Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
1999-08-04
2001-10-30
Dowling, William (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
C353S020000
Reexamination Certificate
active
06309071
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to projection display systems which use reflective spatial light modulators, and more specifically, to such systems which use two polarization states of light to produce color images.
The system shown in
FIG. 1
illustrates the essential components of the optical portion of a conventional projection display system having three reflective spatial light modulators in the form of liquid crystal display (LCD) panels, also known as liquid crystal light valves (LCLV). The prior art system, depicted generally at
10
includes a light source
12
, an illumination mechanism for collecting the light and concentrating it onto the light valves, shown generally at
14
, a polarizing mechanism for polarizing the light, if the light valves modulate via polarization effects, shown generally at
16
, a splitting mechanism for splitting the illumination into three color bands to separately illuminate the three light valves, shown generally at
18
, a recombining mechanism for recombining the three light distributions after reflecting from the light valves, shown generally at
20
, and a projection mechanism for projecting the combined images onto a viewing screen, shown generally at
22
.
Lamp
24
and lamp reflector
26
produce and concentrate the light for this system. A series of dichroic filters
28
,
30
is used to split the light from the lamp
24
into separate red, green, and blue components. The light in each of the three components, or channels, is then polarized with a polarizing beam splitter (PBS)
32
,
34
,
36
, and illuminates three separate LCDs,
38
,
40
,
42
. The LCDs selectively modify the polarization of the light reflected from them allowing some portion of the light to pass back through the PBS. A second series of dichroic filters,
44
,
46
, is used to recombine the modulated light distributions and pass them on to a projection lens
48
imaging all three LCDs onto the viewing screen.
The configuration shown in
FIG. 1
is functional and has been used to implement projection display system products. However, one drawback of such systems is that they are inefficient, utilizing only one half of the light from the light source. This is a particular problem since the displays tend to be dim and it is desired to produce bright images using such displays. Polarization converters have been used to improve optical throughput by converting the randomly polarized light from a light source to a single polarization state. However, such polarization converters are not entirely efficient and can introduce depolarization effects that can effect contrast, and also add additional complexity and cost.
Another drawback of such systems is that color balance is often sacrificed to improve brightness of the projected image. For color displays, one aspect of picture quality is color temperature. This is a subjective evaluation, indicated by the “whiteness” of white. It is assumed by analogy to the photographic film industry that color temperature preferences follow certain geographic patterns. For example, Americans seem to prefer a bluish white color temperature, while Europeans seem to prefer whatever color temperature provides a “truest” skin tone. It is desirable for a color display system to be able to provide whatever color temperature is preferred in a given market. Color balance has been achieved conventionally by providing additional filtering to decrease the intensity of particular color components, thus correcting any imbalance in the light source. However, because image brightness is already a problem in conventional display systems, it is often undesirable to further decrease brightness in order to achieve a more desirable color temperature.
Yet another drawback of the prior art projection display systems is that the large number of components in the architecture shown in
FIG. 1
is cumbersome, and necessitates a relatively large physical size of the system. Still another drawback to these systems is the requirement of a large back working distance for the projection lens.
The prior art projection display systems which have sought to provide full color images have not adequately addressed these drawbacks. Accordingly, there is still a need for a color projection display that efficiently transmits light of both polarization states through the projection display system to yield a bright image, that achieves the desired color temperature but that does not suffer from depolarization effects, that utilizes a small number of components in a small physical size of, the system, and that has a relatively short back working distance for the projection lens.
SUMMARY OF THE INVENTION
The present invention overcomes the drawbacks of the prior art by providing in a first aspect a projection display system comprising a light source that generates light having at least two polarization states and having at least a first color component, a second color component, and a third color component. The system has at least one color component selection device that selectively transmits at different times one of the second and third color components. The system has at least four polarized light modulators. Two of the light modulators each generate a respective image associated with each respective polarization state of the first color component. The other two light modulators each generate a respective image associated with each respective polarization state of one of the second and the third color components transmitted by the color component selection device. The system also has a projection lens for projecting the images from the polarized light modulators.
In a second separate aspect of the invention, a projection display system comprises a light source that generates non-polarized light having at least three color components. A color selection device selectively transmits different color components at different times. A polarization separator has a first optical path for light of a first polarization state and a second optical path for light of a second polarization state. Each of the optical paths produces respective images for each of the three color components. A projection lens projects the images.
In another separate aspect of the invention, a method is provided for displaying color images. First, light is generated having at least two polarization states and at least three color components. The second and third color components are selectively transmitted at different times. Respective images associated with each of the respective polarization states of the first color component are generated. Respective images associated with the respective polarization states of the second and third color components are generated at different times. The images are then projected through a projection lens.
The various aspects of the invention have one or more of the following advantages. The projection display system has the advantage of increased optical efficiency (i.e., brighter output) by utilizing both polarization states of the incident light. Thus, the system provides a brighter projected image by improving the optical transmission from a single light source. In addition, this system will have no depolarization effects caused by a polarization converter, which can effect optical throughput and cause a reduction in contrast. Another advantage of the invention is that a light source not necessarily having the desired color temperature can be used. This permits the light source to be selected on the basis of factors other than color temperature, such as heat, size, cost, and total light output intensity. Yet another advantage of the invention is that color temperature may be customized for different markets. In general, the desired color temperature may be achieved by determining the amount of time during which different color components are transmitted through the projection display system. In addition, the display system may be manufactured to have a relatively small physical size, and also to have a relatively short back working distance for th
Florence James M.
Huang Austin L.
Chernoff Vilhauer McClung & Stenzel LLP
Dowling William
Sharp Laboratories of America Inc.
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