Optics: image projectors – Reflector
Reexamination Certificate
2001-05-17
2002-06-04
Dowling, William (Department: 2851)
Optics: image projectors
Reflector
C353S102000, C385S133000, C385S901000
Reexamination Certificate
active
06398368
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light pipe, and more particularly, to a hollow tapering light pipe.
2. Description of the Prior Art
With the progress of optics, projectors have found broad use in many applications. Generally speaking, projected light intensity is usually an important factor while designing a projector, as the projection quality improves with greater intensities of the projected light.
Please refer to FIG.
1
.
FIG. 1
is a schematic diagram of a prior art light pipe
10
for a projector system
12
. The projector system
12
comprises a light source
14
to generate light
11
and to guide the light
11
to the light pipe
10
, and an image device
16
to project the light gathered by the light pipe
10
to a screen
13
so as to form an image. The light pipe
10
is a hollow rectangular pipe set between the light source
14
and the image device
16
to gather and guide the light
11
. The light pipe
10
comprises an entrance pupil
18
and an exit pupil
19
. The entrance pupil
18
is used to gather the light
11
generated by the light source
14
. Then the light
11
is guided to the image device
16
through the exit pupil
19
.
Please refer to FIG.
2
.
FIG. 2
is a position distribution of the light incident upon the entrance pupil
18
in FIG.
1
. The transverse axis is a distance in the plane
15
in
FIG. 1
from the center of the entrance pupil
18
. The longitudinal axis is the light intensity. As shown in
FIG. 2
, the light closer to the center of the entrance pupil
18
is stronger, and the light farther from the center of the entrance pupil
18
is weaker. In addition, the light pipe
10
does not gather all of the light
11
. The light
24
closer to the center of the entrance pupil
18
enters the light pipe while the light
25
farther from the center of the entrance pupil
18
fails to be gathered by the light pipe
10
.
Please refer to FIG.
3
.
FIG. 3
is the incident angle distribution of the light incident upon the entrance pupil
18
. The transverse axis of
FIG. 3
is the incident angle of the light on the plane
15
, and the longitudinal axis is the light intensity. As shown in
FIG. 3
, the incident angle of a traditional light bulb is in the range of 18-20 degrees. Because the light pipe
10
is a rectangular pipe with homogeneous cross-sections, the angle of the light leaving of the exit pupil
19
is also in the range of 18-20 degrees. Usually, the optic device for the image device
16
, such as the liquid crystal display (LCD) or the digital mirror device (DMD), has an incident angle limitation. Owing to the incident angle limitation, the angle of the light leaving the exit pupil
19
cannot be too large. Usually, light with an angle over 30 degrees cannot be modulated by the liquid crystal display.
Please refer to FIG.
4
.
FIG. 4
is a schematic diagram of another prior art light pipe
20
for the projector system
12
in FIG.
1
. The light pipe
20
, differing from the light pipe
10
, has a tapered body. The exit pupil
23
of the light pipe
20
is larger than the entrance pupil
22
to reduce the incident angle of the light.
Generally speaking, the light pipes
10
,
20
are designed to reduce the light
25
leaking from the light pipes
10
,
20
while maintaining a small light angle. Thus, the light gathering efficiency is improved, and the light intensity is increased. However, owing to the fact that the prior art light pipes
10
,
20
have the entrance pupil
18
,
22
smaller than or equal to the exit pupil
19
,
23
, the light
25
leaking from the light pipe
10
,
20
is usually quite strong without increasing the volumes of the light pipes
10
,
20
. Though an arc lamp with a longer arc length can be used as the light source to reduce the incident angle in
FIG. 3
, it also makes the position distribution of the light in
FIG. 2
smoother. Then the light leaking from the light pipe
10
,
20
increases, degrading the light gathering efficiency.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a light pipe having an exit pupil with a shape that is scaled from the shape of the entrance pupil to increase the light gathering efficiency of the light pipe, and to improve over the disadvantages of the prior art.
The light pipe is designed for a projector system. The projector system comprises a light source to generate light and to guide the light to the light pipe, and an image device to produce an image using the light gathered by the light pipe. The light pipe is a tapered hollow tube set between the light source and the image device. The light pipe comprises an entrance pupil and an exit pupil. The entrance pupil is a square opening at one end of the light pipe. The light generated by the light source is guided to the light pipe through the entrance pupil. The exit pupil is set at another end of the light pipe, and the area of the exit pupil is smaller than the area of the entrance pupil. The light gathered by the light pipe is guided to the image device through the exit pupil. The shape of the exit pupil is scaled from the shape of the entrance pupil so as to increase the light gathering efficiency of the light pipe.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.
REFERENCES:
patent: 3740112 (1973-06-01), Lundgren
patent: 4143966 (1979-03-01), Gandini
patent: 4813765 (1989-03-01), Negishi
patent: 5625738 (1997-04-01), Magarill
patent: 5696865 (1997-12-01), Beeson et al.
patent: 5748376 (1998-05-01), Lin et al.
patent: 5868481 (1999-02-01), Conner et al.
patent: 5884991 (1999-03-01), Levis et al.
patent: 6139156 (2000-10-01), Okamori et al.
patent: WO 96/33435 (1996-10-01), None
patent: WO 00/26721 (2000-05-01), None
Williamson D E/ Cone Channel Condenser Optics/Journal of the Optical Society of America/vol. 42, No. 10/Oct. 1, 1952 pp. 712-715.
Ning X et al/Dielectric Totally Internally Reflecting Concentrators/Optical Society of America, Washington, U.S./vol. 26, No. 2/Jan. 15, 1987/pp. 300-305.
Acer Communications and Multimedia Inc.
Dowling William
Hsu Winston
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