WO1996008736A2

WO1996008736A2 - Optical system for a head mounted display combining high and low resolutions images

Info

Publication number: WO1996008736A2
Application number: PCT/US1995/010798
Authority: WO
Inventors: James L. Fergason
Original assignee: Fergason James L
Priority date: 1994-08-24
Filing date: 1995-08-24
Publication date: 1996-03-21
Also published as: WO1996008736A3; US5808589A; AU4593896A

Abstract

A display system (1) includes a relatively higher resolution display (3) for presenting visual information, and a relatively lower resolution display (2) for presenting visual information, the displays being positioned to present the visual information images therefrom in substantially side-by-side relation, the lower resolution image being provided by the cooperation of focusing optics (20) which form a real image at a retroreflector (22), which reflects light along an optical path conjugate with light incident thereon to provide an image for viewing, and the higher resolution image being provided without passing through the focusing optics (20). A method of display includes forming a relatively lower resolution real image, reflecting the image to the eye of an observer, forming a relatively higher resolution image, and directing the relatively higher resolution image to the eye of the observer such that at least a portion of the relatively lower resolution image circumscribes at least a portion of the relatively higher resolution image.

Description

TITLE: OPTICAL SYSTEM FOR A HEAD MOUNTED DISPLAY

COMBINING HIGH AND LOW RESOLUTION IMAGES

This application is a continuation-in-part of commonly owned U.S. patent applications serial Nos. 08/295,383, filed August 24, 1994, 08/328,371, filed

October 25, 1994, and Provisional patent application Serial No. , filed July

19, 1995 entitled "Optical system and method for a head mounted display providing both front and peripheral fields of view (Express Mail No. EH202553444US), the entire disclosure of which hereby are incorporated by reference.

TECHNICAL FIELD The present invention relates generally, as is indicated, to optical displays, and, more particularly, to head mounted displays, and, even more particularly, to optical displays in which a relatively low resolution image and a relatively high resolution image are combined.

BACKGROUND Various types of head mounted displays are known. An exemplary head mounted display (throughout the following specification the initials "HMD" may be used to mean "head mounted display") includes optics or optical components such as lenses, mirrors or the like, to direct the image from an image source to an eye or to the respective eyes of a person viewing the image (viewer). The image source develops and/or provides an image intended to be viewed and may or may not be part of the HMD. Head mounted display systems are used in the field of virtual reality and also in aircraft, for example, as part of a heads-up display system, and in other fields, too.

A challenge in designing a head mounted display system is to provide an image with highest possible visual quality. Prior head mounted display systems have not taken advantage of the difference in resolving power of the human eye. The human eye is capable of resolving great detail, e.g., a relatively high resolution image, only in a small portion of the field of view. This is a consequence of the fact that one part of the retina, called the fovea, has a higher density of visual receptors than the rest of the retina. Therefore, the remainder of the field of view usually is resolved to a lesser degree than is the field of view impinging or incident on the fovea.

Many prior head mounted display systems use light emitting sources to create an image, such as a cathode ray tube, light emitting diode, etc. Several disadvantages to such light sources and head mounted displays using them are relatively large size, weight, and cumbersome nature. For example, in some virtual reality display systems, counterbalancing weights and support systems are needed to hold or to help to hold the helmet containing the virtual reality image source and optics so that it does not severely weigh down the head, neck, shoulders, etc. of the user.

In some prior display systems a modulator modulates light from a source; the images created are a function of modulation. A liquid crystal cell or liquid crystal display device may be such a modulator. A disadvantage of such modulating systems is the reduction in light output due to light blocking and/or absorption occurring in the modulator. To overcome such reduction in brightness, sometimes the intensity of the light source is increased, which draws additional energy, creates heat, requires a larger light source, etc.

Another disadvantage to prior head mounted display systems is the complexity of the components and of the arrangement of the components to provide the desired display or image output. Complexity, size, and so forth usually increase the cost for such systems and reduce the robustness of the system.

The resolution of an optical display system usually is determined by the number of pixels or pixel elements per unit area of the display or per unit area viewed by a viewer of the display. Sometimes such numbers are referred to as the pixel count, and sometimes the pixel count is the number of pixels in the entire display . Various types of displays for producing an image of visual information for viewing are known. The visual information may be an image of an object that is static or dynamic, a moving or dynamic image such as a motion picture information in the form of alphanumeric characters (regardless of the language), etc. Viewing in accordance with the invention typically refers to as viewing of an image by the human eye or by a pair of human eyes of a person. However, it will be appreciated that features of the invention may be employed when viewing is by another device, such as a still camera, motion picture camera, video camera, charged coupled device, etc.

In many displays circuitry is used to develop electrical signals for delivery to respective pixels to cause the respective pixels to produce a particular light output or to reflect light in a particular way. By operating the respective pixels in a desired way, respective images can be formed, as is known. Moreover, signals usually have to be provided to each pixel to cause the desired optical result thereby. The larger the pixel count (or pixel density), the more complex is the circuitry requirement for the display. For example, the larger number of pixels, the larger will be the number of electrical lines, etc. , required to provide electrical signals to the pixels. Also, as the number of pixels increases, the driving circuitry becomes increasingly complex, and, additionally, the scan rate or refresh rate may decrease. Decreasing the scan rate or refresh rate of the pixels may decrease the resolution of the display. Decreasing the number of pixels, of course, also usually reduces the resolution of the display.

It would be desirable to reduce the pixel count, number of lines for driving the pixels, and/or the complexity of the drive circuitry and/or to minimize the scan rate while providing an image that has relatively high resolution characteristics resolvable by the viewer. It is desirable that a display, especially an HMD, have adequate eye relief and comfort with which images provided by the HMD can be viewed. One aspect of comfort is the distance at which the image is viewed; a comfortable viewing distance is about twenty inches or more, for example, approximate reading distance. An aspect of eye relief is the distance between the eye and the last optical element (such as the output objective of the display) closest to the eye; often it is desirable that such distance be relatively large to provide adequate eye relief. If adequate eye relief is not provided, and/or if the viewing distance at which the image is seen is less than about twenty inches, then the eye may be strained to view the image, which may be uncomfortable and usually is undesirable. It would be desirable to provide a relatively uncomplicated, small and robust display system, especially for a HMD. It also would be desirable to provide a high quality image, e.g. , bright, of good contrast, and of good resolution, for viewing using a HMD, and especially to derive the image to take advantage of the difference in resolving power of the human eye. Further, it would be desirable to obtain a relatively wide field of view in an optical display system, especially a head mounted one, and efficiently to deliver light produced by the light source to the viewer. Efficient delivery of light reduces the brightness requirement of the light source, energy requirements and output heat, while providing good brightness, resolution and contrast of the viewed image. A problem encountered in prior display systems has been the seam which occurs at the junction between two images derived from two different image sources, for example. One example of this problem was manifest in the Cinerama type movie projection system wherein several projectors were used to project images at different locations on a wide area screen. Often a seam existed between the two images. In an HMD such seams can be more visible and more annoying because of the small distances involved and the relatively higher resolution of the images that must be presented to the eye compared to those projected on a distant movie screen. Accordingly, it would be desirable to minimize seams in an HMD or the like.

Additionally, it would be desirable to provide adequate eye relief in a head mounted optical display system.

In the field of computerized drawings and/or graphics, such as engineering drawing, it is customary, now, to display on a monitor an entire image, such as an engineering drawing. The draftsman can view the image and can select that part of the image which it is desired to magnify for better viewing or for modification on a better scale. Various windowing types of programs, computer aided drafting or design programs are available for conventional computers to carry out these tasks.

SUMMARY According to one aspect of the invention a display system, includes a relatively higher resolution display for presenting visual information, and a relatively lower resolution display for presenting visual information, the displays being positioned to present the visual information images therefrom in substantially side- by-side relation.

According to another aspect, a display system, includes a relatively higher resolution display for presenting visual information, and a relatively lower resolution display for presenting visual information, the displays being positioned to present the visual information images therefrom in substantially side-by-side relation, and wherein the lower resolution visual information image is at least substantially adjacent to and/or may surround the higher resolution visual information image. According to another aspect, a display system includes a relatively higher resolution display for presenting visual information, and a relatively lower resolution display for presenting visual information, the displays being positioned to present the visual information images therefrom in substantially side-by-side relation, and wherein each of the displays has plural pixels operative to display the visual information, and wherein the relatively higher resolution display has a larger number of pixels per unit area than the relatively lower resolution display.

According to another aspect, a display system, includes a relatively higher resolution display for presenting visual information, and a relatively lower resolution display for presenting visual information, the displays being positioned to present the visual information images therefrom in substantially side-by-side relation, and wherein each of the displays has plural pixels operative to display the visual information, and wherein the relatively higher resolution display has a larger number of pixels per unit area than the relatively lower resolution display, and a circuit drives the pixels to form images for visual viewing.

According to another aspect, a display system, includes a first display, including a retroreflector, means for focusing an image toward the retroreflector, and beamsplitter means for reflecting and transmitting light relative to the retroreflector, whereby the beamsplitter means one of transmits light and reflects light toward the retroreflector for focusing at or relative to the retroreflector and the other of transmits light and reflects light from the retroreflector for viewing, and a second display including means for presenting a relatively higher resolution image than the image presented by the first display, the display including means for presenting the relatively higher resolution image within the image presented by the first display. According to another aspect a method of display includes forming a relatively lower resolution real image, reflecting the image to the eye of an observer, forming a relatively higher resolution image, and directing the relatively higher resolution image to the eye of the observer such that at least a portion of the relatively lower resolution image circumscribes at least a portion of the relatively higher resolution image.

According to another aspect an optical system for presenting for viewing relatively lower and relatively higher resolution images of visual information includes a retroreflector, means for focusing a real image of visual information toward the retroreflector, light from the retroreflector being reflected to a viewing location as the relatively lower resolution image, and means for forming a relatively higher resolution image for viewing from the viewing location within the relatively lower resolution image.

According to another aspect, a system for viewing at a viewing location an image from an image source includes a retroreflector, means for focusing an image from a viewing source toward the retroreflector, and beamsplitter means for reflecting and transmitting light relative to the retroreflector, whereby the beamsplitter means one of transmits light and reflects light toward the retroreflector for focusing at the retroreflector and the other of transmits light and reflects light from the retroreflector for viewing, and wherein the retroreflector has non-coplanar portions which are positioned to reflect light to the viewing location for seamlessly combining images resulting from light reflected therefrom.

According to one aspect of the invention, a head mounted display system includes a retro-reflector, and optical means for directing light from an image source to the retro-reflector, light reflected by the retro-reflector being provided for viewing. The image source may be included as part of the HMD.

Briefly, according to the invention, light from an image source is directed by focusing optics to a conjugate optics path along which the light is directed to the eye or eyes of a viewer for viewing of an image. In an embodiment of the invention the conjugate optics path is provided by one retro-reflector or more than one retro-reflector which at least substantially maintains the characteristics of the light incident thereon, including the results of the focusing by the focusing optics, while reflecting the light to the eye(s) of the viewer. In an embodiment of the invention a beamsplitter directs incident light from the focusing optics into the conjugate optics path, e.g., reflecting light or transmitting light with respect to the retro-reflector and to the eye(s) for viewing. Also, light directed to the retro-reflector from the focusing optics mentioned above is reflected such that the light continues to have essentially or substantially the same direction it had when it impinged on the retro-reflector so that optically the lens of the eye can appear to be in effect at the focusing optics and the retina of the eye can appear to be in effect at the source of the image. Another aspect is to direct light having image characteristics from a retro¬ reflector to a viewer to provide the viewer an image that is focused at a distance that is relatively easily focused by the viewer's eye without focusing at infinity.

According to another aspect, a display system includes means for forming an image for viewing by an eye of an observer, delivery means for delivering the image from the means for forming to the eye of the observer, and the means for forming and the delivery means being cooperative to provide the image to the eye of the observer at a size at the retina of the eye that is approximately the size of the retina.

According to a further aspect, a head mounted display is relatively compact, light weight, robust and able to provide relatively bright images at a viewing distance from a viewer's eye that provides comfortable eye relief.

According to another aspect, an image can be effectively spread out and viewed as an engineering drawing would, for example; a portion of the image can be selected for high resolution display, e.g. , as with a mouse or the like associated with a computer, and the selected portion then can be displayed in relatively high resolution while other portions are displayed in relatively low resolution. This technique may be used in the field of computer aided design and the like.

Another aspect relates to apparatus for displaying high and low resolution images, comprising an optical switch for switching between two different polarization conditions, a selective reflector for reflecting light from a display respectively to relatively large area and relatively small areas for viewing in a field of view depending on the operation of the optical switch. Another aspect relates to a method for displaying high and low resolution images, comprising an optically switching light between two different polarization conditions, and selectively reflecting light from a display respectively to relatively large area and relatively small areas for viewing in a field of view depending on the optical switching.

One or more of these and other aspects, objects, features and advantages of the present invention are accomplished using the invention described and claimed below.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Although the invention is shown and described with respect to certain preferred embodiments, it is obvious that equivalents and modifications will occur to others skilled in the art upon the reading and understanding of the specification. The present invention includes all such equivalents and modifications, and is limited only by the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the annexed drawings:

Fig. 1 is a schematic illustration of a head mounted display optical system utilizing a retro-reflector and wherein relatively high and relatively low resolution images are combined; Fig. 2 is a schematic illustration of the relatively high and relatively low images presented in the field of view by the system of Fig. 1;

Fig. 3 is schematic illustration of an HMD optical system according to the invention showing a light path for illuminating the low resolution image source;

Figs. 4 and 5 are schematic illustrations of HMD optical systems according to the invention using, respectively, transmissive or reflective low resolution image sources and a shared light source for two display devices for the respective eyes of a viewer;

Fig. 6 is a schematic illustration of a modified optical system using an additional lens component to obtain comfortable viewing distance while reducing the size of the system;

Fig. 7 is a schematic illustration of another embodiment of HMD using plural retro-reflectors, respectively, positioned relative to the beamsplitter;

Fig. 8 is a schematic illustration of exemplary positioning of two non- coplanar portions of a retro-reflector for use as a retro-reflector in the various embodiments of the invention;

Fig. 9 is a schematic illustration of a seamless image produced by an optical system in accordance with the invention using two retro-reflector portions positioned in non-coplanar relation, such as that of Fig. 8;

Fig. 10 is a schematic illustration of another arrangement of curved retro- reflector in accordance with the present invention;

Fig. 11 is a schematic front elevation view of an embodiment of display system having two displays;

Fig. 12 is a schematic side elevation view of the embodiment of Fig. 11;

Figs. 13-15 are schematic illustrations of a display system using a cholesteric reflector; and

Figs. 16-20 are schematic illustrations of display systems for producing electrooptically high and low resolution images in a field of view without the need for a cholesteric reflector.

DESCRIPTION Referring in detail the drawings, wherein like reference numerals designate like parts in the several figures, and initially to Fig. 1, a display system in accordance with the present invention for viewing images of visual information is shown at 1. The display system 1 includes a pair of image sources 2, 3 and an optical viewing system 4 which in a sense is analogous to an eyepiece or objective with which the respective images produced by the image sources 2, 3 can be viewed. The display system 1 also may include a drive circuit 5 which provides electrical signals or other types of signals to one or both of the image sources 2, 3 via connections 6,7 to cause the image sources to display visual information for viewing. The optical viewing system 4 includes an optical system 10 for presenting to the eye 11 of a viewer, such as a person, a relatively low resolution image derived from the image source 2. The optical viewing system 4 also includes a further optical system 12 for presenting to the eye 11 a relatively high resolution image derived from the image source 3.

The eye 11 schematically shown in Fig. 1 includes a retina 13 at the back of the eye and an entrance pupil and lens 14 at the front of the eye. The lens 14 focuses light onto the retina 13 to form images there which are seen by the person. The foveal portion (or fovea) 15 of the retina is marked by the horizontal line 16 at the back of the eye to show the size thereof is smaller than the overall size of the retina 13. The fovea 15 is able to provide greater resolution of images incident thereon than can the other portions 17 of the retina 13. The display system 1 provides to the eye 11 a relatively lower resolution image via the optical system 10 and a relatively higher resolution image via the further optical system 12. The relatively higher resolution image is intended to be focused by the lens 14 of the eye 11 onto the fovea 15, and the relatively lower resolution image is intended to be focused by the lens 14 onto the other portion 17 of the retina 13.

The optical system 10 of the optical viewing system 4 includes focusing optics 20, a beamsplitter 21, and a retro-reflector 22. The focusing optics 20 is shown as a single lens which is intended to direct light via the beamsplitter 21 toward the retro-reflector 22 and forms a real image 23. The real image may be formed and focused at the retro-reflector 22 or it may be behind or in front of the retro-reflector. The optical system 20 may include a plurality of lenses, mirrors, filters, and/or other means used to form the real image as described. The source of image light provided to the focusing optics 20 is the image source 2.

The image source 2 may be a miniature image source of the type disclosed in copending U.S. patent application serial No. 08/275,907, filed July 5, 1994, the entire disclosure of which is hereby is incorporated by reference. Such an image source is an active matrix liquid crystal display device which uses as one of the substrates thereof a single crystal silicon (or other semiconductor material) material. Other types of active matrix liquid crystal display devices can be used as the image source 2. Other types of display devices, such as those which emit light, those which modulate light, e.g. , which is intended to be transmitted or reflected by the display, electro-luminescent devices, cathode ray tube devices, liquid crystal devices, etc., may be used to present light 24 representing an image 25 as an input to the focusing optics 20.

The beamsplitter 21 may be a conventional beamsplitter which reflects approximately 50% of the light incident thereon and transmits approximately 50% of the light incident thereon. If desired, other reflection/transmission ratios may be used. To avoid double images, it may be desirable to provide an anti-reflecting coating or the like on one or both of the surfaces of the beamsplitter 21. The beamsplitter 21 also may be other types of beamsplitters, such as one which reflects plane polarized light which is polarized (e.g., has a transmission axis) in one plane (e.g., electric vector is in that plane) and transmits plane polarized light which is polarized in the orthogonal direction. Furthermore, the beamsplitter 21 may be a device which reflects circular polarized light having one direction of circular polarization and transmits circular polarized light having the opposite direction of circular polarization. Quarter waveplates and/or other devices may be used to cooperate with the beamsplitter 21 and the light incident thereon to obtain the desired beamsplitter function of reflecting and/or transmitting light.

Various types of retro-reflectors 22 may be used in the invention. One example is that known as a corner reflector or a sheet having a plurality of corner reflectors. An example of such a retro-reflector film or sheet material having a plurality of comer cubes is sold by Reflexite Corporation of New Britain, Connecticut. Such material is available, for example, having about 47,000 comer reflectors per square inch. Another retro-reflector material useful in the invention is a material having plural glass beads or other refracting and/or reflecting devices on or in a support, such as a flexible sheet, a rigid sheet, glass, etc. In Fig. 1 solid lines represent the light 24 incident on the retro-reflector 22.

Light rays 24a, 24b, and 24c are shown for example. It will be appreciated that other light rays also may be traced through the optical system to form the real image 23 at or relative to the retro-reflector 22. From the beamsplitter 21 to the retro¬ reflector 22 such light rays are designated 24a', 24b' and 24c', for example. Dotted lines from the retro-reflector 22 designated 24a" and 24c" depict light rays reflected by the retro-reflector to and through the beamsplitter 21 to the entrance pupil and lens 14 of the eye 11. The paths of the light rays 24a', 24a" are conjugate and opposite in direction, and the paths 24c' and 24c" also are conjugate and opposite. Since the above-mentioned light paths are conjugate to and from the retro¬ reflector 22 and since the focusing optics 20 forms a real image 23, e.g., the image 25 is located beyond the focal point of the focusing optics 20, the entrance pupil and lens 14 of the eye 11 can be placed relative to the light incident thereon from the retro-reflector 22 via the beamsplitter 21 such that the entrance pupil and lens become effectively or optically in the same relative position to the image 25 as the focusing optics 20 is to the image 25.

For example, as is seen in the diagram of several light rays presented in Fig. 1 , the extremities of the image 25 represented by light rays 24a, 24c pass through and intersect at the center point A of the focusing optics 20, and correspondingly the light rays 24a" and 24c" pass through and intersect at the center point A" of the lens 14 of the eye 11. Similar relationship would occur with respect to other rays, such as those depicted in Fig. 3, which is described below and also in the parent application identified above.

In the optical viewing system 4 of the display system 1 , the further optical system 12 provides a relatively high resolution image for viewing by the eye 11. The resolution of the image presented by the further optical system 12 preferably is higher or greater than the resolution of the image 23 presented by the optical system 10. This can be accomplished even using the same type of displays, such as transmissive liquid crystal displays, for the image sources 2, 3. For example, the image produced by the image source 2 may be magnified by the focusing optics 20 to form the real image 23. Such magnification reduces resolution; for example, the number of pixels per inch (or some other unit area) at the image 23 is less than the number of pixels per same unit area at the image source 2. However, the image produced by the image source 3 may be viewed without magnification by the focusing optics. Therefore, the number of pixels per unit area, e.g. , resolution, is greater than that of the real image 23. However, the size of the image produced by the image source 3 is coordinated with the size of the real image 23 so that the two blend as one image (register, etc.), which has a relatively low resolution except where the image source 3 is located and viewed, and that portion is in relatively high resolution. If desired, the resolution of the image sources 2, 3 may be different. The further optical system 12 includes the image source 3 and the light path 30 to the entrance pupil and lens 14 of the eye 11. The light path 30 passes through the beamsplitter 21. The image 23' presented by the image source 3 preferably is formed in the same plane as the real image 23 is formed. Therefore, the light rays 30a, 30b representing two of the light rays representing the image 23' also pass through the center A" of the lens 14 and, in particular, are focused onto the fovea 15.

The further optical system 12 includes the image source 3 and the light path 30 through the beamsplitter 21 to the eye 11. The light path 30 through the beamsplitter 21 may be reduced in intensity by approximately 50% due to the transmission and reflection characteristics of the beamsplitter 21, the extra light that is reflected by this beamsplitter 21 being sent up relative to the illustration in Fig. 1 toward the focusing optics 20 and image source 2 where such light may be lost or may be used additionally to brighten the image 25. Alternatively, the beamsplitter 21 may be of the type which transmits all of the light incident thereon in the light path 30, for example, due to the nature of the optical polarization of such light. Further, if desired, the beamsplitter 21 may have an opening therethrough to pass light in the light path 30 without attenuation; such opening being of a size to pass light in the light path 30 where it intersects the beamsplitter 21, but generally minimizing such opening so that the beamsplitter is effective to reflect the light 24 in the manner described above.

Preferably the real image 23 and the image 23' are formed in the same plane or substantially the same plane so that both are focused on the retina 13. However, the higher resolution image 23' from the image source 3 primarily is focused on the fovea 15, and the real image 23 primarily is focused on the other portion 17 of the retina 13. Thus, the higher resolution image is presented to the fovea which has better resolving or higher resolving capability than the other portion 17 of the retina 13. Therefore, the display system 1 cooperates with the image resolving capability of the eye 11.

In the description herein reference to low resolution image, lower resolution image, and relatively low or relatively lower resolution image mean the same thing; and reference to high, relatively high, relatively higher, etc. resolution image also means the same thing. In the description there are two portions of the image presented to the eye 11, one portion being of relatively lower resolution compared to the resolution of the other portion the higher resolution portion.

The high resolution image 23' from the image source 3 is shown being transmitted directly to the eye 11. However, the high resolution image 25 is presented by viewing by the eye as the real image 23 by light reflected from the retro-reflector 22. The image 23 may lose resolution relative to the resolution of the image 25 as a function of the resolving capability, such as the number of reflectors per unit area, of the retro-reflector 22. In the display system 1, if the high resolution image source 3 has a larger number of pixels per unit area than the low resolution image source 2 money, complexity, etc. can be saved and reliability can be increased, as will be appreciated. Alternatively, the number of pixels per unit area may be the same in the two image sources; or the number can be greater in the low resolution image source since it is magnified, but the image source still would provide relatively high resolution image effect since its image is not magnified by the focusing optics.

The drive circuit 5 may be, for example, conventional video circuitry used to receive television signals or circuitry used to receive signals from a computer intended to drive a visual display. The drive circuit 5 may be a conventional drive circuit of a drive currently used in various computers, such as notebook computers which drive active matrix liquid crystal displays, such as circuits used to drive CRT monitors, etc. The drive circuit 5 is coupled by the connection 6, such as a plurality of electrical leads or the like, to the image source 2 to develop the low resolution image 25, and the drive circuit 5 is connected by the connection 7, such as a number of other leads, to the high resolution image source 3 to develop the relatively high resolution image 23'. If the number of pixels per unit area of one image source is larger than that of the other image source, the number of leads or connections in the connection 7 per unit area may differ per image source.

In the embodiment of display system 1 illustrated in Fig. 1 the high resolution image source 3 is embedded in and/or made substantially integral and coplanar with the retro-reflector 22 to present the high resolution image 23' and the low resolution image 23 in relatively coplanar relation; and in such case the real image 23 is formed at the retro-reflector 22. Alternatively, if desired, the high resolution image 23' and the low image resolution 23 may be in different planes. Moreover, if desired, the high resolution image source may be located at a place other than the retro-reflector 22, for example, being located in front or behind the retro-reflector relative to the illustration of Fig. 1, e.g. , to the left or right relative to the illustration.

As was mentioned above, the image sources 2, 3 may be active matrix liquid crystal display devices of the type disclosed in the above-mentioned copending U.S. patent application. However, either or both of the image sources 2, 3 may be other sources of image, light, visual information, etc. for use in the display system 1. For example, one or both of the images 25, 23' may be derived from an image source that is relatively remotely located to the display system 1 , and the respective image may be conveyed to the display system 1 via light transmission through the air, through other optical media, such as fiber optics, through other optical components, such as lenses, etc. The image sources hereof may be high resolution liquid crystal displays having a size on the order of one square inch or less, each. An exemplary image source is one proposed by SONY Corporation in a paper presented at the Society for Information Display, International Display Research Conference, October 10-13, 1994, Monterey, California, entitled "A 1.35-in. -diagonal Wide- Aspect-Ratio poly-Si TFT LCD with 513k Pixels", at pages 414-417 of the conference record.

In an example of the invention, each of the image sources 2, 3 is the same type, namely a light modulating transmissive liquid crystal display. Since brightness of the light from the display 2 is attenuated in the optical path which includes the focusing optics and beam splitter, for example, and possibly due to light reduction at the retro-reflector (and possibly even reduction in intensity due to magnification), it is desirable to balance the intensities of the light output from the light sources 2, 3. Such balancing may include changing intensity, e.g. , cutting down intensity of the image source 3, so that the intensity of the light forming the image 23' at the output of the image source 3 at the retro-reflector 22, for example, and the intensity of the light forming the image 23 as reflected by the retro-reflector will be the same or about the same. For special effects, it may be desired to alter the balance of light intensities.

Compared the light reflecting capability of the image source 3, the retro¬ reflector 22 is a much more efficient light reflecting medium. For example, in response to the incident light 24 which forms the real image 23, the retro-reflector 22 may be approximately three hundred times more reflective than the image source 3. Therefore, the light from the image source 2 which is incident on the image source 3 makes a relatively negligible contribution to the image as viewed by the eye 11.

However, if it is desired to eliminate a portion of the light 24 from being incident on the image source 3, it is possible to provide a blanking of the image source 2. Therefore, where such image source 2 would coordinate with the image source 3, the image source 2 would not emit (transmit, output, etc.) light. Such blanking can be performed by conventional software or by some other technique, as will be appreciated by those having ordinary skill in the art. The display system 1 also preferably includes a housing 40 and a mounting structure 41, such as a temple piece like that used in an eye glass frame, a strap, or other means to mount the display system 1 on the head or other body part of a person so that the eye(s) 11 can view the visual information output therefrom at the exit port or opening 42 of that housing 40. The system 1 can be mounted in another device. The display system 1 shown in Fig. 1 presents an image to one eye 11 of a human observer, for example. The various components shown in Fig. 1 may be duplicated and/or some may be shared to present an image to the other eye of the person. In this way, if desired, true binocular images can be formed and presented for viewing. The images may be stereoscopic in which depth is provided by respective left eye and right eye images to give the sense of depth and distance. Alternatively, the images may be essentially monoscopic so as to present the images for both eyes without any substantial depth. Various conventional means may be used to mount the components of the optical viewing system 4 in the housing 40 to obtain the relative positioning shown in Fig. 1. Additional optical components may be included in the optical viewing system 4, such as linear polarizers, circular polarizers, waveplates, focusing elements, such as lenses or mirrors, prisms, filters, shutters, apertures, diaphragms, and/or other components that may be used to provide a particular type of output image for viewing. Also, the housing 40 may be entirely closed other than for a source of input light and the output port 42 for viewing light/images. However, if desired, the housing may be partly or substantially open whereby simply a frame is used to support the various components in relative position.

In Fig. 2 an example of an image 45 produced by the display system 1 and seen by the eye 11 is shown. The image 45 includes a low resolution portion 46 and a relatively high resolution portion 46', which correspond, respectively, to the images 23, 23' in Fig. 1. The high resolution image portion 46' is generally essentially located in the image 45, for example, in the approximate center (or elsewhere, if desired) and the relatively low resolution portion 46 circumscribes or surrounds the high resolution portion. Therefore, preferably the high resolution image is seen by the fovea 15, and the low resolution image is seen by the rest of the retina 13. Therefore, a viewer can look at the center of the image 45 and see the high resolution image portion 46' with the high resolving portion of the eye and the low resolution image portion 46 with the low resolution resolving portion of the eye. This is acceptable display procedure since it is unnecessary to present a high resolution image to that portion of the eye which is not capable of high resolution resolving. The fact that a high resolution is not required over the entire field of view greatly reduces the total pixel count and the rate at which data must be input to the display system 1, such as the image sources 2, 3.

The images 46, 46' may be presented in side-by-side relation. Also, the low resolution image can be adjacent to or partly or fully surround the high resolution image.

In using the invention a relatively lower resolution real image is formed, and that image is reflected to the eye of an observer (viewer). Additionally, a relatively higher resolution image is formed, and it, too, is directed to the eye of the observe. Preferably, at least a portion of the relatively lower resolution image is adjacent (or even surrounds) a portion or all of the high resolution image, and more preferably, the two images are presented at effectively a seamless junction. Moreover, according to a method of the invention, the relatively high resolution image is presented to the fovea of an eye of an observer, and the lower resolution image is presented to a portion of the retina that does not have the high resolving capability of the fovea.

In making the invention a low resolution image presenting optical system and a relatively high resolution image presenting optical system are combined such that the two images are presented to the eye of an observer and the high resolution image is presented to the fovea or other relatively high resolving portion of the eye or other optical device viewing the image, and the relatively low resolution image is presented to a lower resolving portion of the eye or other optical device receiving or viewing the image. Thus, the display system 1 made in accordance with the invention can be made to fit the viewing characteristics of human vision. That is, the optical viewing system 4 of the invention is able to present the central portion of an image at a higher resolution than the remainder of a field of view intended to be observed by the eye of an observer. The viewer can see a composite image including a high resolution image in the center, for example, that is seamlessly joined to a lower resolution image filling the rest of the field of view.

The relative positioning of the parts of the display system 1 and the other characteristics of those parts, such as, for example, the magnifying power and focal length of the focusing optics 20 can be selected to obtain the desired magnification or not of the low resolution image 23 relative to the size of the image 25. Preferably the image source 2 is beyond the focal distance or focal point of the focusing optics (lens) 20 so the image 23 is a real image.

For some magnification situations, as is described further in detail below, it is desirable to use a relatively short focal length focusing optics 20 such that the focal length thereof is less than that of the lens 14 of the eye 11 to the back of the eye. Also, to provide a relatively large or wide "sweet spot" or place where the eye 11 can be positioned relative to the optical system 4 and/ or the output port 42, while still being able to see a good quality (bright, good resolution, and/or good contrast, etc.) image preferably also with a relatively wide field of view, it is desirable to use a relatively short focal length lens or focusing optics 20, and even more preferably to use such a focusing optics 20, indeed, optical viewing system 4 overall, which has a relatively low f#.

In Fig. 3 is shown an example of a technique for bringing light from a light source 50 to the low resolution image source 2. Specifically, a beamsplitter 51 is placed in position to direct light from the light source 50 to the image source 2. The image source 2 reflects light to form the image 25 which is focused by the focusing optics 20 to form a real image 23 as was described above. The light 24 reflected by the image source 2 is transmitted through the beamsplitter 51 to the beamsplitter 21 from which it is reflected to the retro-reflector 22. Other techniques also may be used to illuminate the image source 2. An example is disclosed in copending U.S. patent application serial No. 08/187,262, filed January 25, 1994, the entire disclosure of which hereby is incorporated by reference.

Alternatively, the image source 2 may be a light emitting display, such as a cathode ray tube or electro luminescent display device. As another alternative, the image source 2 may be a light modulating device, such as a liquid crystal display, which modulates light transmitted therethrough, and in this case the source of the light provided to the image source 2 may be on the side of the image source remote from the focusing optics 20.

According to the invention in which there are two display systems 1 , one for each eye, for example, the light source 50 (or other light source) may be shared by two or more of the image sources, such as the low resolution image sources 2 for the respective eyes. The light source also may be used to provide light to illuminate the high resolution display 3 in one or both optical viewing systems 4 (one for each eye). The high resolution image source 3 may be reflective, transmissive, or light emitting, as was described above with respect to the image source 2. Preferably the image source 3 is a light transmissive LCD and a light source 52, as is exemplified in Fig. 3.

Briefly turning to Fig. 4, an example of a head mounted display system 1 ' in accordance with the invention is shown. The display system 1 ' includes two display systems 1 which are mounted together by a support structure 60, such as a nose bridge piece similar to that used on an eyeglass frame, and/or other support structure in the form of housing 61. The HMD system 1 ' includes two optical viewing systems 4 like the one described above with respect to Fig. 1. The high resolution image sources 2 are transmissive. A beamsplitter 62 and reflector 63 direct light 64, from the light source 65 to the respective image sources 2 to form the low resolution images. Light 66 from the light source 65 also is directed by reflectors, beamsplitters, and/or the like to a back compartment 67 of the system 1 ' provide a source of illumination to one or both of the high resolution image sources 3 of the optical viewing systems 4. For example, the light 66 may travel toward the back compartment 67 and be reflected in that compartment by one or more reflectors, beamsplitters and/or the like to the back (relative to the viewing ports 42), of the system 1 ' to be directed as incident light on respective high resolution image sources 3. The high resolution image sources modulate light transmitted therethrough to form the respective high resolution images.

In using the system 1' illustrated in Fig. 4, the system may be mounted on the head of a person using the nose bridge piece 60 and the temple pieces 41 for support on the head and/or other means to provide appropriate positioning of the output ports 42 relative to the eyes of the user. Alternatively, the system 1' can be positioned in a relatively fixed location, and the eyes may be brought to the output ports 42. The low and high resolution images are formed for the respective eyes, deriving from light 64 or 66 from the light source 65, and the images can be viewed by the respective eyes.

The embodiments illustrated in Figs. 3 and 4 are examples of techniques for providing light to image sources that are not light emitting. Other techniques also may be used to provide light to the image sources. As was mentioned above, took one or more of the image sources may be light emitting.

As another alternative, which is shown schematically in Fig. 5, light from the source 65 is provided to two reflective low resolution image sources 2 of respective optical viewing systems 4 via beamsplitters 70, 71. The images formed by the low image resolution sources 2 can be viewed through the respective output ports 42 by respective eyes. The human eye is most comfortable when viewing an image at a distance of about twenty inches, approximately at the distance at which one would place a book, document, etc. to be read. It is desirable that the final image as seen by the viewer be located at such distance, e.g., approximately twenty inches from the pupil 14 of the eye. This can be accomplished in the manner illustrated in Fig. 6.

The HMD system 1 can be compact and still provide comfortable viewing distance of about twenty inches as is illustrated in Fig. 6 by adding an additional optical system 70 between the beamsplitter 21 and the entrance pupil and lens 14 of the eye 11. In Fig. 6 such optical system 70 is depicted as a single lens; however, it will be appreciated that it may include other optical components as was mentioned above, for example, with respect to the focusing optics 20. In the HMD system 1 of Fig. 6 the viewer is provided with a virtual image 23a of the image source 2 image 25 or of real image 23 at the desired viewing distance (twenty inches, for example) by the cooperation between the focusing optics, retro-reflector, and additional optical system 70. A virtual image 23a' due to viewing the high resolution image 23' through the optical system 70 may be at the location (e.g., in the same plane) of the virtual image 23a from the low resolution image source 2 by locating the high resolution image source 3 at the plane of the real image 23, e.g. , in the plane of the retroreflector 22. Other means also may be used to locate the high resolution image in the desired viewing plane.

It will be evident that the beamsplitter 21 and retro-reflector 22 cooperate to provide the conjugate optics path described herein. It will be appreciated that the beamsplitter 21 may be positioned relative to the focusing optics 20 to reflect light to the retro-reflector 22 and to transmit to the eye 11 light which has been reflected by the retro-reflector. Alternatively, it will be appreciated that the beamsplitter and retro-reflector may be so positioned that the beamsplitter transmits light to the retro¬ reflector and reflects to the eye 11 light which has been reflected by the retroreflector. It will be appreciated that the various features and embodiments illustrated in the several figures hereof may be used in the other embodiments and/or systems illustrated in the various other figures. For example, the additional optics 70 used in the system of Fig. 6 may be used in other embodiments disclosed and illustrated herein. The drive circuit 5 only is illustrated with respect to Fig. 1, but it will be appreciated that such drive circuit may be used in connection with the other embodiments disclosed herein. Other examples of features useful in the various embodiments herein are the several techniques used (and equivalent techniques) for providing light to the image sources.

Fig. 7 illustrates another embodiment of HMD system 100, features of which can be used with the several embodiments described above. In particular, an additional retro-reflector 22a is added at an orientation and location relative to the beamsplitter 21 and the original retro-reflector 22 such that the additional retro¬ reflector reflects some light from the image source that previously was lost to the optical system 10. Specifically, light from the focusing optics 20 and image source 2 is reflected by the beamsplitter 21 to the retro-reflector 22, and the retro-reflector 22 reflects light to the beamsplitter for transmission to the eye 11. Additionally, light from the focusing optics 20 which is transmitted through the beamsplitter 21 to the additional retro-reflector 22a is reflected by the additional retro-reflector 22a back to the beamsplitter 21 for reflection to the eye 11. Although some light from the retro-reflector 22 may be reflected by the beamsplitter back to the image source 2 and some light from the additional retro-reflector 22' may be transmitted through the beamsplitter to the image source 2, such light is not necessarily lost to the optical system 10 of the HMD system 100. Rather, such light may be used to increase the brightness of the light incident on the image source 2 when such source is a reflective one, and, thus, further increase the brightness of the image viewed by the eye 11. It will be appreciated that the HMD 100 increases the amount of light to the viewer, and, thus, increases the brightness of the output image while minimizing the illumination requirements of the optical system 10.

In the display 100 of Fig. 7 there may be one or two high resolution image sources 3, 3a. If only one is used, then to avoid the light from the other retro- reflector in which that image source is not embedded or positioned near, the technique of blanking the image source 2 at areas which would correspond to the location of the high resolution image source may be used to prevent washing out of the high resolution image by light reflected from such other retro-reflector. Also, blanking could be used in those instances when it is desired to have both high and low resolution images produced as described. However, if desired, the blanking could be terminated and the high resolution image source could be turned off. In such case, the other retro-reflector would fill in the image where the image source 3, for example, is located, thereby to provide a full low resolution image in the full field of view in cooperation with the retro-reflector in which the high resolution image source is mounted or positioned. This improved versatility and flexibility of the display 100. If two high resolution image sources were used, e.g., 3 and 3a, as is illustrated in Fig. 7, they could both be positioned so as to be viewed simultaneously and in registration to increase the brightness of each. In such case blanking would not be needed for the reasons described above. However, if desired, blanking could be used. Also, it may be desired to use alternately, e.g. , sequentially or otherwise, the respective high resolution image sources 3, 3a to provide different respective images for a desired optical effect, thus increasing the flexibility of the invention.

In some instances it is possible that the retro-reflector may not be perfectly flat, that it in fact is curved, or that it is not sufficiently large for the HMD system

110. It has been found that the orientation of the retro-reflector 22 in the optical systems of the several embodiments described and illustrated may be other than flat and/or may be in multiple parts. Moreover, the parts need not be perfectly flat or parallel; rather the several parts can be in different orientations, provided the orientations are sufficient to provide the desired retro-reflection function described herein. An example of such non-parallel or linear orientation of a retro-reflector 22a, 22b is illustrated in Fig. 8. An HMD system 110 using such multiple part retro-reflector 23a, 23b, without regard to whether the retro-reflector is flat or the parts thereof are parallel, has been found to be functional in the manner described above to provide images for viewing by the eye 13.

Fig. 9 is a schematic illustration of the image seen by the HMD system 110 of Fig. 8. The image 111 only includes the image formed by the image source 2. It is seen as a checkerboard and there are no seams where the two retro-reflectors 222a, 222b overlap or intersect. Therefore, the checkerboard produced as the image output from the image source 2 appears to the eye 11 as a uniform checkerboard without any discontinuities due to overlapping of the retro-reflectors. Although not shown in Fig. 8 or in the image of Fig. 9, there may be a further image source, such as a high resolution image source 3, located to provide in the plane of the real image formed by the focusing optics 20. The high resolution image then can be viewed with the low resolution image in the manner described above.

Briefly referring to Fig. 10, a system 110' which is similar to the system 110 described above with respect to Fig. 8 is shown. In the system 110' the retro¬ reflector is shown at 222c as a curved retro-reflector. Operation of the system 110' is the same as that described above with respect to Fig. 8.

In Figs. 11 and 12 are shown respective front elevation and side elevation views of an exemplary embodiment of display system 200 according the the invention and embodying the various features of structure and operation described herein, for example, with respect to the various illustrations of the drawings. The front elevation view is looking in the same direction as the eyes 11 of the viewer are looking. A single beam splitter 21 may be shared by both optical system 10, one for each eye and one or both of which may be adjustable laterally to accomodate eye spacing, as is represented by an arrow B, and a single retroreflector 22 also may be shared. Each of the optical systems 10 may have its own beam splitter 21 and image source 2 or combined image sources 2, 3. Also, although only a single image source 2 is shown in Figs. 11 and 12, it will be appreciated that the features of the invention described above using two image sources, each being of different resolution, for example, may be used in the manner described herein.

An advantage to sharing beam splitter 21 in this embodiment is the reduced number of parts and the increase in robustness of the display system 1. This, too, facilitates manufacturing, decreases cost, and increases robustness of the display system 1.

A display system 300 including an electro-optic subsystem 301 to introduce a high resolution area image 302 into a lower resolution field of view area 303 of a displayed image 304 is shown in Figs. 13-15. The high resolution area image may be introduced into the center of the lower resolution field of view area image or elsewhere, as may be desired. In the system 300 light from a projector 306 is alternately switched between right hand and left hand circular polarization. This is accomplished by a polarization switching device 310. It will be appreciated that other optical characteristics may be switched, if desired, equivalently to obtain the desired switching effect described further below to obtain the high and low resolution image portions.

The switching device 310 illustrated in the embodiment here described includes a plane (linear) polarizer 311, a liquid crystal cell 312 and a waveplate 313. In the illustrated embodiment the liquid crystal cell is that known as a variable birefringent liquid crystal cell, sometimes referred to as a surface mode cell or a pi cell, and examples are presented in U.S. Patents Nos. 4,385,806, 4,540,243, and

RE.32,521 and 4,582,396. Depending on the operation or energization of such liquid crystal cell light incident thereon may be changed in plane polarization direction or sense or may be changed from plane polarized light to circular polarized light. Another type of liquid crystal cell useful in the invention is that known as a twisted nematic liquid crystal cell, although at least some of such cells are slower acting than the variable birefringent liquid crystal cells. The waveplate 313 may be a quarter waveplate, for example, although, if appropriately arranged, other types of waveplates alternatively may be used. The alignment of axes of the respective components 311, 312, 313 are shown in the lower right-hand portion of Fig. 13. The transmission axis of the plane polarizer 311 is relatively vertical; the rub axis of the liquid crystal cell (sometimes abbreviated "SMD" for surface mode device) is at a relative 45° to the transmission axis of the polarizer; and the axis of the waveplate is 90° to the axis of the SMD and a relatively opposite 45° to the transmission axis of the polarizer. Other alignments may be used, if necessary, for example, to compensate for residual birefringence of the SMD, etc. The alignments described here are represented by respective arrows in Figs. 13-15.

The projector 306 includes an image source, such as a liquid crystal display, a CRT, etc. The system 300 also includes a beamsplitter 321, retroreflector 322, and selective reflection optics 325. The beamsplitter 321 and retroreflector 322 may be like those described above. The optics 325 includes a cholesteric film 326, a waveplate 327 and a mirror 328. The cholesteric film may be, for example, cholesteric liquid crystal material or a cholesteric liquid crystal polymer material. Such films are known. The illustrated cholesteric film preferably is a right handed white light cholesteric film which is curved to reflect light in a manner described below. The focal length of such curved device is referred to below as f2. The waveplate 327 is a 1/4 lambda waveplate, e.g. , a quarter waveplate, and it has its axis oriented at 45 ° to the plane of polarization of light incident thereon. The mirror

328 (or some other reflector) may be a conventional reflector which is curved to have a focal length referred to below as fl.

In operation of the system 300, light from the projector 306 is alternately switched by the switch 310 between right hand and left hand circular polarization. This is accomplished by switching the SMD 312 variable retarder between approximately 0 and 1/2 lambda retardation. Switching may be slightly different, depending on residual retardation affects of the SMD, for example, and compensation may be provided therefor by appropriate alignment of and/or selection of the components 311, 313. The linear polarization of light provided the SMD may be provided by the polarizer 311 or, alternatively, that polarizer may be eliminated if polarization is provided by the projector 306, itself, for example, if it were a liquid crystal display.

Referring to Fig. 14, the image 302 presented by the display system 300 for viewing from a viewing location 330, for example, is that to be located in the high resolution portion of the image, e.g. , the central portion of the image. The SMD

312 is operated into the 0 retardation or 0 lambda state, e.g. , by applying relatively high voltage thereto, and the light transmitted by the switch 310 is left hand circularly polarized as a result of the cooperation of the direction of plane polarization and the relative 45° angle of the axis of the waveplate 313 with respect thereto. This light is converted to right hand circular polarized light by reflection from the beam splitter 321. Therefore, when it encounters the cholesteric film 326, it is reflected by that film.

The cholesteric film 326 may be made of multiple thin film layers so as to be reflective across the entire white light spectrum. The cholesteric film can be either a fluid liquid crystal or a polymer film. The cholesteric film is curved into a concave mirror as is illustrated and as is described above. Therefore, the light reflected thereby is focused onto the retroreflector 322 with an image size that covers the central portion of the retroreflector 322. Note that the full array of pixels in the display are used in this high resolution image, but they are concentrated in a relatively small area of the retroreflector.

In Fig. 15 the image presented by the display 300 is the low resolution, wide field portion of the field of view. The SMD 312 is switched into the 1/2 lambda state, e.g. , by reducing the voltage thereto. As a result, the plane of polarization of the light output from the SMD is plane polarized in a direction perpendicular to the plane of polarization of the light received from the polarizer 311 or the liquid crystal display of the projector 306. When such light impinges on the waveplate 313, it is converted to right hand polarized light, which is directed to the beamsplitter 321. Upon reflection from the beamsplitter, such light is converted to left hand circular polarized light, and that light is transmitted through the cholesteric film 326 without alteration. It then passes through the 1/4 waveplate 327 and is converted into linearly polarized light. When reflected off the full mirror 328, the plane of polarization is maintained. Upon passing through the quarter waveplate a second time, such light is converted into left hand circular polarized light and is, therefore, once again transmitted through the cholesteric film 326 without alteration. The focal length of the mirror 328 is such that the light is focused on the retroreflector 322 and preferably fills the size of the retroreflector or at least provides a larger field than the high resolution field. The number of pixels in the low resolution display also may be the full array of pixels of the projector 306 and, therefore, the same as the number of pixels of the high resolution image. However, since the pixels of the low resolution image occupy a larger area, the resolution is less than that of the high resolution image. The high resolution imare in the central portion of the field of view preferably meshes seamlessly with the low resolution image filling the balance of the field of view. The high and low resolution images are sequentially presented on the display at a rate rapid enough so that the viewer's eyes fuse or integrate the images together into a single image having the high and low resolution portions. Several systems and methods by which the image presented in a conjugate optics based HMD (head mounted display) can be made consistent with the resolution resolving characteristics of human vision are shown in Figs. 16-20. That is, means by which the central portion of the image can be presented at a higher resolution than the remainder of the field of view are depicted.

The method and system 400 illustrated in Figs. 16 and 17 is one example. Various other combinations of components and orientations can accomplish the same effect as that shown and describe here. In Figs. 16 and 17 is one example of one possible configuration.

In the system 400, a polarizer 401 with a vertical axis is attached to a display 402. A SMD variable retarder 403 (or other liquid crystal or polarization rotating or affecting device) with an axis at 45° relative to the plane of polarization or transmission axis of the polarizer (or liquid crystal display of the display 402) is placed in front of the display. The image from the display is projected by a lens 404 onto a beamsplitter 405. Half the light is transmitted to the group of components 430 at the bottom of the drawing, and half the light is transmitted to the group of components 431 at the left of the drawing. The components 430 include a lens 432, such as a planoconvex lens, a plane polarizer 433 with a relatively vertical transmission axis, and a mirror 434. The components 431 include a piano convex lens 435, plane polarizer 436 with a relatively horizontal transmission axis, and a mirror 437. The lenses 432, 435 have different focal lengths fl, f2, respectively. The image presented on the display 402 is switched between that intended for the low resolution full field of view and that intended for the high resolution central portion. The SMD 403 is switched synchronously with the presentation of the fields. When the low resolution image is presented the voltage applied the SMD 403 is such that the projected light is vertically polarized. When the high resolution image is presented the voltage applied to the SMD 403 is such that the projected light is horizontally polarized.

When the vertically polarized high resolution image is projected the light is absorbed by the components 431 but interacts with and is reflected back from the components 430. In traveling through the lens in the group 430 the beam is expanded to fill the entire field of view.

When the horizontally polarized low resolution image is projected the light is absorbed by the components 430 and interacts with and is reflected back from the components 431. In traveling through the lens 435 the beam is expanded only enough to fill the central portion of the field of view.

Light leaving the image generating section 440 of the system 400 passes through a beamsplitter 441, is retroreflected by the remote retroreflector 442 and is redirected by the beamsplitter 441 to the viewer 11.

This approach to an embedded image has several advantages when compared to others proposed. It is not necessary to physically embed a separate display in the center of the field of view. The optical system utilizes only simple components; and a white light cholesteric reflector is not necessary. The configurations of display and viewing systems of Figs. 18-20 are similar to and operate in a manner similar to that described with respect to Figs. 16 and 17.

The invention may be used in connection with engineering design or computer aided drawing, graphics, design, etc. In the field of computerized drawings and/or graphics, such as engineering drawing, it is customary, now, to display on a monitor an entire image, such as an engineering drawing. The draftsman can view the image and can select that part of the image which it is desired to magnify for better viewing or for modification on a better scale. Various windowing types of programs, computer aided drafting or design programs are available for conventional computers to carry out these tasks. The present invention may present to a viewer a full engineering drawing or some other drawing. Such drawing may be presented by a computer which has an engineering drawing software and a drawing file. It may be desired to view a portion of the drawing in high resolution so as to correct, to improve, to add to, etc. the drawing. A mouse or some other device may be used to point to or to locate a portion of the drawing which is to be displayed in high resolution. After such portion has been selected, the computer can direct the image from that portion for display by the high resolution display 3, for example. This operation is similar to the technique used to "blow up" a design on a CRT or other monitor, using various drawing computer programs. However, in the present invention, rather than magnifying the selected portion of the design, the selected portion simply is shown in relatively high resolution. If desired, the portion also can be magnified and displayed using both high and low resolution as was described above. Thus, the invention relates to a method as described for computer aided designing, etc., wherein a total design or drawing is viewed as a relatively low resolution image, and a portion of the image is "windowed", selected, or the like and is displayed as a relatively high resolution image.

- 30a -

A . configuration is illustrated in Figure id. As seen it is quite similar to that illustrated in Figure l6,The difference lies in the fact that the system utilizes circularly polarized light. The combination of the quarter waveplate with a -45° axis and the SMD with a +45° axis is capable of switching the light between right and left hand circular polarization. The circular polarizer in the bottom and left component groups can be simply conventional circular polarizers or, as illustrated in Figurelβ, a cholesteric liquid crystal.

The main virtue of the configuration in Figure© is that the cholesteric polarizers are, potentially, more efficient than conventional polarizers. The result is an image that is brighter and has a greater contrast ratio.

. configuration of a means to embed a high resolution area into the field of view is illustrated in Figure^. The reason for including the beamsplitter #2 in this configuration is to prevent the viewer from looking directly into the projector.

In this configuration the image produced by the projector group of components is focused on to beamsplitter #1. Note that the distance between the mid point of the beamsplitter and the cholesteric layer is D as is the distance between the cholesteric and the mirror. When the light is right handed circularly polarized it travels through lens #1, is reflected by the cholesteric layer, travels back through lens #1 and is focused on to the retro¬ reflector. When the light is left handed circularly polarized it travels through lens #1, is not effected by the cholesteric and then travels through lens #2. Since the focal length of lens #1 is +fl and that of lens #2 is -f2 there is not any net effect on the focus of the transmitted light rays. The light then goes through the quarter waveplate and is converted to linearly polarization, travels through lens #3, is reflected by the mirror, travels back through lens #3 and the quarter waveplate. In traveling back through the quarter waveplate the light is converted to right hand circularly polarization. It is then transmitted through the cholesteric layer and is focused on to the retro-reflector. (As previously there is no net effect on the focus of the light as it travels through the lens #l/£2 pair.) 30b -

Since the distance between the retro-reflector screen and either lens is large compared to D then the size of the image produced by the light interacting with lens # 1 is twice as large as the image produced by the light interacting with lens #3.

The system works by the display presenting the low resolution, wide field of view portion of the image when the SMD is in the state to right hand circularly polarize the light. The display presents the high resolution, central portion of the image when the SMD is in the state to left hand circularly polarize the light.

As before, the reason for including the beamsplitter #2 in this configuration is to prevent the viewer from looking directly into the projector.

Claims

-31- CLAIMS The embodiments of the invention claimed are, as follows:

1. A display system, comprising a relatively higher resolution display for presenting visual information, and a relatively lower resolution display for presenting visual information, said displays being positioned to present the visual information images therefrom in substantially side-by-side relation.

2. The system of claim 1 , wherein said displays are positioned to present the visual information images one within the other. 3. The system of claim 2, wherein the lower resolution visual information image at least substantially surrounds the higher resolution visual information image.

4. The system of claim 1, wherein each of the displays has plural pixels operative to display the visual information, and wherein the relatively higher resolution display has a larger number of pixels per unit area than the relatively lower resolution display.

5. The system of claim 4, further comprising circuit means for driving said pixels to form images for visual viewing.

6. The system of claim 1 , wherein said relatively lower resolution display comprises an optical device for viewing at a viewing location an image from a source, said optical device including lens means for focusing at a location a real image from the source, and conjugate optics means for receiving light from the lens means and directing light toward a lens input at the viewing location for viewing, at the viewing location, of the real image, said conjugate optics means including means for effectively placing the lens input at the viewing location functionally as though at said lens means, whereby the image from the source effectively is at the image plane of the input lens. 7. The system of claim 6, further comprising an image source for providing images to said optical device. -32-

8. The system of claim 6, said relatively higher resolution viewing source comprising a display positioned to present in a path parallel to at least part of the conjugate optics path a relatively higher resolution image for viewing at the viewing location. 9. The system of claim 1, said relatively lower resolution display comprising an image source, focusing optics, a beamsplitter, and a retroreflector, said focusing optics directing light from said image source toward said retroreflector via said beamsplitter to form an image for viewing.

10. The system of claim 9, said focusing being operative to form a real image from light received from said image source.

11. The system of claim 10, said relatively higher resolution display comprising an image source for located in said retroreflector thereby to present the relatively higher resolution image for viewing while being surrounded by the relatively lower real image. 12. The system of claim 9, said relatively higher resolution image source comprising an image source for presenting the relatively higher resolution image in at least a portion of the relatively lower resolution image.

13. The system of claim 1, each of said displays comprising a reflective active matrix liquid crystal display. 14. The system of claim 13, wherein each of said active matrix liquid crystal displays is formed on a respective semiconductor substrate. 15. A display system, comprising a first display, including a retroreflector, means for focusing an image toward said retroreflector, and beamsplitter means for reflecting and transmitting light relative to said retroreflector, whereby said beamsplitter means one of transmits light and reflects light toward said retroreflector for focusing at said retroreflector and the other of transmits light and reflects light from said retroreflector for viewing, and a second display including means for presenting a relatively higher resolution image than the image presented by said first display, said display including means -33- for presenting the relatively higher resolution image within the image presented by said first display.

16. The display system of claim 15, said means for presenting being positioned at least substantially at said retroreflector. 17. The display of claim 15, wherein said means for focusing forms a real image from light received from an image source.

18. A method of display, comprising forming a relatively lower resolution real image, reflecting the image to the eye of an observer, forming a relatively higher resolution image, and directing said relatively higher resolution image to the eye of the observer such that at least a portion of said relatively lower resolution image circumscribes at least a portion of said relatively higher resolution image.

19. The method of claim 18, wherein said reflecting comprises presenting such relatively lower resolution image at the retina of the eye such that the size of the image is at least approximately the size of the retina of the eye.

20. The method of claim 18, said forming comprises forming a relatively lower resolution image comprises using focusing optics forming a real image from light received from an image source, said reflecting comprises using a retroreflector to reflect light to the eye of an observer, and said directing comprises placing the relatively higher resolution image within the real image viewing viewed by the observer so as to be substantially circumscribed by the relatively lower resolution image.

21. The method of claim 20, said directing step comprising directing the relatively higher resolution image to the eye of an observer so as to be observed primarily by the foveal portion of the retina of the eye, and said reflecting comprising reflecting the relatively lower resolution image to the eye of the observer to be observed primarily by the non-foveal portion of the retina of the eye.

22. An optical system for presenting for viewing relatively lower and relatively higher resolution images of visual information, comprising: a retroreflector, -34- means for focusing a real image of visual information toward the retroreflector, light from said retroreflector being reflected to a viewing location as the relatively lower resolution image, and means for forming a relatively higher resolution image for viewing from the viewing location within the relatively lower resolution image.

23. The system of claim 22, said means for forming comprising means for placing the relatively higher resolution image at a portion of said retroreflector to present the relatively higher resolution image therefrom such that light forming the real image is not reflected by said portion of said retroreflector. 24. The system of claim 22, further comprising means for substantially seamlessly combining the relatively lower and relatively higher resolution images.

25. The system of claim 24, said means for combining comprising an image source for providing the relatively higher resolution image, said image source having at least a portion positioned at said beamsplitter to present the relatively higher resolution image and to prevent reflecting of light from said portion of said beamsplitter.

26. A system for viewing at a viewing location an image from an image source, comprising a retroreflector, means for focusing an image from a viewing source toward said retroreflector, and beamsplitter means for reflecting and transmitting light relative to said retroreflector, whereby said beamsplitter means one of transmits light and reflects light toward said retroreflector for focusing at said retroreflector and the other of transmits light and reflects light from said retroreflector for viewing, and wherein said retroreflector has at least two non-coplanar portions which are positioned to reflect light to said viewing location for seamlessly combining images resulting from light reflected therefrom.

27. The system of claim 26, said retroreflector comprising at least two retro-reflectors.

28. The system of claim 26, said retroreflector portions having the same resolution. -35-

29. The system of claim 26, at least one of said retroreflector portions being non-planar.

30. The system of claim 29, at least one of said retroreflector portions being curved. 31. The system of claim 26, said means for focusing comprising means for forming a real image from light received from an image source.

32. The system of claim 26, said system including a relatively lower resolution display comprising an image source, and said means for focusing and said beamsplitter being cooperative for directing light from said image source toward said retroreflector via said beamsplitter to form a real image for viewing, and a relatively higher resolution display comprising an image source for located relative to said retroreflector thereby to present the relatively higher resolution image for viewing while being surrounded by the relatively lower real image.

33. The system of claim 32, wherein at least one of said image sources comprises an active matrix liquid crystal display.

34. A method of making an optical system for viewing visual information, comprising combining a high resolution image and a low resolution image such that the former is presented for viewing by the foveal portion of an eye and the low resolution image is presented for viewing by the remainder of the eye. 36. A method of viewing visual information, comprising presenting in a field of view a high resolution image for directing to the foveal portion of an eye and presenting the presenting the remainder of the field of view to the other portions of the eye. 37. The method of claim 36, said presenting the low resolution image comprising blanking a portion of the low resolution field of view which overlies the high resolution image.

38. A method for computer aided drawing, comprising displaying a relatively large portion of a drawing as a relatively low resolution image, and displaying a portion of the image as a relatively high resolution image.

39. The method of claim 38, further comprising selecting a portion of the low resolution image for display as a high resolution image. -36-

40. The method of claim 39, comprising using a computer to display the images in a head mounted display.

41. The system of claim 1, including a respective display for each eye of a viewer. 42. The system of claim 9, including a respective display for each eye of a viewer and said beamsplitter being in the light path of both displays.

43. The system of claim 9, including a respective display for each eye of a viewer and said retroreflector being in the light path of both displays.

44. Apparatus for displaying high and low resolution images, comprising an optical switch for switching between two different polarization conditions, a selective reflector for reflecting light from a display respectively to relatively large area and relatively small areas for viewing in a field of view depending on the operation of the optical switch.

45. The apparatus of claim 44, said reflector comprising a cholesteric reflector for reflecting or transmitting light depending on the direction of circular polarization of light incident thereon and a further reflector.

46. The apparatus of claim 45, wherein said cholesteric reflector and said reflector have light focusing capability.

47. The apparatus of claim 44, further comprising a beamsplitter and a retroreflector, said beamsplitter and retroreflector being cooperative with said selective reflector and with light from a display to provide respective relatively high and relatively low resolutions images.

48. The apparatus of claim 47, said optical switch and said selective reflector being cooperative to present sequentially both relatively high and low resolution images for viewing via said beamsplitter and retroreflector such that substantially the same number of pixels comprise the respective relatively high and low resolution images.

49. A method for displaying high and low resolution images, comprising an optically switching light between two different polarization conditions, and selectively reflecting light from a display respectively to relatively large area and relatively small areas for viewing in a field of view depending on the optical switching. -37-

50. The method of claim 49, said selective reflecting comprising using a cholesteric reflector for reflecting or transmitting light depending on the direction of circular polarization of light incident thereon and a further reflector.

51. The method of claim 50, wherein said selective reflection include selectively focusing light at two different size areas.

52. The method of claim 49, further comprising directing light to a beamsplitter and a retroreflector whereby said beamsplitter and retroreflector are cooperative with said selectively reflected light and with light from a display to provide respective relatively high and relatively low resolutions images. 53. The method of claim 52, said optical switching and said selective reflecting being cooperative to present sequentially both relatively high and low resolution images for viewing via the beamsplitter and retroreflector such that substantially the same number of pixels comprise the respective relatively high and low resolution images.