Patent Description:
Head-mounted displays (HMDs) increasingly take the form of conventional eyeglasses with less obtrusive optics for displaying virtual image content along 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 eyes as virtual images that are projected into the wearer's real-world view that is visible through the image light guides.

The 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 points of light at far distance 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.

Vision problems of the wearer's 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 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.

<CIT> discloses a user-wearable diagnostic health system which comprises a frame, an augmented reality display attached to the frame, a light detector attached to the frame and a processor configured to conduct a health analysis of the user based on light detected by the light detector. The frame is configured to mount on the user. The augmented reality display is configured to direct images to an eye of the user. The light detector is configured to detect light reflected from an eye of the user.

<CIT> discloses an apparatus which comprises an optical engine configured to provide one or more light beams, a camera, a waveguide configured to guide the one or more light beams. The waveguide comprises a diffractive in-coupling grating and at least one diffractive out-coupling. The out-coupling grating is configured to out-couple the one or more light beams towards an eye of a user and towards the camera.

<CIT> discloses a combiner optical system which comprises a base plate arranged to cross with the optical axis of an observation eye; a catoptric element provided in the optical path on the base plate and superposing a luminous flux for display on the external light and guiding it to the pupil position of the observation eye; a first dioptric lens, whose surface on the external side is convex; and a second dioptric lens which is arranged to cross with the optical axis on the side of the base plate where the external light is emitted, and whose surface on the pupil position side is concave.

The present disclosure features improvements to HMDs to manage either or both focusing discrepancies between real-world and virtual objects presented to the wearers of HMDs and vision problems affecting the focusing capabilities of the wearers themselves. The wearer's eyes are required to convert virtual images to real images, and the disclosure provides for reducing demands on the wearer's eyes for viewing virtual objects together with real-world objects within the same field of view.

An HMD in accordance with this disclosure has an eye rim section with an aperture through which a wearer can view a real-world object within the ambient environment. While many HMDs are arranged to support binocular vision with an eye rim section provided for each eye, various improvements are described with respect to a single eye rim section for supporting monocular vision with the understanding that a second eye rim section in a symmetric arrangement could be used for supporting binocular or stereoscopic vision.

An image light guide arranged within the aperture of the eye rim section of the referenced head-mounted display includes a transmissive planer waveguide having plane-parallel inner and outer surfaces, an in-coupling optic, and an out-coupling optic. The in-coupling optic directs angularly related image-bearing light beams encoding a virtual object into the waveguide for propagation by internal reflection from the parallel inner and outer surfaces. The out-coupling optic directs the propagating image-bearing light beams from the waveguide toward an eyebox for viewing the virtual object at a first focusing distance from the eyebox. A multifunction optic formed as a single optical element located within the aperture between the inner surface of the waveguide and the eyebox provides both: (a) a negative optical power contribution for diverging the image-bearing beams in advance of the eyebox for viewing the virtual object at a closer second focusing distance from the eyebox, and (b) a corrective optical contribution for reducing a viewer's optical aberrations associated with viewing both the real-world object and the virtual object at the closer second focusing distance. A positive-power optic located within the aperture between the outer surface of the waveguide and the ambient environment compensates for the negative optical power contribution of the multifunction optic without compensating for the corrective optical contribution of the multifunction optic for viewing the real-world object at its actual distance from the eyebox with corrected vision.

The first focusing distance is preferably a hyperfocal to near infinite distance and the closer second focusing distance is preferably less than the hyperfocal distance. For example, the closer second focusing distance can be between <NUM> meters and <NUM> meters or between. <NUM> meters and <NUM> meters. The the corrective optical contribution is preferably set for reducing the viewer's optical aberrations at the closer second focusing distance.

The multifunction optic can be a first of a plurality of multifunction optics, and the first multifunction optic can be removable and replaceable with a second of the multifunction optics to adapt the display to a different optical prescription. The positive-power optic can also be a first of a plurality of positive-power optics. The first multifunction optic and the first positive-power optic can be collectively removable and replaceable with a second of the multifunction optics and a second of the positive-power optics for changing the closer second focusing distance to a different third focusing distance. The second multifunction optic can also provide a corrective optical contribution to reduce the viewer's optical aberrations at the different third focusing distance. Both the multifunction optics and the positive-power optics can each be formed as a single refractive lens element.

A transmissive protective outer cover can be located within the aperture between the positive-power optic and the ambient environment. Alternatively, the positive-power optic can be formed as a lens having a convex outer surface facing the ambient environment and treated with a protective coating.

An augmented reality virtual image display system in accordance with this disclosure provides for managing a viewer's view of a virtual object and a real-world object within a common field of view, particularly where the real-world object is intended to be viewed as less than a hyperfocal distance requiring significant eye accommodation. An image light guide directs angularly related image-bearing light beams encoding the virtual object toward an eyebox for the viewing the virtual object at a first focusing distance from the eyebox. A multifunction optic formed as a single optical element located between the inner side of the image light guide and the eyebox provides both: (a) a negative optical power contribution for diverging the image-bearing beams in advance of the eyebox for viewing the virtual object at a closer second focusing distance from the eyebox, and (b) a corrective optical contribution for reducing a viewer's optical aberrations associated with viewing of both the real-world object and the virtual object at the closer second focusing distance. A positive-power optic on the outer side of the image light guide compensates for the negative optical power contribution of the multifunction optic without compensating for the corrective optical contribution of the multifunction optic for viewing the real-world object at its actual distance from the eyebox with corrected vision.

The multifunction optic is preferably a single refractive lens element. The first focusing distance is preferably a hyperfocal to near infinite distance and the closer second focusing distance is less than the hyperfocal distance, such as between <NUM> meters and <NUM> meters or between. <NUM> meters and <NUM> meters. The corrective optical contribution is preferably set for reducing the viewer's optical aberrations at the closer second focusing distance.

The multifunction optic can be a first of a plurality of multifunction optics, and the first multifunction optic can be removable and replaceable with a second of the multifunction optics to adapt the display system to a different optical prescription. The negative-power contribution of the second multifunction optic can be the same as the negative power contribution of the first multifunction optic, but the corrective optical contribution of the second multifunction optic is different from the corrective optical contribution of the first multifunction optic.

The multifunction optic can be a first of a plurality of multifunction optics and the positive-power optic can be a first of a plurality of positive-power optics. As such, the first multifunction optic and the first positive-power optic are preferably collectively removable and replaceable with a second of the multifunction optics and a second of the positive-power optics for changing the closer second focusing distance to a different third focusing distance. The second multifunction optic preferably provides a corrective optical contribution to reduce the viewer's optical aberrations at the different third focusing distance.

A transmissive protective outer cover can be located between the positive-power optic and the ambient environment from which the real-world object is viewed. Alternatively, the positive-power optic can be arranged as a lens having a convex outer surface that faces the ambient environment and is treated with a protective coating.

The image light guide can include a transmissive planer waveguide having plane-parallel inner and outer surfaces, an in-coupling optic for directing the angularly related image-bearing light beams into the waveguide from an image source for propagation by internal reflection from the inner and outer surfaces, and an out-coupling optic for directing the propagating image-bearing light beams from the waveguide toward the eyebox.

The accompanying drawings are incorporated herein as part of the specification. The drawings described herein illustrate 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.

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 examples of the inventive concepts defined herein. Hence, specific dimensions, directions, or other physical characteristics relating to the examples disclosed are not to be considered as limiting, unless expressly stated otherwise. Also, although they may not be, like elements in various examples described herein may be commonly referred to with like reference numerals within this section of the application.

<FIG> is a schematic diagram showing a simplified cross-sectional view of one conventional configuration of an image light guide <NUM> comprising a planar waveguide <NUM>, an in-coupling diffractive optic IDO, and an out-coupling diffractive optic ODO. The planar waveguide <NUM> includes a transparent substrate S, which can be made of optical glass or plastic, with plane-parallel inner and outer surfaces <NUM> and <NUM>. In this example, the in-coupling diffractive optic IDO is shown as a transmissive type diffraction grating arranged on the inner surface <NUM> of the planar waveguide <NUM>. 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 an incoming image-bearing light WI into the planar waveguide <NUM>. The in-coupling diffractive optic IDO can be located on the inner or outer surface <NUM> or <NUM> of the planar waveguide <NUM> and can be of a transmissive or reflective type in a combination that depends upon the direction from which the image-bearing light WI approaches the planar waveguide <NUM>.

When used as a part of a virtual image display system, the in-coupling diffractive optic IDO couples the image-bearing light WI from a real, virtual or hybrid image source <NUM> into the substrate S of the planar waveguide <NUM>. Any real image or image dimension formed by the image source <NUM> is first converted, e.g. converged toward a focus, into an array of overlapping angularly related 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.

The image-bearing light WI is diffracted (generally through a first diffraction order) and thereby redirected by in-coupling diffractive optic IDO into the planar waveguide <NUM> as image-bearing light WG for further propagation along a length dimension X of the planar waveguide <NUM> by total internal reflection (TIR) from the plane parallel inner and outer surfaces <NUM> and <NUM>. Although diffracted into a different combination of angularly related beams in keeping with the boundaries set by TIR, the image-bearing light WG preserves 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 WG and diffracts (also generally through a first diffraction order) the image-bearing light WG out of the planar waveguide <NUM> as the image-bearing light WO toward a nearby region of space referred to as an eyebox E, within with the transmitted virtual image can be seen by a viewer's eye. The out-coupling diffractive optic ODO can be designed symmetrically with respect to the in-coupling diffractive optic IDO to restore the original angular relationships of the image-bearing light WI among outputted angularly related beams of the image-bearing light 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.

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 planar waveguide <NUM> to encounter the image-bearing light WG multiple times and to diffract only a portion of the image-bearing light WG upon each encounter. The multiple encounters along the length of the out-coupling diffractive optic ODO have the effect of enlarging one dimension of each of the angularly related beams of the image-bearing light WO thereby expanding one dimension of the eyebox E within which the beams overlap. The expanded eyebox E decreases sensitivity to the position of a viewer's eye for viewing the virtual image.

The out-coupling diffractive optic ODO is shown as a transmissive type diffraction grating arranged on the inner surface <NUM> of the planar waveguide <NUM>. However, like the in-coupling diffractive optic IDO, the out-coupling diffractive optic ODO can be located on the inner or outer surface <NUM> or <NUM> of the planar waveguide <NUM> and be of a transmissive or reflective type in a combination that depends upon the direction through which the image-bearing light WG is intended to exit the planar waveguide <NUM>. In addition, the out-coupling diffractive optic could be formed as another type of diffractive optic, such as a volume hologram or other holographic diffraction element, that diffracts propagating image-bearing light WG from the planar waveguide <NUM> as the image-bearing light WO propagating toward the eyebox E.

The perspective view of <FIG> shows an image light guide <NUM> that is 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 beam expansion, the in-coupling diffractive optic IDO is oriented to diffract the image-bearing light WG about a grating vector k1 along planar waveguide <NUM> toward an intermediate turning optic TO, whose grating vector k2 is oriented to diffract the image-bearing light WG in a reflective mode along the planar waveguide <NUM> toward the out-coupling diffractive optic ODO. Only a portion of the image-bearing light WG is diffracted by each of multiple encounters with intermediate turning optic TO thereby laterally expanding each of the angularly related beams of the image-bearing light WG approaching the out-coupling diffractive optic ODO. The intermediate turning optic TO redirects the image-bearing light WG into an at least approximate alignment with a grating vector k3 of the out-coupling diffractive optic ODO for longitudinally expanding the angularly related beams of the image-bearing light WG in a second dimension before exiting the planar waveguide <NUM> as the image-bearing light WO. Grating vectors, such as the depicted grating vectors k1, k2, and k3, extend within a parallel plane of the planar waveguide <NUM> in respective directions that are normal to the diffractive features (e.g., 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.

In the image light guide <NUM> of <FIG>, in-coupling diffractive optic IDO receives the incoming image-bearing light WI containing a set of angularly related beams corresponding to individual pixels or equivalent locations within an image generated by the image source <NUM>, 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 focusing optics, 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. The image light guide <NUM> outputs an expanded set of angularly related beams in two dimensions of the image by providing multiple encounters of the image-bearing light WG with both the intermediate turning optic TO and the out-coupling diffractive optic ODO in different orientations. In the depicted orientation of the planar waveguide <NUM>, the intermediate turning optic TO provides beam expansion in the y-axis direction, and the out-coupling diffractive optic ODO provides a similar beam expansion in the x-axis direction. The relative orientations and respective periods d of the diffractive features of the in-coupling, intermediate turning, and out-coupling diffractive optics IDO, TO, and ODO provide for beam expansion in two dimensions while preserving the intended relationships among the angularly related beams of the image-bearing light WI that are output from the image light guide <NUM> as the image-bearing light WO.

That is, while the image-bearing light WI input into the image light guide <NUM> is encoded into a different set of angularly related beams by the in-coupling diffractive 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 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. 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 <NUM> 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 <NUM> degrees to the grating vectors k1 and k3 of the in-coupling and out-coupling diffractive optics IDO and ODO in such a way that the image-bearing light WG is turned <NUM> degrees. By orienting the grating vector k2 of the intermediate turning optic TO at <NUM> degrees with respect to the grating vectors k1 and k3 of the in-coupling and out-coupling diffractive optics IDO and ODO, the grating vectors k1 and k3 of the in-coupling and out-coupling diffractive optics IDO and ODO are also oriented at <NUM> degrees with respect to each other. 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 k1, 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 k1, k2, and k3 that have unequal magnitudes in relative orientations at which the three grating vectors k1, k2, and k3 sum to a zero vector magnitude.

In a broader sense, the image-bearing light WI that is directed into the planar waveguide <NUM> is effectively encoded by the in-coupling optic, whether the in-coupling optic uses gratings, holograms, prisms, mirrors, or some other mechanism. Any reflection, refraction, and/or diffraction of light that takes place at the input must be correspondingly decoded by the output to re-form the virtual image that is presented to the viewer. Whether any symmetries are maintained or not among the intermediate turning optic TO and the in-coupling and out-coupling diffractive optics IDO and ODO or whether or not any change to the encoding of the angularly related beams of the image-bearing light WI takes place along the planar waveguide <NUM>, 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 WO that is output from the planar waveguide <NUM> preserves or otherwise maintains the original or desired form of the image-bearing light WI for producing the intended virtual image.

The letter "R" represents the orientation of the virtual image that is visible to the viewer whose eye is in 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 WI. A change in the rotation about the z axis or angular orientation of incoming image-bearing light 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 expansion of the angularly encoded beams of the image-bearing light WG along one axis (e.g., along the y axis) of the image. Out-coupling diffractive optic ODO further expands the angularly encoded beams of the image-bearing light WG along another axis (e.g., along the x axis) of the image while maintaining the original orientation of the virtual image encoded by the image-bearing light 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 inner and outer surfaces of the planar waveguide <NUM>.

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 an image light guide <NUM> 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 planar waveguide <NUM> as well as the overall orientations at which the angularly related beams can be directed into and out of the planar waveguide <NUM>.

The image light guides <NUM> and <NUM> as described above are presented as examples of image light guides that are suitable for use in head-mounted displays (HMDs) designed for augmented reality (AR) applications in which virtual image content is superimposed on a real-world view as seen through the transparent planar waveguides <NUM> or <NUM>. Although the virtual image display systems are depicted with single planar waveguides, the display systems may also comprise multiple planar waveguides in a stacked format for separately conveying images in different colors or different portions of the images. In more general sense, the image light guides contemplated herein through which virtual images can be directed to a wearer's eye can take various forms and can include a variety of ways for in-coupling and out-coupling light into and out of a waveguide while still supporting views of the ambient environment through the waveguide. That is, both the out-coupling optic and the waveguide itself should be constructed to not unduly interfere with the wearer's view of the ambient environment through the waveguide. Both virtual objects as conveyed by the image light guide and real-world objects that are seen through the image light guide should be clearly visible to the wearer to support further interactions of the wearer with the ambient environment such as may be informed by the superimposed virtual content.

<FIG> is a schematic depiction of an eye rim section <NUM> of an HMD arranged for an augmented reality application and containing an image light guide <NUM>, such as the previously described image light guides <NUM> and <NUM>, for conveying virtual images to a wearer's eye <NUM> while providing a real-world view through the image light guide <NUM>. In this way, virtual objects <NUM> can be presented to the wearer's eye <NUM> among real-world objects <NUM> that are visible through the image light guide <NUM>. The image-bearing light beams generated from the image source (not shown) typically propagate along and from the image light guide as respective collimated beams that are angularly related to one another for forming virtual images. As a part of a virtual image display system as described above, the image-bearing light beams <NUM> emitted from the image light guide <NUM> appear as if originating from virtual objects <NUM> via the virtual image-bearing light beams <NUM> at a hyperfocal to near infinite focusing distance, e.g. from <NUM> to <NUM> meters to near infinity from wearer's eye <NUM>. In this context, the pupil of the wearer's eye <NUM> is located in an eyebox <NUM> within which the virtual images can be seen by the wearer, and the hyperfocal distance sets the shortest object distance to a normal or corrected eye beyond which objects can be viewed without need for accommodation (i.e., a change in the focal length of the eye).

In contrast to the image-bearing light beams <NUM> emitted directly into the wearer's eye <NUM>, light beams <NUM> from the real-world objects <NUM> transmit through both a transmissive protective outer cover <NUM> and the image light guide <NUM> before reaching the wearer's eye <NUM>. Thus, the transmissive protective outer cover <NUM> can provide filtering or other optical functions that affect the wearer's view of the real-world objects <NUM> without similarly affecting the wearer's view of the virtual objects <NUM>.

<FIG> is a schematic depiction of an eye rim section <NUM> of an HMD having both an image light guide <NUM> as a part of a virtual image display system and a transmissive protective outer cover <NUM> like in the eye rim section <NUM>. Some wearers of the HMD may have difficulty viewing distant objects in focus, a condition referred to as near-sightedness or myopia. The condition affects the wearer's ability to clearly focus both real objects beyond a given distance from the wearer and virtual objects that appear to be located beyond the given distance from the wearer.

A replaceable and customizable corrective optic <NUM> is positioned between the wearer's eye <NUM> and the one or more waveguides of the image light guide <NUM>. The corrective optic <NUM>, which can exploit mechanisms of refraction or diffraction for reformatting transmitted light, is removably mounted within the eye rim section <NUM> of the HMD for providing a desired optical correction (e.g., negative focusing power), such as may be estimated by an optical prescription, for normalizing the wearer's long-distance vision.

The light beams <NUM> from the distant real-world objects <NUM> transmit through both a transmissive protective outer cover <NUM> and the image light guide <NUM> before encountering the corrective optic <NUM> having a desired amount of optical power that reorients or otherwise rearranges the light beams <NUM> into the light beams <NUM> so that the wearer's eye <NUM> can more clearly focus the real-world objects <NUM> without significant aberrations. Similarly, the image-bearing light beams <NUM> emitted from the image light guide <NUM>, which mimics virtual image-bearing light beams <NUM> from the distant virtual objects <NUM>, encounter the corrective optic <NUM> that reorients or otherwise rearranges the light image-bearing light beams <NUM> into the image-bearing light beams <NUM> so that the wearer's eye <NUM> can more clearly focus the distant virtual objects <NUM> without significant aberrations. The corrective optic <NUM> is preferably both attachable to and detachable from eye rim section <NUM>. While the corrective optic <NUM> is especially suitable for correcting nearsightedness, other types of systematic aberrations including astigmatism can also be corrected. For example, the corrective optic can be arranged as a multifocal or bifocal optic for correcting aberrations at different distances.

<FIG> is a schematic depiction of an eye rim section <NUM> of an HMD, which is adapted to allow virtual objects <NUM>, which are generated by a virtual image display system at a hyperfocal to near infinite focusing distance, to appear much closer. For example, in situations where the wearer of an HMD normally views real-world objects within a range requiring a given eye accommodation, virtual objects within the same scene at significantly greater focusing distances can be more difficult to perceive by requiring a significantly less eye accommodation. The wearer of the HMD can experience eye strain switching between the different amounts of accommodation required for viewing the virtual and real-world objects (e.g., between little or no accommodation and a perceptible accommodation involving a noticeable change in eye focal length).

The eye rim section <NUM> includes a negative-power or diverging optic <NUM> acting on the image-bearing light beams <NUM> emitted from the image light guide <NUM> for converting the image-bearing light beams <NUM> into diverging image-bearing light beams <NUM> having the effect that the virtual objects <NUM> with an apparent focus position traced by the virtual image-bearing light beams <NUM> appear closer. However, similarly shortening the focusing distance to the real-world objects <NUM> would not solve the problem of divergent focusing distances between the virtual and real-world objects <NUM> and <NUM>. In addition, the real-world objects <NUM> would not appear in their true positions within the ambient environment.

To restore the desired real-world view through the eye rim section <NUM>, the eye rim section <NUM> also includes a positive-power or converging optic <NUM> located between the image light guide <NUM> and the transmissive protective outer cover <NUM>. In contrast to the negative-power optic <NUM>, which effects the view of both the virtual and real-world objects <NUM> and <NUM>, the positive-power optic <NUM> only affects the view of the real-world objects <NUM>. The light beams <NUM> from the real-world object <NUM> are first converged into light beams <NUM> by the positive-power optic <NUM> and then diverged by the negative-power optic <NUM> into light beams <NUM> at which the original configuration of the light beams <NUM> is restored.

The positive-power optic <NUM> can be defined to have the same magnitude (i.e., absolute value) of optical power but of the opposite sign as the optical power of the negative-power optic <NUM>. For example, the optical power of the positive power optic <NUM> may be denoted as +nD for a positive n-diopter optical power. The optical power of the negative-power optic <NUM> may be denoted as -mD for a negative m-diopter optical power. Acting on the light beams <NUM> from the real-world objects <NUM>, the two optics <NUM> and <NUM> have a combined optical power of (n - m)D. Where "n" and "m" are set equal, the combined optical power may be zero. That is, (n - m)D = 0D diopters. Although the effect of the negative-power optic <NUM> can be cancelled for viewing the real-object <NUM>, the negative-power optic <NUM> retains the power to view the virtual objects <NUM> at a closer distance.

Preferably, the waveguide of the image light guide <NUM> does not impart any significant optical power that would that would significantly alter focus distances to the real-world objects <NUM>. For example, to avoid imparting any refractive power, the one or more transmissive waveguides can be formed with planar surfaces within the viewing aperture of the eye rim section. In addition, the one or more out-coupling optics are preferably arranged to output the image-bearing light beams in a form that presents the virtual objects <NUM> at a hyperfocal to near infinite focusing distance.

In a refractive capacity, the negative-power optic <NUM> can be formed, for example, as a plano-concave lens, a biconcave lens, or negative meniscus lens, and the positive-power optic <NUM> can be formed, for example, as a plano-convex lens, a biconvex lens, or a positive meniscus lens. Alternative, one or both the negative-power and positive-power optics <NUM> and <NUM> can be formed as a holographic optical element (HOE). A convex outer surface of the positive-power optic <NUM> can replace the transmissive protective outer cover <NUM>. Coatings can be applied to the convex outer surface for such purposes as filtering or other protection.

<FIG> is a schematic depiction of an eye rim section <NUM>, which incorporates the features of the eye rim section <NUM> of <FIG>, including the self-cancelling negative-power and positive-power optics <NUM> and <NUM> while also incorporating the corrective optic <NUM> of <FIG>. The negative-power optic <NUM> moves the focusing distance of the virtual objects <NUM> closer to the wearer's eye <NUM>, and the positive-power optic <NUM> cancels this effect for the real-world objects <NUM> visible through the eye rim section <NUM>. The replaceable and customizable corrective optic <NUM>, which is located between the negative-power optic <NUM> and the wearer's eye <NUM>, provides a desired optical correction, such as may be estimated by an optical prescription, for normalizing the wearer's vision, such as long-distance vision. Other types of aberrations as described above for the corrective optic <NUM> can also be corrected.

The corrective optic <NUM> reorients or otherwise rearranges the restored light beams <NUM> into the light beams <NUM> so that the wearer's eye <NUM> can more clearly focus the real-world objects <NUM> without significant aberrations. In addition, the corrective optic <NUM> reorients or otherwise rearranges the image-bearing light beams <NUM> by which the virtual objects <NUM> appear at a closer focusing distance into the image-bearing light beams <NUM> so that the wearer's eye <NUM> can more clearly focus the closer-distance virtual objects <NUM> without significant aberrations.

The corrective optic <NUM>, like the negative-power and positive-power optics <NUM> and <NUM>, can be formed as a refractive lens, a diffraction grating, a holographic optical element (HOE) or a combination thereof. The negative-power optic <NUM> and the corrective optic <NUM> can also be combined into a single optical element in a refractive or diffractive form or combination thereof. As such, the single optical element performing the functions of the corrective optic <NUM> and the negative-power optic <NUM> is preferably attachable to and detachable from the eye rim section <NUM>. The positive-power optic <NUM>, particularly when having a convex outer surface, can replace the transmissive protective outer cover <NUM>. Coatings can be applied to the convex outer surface for such purposes as filtering or other protection.

Preferably, optical power for influencing views of the real-world objects <NUM> is provided by the corrective optic <NUM> in combination with the self-cancelling effects of the negative-power optic <NUM> and the positive-power optic <NUM> rather than from the image light guide <NUM>. Construction of the image light guide can be simplified by conveying each of the image bearing light beams in a substantially collimated form that presents the virtual objects <NUM> at a hyperfocal to near infinite focusing distance. The negative-power optic <NUM> can be arranged together with the corrective optic <NUM> to shorten the focusing distance at which virtual objects <NUM> are presented among the real-world objects <NUM> to the wearer's eye <NUM>.

<FIG> is a top view of an eye rim section <NUM> together with a right temple portion <NUM> and a nose bridge portion <NUM> of an HMD as intended to be oriented with respect to a wearer's eye <NUM>. The eye rim section <NUM> merges with a nose bridge portion <NUM> of the HMD at an inner end and with the right temple portion <NUM> at an outer end.

An image light guide <NUM>, such as previously described, provides for conveying virtual images to a wearer's eye <NUM> while providing a real-world view through the image light guide <NUM>. The image light guide <NUM> is secured within the eye rim section <NUM> but receives its image-bearing light beams from a projector <NUM> as an image source mounted in the right temple portion <NUM> and through a coupling mechanism <NUM> that includes an in-coupling optic as described above.

The eye rim section <NUM> also defines an aperture <NUM> that is covered or at least substantially covered by a transmissive protective outer cover <NUM>, which can be made removable and replaceable. Although the image light guide <NUM> is depicted with a single transparent planar waveguide, the eye rim section <NUM> can be arranged to accommodate multiple planar waveguides such as in a stacked (overlapping) configuration.

<FIG> is a top view of an eye rim section <NUM> together with a right temple portion <NUM> and a nose bridge portion <NUM> of an HMD like the HMD of <FIG>. The right temple portion <NUM> includes the same projector <NUM> and coupling mechanism <NUM> as used in <FIG> to direct angularly related image-bearing light beams into the planar waveguide of the image light guide <NUM>. Also like the eye rim section <NUM> of <FIG>, the eye rim section <NUM> includes the transmissive protective outer cover <NUM>, which can be made attachable to or detachable from the remaining eye rim section <NUM>.

The eye rim section <NUM> also includes both a negative-power optic <NUM> and a positive-power optic <NUM> like the eye rim section <NUM> of <FIG>. The negative-power optic <NUM> converts the image-bearing light beams emitted from the image-bearing light guide <NUM> at a hyperfocal to near infinite focusing distance into diverging image-bearing light beams by which the virtual objects appear closer to the wearer's eye <NUM>. The positive-power optic <NUM> counteracts the effects of the negative-power optic on light beams passing through the aperture <NUM> from the ambient environment so that the wearer sees real-world objects in their actual positions. Like the eye rim section <NUM> of <FIG>, a convex surface of the positive-power optic <NUM> with appropriate coatings can be used in place of the transmissive protective outer cover <NUM>.

<FIG> is a top view of an eye rim section <NUM> together with a right temple portion <NUM> and a nose bridge portion <NUM> of an HMD incorporating all the features of the eye rim section <NUM> and the corresponding right temple and nose bridge portions <NUM> and <NUM> of <FIG>. However, like the eye rim section <NUM> of <FIG>, the eye rim section <NUM> includes a replaceable and customizable corrective optic <NUM>, which is located between the negative-power optic <NUM> and the wearer's eye <NUM>.

Like the corrective optic <NUM> of <FIG>, the corrective optic <NUM> enables the wearer to more clearly focus real-world objects that are visible through the aperture <NUM> as well as to more clearly focus virtual objects generated by the projector, conveyed by the image light guide <NUM>, and presented at a closer focusing distance to the wearer's eye <NUM> by the negative-power optic <NUM>.

As described above, the corrective optic <NUM>, like the negative-power and positive-power optics <NUM> and <NUM>, can be formed as a refractive lens, a diffraction grating, a holographic optical element (HOE) or a combination thereof. The negative-power optic <NUM> and the corrective optic <NUM> can also be combined into a single optical element shown in the form of a lens doublet <NUM>. Other refractive or diffractive forms or combinations thereof could also be used as the considered single element. The lens doublet <NUM> or another form of a single optical element performing the functions of the corrective optic <NUM> and the negative-power lens <NUM> is preferably attachable to and detachable from the remaining eye rim section <NUM>. As also described above, a properly treated convex outer surface of the positive-power optic <NUM> can replace the transmissive protective outer cover <NUM>.

As an example in which the corrective optic <NUM> is combined with the negative-power optic <NUM> in a compound optical element, such as the lens doublet <NUM>, assume that the positive-power optic <NUM> furthest from the wearer's eye <NUM> contributes +<NUM> diopters of optical power. Assuming further that the wearer requires a prescribed correction of -<NUM> diopters of optical power for a correction at the desired viewing distance, then the compound optical element, such as the lens doublet <NUM>, can be arranged to contribute -<NUM> diopters of optical power. The - <NUM> diopters of optical power compensates for the +<NUM> diopters of optical power otherwise affecting the view of real-world objects, preserves the - <NUM> diopters of optical power required to present the generated virtual objects at a closer focusing distance, and corrects the wearer's vision of both the real-world and virtual objects at the desired viewing distance. In a more general sense the optical power "c" of the prescription minus the optical power "p" of the positive-power optic <NUM> equals the optical power "s" of the compound optical element, such as the lens doublet <NUM>, (i.e., s = c - p) to achieve these results.

<FIG> is a top view of an eye rim section <NUM> similar to the eye rim section <NUM> of <FIG> where like numbers refer to like elements. In the eye rim section <NUM>, however, the lens doublet <NUM> as an example of a compound optic is replaced by a multifunction optic <NUM> in the form of a simple lens <NUM> as an example of a single optical element for performing the functions of both the negative-power optic <NUM> and the corrective optic <NUM>. The multifunction optic <NUM> as a single optical element can be formed as a refractive lens, a diffraction grating, a holographic optical element (HOE) or a combination thereof.

The multifunction optic <NUM> is both replaceable and customizable to accommodate different optical prescriptions of the wearer's eye <NUM> for reducing the wearer's optical aberrations associated with viewing virtual objects at the closer focusing distance provided by the negative power that is also incorporated into the multifunction optic <NUM>. In addition, the multifunction optic <NUM> can be customizable to also change the amount of negative power that is incorporated into the multifunction optic <NUM> to alter the focusing distance at which the virtual objects are presented to the wearer's eye. Preferably, the corrective contribution of the multifunction optic <NUM> is set to reduce the wearer's optical aberrations associated with viewing both real-world objects and virtual objects at the altered focusing distance. In addition, any change in the negative power of the multifunction optic <NUM> is preferably matched by a corresponding change in the positive power of the positive-power optic <NUM>, which is made similarly replaceable and customizable to counteract the effects of the negative power contributed by the multifunction optic <NUM> on light beams passing through the aperture <NUM> from the ambient environment so that the wearer sees real-world objects in their actual positions.

<FIG> feature a compound lens holder <NUM> that provides for supporting and collectively replacing the both the positive-power optic <NUM> and the multifunction optic <NUM> within a receptive eye rim section <NUM> of an HMD. In <FIG>, the compound lens holder <NUM> is shown with a rim-like housing <NUM> defining an aperture <NUM> for sustaining a clear view of the ambient environment through the supported positive-power optic <NUM> and the multifunction optic <NUM>.

In the top sectional view of <FIG>, the housing <NUM> engages the outer peripheries of the positive-power optic <NUM> and the multifunction optic <NUM> to maintain a desired optical alignment between the two optics <NUM> and <NUM>. Housing <NUM> further comprises a slot <NUM> providing clearance for accommodating an image light guide such as the image light guide <NUM> shown in <FIG> that is more permanently installed in the depicted eye rim section <NUM> of the HMD.

Similar to the preceding figures, the HMD as shown in the top sectional view of <FIG> includes a right temple portion <NUM> and a nose bridge portion <NUM>. Projector <NUM> and coupling mechanism <NUM> in the right temple portion <NUM> deliver image-bearing beams into the image light guide <NUM>, which is also supported in the right temple portion <NUM>. However, both the right temple portion <NUM> and the nose bridge portion <NUM> are adapted with respective slots <NUM> and <NUM> to slideably receive the compound lens holder <NUM> in a fashion that aligns the aperture <NUM> of the compound lens holder <NUM> with the aperture <NUM> of the eye rim section <NUM> for similarly accommodating the passage of light from both the ambient environment and the image light guide <NUM> toward the wearer's eye <NUM>. Preferably, the compound lens holder <NUM> together with the positive-power optic <NUM> and the multifunction optic <NUM> can be slid into place between the right temple portion <NUM> and the nose bridge portion <NUM> without disturbing the prepositioning of the image light guide <NUM> within the eye rim section <NUM>. The slot <NUM> preferably provides clearance for this purpose.

<FIG> is a top sectional view of the eye rim section <NUM> containing an image light guide <NUM> with the compound lens holder <NUM> removed. Here, the respective slots <NUM> and <NUM> in the right temple portion <NUM> and the nose bridge portion <NUM> are more clearly visible for receiving the compound lens holder <NUM> within the eye rim section <NUM>. The compound lens holder <NUM> containing customized positive-power and multifunction optics <NUM> and <NUM> can be fastened to eye rim section <NUM> in a variety of ways such as by using a set screw (not shown) into right temple and/or nose bridge portions <NUM> and <NUM> or a flexible rubber gasket (not shown).

Multiple compound lens holders <NUM> can be prearranged with customized combinations of the positive-power and multifunction optics <NUM> and <NUM> that can be replaceably positioned within the eye rim section <NUM>. Customizable positive-power and multifunction optics <NUM> and <NUM> can also be removably replaceable within individual compound lens holders <NUM>.

Although the figures illustrate only a portion of an HMD with an eye rim section for just one eye as may be appropriate for a monocular HMD, a second eye rim section in a symmetrical arrangement can be included for a wearer's other eye as a part of a full HMD device for providing binocular or stereoscopic views of both virtual and real-world objects within the wearer's field of view.

Claim 1:
A head-mounted display, comprising:
an image light guide (<NUM>, <NUM>, <NUM>) including:
a transmissive planar waveguide having plane-parallel inner and outer surfaces (<NUM>, <NUM>), wherein a real-world object within an ambient environment is viewable through the image light guide (<NUM>, <NUM>, <NUM>);
an in-coupling optic (IDO, <NUM>) operable to direct angularly related image-bearing light beams (<NUM>) encoding a virtual object into the waveguide from an image source (<NUM>, <NUM>), wherein the image-bearing light beams propagate by total internal reflection, and
an out-coupling optic (ODO) operable to direct the propagating image-bearing light beams (<NUM>) from the waveguide toward an eyebox (E, <NUM>), wherein the virtual object is viewed at a first focusing distance from the eyebox (E, <NUM>);
a multifunction optic (<NUM>) located between the inner surface (<NUM>) of the waveguide and the eyebox (E, <NUM>), wherein the multifunction optic is formed as a single optical element operable to provide: a)
a negative optical power contribution operable to diverge the image-bearing light beams in advance of the eyebox (E, <NUM>), such that the virtual object is viewed at a second focusing distance from the eyebox (E, <NUM>) and the second focusing distance is closer than the first focusing distance, and b)
a corrective optical contribution operable to reduce optical aberrations associated with viewing both the real-world object and the virtual object at the second focusing distance; and
a positive-power optic (<NUM>, <NUM>) located between the outer surface (<NUM>) of the waveguide and the ambient environment, wherein the positive-power optic is operable to compensate for the negative optical power contribution of the multifunction optic without compensating for the corrective optical contribution of the multifunction optic, wherein the real-world object is viewed at its actual distance from the eyebox (E, <NUM>) with corrected vision;
characterized in that
said in-coupling optic is diffractive, said out-coupling optic is diffractive, and by a lens holder (<NUM>) configured to support the multifunction optic (<NUM>), wherein the lens holder (<NUM>) is slideably removeable from the head-mounted display, and wherein the image light guide (<NUM>, <NUM>, <NUM>) is in fixed arrangement with the head-mounted display.