Offset-axis optical power image light guide system

Abstract

A near-eye display system including a first corrective optical element having a first optical power contribution operable to converge or diverge real-world image-bearing light beams in advance of an eyebox to a first focusing distance, and a second corrective optical element arranged between the first corrective optical element and the eyebox. The second corrective optical element having a spherical optical power contribution operable to converge or diverge virtual and real-world image-bearing light beams in advance of the eyebox to a second focusing distance. The first corrective optical element having a first center of correction, and the second corrective optical element having a second center of correction.

Description

OFFSET-AXIS OPTICAL POWER IMAGE LIGHT GUIDE SYSTEMTECHNICAL FIELD

[0001] The present disclosure generally relates to augmented reality systems, and more particularly to optical image light guide systems with diffractive optics operable to convey imagebearing light to a viewer.BACKGROUND

[0002] Head-mounted displays (HMDs) increasingly take the form of conventional eyeglasses with less obtrusive optics for conveying virtual image content with less obstructed views of the ambient environment. Image generators can be supported along eyeglass temples, and substantially transparent image light guides convey the generated images to the wearer's eye(s) as virtual images that are projected into the wearer's real-world view visible through the image light guides.

[0003] The virtual image content can be conveyed along the image light guides as a set of angularly related beams, where the relative angular orientation of each beam in two angular dimensions corresponds to a different position (e.g., pixel) within the generated image. Typically, the beams themselves are collimated as if corresponding to a distant point source located at a unique angular position within the field of view. Thus, when the collimated beams are directed into overlapping positions within a common eyebox, the wearer's eye views the generated images from the eyebox as virtual images located at a distance approaching infinity. However, real-world objects of interest to the wearer may be located much closer and require some noticeable eye accommodation to bring into focus. Viewing virtual objects and real-world objects requiring different focusing accommodations within the same scene can cause eye strain.

[0004] Vision problems within the wearer's eyes caused by refractive errors such as nearsightedness (myopia), farsightedness (hyperopia), and astigmatism, can also present challenges to low profile HMDs resembling conventional eyeglasses. If a wearer's traditional eyeglasses (containing corrective lenses) must be removed to accommodate a low-profile HMD, the wearer's view of both real -world and virtual objects through the HMDs can be compromised.SUMMARY

[0005] The present disclosure is directed to one or more exemplary' embodiments of an image light guide system that manages focusing discrepancies between real -world and virtual objects presented to the viewer and manages vision problems affecting the focusing capabilities of theparticular viewer as well as reducing demands on the viewer’s eyes for viewing virtual objects together with real-world objects within the same field of view.

[0006] In an exemplar}' embodiment, the present disclosure provides for anear-eye display system including a first corrective optical element having a first optical power contribution operable to converge or diverge real-world image-bearing light beams in advance of an eyebox to a first focusing distance; a second corrective optical element arranged between the first corrective optical element and the eyebox. the second corrective optical element having a spherical optical power contribution operable to converge or diverge virtual and real-world image-bearing light beams in advance of the eyebox to a second focusing distance, the first corrective optical element having a first center of correction, and the second corrective optical element having a second center of correction.

[0007] In another exemplary embodiment, the present disclosure provides for a method of manufacturing an image light guide system including providing a set of first corrective optical elements having a spherical optical power contribution; providing a set of image light guides having a spherical optical power contribution; selecting one of the first corrective optical elements from the set; selecting one of the image light guides from the set; customizing a second corrective optical element having at least one of a spherical or cylindrical optical power contribution; and arranging the image light guide between the first corrective optical element and the second corrective optical element in a stacked arrangement, wherein the second corrective optical element is arranged between the image light guide and the eyebox.

[0008] In another exemplary' embodiment, the present disclosure provides for an image light guide system for viewing a virtual object and a real-world object within a common field of view including an image light guide having an inner surface and an outer surface, the image light guide arranged to propagate virtual image-bearing light beams; a first corrective optical element arranged between the image light guide and the real-world object, the first corrective optical element having a first spherical optical power contribution to the real-world image-bearing light beams; an out-coupling optic arranged along the image light guide, the out-coupling optic having a second spherical optical power contribution to the virtual image-bearing light beams; and a second corrective optical element arranged between the image light guide and the eyebox, the second corrective optical element having a third spherical optical power contribution to the virtual and real -world image-bearing light beams, the first corrective optical element having a first center of correction, and the second corrective optical element having a second center of correction.BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0009] The accompanying drawings are incorporated herein as part of the specification. The drawings described herein illustrate embodiments of the presently disclosed subject matter and are illustrative of selected principles and teachings of the present disclosure. However, the drawings do not illustrate all possible implementations of the presently disclosed subject matter and are not intended to limit the scope of the present disclosure in any way.

[0010] FIG. 1 is a top view of an image light guide with an exaggerated thickness for showing the propagation of light from an image source along the image light guide to an eyebox within which the virtual image can be viewed.

[0011] FIG. 2 is a perspective view of an image light guide including an in-coupling diffractive optic, a turning diffractive optic, and out-coupling diffractive optic for managing the propagation of image-bearing light beams.

[0012] FIG. 3 is a top plan schematic view of a portion of an image light guide system according to an exemplary embodiment of the presently disclosed subject matter.

[0013] FIG. 4 is a simplified top plan schematic view of a portion of an image light guide system showing a common field of view according to an exemplary embodiment of the presently disclosed subject matter.

[0014] FIG. 5 is a simplified top plan schematic view of a portion of an image light guide system with a negative-power optical element according to an exemplary embodiment of the presently disclosed subject matter.

[0015] FIG. 6 is a simplified top plan schematic view of a portion of an image light guide system with a negative-power optical element and a positive-power optical element according to an exemplary embodiment of the presently disclosed subject matter.

[0016] FIG. 7 is a simplified top plan schematic view of a portion of an image light guide system with a negative-power optical element, a positive-power optical element, and a corrective optical element according to an exemplary’ embodiment of the presently disclosed subject matter.

[0017] FIG. 8A is a simplified side elevational schematic view of a portion of an image light guide system providing spherical correction to virtual image-bearing light via an out-coupling diffractive optic according to an exemplary embodiment of the presently disclosed subject matter.

[0018] FIG. 8B is a simplified perspective view of a portion of the image light guide system according to FIG. 8A.

[0019] FIG. 8C is a simplified top plan view of a portion of the image light guide system according to FIG. 8A.

[0020] FIG. 8D is a simplified side elevational view of a portion of the image light guide system according to FIG. 8A.

[0021] FIG. 8E is another simplified side elevational schematic view of a portion of an image light guide system providing spherical correction to virtual image-bearing light via an out- coupling diffractive optic according to an exemplary embodiment of the presently disclosed subject matter.

[0022] FIG. 9 is a cross-sectional side view of a portion of a diffractive optic featuring a progressive variation in pitch along a first dimension of the diffractive optic for generating a virtual focus for one dimension of an image.

[0023] FIG. 10 is a perspective view of a portion of a diffractive optic featuring a stepwise variation in an orientation angle of diffractive features along a second dimension of the diffractive optic.

[0024] FIG. 11 is a front view of a portion of an out-coupling diffractive optic featuring an array of outlined zones, each with parallel diffractive features of equal pitch, but with the respective zones varying in pitch along one dimension of the array and varying in orientation angle along another dimension of the array.

[0025] FIG. 12 is a front view of a portion of an out-coupling diffractive optic featuring an array of zones, each zone having a common pitch between each diffractive feature of the first and second sets of output diffractive features, the common pitch vary ing between zones in at least a first dimension according to an exemplary7embodiment of the presently disclosed subject matter.

[0026] FIG. 13 is a front view of a portion of an out-coupling diffractive optic featuring a plurality7of patterns of diffractive features according to an exemplary embodiment of the presently disclosed subject matter.

[0027] FIG. 14A is a simplified side elevational schematic view of a portion of an image light guide system providing spherical and cylindrical correction to real-world image-bearing light according to an exemplary embodiment of the presently7disclosed subject matter.

[0028] FIG. 14B is a simplified side elevational schematic view of a portion of an image light guide system providing cylindrical correction to real-world image-bearing light and virtual imagebearing light according to an exemplary embodiment of the presently disclosed subject matter.

[0029] FIG. 14C is a simplified side elevational schematic view of a portion of an image light guide system providing spherical and cylindrical correction to real-world image-bearing light and cylindrical correction to virtual image-bearing light according to an exemplar}' embodiment of the presently disclosed subject matter.

[0030] FIG. 15A is a simplified side elevational schematic view of a portion of an image light guide system providing digital spherical correction to real-world image-bearing light and virtual image-bearing light and cylindrical correction to real-world image-bearing light and virtual image-bearing light according to an exemplary embodiment of the presently disclosed subject matter.

[0031] FIG. 15B is a simplified side elevational schematic view of a portion of an image light guide system providing digital spherical correction to real-world image-bearing light and virtual image-bearing light and digital cylindrical correction to real-world image-bearing light and virtual image-bearing light according to an exemplary embodiment of the presently disclosed subject matter.

[0032] FIG. 15C is a simplified side elevational schematic view of a portion of an image light guide system providing digital spherical correction to real-world image-bearing light and cylindrical correction to real-world image-bearing light and virtual image-bearing light according to an exemplary embodiment of the presently disclosed subject matter.

[0033] FIG. 15D is a simplified side elevational schematic view of a portion of an image light guide system providing digital spherical correction to real-world image-bearing light and digital cylindrical correction to real-world image-bearing light and virtual image-bearing light according to an exemplary embodiment of the presently disclosed subject matter.

[0034] FIG. 16A is a simplified perspective view of a portion of an image light guide system according to an exemplar}' embodiment of the presently disclosed subject matter.

[0035] FIG. 16B is a simplified side elevational view of a portion of the image light guide system according to FIG. 16 A.

[0036] FIG. 16C is a simplified cross-sectional view of a portion of the image light guide system according to FIG. 16B.

[0037] FIG. 16D is a simplified side elevational view of a portion of the image light guide system according to FIG. 16 A.

[0038] FIG. 16E is a simplified cross-sectional view of a portion of the image light guide system according to FIG. 16D.

[0039] FIG. 16F is a schematic top plan view of a portion of the image light guide system according to an exemplary embodiment of the presently disclosed subject matter.

[0040] FIG. 17A is a simplified side elevational view of a portion of the image light guide system according to an exemplary embodiment of the presently disclosed subject matter.

[0041] FIG. 17B is a schematic of the center of axes of rotation of a corrective optical element and the decentration utilized to correct interpupillary distance offset according to an exemplary' embodiment of the presently disclosed subject matter.

[0042] FIG. 18 is a perspective view of an image light guide system taking the form of a headmounted display according to an exemplary embodiment of the presently disclosed subject matter.DETAILED DESCRIPTION

[0043] It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific assemblies and systems illustrated in the attached drawings and described in the following specification are simply exemplary embodiments of the inventive concepts defined herein. Hence, specific dimensions, directions, or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless expressly stated otherwise. Also, although they may not be. like elements in various embodiments described herein may be commonly referred to with like reference numerals within this section of the application.

[0044] One 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 present disclosure. Reference throughout the specification to “one embodiment"’ or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, the appearance of the phrase “in one embodiment” or “in an embodiment” throughout the specification is not necessarily referring to the same embodiment. However, the particular features, structures, or characteristics described may be combined in any suitable manner in one or more embodiments.

[0045] Where used herein, the terms “first”, “second”, and so on, do not necessarily denote any ordinal, sequential, or priority relation, but are simply used to more clearly distinguish one element or set of elements from another, unless specified otherwise.

[0046] Where used herein, the terms “viewer’; “operator”, “observer”, “wearer”, and “user” are considered equivalents and refer to the person, or machine, that wears and / or views images using a device having an imaging light guide.

[0047] Where 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 widely understood in elementary mathematics. Where used herein, the term “subset”, unless otherwise explicitly stated, refers to a non-empty proper subset, that is. to a subset of the larger set, having one or more members. For a set S, a subset may comprise the complete set S. A “proper subset” of set S, however, is strictly contained in set S and excludes at least one member of set S.

[0048] Where used herein, the terms “coupled,” “coupler,” or “coupling” in the context of optics refer to a connection by which light travels from one optical medium or device to another optical medium or device.

[0049] Where used herein, the terms “wavelength band” and “wavelength range” are equivalent and have their standard connotation as used by those skilled in the art of color imaging and refer to a continuous range of light wavelengths that are used to represent polychromatic images.

[0050] Where used herein, the term “beam expansion” is intended to mean replication of a beam via multiple encounters with an optical element to provide exit pupil expansion in one or more dimensions. Similarly, as used herein, to “expand” a beam, or a portion of a beam, is intended to mean replication of a beam via multiple encounters with an optical element to provide exit pupil expansion in one or more dimensions.

[0051] An optical system, such as a HMD, can produce a virtual image. In contrast to methods for forming a real image, a virtual image is not formed on a display surface. That is, if a display surface were positioned at the perceived location of a virtual image, no image would be formed on that surface. Virtual images have a number of inherent advantages for augmented reality presentation. For example, the apparent size of a virtual image is not limited by the size or location of a display surface. Additionally, the source object for a virtual image may be small; for example, a magnifying glass provides a virtual image of an object. In comparison with systems that project a real image, a more realistic viewing experience can be provided by forming a virtual image that appears to be some distance away. Providing a virtual image also obviates the need to compensate for screen artifacts, as may be necessary when projecting a real image.

[0052] FIG. 1 is a schematic diagram showing a simplified cross-sectional view of one conventional configuration of an image light guide system 10. Image light guide system 10 includes a planar image light guide 12, an in-coupling diffractive optic IDO, and an out-couplingdiffractive optic ODO. The image light guide 12 includes a transparent substrate S. which can be made of optical glass or plastic, with plane-parallel front and back surfaces 14 and 16. In this example, the in-coupling diffractive optic IDO is shown as a transmissi ve-ty pe diffraction grating arranged on, in, or otherwise engaged with the front surface 14 of the image light guide 12. However, in-coupling diffractive optic IDO could alternately be a reflective-type diffraction grating or other type of diffractive optic, such as a volume hologram or other holographic diffraction element, that diffracts incoming image-bearing light beams WI into the image light guide 12. The in-coupling diffractive optic IDO can be located on, in, or otherwise engaged with front surface 14 or back surface 16 of the image light guide 12 and can be of a transmissive or reflective-type in a combination that depends upon the direction from which the image-bearing light beams WI approach the image light guide 12.

[0053] When used as a part of a near-eye or head-mounted display system, the in-coupling diffractive optic IDO of the conventional image light guide system 10 couples the image-bearing light beams WI from a real, virtual or hybrid image source 18 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, angularly related, collimated beams encoding the different positions within a virtual image for presentation to the in-coupling diffractive optic IDO. Typically, the rays within each bundle forming one of the angularly related beams extend in parallel, but the angularly related beams are relatively inclined to each other through angles that can be defined in two angular dimensions corresponding to linear dimensions of the image.

[0054] Once the angularly related beams engage with the in-coupling diffractive optic IDO, at least a portion of the image-bearing light beams WI is diffracted (generally through a first diffraction order) and thereby redirected by in-coupling diffractive optic IDO into the planar image light guide 12 as angularly encoded image-bearing light beams WG for further propagation along a length dimension x of the image light guide 12 by total internal reflection (TIR) betw een the plane-parallel front and back surfaces 14 and 16. Although diffracted into a different combination of angularly related beams in keeping with the boundaries set by TIR, the imagebearing light beams WG preserve the image information in an angularly encoded form that is derivable from the parameters of the in-coupling diffractive optic IDO. The out-coupling diffractive optic ODO receives the encoded image-bearing light beams WG and diffracts (also generally through a first diffraction order) at least a portion of the image-bearing light beams WG out of the image light guide 12, as image-bearing light beams WO, toward a nearby region of space referred to as an eyebox E, within which the transmitted virtual image can be seen by a viewer's eye or other optical component. The out-coupling diffractive optic ODO can be designedsymmetrically with respect to the in-coupling diffractive optic IDO to restore the original angular relationships of the image-bearing light beams WI among outputted angularly related beams of the image-bearing light beams WO. In addition, the out-coupling diffractive optic ODO can modify the original field points’ positional angular relationships producing an output virtual image at a finite focusing distance.

[0055] However, to increase one dimension of overlap among the angularly related beams populating the eyebox E (defining the size of the region within which the virtual image can be seen), the out-coupling diffractive optic ODO is arranged together with a limited thickness T of the image light guide 12 to encounter the image-bearing light beams WG multiple times and to diffract only a portion of the image-bearing light beams WG upon each encounter. The multiple encounters along the length (e.g., a first direction) of the out-coupling diffractive optic ODO have the effect of replicating the image-bearing light beams WG and enlarging or expanding at least one dimension of the eyebox E where the replicated beams overlap. The expanded eyebox E decreases sensitivity to the position of a viewer’s eye for viewing the virtual image.

[0056] The out-coupling diffractive optic ODO is show n as a transmissive-type diffraction grating arranged on or secured to the front surface 14 of the image light guide 12. However, like the incoupling diffractive optic IDO, the out-coupling diffractive optic ODO can be located on. in, or otherwise engaged with the front or back surface 14 or 16 of the image light guide 12 and can be of a transmissive or reflective-type in a combination that depends upon the direction through which the image-bearing light beams WG is intended to exit the image light guide 12. In addition, the out-coupling diffractive optic ODO could be formed as another type of diffractive optic, such as a volume hologram or other holographic diffraction element, that diffracts propagating imagebearing light beams WG from the image light guide 12 as the image-bearing light beams WO propagating toward the eyebox E.

[0057] FIG. 2 illustrates a perspective view' of a conventional image light guide system 10 arranged for expanding the eyebox E in two dimensions, i.e., along both x- and y-axes of the intended image. To achieve a second dimension of eyebox expansion, the in-coupling diffractive optic IDO is oriented to diffract at least a portion of image-bearing light beams WG along a grating vector kl along the image light guide 12 tow ard an intermediate turning optic TO with diffractive features and grating vector k2 oriented to diffract at least a portion of the image-bearing light beams WG in a reflective mode along the image light guide 12 tow ard the out-coupling diffractive optic ODO. It should be appreciated that only a portion of the image-bearing light beams WG are diffracted by each of the multiple encounters with intermediate turning optic TO, thereby laterally replicating each of the angularly related beams of the image-bearing light beams WG as theyapproach the out-coupling diffractive optic ODO. The intermediate turning optic TO redirects the image-bearing light beams WG toward the out-coupling diffractive optic ODO (having a grating vector k3) for longitudinally replicating the angularly related beams of the image-bearing light beams WG in a second direction before exiting the image light guide 12 as the image-bearing light beams WO. Grating vectors, such as the depicted grating vectors kl, k2, and k3. extend within a parallel plane of the image light guide 12 in respective directions that are parallel to the direction of periodicity of the diffractive features (e.g., normal to grooves, lines, or rulings) of the diffractive optics and have respective magnitudes inverse to the period or pitch d (i.e., the on-center distance between the diffractive features) of the diffractive optics IDO, TO, and ODO. It will be apparent to those skilled in the art that light can also be directed into diffracted orders corresponding to grating vectors -kl, -k2, and -k3.

[0058] As shown in FIG. 2, in-coupling diffractive optic IDO receives the incoming imagebearing light beams WI containing a set of angularly related beams corresponding to individual pixels or equivalent locations within an image generated by the image source 18, such as a projector. A full range of angularly encoded beams for producing a virtual image can be generated by a real display together with collimating optics or other optical components, by a beam scanner for more directly setting the angles of the beams, or by a combination such as a one-dimensional real display used with a scanner. In this configuration, the image light guide 12 outputs a replicated set of angularly related beams (replicated in two dimensions) by providing multiple encounters of the image-bearing light beams WG with both the intermediate turning optic TO and the out- coupling diffractive optic ODO in different orientations. In the depicted orientation of the image light guide 12, the intermediate turning optic TO provides eyebox expansion in a first dimension, e.g., the y-axis direction, and the out-coupling diffractive optic ODO provides a similar eyebox expansion in a second dimensions, e.g., the x-axis direction. The relative orientations and respective periods d of the diffractive features of the in-coupling optic IDO, intermediate turning optic TO, and out-coupling diffractive optic ODO provide for eyebox expansion in two dimensions while preserving the intended relationships among the angularly related beams of the image-bearing light beams WI that are output from the image light guide system 10 as the imagebearing light beams WO. It should be appreciated that the periods d of the in-coupling diffractive optic IDO, the intermediate turning optic TO, and the out-coupling diffractive optic ODO, can each include diffractive features having a common (i.e., constant) pitch d, where the common pitch d of each diffractive optic IDO, TO, ODO can be different.

[0059] In the configuration shown, while the image-bearing light beams WI input into the image light guide 12 are encoded into a different set of angularly related beams by the in-couplingdiffractive optic IDO, the information required to reconstruct the image is preserved by accounting for the systematic effects of the in-coupling diffractive optic IDO. The intermediate turning optic TO, located in an intermediate position between the in-coupling and out-coupling diffractive optics IDO and ODO, can be arranged so that it does not induce significant changes to the encoding of the image-bearing light beams WG. As such, the out-coupling diffractive optic ODO can be arranged in a symmetric fashion with respect to the in-coupling diffractive optic IDO, e.g., including diffractive features sharing the same period d. Similarly, the period of the intermediate turning optic TO can also match the common period of the in-coupling and out-coupling diffractive optics IDO and ODO. Although the grating vector k2 of the intermediate turning optic TO is shown oriented at 45 degrees with respect to the other grating vectors, which remains a possible orientation, the grating vector k2 of the intermediate turning optic TO can be oriented at 60 degrees to the grating vectors kl and k3 of the in-coupling and out-coupling diffractive optics IDO and ODO in such a way that the image-bearing light beams WG are turned 120 degrees. By orienting the grating vector k2 of the intermediate turning optic TO at 60 degrees with respect to the grating vectors kl and k3 of the in-coupling and out-coupling diffractive optics IDO and ODO, the grating vectors kl and k3 of the in-coupling and out-coupling diffractive optics IDO and ODO are also oriented at 60 degrees with respect to each other. By basing the grating vector magnitudes on the common pitch shared by the in-coupling, intermediate turning, and out-coupling diffractive optics IDO, TO. and ODO, the three grating vectors kl. k2. and k3 (as directed line segments) form an equilateral triangle and sum to a zero vector magnitude, which avoids asymmetric effects that could introduce unwanted aberrations including chromatic dispersion. Such asymmetric effects can also be avoided by grating vectors kl, k2, and k3 that have unequal magnitudes in relative orientations at which the three grating vectors kl. k2. and k3 sum to a zero vector magnitude.

[0060] In a broader sense, the image-bearing light beams WI that are directed into the image light guide 12 are effectively encoded by the in-coupling diffractive optic IDO, whether the in-coupling optic IDO uses gratings, holograms, prisms, mirrors, or some other mechanism. Any reflection, refraction, and / or diffraction of light that takes place at the input should be correspondingly decoded by the output to re-form the virtual image that is presented to the viewer. Whether any symmetries are maintained among the intermediate turning optic TO, the in-coupling optic IDO, and out-coupling diffractive optic ODO, or whether any change to the encoding of the angularly related beams of the image-bearing light beams WI takes place along the image light guide 12, the intermediate turning optic TO and the in-coupling and out-coupling diffractive optics IDO and ODO can be related so that the image-bearing light beams WO that are output from the imagelight guide 12 preserve or otherwise maintain the original or desired form of the image-bearing light beams WI for producing the intended virtual image.

[0061] As shown in FIG. 2, the letter "‘R” represents the orientation of the virtual image that is visible to the viewer whose eye is positioned within the eyebox E. As shown, the orientation of the letter “R’‘ in the represented virtual image matches the orientation of the letter “R"’ as encoded by the image-bearing light beams WI. A change in the rotation about the z axis or angular orientation of incoming image-bearing light beams WI with respect to the x-y plane causes a corresponding symmetric change in rotation or angular orientation of outgoing light from out- coupling diffractive optic (ODO). From the aspect of image orientation, the intermediate turning optic TO simply acts as a type of optical relay, providing one dimension of eyebox expansion through replication of the angularly encoded beams of the image-bearing light beams WG along one axis (e.g., along the y-axis) of the image. Out-coupling diffractive optic ODO further provides a second dimension of eyebox expansion through replication of the angularly encoded beams along another axis (e.g., along the x-axis) while maintaining the original orientation of the virtual image encoded by the image-bearing light beams WI. The intermediate turning optic TO is typically a slanted or square grating or, alternately, can be a blazed grating and is typically arranged on one of the plane-parallel front and back surfaces of the image light guide 12. It should be appreciated that the representation of the virtual image “R” as created by an image source is comprised of infinitely focused light that requires a lens (e.g., the lens in the human eye) to focus the image so that the orientations discussed above can be detected.

[0062] Together, the in-coupling, turning, and out-coupling diffractive optics IDO, TO. and ODO preferably preserve the angular relationships among beams of different wavelengths defining a virtual image upon conveyance by image light guide 12 from an offset position to a near-eye position of the viewer. While doing so, the in-coupling, turning, and out-coupling diffractive optics IDO, TO, and ODO can be relatively positioned and oriented in different ways to control the overall shape of the image light guide 12 as well as the overall orientations at which the angularly related beams can be directed into and out of the image light guide 12.

[0063] FIG. 3 shows atop plan, schematic view of a portion of an exemplary head-mounted image light guide system 100 according to the present disclosure. In some examples, image light guide system 100 can take the form of a head-mounted display (shown in FIG. 19) or other headmounted optical system. As shown in FIG. 3, the example image light guide system 100 includes an image light guide 102 in the form of a planar waveguide. Although not shown, image light guide 102 can include the same structure, functionality, material, and / or features described above with respect to image light guide 12, e.g., image light guide 102 can include an in-couplingdiffractive optic, an intermediate turning optic, and an out-coupling diffractive optic. Although illustrated as a planar waveguide, it should be appreciated that 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, without limitation, optical glass, quartz, or plastic, with plane-parallel front and back surfaces 104 and 106, respectively. It should be appreciated that, similarly 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 the image light guide 102 by an incoupling diffractive optic (located on the front or back surfaces 104, 106 of the image light guide and configured as transmissive-type or reflective-type diffraction element). Once coupled into image light guide 102, the angularly encoded image-bearing light beams are configured to propagate along a length dimension of the image light guide 102 and exit the image light guide 102 by interaction with an out-coupling diffractive optic, such that at least one image is formed within an eyebox E for viewing by a viewer or other optical component. As described above with respect to image light guide 12, image light guide 102 can also utilize one or more encounters with an intermediate turning optic or the out-coupling optic to expand the size of the eyebox E in one or more dimensions.

[0064] As shown in FIG. 3, image light guide system 100 also includes an image source 108. In some examples, image source 108 is a projector that includes a light source as well as one or more optical components to focus and / or collimate light generated by the light source. In some examples, image source 108 comprises one or more light-emitting diodes (LEDs), organic LEDs (OLEDs), or ultra LEDs (uLEDs). In other examples, image source 108 is a color field sequential projector system operable to pulse image-bearing light of multiple wavebands, for example light from within red, green, and blue wavelength ranges, onto a digital light modulator / micro-mirror array (a “DLP”) or a liquid crystal on silicon (“LCDS”) display. In further examples, image source 108 includes one or more pico-projectors, where each pico-projector is configured to produce a single primary7color band (e.g., red, green, or blue). In another example, image source 108 includes a single pico-projector arranged to produce 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 a wavelength in the range betw een 495 nm and 570 nm, a red band having a w avelength in the range between 620 nm and 750 nm, and a blue band having a wavelength in the range between 450 nm and 495 nm. The substantially collimated light generated by the pico-projector, once coupled, and transmitted through image light guide 102, can be used by image light guide system 100 to formone or more virtual images viewable by a user’s eye or other optical components positioned within eyebox E.

[0065] With continued reference to FIG. 3, image light guide system 100 also includes a frame 110 which includes a right eye-rim section 112 having a right temple 1 14 and a nose-bridge portion 116. Between temple 114 and nose-bridge portion 116, frame 110 includes a right aperture 118 configured to receive image light guide 102 such that during operation of the image light guide system 100, the image light guide 102 is configured to form at least one image related to one or more virtual objects within a viewer’s right eye 120. Although only the right eye-rim section 112 and right eye 120 are illustrated in FIG. 3, it should be appreciated that frame 110 can be symmetrical, i.e., can include a right eye-rim section 112 and left eye-rim section (not shown) where each of the right eye-rim section 112 and the left eye-rim section both include a respective temple and respective image light guides 102 configured to form respective virtual images related to one or more virtual objects within the 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 forming images in both the right and left eye of the viewer. In some examples, frame 110 is made of a metal, plastic, or wood material (or any combination thereof), and is intended to be opaque, i.e., not transmissive to visible light. In some examples, image light guide 102 is removably secured between the temple 114 and nose-bridge portion 116, i.e., image light guide 102 can be removed and / or replaced without the aid of additional tools. Further, it should be appreciated that in one or more exemplary embodiments of image light guide system 100 (whether a binocular system as described above or a monocular system), the image light guide system 100 can include multiple, stacked, image light guides 102. For example, one image light guide 102 of the stack is configured to in-couple and propagate light of a first w avelength range (e.g., light in the red portion of the visible spectrum), while another image light guide 102 of the stack is configured to in-couple and propagate a second wavelength range (e.g.. light in the green and / or blue portions of the visible spectrum).

[0066] Additionally, as shown in FIG. 3, image light guide system 100 can further include a cover window or other protective outer cover 122. In some examples, an anti-reflective coating can be provided on the front and / or back surface of the protective outer cover 122. In some examples, as the protective outer cover 122 is located between the image-light guide 102 and the real-world objects RWO, protective outer cover 122 can provide filtering or other optical functions that affect the viewer’s view' of the real-world objects RWO without affecting the viewer’s view of the virtual objects VO. Further, image light guide system 100 can include an optical coupler 124. Optical coupler 124 can take the form of an in-coupling diffractive optic, such as a plurality or set ofsurface relief gratings or a volume hologram. In some examples, optical coupler 124 can take the form of a prism configured to receive image-bearing light from projector 106 and redirect and / or in-couple the image-bearing tight into image light guide 102. In some examples, optical coupler 124 includes an in-coupling diffractive optic as well as a prism.

[0067] FIG. 4 illustrates a simplified schematic top plan view of one example configuration of a right-eye rim section 112 of image tight guide system 100 where certain components of frame 110 have been removed for clarity. As shown, 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 images related to virtual objects VO (shown as a schematic triangle enclosing the letter “V’) in the eyebox E using at least the in-coupling, TIR, and out-coupling mechanisms of image-light guide 102 discussed above. Additionally, within a common field of view FOV, image light guide 102 is also operable to receive and transmit image-bearing light 128 reflected from real-world objects RWO (shown as a schematic star enclosing the letter “R”) to the eyebox E. As such, the viewer’s right eye 120, is configured to form images associated with virtual objects VO and images associated with real -world objects RWO from within a common field of view FOV. It should be appreciated that the common field of view FOV can encompass a broader or narrower angular field of view" than the field shown, e g., the common field of view' FOV could be wide enough to completely encompass the image tight guide 102 or could only cover 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) illustrate a virtual projection associated with a virtual image originating from a virtual source position. In other words, the dotted tines illustrate virtual image-bearing tight traced back to a virtual focal point within the environment such that tight used to form virtual objects VO within the eyebox E appear to originate from the virtual position of the virtual object VO within the environment and within the common FOV. As shown in FIG. 4, virtual image-bearing light 126 is in-coupled into image light guide 102. propagates along the length dimension (vertically in FIG. 4) of the image light guide 102 via TIR, and is out-coupled as virtual image-bearing tight 128 and is operable to form one or more images within the eyebox associated with one or more virtual objects VO from within the environment. In addition, real- world image-bearing light 130 is transmitted through image tight guide 102 and proceeds to eyebox E and is operable to form one or more images within the eyebox E associated with one or more real-w'orld objects RWO from within the environment and from within a common field of view FOV as the virtual objects VO.

[0068] As mentioned above, image source 108 is configured to produce substantially collimated virtual image-bearing light 126. In examples of image tight guide system 100 where the in-coupling diffractive optic and out-coupling diffractive optic do not introduce optical power into the in-coupled virtual image-bearing light 126, the images associated with virtual objects VO formed within eyebox E will be focused at optical infinity. For some users, particularly users with certain forms of optical maladies such as myopia (near-sightedness) or astigmatism, it may not be desirable to generate images of virtual objects focused at optical infinity. Instead, it may be desirable to focus those objects a closer focusing distance, i.e., a focusing distance less than optical infinity.

[0069] FIG. 5 illustrates a simplified schematic top plan view of one example configuration of a right-eye rim section 112 of image light guide system 100. Although not illustrated for clarity in FIGS. 5-7, it should be appreciated that virtual image-bearing light 126 may be in-coupled into image light guide 102 and can propagate by TIR along a length dimension (vertically in FIGS. 5- 7) of image light guide 102 until it is out-coupled from image light guide 102 as virtual imagebearing light 128A. Additionally, although not shown in FIG. 5, it should be appreciated that virtual objects VO and real -world objects RWO are within a common field of view as show and described with respect to FIG. 4 above. As shown in FIG. 5, image light guide system 100 can also include a negative-power optical element 132 which provides a negative optical power contribution 134 to 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 negativepower optical element 132 operates to diverge incident image-bearing light, reducing the apparent focusing distance of the incident image-bearing light. By positioning the negative-power optical element 132 between the image light guide and the user’s eye 120, the negative-power optical element 132 operates to decrease the focusing distance for virtual objects originally focused at optical infinity. For example, the negative-pow er optical element 132 is configured to diverge virtual image-bearing light 128 A such that the focusing distance of the virtual object VO is reduced from a first focusing distance FD1 (e.g.. optical infinity) to a second focusing distance FD2 associated with virtual image-bearing light 128B, where the second focusing distance is less than the first focusing distance (e.g., less than optical infinity). Although shown schematically in FIG. 5, it should be appreciated that the negative-power optical element 132 can be formed as, without limitation, a piano-concave lens, a biconcave lens, a negative meniscus lens, or any optical element that causes incident light to diverge in predictable ways such that it forms at least one image at a reduced focusing distance from its actual distance to the viewer. In some examples, the second focusing distance FD2 is betw een 0.005 m and 6 m. In other examples, the second focusing distance FD2 is selected between 0.005 m and 4 m.

[0070] As a result of placing a negative-power optical element (e.g., negative-power optical element 132) between the image light guide 102 and the eyebox E, the virtual image-bearing light 128B is focused by the viewer’s eye 120 such that the virtual object VO appears at a second focusing distance FD2 (shown in FIG. 5 by a triangle formed of dotted lines) where the second focusing distance FD2 is shorter than the first focusing distance FD1 with respect to the eyebox E. Additionally, as the negative-power optical element 132 is positioned between the eyebox E and the real-world objects RWO, the negative-power optical element 132 also operates to diverge real-world image-bearing light 130A such that the focusing distance of any real-world objects RWO is also reduced from, for example, a first focusing distance FD1 to a second focusing distance FD2 (shown in FIG. 5 by a star formed of dotted lines). It should be appreciated that real- world objects RWO do not need to be located at a distance greater than 6 meters (20 feet), i.e., an infinity focusing distance, to be affected by the negative optical power contribution of the negative-power optical element. For example, the perceived focusing distance of real-world objects RWO located at a finite focusing distance, e.g., between 1 and 5 meters from the viewer, will also be reduced. If the viewer desires to see the virtual obj ects VO at a closer focusing distance while leaving their perception of the distance to any real-world objects RWO unchanged, the negative optical power contribution 134 of the negative-power optical element 132 must be counteracted with respect to the real-world image-bearing light 130A.

[0071] As shown in FIG. 6, which illustrates a simplified schematic top plan view of one example configuration of a right-eye rim section 112 of image light guide system 100 having both a negative-power optical element 132 and a positive-power optical element 136, where the positivepower optical element 136 provides a positive optical power contribution 138 that is configured to counteract, cancel, or negate the negative optical power contribution 134 of negative-power optical element 132 with respect to images formed from light reflected off real-world objects RWO within the environment. As shown, the positive-power optical element 136 is positioned between the image light guide 102 and the real -world objects RWO, i.e., on the opposing side of image light guide 102 with respect to the negative-power optical element 132. The positive-power optical element 136 operates to converge incident image-bearing light, increasing the apparent focusing distance of any real -world objects RWO. By positioning the positive-power optical element 136 between the image light guide 102 and the real-world objects RWO with the environment, the positive-power optical element 136 operates to increase the focusing distance for real-world objects RWO and counteract, cancel, or negate the reduction of focusing distance of images of the real-world objects RWO caused by the negative-power optical element 132, prior to the real -world image-bearing light BOA reaching the image light guide 102 and / or the negative-power optical element 132. It should be appreciated that the positive-power optical element 136 could be formed as at least a portion of the cover window 122 and / or the positive optical contribution 138 could be provided at least in part by cover window 122.

[0072] In some examples, the negative optical power contribution 134 and positive optical power contribution 138 are measured in diopters. In these examples, the diopter value of the negativepower optical element 132 is equal to, and opposite of. the optical power provided by the positivepower optical element 134. For example, the negative optical power contribution 134 can be selected as at least one of -0.5, -0.75, -1 , -1.5, -2 diopters etc. As such, to preemptively counteract the effect this negative optical power contribution 134 would have on images of real-world objects RWO, the positive optical power contribution 138 of the positive-power optical element 136 is selected to be at least one of +0.5. +0.75, +1, +1.5, +2 diopters, such that the converging effects of the positive-power optical element 136 and the diverging effects of the negative-power optical element 132 perfectly cancel to have no net effect on the real -world position of the real-world objects 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 providing a positive-power optical element 136 between the image light guide 102 and the real-world objects RWO within the environment, where the optical contributions of each optical element 132, 136 have the same magnitude and cancel each other, is that the virtual objects VO will appear at a focusing distance less than optical infinity while the focusing distance of real-world objects RWO remains unchanged.

[0073] As shown in FIG. 6. virtual image-bearing light 126 (shown in FIGS. 3 and 4) is out- coupled from image light guide 102 as substantially collimated virtual image-bearing light 128A. As virtual image-bearing light 128 A refracts through negative-power optical element 132, the light diverges (shown as virtual image-bearing light 128B). Virtual image-bearing light 128B enters the eyebox E and forms an image of the virtual object VO at a second focusing distance FD2 (shown in FIG. 6 as a triangle formed of dotted lines). Additionally, real-world image-bearing light BOA, reflected off real-world objects RWO within the environment, propagates to the image light guide system 100 and encounters positive-power optical element 136, which converges real- world image-bearing light BOA forming real-world image-bearing light BOB. In this example, the positive-power optical element 136 can be formed with a positive optical power contribution of +2 diopters. Real-world image-bearing light BOB is then transmitted through image light guide 102 and encounters negative-power optical element 132 having a negative optical power contribution 134 of -2 diopters. As real-world image-bearing light BOB refracts through negativepower optical element 132, the light is diverged such that the net effect of the positive opticalpower contribution 138 of the positive-optical power element 136 and the negative optical power contribution 134 of the negative-optical power element 132 cancel, and real-world image-bearing tight 130C is operable to form images of real-world objects RWO at their true positions within the environment.

[0074] It should be appreciated that the example described above with respect to +2 and -2 diopter values is merely one example, and that in operation image light guide system 100 can utilize any conceivable diopter setting for both the negative optical power contribution 134 and the positive optical power contribution 138. In some examples, these two diopter values cancel each other and have no net effect on the perceived focusing distance of real-world objects RWO. It should also be appreciated that although shown schematically in FIG. 6, the positive-power optical element 132 can be formed as, without limitation, a piano-convex lens, a biconvex lens, a positive meniscus lens, or any optical element that causes incident light to converge in predictable ways such that it forms at least one image at an increased focusing distance from its actual distance to the viewer.

[0075] In addition to the foregoing, it may also be desirable to correct for a specific viewer’s optical aberrations associated with various refractive maladies such as myopia (near-sightedness), hyperopia (far-sightedness), or astigmatism. To that end, the image light guide system 100, as shown in FIG. 7, can also include one or more corrective optical elements 140 that provide a corrective optical contribution 142 to both the virtual image-bearing tight 128 and real-world image-bearing tight 130. Corrective optical element 140 can be formed as a monofocal, bifocal, or multifocal optical element, such as a refractive lens, diffraction grating, holographic optical element (HOE), or any combination thereof. As such, corrective optical element 140 can provide spherical or cylindrical corrections specific to the particular viewer.

[0076] As shown in FIG. 7, virtual image-bearing tight 126 (shown in FIGS. 3 and 4) is out- coupled from image light guide 102 as substantially collimated virtual image-bearing light 128A. As virtual image-bearing tight 128 A refracts through negative-power optical element 132, the light diverges (shown as virtual image-bearing light 128B). Virtual image-bearing light 128B continues toward the eyebox E until it encounters and refracts through corrective optical element 140. Corrective optical element 140 provides a corrective optical contribution 142 which can be customized for the viewer to offset for the viewer’s particular optical maladies, e.g., myopia (nearsightedness). The corrected virtual image-bearing light 128C then operates to form one or more images of virtual object VO at a corrected distance CD. In examples, where corrective optical element 140 is selected to correct for near-sightedness, corrective optical contribution 142 wi 11 provide a negative optical power, reducing the apparent distance to the virtual object VO (shownin FIG. 7 as a black triangle). It should also be appreciated that as the negative contribution of the corrective optical contribution 142 and the negative optical power contribution 134 of negativepower optical element 132 are positioned in series, the negative power is compounded, and the virtual object VO will appear at a corrected distance CD that appears closer to the viewer than the second focusing distance FD2.

[0077] Additionally, real-world image-bearing light 130A, reflected off real-world objects RWO within the environment, propagates to the image light guide system 100 and encounters positivepower optical element 136, which converges real-world image-bearing light 130A forming real- world image-bearing light 130B. In this example, the positive-power optical element 136 can be formed with a positive optical power contribution of +2 diopters. Real-world image-bearing light 130B is then transmitted through image light guide 102 and encounters negative-power optical element 132 having a negative optical power contribution 134 of -2 diopters. As real-world imagebearing light 130B refracts through negative-power optical element 132, the light is converged such that the net effect of the positive optical power contribution 138 of the positive-optical power element 136 and the negative optical power contribution 134 of the negative-optical power element 132 cancel forming real-world image-bearing light 130C. which represents the true position of the real-world object RWO within the environment. Real-world image-bearing light 130C continues to propagate in the direction of the eyebox E and encounters corrective optical element 140. Continuing with the example above where the corrective optical element 140 is selected to correct for myopia (near-sightedness), the corrective optical contribution 142 will provide a negative optical power, reducing the apparent distance to the real -world object RWO (shown in FIG. 7 as a black star). It should be appreciated that the negative power of the corrective optical element 140 operates to form images within the eyebox E of real -world objects RWO at a corrected distance CD that appears closer to the viewer than the true position of the real-world object RWO (e.g., at first focusing distance FD1).

[0078]

[0079] In an example embodiment, as illustrated in FIG. 8 A, image light guide system 100 includes a first corrective optical element 140 (i.e., a corrective optical element providing spherical correction, e.g., a spherical or hemispherical lens), image light guide 102 having at least an in-coupling optic IDO and an out-coupling optic ODO, and a second corrective optical element 180 (i.e., a corrective optical element providing cylindrical correction, e.g., a cylindrical lens). For example, the in-coupling optic IDO, the optional intermediate optic TO, and the out-coupling optic ODO could be any combination of volume holograms, holographic polymer dispersed liquid crystal (HPDLC), diffractive surface relief gratings, partially reflective surfaces, prisms,diffractive polarization gratings, or other liquid crystal (LC) formed gratings structures. The first corrective optical element 140 is positioned between the image light guide 102 and the real-world object RWO. For example, light reflected from the real -world object RWO propagates as real- world image-bearing light 130A until it reaches the first corrective optical element 140 where real-world image-bearing light 130A forms real-world image-bearing light BOB. Real-world image-bearing light BOB continues to propagate through image light guide 102 and encounters the second corrective optical element 180 where real-world image-bearing light BOB forms real- world image-bearing light 130C. After transmission through the second corrective optical element 180, real-world image-bearing light 130C continues into the eyebox E and is used to form images of real-world object RWO that appear, for example, closer than the true position of the real-world object RWO in the environment and correct for a particular viewer’s optical aberrations, e.g., astigmatism. In some examples, the first corrective optical element 140 can be formed as at least a portion of a cover window 122 (show n in FIGS. 4-12, 8B. and 8C).

[0080] With continued reference to FIG. 8A, the out-coupling optic ODO is configured to provide spherical correction to the virtual image-bearing light 128 (i.e., the out-coupling optic ODO contributes optical power) out-coupled toward the eyebox E. Spherically corrected virtual imagebearing light 128 A is out-coupled from image light guide 102 and propagates to the second corrective optical element 180. As virtual image-bearing light 128A refracts through the second corrective optical element 180, the light converges or diverges and propagates toward the eyebox E as virtual image-bearing light 128B. Second corrective optical element 180 provides a corrective optical contribution which can be customized for the viewer to offset the viewer’s particular non- symmetrical optical maladies, 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 and corrected for the viewers particular malady. In examples where the second corrective optical element 180 is selected to correct for astigmatism, its corrective optical contribution will provide an asymmetric optical power about a piano-axis of the second corrective optical element operating to correct for a particular view er’ s astigmatism. In this embodiment, the real -world image-bearing light 130 and the virtual image-bearing light 128 each experience a spherical correction and a cylindrical correction.

[0081] Referring now to FIGS. 8B-8D, the first corrective optical element 140, the image light guide 102 and the second corrective optical element 180 are aligned and positioned in proximity to each other substantially forming a stacked arrangement. In an example embodiment, the first corrective optical element 140 may be an ophthalmic eyeglass providing spherical correction to the real-world image-bearing light 130. When arranged between the image light guide 102 andthe real-world object, the first corrective optical element 140 may provide the function of a protective cover window 122. As such, cover win ow 122 may include one or more coatings on the inner or outer surface, e.g., scratch-resistant coatings or anti-reflective coatings. In an example embodiment, the stacked arrangement illustrated is a first stacked arrangement and is optically coupled with a user’s right eye and a second stacked arrangement is optically coupled with the user’s left eye substantially forming a binocular image light guide system. In such a binocular image light guide system the first corrective optical element 140, the out-coupling optic ODO, and the second corrective optical element 180 are aligned to a particular user’s interpupillary distance (IPD). As utilized herein, IPD refers to a distance between a user’s two pupils, or in the context of a monocular system, half of the distance between a user’s two pupils. With continued reference to FIG. 8D, an alignment point AP of the first corrective optical element 140 is schematically shown as overlapping at least a portion of the out-coupling optic ODO of the image light guide 102. When assembled, the optical center of the first corrective optical element 140 and / or the second corrective optical element 180 are configured to align with the alignment point AP and is selected based on a particular user’s IPD. Alignment betw een the first corrective optical element 140, the second corrective optical element 180, and the alignment point AP is necessary' to prevent or limit two-dimensional shifts of real-world image-bearing light 130 (e.g., causing double images and / or eye strain) and the virtual image-bearing light 128 (e.g., causing double images and / or eye strain) in a binocular image light guide system 100. In one or more examples a sealing member can be provided around and / or between the 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.

[0082] In an example embodiment, as illustrated in FIG. 8E, image light guide system 100 includes a first corrective optical element 140 (e.g., a spherical or hemispherical lens) and image light guide 102 having at least an in-coupling optic IDO and an out-coupling optic ODO. The first corrective optical element 140 is positioned between the image light guide 102 and the real-world object RWO. For example, light reflected from the 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 I 30A forms real-world image-bearing light BOB. Real-world imagebearing light 130B continues to propagate through image light guide 102 into the eyebox E and is used to form images of real -world object RWO that appear, for example, closer than the true position of the real-world object RWO in the environment.

[0083] With continued reference to FIG. 8E, the out-coupling optic ODO is configured to provide spherical and / or cylindrical correction to the virtual image-bearing light 128 (i.e., the out-couplingoptic ODO contributes optical power) out-coupled toward the eyebox E. Spherically and / or cylindrically corrected virtual image-bearing light 1 8 A is out-coupled from image tight guide 102 and propagates toward the eyebox E as virtual image-bearing tight 128B. An out-coupling optic ODO configured to contribute both spherical and cylindrical correction of the virtual imagebearing light 128 may be referred to herein as providing a compound optical power contribution. In this embodiment, the real-world image-bearing tight 130 and the virtual image-bearing light 128 each experience a spherical correction and the virtual image-bearing tight 128 experiences a cylindrical correction and / or spherical correction.

[0084] To provide spherical correction to the out-coupled virtual image-bearing tight 128, each of the angularly related beams of the image-bearing tight 128 A is no longer collimated, i.e., diverging from a point at infinity, but instead appears to diverge or converge from a point located much closer or further to the image light guide 102. One mechanism for converting a dimension of collimated image-bearing light 128 propagating along the image tight guide 102 into a plurality of diverging beams representing a near focus position in a virtual image is presented in FIG. 9 as a stepped-chirp out-coupling diffractive optic ODO. Grating vector k5 extends parallel to the x- axis in a direction opposite to the direction along which the collimated image-bearing light 128 is propagated. The period d of the diffractive features of the out-coupling diffractive optic ODO increases in a stepwise manner along the same direction of propagation. 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 features, the angle through which the collimated beam is diffracted decreases with successive encounters of the collimated beam along the stepped-chirp out-coupling diffractive optic ODO. At the start of the out-coupling grating ODO, first encountered by the collimated beam, the period d is relatively shortened so that the diffraction angle is increased, and at the end of the out-coupling diffractive optic ODO, the period d is relatively lengthened so that the diffraction angle is decreased.

[0085] Considered in the x-z plane, stepwise adjustments to the period d along the x-axis length of out-coupling diffractive optic ODO provide for diffracting the representative collimated beam through progressively varying diffraction angles so that the light appears to emanate from nearfocus point f. The other angularly related beams of image-bearing light WG are also diffracted through a progression of different diffraction angles with each successive encounter with out- coupling diffractive optic ODO so that the light from each of these beams appears to emanate from a different near-focus point elsewhere in a common focal plane in accordance with their differing angular content.

[0086] Another mechanism for converting a different dimension of a collimated image-bearing light beam 128 propagating along the image light guide 102 into a diverging beam representing a near focus position in a virtual image is presented in FIG. 10, which depicts a portion of the out- coupling diffractive optic ODO featuring a zone-segmented pattern having an angular variation between the zones generally along a y-axis dimension of the diffractive optic. For simplicity, the period d along the x-axis direction is held constant to emphasize the effect of a stepped variation in the angular orientation of the diffractive features. Referring to FIG. 10, the out-coupling diffractive optic ODO may include straight line diffractive features 182 forming contiguous chordal segments of a curve. Measured against the y-axis, the angle cp of the straight line diffractive features 182 varies in a stepwise fashion along the y-axis as chords of a continuous curve. The straight line diffractive features 182 angularly depart from the y-axis orientation in a stepwise fashion with distance from a centerline 184 of the out-coupling diffractive optic ODO along the x-axis, but the angular departures change in sign on opposite sides of the centerline 184. Progressive redirection of the angularly related beams 128 in the y-z plane can be effected by changing an angle cp of diffractive features within the x-y plane of the image light guide 102. Instead of diffracting individual beams of image-bearing light 128 through a progression of different angles associated with successive encounters with the out-coupling diffractive optic ODO, the beams of image-bearing light 128 are diffracted through a progression of angles (3 in the y-z plane as a function of position along the y axis. Thus, considered in the y-z plane, each of the angularly related beams of the image-bearing light 128 A appears to emanate from a unique near-focus point f.

[0087] FIG. 11 shows, in simplified schematic form, a portion of the out-coupling diffractive optic ODO that is divided into a two-dimensional array of zones Z, which combine a stepwise variation in pitch along the x-axis dimension of the array with a stepwise variation in the orientation of the diffractive features in the y-axis dimension of the array. Each of the zones Z include a set of linear diffractive features, which extend parallel to each other and have equal pitch. However, successive zones along the x-axis dimension of the array, and referred to in the array as a row, have respective sets of parallel diffractive features that extend in the same direction but have different periods d (i.e., different pitch). Successive zones along the y-axis dimension of the array, and referred to in the array as a column, have respective sets of parallel diffractive features that extend in progressively different directions through angle <p.

[0088] Each of the zones Z, as shown numbered Z1 through Z12 in FIG. 11, has the shape of a parallelogram having parallel top and bottom sides spaced apart through a distance corresponding to the length of linear diffractive features 182 and also having parallel left and right sides spacedapart through a distance corresponding to a product of the number of linear diffractive features 182 and period d of each of the equally spaced linear diffractive features 182.

[0089] The linear diffractive features 182 within each zone Zn extend in parallel, and the linear diffractive features 182 within each of the zones of a row also extend in parallel. Thus, grating vectors k of the zones within each row7extend in parallel. However, within each row, the pitch (period d) progressively varies in a stepwise manner among the zones of each row. Thus, the magnitudes of the grating vectors k progressively vary along each row. For example, the grating vectors k 1 , k2, and k3 of contiguous zones Z1 , Z2, and Z3 in the same row all extend in the same direction but at different lengths. Similarly, grating vectors k4, k5, and k6 of contiguous zones Z4, Z5, and Z6 extend in the same direction but at different lengths. A similar observation can be made among the grating vectors of the zones Z7, Z8, and Z9 and the zones Z10, Z11, and Z 12 of the other depicted rows.

[0090] Among the zones of each column, the grating vectors progressively change in angular orientation in a stepwise manner through the angle cp. While the displacements between linear diffractive features 182 in the x-axis direction remain constant among the zones within each of the columns, the pitch itself varies as a product of the x-axis displacement and the cosine of angle cp. Thus, the angular orientations of the grating vectors kl, k4, k7, and klO vary7in angle cp a stepwise manner between the contiguous zones Zl, Z4, Z7, and Z10 of a column and the magnitudes of these grating vectors kl, k4, k7, and klO vary as a function of a constant x-axis displacement of the diffractive features within the column and the cosine of angle cp. A similar observation can be made among the grating vectors of the zones Z2, Z5, Z8, and Zl l and the zones Z3, Z6, Z9, and Z12 of the other depicted columns.

[0091] While the zones of each row include upper and lower boundaries that are all aligned in parallel to a common axis, i.e., the x-axis, the zones in each column are aligned along a respective arc. For example, the zones along two columns of the out-coupling diffractive optic ODO are shown in alignment with arcs. Each linear diffractive features 182 segment that extends between the upper and lower boundaries of a zone can be considered as a chord along an arc. The arcs of the different columns within the out-coupling diffractive optic ODO share the same curvature and are distinguished by7different offsets along the x-axis direction. Although the parallel linear diffractive features 182 between the adj acent zones within the individual columns are oriented in different directions, the shared x-axis displacements of the diffractive features in the adjacent zones within each column allow the parallel diffractive features of the adjacent zones to precisely7abut. Thus, the effective forward surfaces of the linear diffractive features 182 within each zone of a column intersect with the effective forward surfaces of the linear diffractive features 182 ofan adjacent zone within the same column, and the effective rearward surfaces of the linear diffractive features 182 within each zone of a column intersect with the effective rearward surfaces of the linear diffractive features 182 of an adjacent zone within the same column. The included angle between the linear diffractive features 182 at each intersection is the supplementary angle to the angular difference between the angular orientations of the diffractive features of the adjacent zones of the column. Thus, the linear diffractive features 182 of each column form a chordal representation of an arc. Superscribed arcs having these chords are offset between the columns of zones but share the same curvature and are thus not concentric.

[0092] Although the zones differ from one another in at least one of pitch and orientation, the pitch and orientation within any given zone remain constant. Thus, each zone can be easily replicated and matched to its adjacent zones that only vary in pitch and orientation, with the zones in each row sharing the same orientation and the zones of each column sharing the same x-axis displacements between linear diffractive features 182.

[0093] In an example embodiment, to achieve cylindrical correction utilizing the out-coupling optic ODO, the zones are configured non-symmetrically. For example, the zones are configured to provide optical power along one axis of the out-coupling diffractive optic ODO. The imagebearing light beams are effectively redirected by the zones from parallel orientation to a series of convergence points along an imaginary line / axis. In an out-coupling optic ODO providing 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 the orthogonal axis.

[0094] In another example embodiment, FIG. 12 shows, in simplified schematic form, a portion of the out-coupling diffractive optic ODO having a first set of diffractive features 186 and a second set of diffractive features 188. First set of diffractive features 186 may be optimized to out-couple a first wavelength range of light (e.g., blue light) and second set of diffractive features 188 may be optimized to out-couple 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., curvilinear) or approximate a curve with linear segments to introduce optical power as described above. In an exemplary embodiment, first set of diffractive features 186 is chirped in a first direction, meaning diffractive features 186 progressively increase in pitch in one direction. For example, first set of diffractive features 186 have a pitch dl progressively increasing in pitch in a first direction (i.e., a direction opposite to the direction of grating vector k4). In an exemplary embodiment, second set of diffractive features 188 is chirped in a second direction different from the first direction. For example, second set of diffractive features 188 comprises pitch d2 progressively increasing in pitch in a second direction (i.e., a direction opposite to thedirection of grating vector k5). In an exemplary embodiment, the pitch progression of second set of diffractive features 188 is equal to the pitch progression of 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.

[0095] With continued reference to FIG. 12, the out-coupling diffractive optic ODO may be divided into a two-dimensional array of zones, for example zones Z1-Z12. Each of zones Z1-Z12 includes a set of linear diffractive features 186, 188. which extend parallel to each other and have equal pitch within each respective zone Z1 -Z12. For example, zone Z1 includes diffractive features 186 including pitch dl and diffractive features 188 including pitch d2. In an exemplary' embodiment, pitch dl is equal to pitch d2. In other example embodiments, pitch dl 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.

[0096] Diffractive features 186 exhibit a stepwise variation in pitch dl along the x-axis dimension of the array, referred to as rows. Thus, in an example, pitch dl in zone Z1 is greater than pitch dl in zone Z2, which is greater than pitch dl in zone Z3. In addition to its ordinary' meaning to those in the art, the term “stepwise variation” is intended to describe that the common pitch (e.g., pitch dl) between diffractive features of the same zone is constant, but the common pitch dl in each successive zone along the x-axis dimension of the array changes, e.g., increases or decreases. Additionally, diffractive features 186 comprise the same (e.g., constant) curvature / grating orientation along the x-axis, namely, diffractive features 186 have the same grating vector 1 4D across zones Z1-Z3 (i.e., the angle of diffractive features 186 across zones Z1-Z3 are the same, and thus diffractive features 186 across zones Z1-Z3 are parallel to each other). This same behavior occurs with respect to diffractive features 186 across the x-axis throughout the array. Diffractive features 186 exhibit a stepwise variation in pitch dl , e.g. , decreasing in each successive zone across zones Z4-Z6, and a constant grating vector k4c. Diffractive features 186 exhibit a stepwise variation in pitch dl, decreasing in each successive zone across zones Z7-Z9, and a constant grating vector k4n. Diffractive features 186 exhibit a stepwise variation in pitch dl, decreasing in each successive zone across zones Z10-Z12, and a constant grating vector k4A. Diffractive features 186 exhibit a stepwise variation in grating vector along the y-axis dimension of the array, referred to as columns. That is, diffractive features 186 of each zone in a column comprise a set of parallel diffractive features having a common pitch dl. that extend in progressively different directions through angle <|). As shown, the angle of diffractive features 186 and their grating vectors k4A, k4n. k4c, k4o differ in zones Zl, Z4, Z7, and Z10, respectively. For example, while diffractive features 186 are linear in each respective zone, diffractive features 186approximate a curved line in the direction of the y-axis dimension. Similarly, diffractive features 186 exhibit the stepwise variation in direction in the column including zones Z2, Z5, Z8, and Zl 1 , and the column including zones Z3, Z6, Z9, and Z12.

[0097] It should be appreciated that grating vectors k4 for diffractive features 186 may increase in magnitude in the x-axis dimension as the pitch dl decreases (i.e., k=2n / A). Thus, the magnitude of grating vector k4o increases in stepwise fashion across zones Z1-Z3. Similarly, in some embodiments, grating vector k5c increases in magnitude in stepwise fashion across zones Z4-Z6, grating vector k5e increases in magnitude in stepwise fashion across zones Z7-Z9, and grating vector k5 \ increases in magnitude in stepwise fashion across zones Z10-Z12.

[0098] Diffractive features 188 exhibit a stepwise variation in pitch d2 along the y-axis dimension of the array (i.e., the columns). Thus, pitch d2 in zone Z1 is greater than pitch d2 in zone Z4, which is greater than pitch d2 in zone Z7 , which is greater than pitch d2 in zone Z10. In addition to its ordinary meaning to those in the art, the term “stepwise variation” is intended to describe that the common pitch d2 within each zone is constant within the zone, but in each successive zone along the y-axis dimension of the array the pitch changes, e.g., increases or decreases. Diffractive features 188 comprise the same curvature / grating orientation along the y-axis, namely, diffractive features 188 have the same grating vector k5A across zones Zl, Z4, Z7. and Z10 (i.e., the angle of diffractive features 188 across zones Zl, Z4, Z7, and Z10 are the same, and thus diffractive features 188 across zones Zl, Z4, Z7, and Z10 are parallel to each other). This same behavior occurs with respect to diffractive features 188 across the y-axis throughout the array. Diffractive features 188 exhibit a stepwise variation in pitch d2, decreasing in each successive zone across zones Z2, Z5, Z8, and Zl 1, and a constant grating vector k5B. Diffractive features 188 exhibit a stepwise variation in pitch d2, decreasing in each successive zone across zones Z3, Z6, Z9, and Z12, and a constant grating vector k5c. Diffractive features 188 exhibit a stepwise variation in grating vector along the x-axis dimension of the array (i.e., the rows). That is, diffractive features 188 of each zone in a row comprises a set of parallel diffractive features d2, having the same pitch, that extend in progressively different directions through angle (f). As shown, the angle of diffractive features 188 and their grating vectors k5 \-k5<- differ in zones Z1-Z3, respectively. While diffractive features 188 are linear in each respective zone, diffractive features 188 approximate a curved line in the direction of the x-axis dimension. Similarly, diffractive features 188 exhibit the stepwise variation in direction in the row including zones Z4-Z6. the row including zones Z7-Z9, and the row including zones Z10-Z12.

[0099] It should be appreciated that grating vectors k5 for diffractive features 188 may increase in magnitude in the y-axis dimension as the pitch d2 decreases. Thus, the magnitude of gratingvector k5 increases in magnitude in stepwise fashion across zones Zl. Z4. Z7, and Z 10. Similarly, in some embodiments, grating vector k B increases in magnitude in stepwise fashion across zones Z2, Z5, Z8, and Zll, and grating vector k5c increases in magnitude in stepwise fashion across zones Z3, Z6, Z9, and Z12.

[0100] It should be appreciated that the vector contributions of either the curve (or approximated curve) and / or the chirp of diffractive features 186, 188 at any given point along out-coupling diffractive optic ODO independently create spherical and / or cylindrical optical power. For example, when the vector contributions of the curve (or approximated curve) and the chirp of diffractive features 186, 188 are combined, two-dimensional optical power is introduced, that if properly balanced would create spherical optical power.

[0101] In another example embodiment, as schematically illustrated in FIG. 13, the out-coupling diffractive optic 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 curved (i.e., curvilinear) or approximate a curve with linear segments to introduce optical power as described above. The second set of diffractive features 192 are linear diffractive features. This out-coupling diffractive optic ODO combines spherical correction functionality with eyebox E expansion functionality.

[0102] With reference now to FIG. 14A, in an example embodiment, the image light guide system 100 includes the first corrective optical element 140 and image light guide 102 having at least an in-coupling optic IDO and an out-coupling optic ODO. The first corrective optical element 140 is positioned between the image light guide 102 and the real-world object RWO. For example, light reflected from the 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 BOA forms real-world image-bearing light BOB. In this embodiment, the first corrective optical element 140 comprises a lens, for example, with a spherical correction component and a cylindrical correction component. Real-world image-bearing light BOB continues to propagate through image light guide 102 into the eyebox E and is used to form images of real -world object RWO that appear, for example, closer than the true position of the real-world object RWO in the environment. The cylindrical correction component of the first corrective optical element 140 focuses real-world image-bearing light BOB about an optical axis in accordance with the particular prescription.

[0103] With continued reference to FIG. 14A, the out-coupling optic ODO is configured to provide a spherical correction and a cylindrical correction to the virtual image-bearing light 128 out-coupled toward the eyebox E. Spherically and cylindrically corrected virtual image-bearinglight 128A is out-coupled from image light guide 102 and propagates toward the eyebox E as virtual image-bearing light 128B. In this embodiment, the real-world image-bearing light 130 and the virtual image-bearing light 128 each experience a spherical correction and a cylindrical correction.

[0104] With reference now to FIG. 14B, in an example embodiment, the image light guide system 100 includes the first corrective optical element 140 and the image light guide 102 having at least an in-coupling optic IDO and an out-coupling optic ODO. The first corrective optical element 140 is positioned between the image light guide 102 and the real-world object RWO. For example, light reflected from the 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, the first corrective optical element 140 comprises a lens, for example, with a cylindrical correction component. Real- world image-bearing light 130B continues to propagate through image light guide 102 into the eyebox E focused to a meridian in accordance with the particular prescription.

[0105] With continued reference to FIG. 14B, the out-coupling optic ODO is configured to provide a cylindrical correction to the virtual image-bearing light 128 out-coupled toward the eyebox E. Cylindrically corrected virtual image-bearing light 128 A is out-coupled from image light guide 102 and propagates toward the eyebox E as virtual image-bearing light 128B. In this embodiment, the real-world image-bearing light 130 and the virtual image-bearing light 128 each experience a cylindrical correction.

[0106] With reference now to FIG. 14C, in an example embodiment, the image light guide system 100 includes the first corrective optical element 140, the image light guide 102 having at least an in-coupling optic IDO and an out-coupling optic ODO. and the second corrective optical element 180. The first corrective optical element 140 is positioned between the image light guide 102 and the real-world object RWO. For example, light reflected from the 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, the first corrective optical element 140 comprises a lens, for example, with a spherical correction component. Real-world image-bearing light I 30B continues to propagate through image light guide 102 to the second corrective optical element 180 where real-world image-bearing light 130B forms real-world image-bearing light 130C. In this embodiment, the second corrective optical element 180 comprises a lens, for example, with a cylindrical correction component. After transmission through the second corrective optical element 180, real-world image-bearing light 130C continues into the eyebox E and is used to form images of real-worldobject RWO that appear, for example, closer than the true position of the real-world object RWO in the environment and correct for a particular viewer’s optical aberrations, e g., astigmatism.

[0107] With continued reference to FIG. 14C, the out-coupling optic ODO is configured to out- couple the virtual image-bearing light 128 A toward the eyebox E without a spherical or cylindrical correction. The virtual image-bearing light 128A is out-coupled from image light guide 102 and encounters the second corrective optical element 180 where the virtual image-bearing light 128A forms cylindrically corrected virtual image-bearing light 128B. In this embodiment, the real-world image-bearing light 130 and the virtual image-bearing light 128 each experience a cylindrical correction, and the real-world image-bearing light 130 also experiences a spherical correction.

[0108] In addition, examples of the image light guide system 100 include both the first corrective optical element 140 and the second corrective optical element 180 contributing spherical correction. Additional examples of the image light guide system 100 include both the first corrective optical element 140 and the second corrective optical element 180 contributing cylindrical correction. Further, the image light guide 102 can contribute either spherical or cylinder correction, or both.

[0109] In one or more example embodiments, the image light guide system 100 may utilize digital spherical and / or cylindrical correction. With reference now to FIG. 15 A, in an example embodiment, the image light guide system 100 includes a cover window 122, the image light guide 102 having at least an in-coupling optic IDO and an out-coupling optic ODO, a digital spherical correction element 200, and the cylindrical correction optical element 180. The cover window 122 is arranged between the image light guide 102 and the real -world object RWO and contributes no, or substantially no, optical power to the real -world image-bearing light 130A. Light reflected from the real-world object RWO propagates as real-world image-bearing light BOA through the cover window 122 and the image light guide 102 until it reaches the digital spherical correction element 200 where real-world image-bearing light BOA forms real-world image-bearing light BOB. For example, the digital spherical correction element 200 comprises a liquid crystal layer operable to provide a spherical correction to incident light. Real-world imagebearing light BOB continues to propagate to the cylindrical correction optical element 180 where real-world image-bearing light BOB forms real-world image-bearing light 130C. In this embodiment, the cylindrical correction optical element 180 comprises a lens, for example, with a cylindrical correction component. After transmission through the cylindrical correction optical element 180, real-world image-bearing light 130C continues into the eyebox E and is used to form images of real-world object RWO that appear, for example, closer than the true position of thereal-world object RWO in the environment and correct for a particular viewer’s optical aberrations, e.g., astigmatism.

[0110] With continued reference to FIG. 15A, the out-coupling optic ODO is configured to out- couple the virtual image-bearing light 128 A toward the eyebox E without a spherical or cylindrical correction. The virtual image-bearing light 128A is out-coupled from image light guide 102 and encounters the digital spherical correction element 200 where virtual image-bearing light 128A forms virtual image-bearing light 128B. The virtual image-bearing light 128B then encounters the cylindrical correction optical element 180 where the virtual image-bearing light 128B forms cylindrically corrected virtual image-bearing light 128C. In this embodiment, the real-world image-bearing light 130 and the virtual image-bearing light 128 each experience a cylindrical correction and a spherical correction.

[0111] With reference now to FIG. 15B, in an example embodiment, the image light guide system 100 includes a cover window 122, the image light guide 102 having at least an in-coupling optic IDO and an out-coupling optic ODO, a digital spherical correction element 200, and the digital cylindrical correction element 202. The cover window 122 is arranged between the image light guide 102 and the real-world object RWO and contributes no, or substantially no, optical power to the real -world image-bearing light BOA. Light reflected from the real-world object RWO propagates as real-world image-bearing light BOA through the cover window 122 and the image light guide 102 until it reaches the digital spherical correction element 200 where real- world image-bearing light BOA forms real-world image-bearing light BOB. For example, the digital spherical correction element 200 comprises a liquid crystal layer operable to provide a spherical correction to incident light. Real-world image-bearing light BOB continues to propagate to the digital cylindrical correction element 202 where real-world image-bearing light BOB forms real-world image-bearing light 130C. For example, the digital cylindrical correction element 202 comprises a liquid cry stal layer operable to provide a cylindrical correction to incident light. After transmission through the digital cylindrical correction element 202, real-world image-bearing light 130C continues into the eyebox E and is used to form images of real-world object RWO that appear, for example, closer than the true position of the real-world object RWO in the environment and correct for a particular viewer’s optical aberrations, e g., astigmatism.

[0112] With continued reference to FIG. 15B, the out-coupling optic ODO is configured to out- couple the virtual image-bearing light 128 A toward the eyebox E without a spherical or cylindrical correction. The virtual image-bearing light 128A is out-coupled from image light guide 102 and encounters the digital spherical correction element 200 where virtual image-bearing light 128 A forms virtual image-bearing light 128B. The virtual image-bearing light 128B then encounters thedigital cylindrical correction element 202 where the virtual image-bearing light 128B forms cylindrically corrected virtual image-bearing light 128C. Tn this embodiment, the real-world image-bearing light 130 and the virtual image-bearing light 128 each experience a cylindrical correction and a spherical correction.

[0113] With reference now to FIG. 15C, in an example embodiment, the image light guide system 100 includes a cover window 122, a digital spherical correction element 200, the image light guide 102 having at least an in-coupling optic IDO and an out-coupling optic ODO, and the cylindrical corrective optical element 180. The cover window' 122 is arranged between the image light guide 102 and the real -world object RWO and contributes no, or substantially no, optical power to the real -world image-bearing light 130A. Light reflected from the real-world object RWO propagates as real-world image-bearing light I 30A through the cover window 122 until it reaches the digital spherical correction element 200 where real -world image-bearing light 130 A forms real -world image-bearing light 130B. For example, the digital spherical correction element 200 comprises a liquid crystal layer operable to provide a spherical correction to incident light. Real -world image-bearing light BOB continues to propagate through the image light guide 102 to the cylindrical corrective optical element 180 where real-world image-bearing light BOB forms real-world image-bearing light 130C. For example, the cylindrical corrective optical element 180 comprises a lens, for example, with a cylindrical correction component. After transmission through the cylindrical correction optical element 180, real -world image-bearing light 130C continues into the eyebox E and is used to form images of real-world object RWO that appear, for example, closer than the true position of the real-world object RWO in the environment and correct for a particular viewer’s optical aberrations, e.g., astigmatism.

[0114] With continued reference to FIG. 15C, the out-coupling optic ODO is configured to out- couple the virtual image-bearing light 128 A toward the eyebox E without a spherical or cylindrical correction. The virtual image-bearing light 128A is out-coupled from image light guide 102 and encounters the digital spherical correction element 200 where virtual image-bearing light 128 A forms virtual image-bearing light 128B. The virtual image-bearing light 128B then encounters the cylindrical corrective optical element 180 where the virtual image-bearing light 128B forms cylindrically corrected virtual image-bearing light 128C. In this embodiment, the real-world image-bearing light 130 and the virtual image-bearing light 128 each experience a cylindrical correction and a spherical correction.

[0115] With reference now to FIG. 15D, in an example embodiment, the image light guide system 100 includes a cover window 122, a digital spherical correction element 200, the image light guide 102 having at least an in-coupling optic IDO and an out-coupling optic ODO, and thedigital cylindrical correction element 202. The cover window 122 is arranged between the image light guide 102 and the real-world object RWO and contributes no, or substantially no, optical power to the real-world image-bearing light 130A. Light reflected from the real-world object RWO propagates as real-world image-bearing light 130A through the cover window 122 until it reaches the digital spherical correction element 200 where real -world image-bearing light 130A forms real-world image-bearing light 130B. For example, the digital spherical correction element 200 comprises a liquid crystal layer operable to provide a spherical correction to incident light. Real -world image-bearing light 130B continues to propagate through the image light guide 102 to the digital cylindrical correction element 202 where real-world image-bearing light BOB forms real-world image-bearing light 130C. For example, the digital cylindrical correction element 202 comprises a liquid crystal layer operable to provide a cylindrical correction to incident light. After transmission through the digital cylindrical correction element 202, real-world image-bearing light 130C continues into the eyebox E and forms images of real-world object RWO that appear, for example, closer than the true position of the real -world object RWO in the environment and correct for a particular viewer’s optical aberrations, e.g., astigmatism.

[0116] With continued reference to FIG. 15D, the out-coupling optic ODO is configured to out- couple the virtual image-bearing light 128 A toward the eyebox E without a spherical or cylindrical correction. The virtual image-bearing light 128A is out-coupled from image light guide 102 and encounters the digital cylindrical correction element 202 where virtual image-bearing light 128A forms cylindrically corrected virtual image-bearing light 128B. In this embodiment, the real-world image-bearing light 130 and the virtual image-bearing light 128 each experience a cylindrical correction and the real -world image-bearing light 130 experiences a spherical correction.

[0117] To increase manufacturing efficiency, the range of diopters and IPD alignments of the first corrective optical elements 140 (i.e., the corrective optical element 140 arranged between the real -world image-bearing light and the image light guide 102) may be limited, and the second corrective optical elements 180 may be customized to correct for a particular viewer’s optical aberrations and / or prism error caused by a difference in IPD of the wearer compared to the IPD of the first corrective optical element 140. For example, the optical power contribution of the first corrective optical element 140 may be limited to one of: +2, 0, and -2 diopters and two standardized IPD alignments. In another example, the optical power contribution of the first corrective optical element 140 may be limited to +3, +2. 0, -2, and -3 diopters and three standardized IPD alignments. In other words, only a relatively small number of diopter powers and IPD alignments need to be provided by the first corrective optical elements 140. Similarly,the optical power contribution of the image light guide 102 may be limited to a range of diopters substantially equal to the optical power contribution of the first corrective optical elements 140.

[0118] Referring now to FIGS. 16A-16C, in an example embodiment, the first corrective optical element 140 and the image light guide 102 are aligned and positioned in proximity to each other substantially forming a stacked arrangement. The first corrective optical element 140 may be an ophthalmic eyeglass providing spherical correction to the real-world image-bearing light 130. When arranged between the image light guide 102 and the real -world object, the first corrective optical element 140 may provide the function of a protective cover window 122. As such, cover window 122 may include one or more coatings on the inner or outer surface, e.g., scratch-resistant coatings or anti-reflective coatings. In an example embodiment, the stacked arrangement illustrated is a first stacked arrangement and is optically coupled with a user’s right eye and a second stacked arrangement is optically coupled with the user’s left eye substantially forming a binocular image light guide system.

[0119] In an example embodiment, the center of correction of the first corrective optical element 140 and the output aperture center of the out-coupling optic ODO are aligned at an alignment point AP. As referred to herein, the center of correction refers to the optical center of an optical element (e.g., a lens). The optical center of an optical element refers to the axis of rotational symmetry (e.g., a point on the principal axis of a lens through which light passes without deviation). As referred to herein, the axis of correction refers to the reference axis about which a cylindrical optical power is determined or defined. The alignment point AP is schematically shown as overlapping at least a portion of the out-coupling optic ODO of the image light guide 102.

[0120] When assembled, the optical center of the first corrective optical element 140 is configured to align with the alignment point AP. However, as illustrated in FIG. 16D, a particular user’s interpupillary distance (IPD) may not match the nominal IPD aligned to the center of the output aperture, resulting in a perceived shift of the real-w orld image. Alignment of the center of correction of the stacked arrangement of the image light guide system 100 with the user's IPD is necessary to prevent or limit two-dimensional shifts of real -world image-bearing light 130 and the virtual image-bearing light 128 (e.g., causing double images and / or eye strain) in a binocular image light guide system 100. This perceived shift of the real-world image-bearing light 130 is referred to as prism error and may be calculated by the following equation, where the IPD misalignment / error is referred to as decentration (measured in millimeters):Prism Error = (Decentration (mm) * Power (diopters)) / 10 (1)

[0121] The second corrective optical element 180 can be customized to correct for and / or offset this prism error and can be added to the stacked arrangement between the image light guide 102 and the user. For example, the second corrective optical element 180 can be customized to contribute the necessary diopters of power to offset the prism error induced by IPD misalignment of the first corrective optical element 140. thereby reducing or eliminating any prism error in the user’s perceived position of a real-world object. In other words, as illustrated in FIG. 16D, the offset of the center of correction DE of the second corrective optical element 180 is arranged in the x-y plane, and correction results from the position of the center of correction DE of the second corrective optical element 180 in the x-y plane relative to the optical center of the first corrective optical element 140. The amount of shift of the center of correction DE of the second corrective optical element 180 relative to the user’s IPD is a function of the remaining power requirements of the system.

[0122] In an example where the IPD misalignment is 2 mm and the first corrective optical element 140 contributes -2 diopters of power, equation (1) provides that the prism error equals -0.4 diopters. To correct this prism error, the second corrective optical element 180 must provide +0.4 diopters of prism error. In this example, the user requires a prescription of -4.25 diopters, and therefore the second corrective optical element 180 must provide -2.25 diopters (-2 diopters from the first corrective optical element 140 and -2.25 diopters from the second corrective optical element 180), equation (1) can be solved for the necessary' Decentration of the second corrective optical element 180 that would result in a +0.4 diopters of prism error:Decentration (mm) = (Prism Error * 10) / Power (diopters) (2)In the given example, the center of correction of the second corrective optical element 180 must be aligned -1.78 mm opposite the alignment point AP about the IPD position of the user (shown as a vertical line in FIG. 16D). The negative (-) value of the decentration to align the center of correction DE of the second corrective optical element 180 indicates that the center of correction DE should be aligned on the side of the measured IPD position of the user opposite the alignment point AP.

[0123] As illustrated in FIG. 16F. in another example embodiment, the second corrective optical element 180 can be customized to contribute the necessary diopters of power to offset the prism error induced by IPD misalignment of the first corrective optical element 140 by creating a wedge in the second corrective optical element 180. For example, the second corrective optical element 180 can be configured to correct for prismatic error through the angular tilting of at least one optical surface. The wedge configured to angularly tilt at least one optical surface of the secondcorrective optical element 180 can be created by increasing the thickness of one side or portion of the second corrective optical element 180. As shown in FIG. 16F, the light transmitted through the second corrective optical element 180 “bends” towards the thick side of the wedge. The image light guide system 100 shown in FIG. 16F comprises a “horizontal” wedge configured to produce a “horizontal” shift. However, a “vertical” wedge, and a combination of a “horizontal” and “vertical” wedge, is also considered by the present disclosure. In another example embodiment, the second corrective optical element 180 can be configured to correct for prismatic error by changing the position of the foci of the curve of the optical surface. In other words, the focus of the curve of the optical surface is shifted in the x-y plane, and correction results from the position of the center of correction DE, the foci, of the second corrective optical element 180 in the x-y plane relative to the optical center of the first corrective optical element 140.

[0124] Referring now to FIG. 17A-17B, in an example embodiment, the second corrective optical element 180 also provides cylindrical correction (e.g., in addition to spherical correction) to correct for, for example, astigmatism for both the virtual image and the real-world image RWO. In an example embodiment, the axes of the cylindrical power dx. dxxof the second corrective optical element 180 are rotated 45° relative to a horizontal (e.g., the x-axis) to accommodate a user’s prescription. As illustrated in FIG. 17B, in an example embodiment, a prescription requires a -4 diopter spherical correction dxand a +2 diopter cylindrical correction dxx. As those skilled in the relevant arts will recognize, under different convention this prescription may be provided as a -2 diopter spherical correction dxand a -2 diopter cylindrical correction dxx. As described above, where a user’s IPD position is 2 mm from the center of correction of the first corrective optical element 140, the second corrective optical element 180 provides +0.4 diopters of prism error to account for the user’s IPD. To account for the 45 degree rotation of the user’s prescription axis as a function of the dxand dxx axes, the following equations provide the positional shift required to align the center of correction of the second corrective optical element 180 such that it offsets the prism error caused by the misaligned center of correction of the first corrective optical element 140:Decentration (mm) = ((Prism Error * Sin(45)) * 10) / Power (diopters) (3)Decentration (mm) = ((Prism Error * Cos(45)) * 10) / Power (diopters) (4)In the example illustrated in FIG. 17B, a single shift of the center of correction referenced to the horizontal, with the cylinder correction rotated correctly, would be a -1.581 mm shift from the IPD position at -18.43° below the horizon. For example, along the -2 diopter axis dxx, decentration equals:-1.414 mm = ((0.4 D * Sin(45)) * 10) / -2 D)While along the -4 diopter axis dx. decentration equals:-0.707 mm = ((0.4 D * Cos(45)) * 10) / -4 D)These decentration values forming the legs (i.e., sides forming a 90° angle) of a right-triangle, the hypotenuse can be calculated to be -1.581 mm. The center of correction DE of the second corrective optical element 180 is shifted from the user’s IPD by 1.581 mm at -18.43° below the horizon.

[0125] It should be appreciated that splitting the optical power contribution between the first corrective optical element 140 and the second corrective optical element 180 will likely induce prism error because the first corrective optical element 140 may not be customized to any particular user’s IPD or complete prescription. However, this arrangement enables more optical prescriptions to be provided in a smaller package than an arrangement locating all optical correction in the customized second corrective optical element 180. In other words, the prism error can be avoided if the first corrective optical element 140 is also customized for each user but that would limit the manufacturability of the product and decrease the range of prescriptions that can be accommodated by single lens correction. As described above, utilizing standardized first corrective optical elements 140 with customized second corrective optical elements 180 greatly increases the manufacturing efficiency of the image light guide system 100, while also providing the ability to correct for a wide range of optical maladies and prescriptions.

[0126] In an example embodiment, the center of correction of the second corrective optical element 180 can be operable to create a perceived shift in the relative position of the virtual image (e.g., in the x-y plane). In another example embodiment, the second corrective optical element 180 can be utilized to change the focal distance of the virtual image. For example, the first corrective optical element 140 may contribute 1 diopter of power and the second corrective optical element 180 may contribute -1 diopter of power, or vice versa, to move the focus of the virtual image from infinity to, without limitation, approximately one meter (1 m) in front of the viewer without affecting the focal distance of the real-world image-bearing light. It should be appreciated that this principle can be applied to any system in which it is desirable to have a different focal distance of the real-world image-bearing light and the virtual image. The optical power of the second corrective optical element 180 may be selected to be any diopter required to change the finite focal distance of the virtual image to the desired position.

[0127] In examples where the image light guide out-coupling diffractive optic ODO includes asymmetric diffractive features (e.g., blazed or slanted diffractive features), high contrast real-world image-bearing light generated by light sources closely located to the out-coupling diffractive optic ODO and incident upon the out-coupling diffractive optic ODO may be undesirably diffracted into, and out of, the image light guide 102. For example, a smart phone display or a vehicle instrument panel(or dashboard) arranged, for example, within two meters (2 m) of the out-coupling diffractive optic ODO may emit high contrast real-world image-bearing light. Because these light source are located close to the out-coupling diffractive optic ODO, the high contrast real-world image-bearing light incident upon the out-coupling diffractive optic ODO functions as if emitted from one or more point sources as uncollimated light. This uncollimated high contrast real-world image-bearing light may produce ghost images of the real world objects or displays being viewed, causing the viewer eye strain and / or generally diminishing the viewing experience. In an example embodiment, an image light guide system 100 is configured to account for uncollimated high contrast real-world image-bearing light generated by closely located light sources by arranging a first corrective optical element 140 contributing positive optical power on the side of the image light guide 102 opposite the eyebox. The first corrective optical element 140 can be configured to partially or completely collimate the high contrast real-world image-bearing light before it is incident upon the out-coupling diffractive optic ODO, effectively minimizing the unwanted ghost images.

[0128] In an example embodiment, the image light guide system 100 may include a first corrective optical element 140 contributing a positive optical power, an image light guide 102 having an out-coupling diffractive optic ODO with blazed diffractive features contributing a positive optical power substantially equal to the optical power of the first corrective optical element 140 arranged between the first corrective optical element 140 and the eyebox, and a second corrective optical element 180 contributing a negative optical power arranged between the image light guide 102 and the eyebox. In an example, the first corrective optical element 140 includes 1 diopter of optical power, the out-coupling diffractive optic ODO includes 1 diopter of optical power, and the second corrective optical element 180 includes -1 diopters of optical power. In another example, the first corrective optical element 140 includes 2 diopters of optical power, the out-coupling diffractive optic ODO includes 2 diopters of optical power, and the second corrective optical element 180 includes -2 diopters of optical power. It should be appreciated that these image light guide system 100 arrangements do not need to, but may, correct for a viewer’s optical aberrations, and are designed to substantially collimate light from nearby high contrast light sources (e.g., within 1.5 meters of the out-coupling diffractive optic ODO) and reduce or eliminate ghost images associated therewith. In any of the foregoing examples, optical power provided by the out-coupling diffractive optic ODO may be cancelled by the optical powerprovided by the second corrective optical element 180, so that there is not a substantial change in focal distance for the virtual image. The optical powers of the out-coupling diffractive optic ODO and the second corrective optical element 180, respectively, can also be different in order to induce a change in focal distance for the virtual image.

[0129] In an example embodiment, digital correction of the angular encoding of the virtual image can be utilized to digitally correct for the perceived shift in the virtual image positioning where the center of the output aperture is not aligned with the center of correction of the first corrective optical element 140.

[0130] It should be appreciated that in any of the foregoing descriptions and illustrations, digital correction elements may be substituted for fixed lenses performing the same function. In any of the example embodiments described herein utilizing one or more lenses (e.g., corrective optical elements 122, 140, 180), the thickness of the lens should be considered. For example, the powers chosen across a lens are selected such that the thickness, measured at the outer perimeter of the lens, of the lenses stays 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 powers balanced across multiple optical elements to allow for a similar lens thickness in any two successive image light guide systems 100. In other words, the optical power provided by the first corrective optical element 140 and the second corrective optical element 180 can be selected such that the total optical power achieved by the system is configured for a particular prescription without increasing the initial thickness of the first corrective optical element 140 or the second corrective optical element 180.

[0131] In any of the example embodiments described herein, optical power in the corrective optical element 122, 140, 200 arranged between the real-world object RWO and the image light guide 102 and optical power in the image light guide 102 may generally be the same. Having the same optical power in these elements facilitates correction of the virtual image and the real-world image to the same focal distance (e.g., optical infinity). In other examples of the embodiments described herein, optical power in the corrective optical element 122, 140, 200 arranged between the real-world object RWO and the image light guide 102 and optical power in the image light guide 102 may be different.

[0132] The perspective view shown in FIG. 18 illustrates one example of image light guide system 100 in a display system for augmented reality viewing of virtual images. The image light guide system 100 uses one or more image light guides (e.g., image light guides 102). Image light guide system 100 is shown as a head-mounted display (HMD) with a right-eye rim section 112 having an image light guide 102R proximate the user’s right eye. The image light guide system100 includes image source 108, such as a pico-projector or similar device, energizable to generate one or more virtual images. Although not illustrated, in one example, image light guide system 100 includes a left-eye optical system including one or more image light guides and a second image source. In examples using both a right-eye rim section 112 and a left-eye rim section, the virtual images that are generated can be a stereoscopic pair of images for 3D viewing. During operation by a user or viewer, the virtual image or images formed by the image light guide system 100 can appear to be superimposed or overlaid onto the real -world scene content seen by the viewer through the right eye image light guide 102R and / or left eye image light guide. Additional components familiar to those skilled in the augmented reality visualization arts, such as one or more cameras mounted on the frame of the HMD for viewing scene content or viewer gaze tracking, can also be provided.

[0133] One or more features of the embodiments described herein may be combined to create additional embodiments which are not depicted. While various embodiments have been described in detail above, it should be understood that they have been presented by w ay of example, and not limitation. It will be apparent to persons skilled in the relevant arts that the disclosed subject matter may be embodied in other specific forms, variations, and modifications without departing from the scope, spirit, or essential characteristics thereof. The embodiments described above are therefore to be considered in all respects as illustrative, and not restrictive. The scope of the invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.

Claims

CLAIMSWhat is claimed is:

1. A near-eye display system, comprising: a first corrective optical element having a first optical power contribution operable to converge or diverge real-world image-bearing light beams in advance of an eyebox to a first focusing distance; a second corrective optical element arranged between the first corrective optical element and the eyebox, the second corrective optical element having a spherical optical power contribution operable to converge or diverge virtual and real-world imagebearing light beams in advance of the eyebox to a second focusing distance, the first corrective optical element having a first center of correction, and the second corrective optical element having a second center of correction.

2. The near-eye display system according to claim 1, wherein the first center of correction is offset from an interpupillary distance position, wherein the offset at least partially induces a prism error.

3. The near-eye display system according to claim 2, wherein the second center of correction is arranged to offset the prism error.

4. The near-eye display system according to claim 3, wherein the second center of correction is arranged opposite the first center of correction about the interpupillary distance position.

5. The near-eye display system according to claim 1, wherein the second corrective optical element includes a cylindrical optical power contribution operable to reduce optical aberrations associated with viewing the real-world object and the virtual object at the second focusing distance, wherein the second corrective optical element includes an axis of correction.

6. The near-eye display system according to claim 5, wherein the axis of correction is arranged above or below a horizontal bisecting the first center of correction.

7. The near-eye display system according to claim 1, wherein the first corrective optical element comprises a liquid crystal layer operable to provide a digital correction of the real-world image-bearing light beams.

8. The near-eye display system according to claim 1, wherein the second corrective optical element comprises a liquid crystal layer operable to provide a digital correction of the real-world image-bearing light beams and the virtual image-bearing light beams.

9. The near-eye display system according to claim 3, wherein the second corrective optical element comprises a wedge.

10. The near-eye display system according to claim 2, wherein the second corrective optical element comprises a focus of an optical surface shifted to offset the prism error.

11. The near-eye display system according to any of claims 1-10, further comprising an image light guide including an out-coupling optic having a spherical optical power contribution operable to converge or diverge virtual image-bearing light beams in advance of the eyebox, wherein the out-coupling diffractive optic comprises an output aperture center, and the output aperture center is offset from an interpupillary distance position.

12. The near-eye display system according to any of claims 1-10, further comprising an image light guide including an out-coupling optic having a spherical optical power contribution operable to converge or diverge virtual image-bearing light beams in advance of the eyebox, wherein the spherical optical power contribution of the out-coupling diffractive optic is substantially equal to the spherical optical power contribution of the first corrective optical element.

13. A method of manufacturing an image light guide system, comprising: providing a set of first corrective optical elements having a spherical optical power contribution; providing a set of image light guides having a spherical optical power contribution; selecting one of the first corrective optical elements from the set; selecting one of the image light guides from the set; customizing a second corrective optical element having at least one of a spherical or cylindrical optical power contribution; arranging the image light guide between the first corrective optical element and the second corrective optical element in a stacked arrangement, wherein the second corrective optical element is arranged between the image light guide and the eyebox.

14. The method according to claim 13. wherein the set of first corrective optical elements comprises a range of +2 diopter, 0 diopter, and -2 diopter spherical optical power contributions.

15. The method according to claim 14. wherein the set of image light guides comprises a range of +2 diopter, 0 diopter, and -2 diopter spherical optical power contributions.

16. The method according to claim 13, wherein the selected image light guide comprises a spherical optical power contribution substantially equal to the spherical optical power contribution of the selected first corrective optical element.

17. The method according to claim 13, wherein the selected first corrective optical element includes a first center of correction, and the second corrective optical element includes a second center of correction, wherein the first center of correction is offset from an interpupillary distance position and induces a prism error, and wherein the second center of correction is arranged to offset the prism error.

18. An image light guide system for viewing a virtual object and a real-world object 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 propagate virtual image-bearing light beams; a first corrective optical element arranged between the image light guide and the real -world object, the first corrective optical element having a first spherical optical power contribution to the real-world image-bearing light beams; an out-coupling optic arranged along the image light guide, the out-coupling optic having a second spherical optical power contribution to the virtual image-bearing light beams; and a second corrective optical element arranged between the image light guide and the eyebox, the second corrective optical element having a third spherical optical power contribution to the virtual and real-world image-bearing light beams. the first corrective optical element having a first center of correction, and the second corrective optical element having a second center of correction.

19. The image light guide system according to claim 18, wherein the first center of correction is offset from an interpupillary distance position, wherein the offset at least partially induces a prism error.

20. The image light guide system according to claim 19, wherein the second center of correction is arranged to offset the prism error.

21. The image light guide system according to claim 20, wherein the second center of correction is arranged opposite the first center of correction about the interpupillary distance position.

22. The image light guide system according to claim 18. wherein the second corrective optical element includes a cylindrical optical power contribution operable to reduce optical aberrations associated with viewing the real-world object and the virtual object, wherein the second corrective optical element includes an axis of correction.

23. The image light guide system according to claim 22, wherein the axis of correction is arranged above or below a horizontal bisecting the first center of correction.

24. The image light guide system according to claim 18, wherein the first corrective optical element comprises a liquid crystal layer operable to provide a digital correction of the real-world image-bearing light beams.

25. The image light guide system according to claim 18, wherein the second corrective optical element comprises a liquid crystal layer operable to provide a digital correction of the real-world image-bearing light beams and the virtual image-bearing light beams.

26. The image light guide system according to claim 18, wherein the out-coupling diffractive optic comprises an output aperture center, wherein the output aperture center is offset from an interpupillary distance position, wherein a prism error induced by the offset is digitally corrected with a change in angular encoding of the virtual image.

27. The image light guide system according to claim 18, wherein the second spherical optical power contribution of the out-coupling diffractive optic is substantially equal to the first spherical optical power contribution of the first corrective optical element.

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