Optical: systems and elements – Single channel simultaneously to or from plural channels – By refraction at beam splitting or combining surface
Reexamination Certificate
2002-08-09
2004-03-30
Dang, Hung X. (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By refraction at beam splitting or combining surface
C359S639000
Reexamination Certificate
active
06714353
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an optical illumination system for a projection system, and more particularly to an optical device with a function of homogenizing and color separation and an optical illumination system for a projector whose size can be reduced by use of the optical device.
2. Description of the Prior Art
Recently, as a kind of a flat display, which is thin in its thickness and can realize a large screen, substituted for a cathode ray tube display, which is limited in its screen size and large in its system size, projectors for projecting pictures of a small-sized screen on a large-sized screen with a magnification are coming into rapid and wide use.
The projectors, which are display devices for realizing pictures on small-sized screen, can employ a cathode ray tube, an LCD (Liquid Crystal Display) or a DMD (Digital Micromirror Device), but use mainly the LCD or the DMD according to a trend of down-sizing in thickness.
The LCD realizes pictures by changing an alignment state of liquid crystal molecules depending upon electrical variations from the external, and controlling an amount of light transmission based on the changed alignment state of liquid crystal molecules. The DMD realizes pictures by changing inclination angles of micromirrors between +10° and −10° depending upon electrical variations from the external, such that a reflection angle of light has two modes.
Such projectors are currently developing with the most important point put on high brightness, miniaturization and lightweight.
More particularly, the projectors are being improved to have a vivid screen even under bright surroundings by employing a lamp used as a source of light with a small magnitude of light emission, fly eye lenses for homogenizing an amount of light, polarization conversion devices for converting light emitted from the source of light into linear polarized light, etc., such that an efficiency of light is increased.
In addition, for the miniaturization and lightweight, the projectors are developing from a three-plate system for realizing colors using three display elements to a single-plate system for realizing colors using one display element.
The projectors employing the single-plate system using one display element use a method of color filters for realizing colors, a method of sequentially providing three primary colors for the display element, a method of separating and scrolling three primary colors, etc.
Among these methods, an optical illumination system using three rotating prisms for changing a traveling direction of colored light and scrolling the colored light separated from dichroic mirrors for color separation can be representative of the method of separating and scrolling three-primary colors.
FIG. 1
is a view showing a structure of a conventional optical illumination system of a projector employing a single-plate system using three rotating prisms.
Referring to
FIG. 1
, the optical illumination system includes first and second fly eye lenses
4
and
6
, a polarizing beam split (referred to as PBS hereinafter) array
8
, first to fourth dichroic mirrors
12
,
24
,
32
and
44
for color separation, first and second total reflection mirrors
16
and
40
for totally reflecting incidence light, first to third rotating prisms
18
,
26
and
28
for changing an optical path depending on their rotation angles, first to seventh condensing lenses
10
,
14
,
30
,
36
,
38
and
46
for condensing light, first and second relay lenses
34
and
42
for relaying an image formation point, and a PBS prism
50
, all of which are arranged on an optical path between a source of light
2
and a display device
52
.
Now, an operation of the optical illumination system of the projector as shown in
FIG. 1
will be described.
The first and second fly eye lenses
4
and
6
make light distribution uniform by dividing white light from the source of light
2
by the unit of lens cell and outputting the divided light to the PBS array
8
.
The PBS array
8
separates the incidence light into linear polarized light having one of optical axes, i.e., P polarized light and S polarized light. Here, the S polarized light is outputted as it is, and the P polarized light is converted and outputted into S polarized light by a ½ wavelength plate (not shown) partially attached on a back side of the PBS array
8
, such that a state of polarization becomes uniform. The first condensing lens
10
condenses the light outputted from the PBS array
8
into the first dichroic mirror
12
.
The dichroic mirror
12
is made of a blue reflection coating for reflecting blue light, and green and red transmission coatings for transmitting green and red light, respectively. The first total reflection mirror
16
totally reflects blue light, which is reflected by the first dichroic mirror
12
and inputted through the second condensing lens
14
, into the first rotating prism
18
.
The second dichroic mirror
24
made of a green reflection coating and a red transmission coating reflects green light into the second rotating prism
26
and transmits red light into the third rotating prism
28
, both of green and red light being incidence light transmitted by the first dichroic mirror
24
and inputted through the third condensing lens
20
.
The first to third rotating prisms
18
,
26
and
28
change traveling directions of blue, green and red light depending on their rotation angles, respectively. More particularly, The first to third rotating prisms
18
,
26
and
28
change image formation positions of blue, green and red light at which images are formed on the display device
52
depending on their rotation angles, respectively, and scroll the image formation positions of the three color light sequentially, while they are rotating independently.
The blue light transmitted through the first rotation prism
18
is inputted to the fourth dichroic mirror
44
via the fourth condensing lens
30
, the third dichroic mirror
32
, and the first relay lens
34
. The green light transmitted through the second rotation prism
26
is inputted to the fourth dichroic mirror
44
via the fifth condensing lens
36
, the third dichroic mirror
32
, and the first relay lens
34
. The red light transmitted through the third rotation prism
28
is inputted to the fourth dichroic mirror
44
via the sixth condensing lens
38
, the second total reflection mirror
40
, and the second relay lens
42
.
The third dichroic mirror
32
is made of a red reflection coating for totally reflect the red light from the second rotating prism
26
and a blue transmission coating for transmitting the blue light from the first rotating prism
18
. The fourth dichroic mirror
44
reflects the incidence blue light and green light and transmits the incidence red light.
Each of the red, green and blue light transmitted or reflected by the first to fourth dichroic mirrors
12
,
24
,
32
and
44
has a S polarization component and is inputted to the PBS prism
50
via the seventh condensing lens
46
and a polarization plate
48
.
The S polarized light inputted from the polarization plate
48
to the PBS prism
50
is reflected at a polarized light split surface
50
A into the display device
52
. In this case, based on different initially set rotation angles of the first to third rotating prism
18
,
26
and
28
, the red, green and blue light form images on different portions of the display device
52
. The different image formation positions are scrolled in a specific direction when the first to third rotating prism
18
,
26
and
28
are driven. The display device
52
scrolls red, green and blue signals in accordance with the red, green and blue light inputted while the different image formation positions are speedily scrolled.
Accordingly, each of the three color signals is implemented in an according pixel of the display device
52
and the implemented three color signals are integrated with time for displaying a color picture. In case that the disp
Park Tae Soo
Um Kee Tee
Birch & Stewart Kolasch & Birch, LLP
Dang Hung X.
LG Electronics Inc.
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