Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-11-15
2004-11-02
Jackson, Jerome (Department: 2815)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S107000, C349S104000, C349S105000, C359S234000, C359S235000, C359S236000, C359S230000, C359S227000, C359S888000
Reexamination Certificate
active
06812979
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a color-separating apparatus for a liquid crystal projector, and more particularly to a color-separating apparatus for a liquid crystal projector of single panel type that is capable of improving light efficiency and color revival property.
2. Description of the Related Art
Generally, a projector projects a minute picture implemented at an internal small-dimension display onto a large-dimension screen with the aid of a projective lens on an expanded scale, thereby displaying a large-scale picture. This projector can be classified into a front projection system in which a picture is projected onto the front side of the screen and a rear projection system in which a picture is projected onto the rear side of the screen. A typical rear projection system of these systems includes a projection television. In the projector, a cathode ray tube (CRT) or a liquid crystal display (LCD) is used as a display device for providing a small-scale image. Recently, there has been highlighted a liquid crystal projector employing the LCD device profitable for making a thin-thickness projector.
The liquid crystal projector generally include a LCD device for providing a picture, a projection lens system for projecting the implemented picture onto the screen on an expanded scale, a light source for providing the LCD device with a light, an illuminating system for controlling a light path between the light source and the LCD device, and a driving circuitry for processing a signal.
The liquid crystal projector trends toward a realization of high brightness resulting from a configuration of better efficient optical system and a modification of a lamp system, or trends toward a simplicity of carrying and installation resulting from an implementation of small-size and light-weight device in spite of a reduced brightness. Such a liquid crystal projector uses a single or three LCD devices for a color realization. Generally, three LCD devices are employed if a high brightness is intended, whereas a single LCD device is employed if an implementation of small size and lightweight device is intended. A liquid crystal projector of single panel type adopting a single LCD device takes advantage of any one of a strategy of using a color filter, a strategy of separating three primary colors and inputting them at a specific angle and a strategy of sequentially sending three primary colors to the LCD device, for color realization's sake. A picture-projecting apparatus in which three primary colors are sequentially sent to the LCD device typically employs a color wheel as shown in FIG.
1
.
Referring to
FIG. 1
, a conventional optical system of a liquid crystal projector employing the color wheel includes a light source
2
for generating a white light, a color wheel
4
for transmitting only a specific color light of the white light from the light source
2
, a condensing lens
6
for condensing a light, a polarizing prism
8
for reflecting and transmitting an incident light depending on a polarization direction thereof, a LCD device
10
for reflecting a light in an image signal to implement a picture light loaded with picture information, and a projective lens
12
for projecting a picture light from the LCD device
10
on an expanded scale.
The color wheel
4
is rotated by means of a motor
14
to transmit only a specific color light of a white light emitted from the light source
2
in accordance with its position. To this end, the color wheel
4
is divided into first to fourth filters
4
A,
4
B,
4
C and
4
D as shown in FIG.
2
. The first to fourth filters
4
A,
4
B,
4
C and
4
D are coated or colored such that they can have a different color transmission characteristic, thereby transmitting red(R), green(G), blue(B) and white(W) lights, respectively. Such a color wheel
4
is rotated to position the first to fourth color filters
4
A,
4
B,
4
C and
4
D on a light path on a time-sequence basis, thereby allowing the red(R), green(G), blue(B) and white(W) lights on a time-sequence basis.
The condensing lens
6
focuses the color lights emitted from the color wheel
4
onto the polarizing prism
8
. The polarizing prism
8
reflects a line-polarized light having a specific direction, that is, a S wave inputted from the condensing lens
6
into the LCD device
10
and, at the same time, outputs a P wave from the LCD device
10
to the projective lens
12
.
The LCD device
10
is a reflective-type device, which continuously realizes red, green and blue picture in response to color lights reflected from the polarizing prism
8
and being incident thereto. The color picture continued by the LCD device
10
passes through the polarizing prism
8
and then is projected on a screen (not shown) on an expanded scale via the projective lens
12
. In this case, an observer recognizes a combined color picture in which specific color pictures projected onto the screen are averaged on a time basis.
However, if the color wheel
4
shown in
FIG. 1
is used, then there is raised a problem in that total light efficiency of the system is reduced to approximately ⅓ because all lights other than color lights transmitting the first to fourth filters
4
A,
4
B,
4
C and
4
D are reflected.
In order to compensate for this problem, there has been suggested an optical system employing a Dichroic mirror for a color separation and a rotation prism for converting progress directions of the separated color lights as shown in FIG.
3
.
Referring to
FIG. 3
, the optical system of the liquid crystal projector includes a fly eye lens
18
and a polarizing beam splitter (PBS) array
20
arranged between on a light path between a light source
16
for generating a light and a first Dichroic mirror
24
for separating the light, first to sixth Dichroic mirrors
24
,
28
,
32
,
46
,
48
and
54
for transmitting and reflecting a specific wavelength band of light, first to third rotating prism
34
,
38
and
42
for changing a light path in accordance with a rotation angle, a polarizing prism
60
, and a LCD device
62
.
The fly eye lens
18
divides a white light emitted from the light source
16
for each cell unit to focus it onto a specific area of the PBS array
20
. The PBS array
20
separates an incident light into line-polarized lights having any one light axis, that is, a P wave and a S wave, and allows the S wave to be outputted as it is while allowing the P wave to be converted into a S wave with the aid of a half wavelength (½&lgr;) plate (not shown) partially attached to the rear side of the PBS array
20
so as to output the S wave. The first condensing lens
22
prevents a spread of a light emitted from the PBS array
20
and being incident to the first Dichroic mirror
24
. The first Dichroic mirror
24
reflects and transmits incident lights in accordance with a wavelength band to separate them.
For instance, the first Dichroic mirror
24
reflects a red light of the incident lights while transmitting a green light and blue light. The second Dichroic mirror
28
reflects a red light reflected from the first Dichroic mirror
24
and being incident thereto via a second condensing lens
26
into the first rotating prism
34
. The third Dichroic mirror
32
reflects a green light of lights transmitting the first Dichroic mirror
24
and being incident thereto via a third condensing lens
30
for allowing it to be progressed toward the second rotating prism
36
while transmitting a blue light for allowing it to be progressed toward the third rotating prism
42
.
Each of the first to third rotating prism
34
,
38
and
42
differentiates a progress direction of the red, green and blue lights in accordance with its rotation angle as shown in
FIG. 4A
to FIG.
4
C. In other words, each of the first to third rotating prism
34
,
38
and
42
differentiates positions of the red, green and blue lights imaged on the LCD device
62
depending on its rotation angel as shown in FIG.
5
A and FIG.
5
B. The red light transmitting t
Fleshner & Kim LLP
Jackson Jerome
LG Electronics Inc.
Nguyen Joseph
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