Wearable 3D augmented reality display

A wearable 3D augmented reality display and method, which may include 3D integral imaging optics.

FIELD OF THE INVENTION

The present invention relates generally to a wearable 3D augmented reality display, and more particularly, but not exclusively, to a wearable 3D augmented reality display comprising 3D integral imaging (InI) optics.

BACKGROUND OF THE INVENTION

An augmented reality (AR) display, which allows overlaying 2D or 3D digital information on a person's real-world view, has long been portrayed as a transformative technology to redefine the way we perceive and interact with digital information. Although several types of AR display devices have been explored, a desired form of AR displays is a lightweight optical see-through head-mounted display (OST-HMD), which enables optical superposition of digital information onto the direct view of the physical world and maintains see-through vision to the real world. With the rapidly increased bandwidth of wireless networks, the miniaturization of electronics, and the prevailing cloud computing, one of the current challenges is to realize an unobtrusive AR display that integrates the functions of OST-HMDs, smart phones, and mobile computing within the volume of a pair of eyeglasses.

Such an AR display, if available, will have the potential to revolutionize many fields of practice and penetrate through the fabric of life, including medical, defense and security, manufacturing, transportation, education and entertainment fields. For example, in medicine AR technology may enable a physician to see CT images of a patient superimposed onto the patient's abdomen while performing surgery; in mobile computing it can allow a tourist to access reviews of restaurants in his or her sight while walking on the street; in military training it can allow fighters to be effectively trained in environments that blend 3D virtual objects into live training environments.

Typically, the most critical barriers of AR technology are defined by the displays. The lack of high-performance, compact and low-cost AR displays limits the ability to explore the full range of benefits potentially offered by AR technology. In recent years a significant research and market drive has been toward overcoming the cumbersome, helmet-like form factor of OST-HMD systems, primarily focusing on achieving compact and lightweight form factors. Several optical technologies have been explored, resulting in significant advances in OST-HMDs. For instance, the well-advertised Google Glass® is a very compact, lightweight (˜36 grams), monocular OST-HMD, providing the benefits of encumbrance-free instant access to digital information. Although it has demonstrated a promising and exciting future prospect of AR displays, the current version of Google Glass® has a very narrow FOV (approximately 15° FOV diagonally) with an image resolution of 640×360 pixels. It offers limited ability to effectively augment the real-world view in many applications.

Despite such promises a number of problems remain with existing OST-HMD's, such as visual discomfort of AR displays. Thus, it would be an advance in the art to provide OST-HMD's which provide increased visual comfort, while achieving low-cost, high-performance, lightweight, and true 3D OST-HMD systems.

SUMMARY OF THE INVENTION

In one of its aspects the present invention may provide a 3D augmented reality display having a microdisplay for providing a virtual 3D image for display to a user. For example, the optical approach of the present invention may uniquely combine the optical paths of an AR display system with that of a micro-InI subsystem to provide a 3D lightfield optical source. This approach offers the potential to achieve an AR display invulnerable to the accommodation-convergence discrepancy problem. Benefiting from freeform optical technology, the approach can also create a lightweight and compact OST-HMD solution.

In this regard, in one exemplary configuration of the present invention, display optics may be provided to receive optical radiation from the microdisplay and may be configured to create a 3D lightfield, that is, a true optically reconstructed 3D real or virtual object from the received radiation. (As used herein the term “3D lightfield” is defined to mean the radiation field of a 3D scene comprising a collection of light rays appearing to be emitted by the 3D scene to create the perception of a 3D scene.) An eyepiece in optical communication with the display optics may also be included, with the eyepiece configured to receive the 3D lightfield from the display optics and deliver the received radiation to an exit pupil of the system to provide a virtual display path. The eyepiece may include a selected surface configured to receive the 3D lightfield from the display optics and reflect the received radiation to an exit pupil of the system to provide a virtual display path. The selected surface may also be configured to receive optical radiation from a source other than the microdisplay and to transmit such optical radiation to the exit pupil to provide a see-through optical path. The eyepiece may include a freeform prism shape. In one exemplary configuration the display optics may include integral imaging optics.

DETAILED DESCRIPTION OF THE INVENTION

Despite current commercial development of HMDs, very limited efforts have been made to address the challenge of minimizing visual discomfort of AR displays, which is a critical concern in applications requiring an extended period of use. One of the key factors causing visual discomfort is the accommodation-convergence discrepancy between the displayed digital information and the real-world scene, which is a fundamental problem inherent to most of the existing AR displays. The accommodation cue refers to the focus action of the eye where ciliary muscles change the refractive power of the crystalline lens and therefore minimize the amount of blur for the fixated depth of the scene. Associated with eye accommodation change is the retinal image blur cue which refers to the image blurring effect varying with the distance from the eye's fixation point to the points nearer or further away. The accommodation and retinal image blurring effects together are known as focus cues. The convergence cue refers to the rotation action of the eyes to bring the visual axes inward or outward to intersect at a 3D object of interest at near or far distances.

The accommodation-convergence mismatch problem stems from the fact that the image source in most of the existing AR displays is a 2D flat surface located at a fixed distance from the eye. Consequently, this type of AR display lacks the ability to render correct focus cues for digital information that is to be overlaid over real objects located at distances other than the 2D image source. It causes the following three accommodation-convergence conflict. (1) There exists a mismatch of accommodation cues between the 2D image plane and the real-world scene (FIG. 1A). The eye is cued to accommodate at the 2D image plane for viewing the augmented information while the eye is concurrently cued to accommodate and converge at the depth of a real 3D object onto which the digital information is overlaid. The distance gap between the display plane and real-world objects can be easily beyond what the human visual system (HVS) can accommodate simultaneously. A simple example is the use of an AR display for driving assistance where the eyes need to constantly switch attention between the AR display and real-world objects spanning from near (e.g. dashboard) to far (e.g. road signs). (2) In a binocular stereoscopic display, by rendering a pair of stereoscopic images with binocular disparities, the augmented information may be rendered to appear at a different distance from the 2D display surface (FIG. 1B). When viewing augmented information, the eye is cued to accommodate at the 2D display surface to bring the virtual display in focus but at the same time the eye is forced to converge at the depth dictated by the binocular disparity to fuse the stereoscopic pair. In viewing a natural scene (FIG. 1C), the eye convergence depth coincides with the accommodation depth and objects at depths other than the object of interest are seen blurred. (3) Synthetic objects rendered via stereoscopic images, regardless of their rendered distance from the user, are seen all in focus if the viewer focuses on the image plane, or are seen all blurred if the user accommodates at distances other than the image plane. The retinal image blur of a displayed scene does not vary with the distances from an eye fixation point to other points at different depths in the simulated scene. In a nutshell, the incorrect focus cues may contribute to issues in viewing stereoscopic displays, such as distorted depth perception, diplopic vision, visual discomfort and fatigue, and degradation in oculomotor response.

In one of its aspects the present invention relates to a novel approach to OST-HMD designs by combining 3D lightfield creation technology and freeform optical technology. 3D lightfield creation technology of the present invention reconstructs the radiation field of a 3D scene by creating a collection of light rays appearing to be emitted by the 3D scene and creating the perception of a 3D scene. Thus, as used herein the term “3D lightfield” is defined to mean the radiation field of a 3D scene comprising a collection of light rays appearing to be emitted by the 3D scene to create the perception of a 3D scene. The reconstructed 3D scene creates a 3D image source for HMD viewing optics, which enables the replacement of a typical 2D display surface with a 3D source and thus potentially overcomes the accommodation-convergence discrepancy problem. Any optical system capable of generating a 3D lightfield may be used in the devices and methods of the present invention. For instance, one exemplary configuration of the present invention uses micro integral imaging (micro-InI) optics for creating a full-parallax 3D lightfield to optically create the perception of the 3D scene. (Persons skilled in the art will be aware that Integral imaging (InI) is a multi-view imaging and display technique that captures or displays the light fields of a 3D scene by utilizing an array of pinholes, lenses or microlenses. In the case of being a display technique, a microlens array in combination with a display device, which provides a set of elemental images each having information of a different perspective of the 3D scene. The microlens array in combination with the display device renders ray bundles emitted by different pixels of the display device, and these ray bundles from different pixels intersect and optically create the perception of a 3D point that appears to emit light and occupy the 3D space. This method allows the reconstruction of a true 3D image of the 3D scene with full parallax information in all directions.) Other optical system capable of generating a 3D lightfield which may be used with the present invention include, but not limited to, holographic display (M. Lucente, “Interactive three-dimensional holographic displays: seeing the future in depth,” Computer Graphics, 31(2), pp. 63-67, 1997; P. A. Blanche, et al, “Holographic three-dimensional telepresence using large-area photorefractive polymer”, Nature, 468, 80-83, November 2010), multi-layer computational lightfield display (G. Wetzstein et al., “Tensor Displays: Compressive light field synthesis using multilayer displays with directional backlighting,” ACM Transactions on Graphics, 31(4), 2012.), and volumetric displays (Blundell, B. G., and Schwarz, A. J., “The classification of volumetric display systems: characteristics and predictability of the image space,” IEEE Transaction on Visualization and Computer Graphics, 8(1), pp. 66-75, 2002. J. Y. Son, W. H. Son, S. K. Kim, K. H. Lee, B. Javidi, “Three-Dimensional Imaging for Creating Real-World-Like Environments,” Proceedings of IEEE Journal, Vol. 101, issue 1, pp. 190-205, January 2013.).

A micro-InI system has the potential of achieving full-parallax 3D object reconstruction and visualization in a very compact form factor suitable for a wearable system. It can dramatically alleviate most of the limitations in a conventional autostereoscopic InI display due to the benefit of well-constrained viewing positions and can be effectively utilized for addressing the accommodation-convergence discrepancy problem in conventional HMD systems. The micro-InI unit can reconstruct a miniature 3D scene through the intersection of propagated ray cones from a large number of recorded perspective images of a 3D scene. By taking advantage of the freeform optical technology, the approach of the present invention can result in a compact, lightweight, goggle-style AR display that is potentially less vulnerable to the accommodation-convergence discrepancy problem and visual fatigue. Responding to the accommodation-convergence discrepancy problem of existing AR displays, we developed an AR display technology with the ability to render the true lightfield of a 3D scene reconstructed optically and thus accurate focus cues for digital information placed across a large depth range.

The challenges of creating a lightweight and compact OST-HMD solution, invulnerable to the accommodation-convergence discrepancy problem, are to address two cornerstone issues. The first is to provide the capability of displaying a 3D scene with correctly rendered focus cues for a scene's intended distance correlated with the eye convergence depth in an AR display, rather than on a fixed-distance 2D plane. The second is to create an optical design of an eyepiece with a form factor as compelling as a pair of eyeglasses.

A block diagram of a 3D OST-HMD system in accordance with the present invention is illustrated inFIG. 2. It includes three principal subsystems: a lightfield creation module (“3D Lightfield Creation Module”) reproducing the full-parallax lightfields of a 3D scene seen from constrained viewing zones; an eyepiece relaying the reconstructed 3D lightfields into a viewer's eye; and a see-through system (“See-through Optics”) optically enabling a non-obtrusive view of the real world scene.

In one of its aspects, the present invention provides an innovative OST-HMD system that integrates the 3D micro-InI method for full-parallax 3D scene optical visualization with freeform optical technology for OST-HMD viewing optics. This approach enables the development of a compact 3D InI optical see-through HMD (InI-OST-HMD) with full-parallax lightfield rendering capability, which is anticipated to overcome the persisting accommodation-convergence discrepancy problem and to substantially reduce visual discomfort and fatigue experiences of users.

Full-parallax lightfield creation method. An important step to address the accommodation-convergence discrepancy problem is to provide the capability of correctly rendering the focus cues of digital information regardless of its distance to the viewer, rather than rendering digital information on a fixed-distance 2D surface. Among the different non-stereoscopic display methods, we chose to use an InI method that allows the reconstruction of the full-parallax lightfields of a 3D scene appearing to be emitted by a 3D scene seen from constrained or unconstrained viewing zones. Compared with all other techniques, an InI technique requires a minimal amount of hardware complexity, which makes it possible to integrate it with an OST-HMD optical system and create a wearable true 3D AR display.

FIG. 3schematically illustrates an exemplary micro-InI unit300. A set of 2D elemental images301, each representing a different perspective of a 3D scene, are displayed on a high-resolution microdisplay310. Through a microlens array (MLA)320, each elemental image301works as a spatially-incoherent object and the conical ray bundles emitted by the pixels in the elemental images301intersect and integrally create the perception of a 3D scene, in which objects appear to be located along the surface AOB having a depth range Z0at a reference plane, for example, to provide the appearance to emit light and occupy the 3D space. The microlens array may be placed a distance “g” from the microdisplay310to create either a virtual or a real 3D scene. The micro-InI unit300allows the optical reconstruction of a 3D surface shape with full parallax information. It should be noted that an InI-based 3D display operates fundamentally differently from multi-view stereoscopic systems where a lenticular sheet functions as a spatial de-multiplexer to select appropriate discrete left-eye and right-eye planar views of a scene dependent on viewer positions. Such multi-view systems produce a defined number of binocular views typically with horizontal parallax only and may continue to suffer from convergence accommodation conflict.

FIG. 4schematically illustrates an alternative configuration of a micro-InI unit400in accordance with the present invention that creates a telecentric 3D lightfield of a 3D scene at surface AOB. A primary difference from the configuration ofFIG. 3lies in the use of additional lenses (lens430and/or lens440) which help to relay the apertures of a microlens array (MLA)420and creates a telecentric 3D lightfield. (R. Martinez-Cuenca, H. Navarro, G. Saavedra, B. Javidi, and M. Martinez-Corral, “Enhanced viewing-angle integral imaging by multiple-axis telecentric relay system,” Optics Express, Vol. 15, Issue 24, pp. 16255-16260, 21 Nov. 2007.) Lens430and lens440have the same focal distance, f1=f2, with lens430directly attached to the MLA420and lens440placed at a focal distance, f1, away. The gap between the microdisplay410and the MLA420is the same as the focal distance, f0, of the MLA420. The main advantages of this alternative design are the potential increase of viewing angle for the reconstructed 3D scene, compactness, ease of integration with the HMD viewing optics, and blocking of the flipped images created by rays refracted by microlenses421of the MLA420other than the correctly paired elemental image401and microlens421.

Although the InI method is promising, improvements are still desirable due to three major limitations: (1) low lateral and longitudinal resolutions; (2) narrow depth of field (DOF); and (3) limited field of view angle. These limitations are subject to the limited imaging capability and finite aperture of microlenses, poor spatial resolution of large-size displays, and the trade-off relationship between wide view angle and high spatial resolution. Conventional InI systems typically yield low lateral and depth resolutions and narrow DOF. These limitations, however, can be alleviated in a wearable InI-HMD system of the present invention. First, microdisplays with large pixel counts and very fine pixels (e.g. ˜5 μm pixel size) may be used in the present invention to replace large-pixel display devices (˜200-500 μm pixel size) used in conventional InI displays, offering at least 50× gain in spatial resolution,FIG. 7. Secondly, due to the nature of HMD systems, the viewing zone is well confined and therefore a much smaller number of elemental images would be adequate to generate the full-parallax lightfields for the confined viewing zone than large-size autostereoscopic displays. Thirdly, to produce a perceived 3D volume spanning from 40 cm to 5 m depth range in an InI-HMD system, a very narrow depth range (e.g. Z0˜3 5 mm) is adequate for the intermediate 3D scene reconstructed by the micro-InI unit, which is much more affordable than in a conventional stand-alone InI display system requiring at least 50 cm depth range to be usable,FIG. 7. Finally, by optimizing the microlenses and the HMD viewing optics together, the depth resolution of the overall InI-HMD system can be substantially improved, overcoming the imaging limit of a stand-alone InI system.

The lightfields of the miniature 3D scene reconstructed by a micro-InI unit may be relayed by eyepiece optics into the eye for viewing. The eyepiece optics not only effectively couples the 3D lightfields into the eye (exit) pupil but may also magnify the 3D scene to create a virtual 3D display appearing to be at a finite distance from the viewer.

As an example,FIG. 5schematically illustrates the integration of a micro-InI unit530with conventional eyepiece optics540. The micro-InI unit530may include a microdisplay510and microlens array520that may be configured in a similar manner to that illustrated inFIG. 3. The micro-InI unit530reconstructs a miniature 3D scene (located at AOB inFIG. 5) which is located near the back focal point of the eyepiece optics540. Through the eyepiece optics540the miniature scene may be magnified into an extended 3D display at A′O′B′ which can then be viewed from a small zone constrained by the exit pupil of the eyepiece optics540. Due to the 3D nature of the reconstructed scene, a different viewing perspective is seen at different locations within the exit pupil.

Among the different methods for HMD designs, freeform optical technology demonstrates great promise in designing compact HIVID systems.FIG. 6Aillustrates the schematics of an exemplary configuration of a wearable 3D augmented reality display600in accordance with the present invention. The wearable 3D augmented reality display600includes a 3D InI unit630and a freeform eyepiece640. The micro-InI unit630may include a microdisplay610and microlens array620that may be configured in a similar manner to that illustrated inFIG. 3. This configuration600adopts a wedge-shaped freeform prism as the eyepiece640, through which the 3D scene reconstructed by the micro-InI unit630is magnified and viewed. Such eyepiece640is formed by three freeform optical surfaces which are labeled as 1, 2, and 3, respectively, which may be rotationally asymmetric surfaces. The exit pupil is where the eye is placed to view the magnified 3D scene, which is located at the virtual reference plane conjugate to the reference plane of the 3D InI unit630. A light ray emitted from a 3D point (e.g. A) located at the intermediate scene is first refracted by the surface 3 of the freeform eyepiece640located closest to the reference plane. Subsequently, the light ray experiences two consecutive reflections by the surfaces 1′ and 2, and finally is transmitted through the surface 1 and reaches the exit pupil of the system. Multiple ray directions from the same object point (e.g. each of the 3 rays from point A), each of which represents a different view of the object, impinge on different locations of the exit pupil and reconstruct a virtual 3D point (e.g. A′) in front of the eye.

Rather than requiring multiple elements, the optical path is naturally folded within a three-surface prism structure of the eyepiece640, which helps reduce the overall volume and weight of the optics substantially when compared with designs using rotationally symmetric elements.

To enable see-through capability for AR systems, surface 2 of the eyepiece640may be coated as a beam splitting mirror. A freeform corrector lens650may be added to provide a wearable 3D augmented reality display690having improved see-through capability. The corrector lens650may include two freeform surfaces which may be attached to the surface 2 of the eyepiece640to correct the viewing axis deviation and undesirable aberrations introduced by the freeform prism eyepiece640to the real world scene. The rays from the virtual lightfield generated by the 3D InI unit630are reflected by surface 2 of the prism eyepiece640, while the rays from a real-world scene are transmitted through the freeform eyepiece640and corrector lens650,FIG. 6C.FIG. 6Cschematically illustrates the integration and raytracing of the overall wearable 3D augmented reality display690. The front surface of the freeform corrector lens650matches the shape of surface 2 of the prism eyepiece640. The back surface 4 of the corrector lens650may be optimized to minimize the shift and distortion introduced to the rays from a real-world scene when the corrector lens650is combined with the prism eyepiece640. The additional corrector lens650is not expected to noticeably increase the footprint and weight of the overall system690.

Thus, in devices of the present invention, the freeform eyepiece640may image the lightfield of a 3D surface AOB, rather than a 2D image surface. In such an InI-HMD system600,690, the freeform eyepiece640can reconstruct the lightfield of a virtual 3D object A′O′B′ at a location optically conjugate to the lightfield of a real object, while in a conventional HMD system the eyepiece creates a magnified 2D virtual display which is optically conjugate to the 2D microdisplay surface.

EXAMPLES

A proof-of-concept monocular prototype of an InI OST-HMD according to the configuration ofFIG. 6Cwas implemented using off-the-shelf optical components,FIG. 8. A micro-lens array (MLA) of a 3.3 mm focal length and 0.985 mm pitch was utilized. (These types of microlenses can be purchased from Digital Optics Corp, SUSS Microoptics, etc.) The microdisplay was a 0.8″ organic light emitting display (OLED), which offered 1920×1200 color pixels with a pixel size of 9.6 μm. (EMA-100820, by eMagin Corp, Bellevue, Wash.) A freeform eyepiece along with a see-through corrector were used of the type disclosed in International Patent Application No. PCT/US2013/065422, the entire contents of which are incorporated herein by reference. The specifications of the eyepiece640and corrector650are provided in the tables below. The eyepiece offered a field of view of 40 degrees and approximately a 6.5 mm eyebox. Due to the strict telecentricity of the eyepiece design, it was adapted to the InI setup with reasonably low crosstalk but with a narrow viewing zone. It is worth noting that adapting this particular freeform eyepiece design is not required for implementing the optical method described in this invention. Alternative eyepieces may be designed and optimized for this purpose.

System Prescription for Display Path

In Error! Reference source not found.1, surfaces #2-#4 specify the free-form eyepiece640. Table 1 surfaces #2 and #4 represent the same physical surface and corresponds to eyepiece surface 1, inFIGS. 6A-6C. Table 1 surface #3 is corresponds eyepiece surface 2, and Table 1 surface #5 corresponds to eyepiece surface 3, inFIGS. 6A-6C.

In Table 2 surfaces #2 and #3 are eyepiece surfaces 1 and 3, modeled the same as in the display path. Surfaces #4, #5 specify the freeform corrector lens650. Surface #4 is an exact replica of Surface #3 (eyepiece surface 2).

TABLE 4Decenter of Surface #2 and #4 of Table 1,relative to Surface #1 of Table 1.Y DECENTERZ DECENTERALPHA TILT6.775E+002.773E+017.711E+00

TABLE 8Decenter of Surface #5 relative to Surface #1 of Table 1.Y DECENTERZ DECENTERALPHA TILT.427E+013.347E+017.230E+01

TABLE 10Decenter of Surface #5 relative to Surface #1 of Table 2.Y DECENTERZ DECENTERALPHA TILT3.358E+004.900E+016.765E+00

As used in the system prescription Tables, e.g., Table 1 or Error! Reference source not found.2, the term “XY Poly” refers to a surface which may be represented by the equation

z=cr21+1-(1+k)⁢c2⁢r2+∑j=266⁢Cj⁢xm⁢ynj=(m+n)2+m+3⁢⁢n2+1,
where z is the sag of the free-form surface measured along the z-axis of a local x, y, z coordinate system, c is the vertex curvature (CUY), r is the radial distance, k is the conic constant, and Cjis the coefficient for xmyn.

For demonstration purposes, a 3D scene including a number “3” and a letter “D” was simulated. In the visual space, the objects “3” and “D” were located ˜4 meters and 30 cms away from the eye position, respectively. To clearly demonstrate the effects of focusing, these character objects, instead of using plain solid colors, were rendered with black line textures. An array of 18×11 elemental images of the 3D scene were simulated (FIG. 9), each of which consisted of 102 by 102 color pixels. The 3D scene reconstructed by the micro-InI unit was approximately 10 mm away from the MLA and the separation of the two reconstructed targets was approximately 3.5 mm in depth in the intermediate reconstruction space.

FIGS. 10A through 10Dshows a set of images captured with a digital camera placed at the eye position. To demonstrate the effects of focus and see-through view, in the real-world view, a Snellen letter chart and a printed black-white grating target were placed ˜4 meters and 30 cm away from the viewer, respectively, which corresponded to the locations of the objects “3” and “D”, respectively.

FIGS. 10A and 10Bdemonstrate the effects of focusing the camera on the Snellen chart and grating target, respectively. The object “3” appeared to be in sharp focus when the camera was focused on the far Snellen chart while the object “D” was in focus when the camera was focused on the near grating target.FIGS. 10C and 10Ddemonstrate the effects of shifting the camera position from the left to the right sides of the eyebox while the camera focus was set on the near grating target. As expected, slight perspective change was observed between these two views. Although artifacts admittedly are visible and further development is needed, the results clearly demonstrated that the proposed method for AR display can produce correct focus cues and true 3D viewing in a large depth range.

A number of patent and non-patent publications are cited in the specification, the entire disclosure of each of these publications is incorporated by reference herein.

REFERENCES