Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
2001-11-30
2002-08-27
Adams, Russell (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
C353S020000, C349S009000
Reexamination Certificate
active
06439725
ABSTRACT:
This application claims the benefit of the Korean Application No. P2000-72707 filed on Dec. 02, 2000, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal projector, and more particularly, to an optical system of a liquid crystal projector with three reflective liquid crystal displays.
2. Background of the Related Art
Recently, as demands on large sized, and high resolution pictures become the stronger, projectors are paid attention as displays, for making enlargement projection of a picture by means of a projection lens system. The picture may be projected in front or rear direction.
The liquid crystal projector projects a light from a light source to a liquid crystal panel, and therefrom to a screen by means of a projection optical system. When the picture is projected to the screen in rear of the liquid crystal panel directly, a distance of projection distance between the screen and the projection optical system requires a large space in rear of the screen, to make the projector thick, that impedes fabrication of a thin projector.
As a solution for this problem, a total reflection mirror may be provided between the screen and the projection optical system, to fold an optical path, that can reduce the thickness of the projector. In this instance, though the thickness of the projector may be reduced further by reducing an angle of dispose of the total reflection mirror, there has been a limit in the angle of dispose between the mirror and the projection optical system for projection of the picture on the screen without distortion, and there has been a limitation in reduction of a system thickness coming from intrinsically required total length of an optical system consisting of a lighting system, the liquid crystal panel, and the projection lens system.
Accordingly, there have been various plans for reducing the total length of the optical system.
FIG. 1
illustrates a related art optical system of a liquid crystal projector, employing a polarizing beam sprite prism which reflects, or transmits an incident light depending on a wavelength and a direction of polarization, for reducing a total length of the optical system.
In detail, the optical system in
FIG. 1
is provided with a fly eye lens (FEL)
42
between a light source
40
and a first total reflection mirror
44
, and a second FEL
46
, a polarizing beam sprite array (PBS array)
47
, and a focusing lens
48
between the first total reflection mirror
44
and a second total reflection mirror
50
.
The optical system of a liquid crystal projector in
FIG. 1
is further provided with a dichroic mirror
52
on an optical path of a light reflected at the second total reflection mirror
50
, a first polarizing beam sprite prism (PBSP)
54
A on an optical path between the first dichroic mirror
52
and a blue liquid crystal panel
56
A, a second PBSP
54
B on an optical path between the first dichroic mirror
52
and a green liquid crystal panel
56
B, a first relay lens
60
, a third total reflection mirror
62
, a second relay lens
64
, fourth, and fifth total reflection mirrors
66
and
68
, a third PBSP
54
C on an optical path between the second PBSP
54
B and a red liquid crystal panel
56
C, a dichroic prism
70
among the first, to third PBSPs
54
A,
54
B, and
54
C, and a projection lens
72
opposite to a light projecting surface of the dichroic prism
70
.
Since the second PBSP
54
B can separate colors, the foregoing optical system can reduce a number of dichroic mirrors, to reduce a total length of the optical system. In this instance, a red light passed through the second PBSP
54
B proceeds along an optical path that is turned in a form surrounding the third liquid crystal panel
56
C by the fourth to sixth total reflection mirrors
62
,
66
, and
68
, and is directed to the third liquid crystal panel
56
C.
In the meantime, in general, a connector
10
is fitted at a side of the third liquid crystal panel,
56
C i.e., at a bottom thereof in
FIG. 1
for connecting the third liquid crystal panel
56
C to external signal lines, causing an interference with the path of the red light. Accordingly, as the path of the red light is required to be spaced away from the connector
10
of the third liquid crystal panel
56
C as far as possible, there is a limitation in reducing the total length of the optical system.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an optical system of a liquid crystal projector that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an optical system of a liquid crystal projector, in which a total length of the optical system is reduced to reduce a thickness of an entire system.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the optical system of a liquid crystal projector for superimposing, enlarging, and projecting pictures displayed on first to third liquid crystal panels by using color lights received through first to third light path changing parts, wherein the first light path changing part includes a first sub-light path part for making a first time alteration of a linearly polarized light component of the color light received from one of the first to third light path changing parts, a second sub-light path part for reflecting the color light from the first sub-light path part, and making a second alteration of the linearly polarized component of a reflected color light, and forwarding to the first sub-light path part, and a third sub-light path part for directing the color light received through the second sub-light path part and the first sub-light path part to the first liquid crystal panel relevant to the color light, wherein the first to third sub-light path parts are arranged spaced away from the first liquid crystal panel, on sides of the first liquid crystal panel respectively except a side the connector is fitted thereto.
The first sub-light path part includes a first &lgr;/2 plate for altering a linearly polarized component of a color light received from one of the second, and third light path changing parts, the second sub-light path part includes a first total reflection mirror for reflecting the color light from the second sub-light path part at a right angle, a second total reflection mirror for reflecting back the color light from the first total reflection mirror, a &lgr;/4 plate for altering a first linearly polarized light in one direction from the first total reflection mirror to a circular polarized light and forwarding the circular polarized light, and altering a circular polarized light from the second total reflection mirror to a second linearly polarized light in the other direction, and forwarding the second linearly polarized light, and the third sub-light path part includes a first polarizing beam sprite prism (PBSP) for transmitting the first linearly polarized light from the first &lgr;/2 plate toward the first total reflection mirror, and reflecting the second linearly polarized light from the first total reflection mirror at a right angle, a second PBSP for reflecting the second linearly polarized light from the first PBSP toward the first liquid crystal panel at a right angle, and a second &lgr;/2 plate for altering the first linearly polarized light from the second PBSP to a second linearly polarized light.
The first, second, and third sub-light path parts further includes at least one refractive lens for preventing light scattering
Adams Russell
Fleshner & Kim LLP
Koval Melissa
LG Electronics Inc.
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