given time stays approximately the same. When the viewer moves their eye to align with a newly defined group of exit pupils, the average brightness remains approximately the same as with the previous group of exit pupils.
According to another aspect of the invention, another embodiment of the exit pupil expanding apparatus is formed by a bundle of aligned optical fibers, (e.g., a fiber optic face plate). One end of each fiber defines a portion of the curved plane which receives the light from the scanning device. Light enters a fiber over a given narrow angle, then exits over an enlarged angle. By creating an exit angle greater than the incident angle the exiting light impinges upon a larger surface of the ensuing eyepiece. The eye piece in turn passes light over an expanded exit pupil. According to variations, to best match the geometry of the eyepiece the fiber bundle defines at its exit surface either one of a flat planar surface or curved planar surface.
According to another aspect of the invention, another embodiment of the exit pupil expanding apparatus is formed by a lens array. The lens array includes several small lenses in which each lens has a diameter on the order of 5-100 microns. Each lens is spaced as closely as possible to each adjacent lens in the array. The array defines a curved plane from sides of each lens facing the scanning device. Such curved plane receives the light from the scanning device. Light enters each lens over a given narrow angle, then exits over an enlarged angle. By creating an exit angle greater than the incident angle the exiting light impinges upon a larger surface of the ensuing eyepiece. As in the fiber bundle embodiment, the eyepiece in turn passes light over an expanded exit pupil.
According to another aspect of this invention, another embodiment of the exit pupil expanding apparatus is formed by a diffuser. The diffuser defines a curved surface corresponding to the intermediate curved image plane. The diffuser evenly spreads the passing light. The light output from the diffuser spans a greater angle than the light incident to the diffuser. Thus, the light output from the diffuser is an expanded beam which passes through the eyepiece to define an expanded exit pupil.
According to another aspect of the invention, some embodiments of the exit pupil expanding apparatus reflect light. The reflected light is used to form the expanded exit pupil(s).
One advantage of this invention is that the shorter light path enabled by avoiding an objective after the scanning device allows for a more compact, lighter weight retinal display device. Another advantage is that a viewer has less difficulty aligning and maintaining alignment with an exit pupil formed at the eyepiece. In particular, the expanded exit pupil, the multiple exit pupils or the multiple expanded exit pupils make it easier for a viewer to align with an exit pupil. Another advantage with regard to the diffractive optical element embodiment is that image brightness is generally uniform among various groups of exit pupils which may form at the viewer's eye. These and other aspects and advantages of the invention will be better understood by reference to the following detailed description taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a virtual retinal display according to an embodiment of this invention;
FIG. 2 is an optical schematic of the virtual retinal display of FIG. 1;
FIG. 3 is a block diagram of the image data interface, light source, and optics subsystem of FIG. 1 according to an embodiment of this invention;
FIG. 4 is a perspective drawing of the scanning subsystem of FIG. 1 according to an embodiment of this invention;
FIG. 5 is an exploded view of the scanning subsystem of FIG. 4;
5 FIGS. 6A and 6B is an optical diagram of the exit pupil expanding apparatus according to one embodiment of this invention;
FIG. 7 is an optical diagram of the exit pupil expanding apparatus according to another embodiment of this inven10 tion;
FIG. 8 is an optical diagram of the exit pupil expanding apparatus according to another embodiment of this invention; and
FIG. 9 is an optical diagram of the exit pupil expanding apparatus according to another embodiment of this invention.
DESCRIPTION OF SPECIFIC EMBODIMENTS Overview
20 FIG. 1 shows a block diagram of a virtual retinal display 10 according to one embodiment of this invention. The display 10 receives image data from a computer device, video device or other digital or analog image data source. Light generated by the display 10 is altered according to the
25 image data to scan an image into the retina of a viewer's eye E.
The retinal display 10 generates and manipulates light to create color or monochrome images having narrow to panoramic fields of view and low to high resolutions. The
30 display 10 does not generate a "real image" as done by CRTs, LCDs or an LED array. Instead, light modulated with video information is scanned directly onto the retina of a viewer's eye E to produce the perception of an erect virtual image. Because a real image is neither generated nor por
35 trayed on a screen, the retinal display is small in size. In particular, the retinal display is suitable for hand-held operation or for mounting on the viewer's head.
The retinal display 10 includes an image data interface 11, a light source 12, an optics subsystem 14, a scanning
40 subsystem 16, an exit pupil expanding apparatus 18, and an eyepiece 20. The image data interface 11 receives a video or other image signal, such as an RGB signal, NTSC signal, VGA signal or other formatted color or monochrome video or image data signal. The light source 12 includes one or
45 more sources of light. In one embodiment red, green and blue light sources are included. The light sources or their output beams are modulated according to the input image data signal content to produce light which is input to an optics subsystem 14. In one embodiment the emitted light is
50 coherent. In another embodiment the emitted light is noncoherent.
Referring to FIG. 2, the optics subsystem 14 serves as an objective to focus the light. For some embodiments in which noncoherent light is received, the optics subsystem 14 also
55 collects the light. The light exiting the optics subsystem 14 converges toward a focal point at image plane 15. Prior to the image plane 15 is the scanning subsystem 16. The scanning subsystem 16 deflects the light and the ensuing focal point to define an image plane of focal points. Typi
60 cally the light is deflected along a raster pattern, although other display formats such as vector imaging also can be used. In one embodiment the scanning subsystem 16 receives a horizontal deflection signal and a vertical deflection signal derived from the image data interface 11. In
65 another embodiment, the scanning subsystem includes a mechanical resonator for deflecting passing light. FIG. 2 shows deflection of light 19 along one axis. As the light 19