Abstract:
The present invention introduces a compact, HUD eyeglass display system of novel design that makes it possible to superimpose a wide-angle, computer-generated view on the real-world view, without obscuring the wearer&#39;s vision or requiring any additional optical element such as beam-splitters or contact lenses. The digital display is visible regardless of which way the wearer turns his eyes, and has great depth of field, so both it and the external scene appear in focus, regardless of the distance to the scene. These head-up display eyeglasses are compatible with prescription lenses.

Description:
[0001]    This patent application claims the benefit of priority of provisional patent application 61/742,623, filed Aug. 15, 2012. 
     
    
     BACKGROUND 
       [0002]    Head-up displays (HUDs) are used to present computer-generated data on top of a view of the real world. The HUD in a fighter aircraft, for example, superimposes instrument readings on the pilot&#39;s view out of the canopy. In larger displays this has typically been achieved by combining the real world view and the computer display view with a half-silvered mirror. HUD eyeglasses, a miniature and portable version of this, are used for augmented reality games, factory automation and aircraft maintenance, to give just a few examples. Head-up eyeglasses present a difficulty, however, because they sit close to the face and do not allow room for such a half-silvered mirror. In general, they have been implemented in prior art by placing a small display screen or other image source in front of one or both eyes, generally slightly above or to one side of the eye, or by using a small array of partially mirrored narrow strips. In either case they partially or completely obstruct the wearer&#39;s view of the world through one eye and present only a limited field of vision. Alternatively they require special contact lenses in addition to special eyeglasses. 
         [0003]    True head-up eyeglasses that don&#39;t require such obstructed vision, provide full-screen computer displays to both eyes and resemble ordinary eyeglasses have long been a subject of science fiction. Their realization would not only enable the applications mentioned above, but would revolutionize mobile computing in general. As personal computing moves from the desktop or laptop to the mobile device, there is acute need for a portable, widescreen, high-resolution display much larger than could fit in a pocket. HUD eyeglasses as described in this invention provide the most versatile solution to answer this need. 
         [0004]    There are many difficulties to developing wide-field HUD eyeglasses, which explains why viable implementations have not been described until now. The first, of course, is finding a compact and effective ocular relay, the optical element in a HUD that receives light from a projector off to one side and redirects it so that it can enter the pupil of the eye and be seen. 
         [0005]    Then, to be commercially successful, such HUD eyeglasses must be comfortable as well as stylish. Besides being lightweight, they must be adapted to the functional characteristics of the human eye which set it apart from other optical instruments, namely:
       1. frequent, rapid changes in accommodation to view objects at different distances will induce eyestrain.   2. the eye moves in its socket (up to 150 degrees horizontally and 120 degrees vertically) as we examine a scene, jumping rapidly from point to point.   3. the head may move as well   4. visual acuity is high only in the center of the retina, and falls off from the center of gaze sharply (e.g. 50% in 3 degrees)       
 
         [0010]    What we call “seeing,” then, includes two distinct phenomena:
       i. detailed vision, where the gaze jumps from point to point as the eye moves in its socket to examine a scene, and   ii. peripheral vision, where surrounding objects are perceived—more or less indistinctly—while the gaze remains fixed.       
 
         [0013]    Taken together, points 1 and 2 imply two seemingly contradictory design requirements for HUD eyeglasses:
       I. the image of the widescreen, digital display should always be in focus with the scene behind it—i.e should have a depth-of-field from, e.g., 1 foot to infinity (corresponding to a near-zero numerical aperture)   II. the light should converge on the eye from a near-hemispherical solid angle       
 
         [0016]    Vitale et al. (U.S. Pat. No. 7,952,059 B2) proposed to address point  2  by using an ellipsoidal mirror as the ocular relay in a HUD. The requirement that light should converge on the eye regardless of which direction the eye is pointed is well satisfied by an ellipsoidal mirror. It has been well known to mathematicians since Euclid that a prolate ellipsoid (a cigar-shaped, 3-dimensional figure formed by rotating an ellipse about its long axis) has two focal points on its long axis such that waves of light (or sound) arising from one focus, when reflected from the inner surface of the ellipsoid, will converge at the other (see  FIG. 1 ). If the center of rotation of the eye is located at one focus of such an ellipsoidal mirror and a source of light is placed at the other, then some rays arising from the light will always be directed straight into the eye regardless of which way it turns in its socket. 
         [0017]    An ellipsoid, however, is too bulbous a shape to make a successful eyeglass lens, and has optical aberrations that pose serious challenges. 
         [0018]    Powell et al. (U.S. Pat. No. 7,656,585 B1), on the other hand, explicitly discuss a Fresnel lens or mirror (they refer to both as a “lens”) and pay lip service to holographic and diffraction lenses, but never mention the notions of ellipsoidal conjugate foci or the importance of eye movements in vision. 
         [0019]    This invention is a HUD eyeglass system that circumvents most of these difficulties, and resolves the contradiction mentioned previously as well. 
         [0020]    In the specification and claims that follow:
       the term “scene” refers to the view of the outside world that a wearer of normal eyeglasses (or none at all) would enjoy,   the term “image” refers to visual data presented to the eye, without regard whether it arises from the natural scene or the HUD&#39;s digital display; or whether that image is composed of text, graphics, video or photos   the term “digital display” refers to the computer-generated image superimposed by the HUD eyeglasses on the view of the scene, regardless whether it is sequentially presented by a raster-scanning laser or simultaneously presented by a LED panel.   the term “ocular relay” refers to the optical element in a HUD that receives light from a projector outside the eye&#39;s gaze and redirects it so that it can enter the pupil of the eye and be seen.       
 
         [0025]    These abbreviations are used throughout the text: 
         [0026]    HUD: Head-Up Display 
         [0027]    HOE: Holographic Optical Element 
         [0028]    LED: Light Emitting Diode 
       SUMMARY 
       [0029]    It is therefore an object of the present invention to provide a HUD eyeglass system that consists of:
       an image projector at the side of the face with a very small exit pupil (i.e. that is almost a point source), and   an eyeglass lens that also serves as an ocular relay, redirecting the light rays from the projector towards the center of the wearer&#39;s eye. The lens also allows light through it like ordinary glasses.       
 
         [0032]    In this way, whichever direction the user looks, the wearer will see the digitally generated image superimposed on the external scene, and in focus with it regardless of how near or far the external object of interest may be. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    It should be understood that, in some figures, details may have been enlarged for clarity rather than drawn to scale. Similar numerals denote similar items throughout the drawings. 
           [0034]      FIG. 1  is a cross section through a prolate ellipsoidal mirror, showing how light rays arising from one of the two foci are reflected to the other. 
           [0035]      FIG. 2  (reproducing FIG. 1A of Vitale et al.) is a perspective view of an ellipsoidal lens in prior art showing how a segment of an ellipsoid can function as an ocular relay. The call-out numbers in this figure are not pertinent here. 
           [0036]      FIG. 3  shows an embodiment of HUD eyeglasses where the projector is a scanning laser and the ocular relay is a Fresnel mirror. The figure shows a horizontal cross-section of the left side of the HUD eyeglasses and their wearer. It does not show the refractive effect of the eye&#39;s cornea and lens, since their positions change with the direction of gaze. 
           [0037]      FIG. 4  is a detail of the Fresnel mirror in  FIG. 3 . 
           [0038]      FIG. 5  a detail view of the scanning laser projector in  FIG. 3 . 
           [0039]      FIG. 6  shows a detail where the projector comprises a LED display screen, a condenser lens, a pinhole and a corrective lens. 
           [0040]      FIG. 7  shows an embodiment of the HUD eyeglasses comprising a scanning laser system and a HOE whose focal points are on opposite sides of lens. The figure shows a horizontal cross-section of the left side of the HUD eyeglasses and their wearer. It does not show the refractive effect of the eye&#39;s cornea and lens, since their positions change with the direction of gaze. 
       
    
    
     DETAILED DESCRIPTION 
       [0041]    Requirement I (in Background, above) that the digital display should be in focus with the scene behind it means that the former should have great depth of field (or equivalently, near-zero numerical aperture). This is well satisfied by a projector with a very small exit pupil. In other words, the projector needs to appear to be nearly a point source. 
         [0042]    As mentioned in Background, using an ellipsoidal mirror as an ocular relay solves the directional problem, because light from a source at one focus is reflected by the mirror so as to pass through the other focus (located at the center of the eye).  FIG. 1  shows a cross section through the major axis of a prolate ellipsoidal shell  115 . Rays of light  135 , originating at the left-hand focus  125 , reflect off the wall  115  and pass through the other focus  125 . This is true also for a HOE, a Fresnel mirror or a Fresnel lens as long as they each have a pair of conjugate foci. In addition, other mirror shapes (e.g. double parabola, spheroid) are possible. 
         [0043]    Unfortunately, the imaging properties of ellipsoidal mirrors and their HOE or Fresnel analogues are poor for sources that are not located exactly at a focus. They exhibit spherical aberration, astigmatism (this is easy to understand in the case of an ellipsoid, since the radii of curvature of the surface are generally not equal) and distortion. The spherical aberration and astigmatism will affect a light source of any finite extent centered at a focus. They may be reduced to an acceptable level by a combination of a) adding a corrective lens to the projector, and b) shrinking the exit pupil of the projector until it becomes nearly a point source. The field distortion, on the other hand, is present for a source of any size, and is evident in  FIG. 1 . Note that the rays emanating from the left-hand focus are regularly spaced every 7.5 degrees, but the converging rays at the right-hand focus are not regularly spaced. Correcting this is discussed below. 
         [0044]    In reducing aberrations, how small can the exit pupil be? One criterion is that the zero-order diffraction image of the projector&#39;s exit pupil (the zero-order pattern is the smallest image feature the projector can generate) not exceed a certain angular size. For example 1 minute of arc is equivalent to the resolution Apple&#39;s retina display held at arms length. This would correspond to a projector exit pupil of about 1.7 mm. Note that the actual resolution from such a projector will vary across the visual field due to changes in magnification, as just discussed. 
         [0045]      FIG. 2 , from Vitale et al. (U.S. Pat. No. 7,952,059 B2) shows the best of the prior art. A bulbous, semi-transparent ellipsoidal ocular relay mirror reflects light from a bulky LED display screen and multi-element lens towards the approximate center of the wearer&#39;s eye (labeled  130  in their numbering system). 
         [0046]      FIG. 3  shows the preferred embodiment of the present invention, comprised of a miniaturized scanning laser system  150 , located in the temple  160  of the eyeglasses, and a flat or gently curved, semi-reflective lens  110  comprised of alternating reflective and clear segments. Although the display system is shown for only one eye, in the preferred embodiment there would be a display system for each eye. 
         [0047]    In this embodiment, the lens  110  is comprised—not of a single mirror—but of narrow strips of ellipsoidal mirrors, separated by clear, non-mirrored spaces (see  FIG. 4 ). In other words, the lens  110  is a Fresnel mirror with interstices  250  between the mirrored strips  240 . The mirrored strips  240  are not parts of single ellipsoid. Instead they are the intersections of a family of confocal ellipses of different radii with a thin shell determined by the shape of the eyeglass lens  110 . 
         [0048]    Each ellipsoidal strip  240  has one focus at the center of the deflection mirror  210  (see  FIG. 5 ), as imaged by the corrective lens  220 , and the other at the approximate center of the wearer&#39;s eyeball  140 . The strip  240  reflects the beam  170 , coming from the mirror  210 , towards the center of the wearer&#39;s eyeball  140 .  FIG. 4  does not attempt to show the refraction of light rays by the optical components of the eye itself. The eyeball  140  rotates in its socket as the direction of gaze changes, and so these optical properties depend on which way the eye is looking. 
         [0049]    The focal point within the eye may be at the center of rotation of the eyeball or somewhat anterior to it. While looking straight ahead at a scene, the eye perceives, through peripheral vision, a field of view extending approximately 150 degrees horizontally and 120 degrees vertically. That will not be the case, however, for the HUD&#39;s digital display. Because of its very small numerical aperture, the digital display will fade to invisibility as it extends away from the center of gaze. In some situations this may be a useful feature, as it helps to make the difference between the digital display and the natural scene more obvious. In others it may be less desirable. It is possible to mitigate this low-peripheral-vision effect by moving the focal point of the ocular relay forward from the center of the eyeball. The tradeoff is that doing so will reduce the width of the field through which the digital display can be seen in focused vision. 
         [0050]    Because the ellipsoidal strips of the eyeglass lens  110  always direct the laser light  170  towards the center of the eye, some part of the projected image will always enter the wearer&#39;s pupil, regardless of which way the eye  140  rotates in its socket. Light  180  from the scene in front of the user can pass through the gaps  250  of clear lens in between the mirrored strips  240  and also enter the viewer&#39;s pupil. 
         [0051]    The brightness of the projected display relative to the outside world can be adjusted by varying the intensity of the laser(s). A photocell or a video camera incorporated into the eyeglass frame  120  could make this adjustment automatically. 
         [0052]    As seen from the wearer&#39;s point of view, approximately 50% of the lens  110  would appear silvered and the rest would be transparent. Seen from the angle of the deflection mirror  210 , however, the size and separation of the mirrored steps can be such that the lens appears to be 100% silvered, and none of the laser beam passes through the lens  110  to be visible to another observer. The computer-generated display is therefore completely private. 
         [0053]    The lattice of mirrored strips  240  is too close to the wearer&#39;s eye to be in focus, and their separation should be small enough to so he or she is not aware of the lattice. On the other hand, their separation should not be so small as to produce noticeable optical diffraction effects. For example, but without restriction, a spacing of 0.5 mm (0.02 inches) might be suitable. 
         [0054]    Although the mirrored strips  240  are shown in  FIG. 4  as projecting from the inner margin of the eyeglass lens, they may also be embedded in the same transparent material (e.g. polycarbonate, CR-39 plastic, Trivex) as the lens, making them easier to keep clean. 
         [0055]    The ellipsoidal lens strips do introduce some optical aberrations. An aspheric corrective lens ( 220  on  FIG. 5 ) largely compensates for these, so the beam  230  from the laser (or lasers)  200  is brought to sharp focus on a spot in the wearer&#39;s retina  190 . In this way the computer-generated raster is imaged on the surface of the retina  190 . 
         [0056]    As mentioned above, the Fresnel mirror distorts the image by its non-uniform magnification. This distortion is corrected by digitally pre-processing the signals to the projectors, introducing opposite and canceling distortions. 
         [0057]    Light  180  from objects in front of the user also forms an image on the retina  190 . As a result, the digital display is superimposed on the view of the external world. Because the digital display has great depth-of-field (small exit pupil), it and the external scene appear in focus at the same time, regardless of the distance to the scene. 
         [0058]    Since the projected display depends only on the mirrored strips on the inside surface of the lens  110  (and has near-infinite depth of field), the outside surface can be uniform or vary in thickness. The HUD eyeglasses are therefore compatible with prescription lenses. 
         [0059]    The scanning laser system  150  is comprised ( FIG. 5 ) of a miniature laser  200 , a movable deflection mirror  210  and an aspheric correction lens  220  which reduces optical aberrations in the HUD system. In a color display,  200  may actually be three optically coaxial lasers of different wavelengths. The deflection mirror  210  rotates or vibrates around both vertical and horizontal axes and deflects the laser beam  230  as its intensity is modulated, so as to generate a raster display  170 . 
         [0060]    A conventional eyeglass frame  120  and temple  160  hold the conventionally shaped eyeglass lens  110  in place on the viewer&#39;s face  130 . 
         [0061]    In a different embodiment, there are no spaces between the mirrored strips, but the mirrors are semi-transparent so that some light from the external scene can reach the eye. 
         [0062]    In another embodiment, the Fresnel mirror on the lens  110  is replaced by a HOE. In general, a HOE can mimic any simple optical element but in this case it would be formed by the interference pattern of two coherent beams diverging from the two conjugate focal points, corresponding to the exit pupil of the projector and the center of the eye. In this way, the HOE is an analogue of an ellipsoid or, more properly, of a thin Fresnel mirror having the same overall shape and foci. 
         [0063]    The HOE is partly transparent so that some light from the external scene can reach the eye. Light  180  from objects in front of the user also forms an image on the retina  190 . As a result, the digital display is superimposed on the view of the external world. Because the digital display has great depth-of-field (small exit pupil), it and the external scene appear in focus at the same time, regardless of the distance to the scene. 
         [0064]    In yet another embodiment, the HOE on the lens  110  is replaced by a diffraction mirror having two conjugate foci, such that light from one focus is diffracted by the diffraction pattern to converge on the other focal point, and the diffraction mirror is positioned such that one focus lies at the exit pupil of the image projector, and its other focus is located at or slightly anterior to the center of the eyeball. 
         [0065]    The diffraction mirror is partly transparent so that some light from the external scene can reach the eye. Light  180  from objects in front of the user also forms an image on the retina  190 . As a result, the digital display is superimposed on the view of the external world. Because the digital display has great depth-of-field (small exit pupil), it and the external scene appear in focus at the same time, regardless of the distance to the scene. 
         [0066]    In yet another embodiment, the scanning laser system is replaced by a projector (see  FIG. 6 ) comprised of:
       a display screen  610  using LED or equivalent technology,   a condenser  620  consisting of one or more lenses,   a diaphragm with a pinhole  630  at the focus of said condenser, and   an aspheric correction lens  220 .
 
This embodiment presents two disadvantages compared to a scanning laser, namely the bulk of the condenser and the limited brightness available from a LED panel compared to a laser.
       
 
         [0071]    In another embodiment (see  FIG. 7 ) of the present invention, the beam  170  of the miniaturized laser scanning system  150  arises in front of the eyeglasses  130  and is directed backward towards the lens  110 , where a HOE redirects the beam to converge at or slightly anterior to the center of the eye  140 . 
         [0072]    In this case the two foci of the HOE are located on opposite sides of the lens  110 , at the exit pupil of the projector and at or slightly anterior to the center of the eye. 
         [0073]    The HOE is partly transparent so that some light from the external scene can reach the eye. Light  180  from objects in front of the user also forms an image on the retina  190 . As a result, the digital display is superimposed on the view of the external world. Because the digital display has great depth-of-field (small exit pupil), it and the external scene appear in focus at the same time, regardless of the distance to the scene. 
         [0074]    In this embodiment, too, the HUD eyeglasses are compatible with prescription lenses. 
         [0075]    A conventional eyeglass frame  120  and extended temple  160  hold the scanning laser  150  and the conventionally shaped eyeglass lens  110  in place on the viewer&#39;s face  130 . 
         [0076]    In a different embodiment similar to  FIG. 7 , the ocular relay is a Fresnel mirror, replacing the HOE. The two foci of the Fresnel mirror are located on opposite sides of the lens  110 , at the exit pupil of the projector and at or slightly anterior to the center of the eye. 
         [0077]    The Fresnel mirrored strips are separated by gaps, or are semi-transparent, allowing Light  180  from the external scene to form an image on the retina  190 . As a result, the digital display is superimposed on the view of the external world. Because the digital display has great depth-of-field (small exit pupil), it and the external scene appear in focus at the same time, regardless of the distance to the scene. 
         [0078]    In this embodiment, too, the HUD eyeglasses are compatible with prescription lenses. 
         [0079]    In yet another embodiment similar to  FIG. 7 , the ocular relay is a Fresnel lens, replacing the Fresnel mirror. The two foci of the Fresnel lens are located on opposite sides of the lens  110 , at the exit pupil of the projector and at or slightly anterior to the center of the eye. 
         [0080]    The Fresnel lens is comprised of prismatic ridges on one or the other the surface of the lens  110 , separated by flat regions that allow light from the external scene to pass through and reach the eye. As a result, the computer-generated display is superimposed on the view of the external world. Because the digital display has great depth-of-field (small exit pupil), it and the external scene appear in focus at the same time, regardless of the distance to the scene. 
         [0081]    In this embodiment, too, the HUD eyeglasses are compatible with prescription lenses. 
         [0082]    In yet another embodiment similar to  FIG. 7 , the ocular relay is a diffraction lens. The two conjugate foci of the diffraction lens are located on opposite sides of the lens  110 , at the exit pupil of the projector and at or slightly anterior to the center of the eye. 
         [0083]    The diffraction lens is partly transparent, allowing light from the external scene to pass through and reach the eye. As a result, the computer-generated display is superimposed on the view of the external world. Because the digital display has great depth-of-field (small exit pupil), it and the external scene appear in focus at the same time, regardless of the distance to the scene. 
         [0084]    In this embodiment, too, the HUD eyeglasses are compatible with prescription lenses. 
         [0085]    In any of the previous embodiments, the beam of the projection system for one or both eyes may be redirected at the wearer&#39;s discretion to project on a nearby wall or screen, so that the wearer can share an image with someone else. 
         [0086]    In any of the previous embodiments, rotations of the wearer&#39;s head may be cancelled by digitally translating or rotating the digital display image in the opposite sense, such that the digital display appears to remain fixed while the wearer&#39;s head moves. The input for this digital preprocessing comes from accelerometers or gyros within the HUD eyeglass system. 
         [0000]    
       
         
               
             
               
               
               
               
             
           
               
                   
               
               
                 REFERENCES CITED 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 61/742,623 
                 August 2012 
                 Stephenson 
                 (provisional) 
               
               
                 7,952,059 B2 
                 May 2011 
                 Vitale et al. 
                 250/208.1 
               
               
                 7,656,585 B1 
                 February 2010 
                 Powell et al. 
                 359/630 
               
               
                 2002/0030637 A1 
                 March 2002 
                 Mann 
                 345/8