Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2000-05-02
2001-08-28
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
C359S631000, C359S633000
Reexamination Certificate
active
06282029
ABSTRACT:
BACKGROUND
The present invention relates to image display systems. In particular, the present invention relates to miniature image display system usable for camcorders, digital cameras, or helmet-mounted displays and other wearable applications.
In the field of miniature image display systems there are continuing challenges to design smaller, lighter, and more energy efficient systems. These challenges stem from the fact that a miniature image display system should preferably be small enough and light enough to for digital cameras or camcorders, or be wearable (mounted on a helmet or on eyeglasses). Further, these goals should be preferably achieved without sacrificing image quality, in particular, contrast ratio and brightness. Such systems may be used for wearable computer systems, gaming systems, viewfinder for camera and camcorders, distance interactions between people or between people and machines, virtual-reality system, and for many other applications.
Typically, desktop computer systems and workplace computing equipment utilize CRT (cathode ray tube) display screens to display images for a user. The CRT displays are heavy, bulky, and not easily miniaturized. For a laptop, a notebook, or a palm computer, flat-panel display is typically used. The flat-panel display may use LCD (liquid crystal displays) technology implemented as passive matrix or active matrix panel. The passive matrix LCD panel consists of a grid of horizontal and vertical wires. Each intersection of the grid constitutes a single pixel, and is controlled by a LCD element. The LCD element either lets light through or blocks the light. The active matrix panel uses a transistor to control each pixel, and is more expensive.
The flat-panel display typically requires external lighting to allow human eyes to see the images displayed on the display panel. This is because flat-panel displays do not generate their own light. For laptop, notebook, or palm computers, external lighting is typically positioned at the back of the flat-panel. The backlighting allows the user to see the images from the front of the flat-panel.
The flat-panels are also used for miniature image display systems because of their compactness and energy efficiency compared to the CRT displays. For miniature image display systems, reflective lighting, rather than the backlighting, is preferred. This is because using the reflective lighting technique, miniature image display systems can be designed having higher energy efficiency compared to the energy efficiency of image display systems designed using the backlighting techniques. The passive matrix displays rotate s-polarized light into p-polarized light when the display is switched on while acting as a normal reflective surface when switched off. Various configurations of miniature display systems using flat-panel display and reflective lighting technique can be found in U.S. Pat. No.5,808,800.
A typical example of a miniature display system
100
is illustrated in FIG.
1
. Referring to
FIG. 1
, the light source
102
is typically one or more LED's (light-emitting diodes). To achieve uniform illumination to reflective type of display, the illumination must be both spatially and angularly uniform, with the angular extent given by the acceptance angle of the viewing optics. That is, preferably, the angle at which the light hits the special light modulator
104
, or the display panel
104
, is perpendicular to the plane of the display panel
104
and the filed angle of the viewing optics.
Typically, a collecting lens
106
is used to collect light from one or more light sources into a slightly convergent light beam to match the telecentricity of the viewing optics. And, an array of micro lenses or a diffuser
108
is used to provide diffusion. Because the light source
102
, the collector
106
, and the diffuser
108
are positioned on the sides of the display panel
104
, the manufacturing of the system
100
is difficult and costly.
The light source
102
must be outside the field of view of a user so as not to block the image generated by the display. Therefore, a polarizing beam splitting cube (“PBS cube”)
110
is often used is used to redirect the light. The PBS cube
110
includes a polarizing beam splitter (PBS)
112
which typically reflect s-polarized light while allowing p-polarized light to pass.
There are several problems associated with such design. Firstly, the bulk of the system
100
is difficult to reduce because distance between the first viewing optics and the display must be at least as great as the shortest dimension of the display. This is because the system
100
must allow sufficient space for the placement of the PBS cube
110
.
Secondly, the bulk of the system
100
is difficult to reduce because the system
100
requires the use of the collecting lens
106
and the diffuser
108
for energy efficient operation. Generally, without the collecting lens
106
and the diffuser
108
much if not most of the light produced by the light source
102
would be wasted.
Thirdly, the bulk of the system
100
is difficult to reduce because the diffuser
108
must be at least as large as the display. This is because, in the illustrated prior art, the diffuser
108
is placed on the side of the collecting lens
106
which is the opposing side of the light source
102
.
Finally, energy efficiency of the system
100
is low. There are several reasons for this. Reason one, only a portion
114
of the light from the light source
102
is captured by the collecting lens
106
and is directed toward the PBS cube
110
. Some
116
of the light from the light source
102
is not captured by the collector
106
and is lost. This is because the light from the light source
102
is typically Lambertian. Lambertian light is light that is emitted in a radiation pattern in which the luminous intensity varies as the cosine of the off-axis angle, and is typically spread to about 120 degrees. In comparison, typical collection lens collects light for about 60 degrees.
Reason two, about ½ of the light
118
from the collector
106
and diffuser
108
is lost because the PBS
112
reflects only the s-polarized light. Accordingly, p-polarized light
120
is transmitted such that it will not each the display panel
104
.
Reason three, after reflecting off the display panel
104
, the light encounters the PBS
112
again. Again, only the p-polarized light
126
passes through the PBS
112
toward the optic lens
130
for viewing at an imaging area
132
. All s-polarized light
128
is reflected by the PBS
112
and is lost.
Assuming that the collector
106
captures about ½ of the light produced by the light source
102
, the system
100
of
FIG. 1
allows only about ⅛ of the light produced by the light source
102
to eventually reach the optic lens
130
. This is due to the combined losses at the collector
106
and at the PBS
112
. This rough estimate does not take into account other losses. For example, energy is lost at the surface of the PBS cube
110
each time the light enters or leaves the PBS cube
110
.
In sum, there exists continuing need for more compact, lightweight, and energy efficient display system that eliminates or minimizes these problems.
SUMMARY
These needs are met by the present invention. According to one aspect of the present invention, a display system has light source for producing light, display panel, conic mirror, and conic polarized reflector. The display panel is preferably coplanar with the light source, allowing less bulky configuration as well as for easier manufacturing process. The conic mirror directs the light from the light source toward the conic polarized reflector (CPR). The CPR reflects the directed light toward the display panel.
According to another aspect of the invention, a light reflector system for miniature display includes a conic mirror shaped to capture light from a light source and to direct the light toward a conic polarized reflector. The conic polarized reflector is shaped to reflect the directed light from the conic
Jusuf Gani
Ma Guolin
Sasser Gary Dean
Agilent Technologie,s Inc.
Mack Ricky
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