Abstract:
A compact, head-mountable display device for transmitting an image to a user&#39;s eye is provided. The display device includes a support fixture comprising an elongated member configured to allow passage of ambient light across a direction of elongation of the elongated member to a user&#39;s eye. A display, such as an LCD, is supported by the support and is operative to provide an image. An eyepiece assembly is supported by the support fixture in proximity to the display to receive the image from the display and to direct the image to the user&#39;s eye. The support fixture also defines an illumination path along the elongated member, and the display is located to receive illumination light on the illumination path from a light source.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Applicant claims priority under 35 U.S.C. §119(e)of U.S. Provisional Applications Ser. No. 60/140,340 filed Jun. 21, 1999 entitled “Light Weight, Compact Eyepiece On A Post,” and No. 60/140,707 filed Jun. 24, 1999 entitled “Light Weight, Compact Eyepiece On A Post,” the disclosures of which are incorporated by reference herein. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     N/A 
     BACKGROUND OF THE INVENTION 
     There are many examples of displays mounted on the head, sunglasses, eyeglasses and the like (for example Perera, U.S. Pat. No. 4,867,551). Perera describes a display mounted on eyeglasses, the limitation of which is the high degree of occlusion of the user&#39;s field of view beyond the display, and the use of non-axial optics that introduces distortion. Other companies, such as VirtualVision, provide displays that are suspended by a cable, gooseneck fixture or other mechanical support in front of one or both of the user&#39;s eyes. Similarly, students at the MIT Media Laboratory have been mounting displays from Reflection Technology on eyewear, in order to provide a computer display in a mobile fashion. These approaches also highly limit the user&#39;s view of the surroundings. 
     Generally, head-mounted and helmet-mounted display systems are based on miniature displays having a diagonal dimension of 4 cm or less. The display systems that use such miniature displays must provide a lens near the eye for magnification, and to make possible comfortable viewing at near distances. We term the lens and any other associated optics that must be placed near the eye the “eyepiece.” Most prior art head-mounted systems also place the display (for example a miniature liquid crystal flat panel display) near the eye as well, which requires both a support fixture for the eyepiece, and a conduit for electrical cables to the display. These components (wires, liquid crystal display, illumination source and any other required circuits) are placed within an opaque housing near the eye. Consequently, such systems block a portion of the user&#39;s visual field, and also obscure the user&#39;s face. For liquid crystal displays, the illumination source accounts for a large amount of the volume of the eyepiece. 
     In a recent patent (U.S. Pat. No. 6,023,372), we described a method of supporting an eyepiece near the eye at the end of a transparent opto-mechanical structure (FIG.  1 ). Data or images are relayed to the device by a cable which may comprise wire, one or more optical fibers as described in U.S. Pat. No. 5,715,337, or a fiber optic coherent bundle image conduit. The advantage of this prior art approach is the low obscuration of the user&#39;s vision inherent in the use of a transparent opto-mechanical support for the eyepiece. 
     SUMMARY OF THE INVENTION 
     This invention comprises a new approach to a light weight, compact head-mounted display system that combines an image relay system and mechanical support with a simple mounting system that can be applied to eyeglasses or other head gear. The invention involves mounting of a display, such as a liquid crystal display, against an eyepiece at the end of a clear supporting structure, with illumination provided through a transparent opto-mechanical support fixture that suspends the eyepiece near the eye. The opto-mechanical support fixture may be like that described in U.S. Pat. No. 6,023,372, the disclosure of which is incorporated by reference herein. In an alternative embodiment, the invention involves mounting of the liquid crystal display against an eyepiece with a visually minimal opaque mechanical support, and with the illumination provided through free space. The device is particularly suitable for use as an interface to computers, personal digital assistants, and cellular telephones. 
     More particularly, the invention provides a compact, head-mountable display device for transmitting an image to a user&#39;s eye. The display device includes a support comprising an elongated member configured to allow passage of ambient light across a direction of elongation of the elongated member to a user&#39;s eye. A display, such as an LCD, is supported by the support and is operative to provide an image. An eyepiece assembly is supported by the support fixture in proximity to the display to receive the image from the display and to direct the image to the user&#39;s eye. The support also defines an illumination path along the elongated member, and the display is located to receive illumination light on the illumination path from a light source. 
     The invention is advantageous in that it permits the display to be located near the eyepiece, so that the eyepiece may have a shorter focal length and consequently provide higher magnification, and it allows the illumination source to be remote from the eyepiece and display. As can be seen in the drawings, the display itself is relatively low in volume, and in the case of an LCD is largely glass, and thus can be integrated in the eyepiece without a high degree of obscuration of the user&#39;s vision. Although the eyepiece has slightly greater obscuration than the prior art device in U.S. Pat. No. 6,023,372, the greater magnification obtainable from the shorter focal length of the eyepiece is an advantage that may be preferable in many applications. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 illustrates a prior art opto-mechanical fixture; 
     FIG. 2 is a schematic top view of an opto-mechanical support fixture with eyepiece and display according to the present invention; 
     FIG. 3 is an isometric view of the opto-mechanical support fixture of FIG. 2; 
     FIG. 4 is a schematic top view of a further embodiment of an opto-mechanical support fixture with eyepiece and display; 
     FIG. 5 is a schematic top view of a still further embodiment of an opto-mechanical support fixture with eyepiece and display; 
     FIG. 6 is a schematic top view of a still further embodiment of an opto-mechanical support fixture with eyepiece and display; 
     FIG. 7 is a schematic top view of a still further embodiment of an opto-mechanical support fixture with eyepiece and display; 
     FIG. 8 is an isometric view of the opto-mechanical support fixture with eyepiece and display of FIG. 7; 
     FIG. 9 is a schematic top view of the opto-mechanical support fixture and a housing containing circuits and illuminator with eyepiece and display with mounting fixture for mounting to a spectacle frame; 
     FIG. 10 is a schematic front view of the opto-mechanical support fixture with eyepiece and display mounted to a headband; 
     FIG. 11A is a bottom view of an opto-mechanical support fixture with eyepiece and display and circuitry; 
     FIG. 11B is a side view of the opto-mechanical support fixture of FIG. 11A; and 
     FIG. 12 is a schematic illustration of an opto-mechanical support fixture with eyepiece and display as an interface to a cellular telephone, computer, or personal digital assistant. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 2 illustrates a first embodiment of the invention. A transmissive LCD  20 , for example the Kopin Cyber Display P/N KCD-QM02-AA (consisting primarily of glass when the mechanical plastic housing is removed), is placed between a prism  30  and a clear mechanical support fixture  10 , to which a light source  12  is attached. Light from the light source  12 , indicated by the ray  43 , is transmitted through the clear mechanical support fixture  10  and is incident on the back side of the LCD  20 , which may comprise an active matrix LCD (AMLCD). The LCD modulates the light to form an image which is relayed to the eye of the observer by an eyepiece assembly, such as prism  30  and lens  40 , which magnifies the image so that it can be conveniently viewed. The prism  30  may be metal-coated, or may be replaced by a mirror. Images of the ambient scene, indicated by ray  44 , pass through support  10  to the eye of the user. 
     If the focal length of the lens  40  equals the optical distance between the lens and the LCD, the image is observed at infinity. Other focal lengths can be employed to place the image at the desired distance, in accordance with Newton&#39;s lens equation or its equivalents. The manner of conveying electrical signals to the LCD will be described herein later. 
     An advantage of this device is that the object plane (i.e. the LCD) is in proximity (within 5 to 20 mm) to the eyepiece, thus simplifying the optical relay and reducing the focal length of the eyepiece. The reduction in focal length increases the magnification of the system and produces a larger image. 
     In most of the drawings, only a single ray is shown for clarity, but it should be understood that the functioning of the invention requires a plurality of rays and optical paths. It should also be understood that when single lens surfaces are shown, they may represent a system of multiple lens surfaces. Additionally, for the exposition of the optical principles, only the essential optical elements are shown, but is to be understood that the associated housings, clamps and circuits that may or may not be shown can be applied to any of the optical designs. 
     A feature of this invention is the clear mechanical support fixture  10 . The support fixture is clear for two reasons: so that illumination rays can be transmitted to the display, and so that the user&#39;s vision of rays  44  is not blocked by the support fixture. 
     FIG. 3 illustrates a perspective drawing of the embodiment of the invention shown in FIG.  2 . The top surface  19  and bottom surface  17  (FIG. 11) of the support fixture  10  may be painted black and may be unpolished, since these surfaces are not in the view of the user (ambient rays do not pass through surfaces  17  and  19  to the eye). Alternatively, a thin plastic layer may be placed against surfaces  17 ,  19  for added mechanical strength or to hide circuits. Ambient rays  44  do pass through surface  18  and its opposite surface (not shown) and so surface  18  and its opposing surface should be clear, flat and smooth. 
     A see-through eyepiece may also be used in this invention, as shown in FIG. 4, which also shows a manner of collimation of the illumination light. An LED  275  provides light to a collimating lens  276  which, as indicated by ray  43 , proceeds through the support fixture  10  to the LCD  20 . Polarized light from the LCD passes polarization beam splitter  300  and quarter wave plate  320 , and is then reflected by focusing mirror  310 . Upon reflection, the light passes a second time through quarter wave plate  320 . Having passed twice through the quarter wave plate, the polarization angle of the light is in a condition to be reflected at polarization beam splitter  300 , and accordingly passes to the eye. 
     In another embodiment shown in FIG. 5, a reflective LCD  21  is used. The reflective display is for example of the type manufactured by Microdisplay Corporation, of San Pablo, Calif. The prism shown in FIG. 2 is replaced by a polarization beam splitter cube  130  that serves as the polarizer and analyzer for the reflective LCD. Light from the illuminator  12 , represented by rays  43 , passes through the mechanical support  10  to the cube  130 , and one linear polarization passes to the reflective LCD  21 . The LCD  21  reflects and rotates the polarization of the incident light at each pixel in accordance with a control signal, so that the desired image is relayed to the eye through cube  130  and eye lens system  40 . 
     In all of the foregoing embodiments, the length of the clear support  10  is independent of the focal length of the imaging optics, meaning that the length of support fixture  10  can be made large. A typical length of support fixture  10  is in the range of 1 to 10 cm. However, if the illumination is sufficiently bright or sufficiently collimated, the length may be increased, and the support may be curved, so that the illumination source may be placed behind the ear, and light may be relayed by support fixture  10  around the head from the ear to the eyepiece. If the curvature is properly designed, the light may be contained in a clear support fixture  10  by total internal reflection, similar in nature to the principals governing optical fiber. 
     In a further embodiment, an emissive display, such as an active matrix electroluminescent display of the type manufactured by Planar Corporation of Beaverton, Oreg., may be substituted for the reflective LCD. FIG. 6 shows how such a display is employed. The support fixture  10  is terminated in a wedge that has a mirror coating  131 , to reflect light from the display  22  to the lens system  40 . The clear mechanical support fixture permits the user to have a view free from obstructions of the mechanical features of the eyepiece support fixture, as indicated by ray  44 , but in this embodiment does not relay light to the self-emissive display. 
     Note that in another embodiment, the mechanical support fixture may be hollow, or may be reduced to a thin plate or post  201 , as shown in FIGS. 7 and 8. In this embodiment, for the case of the LCD, the light  43  from the illumination source  12  may be conveyed to the LCD  20  in free space  210 , along a straight path. The support structure  201  must however carry the electrical signals from cable  60  to the display, through a miniature cable  16  (FIG.  8 ). Such cables, comprising a plurality of micro-coaxial cables, are available from Gore. 
     The devices shown in FIGS. 3-8 are intended to be mounted in front of one eye of the user by fixtures mounted to spectacle frames or to headbands. Two units can be used for viewing by two eyes. FIG. 9 shows a complete illustration of a system in accordance with this invention, intended for spectacle mounting. Signals are supplied to the unit by cable  60  that is anchored to housing  70 . The housing  70  may contain integrated or discrete circuits  50  that are connected to the display by circuit  71 . A second circuit  6  delivers power to LEDs  5 . Illumination from LEDs  5  is incident on lens system  42 , which collimates rays  43  that are transmitted to display  20  through support  10 . Clamp  73  mounted on arm  72  serves to fix the unit to spectacles. A microphone (not shown) may be included within enclosure  70  for audio input. 
     Alternatively, as shown in FIG. 10, the display unit may be mounted on a boom  440  that is attached to a headband  410 . The headband may also be fitted with an earpiece  430  for receiving audio output signals. The boom may be provided with a microphone for audio input. A pad  420  may be attached to the headband, or may be replaced with an earpiece for stereo audio. 
     Referring to FIG. 9, the light conduit  10  that also serves as the mechanical support can serve as an effective light collector. A degree of collimation is made possible by a collimating lens  42  (FIG. 9) near the light source. Note that some of the light beyond the solid angle subtended by the display that ordinarily would not reach the display, is trapped by total internal reflection in the light conduit, thus improving the light collection efficiency of the conduit. Various techniques are possible including the use of specular metallic coatings or white diffuse reflectors near the illuminator, or even the complete embedding of the LED  5  within the material that forms the light conduit as shown in FIG.  11 . 
     The display located at the eyepiece requires power, clock and data signals. These signals can be provided by attaching Kapton flexible circuitry  16  (FIG. 3) to the top surface or bottom surface of the support structure  10 . The flexible circuit need not be clear, because it is thin (less than 1 mm) and does not block significantly the view of the ambient scene, and may be joined directly to the LCD by techniques known in the art. Alternatively, the signals can be provided by coaxial cables fixed to the top or bottom surface of the support  10 . 
     The optical support fixture  10  is formed from glass by means known in the art, or by injection molding of clear plastics such as polymethylmethacrylate (acrylic) or polycarbonate, or by casting of plastics, polycarbonate resin, CR39, or epoxy resins or alternatively by machining of clear solid plastics. Organic materials generally provide lower weight than glass. FIG. 11 shows how the interconnect can be routed within a solid optical support fixture  10  formed by casting. FIG. 11 a  shows a view from the bottom showing the Kapton circuit  450  carrying signals to the LCD, and the Kapton circuit  451  carrying power to the LEDs  5 . The Kapton circuit is embedded slightly below the surface. Note that the circuit  451  does not block rays from the ambient scene  44 . The light source (LEDs) and the LCD are cast within the optical support fixture  10 . FIG. 11 b  shows a side view, in which the interconnect circuits  450 ,  451  emerge from the optical support fixture  10  near the illuminator and thus can be housed within enclosure  70  (FIG.  9 ). A reflector  390  is placed around the optical support fixture  10  in the vicinity of the LEDs  5  to reflect light from the LEDs into the optical path to the display  20 . 
     The display and illumination system may be provided with an ear piece and microphone to serve as an interface to a cellular telephone, computer, or personal digital assistant. FIG. 12 illustrates such a system. The housing  70  is provided with an opening  620  behind which is provided an audio microphone in communication with an RF circuit  600  via cable  60 . An ear piece  630  to enable the user to hear audio output is provided and is in communication with the radio frequency (RF) circuit  600  by cable  60 . RF circuit and power source (batteries) are located within an enclosure, comprising one of any number of commercial digital or analog RF devices including for example the Bluetooth interface commercialized by Ericsson and its partners. The RF circuit provides communication with a cellular telephone, computer, personal digital assistant, or other electronic device. Unit  600  is worn behind the head and cable  60  is also used to retain the spectacle frames  610  on the head of the user. Note that in some applications, the cellular telephone may be incorporated within unit  600  itself or even within the housing  70 . Although this diagram shows the unit mounted to spectacle frames  610  by clamp  73 , a similar device may be constructed for the headset shown in FIG.  10 . 
     The invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims.