image light guide 102A and the right-eye image light guide 102B described in FIG. 14E may be replaced with a single planar image light guide 102 including incoupling diffractive optical elements IDOA, IDOB and outcoupling diffractive optical elements ODOA, ODOB disposed along at least one of surfaces 104 or 106 of the image light guide 102. In an exemplary embodiment, the incoupling diffractive optical elements IDOA, IDOB may be replaced with a single incoupling diffractive optical element IDO configured to direct substantially 50% of the incoupling image-bearing light to each of the outcoupling diffractive optical elements ODOA, ODOB. For example, the diffractive features of the incoupling diffractive optical element IDO may be a symmetrically tilted grating.

[0076] 14G, in an exemplary embodiment, rather than configuring the pitch of the outcoupling diffractive optical elements ODOA, ODOB to change the relative angular alignment of the incoupled image-bearing light beams and output image-bearing light beams 128AL, 128AR, optical wedges 300A, 300B may be used to change the relative angular alignment of the incoupled image-bearing light beams and output image-bearing light beams 128AL, 128AR to change the convergence point of the virtual object conveyed by the output image-bearing light beams 128AL, 128AR. For example, optical wedge 300A may be positioned between image light guide 120A and real-world object RWO and between incoupling diffractive optical element IDOA and image source 18, and optical wedge 300B may be positioned between image light guide 120A and eyebox E. Although FIG. 14G illustrates only image light guide 120A and corresponding optical wedges 300A, 300B, it will be understood that a binocular system may also utilize image light guide 120B and corresponding optical wedges 300A, 300B disposed for the other eye.

[0077] Considered in the xz plane, the gradual adjustment of the period d along the x-axis length of the outcoupling diffractive optical element ODO provides for diffracting a representative collimated beam through progressively varying diffraction angles so that the light appears to emanate from a near focal point f. Also, other angle-related beams of image-bearing light WG successively encounter the outcoupling diffractive optical element ODO and are diffracted by progressively different diffraction angles, so that the light from each of these beams, with its respective angular content, appears to emanate from a different near focal point elsewhere in the common focal plane.

[0078] Another mechanism for converting the different dimensions of the collimated image-bearing light beam 128 propagating along the image light guide 102 into diverging beams representing near-focus positions within the virtual image is shown in FIG. 15, which shows a portion of an outcoupling diffractive optical element ODO exhibiting a zone-segmented pattern with angular variations between zones generally along the y-axis dimension of the diffractive optical element. For simplicity, the period d along the x-axis is held constant to emphasize the effect of step variations in the angular orientation of the diffractive features. Referring to FIG. 15, the outcoupling diffractive optical element ODO may be configured to include linear diffractive features 182 that form continuous, convoluted segments of a curve. When measured relative to the y-axis, the angle φ of the linear diffractive features 182 varies stepwise along the y-axis as the chord of the continuous curve. The linear diffractive features 182 angularly deviate from the y-axis orientation in a stepwise manner with distance from a centerline 184 of the outcoupling diffractive optical element ODO along the x-axis, but the angular deviation varies at marks on either side of the centerline 184. The gradual redirection of the angle-related beams 128 in the y-z plane can be achieved by changing the angle φ of the diffractive features in the x-y plane of the image light guide 102. Instead of diffracting individual beams of image-bearing light 128 through different angular progressions encountering successive outcoupling diffractive optical elements ODO, the beams of image-bearing light 128 are diffracted through progressions of angle β in the y-z plane as a function of position along the y-axis. Thus, when considered in the y-z plane, each of the angle-related beams of image-bearing light 128A appears to emanate from a unique near focus point f.

[0079] FIG. 16 shows, in simplified schematic form, a portion of an outcoupling diffractive optical element ODO divided into a two-dimensional array of zones Z, which combine a graduated variation in pitch along the x-axis dimension of the array with a graduated variation in the orientation of the diffractive features in the y-axis dimension of the array. Each of the zones Z includes a set of linear diffractive features that extend parallel to one another and have equal pitch. However, successive zones along the x-axis dimension of the array, referred to as rows in the array, have respective sets of parallel diffractive features that extend in the same direction but have different periods d (i.e., different pitches). Successive zones along the y-axis dimension of the array, referred to as columns in the array, have respective sets of parallel diffractive features that extend in progressively different directions through an angle φ.

[0080] Each of the zones Z, numbered Z1 through Z12 in Figure Z16, has a parallelogram shape with parallel upper and lower sides spaced apart by a distance corresponding to the length of the linear diffraction features 182, and with parallel right and left sides spaced apart by a distance corresponding to the product of the number of linear diffraction features 182 and the period d of each of the evenly spaced linear diffraction features 182.

[0081] The linear diffraction features 182 within each zone Zn extend parallel, and the linear diffraction features 182 within each of the zones in a column also extend parallel. Thus, the lattice vectors k of the zones in each column extend parallel. However, within each column, the pitch (period d) gradually changes in steps between the zones in each column. Thus, the magnitude of the lattice vector k gradually changes along each row. For example, the lattice vectors k1, k2, and k3 of consecutive zones Z1, Z2, and Z3 in the same column all extend in the same direction but at different lengths. Similarly, the lattice vectors K4, k5, and k6 of consecutive zones Z4, Z5, and Z6 extend in the same direction but at different lengths. A similar observation can be made between the lattice vectors of zones Z7, Z8, and Z9 and zones Z10, Z11, and Z12 in the other illustrated columns.

[0082] Within each row of zones, the grating vectors gradually change angular orientation in steps through the angle φ. While the displacement between linear diffractive features 182 in the x-axis direction remains constant between zones within each row, the pitch itself varies as the product of the x-axis displacement and the cosine of the angle φ. Thus, the angular orientations of grating vectors k1, k4, k7, and k10 change stepwise through the angle φ between successive zones Z1, Z4, Z7, and Z10 of the row, and the magnitudes of these grating vectors k1, k4, k7, and k10 vary as a function of the constant x-axis displacement of the diffractive features within the row and the cosine of the angle φ. Similar observations can be made between the grating vectors of zones Z2, Z5, Z8, and Z11 and zones Z3, Z6, Z9, and Z12 of the other illustrated rows.

[0083] The zones in each row include upper and lower boundaries that are all aligned parallel to a common axis, i.e., the x-axis, but the zones in each row are aligned along a respective arc. For example, the zones along two rows of the outcoupling diffractive optical element ODO are shown aligned with a circular arc. Each linear diffractive feature 182 segment extending between the upper and lower boundaries of a zone can be considered an arc along an arc. The arcs in different rows within the outcoupling diffractive optical element ODO share the same curvature and are distinguished by different offsets along the x-axis. Although the parallel linear diffractive features 182 between adjacent zones within each row are oriented in different directions, the shared x-axis displacement of the diffractive features in adjacent zones within each row allows the parallel diffractive features of adjacent zones to abut precisely. Thus, the effective forward surfaces of the linear diffractive features 182 in each zone of a row intersect with the effective forward surfaces of the linear diffractive features 182 in an adjacent zone in the same row, and the effective rearward surfaces of the linear diffractive features 182 in each zone of a row intersect with the effective rearward surfaces of the linear diffractive features 182 in an adjacent zone in the same row. The included angle between the linear diffractive features 182 at each intersection is the complement of the angular difference between the angular orientations of the diffractive features in adjacent zones of the row. Thus, the linear diffractive features 182 in each row form a topological representation of a circular arc. The upward arcs of these arcs are offset between the rows of zones, but share the same curvature and are therefore not concentric.

[0084] The zones differ from one another in at least one of pitch and orientation, but the pitch and orientation within any given zone remain constant. Thus, each zone can be easily replicated and matched to its neighboring zones that differ only in pitch and orientation, the zones in each row share the same orientation, and the zones in each row share the same x-axis displacement between the linear diffractive features 182.

[0085] In an exemplary embodiment, to achieve cylindrical correction using the outcoupling optical element ODO, the zones are configured asymmetrically. For example, the zones are configured to provide optical power along one axis of the outcoupling diffractive optical element ODO. The image-bearing light beam is effectively redirected by the zones from a parallel orientation to a series of convergent points along an imaginary line / axis. In an outcoupling optical element ODO that provides both spherical and cylindrical correction, the zones may be configured to provide a first optical power along one axis and a second optical power along an orthogonal axis.

[0086] In another exemplary embodiment, FIG. 17 illustrates, in simplified schematic form, a portion of an outcoupling diffractive optical element ODO having a first set of diffractive features 186 and a second set of diffractive features 188. The first set of diffractive features 186 may be optimized to not couple out a first wavelength range of light (e.g., blue light), and the second set of diffractive features 188 may be optimized to outcouple a second wavelength range of light (e.g., red light). In an exemplary embodiment, the first and second sets of diffractive features 186 and 188 at least partially overlap and are curved (i.e., curved) or approximated curves with linear segments, as described above, to introduce optical power. In an exemplary embodiment, the first set of diffractive features 186 are chirped in a first direction, meaning that the diffractive features 186 have a pitch d1 that gradually increases in one direction (i.e., the direction opposite to the direction of the grating vector k4). In an exemplary embodiment, the second set of diffractive features 188 are chirped in a second direction different from the first direction. For example, the second set of diffractive features 188 include a pitch d2 that gradually increases in pitch in the second direction (i.e., the direction opposite to the direction of the grating vector k5). In an exemplary embodiment, the pitch progression of the second set of diffractive features 188 is equal to the pitch progression of the first set of diffractive features 186. In other exemplary embodiments, the pitch progression of the second set of diffractive features 188 is not equal to the pitch progression of the first set of diffractive features 186.

[0087] Continuing with reference to FIG. 17 , the outcoupling diffractive optical element ODO may be divided into a two-dimensional zone array, e.g., zones Z1-Z12. Each of the zones Z1-Z12 includes a set of linear diffractive features 186, 188 that extend parallel to one another and have equal pitches within the respective zones Z1-Z12. For example, zone Z1 includes diffractive features 186 with a pitch d1 and diffractive features 188 with a pitch d2. In an exemplary embodiment, pitch d1 is equal to pitch d2. In other exemplary embodiments, pitch d1 is not equal to pitch d2. In an exemplary embodiment, each zone has the form of a diffractive optical element with crossed linear diffractive features.

[0088] Diffractive features 186 exhibit a stepped variation in pitch d1 along the x-axis dimension of the array, referred to as a column. Thus, in one example, the pitch d1 of zone Z1 is greater than the pitch d1 of zone Z2, which is greater than the pitch d1 of zone Z3. In addition to its ordinary meaning to one skilled in the art, the term "stepped variation" is intended to describe a situation in which the common pitch (e.g., pitch d1) between diffractive features of the same zone is constant, but the common pitch d1 of each successive zone along the x-axis dimension of the array varies, e.g., increases or decreases. Furthermore, diffractive features 186 include the same (e.g., constant) curvature / grating orientation along the x-axis, i.e., diffractive features 186 exhibit the same grating vector k4 across zones Z1-Z3. D (i.e., the angle of the diffractive features 186 is the same across zones Z1-Z3, and the diffractive features 186 are parallel to one another across zones Z1-Z3). This same behavior occurs for the diffractive features 186 across the x-axis throughout the array. The diffractive features 186 exhibit a gradual variation in pitch d1, e.g., decreasing with each successive zone across zones Z4-Z6, with a constant lattice vector k4 C The diffraction feature 186 shows a stepwise variation in pitch d1, decreasing with each successive zone across zones Z7-Z9, with a constant lattice vector k4 B The diffraction feature 186 shows a stepwise variation in pitch d1, which decreases with each successive zone across zones Z10-Z12, with a constant lattice vector k4 AThe diffractive features 186 exhibit a gradual variation of the grating vector along the y-axis dimension of the array, referred to as the column. That is, the diffractive features 186 of each zone within the column include a set of parallel diffractive features with a common pitch d1 that extend in progressively different directions through an angle φ. As shown, the angles of the diffractive features 186 and their grating vector k4 A , k4 B , k4 C , k4 D is different for each of zones Z1, Z4, Z7, and Z10. For example, while diffractive feature 186 is linear in each zone, diffractive feature 186 approximates a curve in the y-axis dimension. Similarly, diffractive feature 186 exhibits a gradual change in direction for the row that includes zones Z2, Z5, Z8, and Z11, and the row that includes zones Z3, Z6, Z9, and Z12.

[0089] It should be understood that the grating vector k4 of the diffractive feature 186 may increase in magnitude in the x-axis dimension as the pitch d1 decreases (i.e., k=2π / Λ). Thus, the grating vector k4 D The magnitude of lattice vector k5 increases in a stepwise manner across zones Z1-Z3. Similarly, in some embodiments, C increases in magnitude in a stepwise manner across zones Z4 to Z6, and the lattice vector k5 B increases in magnitude in a stepwise manner across zones Z7–Z9, and the lattice vector k5 A increases in magnitude in a stepwise manner across zones Z10 to Z12.

[0090] Diffractive features 188 exhibit a gradual variation in pitch d2 along the y-axis dimension of the array (i.e., column). Thus, the pitch d2 of zone Z1 is greater than the pitch d2 of zone Z4, which is greater than the pitch d2 of zone Z7, which is greater than the pitch d2 of zone Z10. In addition to its ordinary meaning to those skilled in the art, the term gradual variation is intended to describe that the common pitch d2 within each zone is constant within the zone, but the pitch varies, e.g., increases or decreases, in each successive zone along the y-axis dimension of the array. Diffractive features 188 include the same curvature / grating orientation along the y-axis, i.e., diffractive features 188 exhibit the same grating vector k5 across zones Z1, Z4, Z7, and Z10. A (i.e., the angle of the diffractive features 188 is the same across zones Z1, Z1, Z4, Z7, and Z10, and therefore the diffractive features 188 are parallel to one another across zones Z1, Z1, Z4, Z7, and Z10). This same behavior occurs for the diffractive features 188 across the y-axis throughout the array. The diffractive features 188 exhibit a step variation in pitch d2, decreasing with each successive zone across zones Z2, Z5, Z8, and Z11, with a constant lattice vector k5 B Diffraction feature 188 shows a stepwise variation in pitch d2, decreasing with each successive zone across zones Z3, Z6, Z9, and Z12, with a constant lattice vector k5 C diffractive features 188 exhibit a gradual variation in grating vector along the x-axis dimension (i.e., row) of the array. That is, the diffractive features 188 in each zone of the column include a set of parallel diffractive features d2 with the same pitch that extend in progressively different directions through an angle φ. As shown, the angles of the diffractive features 188 and their grating vectors k5 A ~k5 C is different for each of zones Z1-Z3. Diffraction feature 188 is linear in each zone, but diffraction feature 188 approximates a curve in the direction of the x-axis dimension. Similarly, diffraction feature 188 exhibits gradual variations in the direction of the row including zones Z4-Z6, zones Z7-Z9, and zones Z10-Z12.

[0091] Of course, the grating vector k5 of the diffractive feature 188 may increase in magnitude in the y-axis dimension as the pitch d2 decreases. A The magnitude of the lattice vector k5 increases in magnitude in a stepwise manner across zones Z1, Z4, Z7 and Z10. Similarly, in some embodiments, B increases in magnitude in a stepwise manner across zones Z2, Z5, Z8, and Z11, and the lattice vector k5 C increases in magnitude in a stepwise manner across zones Z3, Z6, Z9, and Z12.

[0092] It will be appreciated that the vector contributions of either the curve (or approximation) and / or chirp of the diffractive features 186, 188 at any given point along the outcoupling diffractive optical element ODO independently produce spherical and / or cylindrical optical power. For example, the vector contribution of the curve (or approximation) combined with the chirp of the diffractive features 186, 188 introduces a two-dimensional optical power that, when properly balanced, produces a spherical optical power.

[0093] In another exemplary embodiment, as shown schematically in FIG. 18 , the outcoupling diffractive optical element ODO includes a first set of diffractive features 190 and a second set of diffractive features 192. The first set of diffractive features 190 are curvilinear (i.e., curved) or approximate linear segments and curves to introduce optical power, as described above. The second set of diffractive features 192 are linear diffractive features. This outcoupling diffractive optical element ODO combines a spherical correction function with an eyebox E expansion function.

[0094] 19A , in an exemplary embodiment, image light guide system 100 includes first corrective optics 140 and image light guide 102, which have at least an incoupling optic IDO and an outcoupling optic ODO. First corrective optics 140 are disposed between image light guide 102 and real-world object RWO. For example, light reflected from real-world object RWO propagates as real-world image-bearing light 130A until it reaches first corrective optics 140, where real-world image-bearing light 130A forms real-world image-bearing light 130B. In this embodiment, first corrective optics 140 comprises, for example, a lens having a spherical correction component and a cylindrical correction component. Real-world image-bearing light 130B continues to propagate through image light guide 102 and enters eyebox E, where it is used to form an image of real-world object RWO, for example, closer than the real-world object RWO's true location in the environment. The cylindrical correction component of first corrective optic 140 focuses real-world image-bearing light 130B around an optical axis according to a particular prescription.

[0095] 19A , outcoupling optics ODO is configured to provide spherical and cylindrical correction to virtual image-bearing light 128 that is outcoupled toward eyebox E. Spherically and cylindrically corrected virtual image-bearing light 128A is outcoupled from image light guide 102 and propagates toward eyebox E as virtual image-bearing light 128B. In this embodiment, real-world image-bearing light 130 and virtual image-bearing light 128 are spherically and cylindrically corrected, respectively.

[0096] 19B, in an exemplary embodiment, image light guide system 100 includes first corrective optical element 140 and image light guide 102 having at least incoupling optical element IDO and outcoupling optical element ODO. First corrective optical element 140 is disposed between image light guide 102 and real-world object RWO. For example, light reflected from real-world object RWO propagates as real-world image-bearing light 130A until it reaches first corrective optical element 140, where real-world image-bearing light 130A forms real-world image-bearing light 130B. In this embodiment, first corrective optical element 140 includes, for example, a lens with a cylindrical correction component. Real-world image-bearing light 130B continues to propagate through image light guide 102 into eyeglasses E, where it is meridian-focused according to a particular prescription.

[0097] 19B , outcoupling optics ODO is configured to provide cylindrical correction to virtual image-bearing light 128 that is outcoupled toward eyebox E. Cylindrically corrected virtual image-bearing light 128A is outcoupled from image light guide 102 and propagates toward eyebox E as virtual image-bearing light 128B. In this embodiment, real-world image-bearing light 130 and virtual image-bearing light 128 are each cylindrically corrected.

[0098] 19C , in an exemplary embodiment, image light guide system 100 includes first corrective optical element 140, where image light guide 102 has at least incoupling optical element IDO and outcoupling optical element ODO, and second corrective optical element 180. First corrective optical element 140 is disposed between image light guide 102 and real-world object RWO. For example, light reflected from real-world object RWO propagates as real-world image-bearing light 130A until it reaches first corrective optical element 140, where real-world image-bearing light 130A forms real-world image-bearing light 130B. In this embodiment, first corrective optical element 140 includes, for example, a lens with a spherical correction component. Real-world image-bearing light 130B continues to propagate through image light guide 102 to second corrective optical element 180, where real-world image-bearing light 130B forms real-world image-bearing light 130C. In this embodiment, second corrective optics 180 includes, for example, a lens with a cylindrical corrective component. After transmitting through second corrective optics 180, real-world image-bearing light 130C continues into eyebox E and forms an image of real-world object RWO', for example, closer than the real-world object RWO's true position in the environment, and is used to correct for optical aberrations of the particular viewer, such as astigmatism.

[0099] 19C , outcoupling optics ODO is configured to outcouple virtual image-bearing light 128A toward eyebox E without spherical or cylindrical correction. Virtual image-bearing light 128A is outcoupled from image light guide 102 and encounters second corrective optics 180, where virtual image-bearing light 128A forms cylindrically corrected virtual image-bearing light 128B. In this embodiment, real-world image-bearing light 130 and virtual image-bearing light 128B are each cylindrically corrected, and real-world image-bearing light 130 is also spherically corrected.

[0100] Further, embodiments of image light guide system 100 include both first corrective optical element 140 and second corrective optical element 180 that contribute to spherical correction. Additional embodiments of image light guide system 100 include both first corrective optical element 140 and second corrective optical element 180 that contribute to cylindrical correction. Further, image light guide 102 can contribute to either spherical or cylindrical correction, or both.

[0101] In one or more exemplary embodiments, image light guide system 100 may utilize digital spherical and / or cylindrical correction. Referring now to FIG. 20A , in an exemplary embodiment, image light guide system 100 includes cover window 122, and image light guide 102 has at least incoupling optics IDO and outcoupling optics ODO, digital spherical correction element 200, and cylindrical correction optical element 180. Cover window 122 is disposed between image light guide 102 and real-world object RWO and contributes no, or substantially no, refractive power to real-world image-bearing light 130A. Light reflected from real-world object RWO propagates as real-world image-bearing light 130A through cover window 122 and image light guide 102 until it reaches digital spherical correction element 200, where it forms real-world image-bearing light 130B. For example, digital spherical correction element 200 comprises a liquid crystal layer operable to provide spherical correction to incident light. Real-world image-bearing light 130B continues to propagate into cylindrical corrective optics 180, where it forms real-world image-bearing light 130C. In this embodiment, cylindrical corrective optics 180 comprises, for example, a lens with a cylindrical corrective component. After transmitting through cylindrical corrective optics 180, real-world image-bearing light 130C continues into eyebox E and forms an image of real-world object RWO', for example, closer than the real-world object RWO's true position in the environment, and is used to correct for a particular viewer's optical aberrations, such as astigmatism.

[0102] 20A , outcoupling optics ODO is configured to outcouple virtual image-bearing light 128A toward eyebox E without spherical or cylindrical correction. Virtual image-bearing light 128A is outcoupled from image light guide 102 and encounters digital spherical correction element 200, which forms virtual image-bearing light 128B. Virtual image-bearing light 128B then encounters cylindrical correction optics 180, which forms cylindrically corrected virtual image-bearing light 128C. In this embodiment, real-world image-bearing light 130 and virtual image-bearing light 128 are cylindrically and spherically corrected, respectively.

[0103] 20B , in an exemplary embodiment, image light guide system 100 includes cover window 122, and image light guide 102 has at least incoupling optical element IDO and outcoupling optical element ODO, digital spherical corrector 200, and digital cylindrical corrector 202. Cover window 122 is disposed between image light guide 102 and real-world object RWO and contributes no, or substantially no, refractive power to real-world image-bearing light 130A. Light reflected from real-world object RWO propagates as real-world image-bearing light 130A through cover window 122 and image light guide 102 until it reaches digital spherical corrector 200, where it forms real-world image-bearing light 130B. For example, digital spherical corrector 200 comprises a liquid crystal layer operable to provide spherical correction to incident light. Real-world image-bearing light 130B continues to propagate to digital cylindrical corrector 202, where it forms real-world image-bearing light 130C. For example, digital cylindrical corrector 202 may comprise a liquid crystal layer operable to provide cylindrical correction to incident light. After transmitting through digital cylindrical corrector 202, real-world image-bearing light 130C continues into eyebox E, where it forms an image of real-world object RWO', e.g., closer to the real-world object RWO's true position in the environment, and is used to correct for a particular viewer's optical aberrations, such as astigmatism.

[0104] 20B , outcoupling optics ODO is configured to outcouple virtual image-bearing light 128A toward eyebox E without spherical or cylindrical correction. Virtual image-bearing light 128A is outcoupled from image light guide 102 and encounters digital spherical corrector 200, which forms virtual image-bearing light 128B. Virtual image-bearing light 128B then encounters digital cylindrical corrector 202, which forms cylindrically corrected virtual image-bearing light 128C. In this embodiment, real-world image-bearing light 130 and virtual image-bearing light 128 are cylindrically and spherically corrected, respectively.

[0105] 20C , in an exemplary embodiment, image light guide system 100 includes cover window 122, digital spherical corrector 200, image light guide 102 having at least incoupling optical element IDO and outcoupling optical element ODO, and cylindrical corrector optical element 180. Cover window 122 is disposed between image light guide 102 and real-world object RWO and contributes no, or substantially no, refractive power to real-world image-bearing light 130A. Light reflected from real-world object RWO propagates through cover window 122 as real-world image-bearing light 130A until it reaches digital spherical corrector 200, where it forms real-world image-bearing light 130B. For example, digital spherical corrector 200 comprises a liquid crystal layer operable to provide spherical correction to incident light. Real-world image-bearing light 130B continues to propagate through image light guide 102 to cylindrical corrective optics 180, where real-world image-bearing light 130B forms real-world image-bearing light 130C. For example, cylindrical corrective optics 180 may comprise, for example, a lens having a cylindrical corrective component. After transmitting through cylindrical corrective optics 180, real-world image-bearing light 130C continues into eyebox E and forms an image of real-world object RWO', e.g., closer than the real-world object RWO's true position in the environment, and is used to correct for a particular viewer's optical aberrations, such as astigmatism.

[0106] 20C , outcoupling optics ODO is configured to outcouple virtual image-bearing light 128A toward eyebox E without spherical or cylindrical correction. Virtual image-bearing light 128A is outcoupled from image light guide 102 and encounters digital spherical correction element 200, which forms virtual image-bearing light 128B. Virtual image-bearing light 128B then encounters cylindrical correction optics 180, which forms cylindrically corrected virtual image-bearing light 128C. In this embodiment, real-world image-bearing light 130 and virtual image-bearing light 128 are cylindrically and spherically corrected, respectively.

[0107] 20D , in an exemplary embodiment, image light guide system 100 includes cover window 122, digital spherical corrector 200, image light guide 102 having at least incoupling optical element IDO and outcoupling optical element ODO, and digital cylindrical corrector 202. Cover window 122 is disposed between image light guide 102 and real-world object RWO and contributes no, or substantially no, refractive power to real-world image-bearing light 130A. Light reflected from real-world object RWO propagates as real-world image-bearing light 130A through cover window 122 until it reaches digital spherical corrector 200, where it forms real-world image-bearing light 130B. For example, digital spherical corrector 200 comprises a liquid crystal layer operable to provide spherical correction to incident light. Real-world image-bearing light 130B continues to propagate through image light guide 102 to digital cylindrical corrector 202, where real-world image-bearing light 130B forms real-world image-bearing light 130C. For example, digital cylindrical corrector 202 comprises a liquid crystal layer operable to provide cylindrical correction to incident light. After transmitting through digital cylindrical corrector 202, real-world image-bearing light 130C continues into eyebox E, where it forms an image of real-world object RWO', e.g., closer to the real-world object RWO's true position in the environment, and corrects for optical aberrations of the particular viewer, such as astigmatism.

[0108] 20D , outcoupling optics ODO is configured to outcouple virtual image-bearing light 128A toward eyebox E without spherical or cylindrical correction. Virtual image-bearing light 128A is outcoupled from image light guide 102 and encounters digital cylindrical correction element 202, which causes virtual image-bearing light 128A to form cylindrically corrected virtual image-bearing light 128B. In this embodiment, real-world image-bearing light 130 and virtual image-bearing light 128B are each cylindrically corrected, and real-world image-bearing light 130 is spherically corrected.

[0109] It should be understood that in any of the foregoing descriptions and examples, the digital corrective elements may be replaced with fixed lenses that perform the same function. In any of the exemplary embodiments described herein that utilize one or more lenses (e.g., corrective optics 122, 140, 180), lens thickness should be considered. For example, the power selected across the lenses is selected so that the lens thickness, measured at the periphery of the lens, remains the same across each image light guide system 100. To this effect, upper and lower diopter power limits are selected for each lens, and the power is balanced across multiple optical elements to allow for similar lens thicknesses in any two consecutive image light guide systems 100. In other words, the optical power provided by first corrective optic 140 and second corrective optic 180 may be configured so that the total optical power achieved by the system is configured for a particular prescription without increasing the initial thickness of first corrective optic 140 or second corrective optic 180.

[0110] In any of the exemplary embodiments described herein, the refractive power of the corrective optics 122, 140, 200 disposed between the real-world object RWO and the image light guide 102 is substantially the same as the refractive power of the image light guide 102. Having the same refractive power for these elements facilitates correcting the virtual image and the real-world image to the same focal length (e.g., optical infinity). In other examples of the embodiments described in this disclosure, the refractive power of the corrective optics 122, 140, 200 disposed between the real-world object RWO and the image light guide 102 may be different from the refractive power of the image light guide 102.

[0111] The perspective view shown in FIG. 21 illustrates an example of an image light guide system 100 within a display system for augmented reality display of virtual images. Image light guide system 100 uses one or more image light guides (e.g., image light guide 102). Image light guide system 100 is shown as a head-mounted display (HMD) having a right-eye rim section 112 with image light guide 102R proximate to a user's right eye. Image light guide system 100 includes an image source 108, such as a picoprojector or similar device, that can be energized to generate one or more virtual images. Although not shown, in one embodiment, image light guide system 100 includes a left-eye optical system that includes one or more image light guides and a second image source. In an embodiment using both right-eye rim section 112 and left-eye rim section 112, the generated virtual image may be a stereoscopic image for 3D display. During operation by a user or viewer, the virtual image or images formed by image light guide system 100 may appear superimposed or overlaid on real-world scene content seen by the viewer through right-eye image light guide 102R and / or left-eye image light guide 102R. Additional components familiar to those skilled in the art of augmented reality visualization may also be provided, such as mounting one or more cameras on the frame of the HMD for viewing scene content or viewer eye tracking.

[0112] One or more features of the embodiments described in this disclosure 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 can be embodied in other specific forms, modifications, and variations 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 present 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 system for viewing virtual objects and real-world objects within a common field of view, comprising: an image light guide having an inner surface and an outer surface, the image light guide being positioned to direct an image-bearing light beam of the virtual object toward an eyebox at a first focused distance; a first corrective optical element disposed between the image light guide and the real-world object, the first corrective optical element having a spherical light output contribution operable to converge or diverge a real-world image-bearing light beam before the eyebox to a second focused distance that is shorter than the first focused distance; an outcoupling optic disposed along the image light guide, the outcoupling optic having a spherical light output contribution operable to converge or diverge a virtual image-bearing light beam to a second focal distance before the eyebox that is shorter than the first focal distance; an image light guide system including: a second corrective optical element positioned between the image light guide and the eyebox, the second corrective optical element having a cylindrical optical contribution operable to reduce optical aberrations associated with viewing the real-world object and the virtual object at the second focusing distance;

2. 10. The image light guide system of claim 1, wherein the second corrective optical element comprises a liquid crystal layer operable to provide digital correction of the real-world image-bearing light beam and the virtual image-bearing light beam.

3. The image light guide system of claim 1 , wherein the first corrective optical element comprises a liquid crystal layer operable to provide digital correction of the real-world image-bearing light beam.

4. 2. The image light guide system of claim 1, wherein the optical center of the first corrective optical element and the optical center of the second corrective optical element are aligned at an overlapping alignment position with the outcoupling optical element to limit two-dimensional shift of real-world image-bearing light.

5. The image light guide system of claim 4 , wherein the alignment position is selected as a function of a user's interpupillary distance.

6. 1. An image light guide system for viewing virtual objects and real-world objects within a common field of view, comprising: an image light guide having an inner surface and an outer surface, the image light guide being positioned to direct an image-bearing light beam of the virtual object toward an eyebox at a first focused distance; a first corrective optical element disposed between the image light guide and the real-world object, the first corrective optical element having a spherical light output contribution operable to converge or diverge a real-world image-bearing light beam before the eyebox to a second focused distance that is shorter than the first focused distance; an outcoupling optical element disposed along the image light guide, the outcoupling optical element having a composite light output contribution operable to converge or diverge a virtual image-bearing light beam before the eyebox to a second focal distance that is smaller than the first focal distance, and a cylindrical optical contribution operable to reduce optical aberrations associated with viewing the real-world object and the virtual object at the second focal distance.

7. The image light guide system of claim 6 , wherein the first corrective optical element comprises a liquid crystal layer operable to provide digital correction of the real-world image-bearing light beam.

8. The image light guiding system of claim 6 , wherein the outcoupling optical element comprises a stepped chirped outcoupling diffractive optical element.

9. 7. The image light guide system of claim 6, wherein the outcoupling optical element comprises a zone-segmented pattern having an angular change between the linear diffractive features between the zones along one dimension of the outcoupling optical element.

10. 7. The image light guide system of claim 6, wherein the outcoupling optical element comprises a zone-segmented array of linear diffractive features having a gradual change in pitch along a first dimension of the array and a gradual change in orientation of the diffractive features along a second dimension of the array.

11. The image light guide system of claim 6 , wherein the first corrective optical element includes a cylindrical optical contribution operable to reduce optical aberrations associated with viewing the real-world object at the second focusing distance.

12. 7. The image light guide system of claim 6, further comprising a second corrective optical element positioned between the image light guide and the eyebox, the second corrective optical element having a corrective optical contribution operable to reduce optical aberrations associated with viewing the real-world object at the second focusing distance.

13. 1. An image light guide system for viewing virtual objects and real-world objects within a common field of view, comprising: an image light guide having an inner surface and an outer surface, the image light guide being positioned to direct an image-bearing light beam of the virtual object toward an eyebox at a first focused distance; an outcoupling optic disposed along the image light guide; a digital spherical correction element disposed between the image light guide and the eyebox, the digital spherical correction element having a spherical light output contribution operable to converge or diverge a real-world image-bearing light beam and a virtual image-bearing light beam before the eyebox to a second focal distance that is smaller than the first focal distance; a cylindrical correction optical element disposed between the digital spherical correction element and the eyebox, the cylindrical correction element having a cylindrical optical contribution operable to reduce optical aberrations associated with viewing the real-world object and the virtual object at the second focusing distance.

14. The image light guiding system of claim 13 , wherein the cylindrical correction element comprises a digital cylindrical correction element.

15. 1. A binocular imaging light guide system for viewing virtual objects and real-world objects within a common field of view, comprising: an image light guide having an inner surface and an outer surface, the image light guide positioned to incouple a collimated image-bearing light beam of a virtual object; a first outcoupling optical element and a second outcoupling optical element disposed along the image light guide, the first and second outcoupling optical elements each comprising diffractive features having a pitch configured to position a convergence point of the virtual object closer than a focal plane at infinity;

16. The image light guide system of claim 15, wherein the convergence point is located within 1 to 4 meters of the eyebox.

17. 16. The image light guide system of claim 15, wherein the first and second outcoupling optical elements each comprise a step-chirped diffractive feature configured to apply cylindrical power to the first and second outcoupling optical elements.

18. 16. The image light guide system of claim 15, wherein the first and second outcoupling optical elements each comprise a zone-segmented pattern having an angular change between the linear diffractive features between the zones along one dimension of the outcoupling optical element.

Images