Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
1999-09-10
2002-08-13
Mack, Ricky (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S633000
Reexamination Certificate
active
06433935
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention generally relates to compact electronic display systems. More specifically, the invention relates to illumination systems for use with compact electronic display systems.
2. Descrinption of Related Art
A continuing objective in the field of electronics is the miniaturization of electronic devices. Most electronic devices include some form of display system which provides information to the user. As electronic devices are miniaturized, display systems are needed which can be incorporated into increasingly smaller devices. It is thus important that the space required to house these display systems be reduced. In one regard, it is desirable that the thickness of the displav system be reduced, the thickness of the display referring to the dimension of the display system which is perpendicular to the plane of the image formed by the display.
In general, the image provided by an electronic display may be either a real image or a virtual image. One approach to reducing the size of a display system is through the formation of a virtual image instead of a real image. A variety of virtual image displays have been described including those described in U.S. Pat. Nos. 5,644,323; 5,625,372; 5,684,497; 5,771,124; 5,838,498; 5,870,068; 5,892,624; 5,905,478, each of which are incorporated herein by reference.
A real image refers to an image which is observed directly by the unaided human eye. A real image exists at a given location when a real image can be observed by the unaided eye if a viewing surface is positioned at the location. A photograph is an example of a real image. Examples of electronic displays which provide real images include liquid crystal displays, CRT monitors. and projection screens.
Compact electronic devices, because of their small size, have a limited surface area on which to provide a real image. Since the amount of detail that the human eye can resolve per unit area is limited, devices which provide a real image are only able to provide a limited amount of legible information per display screen.
By contrast to real image displays, virtual image displays provide a virtual image, i.e., an image which, if a viewing surface were positioned at the location of the virtual image, no image would be observed by the eye. By definition, a virtual image can exist at a location where no display surface exists. An example of a virtual image is the image of fine print viewed through a magnifying glass.
In the case of a virtual display, the image is first formed by an imaging component referred to as the source object. As with real image displays, the source object may be a CRT or a liquid crystal display, but it is usually miniaturized to reduce the overall size of the display system. Magnifying optics are then utilized to form the virtual image that is actually seen by the viewer. Source objects may actually generate the light that is viewed as in the case of a CRT or luminescent device. Such a display is said to be an emissive display. Alternatively, the display may be non-emissive such as a liquid crystal display which requires illumination from an external source of light.
Virtual image displays provide an image which appears to be larger than the source object. As a result, the size of the virtual image, as perceived by the user, is limited by the magnification of the display system as opposed to the size of the electronic display. This enables virtual image displays to provide the user with a greater amount of legible information per display screen than real image displays in the same space. It also enables a virtual image display to be designed which provides the same amount of information per screen as real image displays in a smaller space.
An important aspect of the functioning of a virtual image display is the ease of viewing the virtual image. In this regard, it is important for the display to provide a wide apparent angular width of the virtual image, commonly referred to as the field of view of the virtual image. The full field of view is defined as the ratio of the largest apparent dimension of the virtual image to the apparent distance to the virtual image. It is generally equivalent to the field of view for a real image display surface. A need exists for a virtual image display system which provides a wide field of view.
A wide field of view requires a large aperture through which the image is viewed in order to have a comfortable distance between the display and the eye, which is referred to as the eye relief of the display. Another important property of a virtual display is a large amount of space within which the eye can move and still see the image. This space is referred to as the eye-box.
If the source object of the display is non-emissive, the display must be illuminated by a source of light such as a lamp or LED. When the microdisplay is a non-emissive, reflective display, the illumination must be provided from the front side of the display, which is made more difficult by the need to view the image created on the front side of the display. It is important that this illumination provide ample light such that the resulting image is bright and that the image has sufficient contrast between bright and dark portions of the image. In the case of a transmissive liquid crystal display, the illumination is provided from the rear side of the display and is referred to as backlighting.
Since virtual image displays are frequently used in portable devices, it is important for the displays to be energy efficient. Hence, it is desirable for the displays to use a low amount of energy for illumination. A need therefore exists for a display system which provides a bright virtual image. A further difficulty associated with virtual image displays is irregularities in the illumination of the source object. A need therefore also exists for a display system which provides a virtual image having substantially uniform illumination across the image.
SUMMARY OF THE INVENTION
The present invention relates to illumination systems for use in virtual image display systems. In general, the virtual image display systems of the present invention include a non-emissive, reflective microdisplay which forms a source object; an optical system which forms a magnified, virtual image of the source object from light reflected off the microdisplay; a light source system which produces light to illuminate the microdisplay; and illumination system according to the present invention.
In one embodiment, the illumination system forms at least two virtual light sources to illuminate the microdisplay. In one variation, the at least two virtual light sources include a first virtual light source positioned approximately in front of and directly over the microdisplay and second virtual light source positioned over and to one side of the microdisplay. The illumination system may also form three or more virtual light sources to illuminate the display system. In one variation, the at least three virtual light sources include a first virtual light source positioned approximately in front of and directly over the microdisplay, a second virtual light source positioned over and to a first side of the microdisplay, and a third virtual light source positioned over and to a second side of the microdisplay.
In another embodiment, the illumination system directs light from the light source system through the illumination system to the microdisplay such that the angles of incidence of light which illuminates the microdisplay varies across the microdisplay over an angular range that is greater than would be provided by the light source system if the light source system were to directly illuminate the microdisplay.
In another embodiment, the illumination system directs light from the light source system through the illumination system to the microdisplay such that the angles of incidence of light which illuminates the microdisplay varies across the microdisplay over an angular range of at least 40 degrees. In one variation, the angles of incidence of ligh
Chuang Chih-Li
Curley Michael J.
Kintz Gregory J.
Li Zheng-Wu
Mack Ricky
Three-Five Systems, Inc.
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