Abstract:
A mechanism for adjusting an apparatus for the inter-pupilar distance of a user is disclosed. Example embodiments of the disclosed mechanism use gears that link the movements of eye-optics and reflectors placed along the optical path. When the eye-optics are adjusted, this movement causes a movement in the linked reflectors that maintains a constant length for the optical path.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is related to concurrently filed, co-pending, and commonly assigned U.S. patent application Ser. No. ______, [Attorney Docket No. 54729-P005US-10304870], entitled “MULTIPLE IMAGING ARRANGEMENTS FOR HEAD MOUNTED DISPLAYS,” the disclosure of which is hereby incorporated herein by reference. 
     
    
     PRIORITY  
       [0002]     The present application claims priority to Hungarian Patent Application, Serial No. P 02 03993, Filed, Nov. 19, 2002, entitled “OPTICAL SYSTEM FOR A BINOCULAR VIDEO SPECTACLE,” the disclosure of which is hereby incorporated herein by reference.  
       TECHNICAL FIELD  
       [0003]     The invention relates generally to visual displays and more specifically to optical arrangements for head mounted systems that use a single display.  
       BACKGROUND OF THE INVENTION  
       [0004]     Head Mounted Displays (HMDs) are a class of image display devices that can be used to display images from television, digital versatile discs (DVDs), computer applications, game consoles, or other similar applications. A HMD can be monocular ( a single image viewed by one eye), biocular (a single image viewed by both eyes), or binocular (a different image viewed by each eye). Further, the image projected to the eye(s) may be viewed by the user as complete, or as superimposed on the user&#39;s view of the outside world. HMD designs must account for parameters such as image resolution, the distance of the virtual image from the eye, the size of the virtual image (or the angle of the virtual image), the distortions of the virtual image, the distance between the left and the right pupil of the user (inter pupillar distance (IPD)), diopter correction, loss of light from image splitting and transmission, power consumption, weight, and price. Ideally, a single HMD would account for these parameters over a variety of users and be able to display an image regardless of whether it was a stereo binocular image or a simple monoscopic image.  
         [0005]     If the resolution of a picture on the HMD&#39;s internal display is 800×600 pixels, an acceptable size for the virtual image produced by the HMD&#39;s optics is a virtual image diameter of approximately 1.5 m (52″-56″) at 2 m distance which corresponds to approximately a 36° angle of view. To properly conform to the human head and eyes, the IPD should be variable between 45 mm and 75 mm. In order to compensate for near- and farsightedness, at least a ±3 diopter correction is necessary.  
         [0006]     The use of only one microdisplay in the HMD (instead of using one for each eye) drastically reduces the price of the device. Typically, an arrangement for such a unit positions a microdisplay between the user&#39;s eyes. The image produced is then split, enlarged, and separately transmitted to each eye. There are numerous designs known in the art for beam splitting in single display HMDs with a center mounted display, but none are known that provide a solution that is cheap, light weight, small in size, and capable of displaying all varieties of images.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     Embodiments of the present invention reduce the splitting volume of head mounted displays by focusing the image produced by a single display screen and splitting that image near its focal point. The separate sub-images are then focused and propagated through a plurality of optical sub-paths delivering the image to separate locations.  
         [0008]     Some embodiments utilize an asymmetrical V-mirror splitter which can consist of a partially reflective surface and a fully reflective surface placed near the focal point of the image. A portion of the light containing the image information is then reflected by the partially reflective surface and can be channeled to one eye, while the remaining portion of the light is reflected by the fully reflective surface and channeled to the other eye.  
         [0009]     Some embodiments may also utilize diffusers onto which real images of the display are formed. Real images are projected onto diffusers by transition optics having a small numerical aperture, and transmitted to a viewer&#39;s eyes by optics having a larger numerical aperture.  
         [0010]     Some embodiments may also utilize rotating reflectors. By reflecting the split images off of multiple reflectors, the path of these images can be altered in a manner that allows the embodiments to adjust for the inter pupillar distances of different users. Other embodiments utilize the synchronized movement of multiple optical blocks to adjust for the interpupillary distance of different users.  
         [0011]     Further embodiments may also utilize a light source to illuminate the display. One possible arrangement may include individual sources of narrow wavelength light arranged to approximate a single wide band source.  
         [0012]     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized that such equivalent constructions do not depart from the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which:  
         [0014]      FIG. 1  illustrates a top view of a head mounted display arranged according to an embodiment of the present invention;  
         [0015]      FIG. 2  illustrates a prospective view of a head mounted display arranged according to an embodiment of the present invention;  
         [0016]      FIG. 3  illustrates a prospective view of a head mounted display arranged according to an embodiment the present invention;  
         [0017]      FIGS. 4A and 4B  illustrate a prospective view of a head mounted display arranged according to an embodiment of the present invention;  
         [0018]      FIGS. 5A and 5B  illustrate a prospective view of a head mounted display arranged according to an embodiment of the present invention;  
         [0019]      FIG. 6  illustrates a top view of a portion of a head mounted display arranged according to an embodiment of the present invention;  
         [0020]      FIG. 7  illustrates a top view of a portion of a head mounted display arranged according to an embodiment of the present invention;  
         [0021]      FIG. 8  illustrates a top view of a portion of a head mounted display arranged according to an embodiment of the present invention; and  
         [0022]      FIG. 9  illustrates a top view of a portion of a head mounted display arranged according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]      FIG. 1  illustrates a top view of head mounted device  100  arranged according to an embodiment of the present invention. Sub-image creation section  101 , within device  100 , creates a plurality of sub-images from a single image source into a plurality of optical sub-paths. Display  110  can be any suitable apparatus or screen operable to display a visual image of data, such as a liquid crystal display (LCD) screen. Display  110  is situated along a display axis  111 , which, in the embodiment shown, is normal to the screen of display  110  and perpendicular to facial plane  170  of a user. Display  110  is designed to project a display image along optical path  112 . In the arrangement of section  101 , optical path  112  lies along display axis  111 . Display lens  115  is located along, and perpendicular to, optical path  112 , and has display lens focal point  124 . Display lens focal point  124  lies on optical path  112 , and section  101  is arranged such that display lens focal point  124  lies within splitter  120 . By focusing the display image before it is split, the splitting of volume of sub-image creation section  101  can be greatly reduced. A small splitting volume allows an embodiment to use small, light-weight splitting elements and allows HMD designs to include advantageous arrangements and additional optical elements that improve image quality and can increase the size of the image viewed by a user. The embodiment of  FIG. 1  is arranged to produce an image through (approximately) collimated light emanated by (or being reflected from) display  110 , thus splitter  120  is placed proximate to display lens focal point  124 . The embodiments are not limited to this arrangement however, as splitter  120  should be arranged in the position most appropriate to the focused image. For example, if display  110  emits, transmits, or reflects non collimated light, the display image will be focused to a “point” that is not display lens focal point  124 , and embodiments will arrange splitter  120  in a position proximate to this focal area.  
         [0024]     In embodiments using the arrangement of section  101 , splitter  120  is an asymmetric V-mirror splitter composed of a partially reflective surface  121  and a fully reflective surface  122 . The proximity of surfaces  121 ,  122  will be dependent upon the size of splitter  120  and the amount of splitter volume reduction section  101  is arranged to produce. Section  101  is further arranged so that surface  121  and surface  122  share a common edge, and are arranged asymmetrically about display axis  111 . Section  101  can thus split a display image of display  110  into two separate display sub-images. The term sub-image is used to describe the multiple images of a display created by the various embodiments of the present invention. The sub-images of  FIG. 1  contain all of the information of a display, but embodiments may use sub-images that contain only a portion of an image.  
         [0025]     Upon striking partially reflective surface  121 , a portion of a display image is reflected along left-eye optical sub-path  140 , and becomes a left-eye sub-image. The portion of a display image not reflected by partially reflective surface  121  passes through and strikes fully reflective surface  122 , becoming a right-eye sub-image, which is reflected along right-eye optical sub-path  130 . The result is an identical left-eye sub-image and right-eye sub-image traveling in opposite directions and containing identical image information.  
         [0026]     Left-eye sub-image will follow optical sub-path  140  and be channeled to left eye  146  of a user. Placed along optical sub-path  140  is left-eye reflector  142 , which is a fully reflective surface arranged to redirect left-eye optical sub-path  140  by 90° and into left eyepiece optics  145 . The right-eye sub-image will follow optical sub-path  130  and be channeled to right eye  136  of a user. Placed along optical sub-path  130  is right-eye reflector  132 , which is a fully reflective surface arranged to redirect right-eye optical sub-path  130  by 90° and into right eyepiece optics  135 . Right eyepiece optics  135  and left eyepiece optics  145  can be a single lens or a combination of several lenses designed to appropriately magnify a right-eye sub-image for viewing by right eye  136  of the user and a left-eye sub-image for viewing by left eye  146  of the user, respectively.  
         [0027]     Eyepiece optics  135  and  145  are adjustable single lenses, but other embodiments may use multiple lenses or any other arrangement that appropriately focuses a right-eye sub-image and a left-eye sub-image for viewing by right eye  136  and left eye  146 , respectively. Further, although reflectors  142 ,  132  of device  100  are depicted as mirrors, embodiments are not limited to the use of mirrors for redirecting an optical sub-path. Rather, prisms, partially reflective surfaces, polarizing beam splitters, or any other suitable arrangements can be used for redirecting an optical sub-path.  
         [0028]     Device  100  is also capable of adjusting for the varying IPDs of different users through the synchronized movements of optical elements. Right eyepiece optics  135  and left eyepiece optics  145  can shift through movements  152  and  151  respectively to create IPD  150   a  and IPD  150   b , when section  101  shifts through movement  155 . When IPD distance  150   a  is changed to IPD  150   b , section  101  is simultaneously shifted toward facial plane  170  in movement  155  (downwards in the view of  FIG. 1 ). When IPD  150   b  is changed to  150   a , section  101  is simultaneously shifted away from plane  170  (upwards in the view of  FIG. 1 ). These synchronized movements allow device  100  to adjust to accommodate for the entire range between IPD  150   a  and  150   b  while maintaining constant distances between surfaces  122 ,  121  and eyepiece optics  135 ,  145  along sub-paths  130  and  140 , respectively. Device  100  is also capable of diopter correction through additional adjustments of movement  153  of left eyepiece optics  145  and movement  154  of right eyepiece optics  135 .  
         [0029]      FIG. 2  illustrates a prospective view of head mounted device  200  arranged according to an embodiment of the present invention. Head mounted device  200  includes section  101 , as described in relation to  FIG. 1 , which operates to split a display image of display  110  into a left-eye sub-image traveling along left-eye optical sub-path  140  and a right-eye sub-image traveling along right-eye optical sub-path  130 . For device  200 , left-eye transition optics  243  are placed along left-eye optical sub-path  140  to adjust the left-eye sub-image for reflection by left-eye reflector  142  onto left-eye diffuser  244 . The left-eye sub-image strikes the left-eye diffuser  244  and creates a real image of the display on the diffuser surface. The left eyepiece compound optics  245  then magnifies this real image appropriately for left eye  146 .  
         [0030]     The embodiment depicted in  FIG. 2  is described using diffusers onto which real images are projected in order to prepare the image. Transition optics, having a small numerical aperture, project a real image onto the diffuser surface, and eyepiece optics having a large numerical aperture transport the image to the eyes of a user. Rather, any appropriate means may be used including microlens arrays, diffraction gratings, or other diffractive surfaces. For the purposes of the present invention, it will be understood that “diffuser” as used to describe the embodiments of the present invention, refers to all such means used to convert incident angular power density into an appropriate exiting angular power density.  
         [0031]     In  FIG. 2 , a right-eye sub-image follows the right-eye optical sub-path  130  into right eye transition optics  233 . The right eye transition optics  233  adjusts the right-eye display sub-image appropriately for reflection by right-eye reflector  132  onto right-eye diffuser  234 . The right-eye sub-image strikes right-eye diffuser  234  and creates a real image. This real image is adjusted by right eyepiece compound optics  235  appropriately for right eye  136 . Device  200  is capable of diopter correction through movement  253  of left-eye compound optics  245  and of movement  254  of right-eye compound optics  235 .  
         [0032]     Device  200  is also capable of IPD adjustment through multiple synchronous movements. IPD  150  can be shortened by shifting left-eye compound optics  234  to the right with movement  251 , and right-eye compound optics  235  to the left with movement  252 . For the embodiment of  FIG. 2 , segment  240  of optical sub-path  140  lies between transition optics  243  and diffuser  244 , and segment  230  of optical sub-path  130  lies between transition optics  233  and diffuser  234 . Thus, as compound optics  235  and  245  are shifted in movement  252  and  251  to shorten distance  150 , center section  201  should be shifted away from the facial plane  170 . The embodiment of  FIG. 2  describes one combination of synchronous movements that result in IPD adjustment, but embodiments of the present invention are not limited to the synchronous movements of  FIG. 2 .  
         [0033]      FIG. 3  illustrates a prospective view of a head mounted device arranged according to an embodiment of the present invention. Head mounted device  300  includes section  101 , as described in relation to  FIG. 1 , to split a display image of display  110  into a left-eye sub-image traveling along left-eye optical sub-path  140  and a right-eye sub-image traveling along right-eye optical sub-path  130 . In the embodiment depicted in  FIG. 3 , a left-eye display sub-image follows left-eye optical sub-path  140  and passes through a left-eye real image reflector  342  to strike left-eye reflective diffuser  343 , thus creating a real image. This real image is then reflected by left-eye real image reflector  342  into left eyepiece optics  145 . Left eyepiece optics  145  adjusts a reflected real image appropriately for left-eye  146 . A right-eye display sub-image will follow right-eye optical sub-path  130  passing through right-eye real-image reflector  332  to strike right-eye reflective diffuser  333 , thus creating a real image. This real image is reflected by right-eye real-image reflector  332  into right eyepiece optics  135  which will adjust a reflected real-image appropriately for right-eye  136 .  
         [0034]     The embodiment depicted in  FIG. 3  is described as using reflective diffusers on which real images are formed. The present invention is not limited to the use of any one type of diffuser. Rather, the embodiments may use any appropriate diffuser, as previously described, and may be any appropriate shape such as spherical, flat, or aspheric.  
         [0035]     The embodiment in  FIG. 3  is also capable of diopter correction through movement  153  of left eyepiece optics  145  and movement  154  of right eyepiece optics  135 . Left-eye real-image reflector  342  and left eyepiece optics  145  collectively make up left eyepiece  360 . Right-eye real-image reflector  332  and right eyepiece optics  135  collectively make up right eyepiece  361 .  
         [0036]     Device  300  is capable of IPD adjustment through multiple simultaneous movements. The embodiment of  FIG. 3  simultaneously moves left eyepiece  360  and right eyepiece  361  through movements  351  and  352  respectively to set the correct IPD. At the same time, movement  153  of left eyepiece optics  145  and movement  154  of right eyepiece optics  135  are moved to maintain the optical path lengths between eyepiece optics  145 ,  135  and reflective diffusers  343 ,  333 .  
         [0037]     In device  300 , left-eye real-image reflector  342  and right-eye real-image reflector  332  are partially reflective surfaces, but embodiments are not limited to the arrangement depicted. Rather, embodiments may easily be adapted to any arrangement, such as those using prisms, or polarizing beam splitters, that appropriately reflect light into eyepiece optics  135  and  145  and transmit light from optical paths  130 ,  140  towards reflective diffusers  333 ,  343 , respectively.  
         [0038]      FIGS. 4A and 4B  illustrate a prospective view of head mounted device  400  arranged according to an embodiment of the present invention. Head mounted device  400  uses right angle sub-image creation section  401  to create a plurality of display sub-images from a single image source. Similar to section  101  described in  FIGS. 1-3 , section  401  splits a display image of display  110  into left-eye sub-image traveling along left-eye optical sub-path  140  and a right-eye sub-image traveling along right-eye optical sub-path  130 . In section  401 , display  110  and display optics  115  are rotated 90° from section  101  of  FIGS. 1 through 3 . Display  110  projects a display image along optical path  112  where it is focused by display optics  115 . A display image then strikes display reflector  416 , which redirects the optical path  112  by 90°. Reflector  416  causes a focused display image to be directed into splitter  120 . By redirecting the optical path with reflector  416 , the total volume of section  401  is reduced. The volume may be further reduced by adding additional similar reflectors. In section  401 , splitter  120  is arranged such that partially reflective surface  121  and fully reflective surface  122  are parallel to display axis  111 , and reflected focal point  424  of the display optics  115  lies inside of splitter  120 . Partially reflective surface  121  reflects a portion of a display image as a left-eye display sub-image to follow left-eye optical sub-path  140  such that it strikes left-eye reflector  142 . The portion of the display image not reflected by partially reflective surface  121  is reflected by fully reflective surface  122  as a right-eye sub-image along right-eye optical sub-path  130  such that it strikes right-eye reflector  132 .  
         [0039]     Device  400  uses “real” images in a manner similar to device  200  of  FIG. 2 . For device  400 , a left-eye display sub-image is reflected to left-eye diffuser  243 , where a real image is created. This real image is then transported to left-eye  146  by left eyepiece optics  145 , which is designed to appropriately focus a left-eye sub-image for viewing by left-eye  146 . A right-eye display sub-image will be reflected onto right-eye diffuser  234  creating a real image, which is transported to right-eye  136  by right eyepiece optics  135 , which is designed to appropriately focus a right-eye sub-image for viewing by right-eye  136 . Device  400  is capable of diopter correction through movement  153  of left eyepiece optics  145  and movement  154  of right eyepiece optics  135 .  
         [0040]      FIG. 4B  illustrates the IPD correction capability of device  400 . In this embodiment, fully reflective surface  122  and partially reflective surface  121  are rotatable about splitter axis  423  and with respect to each other. When fully reflective surface  122  is rotated clockwise about axis  423  and partially reflective surface  121  is rotated counter-clockwise, right-eye optical sub-path  130  and left-eye optical sub-path  140  are deflected out of the plane, and are no longer 180° from each other. When right-eye optical sub-path  130  and left-eye optical sub-path  140  are deflected some angles theta (θ) and theta prime (θ′), the result is that device  400  has adjusted IPD  450 . Eyepieces  460  and  461  rotate inward simultaneously with the rotation of surfaces  121 ,  122 . Eyepiece  460  rotates counterclockwise to follow the downward deflection of sub-path  140 , and eyepiece  461  rotates clockwise to follow the downward deflection of sub-path  130 . These simultaneous rotations result in adjusted IPD  450 .  
         [0041]      FIGS. 5A and 5B  illustrate a prospective view of a head mounted display  500  arranged according to an embodiment of the present invention. For head mounted device  500 , section  101  is again used to split the display image of display  110  into a left-eye sub-image traveling along left-eye optical sub-path  140  and a right-eye sub-image traveling along right-eye optical sub-path  130 . For display  500 , a left-eye display sub-image will strike a left-eye reflector  142  causing left-eye optical sub-path  140  to be redirected 90°. A left-eye display sub-image will then strike second left-eye reflector  543 , which also causes left-eye optical sub-path  140  to be redirected 90°. Left-eye reflector  142  and second left-eye reflector  543  are arranged along a common left-eye reflector axis  541 . Once a left-eye display sub-image has been reflected by the second left-eye reflector  543 , it is reflected by third left left-eye reflector  544  and redirected onto left-eye diffuser  243 .  
         [0042]     Similarly, a right-eye display sub-image will strike a right-eye reflector  132  causing right-eye optical sub-path  130  to be redirected 90°. A right-eye display sub-image will then strike second right-eye reflector  533 , which also causes right-eye optical sub-path  130  to be redirected 90°. Right-eye reflector  132  and second right-eye reflectors  533  are arranged along a common right-eye reflector axis  531 . Once a right-eye display sub-image has been reflected by second right-eye reflector  533 , it is reflected by third right-eye reflector  534  and redirected onto right-eye diffuser  233 .  
         [0043]     A real-image created on left-eye diffuser  243  is transmitted to left-eye  146  by left eyepiece optics  145 . Left eyepiece  560  is made up of second left-eye reflector  543 , third left-eye reflector  544 , left-eye diffuser  243 , and left eyepiece optics  145 , collectively. A real-image created on right-eye diffuser  233  is transmitted to right-eye  136  by right eyepiece optics  135 . Right eyepiece  561  is made up of second right-eye reflector  533 , third right-eye reflector  534 , right-eye diffuser  233 , and right eyepiece optics  135 , collectively. Device  500  is capable of diopter correction through movement  153  of left eyepiece optics  145  and movement  154  of right eyepiece optics  135 .  
         [0044]     Device  500  can adjust IPD  150  as depicted in  FIG. 5B . In Device  500 , left eyepiece  560  is rotatable about axis  541  with respect to left-eye reflector  142 . When left eyepiece  560  rotates counter-clockwise about left-eye reflector axis  541 , optical sub-path  140  is deflected from its previous path by some angle phi (φ). Similarly, right eyepiece  561  is rotatable about axis  531  with respect to right-eye reflector  132 . When right eyepiece  561  rotates clockwise about the right-eye reflector axis  531 , optical sub-path  130  is deflected some angle phi prime (φ′) from its previous path. These deflections result in left eyepiece  560  and right eyepiece  561  rotating in the plane of the users face to adjusted IPD  550 .  
         [0045]      FIG. 6  illustrates a top view of a portion of a head mounted device arranged according to an embodiment of the present invention.  FIGS. 1-5  have depicted embodiments using sub-image creation sections  101  and  401 . However, embodiments are not limited to these arrangements. In  FIG. 6 , sub-image creation section  600  includes display  110  arranged normal to display axis  111 . Display  110  projects a display image along optical path  112 . A display image can then be focused by display lens  115  having a lens focal point  124 . Splitter  620  is a symmetric V-mirror splitter composed of right fully reflective surface  622  and left fully reflective surface  621  that share a common edge and are arranged symmetrically about display axis  111 .  FIG. 6  has been depicted and described using fully reflective surfaces, but such arrangements may be readily adapted to the use of polarizing beam splitters or partially reflective surfaces as well. The arrangement of section  601  results in a display image projected by display  110  which is focused by display lens  115  and split into two display sub-images, one reflected along right-eye optical sub-path  130  and one along left-eye optical sub-path  140 .  
         [0046]     Further optimization of the various embodiments of the present invention can be made by the use of collimated (or approximately collimated) light. A display that (approximately) produces, reflects, or is illuminated by collimated light can improve image quality and simplifies device arrangement. There are numerous methods of producing and providing collimated light to different aspects of HMD&#39;s, and embodiments are not limited to any one.  
         [0047]      FIG. 7  illustrates a top view of a portion of a head mounted device arranged according to the present invention. In sub-image creation section  700 , display  110  is arranged normal to display axis  111 . Display lens  115  is interposed between display  110  and splitter  620 . Splitter  620  is arranged as a symmetric V mirror splitter with fully reflective surface  621  and fully reflective surface  722 . Focal point  124  of lens  115  is proximate to splitter  620 . Display  110  is illuminated by light sources  708  and  709  which are reflected by source reflector  707 , which may be a polarization splitter, or a partially reflective mirror, or other appropriate reflector. Sources  708  and  709  are arranged adjacent to display axis  111  and in a plane with reflected focal point  124 R. The sub-image created by source  708  and display  110  will be focused by lens  115  and incident upon reflective surface  722  of splitter  620 . When display  110  is illuminated by source  709 , a separate display sub-image is created and focused by lens  115 . Because source  709  is positioned below reflected focal point  124 R, the sub-image created by source  709  and display  110  will be focused by lens  115  and incident upon reflective surface  621  of splitter  620 .  
         [0048]     In the embodiment of  FIG. 7 , two complete and independent images (referred to again as sub-images) of display  110  are created, and each sub-image is a full image of display  110 . In the embodiment of  FIG. 7 , splitter  620  does not split a single image to create sub-images, but rather splits the angular space of the display reflection allowing the independently created images to be redirected along separate paths.  
         [0049]      FIG. 8  illustrates a top view of a portion of a head mounted device  800  arranged according to an embodiment of the present invention using sub-image creation section  101 . Blue source light  801  is arranged along the source light optical path  806 , preferably in a position at or near reflective focal point  124 R of display optics  115 . Blue source light  801  may be any light source capable of producing blue light, such as Nichia NSC×100 series light emitting diode (LED). Light from blue source  801  passes through a first color filter  804  arranged at an appropriate angle to the optical path and selected in order to pass blue light and to reflect green light. Green source  802  is placed adjacent to source light optical path  806  and arranged in order to reflect light off of first color filter  804  in a way that simulates placing green source  802  in the same location as blue source  801 . Blue light and the reflected green light follow source light optical path  806  passing through second color filter  805  arranged at an appropriate angle to source light optical path  806 .  
         [0050]     Second color filter  805  is selected such that it passes blue and green light, but reflects red light. Red source  803  is placed adjacent to source light optical path  806  and arranged in order to reflect light of second color filter  805  in a way that simulates placing red source  803  in the same location as blue source  801 . Blue light, reflected green light, and reflected red light then follows source light optical path  806  and is reflected by source light reflector  807 . In the depicted embodiment, source light reflector  807  can be a polarizing reflector arranged about display axis  111  and along optical path  112 . The combined blue, green, and red light is polarized and reflected off of source light reflector  807 , through display optics  115 . In the depicted embodiment, display optics  115  is a lens selected to have a focal point of  124  (and a reflected focal point  124 R). When passed through display optics  115 , the combined blue, green, and red light is collimated and illuminates display  110 .  FIG. 8  depicts the illumination of display  110  from a single direction, but the embodiments are not limited to a single direction. Rather, the illumination system of  FIG. 8  can be easily adapted for multiple direction illumination as in  FIG. 7 .  
         [0051]     The embodiments of the present invention are not limited to arrangements that place an image splitter proximate to the focal point of a focusing optic. Rather, embodiments of the present invention are able to reduce the splitting volume of various applications, by positioning the image splitter to split a display image focused in a small area.  
         [0052]      FIG. 9  illustrates the reduced splitting volume created by embodiments of the present invention. In  FIG. 9 , display  110  is illuminated, thus creating a display image. The display image propogates along optical path  112  arranged along display axis  111 . Display lens  115 , having a display lens focal point  124   a , focuses the display image in order to provide a reduced splitting volume. The point where the splitting volume is smallest will depend on the light illuminating the display.  
         [0053]     When display  110  is illuminated by source  908   a  positioned at reflective display lens focal point  924   a , display lens  115  will collimate the light reflected from source reflector  707 . This results in a display image that is focused by display lens  115  to approximately display lens focal point  124   a . When display  110  is illuminated by source  908   b  positioned at point  924   b  which is closer to display axis  111 , the light reflected from source  707  will be divergent as it strikes display  110 . Thus, the display image will be focused to approximately point  124   c . When display  110  is illuminated by source  908   c , positioned at a point  924   c  which is farther away from display axis  111 , the light reflected from source reflector  707  will be convergent as it strikes display  110 . Thus, the display image will be focused to approximately point  124   b . Embodiments of the present invention can thus be arranged to split the display image at whichever point is most appropriate.  
         [0054]     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.